Inter-annual Variation of Southwest Monsoon and ENSO in Thailand

Ms. KornraweeSitthichivapak, Director, Climatology Center. Mr. Charoon Laohalertchai, Director, Northern Meteorological Center, Chiangmai. Ms. SugunyaneeYavinchan, Director, Numerical Weather Prediction.

To study impact of ENSO on SW Monsoon over Thailand

To study mechanism of SW Monsoon, linking to ENSO

30 years (1971 – 2000) meteorological dataParameters: MSLP, Wind at 850 and 200 hPaClimatological data from TMDData Reanalysis from ECMWF

Analyze monthly wind direction and its speed from July to September at 850 and 200 hPa

Compare monthly wind direction and its speed between ENSO year and neutral year

Analyze pattern winds for starting and ending of the rainy season (account for topography)

Compare pattern winds for starting and ending of the rainy season between ENSO year and neutral year

To know the variability of the wind patterns

for starting and ending of the rainy season

To know the variability of the wind patterns during the SW monsoon in the ENSO year.

Monsoon is the result of the shift of the Inter Tropical Convergence Zone (ITCZ) under the influence of the vertical sun

the South East Trade winds of the Southern Hemisphere have to cross the equator to reach the ITCZ

Coriolis effect in northern hemisphere to turn to its right are deflected eastwards in the Northern Hemisphere transforming into South West trades.

orographic rain

MAY

JUNE

JULY

AUGUST

SEPTEMBER

OCTUBER

Surface wind upper wind

Edward Linacre and Bart Geerts:1997

1980 is a neutral year Southwest wind prevail Andaman sea , southern Thailand and upper Thailand

1997 is a El ni no year

Westerly wind prevailAndaman sea and

Thailand

1988 is Lanina yearthe active southwest monsoon prevail Andaman sea and Thailand

1980 is a neutral yearthe active Easterly wind prevail south China sea , upper Thailand. The Southern Thailand is westerly wind.

1997 is Elnino yearEasterly wind prevail South China Sea and Thailand.

1988 is a Lanina Year Northeast wind prevail Northeast Thailand For Southern Thailand is active westerly wind

850 and 200 hPa mean wind JJAS in neutral year 850 and 200 hPa mean wind JJAS in strong El- Nino year 850 and 200 hPa mean wind JJAS in strong La- Nina year

850 hPa Elnino Neutral

Lanina

Elnino Neutral Lanina

200 hPa

Criteria used by the Thai meteorological Department Upper level, westerly wind is changed to easterly Lower level, wind is changed to westerly or

southwest wind In any 5-day period, there must be at least

3continuous days with rain, or the total 5-day rain must be at least 25 mm with the minimum daily rain of 5 mm.

ศูนยภ์มูอิากาศ กรมอุตนิุยมวทิยา The Meteorological Department (TMD)Climatological Center

Onset of rainy season in Thailand ( -19712000)M

ay

El nino Lanina Neutral

ศูนยภ์มูอิากาศ กรมอุตนิุยมวทิยา The Meteorological Department (TMD)Climatological Center

Analysis data from 1971-2000 found that Neutral year : the beginning of rainy season is mostly

mid May El nino year : the beginning of rainy season is late than

neutral year La nina year : the beginning of rainy season is earlier

than neutral year Analysis of monsoon pattern during May found that La nina year : Southwest monsoon prevail over the

Andaman sea, Thailand and the Gulf of Thailand is stronger and clearer than neutral year and El nino year.

El nino year : Mostly westerly wind prevail the Andaman sea Thailand and the Gulf of Thailand

For the end of rainy season is mostly mid October all condition.

El nino year :850 hPa Southwest monsoon prevail over upper Thailand and

more active than normal200 hPa Easterly wind prevail over Thailand and active than

normal La nina Year : 850 hPa Southwest monsoon prevail over upper Thailand and

weakly than normal200 hPa Easterly wind prevail over Thailand and weakly than

normal

Thank You Thank You for for

your kind Attentionyour kind Attention