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1) Kay et al., study: In a warmer world with thinner ice, sea-ice extent is increasingly sensitive to year-to-year variability in weather and cloud patterns. ...

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The Disappearance Act of 2007

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NASA Satellites Help Lift Cloud of Uncertainty on Climate Change

2007 American Geophysical Union Fall Meeting


Dr. Graeme Stephens, principal investigator, CloudSat mission; university professor, Colorado State University, Fort Collins, Colo.

Dr Jen Kay, postdoctoral fellow, National Center for Atmospheric Research, Boulder, Colo.

John Haynes, Ph.D. student, Department of Atmospheric Sciences, Colorado State University


Recent “A-Train” Studies Offer Important Insights Into Earth’s Climate

1) Kay et al., study: In a warmer world with thinner ice, sea-ice extent is increasingly sensitive to year-to-year variability in weather and cloud patterns.

2) Haynes et al., study: Clouds rain more frequently than we thought. They also rain more in higher latitudes than we thought.

3) Lebsock and Stephens study: We are now beginning to see direct, global evidence of aerosol brightening of clouds and distinct correlations with decreased precipitation.


The “A-Train” Gives Us Unprecedented Capabilities For Observing Earth

The new A-Train observations tell us much more about weather and climate-sensitive processes than can possibly be gleaned from any one instrument alone.


Viewing Earth Actively Has Become the New Paradigm for Earth Observations

The CloudSat radar measures the time delay and magnitude of the reflected signal

A fraction of these pulses reflect back while others continue downward, some being absorbed and thus lost

What makes CloudSat’s radar special is its sensitivity - it is able to see both small cloud particles as well as larger raindrops and snowflakes.


CloudSat Gives Us Radar Views of Weather

on Scales Not Seen Before

1400 km


Example of CloudSat ‘quicklook’ data taken directly from the CloudSat data processing center (











Polar Clouds Were Difficult To Observe

Before CloudSat and CALIPSO

South Pole, June 2007

The synergy of A-Train measurements - data sources have been collected and co-located through the A-Train data depot - poster A53D-1433; (Kempler et al.)and also at the CloudSat Data Processing Center.

the disappearance act of 2007

The Disappearance Act of 2007

Sea Ice Minimum Extent Time Series

Source: National Snow and Ice Data Center

New Record Minimum - Sept. 2007


A-Train Data Reveal Dramatic Reductions

in 2007 Melt Season Cloudiness

These Arctic cloud reductions are associated with anomalous weather patterns.The increase in sunshine could melt 0.3 meters of ice or warm the surface ocean by 2.4 degrees Kelvin.Kay et al. (2007)


Thinning Sea Ice is Vulnerable to Year-to-Year Weather Variability

The summer 2007 observed cloud decreases are anomalous but not unprecedented.

MODIS - June 2, 2007


How Often Does it Rain (Over the Oceans) ?

The Fraction of Oceanic Clouds That Precipitate


The global mean value is ~0.13, i.e., on average, about 13 percent of the clouds observed over our oceans at any time are producing rain. This fraction is much higher than previously speculated (0.08).

Haynes et al., 2007


The Dreary Extra-Tropics

Total Seasonally Accumulated Precipitation

The new results suggest that it rains more (in amount as shown) and frequency(not shown) than other observations indicate or is predicted by climate models, especially in the winter season.


Aerosol Pollution is Making Clouds Brighter

Polluted clouds = more drops, smaller drops, less precipitation, more reflected sunlight

Clean clouds = fewer drops,

larger drops, more precipitation,

less reflected sunlight

Lebsock and Stephens, 2007


A simple example of the Twomey effect - the tracks of ships below the clouds appear in clouds through the ship effluents that act as an enhanced source of cloud condensation nuclei.

Pollution Fingerprints in Clouds and Rain

Two Principle Influences in ‘Warm’ (Liquid Water) Clouds:

Changes to Cloud Reflection (Twomey Effect)

2) Changes to Precipitation


More Aerosol

Dark Clouds Do Have a Bright Lining

It’s not just the smaller particle sizes of polluted clouds that determine increases in reflected solar radiation.

Raining clouds in high aerosol air are thicker, wetter and more reflective.


More Aerosol

It Also Rains Less in High Aerosol Air

The probability of precipitation decreases dramatically as aerosols increase - this has been hypothesized for a long time but now it is confirmed with observations.



The new observations collected from CloudSat combined with other A-Train

observations are beginning to shed new understanding on important

climate processes.

These new observations tell us about:

Cloud changes in the polar regions, and the effects of these changes on the energy balance of the Arctic, their relation to weather changes and their role in sea ice change.

How frequently clouds rain and how much rain falls over the global oceans - thus offering insight into processes critical to the cycling of fresh water.

How properties of clouds AND precipitation together change with increasing aerosol, thus offering new insights into how aerosol might indirectly affect climate.


No Precipitation

Certain Precipitation

Water and Particle Size Properties of Warm Clouds From

A-Train Data


The aerosol forcing factors

of climate are highly uncertain and aerosol indirect effects are most uncertain of all.

IPCC, 2007




1300 km (800 mi)


2007-2006 Cloud and Surface Radiation Differences

Radiation Calculations by T. L’Ecuyer (CSU).

These radiation differences alone could melt ~0.3 meters of sea ice

and increase ocean mixed layer temperatures by ~1.6 degrees Kelvin.