The Canadian LAM 3D-Var continental analysis system

We present the next generation Canadian Continental Data Assimilation System (DAS) developed at the Meteorological Service of Canada (MSC). This system aims at producing analysis of synoptic and mesoscale weather in the 48h range.

Key features of the new DAS are:

(1) the current operational regional model (GEM-REG), which is a global variable-resolution grid model with a

15km uniform resolution over North-America and lower resolution elsewhere will be replaced by a Limited-Area continental 15km uniform resolution over North-America piloted by a global 55km uniform grid model.

(2) The new analysis is done on the same spatial extension of the LAM-15km grid but produces analysis increments at 55 km resolution (as compared to 180 km for the current operational system) It uses a three-dimensional variational approach as a first implementation (referred to as the LAM3D data assimilation system).

As a first crucial demonstration, we show that the LAM3D system matches the results (over the 48h range) of GEM-REG for mass/wind fields and precipitation given the same set of observations. Secondly, emphasis is put on the lower atmosphere vertical motion and moisture fileds in order to tackle the difficult problem of precipitation forecast improvements. We use a short time-tendency diabatic tangent-linear Implicit Nonlinear Normal Mode approach to ensure coherent diabatically forced low-level vertical motion. On the data side, to provide further information on the moisture field, ground based GPS observations are now used in the LAM3D system. A 4D-Var extension is also systematically evaluated and we report on this also.

The operational implementation of LAM3D is scheduled for Fall 2009.