The Surface Features of Southwest Monsoon Onset over Thailand

The Surface Feature of SouthwestMonsoon Onset Over ThailandPrasarn SangwaldachPrungchan WongwisesRobert. H. B. Exell andDusadee SukawatThe Joint Graduate School of Energy and Environment,King Mongkut’s University of Technology Thonburiprasarn@tmd.go.th

Outline• Background• Methodology• Numerical Simulation• Conclusion

Background1. Schematic of the southwest monsoon- The monsoon is a seasonal wind.- persistent winds with seasonal change in direction incertain local areas, duration and periods every.- results from thermodynamic difference between thesea and continent.Jay S. Fein and Pamela L. Stephens (1987), Monsoons

Background (continue)2. Asian southwest monsoon- The Siberian plateau is now warmer than the seas.- The winds blow from from high pressure areas in the seato the low pressure areas or warm cyclone in the continentLLHJay S. Fein and Pamela L. Stephens (1987), Monsoons

Background (continue)- The agriculture in Thailand are favored by thetropical monsoon climate- Some studies are shown that the meteorological elementshave significant effects on the onset process.a) The monthly mean surface air temperaturesexceed 33-35°C in the land areas of northwest Indiaand adjoining areas (Joshi,1990)b) The progressive development of heat lows before andduring the monsoon onset is the major causative factorsof the Indiansummer monsoon circulation (Rao, 1976)c) Through extends from the sea level to 500 hPa(Keshavamurty, 1970)

Questions1. How to indicate the onset date.2. How the meteorological parameters change duringthe monsoon onset period.3. What are meteorological parameters which the mostimpact to southwest monsoon onset in Thailand.

MethodStartData collectionPlot selected parametersECMWFTMDEvaluate outputAnalysis andselect monsoonOnset dateResult discussionConclusionRun MM5 Model

The southwest monsoon onsetofficial definition of TMD.- The low-level wind direction change to Southor Southwest component- The upper wind direction must change fromWest to East component- There are continuous 3 rainy-days in the period of5 days and not less than 5 mm in each day and thecumulate rainfall in the period must not less than25 mm.

Problems• Not suitable for real time forecasting.• Can not use in case of abnormal rainfall(heavy rainfall, tropical cyclone, etc.)• Try to use dynamical parameters from NWP Model.• Can use the parameters from the existing forecastingmodel (MM5, TMD, ECMWF).

Southwest Monsoon Onset Date in MayArea 1996 1997 1998 1999 2000Upper Thailand 7 18 17 4 15The periods of this study- case 1 1-14 May 1996,- case 2 11-25 May 1997,- case 3 10-24 May 1998,- case 4 28 April - 10 May 1999, and- case 5 8-22 May 2000.

The result interested parameters1.Surface air temperature2.Sea level pressures3.Surface relative humidity4.Surface sensible heat flux5.Wind field at 850, 500 and 200 hPa6.Vertical relative humidity* The results show only sample in 1996 but the otheryears are reasonable

Wind fields at 850 hPaAt 00 UTC on 2/5/1996 At 00 UTC on 7/5/1996At 00 UTC on 12/5/1996

Wind fields at 500 hPaAt 00 UTC on 2/5/1996 At 00 UTC on 7/5/1996At 00 UTC on 12/5/1996

Wind fields at 200 hPaAt 00 UTC on 2/5/1996 At 00 UTC on 7/5/1996At 00 UTC on 12/5/1996

Surface relative humidity (%)At 00 UTC on 2/5/1996 At 00 UTC on 7/5/199680-85 %80-90 %At 00 UTC on 12/5/199685-95 %

Vertical relative humidityAt 00 UTC on 2/5/1996 At 00 UTC on 7/5/199690 %500-100 hPa90 %1000-700 hPa90 %1000-700 hPa90 %1000-700 hPaAt 00 UTC on 12/5/199690 %1000-700 hPa90 %1000-700 hPa90 %1000-700 hPa

Surface air temperature (°C)At 00 UTC on 2/5/1996 At 00 UTC on 7/5/199628-29 °C30 °CAt 00 UTC on 12/5/199627-29 °C

Sea level pressure (hPa)At 00 UTC on 2/5/1996 At 00 UTC on 7/5/19961008-1010 hPa1009-1010 hPaAt 00 UTC on 12/5/19961009-1011 hPa

Surface sensible heat flux (W/m 2 )At 00 UTC on 2/5/1996 At 00 UTC on 7/5/1996100-200 W/m 2100-300 W/m 2 100-200 W/m 2At 00 UTC on 12/5/1996

Comparison of model RMSE values withWMO Standards.Root mean square error of 1996 1997 1998 1999 2000 2002Limits forerrorsSurface air temperature (°C) 1.36 0.93 1.49 0.97 1.02 1.16 4 °CSea level Pressure (hPa) 0.43 1.22 1.51 0.43 0.42 1.78 2hPaSurface relative humidity(%)1.74 1.52 1.59 1.72 1.69 1.44 15%

Conclusion• The surface air temperature, sea level pressure, andsensible heat flux were the most important indicators ofthe monsoon onset over Thailand.•The surface air temperature and sensible heat fluxincreased before and during the monsoon onset, and fellduring the period after the monsoon onset.Temperature Sensible heat fluxTemperatureSensible heat fluxTemperature (?C)30.53029.52928.52827.5271 2 3 4 5Onset periodSensible heat flux (W/m2)3503002502001501005001 2 3 4 5Onset period

Conclusion (continued)• The sea level pressure and surface relative humidityincreased before and during the monsoon onset, and werestationary during the period after the monsoon onset.•The vertical relative humidity and wind field at 850 hPa,500 hPa and 200 hPa were the major characteristics of thesouthwest monsoon throughout the period.Sea level pressure Relative humiditySea level pressureRelative HumiditySea level pressure (hPa)1012101110101009100810071006Relative humidity (%)100959085807510051 2 3 4 5701 2 3 4 5Onset periodOnset period

Conclusion (continued)•The vertical relative humidity and wind field at850 hPa, 500 hPa and 200 hPa were the majorcharacteristics of the southwest monsoonthroughout the period.

The proposal for new monsoon onsetdefinition for ThailandParametersBefore the monsoononsetDuring the monsoononsetAfter the monsoon onsetSurface air temperature °C 28-29 30

Acknowledgments• This work was supported by the Joint Graduate School ofEnergy and Environment, King Mongkut’s University ofTechnology Thonburi.• Special thanks are offered to the European Center forMedium Range Weather Forecasting (ECMWF) andThai Meteorological Department (TMD) for data supportedand Penn State/NCAR for (MM5) version 3 model anddocuments.

Thank you for your attention