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The Earth

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Earth s Radiation Balance and Cloud Radiative Forcing The Earth s surface is kept warm through one source: the Sun. It is the primary source for Earth s energy. – PowerPoint PPT presentation

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Title: The Earth


1
Earths Radiation Balance and Cloud Radiative
Forcing
The Earths surface is kept warm through one
source the Sun. It is the primary source for
Earths energy. Some of the incoming sunlight and
heat energy is reflected back into space by the
Earths 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.
2
Solar Constant measured by satellites at TOA
11-yr solar cycle
3
How does the Earth Respond?
Earth System Response
Forces Acting On the Earth System
IMPACTS
Feedback
Of the total forcing of the climate system, 40
is due to the direct effect of greenhouse gases
and aerosols, and 60 is from feedback effects,
such as increasing concentrations of water vapor
as temperature rises.
4
Major Climate System Elements
Water Energy Cycle
Carbon Cycle

Coupled Chaotic Nonlinear
Atmosphere and Ocean Dynamics
Atmospheric Chemistry
5
Radiative Forcing from 1750 to 2000
Anthropogenic Forcings
IPCC, 2001
6
Human Influence on Climate
Carbon Dioxide Trends 100yr lifetime
Methane Trends
Sulfate Trends
Global Temperature Trends
From M. Prather University of California at Irvine
7
Global Radiation Budget
8
Daily mean solar flux at TOA
  • The Sun is closest to the Earth in Jan. So more
    solar energy received in SH than in NH.
  • At the equinoxes, the solar insolation is at a
    Max at the equator and is zero at the poles.
  • 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.

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Top-of-Atmosphere Radiation Budget (Incoming
Solar Outgoing Longwave)
A Planetary Albedo S0 Solar Irradiance Te
Earth Radiative Temperature Ts Equilibrium
Surface Temperature
1 relative error in A ? ?1 W m-2 flux error ?
?0.5?C error in Ts 2xCO2 gt 4 W m-2
11
The Greenhouse Effect
Solar Radiation
Longwave Radiation
12
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
13
Cloud Radiative Forcing
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) gt Clouds have a
cooling effect on Climate Positive FNet(cloud)
gt Clouds have a warming effect on Climate
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.

15
235 W m-2
265 W m-2
57 W m-2
342 W m-2
107 W m-2
342 W m-2
285 W m-2
235 W m-2
Earth (With Clouds)
Earth (No Clouds)
FSW (cloud) -50 W m-2
FLW (cloud) 30 W m-2
gt Net Effect of Clouds -20 W m-2
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A brief history of ERB missions
27
CERES Data Processing Flow
CERES Data
6 Months
6 Months
6 Months
6 Months
CERES Calibration/ Location
ERBE Inversion
ERBE Averaging
ERBE-Like Products
Cloud Imager Data
18 Mo.
30 Mo.
Cloud Identification TOA/Surface Fluxes
Angular Distribution Models
24 Mo.
Atmospheric Structure
Diurnal Models
36 Mo.
36 Mo.
Surface and Atmospheric Fluxes
CERES Surface Products
Geostationary Data
42 Mo.
Time/Space Averaging
Algorithm Theoretical Basis Documents
http//asd-www.larc.nasa.gov/ATBD/ATBD.html Valida
tion Plans http//asd-www.larc.nasa.gov/valid/v
alid.html
42 Mo.
CERES Time Averaged Cloud/Radiation TOA, SFC,
Atmos
28
CERES Advances over Previous Missions
  • Calibration Offsets, active cavity calib.,
    spectral char.
  • Angle Sampling Hemispheric scans, merge with
    imager matched surface and cloud
    properties new class of angular, directional
    models
  • Time Sampling CERES calibration 3-hourly geo
    samples new 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

29
CERES Instrument
TRMM Jan-Aug 98 and Mar-Apr 2000 overlap with
Terra
Terra Mar 00 - present planned life 2006
Aqua July 02 start Now in checkout Planned life
to 2008
NPOESS TBD gap or overlap? 2008 to 2011 launch
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CERES LW Terra Results - July 2000
CERES Clear-Sky TOA Longwave Flux (W m-2)
CERES TOA Longwave Cloud Forcing (W m-2)
34
CERES SW Terra Results - July 2000
CERES Clear-Sky TOA Shortwave Flux (W m-2)
CERES TOA Shortwave Cloud Forcing (W m-2)
35
CERES Net Cloud Forcing (July, 2000)
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Li and Leighton (1993)
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Li and Leighton (1993)
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Solar Energy Disposition (in percentage)
30
100
2420 28
46 50 42
  • The upper values are from satellite, middle ones
    from GCMs and the bottom from limited surface data

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Forces Acting on Climate (in Watts per meter2)
Forcing (W/m2)
60
Assessment of Cloud Absorption and Earths
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?

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Li et al. (Nature, 1995)
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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

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Li (J. Climate, 1998)
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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.

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Relatioship between TOA albedo and atmospheric
transmittance
79
A summary of the consistency among the data
collected by various instruments
80
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.

81
Potential Causes for Apparent CAA
  • NB to BB conversion due to the use of
    non-calibrated NB operational weather satellite
    data
  • Calibration in satellite and/or aircraft
    measurements
  • Inadequate analysis method prone to
    mis-interpretation
  • Issues with the slope approach
  • Issues with CRF approach
  • 4. Representative of measurements surface
    albedo

82
Home Work Due on Apr. 6 (email me)
  • When the earth was formed some 5 billion years
    ago, the sun was about 30 of todays 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.
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