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
Chiang Mai

Eastward
Line shape

Jul 99Aug 98

Jul 98Jun 98

May 98050100(%Echo area (over 10 DBZ)
in each stripe; MAY to JUL 1999
Windward side(western area)
20

Mountainousregion

(%)

15

111034567891220

reg01
reg02
reg03
reg04

Lee side(eastern area)

(%)

20

reg05
reg06
reg07

151510101055505101520(LT)05101520(LT)(%)

0reg08
reg09
reg10
reg11

5101520(LT)Echo area (over 10 DBZ)
in each stripe; October 1999
Lee side(western area)
20

Mountainous
region

(%)

20

reg01
reg02
reg03
reg04

15

1110345678912Windward side(eastern area)

(%)

20

reg05
reg06
reg07

1515

10

10

10

5550

5101520(LT)05101520(LT)

(%)
reg08
reg09
reg10
reg11

0

5101520(LT)Tracking process of radar echoes

If overlap of two echoes exceeds 50% of
the smaller one,the movement of the center of gravity ofeach echo is defined as the movement ofthe echo.

Test of the tracking algorism

An example of the echo tracking

28

Contribution of each region to echo area ofthe specified region (May – Jul, ’98 – ’00)

15
141(x104km2)

2020Reg 8

1020

Reg 9

1010

1

5

10

15

2025(region)

Reg 1015101520

125(region)

51015

2025(region)z Echoes originate in mountains constitute the diurnal peak echoarea in mountains.
z In leeside regions, contributions of echoes originate in the sameregion decreases, and contribution of echoes coming from the2020
Reg 11upwind region increases.
Reg 12Reg 1320101010

1510152025(region)

1510152025(region)

1510152025(region)

28

Contribution of each region to echo area ofthe specified region(Oct, ’98 – ’00)

15
141(x104km2)

55Reg 22Reg

1510152025(region)

5Reg 33Reg

15101520Reg 4Reg
4125(region)

510152025(region)z The contributing region in October is symmetric to those inMay-July, when the major wind direction is reversed(x104km2)

55Reg 55
Reg

1510152025(region)

5Reg 6110152025(region)

Reg 7Reg

1510152025(region)

28

Contribution of smaller echoes（< 800km2 ≒28x28km）(May – Jul, ’98 – ’00)
150(x104km2)
2

Reg 1075150

151(x104km2)
2

Reg 1175
11(x104km2)
1010550150

48

12 16 20 (LT)Reg 12(x104km2)
275015048121620 (LT)Reg 1375
11(x104km2)
1010550(x104km2)
248121620 (LT)048121620 (LT)

14

28

Contribution of larger echoes（> 800km2 ≒28x28km)(May – Jul, ’98 – ’00)
150(x104km2)
2

Reg 10150

151(x104km2)
2

Reg 117575

11(x104km2)
10

10

5

50150

4812 1620 (LT)Reg 12(x104km2)
2

75

0150

48121620 (LT)Reg 1375
11(x104km2)1010550(x104km2)
24812 1620 (LT)04812

1620 (LT)14

Diurnal variation of radar echoes ~diurnal variation of precipitation
Total diurnal variationReg 11

Total variation has
similar characteristics
to the larger echovariation.

Contribution oflarger echoes
Reg 11Moving from monsoon windward region.
Phase of diurnal variation depends on thedistance from mountains.

Contribution ofsmaller echoes
Reg 11

Small convective clouds born above theeach area.
Phase doen’t differ much between areas.

Andeach 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 theobservation, results are very
promising.