Pressure and Temperature Differences between Vaisala RS80 and RS92 Radiosonde Systems

Abstract

In several twin flight campaigns, Vaisala RS80 radiosonde systems report lower temperatures than Vaisala RS92 systems in the daytime. Simultaneous differences increase from less than 0.1 K at pressure altitudes below 100 hPa to 0.7 K at 10 hPa. Much of the difference can be explained by an overcorrection of the RS80 radiation error. At night, RS92 and RS80 sounding systems report very similar simultaneous temperatures throughout the atmosphere. Geopotential heights from RS92 pressure, temperature, and humidity data (pTU heights) are within 25 m of geopotential heights from the RS92 global positioning system data (GPS heights) from the ground up to about 70 hPa. At higher altitudes, RS92 sondes produced after July 2004 show nearly identical pTU and GPS heights, but other manufacturing batches show systematic differences, up to ±100 m near 10 hPa. RS80 sondes provide much less accurate pressure and geopotential height. On average, they give up to 1 hPa higher pressure and 20 m lower pTU heights than RS92 sondes in the troposphere, and lower pressures and larger heights in the stratosphere (e.g., by ?0.4 hPa and +100 m near 10 hPa). Previous intercomparisons have found similar differences between the two sonde types. As expected from these simultaneous pressure and temperature differences, the transition from Vaisala RS80 to RS92 sondes at German radiosonde stations between 2003 and 2005 has produced artificial increases in stratospheric temperature records, particularly during daytime (1200 UTC), but due to the wrong RS80 pressures, also at night (0000 UTC). The spurious daytime temperature step reaches +0.3 ± 0.2 K at 50 hPa and +0.7 ± 0.4 K at 10 hPa, the nighttime step reaches +0.1 ± 0.1 K at 50 hPa and +0.35 ± 0.2 K at 10 hPa (2σ uncertainties). The mean difference between day- and nighttime temperatures (1200?0000 UTC) has increased as well, by 0.1 ± 0.06 K at 70 hPa and by 0.76 ± 0.16 K at 10 hPa. In the troposphere and at levels below 100 hPa no significant differences are found, although there are indications for higher daytime temperatures, possibly up to 0.1 K, from RS92 sondes. Results indicate that RS92 sondes are more accurate. Historic temperature records from RS80 sondes should be corrected for use in climate studies.