Analysis of Seasonal and Daily Mid-Latitude Tropopause Pressure Using GPS Radio Occultation Data and NCEP-NCAR Reanalyses

摘要

In the last decades the tropopause has received renewed attention for the analysis of atmospheric variability and, more in general, for climate studies. GPS (Global Positioning System) radio occultation measurements can provide accurate values of temperature and height of the tropopause, as recently shown in several papers, due to the high vertical resolution of this observing technique and the limited disturbance from water vapor, scarse in the tropopause region. The relatively high density of radio occultation measurements in the mid and high latitude regions enables to evaluate the horizontal scale of variability of the tropopause with sufficient accuracy. Data from GPS/MET (GPS Meteorology) and CHAMP (Challenging Minisatellite Payload) have been recently used to study the relationship between tropopause variability in tropical regions and convective structures. In this paper we focus on the analysis of variability of the tropopause structure in mid and high latitudes by comparing NCEP-NCAR (National Centers for Environmental Prediction — National Center for Atmospheric Research) reanalyses and radio occultation data from the CHAMP satellite. The comparison shows good agreement of the tropopause pressure fields both in total and seasonal means. The comparison between two single days shows that the current number of CHAMP measurements is insufficient to correctly retrieve the global tropopause field. In the next years, when more satellites will be equipped with GPS radio occultation payloads, the daily tropopause field will be better retrieved.