AGSSB ABSTRACTS

An Analysis Of The Relationship Between The Position Of The Major Wind Discontinuity And The Position Of Areas Of Rainfall Over The Philippines
Gaudioso R. Tabamo
1970

The intertropical convergence zone is defined by different writers in different ways and it has been discussed under many different names. There is also difference of opinion as to whether rainfall occurs in separate patches or as a continuous belt along the major wind discontinuity or whether it is dispersed over a narrow zone or a wider zone in the general vicinity of the wind discontinuity. In general, it is implied from the literature that the more prominent wind discontinuity at some level or levels in the tropical atmosphere is sometimes associated with close or distant precipitation.

The association of precipitation with wind discontinuity has been implicitly accepted without proof, and the lines or zones which have been drawn on published synoptic charts appear to be a composite representation of rainfall and wind-field. To determine whether the major wind discontinuity is associated in some way with areas of rainfall and whether there is a zone of rainfall along the wind discontinuity or whether rainfall is dispersed over a wide zone, completely separate analyses of wind-fields and of the rainfall charts over the Philippines have been made in the present study and these have been related graphically. For determination of the wind field there are 11 pilot ballon stations and 46 synoptic observing stations, approximately 70 miles apart, which regularly report the direction of movement of the lowest and middle clouds at various levels. The scarcity of observations of wind-speed make computations of convergence impracticable. Therefore, the wind discontinuities which emerged from the analyses were really the assymptote of confluence in the streamlines in the lower 2000 to 4500 feet of the atmopshere, so that it was not practicable to take into account any slope in the surface of separation between two airstreams in the present study. Since the analyses show that the wind discontinuity can undergo considerable displacement in one day and because near the coast its position may also be affected by the difference between land and sea temperatures, analyses of the wind field have been made twice daily, at 0000 GMT and 1200 GMT, respectively.

For the determination of the rainfall patterns, rainfall observations are available at 46 synoptic stations in the Philippines, representing an average spacing of approximately 70 miles between stations. It was realized that, with an observing network over land, the diurnal temperature variation might have an influence on rainfall, and therefore separate precipitation charts for the periods 1800-0600 GMT and 0600-1800 GMT (each of which includes a time of wind observations) have been analyzed so that any diurnal effect would be discernible and, if appreciable, could be investigated. The analyses have been extended over the surrounding seas with the aid of cloud pictures from weather satellites.

The period examined in this study is June to October, 1964-1967, and the major wind discontinuity is discernible over the Philippines on 473 of the 12-hourly wind charts drawn during this period.

It was found that, in the majority of cases, rainfall was greater at one or both sides of the wind discontinuity than at the discontinuity itself. Since the most likely explanation of this is that the surface of wind-discontinuity possesses slope, a new investigation requiring special observations over a long period has been proposed. Another proposal for further investigation has been made in relation to the diurnal variation of rainfall.

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Maximum Rainfall Values Over Luzon For Duration of 1 And 2 Days And Return Period From 2 To 50 Years
Cipriano C. Ferraris, Bernardo M. Soriano, Jr.
1973

This paper represents an attempt to elaborate the generalized charts of maximum rainfall for different durations and return periods required for the design of small hydraulic structures. In this study, the generalized charts are given for one-day and two-day rainfall and return periods of 2, 5, 10, 15, 25 and 50 years. The results should be applied in a precautionary manner taking into consideration that some of the stations have rainfall data for a continuous period of only 8 years.

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A Study On The Effectiveness Of Four Mathematical Models On The Development Of Sweet Corn (H801) And The Daily Variations Of Solar Radiation And Air Temperature
Emma P. Amores-Vergara
1973

Different mathematical models for assessing the effects of weather on crop development were considered and reviewed. Three popularly used in linear models - the average span, the Reaumur's degree-day equation and the Nuttonson's photothermal equation - and the non-linear equation called the triquadratic model as postulated by Robertson (1968) were tested using meteorological and astronomical data from the Science Garden and the Radiation Center, Philippine Weather Bureau, in Diliman, Quezon City. However, evidences gathered from a year's experiment in the Science Garden consisting of twelve (12) monthly plantings of sweet corn of the H801 variety and also from other investigations along this area pointed to the triquadratic model as postulated by Robertson in 1968 to be the best mathematical expression for calculating the effects of the thermal and solar radiation environment on crop development among the models employed.

The triquadratic model consists of three quadratic terms. They are solar radiation, maximum air temperature and minimum air temperature. The equation integrates these three factors over reasonably short phenological periods during which the physiological processes of the crop are relatively uniform. Furthermore, the triquadratic equation treats the day temperature and the night temperature separately on a daily basis so that extreme conditions are included. These give the triquadratic estimates on crop-weather relationship a more sound physical basis. Moreover, the triquadratic model requires electronic data processing procedures since it has to cope with the series of iteration processes and regression analyses for its mathematical calculations.

Some notable observations emerged from this study as a result of the experiments on sweet corn conducted in the Science Garden. Prominent among these findings were: (1) the average span of time from one stage to another of the crop was dependent on the meteorological environment and (2) the Reaumur's degree-day equation and the Nuttonson's photothermal equation could not fully explain the effects of weather variables on the rate of plant development throughout the different stages of the crop.

One significant conclusion which surfaced from the triquadratic analysis of sweet corn is that the crop's response to solar radiation and air temperature vary from one phenological period to another and that this behavior, inherent in the development stage, is obviously reflected from its coefficients whose values change with the life cycle of the plant.

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Air Pollution Model For Metropolitan Manila Area Using The Gaussian Distribution
Renato R. Abcede
1976

The purpose of this study is to apply the Gaussian Model in estimating relative air pollution concentration over the Metropolitan Manila arising from urban continuous point sources.

The computations were carried out using a fifteen meter effective height of all continuous point sources. The calculation of relative pollution concentrations at the ground and at the 15-meter level was made using a diffusion equation whose primary variables are thermal stability, the generalized diffusion coefficients, and wind speed and direction.

Prevailing wind speed and direction over the study area for each month were used in the computations. Average concentrations for each month over the domain represented by a system of 1-km grid squares for three different stability conditions (unstable, neutral and moderate inversion) were computed. Values were analyzed and isopleths of pollution concentrations were presented.

The results show that:

• During the Northeast Monsoon, pollution concentrates in the Guadalupe (Makati), Bagong Ilog (Pasig), Ermita and Pandacan (Manila) and Baclaran (Rizal) areas.
• During the Southwest Monsoon, pollution concentration concentrate in the Guadalupe, Bagong Ilog, Ermita and Pandacan, Baclaran and also in the Cubao and Balintawak (Quezon City) areas.
• During the transition period from the Northeast to the Southwest monsoon seasons, pollutants were noted to be concentrated in the Guadalupe, Mandaluyong, Cubao and Quiapo areas.
• Maximum concentration at the ground and at 15-meter level were observed to be relatively closer to the source in an unstable condition and relatively far downwind of the source in a stable condition.

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Storm Surge Potentials Of Selected Philippine Coastal Basins
Catalino P. Arafiles, Catalino P. Alcances, Jr.
1978

A historical review of storm surges in the Philippines for the period 1897-1975 reveals certain areas inundated by storm surges. To identify storm surge potentials of Philippine basins, peak storm surges were estimated with the use of a simple empirical relation requiring only the knowledge of three meteorological parameters and the basin shoaling factor. The shoaling factor for each basin was computed by the use of a set of regression equations. Comparisons of actual observed storm tide and computed storm surge shows that the effect of coastal configuration and astronomical tide significantly affect the magnitude of the total storm tide.

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Seismicity Of The Philippines And The Expectations Of Maximum Earthquake Motions
Rolu P. Encarnacion
1981

The study of the seismicity of a certain locality has always been the obsession of many earthquake scientists, since seismicity is the general view of the frequency of earthquakes in a certain place during a certain period. This research paper deals with the Philippine seismic activities for the period 1901 to 1974. With the aid of the basic equation of the Gutenberg-Richter's statistical relation and a modification of this relation by Peter Welkner, 6-value had been determined and subsequently, a-value, which is regarded as the index of the mean annual seismic activity, was also computed for the area of study correspondingly.

Nevertheless, the highlight of this report is on the estimation of expected maximum earthquake motions, that is; the particle velocity at the base rock and the acceleration on the ground at their extreme values for some return periods. For the maximum velocity calculations, Kanai's attenuation model was used and for the maximum acceleration, the average of McGuire and Oliveira's attenuation models were considered. In this aspect, the author utilized computer programs in the analysis and calculation schemes. There were 19 selected sites of the country which were run through the computer program and yielded results favorably in accordance with Philippine seismicity. The importance of these results lies on the fact that it projects a probability of occurrence of at least some destructive tremors during a specific time interval. In seismological point of view, this probability is better known as the earthquake risk over a specified location and on a certain period of time. Furthermore, the probability value will be very useful in the field of Earthquake Engineering.

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A Probable Correlation Between 500-Mb Vorticity Advection And Large-Scale Precipitation
Bernardo M. Soriano, Jr.
1981

In this study, the technique of determining a statistical relationship between a desired meteorological element and parameters from a dynamical model at some projection time was applied to predict precipitation amounts associated with large-scale atmospheric phenomena at three forecast intervals. The 500-mb vorticity advection, which is one of the output parameters of the Barotropic Model developed by the Department of Meteorology and Oceanography, University of the Philippines, was used as predictor in this technique called Model Output Statistics (MOS).

Regional and general simple regression equations were derived on two different grid networks over the Philippines after intermediate preparation of limited available data. This indicated a higher correlation between the variables in the finer grid mesh where curvilinear equations were then obtained. Tests of significance on correlation coefficients favored the non-linear formulas. However, generalized equations of both sets of formula did not have significant difference.

Experiments on ten independent tropical cyclone cases revealed that the curvilinear equations yield generally closer regional estimates over the three forecast intervals. However, predictions were underestimated. The discrepancy of the estimates was attributed to the preponderance of less significant vorticity advection values in the curvilinear formulas. In view of the small diference between the predictions of the two sets of equation and due to the higher significance of the correlation in the curvilinear equations, the use of the last set of formulas was preferred.

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Relationships Among The Meteorological Parameters Observed On Board R/v Researcher And R/v Albacora
Emma A. Vergara, Araceli L. Fontano, Cynthia A. Pajadan
1981

The study aimed to monitor the weather conditions in the open oceans within the Philippine area of responsibility, with particular interest on the state of the sea. The variables ranging from 24 to 27 were used in a stepwise-regression analysis. The technique had offered a fairly reasonable forecasting tool as an alternative due to the lack of any study on parameters like wind waves and swells. In cases where only the wind speed value (FF) would be available, the height of the swell (SHGT) could be roughly expressed as:

                                                      SHGT = -0.0221 + 0.3046 FF

The height of the wind waves (WHGT) at a given day (YY) and wind speed (FF) could be estimated in the form:

                                                      WHGT = 2.7 - 0.113 YY + 0.147 FF

Beyond these preliminary findings, no clear-cut conclusions could be made due to the constraints imposed by the limited observations. It would be worthwhile to consider extending the data input in terms of time and area coverage, in future studies.

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One Dimensional Numerical Model For Storm Surge Prediction
Rolu P. Encarnacion
1984

The Philippines, having the highest annual frequency of tropical cyclones in the world, is considered as a naturally surge-prone area. However, operational application of storm surge prediction schemes in the country are still in the formulative stages of development. This study is a modest contribution to these efforts. A one-dimensional numerical storm surge prediction model is formulated and developed in this paper.

The domain of the model is oriented perpendicular to the coast over a model basin in which the bottom slopes can be varied. The forcing function consists of surface wind generated by model typhoons. Experiments were performed with various formulations of the bottom stress. Several conceivable behaviors of the model typhoons were simulated in the experiments.

The results indicated that the model had performed well in simulating the observed storm surges in Baler, Aurora in 1981. This paper attempted to explain the prediction results with established theories and concepts regarding the behavior and movements of the sea under the actions of the driving and forcing effects of tropical cyclones particularly in the generation of the surges at the coast.

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Storm Surge Numerical Model For Manila Bay
Santiago T. Martin
1985

A storm surge numerical model was developed to compute storm surges induced by a typhoon crossing Manila Bay. The linearized form of the vertically integrated equations of motion for shallow water were used. Five experiments were performed for each of the four cases of typhoon track. Results showed that for a typhoon crossing any point of the bay at any direction from the eastern side, the peak surge occurs at the northern portion of the bay. The highest value is generated by a typhoon moving westward and crosses the center of the bay.

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A Study Of Earthquake Swarm In Siquijor Area
Melba P. Cristobal, Hernando O. Pantoja, Jr., Rolu P. Encarnacion
1987

An earthquake swarm occured in Siquijor Island which lasted for 4 months from December 1980 to March 1981 and was felt intensively in Lazi where epicentral locations were confined. The b value for this type of seismic activity was obtained applying the least squares method with the frequency of events and amplitude as the parameters.

The b defines its relation to a seismotectonic parameter which varies among regions of different geotectonic structures. It also follows a certain pattern to what kind of characteristic the earthquakes fall.

The computed b value in this group of earthquake study is 0.6, a low value belonging to the range when the activity is tectonic in origin. This study further suggests that faulting is a major contributory factor to the continuous generation of ground tremors increasing then decreasing for some period after enough energy has been released.

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Statistical Method Of Forecasting Thunderstorm Over Metro Manila
Esperanza O. Cayanan, Cynthia P. Celebre
1987

Thirty weather elements observed at 0000Z covering the months of March, April and May for a period of 25 years (1961-1985), were chosen as predictors in this study. By using the stepwise regression analysis, three equations for thunderstorm forecasting were derived. The first forecast equation is applicable for March-May period and was formulated using only the first twenty-five predictors. The second equation is adopted for the month of May, using the same predictors. The last equation is adopted for the March-May period and was formulated using all the thirty predictors. Results showed that Equation 3 could be a good tool in forecasting thunderstorms if further testing and refinement is undertaken.

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Ecological Changes Brought About By Human Intervention In The Manila Bay And Its Coastal Areas
Shirley V. Almazan, Catalino P. Arafiles, Bernardo M. Soriano, Jr.
1989

The Manila Bay is one of the Philippines' important bodies of water which is being subjected to tremendous stresses due to the burgeoning population of the Metropolitan Manila Area. Several human activities such as reclamation and wastewater disposal have greatly affected the features of the Bay. These activities and their impacts on the coastal environment are presented in this paper.

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Long Period Variations Of Tropical Cyclones In The Western North Pacific
Carina G. Lao
1989

The long period variations of tropical cyclone occurrence (both frequency and tracks) have been studied. These variations of tropical cyclone have been related with rainfall, pressure, El Niño and the Quasi-Biennial Oscillation. The resulting relationships have been used to develop statistical methods for seasonal prediction.

The frequency of the tropical cyclone occurrence is specified in terms of cyclone days. The relationship between these cyclone days and the different variables mentioned earlier are studied by the ranking method, correlation analysis, compositing and spectral analysis. Prediction equations are developed to predict the total annual number of cyclone days, as well as the corresponding number for selected periods of the typhoon season.

The significant periods which are revealed by the analysis of the long period variations of the cyclone days correspond to periodicities of 36, 24 and 14 months. These periods are also found in the time series of rainfall and pressure. The periodicity at 24 months could be related to the Quasi-Biennial Oscillation.

The study also indicates that the most important relationship is between the frequency of tropical cyclone occurrence and rainfall in Nauru and Galapagos; and pressure in Darwin, which occur a few months before the typhoon season.

With respect to El Niño, there are more tropical cyclones during periods of moderate to strong El Niño. On the otherhand, with respect to Quasi-Biennial Oscillation, more tropical cyclones occur when the 30 mb. zonal wind has easterly component.

The regression equations which have been developed in this study are tested using dependent and independent data sets. The results show that the most accurate prediction equation is the one which predicts the number of cyclone days for the second half of the cyclone season (SEPD).

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Graphical Method Of Rainfall Prediction Over Northeastern Mindanao
Eugenio M. Aquino, Esperanza O. Cayanan, Cynthia P. Celebre
1989

A graphical method of forecasting rainfall over northeastern Mindanao was developed. Eighteen weather elements observed at NAHA (Japan) at 0000Z for a period of 20 years for the months of December, January and February were considered. Four out of these elements were used as predictors. Rainfall data from three stations in the Philippines were utilized as the dependent variable in the study. The method showed encouraging results.

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Variations Of Tropical Cyclones In The Western North Pacific
Carina G. Lao, Rafael P. Lao, Benjamin R. Ofina
1990

This study attempts to improve the first paper of Lao (1989). The relationship between the variations of tropical cyclones in the Western North Pacific, in terms of cyclone days, and the rainfall and pressure of selected stations in Thailand and Hongkong, in addition to the previous data have been studied. The resulting relationships have been used to develop statistical methods for seasonal prediction.

The relationship between these cyclone days and the different variables are studied by the same methods used in the paper of Lao (1989).

Significant correlations are found between the Ubon Ratchathani (Thailand) rainfall and cyclone days. Years with relatively many tropical cyclones are preceded by high rainfall values in this area.

The regression equations which have been developed in this study are verified using one dependent data set and two independent data sets.

The results show that the most accurate prediction is one which predicts the number of cyclone days for the first half of the cyclone season (MAUG). This study suggests that the Western North Pacific tropical cyclone activity is predictable some months prior to the start of the cyclone season.

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Sea Breeze Rainfall Associated With Large Scale Synoptic Condition
Shirley V. Almazan
1990

A numerical model for studying sea breeze rainfall is described. The model uses two-dimensional, time-dependent primitive equations and includes equations for predicting rain and cloud amounts explicitly. Integration of the model has been made to simulate the development of a sea breeze over flat terrain. The large scale prevailing conditions used in the simulation correspond to cases with no prevailing flow, with onshore prevailing flow and with offshore prevailing flow during the rainy season. Experiments on the effect of vertical stability on the characteristics of sea breeze rainfall were also made. The results show that the model is able to simulate the sea breeze circulation reasonably well. In addition, the results also show the development of rainfall in the early afternoon, its intensification with time and its subsequent weakening.

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Simulation Of Cloudiness And Rainfall During The Northeast Monsoon Cold Surge
Rolu P. Encarnacion
1991

A numerical model of the cold surge is developed to simulate cloudiness and rainfall over a warm ocean surface and a land mass with prominent topographic features. The model atmosphere consists of 3 layers: a) surface layer b) mixed layer and c) stable layer. The set of primitive equations is averaged in the mixed layer to yield prediction equations for the horizontal components of the wind, potential temperature and mixing ratio in the layer, and the height of the base of the overlying stable layer. Parameterizations of the interactions between the well-mixed convective layer with both the underlying and overlying layers are employed so that time dependent calculations could be limited to the well-mixed layer.

The model is used to study the dependence of cloudiness and rainfall associated with a cold surge on the prevailing synoptic conditions. A radiosonde observation representing inland conditions is utilized to define the initial state of the atmosphere for a control run. The control run and other numerical integrations (experiments) were used to analyze the cloudiness and rainfall patterns. Two groups of experiments were performed in this study: a) cold surge flow from land mass to warmer ocean surface and b) cold surge flow from the ocean to a warmer land mass with topography.

The results show that the model is capable of simulating the behavior of the atmosphere during cold surge episodes. The predicted variables are found to be reasonable and physically realistic.

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A Modeling Investigation Of Sea Breeze Rainfall
Shirley V. Almazan
1992

A numerical model for studying the development of sea breeze rainfall in the vicinity of a straight coastline is described. The model is based on the time dependent primitive equations which is able to describe explicitly the formation of rain and its subsequent space and time variations. The description is done by incorporating a prediction equation for rain water which is derived through a parameterization of cloud microphysical processes. Integration of the model has been made to simulate the development of a sea breeze over a flat terrain. The large scale prevailing conditions used in the simulation correspond to cases with no prevailing flow, with onshore (sea to land) prevailing flow and with offshore (land to sea) prevailing flow during the rainy season. Experiments on vertical stability, relative humidity, vertical windshear and surface heating in relation to the characteristics of sea breeze rainfall are also made. The experiments show that the model is able to simulate the sea breeze rainfall reasonably well.

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Influence Of Environmental Conditions On Tropical Waves
Bernardo M. Soriano, Jr.
1992

The dependence of the structure and intensity of tropical waves on the vertical profiles of the basic state is studied. A two-dimensional version of the primitive equations in cartesian (x, z) coordinates is integrated to determine the effect of the vertical profiles of the basic zonal wind, the initial temperature and the initial humidity. Microphysical processes are included by use of conservation equations for cloud water, water vapor and rain water. In general, the numerical model is initialized by prescribing a perturbation in the temperature field of 1°K over a horizontal distance of about 60 km from the center and from the surface up to the 900 m ( ^~ 900 hPa) level.

Results of experiments without the prevailing zonal wind indicate that the structure and intensity of the wave are influenced more by the vertical profile of the initial perturbation temperature. The depth of the trough and the strength of the winds around the upper level ridge during the early periods are found to be directly proportional to the position of the perturbation temperature. The intensity of the winds around the trough seems to depend on the magnitude of the perturbation temperature and the humidity of the troposphere during these periods. The wind patterns at these times may be the result of the approximate geostrophic balance condition that is assumed at the initial time. When the other forces become significant, the structure of the wave becomes more or less similar in all cases while the intensity of the winds is still a function of the initial perturbation temperature and initial humidity.

The wave structure and intensity are greatly influenced by the vertical profile of the mean zonal wind also during the early periods, i.e. the trough and ridge axes tend to lean towards the direction of the vertical shear of the zonal wind component. However, in the latter periods, the axes incline toward the direction of the prevailing zonal wind which likewise determine the rate and direction of propagation of the wave. The prevailing zonal flow reduces the intensity of the winds around the wave throughout the integration period. The winds seem to intensify near the lateral boundaries possibly due to the increased horizontal diffusion, which is specified at four grid points near it, and to the no-gradient boundary condition there and zero vertical advection at the top boundary. In general, however, the simulations seem to agree with the results of Kurihara and Kawase (1985) and the observations of Reed and Recker (1971) and Thompson et al, (1979).

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Rainfall Probability Forecasting At Selected Airport Stations In The Philippines
Esperanza O. Cayanan, Lourdes V. Tibig, Carina G. Lao
1992

A short-term statistical model to predict rainfall probability was developed for seven airport stations namely Ninoy Aquino International Airport (NAIA), Mactan International Airport, Laoag, Legaspi, Iloilo, Davao and Zamboanga Domestic Airports based on Markov chain technique. To determine the probability of rainfall, multiple linear least squares regression was applied on 14 covariates using a 16-year data set. The performance of the model was verified using the Half-Brier score and actual testing was undertaken by employing a 3-year independent data set. Most of the monthly forecast equations attained a high percentage accuracy of forecast. However, it is recommended that the use of the model should be supported by subjective analysis.

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Fabrication And Development Of Meteorological Balloons
Teodora B. Domingo
1992

In support of the self-reliance program of the government, a project on the fabrication and development of 100-gm. and 350-gm. meteorological balloons to conform with the quality and standard set by the World Meteorological Organization was initiated in the PAGASA in 1979

Meteorological balloons appear a deceptively very simple device but its fabrication requires accurate instruments and engineering design and elaborate care in compounding. The latex emulsion is compounded with vulcanizing agents, accelerators and antioxidants.

Services to the public through reliable forecast, a factor affecting commerce and industry, shipping and agriculture, is dependent on intensive vertical analysis of the upper atmosphere. Accurate weather forecasting demands availability of upper air data, obtained with the aid of meteorological balloons and production of these balloons is the core of this study.

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A Study Of 40- To 50-Day Oscillation In The Philippines
Cynthia P. Celebre
1993

The occurrence and characteristics of the 40- to 50-day oscillation in the Philippines is studied. Station pressure, rainfall and wind data from different stations located in the country were filtered and subjected to spectral and cross-spectral analyses.

Results of the spectra of station pressure indicate that the oscillation extends from the southernmost (Zamboanga) to the northernmost (Basco) station and from the extreme western (Pto. Princesa) to the easternmost (Guiuan) station. Spectra of wind data showed that the phenomenon seems to be present at all levels of the atmosphere, while spectral peaks at the periods of interest are also present for rainfall. Cross-spectral results of station pressure also indicate that the oscillations in one station are also present in other stations. The phase angle distribution suggests that most oscillations in the area of study propagate westward near the equator, then northwestward to north northwestward in the higher latitudes. Some disturbances that originate from the west travel northeastward to northward. One possible application of the results of this study is the determination of the probable preferred seasonal tracks of tropical cyclones in the Philippines.

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A Study Of Long Duration Rainfall Episode In The Philippines During The Southwest Monsoon
Esperanza O. Cayanan
1994

A long duration rainfall episode which happened during the last two weeks of August 1990 was investigated in order to establish some indicators to predict the future occurrence of a similar phenomenon. The synoptic situations before, during and after the rainfall episode were studied and described. The investigation involved analyses of surface pressure charts, wind profile from surface to 200 hPa levels, important weather systems like tropical cyclones and satellite imageries. Composite maps of surface pressure and geopotential heights at 850 hPa level were preparted. Results showed that the rain episode was caused by the Intertropical Convergence Zone (ITCZ) which passed thru the islands of Batanes connecting with the monsoon trough over China Mainland. The passage of three tropical cyclones during the period activated the ITCZ and enhanced the southwest monsoon flow over the western sections of Luzon, thereby increasing the intensity of rainfall over the area.

The distribution of rainfall in time and space was also examined. It was noted that the long duration rainfall episode started over Southwestern Luzon (Palawan) moving northward and westward. The intensity of rainfall also increases in the same direction. A preliminary criterion for defining a rainfall episode as a SW wet spell was proposed after the investigation.

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Numerical Model For Storm Surge Prediction Incorporating Overland Flooding
Vicente B. Malano
1994

A numerical model is developed for storm surge prediction incorporating overland surges. The model is formulated using the depth-integrated form of the transport equations applicable for storm surges and is applied over an idealized basin with straight coast. Movement of land/sea boundary is one dimensional. The local water elevation and the sea surface slope are examined first to regulate the movement of the boundary. The forcing function of the model consists of surface wind generated by a symmetric cyclone model of Jelesnianski with inflow angle of 15 degrees. The effects of inland inundation of sea water are investigated by varying the slope of inland elevation as well as the basin size and shape. The model is simulated with observed surges in the Bay of Baler and Tandag, Surigao del Sur Basin with considerable success.

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Experiments In Determination Of Radar Reflectivity - Rainfall Intensity (Z-R) Relations In The Philippines
Fredolina D. Baldonado
1996

The approach to the determination of radar reflectivity - rainfall intensity (Z-R) relationship is discussed. Calculations of the simultaneous reflectivity factors and rain rates in a volume of air are performed based on the solution to the radar equations by infusion of the different radar parameters and the measurement of return power of the electromagnetic wave. Linear regressions are applied to the transformed data sets and constants and coefficients in the relations that take the form Z=ARb are determined. A set of empirical Z-R relations for different locations in a river basin as well as for particular storms are obtained. The experimental average relation, Z = 66.8R2.61 is likewise determined.

The relationships show differences in excess of 50% in rainfall rate at the same reflectivity. These differences may be associated with differences in synoptic conditions affecting rain types, geographic location and to variations in precipitation with height.

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Analysis And Prediction Of 5-Day Total Rainfall
Carina G. Lao
1998

Philippine summer rainfall, which contributes to 60 percent of the annual rainfall over most parts of the country, is very vital to the national economy. In the light of the importance of this parameter, this study investigated the variability and characteristics of summer rainfall and its relationship with other parameters. The results were used to formulate equations for the prediction of 5-day total rainfall in Luzon and Manila 5 days in advance.

Linear regression equations were developed for predicting 5-day total rainfall in the summer month of June for 5 areas lying mainly in Northern Luzon, Central Luzon and Manila. The potential predictors considered were 5-day mean surface pressure, 850-, 700-, and 500-hPa pressure heights of stations surrounding the Philippines (Nanning, Ponape and Marianas), and 5-day mean station pressure, rainfall, relative humidity, dew point depression and cloud cover of 11 selected stations in the Philippines. The selection of predictors was done by considering three basic principles, namely, physical relationship with the predictand, availability and predictability. Also, previously observed averaged rainfall (5-day lag) was used as additional predictor. These were preliminarily screened by correlation and then by stepwise regression. A 7-year period of data (1984-1990) was used in the study.

The results of the preliminary investigation showed that rainfall tends to occur concurrently in the 5 areas of the study. The rain episodes are common to all stations that were selected for the study based on a 14-year period (1981-1994).

The relationship between area-averaged rainfall and average surface pressures was determined using time series analysis. Results show that the surface pressures in Marianas, Nanning and Ponape have good relationship with rainfall in the 5 areas of study. If the pressure in Marianas is high (low), rainfall in each area of study is high (low). The opposite results were obtained between rainfall in each area and pressures in Nanning and Ponape.

Prior to the regression analysis, the possible predictors 5 to 12 days before the period to be predicted were correlated with rainfall in the 5 areas of study. Also, 10 sets of data for the predictand/predictors for the 5 areas and for 5-day lag period were also correlated and regressed to determine their relationships with rainfall. Results show that 2 (Area 1 total rainfall and Baguio relative humidity), 2 (Area 2 total rainfall and Baguio rainfall), 10 (Area 3 total rainfall, Ponape and Nanning surface pressures, heights of 850- and 500-hPa level pressure in Nanning, heights of 700- and 500-hPa level pressure in Marianas, pressures of Dumaguete and Dagupan, and Baguio rainfall), 8 (Area 4 total rainfall, heights of 700- and 500-hPa level pressure in Marianas, surface pressures of Dumaguete, Baguio, Catarman and Ambulong, and Baguio rainfall), and 8 (Area 5 total rainfall, Nanning surface pressure, heights of 850- and 700-hPa level pressure in Nanning, height of 850-hPa level pressure in Marianas, surface pressures of Dumaguete and Tacloban and Baguio rainfall) predictors are highly correlated with the rainfall of Areas 1, 2, 3, 4 and 5, respectively, for the month of June, 5 days in advance.

Utilizing the 7-year period of 210 cases on dependent data, results of the verification show that the performance efficiency for each of the 5 areas is more than 80%. Using 4-year independent data (1992-1995), the overall performance efficiency of the regression scheme conducted on 120 cases for each of the 5 areas which is more than 83% is also considered remarkable and promising.

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Rainfall Probability And Visibility Forecasting At Selected Airport Stations In The Philippines
Esperanza O. Cayanan, Bernardo M. Soriano, Jr.
1999

Short range objective techniques of forecasting rainfall probability and visibility at three airport stations in the Philippines (Cagayan de Oro City, Roxas City and Dumaguete City) were developed using stepwise regression analysis. A 15-year data set (1978-1992) was used as developmental data and a three-year data set (1993-1995) was utilized for forecast skill verification. Both rainfall probability and visibility forecast equations for January, February and December (northeast monsoon months) for Cagayan de Oro City Airport can be used operationally at a significant level of accuracy. The forecast equations developed for Roxas City Airport gave insignificant results for most of the months. For Dumaguete City Airport, rainfall probability equations for April and November and visibility forecast equations for March and April attained good results.

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Storm Surge Prediction For Leyte Gulf Area
Vicente B. Malano, Bernardo M. Soriano, Jr., Marino L. Mendoza
1999

A numerical model is developed for storm surge prediction incorporating overland surges over the Gulf of Leyte. The model is formulated using the depth-integrated form of the transport equations applicable for storm surges. Movement of land/sea boundary is one dimensional. The forcing function of the model consists of surface wind generated by a symmetric cyclone model of Jelesnianski with inflow angle of 15 degrees. The model domain is divided into 30 x 41 grids with 1 km spacing. At each grid point, the maximum water height is computed during the 24-hour model time.

Results reveal that the maps of mean envelope of water can be used to predict storm surge over the Gulf of Leyte. With the aid of these maps, improvement of the model can be achieved by incorporating more theoretical typhoons with different characteristics, e.g. radius of maximum winds and typhoon intensity and movement. A similar study can be replicated in other surge-prone areas of the country.

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A Study On Rainfall Intensity For Flood Estimation In San Juan River
Shirley J. David, Gaspar B. Salaguste
1999

The study relates the behavior of rainfall intensity and water level during the passage of the tropical cyclone. The observation of 3-hourly rainfall data from the Science Garden Synoptic Station and the water level from the San Juan River Basin in Quezon City is considered from the time the tropical cyclone entered the Philippine Area of Responsibility (PAR) in order to have a longer series available for the estimation procedures.

The study made use of the regression technique, the Linear Regression with Autocorrelated Errors, to account for the serial correlation that is present in the data. The performance of the developed model is accounted for by using the Mean Absolute Percentage Error (MAPE).

Contrary to most hydrological literatures, rainfall intensity in this particular study was found to be an insignificant parameter to explain the water level in a river. This was attributed to the possibility of non-representativeness of the rainfall data considered in the development of the model. The results showed that lags 1 and 6 are the significant time that have bearing on the consequent behavior of water level.

It is suggested that more cases should be studied to come up with more conclusive results.

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Development Of Wave Model For Selected Philippine Seas
Vicente B. Malano, Bernardo M. Soriano, Jr., Marino L. Mendoza
2000

A numerical/spectral model is adapted over the eastern coast of Luzon and the Bicol Region to predict its state. The model is formulated based on the energy balance equation for deep water. The forcing function of the model consists of surface wind generated by the cyclone model of Holland with inflow angle of 25 degrees. The model domain is divided into 17 x 17 grids with 1 degree spacing. There are five typhoon cases that are investigated in this project. Validations of the model output are investigated using the TOPEX/Poseidon data.

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Regional Rainfall Probability Forecasting In The Philippines
Esperanza O. Cayanan, Bernardo M. Soriano, Jr.
2000

Statistical rainfall forecasting models for the Visayas, Mindanao and Bicol Regions are developed using stepwise regression analysis. For Visayas and Mindanao, a set of 16-year rainfall observations, which are lagged for three hours, was utilized as developmental data and two to three-year independent data for testing. The predictors for the Visayas Region are weather parameters observed at Mactan, Iloilo and Tacloban. Results indicate appreciable performance of the January and February equations while further independent testing is recommended for the May, June and September equations.

For the Mindanao Region, the predictors are from Cagayan de Oro, Davao and Zamboanga. Evaluation of forecasts showed good performance for the June equation, but a longer period of test data is recommended to add more confidence in the forecast. More test data are also recommended for the December, January and February equations to check their real performance. Based on the observed rainfall pattern, it is suggested that Mindanao be divided into eastern and western forecast areas which means that two sets of forecast equations have to be developed.

In the Bicol Region, the predictor data, lagged for one day, from Daet, Legaspi and Virac were used in the regression. Insignificant correlation was obtained, hence a statistical model of shorter time lag and forecast range is proposed.

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Analysis Of Storm Surge Potential Of Various Landfalling Tropical Cyclones
Julie M. Nimes, Fredolina D. Baldonado
2000

Eleven occasions of tropical cyclone occurrences in three categories of depression (winds up to 64 kph), storm (winds > 64 < 119 kph) and typhoon (winds greater than or equal to 119 kph) that made landfall in Albay Gulf were studied including the water level responses due to associated cyclone surges. The time series of water level observations (observed, surge and astronomical tide levels) and the different cyclone parameters (wind and pressure) were examined and other parameters such as radius of maximum winds, landfall point and cyclone angle of approach were investigated. Other physical factors affecting surge levels such as the bathymetry, topography and coastal configuration of the Gulf were likewise described. Eventually, notable surges at the Gulf were compared with those at San Miguel Bay.

The study was supplemented by a statistical dynamical surge model, which gave considerable insight into the expected peak water level at cyclone landfall.

Results show that the different cyclone intensities induce different water level responses. Reasons are proposed for the observed differences.

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An Observational Study On The Rainfall Distribution Structure Of TC Jelawat And TC Saomai By Using Satellite Data
Edino Nonato Leonardo Nolasco
2001

Precipitation information is critical to understanding the hydrologic balance on the global scale and in understanding the complex interactions among the components within the hydrologic cycle. Past researches concentrate mostly on the mean precipitation amount on an hourly, daily, monthly and even yearly basis. In this research our main objective is to know the rainfall distribution structure of a tropical cyclone using satellite data. This paper involves the investigations of rainfall structures of the two tropical cyclone systems that have made landfall over the Island of Okinawa not too long ago, tropical cyclones Jelawat (August 2000) and Saomai (September 2000), using the Geostationary Meteorological Satellite (GMS) data and the Tropical Rainfall Measuring Mission (TRMM) data. GMS data have cloud temperatures in a wide area but have no information about rainfall amount. As for the TRMM data, it has information of rainfall amount but only in restricted regions and time. We succeeded to obtain coarse rainfall structures in a wide area and finally we show the evolution of the total rainfall amount of the tropical cyclones.

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The Effect Of El Niño And La Niña On Philippine Rainfall
Gilda C. Borja
2001

The effects of El Niño/La Niña on Philippine rainfall were studied. The study focused on determining the regional variations of these effects as well as their dependence on the intensity and magnitude of El Niño and La Niña. Rainfall stations all over the country were classified into climate types. Correlation analysis showed that except for type I climate, not all stations belonging to the same climate type have the same rainfall characteristics. It was therefore necessary to sub-group Type III and Type IV climate into two.

Results of lag-correlation analysis between sea surface temperature anomalies and rainfall anomalies show that a tendency of increasing sea surface temperature anomaly (SSTa) is likely to be followed or preceded by a decreasing rainfall anomaly. This was observed for all climate types except for Type I which showed an increasing rainfall after a lag of four months. This could mean that some other factor or system is affecting the areas with Type I climate.

Time series analysis was presented to show the general relationship between rainfall variations and the corresponding sea surface temperature anomalies covering the period 1961-1997. For purposes of smoothing and filtering the rainfall anomaly, running mean or moving average was employed.

In order to determine the general characteristics of rainfall variations, composites were constructed for seven warm episodes (El Niño) and six cold episodes (La Niña) during the period 1961-1997. A composite shows the time variations of the rainfall anomaly curve, with the corresponding curve of SSTa for a three-year period centered at the El Niño or La Niña year. For more intense El Niño, the duration of negative rainfall anomalies was found to be longer and the magnitude is bigger, and positive rainfall anomalies occurred mostly on the last quarter of the La Niña year until the second quarter of the following year for a strong La Niña.

Maps showing geographical variations of rainfall anomalies, both for El Niño and La Niña episodes, show that each episode or event behaves differently in their effects, intensity and magnitude and likewise the areas affected.

Differential maps were constructed to compare events with very similar SSTa, viz; 1979 and 1976 El Niño and 1970 and 1964 La Niña. The rainfall variation during El Niño may be due to cyclone passage over Luzon areas, and the Intertropical Convergence Zone, ITCZ for the lower latitudes. During La Niña differences occur mostly along climate type. Areas of Type I climate are drier, while the rest of the country is wetter, due to weaker southwest monsoon activity and longer period of occurrence of the northeast monsoon or trades.

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Probability Estimation Of Rainfall Incidence At Selected Synoptic Stations In The Philippines
Shirley J. David
2002

The study made use of the first-order three-state Markov chain process to characterize rainfall occurrences. Light rainfall occurs when rainfall amount ranges from 0 - 2.5 mm, moderate rainfall with amount from 2.6 - 15 mm and 15.1 mm or more as heavy rainfall. Data on daily rainfall from seven synoptic stations considered. Factors such as year, month, station and episode (El Niño and La Niña events) were considered to analyze the estimated transition probabilities. To understand and explain the variability that might be inherent to the estimated transition probabilities analysis of variance, variance component analysis and the lag-correlation analysis were used.

The analysis of variance was used for the purpose of determining the significant factors that might explain the estimated transition probabilities. Significant factors were further subjected to variance component analysis. Lag correlation analysis was used to determine if there is a significant relationship between the estimated transition probabilities and the Lagged-Southern Oscillation Index, which was lagged up to eighteen months.

Based on the results of the analysis of variance using the generalized linear models (GLM) procedure of Statistical Analysis Software (SAS), it was noted that for light-to-light and heavy-to-heavy transitions the significant factors were month, station and episode whereas for the other transitions such as light-to-moderate, light-to-heavy, moderate-to-light, moderate-to-moderate, moderate-to-heavy, heavy-to-light, and heavy-to-moderate, month and station were found to be significant.

The estimates of the variance components revealed that the variance associated with the experimental errors are cosiderably larger than the estimated variances of the significant factors considered to have influenced the estimated transition probabilities.

The relationship between the Lagged-Southern Oscillation Index (SOI) and the estimated transition probabilities were determined using the Lag-correlation analysis. The results showed a weak correlation between the estimated transition probabilities and SOI of preceding years nor same year.

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Impact Of Long Duration Atmospheric Variability On Surface Water Supply
Gilda C. Borja, Jocelyn B. Balacuit
2002

The general objective of this study is to combine the salient hydrologic and meteorological variables to derive new variables that would be useful in examining surface water supplies. It also aims to develop a climatology of water variability and demand to examine these for possible critical periods, when a deficit (demand is greater than storage) is expected to occur. Specifically, this study aims to predict long-range seasonal variation of rainfall and surface water supply in the Bicol Region.

The surface water supply in the Bicol Region, particularly the Bicol River Basin was examined for 36 years, 1960-1996. A hydrologic accounting system, using rainfall and temperature as inputs was used to derive variables such as Potential Evapotranspiration (PET), soil moisture and runoff. These were combined with the basic hydrologic variables (stream discharge and lake contents).

Annual and monthly rainfall during normal wet and dry years were calculated and plotted to derive the geographical rainfall variations in the study area. It was also used to combine with other basic variables to derive additional variables such as Delta, storage and demand.

Complete time-series climatologies for all variables were presented.

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A Study Of Tropical Cyclone Activity Over Northwest Pacific Before, During And After The 1997-1998 El Niño Episode
Jori J. Loiz
2003

The variations of tropical cyclone activity in the Northwest Pacific, particularly in the Philippine Area of Responsibility (PAR), are greatly influenced by an atmospheric and oceanographic phenomenon called El Niño-Southern Oscillation (ENSO), which occurs every 2 to 9 years. This phenomenon affects the Philippine economy since it is mainly agriculturally-based. Agriculture is dependent on rainfall which is contributed largely by tropical cyclones that enter or originate in the PAR.

This study is an attempt to determine the effects of El Niño, particularly the 1997/1998 event, on the tropical cyclone activity in the PAR. NCEP/NCAR reanalyzed charts of mid-tropospheric humidity, upper-level divergence, outgoing longwave radiation (OLR) anomaly, sea surface temperature (SST) anomaly and wind vectors in 850- and 200-hpa are used in the study. These parameters are mentioned by Gray (1977) as essential factors in tropical cyclone formation.

Reduction of tropical cyclone formation and activity is observed at the height of the occurrence of ENSO. Also, the opposite is observed when the cold episode, which is called La Niña, starts to affect the region.

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ENSO Events And Impacts On Angat And Magat Water Reservoirs
Vivien S. Esquivel
2004

The reliability of our water resources is of today’s great concern. An assessment would be of great help to water resources managers and policy makers in that it would show the changes in the efficiency of the present water resource systems under extreme climate events like El Niño and La Niña.

A statistical analysis was undertaken in this study, relating the behavior of inflows of Angat and Magat water reservoirs with the corresponding El Niño indices i.e., sea surface temperature anomalies (SSTA) and Southern Oscillation Index (SOI).

Standardized monthly inflow anomalies from April to March of the following year to concide with the rain-year were averaged and plotted in a time series to show the general relationship between inflow and the corresponding sea surface temperature anomalies and Southern Oscillation Index. With Angat water reservoir, four (4) negative anomalies were experienced out of the six (6) El Niño episodes and two (2) positive anomalies. On the other hand, five (5) out of six (6) La Niña episodes exhibited positive anomalies and one (1) negative anomaly. Magat water reservoir experienced four (4) negative anomalies during the six (6) El Niño events and four (4) positive anomalies during the six (6) La Niña events.

To examine further the effects of ENSO, continuous monthly-standardized inflow anomaly data from 1970 to 2002 observed in Angat and Magat water reservoirs were also assembled in a time series. These data were lag correlated from 0 to 12 months with the corresponding SSTA and SOI averages and found to have consistent negative values with SSTA and the opposite with SOI. SSTA’s strongest relationship with inflow is on the 4th month lag time and SOI’s strongest relationship with inflow is on the 3rd month lag time. These relationships refer to both reservoirs. Magat exhibited higher correlation values than Angat.

Composites for a 36-month period of each El Niño and La Niña events were also presented to show the magnitude of inflow anomalies during these extreme climate events. El Niño composites were centered at the peak of SST positive anomaly, while La Niña composites were centered at the peak of SOI positive anomaly. Negative inflow anomalies on both reservoirs are significant during El Niño years. La Niña years did not cause much impact on inflow anomalies and their effects are comparable to normal years.

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Simulation Of Sea And Mountain Breezes Over Metro Manila
Cynthia P. Celebre
2004

Terrain-induced meso-scale circulations such as sea and mountain breezes occurring over Metro Manila were examined. The study involved observational as well as theoretical phases.

The observation stage that was undertaken on 14-16 May 2002 aimed to use the gathered data to initialize and validate the model as well as determine the variations of the structure of the lower atmosphere during the daytime. During the study period, NAIA, Port Area, and Science Garden synoptic stations were used. The PAGASA Astronomical Observatory was temporarily employed by installing instruments that observed relative humidity, dry bulb temperature and wind speed and direction. The radiosonde mobile van of the Natural Disaster and Research Branch (NDRB) of PAGASA was also employed. A simultaneous three-hourly release of pilot balloons was also made at the PAGASA Astronomical Observatory and the Planetarium in Rizal Park in Manila. A vehicle moving every hour from 8AM to 5PM from Quirino Grandstand towards inland was also part of the observation program.

Analyses of specific humidity, temperature and wind speed and direction showed that Port Area was frequently affected by sea breeze although the circulation penetrated inward up to the vicinity of the PAGASA Astronomical Observatory. Onset of sea breeze in NAIA was difficult to determine due to the effect of Manila Bay and Laguna de Bay on the area.

The second segment applied the Advanced Regional Prediction System (ARPS) numerical model that was developed by the Center for Analysis and Prediction of Storms (CAPS) of the University of Oklahoma, U.S.A. It was utilized to simulate the meso-scale circulations occurring over the domain during the day.

The ARPS Version 4.0 was implemented for the entire Metro Manila Area including the Manila Bay and Laguna de Bay. With a 2-km grid spacing, the horizontal domain had 55 x 55 grid points spanning about 110 km x 110 km (1° latitude x 1° longitude). The study made use of the three-dimensional Cartesian geometry (X, Y, Z) with 80-grid points and 200 m grid distance in the vertical.

Six experiments were designed to determine the effects of various factors such as wind speed, wind direction and land use on a flat or with terrain domain, in the development of terrain-induced meso-scale circulations. The results of these experiments showed that for a flat domain, rainfall occurred near the urban area for low wind speed. Increasing the wind speed caused the rainfall to move farther from the urban area but no rainfall was observed for the maximum wind speed used. The amount of accumulated rainfall, was greatest for the lowest wind speed. It was also observed that changes in the wind direction caused changes in the location of cloud and rainfall formation.

For a domain with terrain, it was observed that the urbanization effect with respect to temperature was not evident in all simulations since cloud and rainfall were observed near the mountain. Accumulated rainfall increased for the 2 m/s wind but no rainfall was also noticed for the 5 m/s wind speed.

A late formation of cloud was observed when only rural and water surfaces were utilized instead of also including an urban area as land use. Results also displayed that cloud and rainfall occurrences were located at the eastern most section of the domain.

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The Effect Of Moving Storm Rainfall Over Angat Basin
Nestor B. Nimes
2004

Series of experiments are conducted to demonstrate the effect of moving storm rainfall over a catchment such as the Angat basin. Four (4) years of hourly rainfall accumulation from three (3) gaging locations in the study area comprise the dataset used in the study. First and second order moments (mean, variance, auto-covariance and cross-covariance) are evaluated and used to establish the different parameters of the Neyman-Scott stochastic, space-time rainfall model. The model is based on clustering principle in storms and the random characteristics of storm rainfall. The parameters are established by the application of the Newton-Raphson Iterative Non-Linear Least Squares and the Fletcher-Reeves Conjugate Gradient methods for optimization.

Rainfall fields are generated with specified storm direction of movement and at different speeds. Eight (8) cardinal directions and five (5) storm speeds are applied and produced seventy two (72) hours of rainfall traces in various amounts and spatial distribution over the basin.

The effect of moving storm rainfall is investigated by the application of the National Weather Service-PC version model (NWS-PC) in the simulated runoff hydrographs based on the stochastically generated rainfall data, soil data and basin characteristics as input. Corresponding inflows are investigated in terms of times to peak, peak discharges and total volumes.

Results show that most of the maximums of the rainfall fields generated are located at the exit of the storms except the one coming from the south, where the maximum of the rainfall field is located in the east side instead in the north. This finding shows a notable variability in the location of maximums in the rainfall field at different directions. The variation in the total maximum generated rainfall at different directions is range from 195 mm. to 240 mm. This variation at different directions of storm may be small, but cannot be disregarded. Apparently, the variation in the pattern of minimum and maximum values in the rainfall field is significant on the distribution of the rainfall field, in its location and its spatial distribution. The findings mentioned above, indicate that at different storm directions influence the spatial rainfall distribution, while different speeds affect considerably the magnitude of rainfall over the basin.

The investigation shows that the variations on the times to peak both in the direction and speed are quite considerable at the 50% CDF but not at the 90% CDF. There are significant variations in the times to peak in the 10 kph and 20 kph speeds based on different directions, while other speeds have no indication of variations. The slower storms generated large amount of rainfall than the faster storms in all directions. In slower storms, the peak discharges and the corresponding total volumes are higher than the faster storms in all directions. Hence, the storm movements have significant effect on inflow in the Angat reservoir and cannot be neglected in proper evaluation and assessment for dam operation.

The Neyman-Scott stochastic, space-time rainfall model is recommended for hydrologic simulation studies because of its capability to capture the rainfall physical structure and characteristics, and its ability to capture the space-time structure of the rainfall process. Likewise, the National Weather Service PC version model for runoff simulation is also recommended because it can run fast on desktop computers both in calibration and simulation mode. Moreover, it is flexible in its input, parameterization and output operation and can be applied in any type of basin.

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Markov Chain Model For Daily Rainfall Occurrence At Selected Synoptic Stations Over Luzon
Shirley J. David
2004

The study made use of the first-order three-state Markov chain process to characterize rainfall occurrences. The three states were defined as light, when rainfall amount ranges from <60mm/24 hr, moderate, when rainfall amount ranges from 60 – 180 mm/24 hr and heavy, when rainfall amount is >180mm/24 hr. To derive the transition probability matrices the method of maximum likelihood was used in the estimation of the transition probabilities. Data on daily rainfall from nine (9) synoptic weather stations were considered. Factors such as month, station and Sea Surface Temperature anomalies (Ssta) were considered to analyze the estimated transition probabilities. To understand and explain the variability that might be present in the estimated transition probabilities the analysis of variance using the Generalized Linear Models (GLM) procedure were performed.

The analysis of variance approach was used to determine the significant factors that might explain the estimated transition probabilities. Based on the results of the analysis of variance using the GLM procedure of the Statistical Analysis System (SAS), it was noted that for light-to-light transition no factors were found to significantly affect its occurrence. For the light-to-moderate, light-to-heavy, moderate-to-light, moderate-to-moderate, moderate-to-heavy, heavy-to-light, heavy-to-moderate and heavy-to-heavy the factor SSTa was found to have significant contribution in their variability. Aside from SSTa, month and station appear to be significant factors to consider in explaining the variations in the following transitions light-to-moderate, light-to-heavy, moderate-to-light, moderate-to-moderate and heavy-to-light. For the transition moderate-to-heavy the factor station, aside from Ssta, was found to significantly affect its variability. For heavy rainfall occurrences preceded by moderate rainfall occurrences the factor month was also found to be significant.