The Viking Meteorology Experiment is one of nine experiments to be carried out on the surface of Mars by each of two Viking Landers positioned at different latitudes and longitudes in the Northern Hemisphere. The meteorology experiment will measure pressure, temperature, wind speed, and wind direction at 1J h intervals throughout the Martian day. The duration of each measurement period, the interval between data samples for a measurement period, and the time at which the measurement period is started will be varied throughout the mission. The scientific investigation and the sensors and electronics used for making the atmospheric measurement are discussed.
We have examined data from three aircraft field tests designed, in part, to measure the size of the vortex cores generated by the aircraft. The field tests were performed between 1990 and 1997 at Idaho Falls, ID, Wallops Island, VA, and John F. Kennedy International Airport (JFK) in NY. At Idaho Falls, an instrumented 200-foot tower was used to measure velocities in the wakes of Boeing 727, 757 and 767 aircraft flown upwind of the tower. In the Wallops Island test, velocities and smoke trails behind a Lockheed-Martin C-130 aircraft were measured by an instrumented North-American Rockwell OV-10 aircraft flown behind the C-130. For the JFK tests, the vortex wakes of landing aircraft were measured by a Continuous Wave lidar operated by MIT/Lincoln Laboratories. The results from all three field tests are quite consistent, and suggest that the size of the velocity cores in trailing vortices behind an aircraft is on the order of one percent of the wingspan of the aircraft, where core size is defined as the radial distance from the vortex center to the point of maximum tangential velocity. We note that numerical simulations of trailing vortex evolution typically use velocity vortex core sizes in the range from five to twelve percent of the wingspan of an aircraft. Thus, the values of velocity core size used in numerical models are significantly larger than the full-scale values reported here. We also show that a typical size of smoke trails, where smoke is used to visualize the vortices behind an aircraft, is approximately twice the size of the velocity core.
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