Clouds and Climate Through

a Soda Straw

Mark Miller

Visible

Infrared

Sun’s Radiation6000 K

Earth’s Radiation288 K

0.5 3 10

Wavelength (micrometers)

Qua

ntit

y o f

Ra d

iati

on

Visible Satellite Photo

Infrared Satellite Image

Source: NASA/ Earth Radiation Budget Experiment

“The study of climate and climate change is hindered by

a lack of information on the effect of clouds on the

radiation balance of earth.”

•Ramanathan et al., 1989: Science, 243, 57-62.

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

What Cloud Properties Change the Net Radiation Received at the Surface?

1. Amount of the sky that is covered

2. Thickness

3. 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!

The ARM Southern Great Plains Site

SGPCentral FacilitySODA STRAW

ExtendedMeasurementFacilities

Oklahoma City

Wichita

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

A Time Series

The Past Few Days in Oklahoma…

…have been for the birds!

3/20/08 3/21/08 3/22/08 3/23/08

•500 nm

•RV Ron Brown

•Central Pacific

•AOT=0.08

•Sea of Japan

•AOT=0.98

•AMF

•Niamey, Niger

•AOT=2.5-3

Sky Imaging

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

•V=4500m

•V=700m, Mass Concentration=1,700g m-3

Niamey, Niger, Africa

•0000

Negligible

Return

Cloud

Droplets

Cloud

and/or

Aerosol

•0000 •1200•0

•5

•10

•15

•20

Time (UTC)

Hei

gh

t (k

m)

•Biomass Burning•Dust

•LIQUID CLOUDS

•Dust product (upper) and GERB OLR (lower) for 1200UT on 8 March 2006

Cloud

Lake Chad

Dust

Ene

rgy

Ret

urne

d to

Rad

ar

Size of Cloud Particle

At a Given Wavelength

Ene

rgy

Ret

urne

d to

Rad

ar

Radar Wavelength

A Cloud Particle At Different Wavelengths

radius6 wavelength-4

Ene

rgy

Abs

orbe

d by

Atm

osph

ere

Radar Wavelength

35 GHz

94 GHz

MaximumPropagation

Distance

20-30 km

10-15 km

8 mm3.2 mm

The DOE 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

Solid Overcast

Cloud Transition

Broken Cloud

Azores

Applications of Surface-Based Cloud Observing Systems

Example: Marine Cloud Transitions

Application of Surface-Based Remote Sensing to a Cloud “Problem”

•Marine Stratocumulus Transition

Ocean Surface

Mid-latitudes Tropics

0.5 km

2 km

Ocean Surface

Mid-latitudes Tropics

0.5 km

2 km

THEORY

OBSERVED

5-km

10-km

15-km

Cloud TopHeight

Probability1% 10%

Tropical Western PacificJan 1999 June 1999

3% 1% 10%3%Probability

Retrieving Liquid Cloud Composition

+

Radar Echo

Intensity

Hei

ght

Total Liquid Water

(Microwave Radiometer)

Particle Size

Num

ber

Mode Radius??

+ =Mode Radius

Hei

ght

Number

Concentration??

Width

Number

Concentration

Hei

ght

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

Active and Passive Cloud Remote Sensors (cont.)

• Wind Profiler – 75-m, 6-min resolution– 915 MHz [1270-1400 MHz COPS]– Minimum Height: 120-m– Maximum height: 5.5-km

• Atmospheric Emitted Radiance Interferometer (AERI)– 3-19.2 m (1 cm-1 resolution)– 6-min resolution (20-30 sec possible for COPS)– 1.3 degree field-of-view

AERI Spectra

Analysis of the Impact of Clouds on Radiation

Remotely-Sensed Information about Cloud Structure and Composition

Existing Theoretical Models of Radiation Transfer Through Clouds

Compare with Coincident Measurements of the Energy Budget

Compute the Energy Budgets at the Surface andTop-of-Atmosphere

Meteorological Models

• Global Climate Model (GCM)– Forecast Period: Decades to Centuries– Resolution: ~300-km x 300-km– Crude Representations of Many Processes

• Numerical Weather Prediction Model (NWP)– Forecast Period: Hours to a Few Days– Resolution: 29-km x 29-km– Better Representations of Many Processes

• Cloud Resolving Model (CRM)– Forecast Period: Hours– Resolution: 1-km x 1-km– Detailed Representations of Processes

Super-Parameterizations: The Grabowski, Randall, and Arakawa Scheme

55-N

60-N

172-W 157-W

CLIMATE MODELGRID CELL

2-DimensionalCloud Resoving Model

3-DSimulation

5-10 years?

Summary

• Collecting and analyzing large data sets to better understand cloud behavior

• Observations are more compatible with evaluation of cloud resolving models than current GCMs

• New “super-parameterizations” in GCMs appears to be the path forward: 5-10 years– Based on cloud resolving models