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