Clouds and Radiation
description
Transcript of 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. 277There has been an increase in clouds and precipitation, whichreduce 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
TOA
Surface
Insolation OLRReflectedSW
UpwellingandDownwellingSW and LW
Incoming – Outgoing= net radiation into column
Downwelling–Upwelling= net radiation into surface
Radiative Flux Divergence = net radiation into column - net radiation into surface
• positive values imply heating• negative values imply cooling
Radiative Flux Divergence Primer
TOA
Surface
Insolation OLRReflectedSW
UpwellingandDownwellingSW and LW
• positive values imply heating• negative values imply cooling
Radiative Heating Rate Profile
neg pos
NET
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
Space
~2-km
High Clouds
~10-km
COOLING WARMING
𝑂𝐿𝑅∝𝜀𝜎 𝑇4
Cirrus and Cumulus from the Space Shuttle
Courtesy NASA CERES
Figure 2.10
• IPCC Working Group I (2007)
Representing Clouds in Climate Models
55-N
60-N
172-W 157-W
CLIMATE MODELGRID CELL
WeatherForecastModel Grid Cell
CloudResolvingModels:Less ThanWidthOf Lines
Clouds and Radiation Through
a Soda Straw
Surface Radiation
Calibration Facility
MeteorologicalTower
Multiple Radars
MultipleLidars
2-kmClouds
Through a SODA
STRAW!
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
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)
Hei
ght (
km)
• Biomass Burning• Dust
• LIQUID CLOUDS
VHFUHF10 cm
1/3
4
8 mm
3.2 mmcloud radars
Ener
gy A
bsor
bed
by A
tmos
pher
e
Radar Wavelength
35 GHz
94 GHz
MaximumPropagation
Distance
20-30 km
10-15 km
8 mm3.2 mm
The DOE ARM Cloud Radars
Small Cloud Particles Typical Cloud Particles Very Light Precipitation
Surface
10-km
20-kmCloud Radar Data from Southern Great Plains
Black Dots:Laser MeasurementsOf CloudBase Height
7:00 pm 7:00 am 7:00 pmtime
Small Cloud Particles Typical Cloud Particles Very Light Precipitation
Surface
10-km
20-kmCloud Radar Data from Southern Great Plains
Black Dots:Laser MeasurementsOf CloudBase Height
ThinClouds
Insects
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
Surface
2-km
10-km
Laser Radar
Base
RadarEcho
Top
Base
TopLow
RadarSensitivity
RadarEcho
RadarEcho
MicrowaveRadiometer
Emission
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
7:00 pm 7:00 am 7:00 pm
1 4 10 17 25
Liquid Cloud Particle Mode Radius
Micrometers
Hei
ght (
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
altit
ude
(km
)
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
34
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 heightsOMI & HIRLDS – AerosolsMLS& TES - H2O & temp profilesMLS & HIRDLS – Cirrus clouds
Glory
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 WangUniversity of Wyoming
MicrowaveLimb
Sounder
ECMWF CloudSat
A-Train Cloud Ice
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.
Sun
Cloud Droplet
ScatteredLight
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