ECMWF Land Data Assimilation System (LDAS)
The land-surface analysis includes the screen-level parameters analysis, the snow depth analysis, the soil moisture analysis, the soil temperature and snow temperature analysis.
The screen level parameters analysis and the snow analysis rely on a 2-dimensional Optimal Interpolation (2D OI).
The soil moisture analysis is based on a simplified Extended Kalman Filter (EKF).
The soil and snow temperature analysis uses a 1-dimensional OI (1D OI).
The structure of the land surface analysis components and their dependencies are shown in Figure 1. Firstly, a screen-level analysis is performed for temperature and humidity. Secondly, the snow analysis and the soil moisture analysis are conducted. Then the soil temperature and snow temperature analysis is performed. Analysed screen-level temperature and relative humidity are used as input of the simplified EKF soil moisture analysis. while screen-level analysis temperature increments are used as inputs of the 1D OI soil and snow temperature analysis.
Land analysis is run separately from the upper-air analysis. It feedbacks to the upper-air analysis of the next cycle through its influence on the short forecast that propagates information from one cycle to the next. Reciprocally, the 4D-Var influences through the short forecasts the land surface analysis from one cycle to the next. The OI analyses of screen level parameters, snow depth, snow and soil temperature are performed at fixed times at 0000, 0600, 1200, and 1800 UTC. The simplified EKF analysis runs at the same time as the 4D-Var windows for both the delayed cut-off and the early delivery analyses space.To help you on your way, we've inserted some of our favourite macros on this home page. As you start creating pages, blogging and commenting you'll see the macros below fill up with all the activity in your space.