Diurnal Variation of Precipitation over Northern Thailand –Radar Observation– T. Satomura, K. Okumura(Kyoto University) T. Oki (RIHN), Warawut Khantiyanan (BRRAA) and TMD Chiang Mai Radar staffs

Working Hypothesis

Radar Sites

Averaged Variation

Echo area (over 10 DBZ) in each stripe; MAY to JUL 1999 11 3 4 5 6 7 8 9 10 1 2 Windward side (western area) Mountainous region Lee side (eastern area) (%) 10 20 15 5 (%) 10 20 15 5 (%) 10 20 15 5 reg01 reg05 reg08 reg02 reg06 reg09 reg03 reg07 reg10 reg04 reg11 5 10 15 20 (LT) 5 10 15 20 (LT) 5 10 15 20 (LT)

Echo area (over 10 DBZ) in each stripe; October 1999 11 3 4 5 6 7 8 9 10 1 2 Lee side (western area) Mountainous region Windward side (eastern area) (%) 10 20 15 5 (%) 10 20 15 5 (%) 10 20 15 5 reg01 reg05 reg08 reg02 reg06 reg09 reg03 reg07 reg10 reg04 reg11 5 10 15 20 (LT) 5 10 15 20 (LT) 5 10 15 20 (LT)

Tracking process of radar echoes If overlap of two echoes exceeds 50% of the smaller one, the movement of the center of gravity of each echo is defined as the movement of the echo.

Test of the tracking algorism

An example of the echo tracking

14 1 15 28 Contribution of each region to echo area of the specified region (May – Jul, ’98 – ’00) (x104km2) 20 20 20 Reg 8 Reg 9 Reg 10 10 10 10 1 5 10 15 20 25 1 5 10 15 20 25 1 5 10 15 20 25 (region) (region) (region) Echoes originate in mountains constitute the diurnal peak echo area in mountains. In leeside regions, contributions of echoes originate in the same region decreases, and contribution of echoes coming from the upwind region increases. 20 20 20 Reg 11 Reg 12 Reg 13 10 10 10 1 5 10 15 20 25 1 5 10 15 20 25 1 5 10 15 20 25 (region) (region) (region)

14 1 15 28 Contribution of each region to echo area of the specified region(Oct, ’98 – ’00) (x104km2) 5 5 5 Reg 2 Reg 2 Reg 3 Reg 4 Reg 3 Reg 4 1 5 10 15 20 25 1 5 10 15 20 25 1 5 10 15 20 25 (region) (region) (region) The contributing region in October is symmetric to those in May-July, when the major wind direction is reversed (x104km2) 5 5 5 Reg 5 Reg 5 Reg 6 Reg 7 Reg 7 1 5 10 15 20 25 1 10 15 20 25 1 5 10 15 20 25 (region) (region) (region)

14 1 15 28 Contribution of smaller echoes （< 800km2 ≒28x28km） (May – Jul, ’98 – ’00) 150 (x104km2) 150 (x104km2) Reg 10 2 Reg 11 2 75 75 1 1 (x104km2) 10 10 5 5 4 8 12 16 20 (LT) 4 8 12 16 20 (LT) 150 (x104km2) 150 (x104km2) Reg 12 2 Reg 13 2 75 75 1 1 (x104km2) 10 10 5 5 4 8 12 16 20 (LT) 4 8 12 16 20 (LT)

14 1 15 28 Contribution of larger echoes （> 800km2 ≒28x28km) (May – Jul, ’98 – ’00) (x104km2) 150 150 (x104km2) Reg 10 2 Reg 11 2 75 75 1 1 (x104km2) 10 10 5 5 4 8 12 16 20 (LT) 4 8 12 16 20 (LT) 150 (x104km2) 150 (x104km2) Reg 12 2 Reg 13 2 75 75 1 1 (x104km2) 10 10 5 5 4 8 12 16 20 (LT) 4 8 12 16 20 (LT)

Diurnal variation of radar echoes ~ diurnal variation of precipitation Total diurnal variation Total variation has similar characteristics to the larger echo variation. Reg 11 Contribution of larger echoes Contribution of smaller echoes Reg 11 Reg 11 風下の各小領域での日変化は、15時前後にその小領域内で発生する小規模対流雲による日変化と、風上から移動する大きなシステムによる、山岳地帯からの距離によって位相の違う日変化との重ねあわせでできている Moving from monsoon windward region. Phase of diurnal variation depends on the distance from mountains. Small convective clouds born above the each area. Phase doen’t differ much between areas.

And each region has each diurnal variation Ohsawa et al. (2001)

Thus we started 3D simulations Triply nested (54km, 18km, 3km) Nonhydrostatic MM5 Though phase of diurnal variation of precipitation is 2-3 hours behind from the observation, results are very promising.