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

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Simultaneous Presence of 30 and 60 days ISO modes
in Indian Summer Monsoon Observed from TRMM
Merged Rainfall Data M S Narayanan National
Atmospheric Research Laboratory, Gadanki
  Shivani Shah, C.M. Kishtawal, V.
Sathiyamoorthy Meteorology Oceanography Group
(MOG), SAC M. Rajeevan India Meteorological
Department, Pune R. H. Kriplani Indian Institute
of Tropical Meteorology, Pune 3rd ISRO CNES
joint Workshop on Megha Tropiques 19th October
2005  
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Megha Tropiques MADRAS MW sensors

• 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

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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

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

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

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OBJECTIVES

• Validation of daily TRMM merged rainfall over
  
• Indian land mass, and
• Studying Monsoon ISO oscillations in rainfall

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333 grids
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1
3

• TRMM data for 1998 to 2003

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Validation
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1998
2002
2001
Frequency Distribution
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2001
2002
1998
(a) Grids in which 3B42 shows 1 mm or more rain
and IMD analysis shows no rain
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
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2001
y 0.1996x 5.2187 CC 0.33
y 0.2754 x 4.2841 CC 0.54
(a) Individual days
IMD
(b) Seasonal mean
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July 2001
Seasonal 2001
23rd July 2001
15 July 2001 - IMD
15 July 2001 3B42
Difference 15 July 2001
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Seasonal variance in daily rainfall in 3B42 and
IMD for 2001 and 2002
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Box1 -2001
3? x 3?
1? x 1?
y 0.5355x 1.5158 CC 0.63
y 0.7442x 0.4822 CC 0.83
5? x 5?
y 0.7632x 0.3377 CC 0.87
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MINICOY
y 0.6907x 2.2288 cc 0.69
PORTBLAIR
y 0.4648x 3.3735 cc 0.72
Comparison over the oceans ( 5 day running mean)
Minicoy and Port Blair
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All India Scale
For studying Intra Seasonal Periodicities
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2001
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
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All India Seasonal Rainfall (cm)
Monthly All India average rainfall
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Rain Rate
Time series of IMD and 3B42 rain at all India
scale for 2003
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IMD All India - 2003
TRMM All India - 2003
Wavelet showing various modes in IMD and 3B42
rainfall
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Contribution of 10 20 day mode
P o w e r
Contribution of 30 - 60 day mode
Contribution of 10 20 day and 30 60 day
modes in different years
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IMD All India - 2003
TRMM All India - 2003
Wavelet showing various modes in IMD and 3B42
rainfall
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IMD All India - 2003
TRMM All India - 2003
Significance of the various periodicities at 95
confidence
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1998
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2001
25
2003
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Rainfall over the oceans
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Oceanic Winds
DS 3 2000 Bay of Bengal
2 4 8 16 32 64
Buoy
Period (Day)
2 4 8 16 32 64
TMI
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SST
DS 1 1998 Arabian Sea
2 4 8 16 32 64
Buoy
Period (Day)
2 4 8 16 32 64
TMI
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Water Vapour over the oceans
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Global Wavelet
Variance (m/s2)
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Hovmollor plot showing propagation
characteristics of the 30 and 60 day modes
for rainfall and NCEP 850 mb winds for the year
2001
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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
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Mean July - 1998
3B42 1 x 1 deg Version -5
IMD
GPCP
3B42 0.25 x 0.25 deg Version - 6
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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