Comparison of ERA40 cloud top phase with POLDER-1 observations
Abstract
A detailed grid-point-based comparison of the cloud top phase derived from the 40-year reanalyses (ERA40) of the European Centre for Medium-Range Weather Forecasts (ECMWF) with satellite measurements is presented. For this purpose an algorithm is implemented to extract a two-dimensional "satellite-like" field of the cloud top phase from ERA40 data. This field is compared with cloud top phase data from the Polarization and Directionality of the Earth Reflectances (POLDER-1) instrument which was in orbit from November 1996 to June 1997. The thermodynamic cloud phase in ERA40 data is parameterized as a function of temperature with pure liquid clouds above 0°C, pure ice clouds below -23°C and mixed clouds in between. The matching performance of clouds derived from ERA40 with clouds observed by POLDER-1 is best in the extratropical storm track regions and over the tropical continents. Detailed comparison of the cloud top phase for grid points where both data sets indicate a cloud shows a relatively good agreement for warm (T > 0°C) and cold (T < -30°C) clouds. In the intermediate temperature range, ERA40 contains too many ice clouds compared to POLDER-1. The comparison reveals only small seasonal variations. A slightly revised parameterization for the phase partitioning of condensed cloud water is suggested (shifting the thresholds by -10°C), which leads to a generally improved agreement between cloud top phases derived from ERA40 and POLDER-1.
- Publication:
-
Journal of Geophysical Research (Atmospheres)
- Pub Date:
- March 2008
- DOI:
- 10.1029/2007JD009234
- Bibcode:
- 2008JGRD..113.5209W
- Keywords:
-
- Atmospheric Processes: Clouds and aerosols;
- Atmospheric Processes: Global climate models (1626;
- 4928);
- Atmospheric Processes: General or miscellaneous;
- ERA40;
- cloud phase;
- POLDER