Clouds and Radiation

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. 277

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

– Net column latent heating = Precipitation mass * L, where L = latent heat

– Radiative Heating– Net column radiative heating= net incoming minus net

outgoing

– Profiles of diabatic heating impact atmospheric dynamic and thermodynamic structure

Radiative Heating and Cooling of the atmospheric column

𝑆=𝑖𝑛𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛

𝐹 𝑇𝑂𝐴𝑆𝑊❑ ↓=𝑆

) S𝐴≡𝑎𝑙𝑏𝑒𝑑𝑜

) S

S

S

𝑆𝑢𝑟𝑓𝑎𝑐𝑒𝐻𝑒𝑎𝑡𝑖𝑛𝑔

𝑎𝑠𝑤

SHORTWAVEλ=1-4 μmincludes visible banda cloud-free column

𝐹𝑆𝑓𝑐𝐿𝑊↑=𝜀𝑠𝜎𝑇 𝑠

4

𝜀≡𝑒𝑚𝑖𝑠𝑠𝑖𝑣𝑖𝑡𝑦

/Cooling

𝑎𝐿𝑊

𝐹 𝑇𝑂𝐴𝐿𝑊↑= (1−𝑎𝐿𝑊 )𝜀𝑠𝜎𝑇 𝑠

4 𝐹𝑇𝑂𝐴𝐿𝑊↑=𝑎𝐿𝑊 𝜀𝑎𝜎𝑇 𝑎

4

𝐹𝑇𝑂𝐴𝐿𝑊↑=𝑎𝐿𝑊 𝜀𝑎𝜎𝑇 𝑎

4

LONGWAVEλ > 4 μm

Radiative Flux Divergence Primer

Radiative Flux Divergence = net radiation into column - net radiation out of column

• positive values imply heating• negative values imply cooling

𝑆𝑊 𝐿𝑊

𝑛𝑒𝑡

neg pos

NET

𝑆=𝑖𝑛𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛

𝑎𝑠𝑤

SHORTWAVE

𝑆=𝑖𝑛𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛

𝑎𝑠𝑤

SHORTWAVEcirrus (ice clouds)

• thin• wispy• semi-transparent

o optically thin

𝑆=𝑖𝑛𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛

𝑎𝑠𝑤

SHORTWAVE

cumulus convectionand other optically thickclouds(liquid/mixed/ice)

• base near surface• > 30% coverage• vertical development• layer clouds

Cirrus and Cumulus from the Space Shuttle

Courtesy NASA CERES

𝑎𝐿𝑊

LONGWAVE

𝑎𝐿𝑊

LONGWAVE

cumulus convectionand other optically thickclouds(liquid/mixed/ice)

𝑎𝐶𝑙𝑜𝑢𝑑𝐿𝑊

𝑎𝐿𝑊

LONGWAVE

𝑎𝐶𝑙𝑜𝑢𝑑𝐿𝑊

cirrus (ice clouds)• cold cloud tops

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

~2-km

High Clouds

~10-km

COOLING WARMING

𝑂𝐿𝑅∝𝜎𝑇𝑐𝑡𝑜𝑝4

𝑇 𝑠𝑢𝑟𝑓𝑎𝑐𝑒

What types of remote sensors do we use to make cloud measurements?

• 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– no measure of ice water content

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)

Heig

ht

(km

)

• Biomass Burning• Dust

• LIQUID CLOUDS

VHFUHF10 cm

1/3

4

8 mm

3.2 mmcloud radars

3.2 mm95 GHz

8.0 mm35 GHz

MaximumPropagation

Distance

20-30 km 10-15 km

Cloud Radar Wavelengths

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

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(Courtesy: Lynne DiPretore)

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

Surface

2-km

10-km

Laser Radar

Base

RadarEcho

Top

Base

TopLow

RadarSensitivity

RadarEcho

RadarEcho

MicrowaveRadiometer

Emission

Multiple remote sensors required to measure non- and weakly precipitating clouds

7:00 pm 7:00 am 7:00 pm

1 4 10 17 25

Liquid Cloud Particle Median Radius

Micrometers

Heig

ht

(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

alti

tud

e (k

m)

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

36

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 heights

OMI & HIRLDS – Aerosols

MLS& TES - H2O & temp

profiles

MLS & HIRDLS – Cirrus

clouds

Glory

CloudSat (Hurricane Ike)

37

CloudSat

38

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.

MicrowaveLimb

Sounder

ECMWF CloudSat

A-Train Cloud Ice

Visual Images of the Sky• cloud coverage (versus cloud fraction)• simple! digitize images and …• daytime only• integrated quantity

Lidar/Radar combined ice microphysics - new A-Train ice cloud microphysics

Zhien Wang

University of Wyoming