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 data  Parameters: MSLP, Wind at 850 and 200 hPa  Climatological data from TMD  Data 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 sunInter Tropical Convergence Zonevertical 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. Coriolis effectNorthern Hemisphere  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 prevail Andaman sea and Thailand 1988 is Lanina year the active southwest monsoon prevail Andaman sea and Thailand

1980 is a neutral year the active Easterly wind prevail south China sea, upper Thailand. The Southern Thailand is westerly wind is Elnino year Easterly wind prevail South China Sea and Thailand 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 NeutralLanina 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. ศูนย์ภูมิอากาศ กรม อุตุนิยมวิทยา The Meteorological Department (TMD) Climatological Center

Onset of rainy season in Thailand ( ) May El ninoLaninaNeutral ศูนย์ภูมิอากาศ กรม อุตุนิยมวิทยา The Meteorological Department (TMD) Climatological Center

 Analysis data from 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 normal 200 hPa  Easterly wind prevail over Thailand and active than normal La nina Year : 850 hPa  Southwest monsoon prevail over upper Thailand and weakly than normal 200 hPa  Easterly wind prevail over Thailand and weakly than normal

Thank You for your kind Attention