Earth Radiation Budget Studies over the tropical

monsoon region using satellite data

P. C. Joshi

Meteorology and Oceanography Group

Space Applications Centre (ISRO)

Radiation Balance of the Earth

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)

Earth Radiation Budget Satellites

Instrument & Satellite

Altitude

(km)

Resolution

(km)

Inclination

(Deg)

Period

ERBE-ERBS (PT-72day)

610 30 57 Nov 84- Feb90

ERBE-NOAA9 812 45 99 Feb85-Jan87

ERBE-NOAA10 830 45 99 Oct86-May89

ScaRaB/ Meteor

(PT - 209Day )

1200 60 82.6 Feb94-Mar95

ScaRab/ Resurs 830 45 99 Aug98-Apr99

CERES/TRMM (PT- 46 Day)

350 10 35 Jan98-Aug98

CERES/Terra 705 25 99 Mar2000 onward

CERES/Aqua 705 25 99 Jul2002 onward

ERB Missions

Instruments

Shortwave 0.2-5.0 m

Longwave 5.0-50.0 m

Total waveband

0.2-50.0 m

ERBE Scanner

Shortwave 0.2-5.0 m

Window Channel

8.0-12.0 m

Total waveband

0.2-50.0 m

CERES/TRMM

Visible (VIS) 0.55-0.65 m

Solar (SW) 0.2-4.0 m

Total (TW) 0.2-200 m

IR Window (IR)

10.5-12.5 m

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

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 2.52.5 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

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

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

Understandings from the ERB satellites

YEARLY AVERAGE NET RADIATION (ERBS)

(Difference between Absorbed SW and Emitted LW)

Wm-2Positive = WarmingNegative = Cooling

The zonal distribution of net radiation is shown for July 1985 and January 1986 (ERBE Data)

Positive = WarmingNegative = Cooling

Five year (1985-89) average Net Cloud Radiative Forcing in JJAS and April (ERBS)

Wm-2

10 June 1994

Comparison of OLR from ScaRaB and INSAT

ScaRaB broadband data provided a chance to validate the OLR derived from INSAT narrowband.

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)

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.

Cloud Radiative Forcing over the Asian Monson Region

Scatter plot between Shortwave and Longwave Cloud Radiative Forcing

Imbalance

Balance

Asian Monsoon Region

West Pacific Region

1985 1986 1987 1988 19890

20

40

60West Pacific Region

Year

0

20

40

60

Clo

ud A

mou

nt (%

)

Asian Monsoon Region

Low Middle High

High, Mid and Low Cloud amount over Asia and West Pacific Warm Pool

Jet is responsible for the large high cloud amounts

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

Cloud Top Temperature

INSAT Vis Imagery

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.

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.

Variation of high cloud amount with variations in TEJ

-25 -20 -15 -10 -5 0

Velocity (m/s)

This scatter plot confirms that the high cloud amount increase with increase in the speed of TEJ

-25 -20 -15 -10 -5 0 5

-80

-60

-40

-20

0

20Y = -5.95 +1.8 X

R = 0.48

NCRF

Velocity (ms-1)

0

30

60

90

120

150

180Y = 51.3 - 1.2 X

R = -0.37

LCRF

Clo

ud R

adia

tive

Forc

ing

(Wm

-2)

-180

-150

-120

-90

-60

-30

0Y = -56.6 + 3.03 X

R = 0.56

SCRF

SCRF Vs Wind

LCRF Vs Wind

NCRF Vs Wind

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

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?

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

Data Gap over the Asian Monsoon region

ERBS June 1988

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

Comparison of Outgoing Longwave radiation (W/m2) derived from INSAT-3A and NOAA, for 15 Oct. 2004

Operational Uses

1. Atmospheric Model Diagnosis

2. Initialization

3. Assimilation

THANKS