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
There has been an increase in clouds and precipitation, which
reduce solar radiation available for actual and potential
evapotranspiration but also increase soil moisture and make the
actual evapotranspiration closer to the potential
evapotranspiration. 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
– Condensation (warming)
– Evaporation (cooling)
– Net column latent heating = Precipitation mass * L
– where L = latent heat
– Radiative Heating
– Incoming solar
– Outgoing IR
– Net column radiative heating= net incoming minus net outgoing
– Profiles of diabatic heating impact atmospheric
dynamic and thermodynamic structure
Radiative Flux Divergence Primer
Insolation Reflected OLR
SW
Incoming – Outgoing= net radiation into column
TOA
Radiative Flux Divergence = net radiation into column - net radiation into surface
•positive values imply heating
•negative values imply cooling
Upwelling
and
Downwelling
SW and LW
Surface
Downwelling–Upwelling= net radiation into surface
Radiative Heating Rate Profile
Insolation Reflected OLR
SW
TOA
•positive values imply heating
•negative values imply cooling
Upwelling
and
Downwelling
SW and LW
Surface
neg
pos
NET
What Cloud Properties Change the
Radiative Heating Rate Profile?
1. Hemispheric cloud coverage cloud
2. Optical thickness of individual clouds and
layers
3. Height in the atmosphere
4. 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?
Space
High Clouds
𝑂𝐿𝑅 ∝ 𝜀𝜎𝑇 4
~10-km
Low Clouds
~2-km
COOLING
WARMING
Cirrus and Cumulus from the Space Shuttle
Courtesy NASA CERES
Figure 2.10
•IPCC Working Group I (2007)
Representing Clouds in Climate Models
CLIMATE MODEL
GRID CELL
60-N
Weather
Forecast
Model
Grid Cell
55-N
172-W
157-W
Cloud
Resolving
Models:
Less Than
Width
Of Lines
Clouds and Radiation
Through
a Soda Straw
2-km
Clouds
Through a
SODA
STRAW!
Meteorological
Tower
Multiple
Radars
Calibration Facility
Multiple
Lidars
Surface Radiation
What types of remote sensors do we
use to make cloud measurements?
• Visible and Infrared Sky Imagers
• Shadowband and Narrow Field of View Radiometers
• 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
– Presently not measuring total ice content
Visual Images of the Sky
•cloud coverage (versus cloud fraction)
•simple! digitize images and …
•daytime only
•integrated quantity
Lidar Data from Southern Great Plains
20-km
No Signal
10-km
Low
Clouds
Ice
Clouds
7:00 pm time
Negligible Return
7:00
am
24 Hours
Cloud and Aerosol Particles
Surface
7:00 pm
Cloud droplets
Niamey, Niger, Africa
Height (km)
•20
Cloud
Droplets
•15
•10
•5
•LIQUID CLOUDS
•Biomass Burning
•Dust
•0
•0000
Cloud
and/or
Aerosol
Negligible
Return
•1200
Time (UTC)
•0000

4
3.2 mm
8 mm
cloud radars
10 cm UHF

1/3
VHF
Energy Absorbed by Atmosphere
94 GHz
35 GHz
Maximum
Propagation
Distance
10-15 km
20-30 km
3.2 mm
8 mm
Radar Wavelength
The DOE ARM Cloud Radars
Cloud Radar Data from Southern Great Plains
20-km
Black Dots:
Laser
Measurements
Of Cloud
Base Height
10-km
7:00 pm time
Small Cloud Particles
7:00 am
Typical Cloud Particles
Surface
7:00 pm
Very Light Precipitation
Cloud Radar Data from Southern Great Plains
20-km
Black Dots:
Laser
Measurements
Of Cloud
Base Height
10-km
Insects
Thin
Clouds
7:00 pm time
Small Cloud Particles
7:00 am
Typical Cloud Particles
Surface
7:00 pm
Very Light Precipitation
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
Top
10-km
Low
Radar
Sensitivity
Radar
Echo
Base
Base
Radar
Echo
Top
2-km
Radar
Echo
Emission
Laser Radar Microwave
Radiometer
Surface
•GFS cloud initialization data
•mandatory radiosonde data
•satellite retrievals of
temperature
•satellite-derived cloud motion
vector
•aircraft
•cloud fraction parameterization:
Xu and Randall (1996)
Height
(km)
•August
•GFS 10-15 km cloud fraction
larger than AMF
•AMF 0-10 km cloud fraction larger
than GFS
Cloud Fraction (%)
Kollias, P, M.A. Miller, K.Johnson, M. Jensen, D. Troyan, 2008
Liquid Cloud Particle Mode Radius
Height (km)
6
4
2
0
7:00 pm
1
time
4
7:00 am
10
7:00 pm
17
25
Micrometers
Miller and Johnson, 2003
Tobin et al., 2007
Clouds and Radiation
from Space (and high altitude)
June 12, 2006 Oklahoma
CPL backscatter profiles and MAS comparison
Matt McGill/NASA Goddard
km
+37
0
-37
altitude (km)
6
4
2
0
19:30
0
time (UTC)
distance (km)
19:53
275
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
Afternoon Constellation Coincidental Observations
Aura
CALIPSO
Glory
CloudSat
PARASOL
OMI - Cloud heights
OMI & HIRLDS – Aerosols
MLS& TES - H2O & temp
profiles
MLS & HIRDLS – Cirrus clouds
34
Aqua
OCO-2?
CALIPSO- Aerosol and cloud heights
MODIS/ CERES
Cloudsat - cloud droplets
IR Properties of Clouds
PARASOL - aerosol and cloud
polarization
AIRS Temperature and
Glory-aerosol size and chemistry
H2O Sounding
(Source: M. Schoeberl)
CloudSat (Hurricane Ike)
35
CloudSat
36
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.
Lidar/Radar combined ice microphysics
- new A-Train ice cloud microphysics
Zhien Wang
University of Wyoming
A-Train Cloud Ice
Microwave
Limb
Sounder
ECMWF
CloudSat
What We Know About Solar
Radiation and Clouds
Solid theoretical foundation for interaction
between a single, spherical liquid cloud
droplet and sunlight and populations of
spherical droplets.
Cloud Droplet
Sun
Scattered
Light
What We Know About Solar
Radiation and Clouds
• Some theoretical foundation for interaction of
sunlight and simple ice crystal shapes
The Real World
What We Wish We Knew About
Solar Radiation and Clouds
1.
How do we compute the total impact of a
huge collection of diverse individual cloud
particles?
2. What are the regional differences in
cloud composition, coverage, thickness,
and location in the atmosphere?
3. If we knew (1) and (2), how do we
summarize all of this information so that
it can be incorporated into a climate
model?
What We Know About Outgoing
Terrestrial Radiation and Clouds
• Good theoretical foundation for interaction
of terrestrial radiation and cloud water
content (liquid clouds).
• Particle:
– radius somewhat important in thin liquid clouds
– shape and size somewhat important in high
level ice clouds (cirrus)
• Aerosols?
Miller and Slingo, 2007