clouds and radiation. “..there are substantial uncertainties in decadal trends in all data sets...
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Clouds and Radiation
Clouds and Radiation
Clouds and Radiation“..there are substantial uncertainties in decadal trends in all data sets and at present there is no clear consensus on changes in total cloudiness over decadal time scales.”
IPCC-The Scientific Basis-Chapter 3, p. 277
An increase in both clouds and precipitation has occurred over many parts of the land surface (Dai et al., 1999, 2004a, 2006), although not in the tropics and subtropics (which dominate the global land mean; Section 3.3.2.2).
IPCC-The Scientific Basis-Chapter 3, p. 279
IPCC WG1 AR4 Report
Variability caused by model representations of clouds
How do Clouds Alter the State of the Atmospheric Column?
• Diabatic Heating Profiles – Latent Heating
– Net column latent heating = Precipitation mass * L, where L = latent heat
– Radiative Heating– Net column radiative heating= net incoming minus net
outgoing
– Profiles of diabatic heating impact atmospheric dynamic and thermodynamic structure
Radiative Heating and Cooling of the atmospheric column
𝑆=𝑖𝑛𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛
𝐹 𝑇𝑂𝐴𝑆𝑊❑ ↓=𝑆
) S𝐴≡𝑎𝑙𝑏𝑒𝑑𝑜
) S
S
S
𝑆𝑢𝑟𝑓𝑎𝑐𝑒𝐻𝑒𝑎𝑡𝑖𝑛𝑔
𝑎𝑠𝑤
SHORTWAVEλ=1-4 μmincludes visible banda cloud-free column
𝐹𝑆𝑓𝑐𝐿𝑊↑=𝜀𝑠𝜎𝑇 𝑠
4
𝜀≡𝑒𝑚𝑖𝑠𝑠𝑖𝑣𝑖𝑡𝑦
/Cooling
𝑎𝐿𝑊
𝐹 𝑇𝑂𝐴𝐿𝑊↑= (1−𝑎𝐿𝑊 )𝜀𝑠𝜎𝑇 𝑠
4 𝐹𝑇𝑂𝐴𝐿𝑊↑=𝑎𝐿𝑊 𝜀𝑎𝜎𝑇 𝑎
4
𝐹𝑇𝑂𝐴𝐿𝑊↑=𝑎𝐿𝑊 𝜀𝑎𝜎𝑇 𝑎
4
LONGWAVEλ > 4 μm
Radiative Flux Divergence Primer
Radiative Flux Divergence = net radiation into column - net radiation out of column
• positive values imply heating• negative values imply cooling
𝑆𝑊 𝐿𝑊
𝑛𝑒𝑡
neg pos
NET
𝑆=𝑖𝑛𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛
𝑎𝑠𝑤
SHORTWAVE
𝑆=𝑖𝑛𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛
𝑎𝑠𝑤
SHORTWAVEcirrus (ice clouds)
• thin• wispy• semi-transparent
o optically thin
𝑆=𝑖𝑛𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛
𝑎𝑠𝑤
SHORTWAVE
cumulus convectionand other optically thickclouds(liquid/mixed/ice)
• base near surface• > 30% coverage• vertical development• layer clouds
Cirrus and Cumulus from the Space Shuttle
Courtesy NASA CERES
𝑎𝐿𝑊
LONGWAVE
𝑎𝐿𝑊
LONGWAVE
cumulus convectionand other optically thickclouds(liquid/mixed/ice)
𝑎𝐶𝑙𝑜𝑢𝑑𝐿𝑊
𝑎𝐿𝑊
LONGWAVE
𝑎𝐶𝑙𝑜𝑢𝑑𝐿𝑊
cirrus (ice clouds)• cold cloud tops
What Cloud Properties Change the Radiative Heating Rate Profile?
1. Hemispheric cloud coverage cloud2. Optical thickness of individual clouds
and layers3. Height in the atmosphere4. Layer coherence (or overlap)5. Composition
• Contain ice crystals, liquid water, or both?• Particle sizes?• Particle concentrations?
How Does the Location of Cloud Impact the Surface Temperature?
Low Clouds
~2-km
High Clouds
~10-km
COOLING WARMING
𝑂𝐿𝑅∝𝜎𝑇𝑐𝑡𝑜𝑝4
𝑇 𝑠𝑢𝑟𝑓𝑎𝑐𝑒
What types of remote sensors do we use to make cloud measurements?
• Vertically-Pointing Lasers (LIDARs)– measure the height of the lowest cloud base– below cloud concentrations of aerosol and water vapor– beam quickly disperses inside cloud
• Cloud Radars– cloud location and microphysical composition– in-cloud updrafts, downdrafts, and turbulence
• Microwave Radiometers– measure the total amount of liquid water in
atmosphere– can’t determine location of liquid– no measure of ice water content
Negligible Return Cloud and Aerosol Particles Cloud droplets
Surface
10-km
20-km
24 Hours
Lidar Data from Southern Great Plains
IceClouds
LowClouds
No Signal
7:00 pm 7:00 am 7:00 pmtime
Niamey, Niger, Africa
• 0000
NegligibleReturn
Cloud Droplets
Cloudand/orAerosol
• 0000 • 1200• 0
• 5
• 10
• 15
• 20
Time (UTC)
Heig
ht
(km
)
• Biomass Burning• Dust
• LIQUID CLOUDS
VHFUHF10 cm
1/3
4
8 mm
3.2 mmcloud radars
3.2 mm95 GHz
8.0 mm35 GHz
MaximumPropagation
Distance
20-30 km 10-15 km
Cloud Radar Wavelengths
The DOE ARM Cloud Radars
Small Cloud Particles Typical Cloud Particles Very Light Precipitation
Surface
10-km
20-km
Cloud Radar Data from Southern Great Plains
Black Dots:Laser MeasurementsOf CloudBase Height
7:00 pm 7:00 am 7:00 pmtime
Evolution of Cloud Radar Science
• Cloud Structure and Processes• Cloud Statistics • Cloud Composition
diurnal variation in cloud fractional coverage and surface precipitation for June 2006 over Lamont, Oklahoma(Courtesy: Lynne DiPretore)
Height(km)
Cloud Fraction (%)
• GFS cloud initialization data• mandatory radiosonde data• satellite retrievals of
temperature• satellite-derived cloud motion
vector• aircraft• cloud fraction parameterization:
Xu and Randall (1996)
• August• GFS 10-15 km cloud fraction
larger than AMF• AMF 0-10 km cloud fraction
larger than GFS
Kollias, P, M.A. Miller, K.Johnson, M. Jensen, D. Troyan, 2008
Surface
2-km
10-km
Laser Radar
Base
RadarEcho
Top
Base
TopLow
RadarSensitivity
RadarEcho
RadarEcho
MicrowaveRadiometer
Emission
Multiple remote sensors required to measure non- and weakly precipitating clouds
7:00 pm 7:00 am 7:00 pm
1 4 10 17 25
Liquid Cloud Particle Median Radius
Micrometers
Heig
ht
(km
)
2
4
6
0time
Miller and Johnson, 2003
Tobin et al., 2007
Clouds and Radiation from Space (and high
altitude)
0
2
4
6
alti
tud
e (k
m)
19:30 19:53
June 12, 2006 OklahomaCPL backscatter profiles and MAS comparison
distance (km)0 275
0
+37
-37
km
time (UTC)
Matt McGill/NASA Goddard
A-TRAIN CONSTELLATION
The Afternoon or "A-Train" satellite constellation presently consists of 5 satellites
Two additional satellites, OCO and Glory, were supposed to join the constellation
OCO was lost during a launch failure on 2/24/2009.Glory is scheduled to launch (02/23/11)
Approx equator crossing times
36
Afternoon Constellation Coincidental Observations
(Source: M. Schoeberl)
MODIS/ CERES IR Properties of Clouds
AIRS Temperature and H2O Sounding
Aqua
CloudSatPARASOL
CALIPSO- Aerosol and cloud heightsCloudsat - cloud dropletsPARASOL - aerosol and cloud polarizationGlory-aerosol size and chemistry
CALIPSOOCO-2?Aura
OMI - Cloud heights
OMI & HIRLDS – Aerosols
MLS& TES - H2O & temp
profiles
MLS & HIRDLS – Cirrus
clouds
Glory
CloudSat (Hurricane Ike)
37
CloudSat
38
Radar/Lidar Combined Product Development
• Formation flying is a key design element in cloudsat • CloudSat has demonstrated formation flying as a practical observing strategy for EO.• Overlap of the CloudSat footprint and the CALIPSO footprint, within 15 seconds, is
achieved >90% of the time.
MicrowaveLimb
Sounder
ECMWF CloudSat
A-Train Cloud Ice
Visual Images of the Sky• cloud coverage (versus cloud fraction)• simple! digitize images and …• daytime only• integrated quantity
Lidar/Radar combined ice microphysics - new A-Train ice cloud microphysics
Zhien Wang
University of Wyoming