Figure 2.10

•IPCC Working Group I (2007)

Clouds and Radiation Through

a Soda Straw

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

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?

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

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

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

Miller and Slingo, 2007

Tobin et al., 2007