Second Flight of MAHRSI Experiment to Explore Summer Polar Middle Atmosphere

7/27/1997 - 43-97r
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The Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI), a remote sensing instrument developed by the Naval Research Laboratory (NRL), is scheduled to begin its second data-collecting mission this summer to map the distribution of two important gases in the middle atmosphere. In the fall of 1994, MAHRSI obtained the first global measurements of the hydroxyl radical (OH) in the middle atmosphere, providing unprecedented information on the chemical family that is believed to determine the natural balance of ozone in the altitude region above 35 kilometers (km).

MAHRSI will fly on the German Space Agency's Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere -- Shuttle Pallet Atmosphere Satellite (CRISTA/SPAS). CRISTA/SPAS will be deployed from the space shuttle Discovery's robot arm during NASA's STS-85 mission, planned for launch on August 7. During nine days of free flight, MAHRSI will measure OH and nitric oxide by sensing the ultraviolet (UV) radiation emitted and scattered by the atmosphere.

MAHRSI's first set of measurements, which were made in November 1994, provide a detailed picture of the morning build-up of the OH profile. This second flight will provide an opportunity to observe afternoon OH levels at smaller solar zenith angles (the angle of the Sun from overhead). The new observations will also provide the opportunity to explore the photochemistry of the summer polar region.

A different instrument on NASA's Upper Atmosphere Research Satellite (UARS) has seen values of water vapor (the "parent" molecule of OH) at high altitudes in this region that are so large that they cannot be explained by current theory. The MAHRSI science team has found that the high values observed during the 1994 UARS flight are in excellent agreement with the MAHRSI OH measurements. Dr. Robert Conway of NRL's Space Science Division, MAHRSI principal investigator, notes, "the highest values of water vapor ever observed by UARS were near the north pole in August so the new OH measurements should provide an exciting test of the current theory of formation of OH and its role in ozone photochemistry."

MAHRSI obtains its measurements by detecting ultraviolet glow (a result of absorbed sunlight) from gases at high altitudes and repeatedly measuring the brightness of the glow in long, narrow strips across the horizon. MAHRSI then forms an image of the glowing gas layers fromwhich the scientists can make density profiles maps.

To correspond with the CRISTA/SPAS mission, researchers from all over the world will participate in the CRISTA/MAHRSI Campaign 2. This three-week cooperative science campaign includes the collection of complementary and correlative measurements from ground-based stations, balloons, rockets, aircraft and satellites. These measurements will become part of a database that will be used to validate the CRISTA and MAHRSI observations.

To learn more about MAHRSI's next mission, reference the MAHRSI home page at

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