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
0 50 100
May 98
Jun 98
Jul 98
Aug 98
Jul 99
Chiang MaiEastwardLine shape
(%)
Echo area (over 10 DBZ) in each stripe; MAY to JUL 1999
Windward side(western area)
Mountainousregion
Lee side(eastern area)
0 5 10 15 20(LT)
0 5 10 15 20(LT)
reg01reg02reg03
reg05reg06
1234567891011
(%)
10
20
15
5
(%)
10
20
15
5
reg07
(%)
10
20
15
5
0 5 10 15 20(LT)
reg08reg09reg10reg11reg04
Echo area (over 10 DBZ)in each stripe; October 1999
Lee side(western area)
Mountainousregion
Windward side(eastern area)
0 5 10 15 20(LT)
1234567891011
0 5 10 15 20(LT)
(%)
10
20
15
5
(%)
10
20
15
5
(%)
10
20
15
5
reg01reg02reg03reg04
reg08reg09reg10reg11
reg05reg06reg07
0 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
Contribution of each region to echo area of the specified region (May – Jul, ’98 – ’00)
(x104km2)
141
1528
20
10
5 2515101 20(region)
20
10
5 2515101 20(region)
20
10
5 2515101 20(region)
20
10
5 2515101 20(region)
20
10
5 2515101 20(region)
20
10
5 2515101 20(region)
Reg 8
Reg 12 Reg 13
Reg 10Reg 9
Reg 11
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.
Contribution of each region to echo area of the specified region(Oct, ’98 – ’00)
(x104km2)
141
1528
Reg 25
5 2515101 20(region)
Reg 55
5 2515101 20(region)
Reg 35
5 2515101 20(region)
Reg 75
5 2515101 20(region)
Reg 45
5 2515101 20(region)
(x104km2)
Reg 2
Reg 6
Reg 7
Reg 4Reg 3
Reg 5
The contributing region in October is symmetric to those in May-July, when the major wind direction is reversed
5
2515101 20(region)
Contribution of smaller echoes （ < 800km2 28x28km≒ ）
(May – Jul, ’98 – ’00)
150
75
10
5
2
1
(x104km2)
(x104km2)
0 4 8 16 20 12 (LT)
150
75
10
5
2
1
(x104km2)
(x104km2)
0 4 8 16 20 12 (LT)
150
75
10
5
2
1
(x104km2)
0 4 8 16 20 12 (LT)
150
75
10
5
2
1
(x104km2)
0 4 8 16 20 12 (LT)
Reg 12
Reg 10 Reg 11
Reg 13
141
1528
Contribution of larger echoes（ > 800km2 28x28km)≒
(May – Jul, ’98 – ’00)
150
75
10
5
2
1
(x104km2)
(x104km2)
0 4 8 16 20 12 (LT)
150
75
10
5
2
1
(x104km2)
(x104km2)
0 4 8 16 20 12 (LT)
150
75
10
5
2
1
(x104km2)
0 4 8 16 20 12 (LT)
150
75
10
5
2
1
(x104km2)
0 4 8 16 20 12 (LT)
Reg 10
Reg 13Reg 12
Reg 11
141
1528
Diurnal variation of radar echoes ~ diurnal variation of precipitation
Total diurnal variation
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.
Reg 11Reg 11
Reg 11
Contribution of larger echoes
Contribution of smaller echoes
Total variation has similar characteristics to the larger echo variation.
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 the observation, results are very promising.
