Simultaneous Presence of 30 and 60 days ISO modes in Indian Summer Monsoon Observed from TRMM Merged

Rainfall Data

M S NarayananNational Atmospheric Research Laboratory, Gadanki

 Shivani Shah, C.M. Kishtawal, V. Sathiyamoorthy

Meteorology & Oceanography Group (MOG), SAC

M. Rajeevan India Meteorological Department, Pune

R. H. KriplaniIndian Institute of Tropical Meteorology, Pune

3rd ISRO – CNES joint Workshop on Megha Tropiques 19th October 2005

 

Instantaneous Rainfall – over oceans and Land 19, 22, 37, 85 GHz

Less utility – because of poor temporal sampling (3-4 per day)

Rainfall highly variable in space and time

Megha – Tropiques – MADRAS MW sensors

Products from TRMM Project – (Predecessor to Megha Tropiques)

24 hr accumulated daily rainfall at 1° x 1° produced in combination with IR / Vis data from Geostationary satellite

- 3B42 version 5 (global) from 1998 to 2003 (now version 6)

3B43 monthly rainfall

Merged Rainfall from MW (TRMM), Meteosat (IR) & Gauge

Rain-rate : CTT Threshold,Texture based C/S Separation

Rain-rate : MW Emission/Scattering algorithms

Tuning of Vis/IRRain algorithmUsing MW and

gauge rain

Tun

ing

Par

amet

ers

for

Mer

ger

Rai

nfal

l

Observations from

Gauge Network

TRMM

MeteosatMerged

Such data set for TRMM available from 1998 to dateAlso GPCP 1DD from 1996 to date

OBJECTIVES

Validation of daily TRMM merged rainfall over

Indian land mass, and

Studying Monsoon ISO oscillations in rainfall

1 2

3

333 grids

TRMM data for 1998 to 2003

1998 2002

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100Rain Rate (mm/day)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

Log

( N )

2001

Frequency Distribution

1998 20022001

1998 2001 2002

(b) : Grids in which IMD analysis shows 1 mm or more rain and 3B42 has no rain

(c) : Average percentage of days (all six years – monsoon months) in which 3B42 shows no rain, for cases when IMD shows 1 mm or more rain

(a) : Grids in which 3B42 shows 1 mm or more rain and IMD analysis shows no rain

2001

y = 0.1996x + 5.2187CC = 0.33

y = 0.2754 x + 4.2841CC = 0.54

IMD

(a) Individual days

(b) Seasonal mean

15 July 2001 - IMD15 July 2001 – 3B42 Difference – 15 July 2001

July 2001

Seasonal 2001

23rd July 2001

Seasonal variance in daily rainfall in 3B42 and IMD for 2001 and 2002

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30 35 40 45

IMD

3B42

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

IMD

3B42

3 x 3

5 x 5

1 x 1 Box1 -2001

y = 0.5355x + 1.5158CC = 0.63

y = 0.7442x + 0.4822CC = 0.83

y = 0.7632x + 0.3377CC = 0.87

MINICOY

PORTBLAIR

Comparison over the oceans ( 5 day running mean) – Minicoy and Port Blair

y = 0.6907x + 2.2288cc = 0.69

y = 0.4648x + 3.3735cc = 0.72

For studying Intra Seasonal Periodicities

IMD - daily 3B42 - daily

IMD – 5 day running mean 3B42 – 5 day running mean

Time series of all India daily and running mean pentad rainfall

2001

Year Observed 3B42

1998 90.3 87.6

1999 84.0 78.4

2000 80.8 76.1

2001 80.7 77.5

2002 71.2 63.6

2003 89.8 87.4

All India Seasonal Rainfall (cm)

Year June July August September

IMD 3B42 IMD 3B42 IMD 3B42 IMD 3B42

1998 227 158 328 278 288 245 213 193

1999 211 152 317 251 245 211 187 170

2000 231 190 294 243 261 195 141 133

2001 257 224 317 239 234 184 127 127

2002 206 178 167 126 269 239 140 93

2003 218 174 324 302 235 232 145 166

Monthly All India average rainfall

0

5

10

15

20

251 5 9 13

17

21

25

29

33

37

41

45

49

53

57

61

65

69

73

77

81

85

89

93

97

101

105

109

113

117

121

3b42

imd

1 June – 30 September

Time series of IMD and 3B42 rain at all India scale for 2003

Rai

n R

ate

IMD – All India - 2003 TRMM – All India - 2003

2

4

8

16

32

64

Mode

2

4

8

16

32

64

Mode

Wavelet showing various modes in IMD and 3B42 rainfall

Power

Year

Year

Power

Contribution of 10 – 20 day mode

Contribution of 30 - 60 day mode

Contribution of 10 – 20 day and 30 – 60 day modes in different years

IMD – All India - 2003 TRMM – All India - 2003

2

4

8

16

32

64

Mode

2

4

8

16

32

64

Mode

Wavelet showing various modes in IMD and 3B42 rainfall

IMD – All India - 2003 TRMM – All India - 2003

Significance of the various periodicities at 95 % confidence

2

64

16

32

8

4

Global Wavelet

Variance (mm2)

2

64

16

32

8

4

Global Wavelet

Variance (mm2)

1998

2001

2003

Rainfall over the oceans

Buoy

TMI

DS 3 2000 Bay of Bengal

2

4

8

16

32

64

2

4

8

16

32

64

Per

iod

(D

ay)Oceanic Winds

Buoy

TMI

DS 1 1998 Arabian Sea

2

4

8

16

32

64

2

4

8

16

32

64

Per

iod

(D

ay)SST

Water Vapour over the oceans

Global Wavelet

Variance (m/s2)

Hovmollor plot showing propagation characteristics of the ~ 30 and ~ 60 day modes : for rainfall and NCEP 850 mb winds for the year 2001

2003 : No clear propagation for wind or rainfall

1998 : Northward for 30 day for both wind and rainfall

Overall : Inconclusive – but both parameters show similar trend in both modes

GPCP

3B42 1° x 1° deg Version -5

3B42 0.25° x 0.25° deg Version - 6

IMD

Mean July - 1998

Conclusions & Future Work

* 3B42 limitation in picking variability & high rainfall

* Differences in Specific boxes IR estimates also to be improved for merged rainfall Comparison with version 6 and GPCP 1DD

* Useful for studying ISO / IAV* Simultaneous ~ 30 and ~ 60 days modes seen in some years* Linkage with Interannual Variations