Comparison of Weighted Mean Temperature in Greenland Calculated by Four Reanalysis Data

Abstract

The weighted mean temperature ( Tm) is a critical parameter for precipitable water vapor (PWV) retrieval in global navigation satellite system (GNSS) meteorology. Reanalysis data are an important data source for Tm calculation and Tm empirical model establishment. This study uses radiosonde data to evaluate the accuracy and the spatiotemporal variation of Tm that is derived from four reanalysis data, namely, the release of the fifth-generation accurate global atmospheric reanalysis (ERA5), the modern-era retrospective analysis for research and applications version 2 (MERRA-2), the NCEP/DOE, and the NCEP/NCAR, from 2005 to 2019 in Greenland, due to the paucity of research on the performance of Tm in the polar region that is derived from reanalysis data, particularly on a long temporal scale. The results were as follows: (1) The 15-year mean bias errors (MBEs) and root mean square errors (RMSEs) of Tm that were obtained from the four reanalysis data are 0.267 and 0.691 K for the ERA5, −0.247 and 0.962 K for the MERRA-2, 0.192 and 1.148 K for the NCEP/DOE, and −0.069 and 1.37 K for the NCEP/NCAR. The Tm that was derived from the ERA5 (ERA5 Tm) has the highest accuracy, followed by the MERRA-2 Tm, the NCEP/DOE Tm, and the NCEP/NCAR Tm. (2) In the inter-annual stability of the Tm precision compared with the radiosonde data, the results of the ERA5 are the most stable, followed by the NCEP/DOE Tm, the NCEP/NCAR Tm, and the MERRA-2 Tm. The ERA5 Tm have improved from 2005 to 2019. (3) The Tm accuracy that was computed by the four reanalysis data exhibits significant seasonal variation characteristics in Greenland, as follows: the summer and the autumn accuracy is higher than that in the winter and the spring, which may be related to the variation of the surface temperature (Ts) accuracy. (4) The Tm that was estimated from the four reanalysis data exhibits a consistent spatial distribution, as follows: the Tm is smaller in the middle region of Greenland and is greater at the island’s edge. The comparative study of Tm that is obtained from the four reanalysis data can serve as a reference for future research on Tm model development and water vapor retrieval in polar regions by utilizing reanalysis data.

Keywords

• reanalysis data
• radiosonde data
• Greenland
• weighted mean temperature