figure 2.10 ipcc working group i (2007) clouds and radiation through a soda straw
Post on 21-Dec-2015
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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
Representing Clouds in Climate Models
55-N
60-N
172-W 157-W
CLIMATE MODELGRID CELL
WeatherForecastModel Grid Cell
CloudResolvingModels:Less ThanWidthOf Lines
What Cloud Properties Change the Radiative Heating Rate
Profile?1. Amount of the sky that contains cloud2. Thickness of individual clouds and
layers3. Composition
• Contain ice crystals, liquid water, or both?• Particle sizes?• Particle concentrations?
4. Height in the atmosphere
How Does the Location of Cloud Impact the Surface Temperature?
Low Clouds
Space
~2-km
High Clouds
~10-km
COOLING WARMING
What We Know About Solar Radiation and Clouds
• Solid theoretical foundation for interaction between a single, spherical liquid cloud droplet and sunlight
•Sun
•Cloud Droplet
•Scattered
•Light
What We Know About Solar Radiation and Clouds
• Some theoretical foundation for interaction of sunlight and simple ice crystal shapes
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?
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• 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– Information about cloud location and composition
• 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
Laser 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
En
erg
y R
etu
rned
to R
ad
ar
Size of Cloud Particle
At a Given Wavelength
En
erg
y R
etu
rned
to R
ad
ar
Radar Wavelength
A Cloud Particle At Different Wavelengths
radius6 wavelength-4
En
erg
y A
bso
rbed
by A
tmosp
here
Radar Wavelength
35 GHz
94 GHz
MaximumPropagation
Distance
20-30 km
10-15 km
8 mm3.2 mm
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
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
ThinClouds
Insects
7:00 pm 7:00 am 7:00 pmtime
Surface
2-km
10-km
Laser Radar
Base
RadarEcho
Top
Base
TopLow
RadarSensitivity
RadarEcho
RadarEcho
MicrowaveRadiometer
Emission
Evolution of Cloud Radar Science
• Cloud Structure and Processes• Cloud Statistics • Cloud Composition
5-km
10-km
15-km
Cloud TopHeight
Probability1% 10%
Tropical Western PacificJan 1999 June 1999
3% 1% 10%3%Probability
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