Wednesday, 23 June 2004: 11:00 AM
Measurements of air velocity have been made in the vicinity of Mount Washington in New Hamphire and Mauna Kea in Hawaii using the GroundWinds direct-detection lidar facilities. On several occasions, balloon-borne thermosondes and radiosondes were launched nearby for direct comparison. The lidar measures a time series of velocity parallel to the laser beam for each altitude. The vertical angle is fixed at a 45 degree angle, but may scan horizontally. The altitude range depends strongly on the choice of temporal averaging; long average times of 10 seconds can result in data as high as 20 km. Shorter averaging times do not achieve data at high altitudes, but allow direct measurements of turbulence. The thermosonde measures the temperature difference between two sensors spaced one meter apart, then computes the temperature turbulence parameter. Comparison between turbulence measured with the lidar to turbulence measured with the thermosonde shows excellent agreement for altitudes up to 4 km. A strong turbulent layer is common downwind of the mountain top at the altitude of the mountain top. Waves are evident in both the lidar data and the thermosonde data, expecially for the altitude range corresponding to the mountain. These waves are evident at both sites.
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