Analysis of 2 meter temperature and relative humidity

Abstract

This note documents the recent installation of the analysis of the near surface parameters into the HIRLAM system. It is intended to explain why this analysis is primarely needed for the new surface parameterization that is being developed, although a version able to run within the old surface parameterization context has been prepared also. A procedure for the vertical reduction of the first guess fields to the station height has been introduced, and is specially useful in complex terrain. Since the method of analysis is Optimum Interpolation, a re-evaluation of the statistics of the first guess errors was necessary. First guess error covariances have been obtained for a selection of stations in Spain and in Scandinavia for winter and summer, in order to study the possible dependence on season and latitude. The effect of the orography as source of anisotropy, both because to the coastline and the inland topography, is included in the formulation of a new structure function.