Variations Of Tropical Cyclones In The Western North Pacific

Carina G. Lao, Rafael P. Lao, Benjamin R. Ofina

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.

Cloud Classification

Flaviana D. Hilario

Two methods (maximum likelihood and parallelepiped) of classifying clouds types and terrestial surfaces at daytime using three channels of the Advanced Very High Resolution Radiometer (AVHRR) are presented. Using spectral information, five cloud types (low, cumulus, cirrus over land, high and combination of high and low), land, sea, and snow were identified. Both methods were able to classify land, sea, low, cirrus over land and high clouds fairly well. The use of the ratio of Channel 2 to Channel 1 helped in recognizing sunglint and snow as well as providing a very clear distinction between land and water surfaces which is not possible with the use of two-channel (visible and infrared) classification. However, difficulties were encountered by both techniques in identifying cumulus clouds and combination of high and low clouds. A visual comparison with the manual nephanalysis done by the Royal Meteorological Society showed that the maximum likehood was found to give better classified images than the parallelepiped but the latter is much faster. For better visual analysis, a majority filter was applied to the classified images. The smoothing technique resulted in less unclassified pixels for the parallelepiped classification and bigger cloud type areas for both methods.

Sea Breeze Rainfall Associated With Large Scale Synoptic Condition

Shirley V. Almazan

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.