The Effects Of Orography On Wind, Cloud, And Rainfall Patterns During Typhoon Ketsana (2009)
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Date
2012-03
Authors
Tan, Fuyi
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Publisher
Universiti Sains Malaysia
Abstract
Understanding the orographic effect is crucial for both disaster prevention and weather prediction for events such as tropical cyclones (TCs). Because of the complexity of orographic effects, due to the presence of mountains, the influence of orography on TCs remains unclear and is an active area of scientific research. The objective of this study is to investigate the effects of orography on the rainfall, wind, and cloud systems of the TCs in Malaysia, as this type of study has never been performed in Malaysia. Indochina is taken into consideration because it encountered the landfall of Typhoon Ketsana within the study period, allowing a comparison of the direct impact and the tail-end effect (indirect impact) of the typhoon in terms of wind, cloud, and rainfall on the orographic effects.
Remote sensing techniques have been used to study the impacts of TCs. Using data from the Fengyun 2D (FY-2D) satellite, we observed the development and structure of Typhoon Ketsana, which occurred from September 21 to October 4, 2009. To determine the relationship of the typhoon with the orographic effect, remote sensing techniques such as the Global Digital Elevation Model (GDEM) from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite, wind information from the Navy Operational Global Atmospheric Prediction System (NOGAPS), and radiosonde data were applied in this study.
This study provides an example of how the orographic effect is important to weather forecasters, as high mountain ranges were able to influence the distribution of the cloud, rainfall and even wind flow patterns during the typhoon season; but how significant or obvious the relationship between the orography and the typhoon’s impacts were depended on the intensity of the typhoon system and its movement. From this study, the following conclusions can be drawn: 1) rainfall tends to be distributed over high mountain regions; 2) wind flow will change its direction upon encountering any restrictions, especially those of high terrain regions; and 3) cloud patterns are deformed by high mountains and tend to flow with the mountains’ structure because of the orographic effects.
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Keywords
Orographic effect is crucial for both disaster prevention , weather prediction for events such as tropical cyclones