Geoscience Reference
In-Depth Information
The variation in rainfall is caused by many factors. One of the interest-
ing factors is the ENSO phenomenon. Although the center of this event is in
the equatorial Pacific, many researchers have indicated that the impacts of
this phenomenon on the climates cover more than 75% of the earth.
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Some of the examples are the change in the pattern of floods, droughts,
cyclone, and severe storm activity.
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There are two phases of ENSO:
warm events (known as El Nino) and cold events (known as La Nina). In
general, when El Nino event occurs, the first visible impact is an increase
in rainfall in the eastern Pacific, including parts of South America, and
a decrease in rainfall in the western Pacific locations such as Australia,
Indonesia, Southeast Asia, and the Philippines. The amount of rainfall
opposite to El Nino event, is on the La Nina event.
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That is, a decrease in
rainfall in the eastern Pacific and parts of South America, and an increase
in rainfall in the western Pacific.
Recently, the regional climate model is increasingly being used for
simulating the characteristic of rainfall. In this study, the case studied in
ENSO during 1997-2000 was chosen to investigate the characteristic of
rainfall in each region of Thailand. There are two events of ENSO during
this period: El Nino year 1997-1998 and La Nina year 1999-2000. Basically,
the area average is used to summarize the rainfall during the rainy season
of Thailand. The anomaly months were simulated by the RAMS model.
2. Methodology
2.1
. The observed data analysis
The monthly rainfall data during 1 January 1972-31 December 2001 are
taken from Thai Meteorological Department. These data were selected to
study the amount of rainfall over Thailand during the ENSO year and
the normal year. All the observed stations were scattered in six regions
including 16 stations in northern, 16 stations in northeastern, 10 stations
in central, 10 stations in eastern, 14 stations in southern (east coast), and
5 stations in southern (west coast) part of Thailand.
2.2
.Modelsimulation
The regional climate model based on the RAMS
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version 6.0, developed
at Colorado State University, was employed for these experiments. The
basic equations were a set of nonhydrostatic compressive dynamic equations
