Altitude misestimation caused by the Vaisala RS80 pressure bias and its impact on meteorological profiles

Abstract

Abstract. Previous research has found that conventional radiosondes containing a traditional pressure sensor can be subject to a pressure bias, particularly in the stratosphere. This study examines this pressure bias, and the resulting altitude misestimation, and considers its impact on temperature, ozone, and water vapor profiles, using data obtained between December 2003 and January 2010 during the Soundings of Ozone and Water in the Equatorial Region (SOWER) campaigns. The observation package consisted of a radiosonde (Vaisala RS80), ozone and water vapor sondes, and a global positioning system (GPS) sensor. More than 30 soundings are used in this study. As GPS height data are thought to be highly accurate, they can be used to calculate pressure. The RS80 pressure bias in the tropical stratosphere was estimated to be −0.4 ± 0.2 hPa (1σ) between 20 and 30 km. As this pressure bias is negative throughout the stratosphere, it leads to altitude misestimation when heights are calculated, as this is usually achieved using the hydrostatics equation. We estimated the error in geometric height to be 42 ± 24, 110 ± 39, and 240 ± 90 m (1σ) at 20, 25, and 30 km, respectively. Because of the altitude misestimation, we saw some differences in observation parameters having a vertical gradient. For the temperature profiles, the differences were approximately −0.2 ± 0.2, −0.2 ± 0.4, and −0.3 ± 0.8 K (1σ) at 20, 25, and 30 km, respectively. For the ozone profiles, there was a maximum of ozone partial pressure at around 27 km. Therefore, the differences do not monotonically increase with increasing altitude, and they are estimated to be −1.9 ± 1.6, −0.7 ± 1.0, and 3.1 ± 2.2% (1σ) at 20, 25, and 30 km, respectively. For the water vapor profiles, as there are minima and maxima associated with the stratospheric tape recorder signal, the differences are affected by the phase of the tape recorder. If we align water vapor profiles using a water vapor minimum, the differences are estimated to be −2.7 ± 8.1% at 0.5 km and 1.5 ± 1.0% (1σ) at 4 km above the water vapor minimum around the cold point tropopause. These biases in the meteorological soundings obtained using the RS80 may have generated an artificial trend in the meteorological records when radiosondes were changed from the RS80, which had no GPS sensor, to the new ones with a GPS sensor. Therefore, it is important to take these biases into account in climate change studies.