The Earth’s surface is kept warm

through one source: the Sun. It is the

primary source for Earth’s energy.

Some of the incoming sunlight and

heat energy is reflected back into

space by the Earth’s surface, gases in

the atmosphere, and clouds; some of

it is absorbed and stored as heat.

When the surface and atmosphere

warm, they emit heat, or thermal

energy, into space. The “radiation

budget” is an accounting of these

energy flows. If the radiation budget

is in balance, then Earth should be

neither warming nor cooling, on

average.

Clouds, atmospheric water vapor and

aerosol particles play important roles

in determining global climate through

their absorption, reflection, and

emission of solar and thermal energy.

Earth’s Radiation Balance and Cloud Radiative ForcingEarth’s Radiation Balance and Cloud Radiative Forcing

04/21/23 2

Solar Constant measured by satellites at TOA

11-yr solar cycle

EarthEarthSystemSystemResponseResponse

How does the Earth Respond?

IMPACTS

Feedback

Of the total forcing of the climate system, 40% is due to the Of the total forcing of the climate system, 40% is due to the direct effect of greenhouse gases and aerosols, and 60% is direct effect of greenhouse gases and aerosols, and 60% is from feedback effects, such as increasing concentrations of from feedback effects, such as increasing concentrations of

water vapor as temperature rises.water vapor as temperature rises.

Forces ActingForces ActingOn the EarthOn the EarthSystemSystem

Major Climate System ElementsWater & Energy CycleCarbon Cycle

Atmospheric Chemistry

CoupledCoupledChaoticChaoticNonlinearNonlinear

Atmosphere and OceanAtmosphere and OceanDynamicsDynamics

Radiative Forcing from 1750 to 2000Radiative Forcing from 1750 to 2000

IPCC, 2001IPCC, 2001

Anthropogenic Forcings

From M. Prather University of California at Irvine

Human Influence on ClimateHuman Influence on Climate

Carbon Dioxide Trends: 100yr lifetime

Methane Trends

Sulfate Trends

Global Temperature Trends

Global Radiation Budget

04/21/23 8

Daily mean solar flux at TOADaily mean solar flux at TOA

1) The Sun is closest to the Earth in Jan. So more solar energy received in SH than in NH.2) At the equinoxes, the solar insolation is at a Max at the equator and is zero at the poles.3) At the SS of NH, daily solar insolation reaches a Max at NP. At the WS of NH, the Sun does not rise above north of about 66.5o, where solar insolation is zero.

1% relative error in A

1 W m-2 flux error 0.5C error in Ts

2xCO2 => +4 W m-2

Top-of-Atmosphere Radiation Budget(Incoming Solar = Outgoing Longwave)

A = Planetary Albedo

S0 = Solar Irradiance

Te = Earth Radiative Temperature

Ts = Equilibrium Surface Temperature

The Greenhouse Effect

Longwave Radiation

Solar Radiation

Clouds have been classified as the highest priority in climate change by the U.S. climate change research initiative because they are one of the largest sources of uncertainty in predicting potential future climate change

12

The effect of clouds on the Earth's radiation balance is measured as the difference between clear-sky and all-sky radiation results

FX(cloud) = FX(clear) – FX(all-sky)

FNet(cloud) = FSW(cloud) + FLW(cloud)

where X= SW or LW

Negative FNet(cloud) => Clouds have a cooling effect on Climate

Positive FNet(cloud) => Clouds have a warming effect on Climate

Cloud Radiative Forcing

04/21/23 14

Cloud Radiative Forcing (CRF)

Since cloud-base temperature is typically greater than the clear-sky effective atmospheric radiating temperature, CRFLW is generally positive.

The magnititude of CRFLW is strongly dependent on cloud-base height (i.e., cloud-base temperature) and emissivity.

Conversely, clouds reflect more insolation than clear sky, therefore, CRFSW is always negative over long time averages or large spatial domains. The magnititude of CRFSW cooling strongly depends on the cloud optical properties and fraction, and varies with season.

Earth (No Clouds) Earth (With Clouds)

57 W m-2342 W m-2107 W m-2

342 W m-2

235 W m-2285 W m-2

235 W m-2265 W m-2

FSW (cloud) =-50 W m-2

FLW (cloud)= 30 W m-2

=> Net Effect of Clouds = -20 W m-2

A brief history of ERB missions

CERES Data Processing Flow

CERES Calibration/Location

Cloud Identification;TOA/Surface Fluxes

Surface andAtmospheric Fluxes

Time/SpaceAveraging

ERBEInversion

ERBEAveraging

AngularDistribution

Models

DiurnalModels

CERES Surface Products

CERES Time AveragedCloud/Radiation

TOA, SFC, Atmos

ERBE-Like Products

Algorithm Theoretical Basis Documents: http://asd-www.larc.nasa.gov/ATBD/ATBD.htmlValidation Plans: http://asd-www.larc.nasa.gov/valid/valid.html

CERESData

Cloud ImagerData

AtmosphericStructure

GeostationaryData

6 Months 6 Months 6 Months 6 Months

18 Mo.

24 Mo.

30 Mo.

36 Mo.36 Mo.

42 Mo.

42 Mo.

CERES Advances over Previous Missions• Calibration Offsets, active cavity calib., spectral char.• Angle Sampling Hemispheric scans, merge with imager

matched surface and cloud propertiesnew class of angular, directional models

• Time Sampling CERES calibration + 3-hourly geo samplesnew 3-hourly and daily mean fluxes

• Clear-sky Fluxes Imager cloud mask, 10-20km FOV• Surface/Atm Fluxes Constrain to CERES TOA, ECMWF

imager cloud, aerosol, surface properties• Cloud Properties Same 5-channel algorithm on VIRS,MODIS

night-time thin cirrus, check cal vs CERES• Tests of Models Take beyond monthly mean TOA fluxes

to a range of scales, variables, pdfs• ISCCP/SRB/ERBE overlap to improve tie to 80s/90s data.• CALIPSO/Cloudsat Merge in 2006 with vertical aerosol/cloud

Move toward unscrambling climate system energy components

CERES InstrumentTRMM:TRMM:Jan-Aug 98Jan-Aug 98and Mar-Apr 2000and Mar-Apr 2000overlap with Terraoverlap with Terra

Terra: Terra: Mar 00 - presentMar 00 - presentplanned life: 2006planned life: 2006

Aqua: Aqua: July 02 startJuly 02 startNow in checkoutNow in checkoutPlanned life to 2008Planned life to 2008

NPOESS: NPOESS: TBD: gap or overlap? TBD: gap or overlap? 2008 to 2011 launch2008 to 2011 launch

CERES Clear-Sky TOA Longwave Flux (W m-

2)

CERES TOA Longwave Cloud Forcing (W m-2)

CERES LW Terra Results - July 2000

CERES Clear-Sky TOA Shortwave Flux (W m-2)

CERES TOA Shortwave Cloud Forcing (W m-2)

CERES SW Terra Results - July 2000

CERES Net Cloud Forcing (July, 2000)

Li and Leighton (1993)

Li and Leighton (1993)

Solar Energy Disposition(in percentage)

• The upper values are from satellite, middle ones from GCMs and the bottom from limited surface data

3030100100

464650504242

242242002828

Forces Acting on Climate(in Watts per meter2)

Forc

ing

(W

/m2)

Assessment of Cloud Absorption and Earth’s

Radiation Budget

• What is going on with recent debate on cloud absorption problem following ARESE ?

• What is the most sound value for global surface solar radiation budget at present?

Li et al. (Nature, 1995)

Validation of satellite SRB estimates to check if the difference increases with cloud cover

Hypothesis to be tested

If CAA exists, satellite retrieval of SRB would not agree with ground-based observations, and the difference would increase with cloud amount

Li (J. Climate, 1998)

Summary of ARESE Studies

• Cloud absorption anomaly is not supported by ground-based, nor space-borne measurements.

• The central piece of information supports cloud absorption anomaly comes from TSBR aboard Egrett, which are inconsistent with other measurements.

4000 6000 8000 10000 12000 14000 1600040

45

50

55

60

65

70

75

40

45

50

55

60

65

70

75

GOES-8

TSBR

SSP DATA DATA OVER CF SW ScaRaB

SW

(1)=

SW(GOES-8) -

SW(TSBR) = 5.0 %

SW

(2)=

SW(SSP) -

SW(TSBR) = 13.4 %

EGRETT ALTITUDE CORRECTED TO TOA ANDGOES-8 PIXEL AND EGRETT FOV INTEGRATED

SW BROAD-BAND ALBEDO

SW

ALB

ED

O [%

]

TIME, SEC

Relatioship between TOA albedo and atmospheric transmittance

0 20 40 60 80 1000

20

40

60

80

100

TO

A

AL

BE

DO

[%

]

ATMOSPHERIC TRANSMITTANCE [%]

slope = -0.817 ScaRaB 94-95 slope = -0.789 SSP BASED DATA slope = -0.774 GOES-7 APRIL 94 slope = -0.615 GOES-8 ARESE 95 slope = -0.571 TSBR

30 MINUTES STANDARD

DEVIATION F <20 W m-2

A summary of the consistency among the data collected by various instruments

TSBR

BSRN, SIROS, MFRSR, MWR, RADAR

GOES-7

ScaRaB

0.06

0.14

0.08

GOES-8 TDDR

SSP

Evidence from the following Investigations

1. Validation of satellite SRB estimates to check if the difference increases with cloud cover

2. Use of TOA satellite and ground-based BB SRB data to determine atmospheric absorption

3. Use of measurements of surface, atmospheric and cloud variables to compute and compare TOA and surface solar fluxes

4. Use of NB satellite spectral data to retrieve cloud optical properties from which BB fluxes are compared and compared with satellite BB fluxes

5. Use of ground-based radiation to retreive cloud optical depth from which TOA fluxes are estimated and compared.

Potential Causes for Apparent CAA

1. NB to BB conversion due to the use of non-calibrated NB operational weather satellite data

2. Calibration in satellite and/or aircraft measurements

3. Inadequate analysis method prone to mis-interpretation: Issues with the slope approachIssues with CRF approach

4. Representative of measurements – surface albedo

• When the earth was formed some 5 billion years ago, the sun was about 30% of today’s brightness. When the sun ceases illuminating, its brightness is estimated to be 3 times brighter. Estimate changes in planet temperature relative to the current.

• Based on the global energy balance diagram, summarize the sinks and sources of energy at the top, bottom and inside of the atmosphere.

• When the earth was formed some 5 billion years ago, the sun was about 30% of today’s brightness. When the sun ceases illuminating, its brightness is estimated to be 3 times brighter. Estimate changes in planet temperature relative to the current.

• Based on the global energy balance diagram, summarize the sinks and sources of energy at the top, bottom and inside of the atmosphere.

Home Work

Due on Apr. 6 (email me)

Home Work

Due on Apr. 6 (email me)