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SSL 1996 Annual Report - Earth Science

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Earth Systems Science

[Taking the Earth's Temperature][A Windsock Made of Light][Lightning Counts]

While every child is taught the water cycle in grade school, scientists are still learning the full range and depth of its subtle workings, including how the distribution, movement, and properties of water and water-vapor affect the Earth's climate. SSL research in Earth science, an important component of NASA's Mission to Planet Earth (MTPE), is carried out by scientists at the Global Hydrology and Climate Center (GHCC).

Taking the Earth's Temperature

In January 1996, the American Meteorological Society presented its annual Special Award to Dr. Roy Spencer of SSL and Dr. John Christy of the University of Alabama in Huntsville for developing a precise global record of the Earth's temperature from polar-orbit weather satellites. This work has fundamentally advanced our ability to monitor the Earth's climate from space.

 
 SSL and UAH investigators used 17 years of data from satellite instruments to determine that temperatures of the lower stratosphere have cooled substantially, while the lower troposphere has cooled slightly since 1979. Note that the scales of the graphs (left) are different and that the entire troposphere chart would fit within the 0.5-degree band of the stratosphere chart.

 

Using data gathered by spaceborne microwave sounding instruments, Spencer and Christy calculated seasonally adjusted temperature variations for the entire Earth, and with a data set that spans nearly 20 years, chronicled the temperature in the lower troposphere and the lower stratosphere.

Stratospheric data indicate extreme sensitivity to events such as volcanic eruptions by El Chichon in Mexico (1982) and Mt. Pinatubo in The Philippines (1991), and show a net cooling trend consistent with ozone depletion. Tropospheric data demonstrate a slight overall cooling trend.

Spencer and Christy continue their research. What once might have been an academic pursuit has implications beyond the laboratory. While other scientists may use the data to test the reliability of global climate models developed in a computer, national and international policymakers may use it to address complex and sometimes controversial environmental issues, such as global warming.

A Windsock Made of Light

Measuring the wind is as simple as watching how fast the clouds go by. But when the clouds are not there, how can you even tell if the winds are blowing? That problem has vexed meteorologists even in the age of weather satellites which can see only cloud tops. The answer, being developed at SSL, is to use a laser to measure the speed of tiny particles in clear air.

During July, GHCC and its partners demonstrated the ability to measure atmospheric winds remotely using laser radar (lidar). A series of research aircraft flights using the Multi-center Airborne Coherent Atmospheric Wind Sensor (MACAWS) provided data to understand the meteorological processes, and is expected to assist in the design of a satellite to measure global winds from space. The wind sensor, a coherent Doppler lidar unit, uses pulses of laser light to measure winds from a distance by observing frequency shifts of the backscattered light that result from the motion of the air (the same technique as measuring a star's speed through its "red shift").

 
 MACAWS (left) was flown over the northwest aboard NASA's DC-8 research aircraft to determine how well lasers can measure winds by using the doppler effect with lasers. Colors in the plots at right depict wind speeds as measured along the laser's line of sight.

 

In 17 flights on the NASA DC-8 research aircraft, MACAWS measured wind speeds over Washington, Alaska, Texas, and California, and simulated operation of a satellite instrument. Additionally, the experiment gathered information on the operational capabilities of lidar and signal processor performance under less than ideal conditions. MACAWS and related work at SSL will assist us in designing a satellite instrument to measure global winds from space.

Lightning Counts

Besides winds, lightning long has been an accepted measure of atmospheric energy. Since 1925, scientists have accepted that the global lightning flash rate is on the order of 100 flashes per second. In 1996, scientists from SSL's Earth System Science Division and the GHCC produced the first-ever high-resolution global maps of the annual cycle of lightning, observed from space by the Optical Transient Detector (OTD) instrument. Launched in April 1995, the OTD has yielded a new estimate for the global flash rate of lightning. Initial results from OTD's 15 months of operation show that the global flash rate is only about half the previous accepted value, or 40-50 flashes per second.

 
 Three months of observations by the Optical Transient Detector, show where weather systems release the most lightning strikes, such in the tornadic storm cell (right) seen by a visible-light camera working with OTD.

 

This finding has many implications for understanding atmospheric electrical phenomena. Detection of lightning is an important means to diagnose the intensity, structure, and life of thunderstorms. OTD data also indicate that lightning rates may be linked to tornado formation. This attracted the attention of national media in the wake of the hit movie, Twister.


[Introduction][Physics and Astronomy][Earth System Science]

[Microgravity Science and Applications][ Science Systems]

[SSL Management][Notable Events][Communicating Scientific Knowledge]


Authors: Dr. John Horack, Dave Dooling
Curator: Bryan Walls
NASA Official: Dr. Gregory S. Wilson, Director

Last updated March 5, 1997