Abstract
Abstract To improve the assimilation of Advanced Microwave Sounding Unit-A and -B (AMSU-A and -B) observations over land, three methods, based either on an estimation of the land emissivity or the land skin temperature directly from satellite observations, have been developed. Some feasibility studies have been performed in the Météo-France assimilation system in order to choose the most appropriate method for the system. This study reports on three 2-month assimilation and forecast experiments that use different methods to estimate AMSU-A and -B land emissivities together with the operational run as a control experiment. The experiments and the control have been subjected to several comparisons. The performance of the observation operator for simulating window channel brightness temperatures has been studied. The study shows considerable improvements in the statistics of the window channels’ first-guess departures (bias, standard deviation). The correlations between the observations and the model’s simulations have also been improved, especially over snow-covered areas. The performances of the assimilation system, in terms of cost function change, have been examined: the cost function is generally improved during the screening and remains stable during the minimization. Moreover, comparisons have been made in terms of impacts on both analyses and forecasts.
Highlights
Microwave observations from the Advanced Microwave Sounding Unit-A and -B [AMSU-A and -B; or Microwave Humidity Sounder (MHS)] instruments have been widely used in numerical weather prediction (NWP) to improve the initial conditions for short-range forecasts
The fits of the AMSU observations compared to the first guesses (FGs) or the anaysis have been improved, taking into account the large amount of added data over land
The results are from August 2006 and are given for EXP1 (Fig. 1a for AMSU-A and Fig. 1b for AMSU-B), for EXP2 (Fig. 1c for AMSU-A and Fig. 1d for AMSU-B), and for EXP3 (Fig. 1e for AMSU-A and Fig. 1f for AMSU-B)
Summary
Microwave observations from the Advanced Microwave Sounding Unit-A and -B [AMSU-A and -B; or Microwave Humidity Sounder (MHS)] instruments have been widely used in numerical weather prediction (NWP) to improve the initial conditions for short-range forecasts. The list of conditions to be satisfied for a given channel (listed in Table 1) is not exhaustive. Significant progress has already been achieved in the use of AMSU measurements in NWP, but in some areas the data remain underutilized. Priority was given to the use of AMSU measurements over seas, together with measurements for which the contribution of the surface is negligible. It should be pointed out that a classification-based emissivity scheme that uses regressions and empirical models (Weng et al 2001; Grody 1988) has been used in NWP and has facilitated the assimilation of AMSU channels over land.
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