Issue 66
June 15, 2006

EnviroZine: Environmnent Canada's On-line Newsmagazine

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Looking at Clouds Inside and Out

Cloud – photo: Kristina Fickes – Click to enlarge

Clouds give texture to our skies. Puffy cumulus clouds can accentuate the blueness of a partly cloudy day, while a grey blanket of stratus clouds can block the sun for extended periods and signal an impending storm.

Most people can observe these cloud effects with their own eyes. Conventional weather and climate satellites show some more detail, but they only provide imagery similar to what our eyes can: two-dimensional views of cloud fields. For all we know of what clouds are and how they look from the outside, we know relatively little about their life-cycles and three-dimensional structure.

Thanks to CloudSat, a NASA research satellite that is equipped with a cloud- profiling radar, scientists have access to new images of the vertical cross section of clouds. This will help to determine what's inside the clouds: their inner structure, thickness, mass, and radiative properties.

Launching of CloudSat on April 28, 2006 – Click to enlarge

For the first time, the high frequency radar aboard CloudSat will provide a global view of the vertical structure of clouds in combination with their horizontal variability. For example, CloudSat's radar will be able to estimate the altitude of many cloud bases. This goes well beyond what can be obtained from passive imagers on conventional satellites.

This new 3D technology is expected to improve weather predictions, advance knowledge of the hydrological system, and help determine the role of clouds in climate and climate change.

Getting the facts on clouds

Clouds are ephemeral entities that are constantly shifting and changing their shape, size, and composition. This makes studying them, and their impact on the weather and climate, difficult. That's why literally getting a much better picture will make a big difference.

Clouds influence the amount of solar energy absorbed by the Earth-atmosphere system.

Rayed Sunset At Altitude. Photo: © COREL Corporation, 1994. – Click to enlarge.

Through improved understanding of the cloud radiative characteristics, CloudSat will help fill gaps in knowledge regarding how radiant energy from the Sun and Earth is distributed between the surface and the atmosphere.

The life expectancy of this satellite is just 22 months, but during this period it will provide key information about how well clouds are represented in global weather and climate models and how well our models can explain present conditions.

Fast Facts

Clouds influence the amount of solar energy retained in the atmosphere and the amount reflected back into space. Even small changes in cloud cover and cloud optical properties can alter climate significantly.

CloudSat represents the first cloud-profiling radar to orbit Earth.

Since Canada has expertise in space radar, NASA invited the Canadian Space Agency to participate in the CloudSat mission in 1998.

CloudSat orbits in formation as part of the A-Train constellation of satellites including Aqua, CALIPSO, PARASOL, and Aura.

Related Sites

CloudSat – Looking at clouds in 3-D

Tutorials on Meteorology

Weather Phenomena Tutorial

CloudSat – NASA

Canadian CloudSat/Calypso Validation Project

Dr. Howard Barker of Environment Canada said, "In order to model future climates, you have to be able to model present-day climate."

"One of the main purposes of Environment Canada is to provide better weather forecasts and predictions of climatic change." Barker said. "For the past 15 years, clouds have been identified as the most uncertain element of the system. If we can improve the representation of clouds in numerical models, it stands to reason that we'll be able to produce better weather forecasts and have more confidence in climate predictions."

Going into orbit for answers

CloudSat was developed by NASA in partnership with the Canadian Space Agency. Canada contributed two major components in its development. The first is an extended interaction klystron (EIK) for CloudSat's cloud-profiling radar. This EIK is a rugged, lightweight, compact vacuum tube. It serves as an amplifier, increasing low-power signals to high-power radar pulses that are strong enough to probe clouds from top to bottom from over 700 kilometres away. This profiling tool will "see" into the clouds like a doctor using a CAT scan.

The second Canadian-made component is the receiver of the radio frequency electronics subsystem that allows CloudSat to detect and receive low-power radar pulses returning from the atmosphere.

As of late May 2006, CloudSat was manoeuvred into formation with other satellites in the A-train constellation. Known as the A-train (A standing for Aqua, the leading satellite in the constellation), the grouping includes CloudSat, in conjunction with CALIPSO, Aura, and PARASOL.

CALIPSO was launched on the same Delta rocket as CloudSat. Aqua, Aura, and PARASOL are already active. A sixth satellite, OCO, will be launched in 2008.

CALIPSO will be able to detect thin clouds and aerosols, and will provide accurate estimates of cloud top altitudes. The Aqua satellite has several conventional-style radiometers on board. Aura studies air quality, the ozone layer, and climate change. PARASOL senses how sunlight is polarized by clouds and atmospheric aerosols.

The true novelty of CloudSat and the rest of the A-train is the highly varied, yet simultaneous, view of clouds that they will provide to atmospheric scientists. The synergy of these diverse sources of data will set the stage for advances in our representation of clouds in global models, and in planning for future cloud research missions.

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Issue 66 June 15, 2006

Looking at Clouds Inside and Out

Getting the facts on clouds

Going into orbit for answers

Issue 66
June 15, 2006