Influence of the Upper Tropospheric Wind shear upon Cloud Radiative Forcing in the Asian Monsoon Reg

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Earth Radiation Budget Studies over the tropical
monsoon region using satellite data
P. C. Joshi Meteorology and Oceanography
Group Space Applications Centre (ISRO)
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Radiation Balance of the Earth
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Earth Radiation Budget Satellites
Radiation Budget Satellites are designed to
measure the radiation budget of the Earth from
space. They use broadband channels to measure
emitted longwave and reflected shortwave fluxes
from the Earth-atmosphere system.

• Major ERB Missions
• Earth Radiation Budget Experiment US
• ScaRa-1 2 France, Russia Germany
• CERES (TRMM, Aqua, Terra) Japan/US
• Geostationary ERB (European Union)
• ScaRaB/MT (India, France)

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ERB Missions
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Instruments
ERBE Scanner
CERES/TRMM
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ScaRaB Scanner

• Two Narrow channels are added to test the
  cloud/Clear-sky detection
• MT Altitude 820 km, Inclination 20? ,
  Resolution (nadir) 45 (40?) km

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• ScaRaB Data Processing
• Data Processing of ScaRaB is similar to ERBE
  processing
• Determination of the scene type (Cloud cover
  estimate using maximum likelihood technique)
• Spectral corrections applied to deduce SW
  radiance from the filtered SW radiance (required
  due to the imperfect flatness of spectral
  response)
• Apply scene type-dependent angular correction
  models to deduce SW and LW fluxes of the pixel as
  a function of the measured radiances
• These fluxes are averaged over a geographical
  area of 2.5??2.5? latitude and longitudes.
• Diurnal models are then applied in order to
  compute regional monthly mean values of the mean
  and clear-sky fluxes.
• --Duvel et al, 2001, BAMS

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Understandings from the ERB satellites

• Before satellite era, key climate variables like
  Albedo, net radiation are computed from model
  calculations.
• Satellites revealed that the Planet is darker
  than theoretical values.
• On global annual mean basis, absorbed solar
  radiation is in balance with the outgoing
  longwave radiation
• Balance between solar and longwave radiation also
  exists on hemispherical scale.
• Quantitative estimates about the atmospheric
  greenhouse effect.

---Ramanathan, 1987
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Understandings from the ERB satellites

• Accurate measurement of the solar constant.
• Meridional transport of energy by the atmosphere
  and oceans
• Regional radiative forcing (deserts, monsoon,
  etc)
• Net radiative effects of the clouds on climate
• Influence of cloud radiative forcing on the
  general circulation.

---Ramanathan, 1987
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YEARLY AVERAGE NET RADIATION (ERBS) (Difference
between Absorbed SW and Emitted LW)
Positive Warming Negative Cooling
Wm-2
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The zonal distribution of net radiation is shown
for July 1985 and January 1986 (ERBE
Data) Positive Warming Negative Cooling
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Five year (1985-89) average Net Cloud Radiative
Forcing in JJAS and April (ERBS)
Wm-2
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Comparison of OLR from ScaRaB and INSAT
ScaRaB broadband data provided a chance to
validate the OLR derived from INSAT narrowband.
10 June 1994
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Cloud Radiative Forcing over the Asian Monson
Region

• ERB satellites provided opportunity to study the
  radiative forcing of the Clouds.
• Clouds either cool or warm the planet depending
  on how much area they cover, how thick they are
  and how high they are.
• Averaged over the Globe, Cooling by the clouds
  is about -50 Wm-2 and warming is about 30 Wm-2.
  So net effect of clouds is cooling (-20 Wm-2)
• But on an average deep convective clouds of the
  tropics neither cool or warm (Kiehl and
  Ramanathan, 1990)

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Cloud Radiative Forcing over the Asian Monson
Region

• Rajeevan and Srinivasan (2000) showed that during
  the summer monsoon season (June to September)
  near cancellation of SCRF and LCRF is not valid
  in the Asian monsoon region
• Our study suggested that TEJ (Prominent only over
  Asia) efficiently redistributes the liquid/ice
  particles brought up by deep convection and
  increase the high cloud amount (Sathiyamoorthy et
  al, 2004)
• Increased clouds block the incoming SW radiation
  and thereby cool the region.

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Scatter plot between Shortwave and Longwave Cloud
Radiative Forcing
Asian Monsoon Region
West Pacific Region
Balance
Imbalance
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High, Mid and Low Cloud amount over Asia and West
Pacific Warm Pool
Jet is responsible for the large high cloud
amounts
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Cloud Top Temperature
INSAT Vis Imagery
INSAT imagery and cloud top temperature suggest
that the deep convective clouds are spread at the
upper levels Low level clouds in the Arabian Sea
are undisturbed
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Mean Wind at the Upper Troposphere (200 hPa) JJAS
Strong Winds in the form of Tropical Easterly Jet
found only over Asia increase the high cloud
amount by spreading the vertically growing
monsoon clouds.
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Cirrostratus Cloud amount in July from ISCCP-D2
(1983-2001)
ISCCP data suggest that the spreading of
vertically growing cloud by the jet increase
Cirrostratus clouds.
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Variation of high cloud amount with variations
in TEJ
This scatter plot confirms that the high cloud
amount increase with increase in the speed of TEJ
-25 -20 -15 -10 -5
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Velocity (m/s)
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Association between Jet speed and Cloud Radiative
Forcing
For a 10 m/s increase in the speed of jet SCRF
increases by 30Wm-2 LCRF increases by 12
Wm-2 NCRF increases by18 Wm-2
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• Challenges
• Satellites estimates of the Net radiation
  provide a non-zero value (5 Wm-2). Due to
  instrumental problems?
• Long-term trend if any in radiation budget
  quantities.
• Earth radiation balance during major ENSO, Major
  Volcanic events, severe monsoons.
• Poor temporal coverage of sun-synchronous ERB
  satellites over Tropics.
• Large data gaps in estimating clear-sky fluxes
  over the permanently covered regions including
  Asian monsoon region.
• Do clouds decrease or increase Global Warming?

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Sensitivity studies indicate that relatively
small changes in global cloudiness can have a
large impact on our climate system.
50 increase in carbon dioxide may warm the Earth
much less than a 50 increase in the amount of
high cirrus clouds. -CERES Document
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Data Gap over the Asian Monsoon region ERBS June
1988
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• Poor Temporal Coverage over the Tropics in
  earlier ERB missions (except CERES/TRMM)
• Emitted longwave and reflected shortwave
  underwent large changes during the observational
  period of CERES/TRMM due to the strongest El Nino
  of the century
• So more reliable estimates over the tropics is
  necessary

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Comparison of Outgoing Longwave radiation (W/m2)
derived from INSAT-3A and NOAA, for 15 Oct. 2004
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• Operational Uses
• Atmospheric Model Diagnosis
• Initialization
• Assimilation

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THANKS