A HIGH-ALTITUDE SITE SURVEY FOR SOFIA

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a modi fied Boeing 747-SP equipped with a 2.5 m telescope dedicated to astron omical research. Currently under joint development by the US (NASA) an d Germany (DLR), it is scheduled to begin operations in late 2001. The ability of SOFIA to carry out its mission will depend strongly on the meteorological conditions at and above flight altitudes in the vicini ty of its home base. The most important meteorological factors are the frequency of high-altitude clouds and the magnitude of the water vapo r overburdens. This paper performs a high-altitude site survey by gath ering together the best available meteorological data, defining metric s, and evaluating them for a variety of sites. These metrics are found to corroborate past airborne experience and to be consistent with wel l-known global circulation patterns, convection, and upper tropospheri c dynamics. They indicate that I:here are significant variations in th e weather at SOFIA flight altitudes. Particularly in summer, some cont inental US sites are shown to be worse than Hawaii, where high-altitud e cirrus clouds and the associated moisture have historically caused s ignificant losses in the amount and quality of the astronomical data c ollected by NASA's Kuiper Airborne Observatory. SOFIA's planned home b ase, Moffett Field? CA, is found to have excellent high-altitude weath er and to be one of the best continental US sites.