Paraglider flight logs as hypsometers: daily temperature profiles of an Alpine valley, its diurnal heating, and the nearly level ceiling of thermals

Jörg Korner

A paraglider flight recorder writes a barometric and a GNSS altitude every second. Between two pressure levels, the difference in GNSS altitude is the thickness of the layer, set by its mean virtual temperature: each recorder is a hypsometer, and a fleet of them a sounding network over every flown slope. Applied to 31 677 logs from dedicated instruments in the Valais, Swiss Alps, the method yields a temperature profile between 1400 and 3900 m for 437 flying days of 2011–2026. Against the Payerne radiosonde the midday profiles agree between 2200 and 3600 m to a median of +0.6 K, with a spread of 1.0–1.8 K over 375 days. Climbing and sinking flight give the same profiles to 0.2 K; instrument families differ by ±0.5 K in absolute level, not in differences within a day. Between 07–10 and 14–18 UTC the air over the valley warms by 4.0 K at 1940 m and 1.7 K at 3020 m, the same within one 10-km cell as over the whole valley, against a few tenths of a kelvin in the free atmosphere, storing 2.5 MJ m-2 between 800 and 700 hPa. The ceiling of thermal lift, the upper envelope of the observed climbs in cells of 2.5–10 km, rises only 210–320 m for 1000 m of terrain (factors 0.21–0.32), the hour of day accounting for less than 0.1. Thin warm layers along slopes do not change the weight of the column and are invisible; the profiles therefore do not depend on where pilots fly.