As part of a feasibility study for a Southern Hemisphere horizontal sounding system, for five mid-season months daily 500-mb geostrophic trajectories of 14 days' duration were constructed from four possible constant-level balloon launch sites in the Southern Hemisphere. In the main belt of westerlies such a balloon release rate would yield upper-air data at approximately 1000 n mi intervals at any given time, and would yield data at approximately 750 n mi intervals if “off-time” reports could be utilized. A seven-station radio-direction-finding network, including one station in Antarctica, appears capable of providing constant-level balloon positioning with at least a 60 per cent chance of obtaining a “fix” based upon three or more bearings south of latitude 40S and at least a 70 per cent chance of obtaining “fix” based upon two or more bearings south of 25S.

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1 A portion of this work has been supported by the National Science Foundation as part of the Polar Meteorology Research Project of the U. S. Weather Bureau.