Global radiosonde balloon drift statistics

Abstract

[1] The drift of radiosonde balloons during their ascent has generally been considered a negligible factor in applications involving radiosonde observations. However, several applications envisioned for observations from the Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN) require estimates of balloon drift. This study presents a comprehensive global climatology of radiosonde balloon drift distance and ascent time, based on 2 years of data from 419 stations, with particular attention to GRUAN stations. Typical drift distances are a few kilometers in the lower troposphere, ∼5 km in the midtroposphere, ∼20 km in the upper troposphere, and ∼50 km in the lower stratosphere, although there is considerable variability due to variability in climatological winds. Drift distances tend to increase with height above the surface, be larger in midlatitudes than in the tropics, be larger in winter than in summer, and vary with wind (and consequent balloon drift) direction. Most estimates of elapsed time from balloon launch to various pressure levels, due to vertical balloon rise, have median values ranging from about 5 min at 850 hPa to about 1.7 h at 10 hPa, with ranges of about 20% of median values. Observed elapsed times exceed those estimated using assumed 5 or 6 m/s rise rates.