Representation of low-tropospheric temperature inversions in ECMWF reanalyses over Europe
Although tropospheric temperature inversions are thought to be an important feature of climate as well as a significant factor affecting air quality, low-level cloud formation, and the radiation budget of the Earth, a quantitative assessment of their representation in atmospheric reanalyses is still missing from the scientific literature. Here, we provide new evidence of the occurrence of low-tropospheric temperature inversions and associated uncertainties in their parameters existing among reanalyses produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) and upper-air soundings for Europe covering the period 2001-2010. The reanalyses utilized here may be grouped into two categories: (1) surface-input reanalyses represented by ERA-20C and CERA-20C as well as (2) full-input reanalyses represented by ERA-Interim and ERA5. The upper-air soundings were derived from the Integrated Global Radiosonde Archive (IGRA), version 2. The data consist mainly of air temperature and geopotential height from the model levels (ModLev) and pressure levels (PresLev)of ECMWF reanalyses. The results have demonstrated that the frequency of surface-based inversions (SBI) and elevated inversions (EI) is largely in agreement among the reanalyses. The quality of their representation is, however, determined by the inversion type, season, and region. Over the vast majority of IGRA upper-air stations, SBI frequency is overestimated and EI frequency is underestimated by ECMWF reanalyses. Substantially larger uncertainties arise from the selection between the data of ModLev and PresLev of the reanalyses– the differences in the frequency of the temperature inversions calculated based on those data are particularly large for summertime SBI suggesting that PresLev are not capable of resolving the main features of shallow and weak SBI.