71 Multiple Radar Data Assimilation and Short-Range Precipitation Forecast of a Cold Front

Monday, 28 August 2017
Zurich DEFG (Swissotel Chicago)
Rute Ferreira, INPE, Cachoeira Paulista, Brazil; and T. Biscaro, M. P. Alves Jr, L. E. R. Zea, D. L. Herdies, and E. P. Vendrasco

Multiple-Radar Data Assimilation and Short-Range Precipitation Forecast of a Cold Front

Cold fronts are responsible for creating the environmental condition for convective initiation in short range forecast. The convection associated with it can be responsible for occurrence of mesoscale convective systems, squall lines, and other prefrontal precipitant systems.

The goal of this work is using radar data assimilation to evaluate the potential of eliminating spurious convection with minimum threshold insertion of reflectivity and assimilation of 'no-precipitation' in a cold front and its associated convection.

One case study with high precipitation was selected and simulations were performed assimilating data from eight radars in south and southwest of Brazil and Paraguay among other conventional data from the Global Telecommunication system (GTS).

The atmospheric model and the assimilation system used are the WRF Data Assimilation (WRFDA) 3D-Var. The radial velocity was directly assimilated, while the reflectivity was converted to rainwater mixing ratio before the assimilation process using an exponential relationship. The no-precipitation data is related with all reflectivity observations below the threshold value of 5 dBZ. The cycles of data assimilation consists of four 1-h cycles assimilating radar and conventional data. After the assimilation process, a forecast was carried out.

The forecasted precipitations with and without assimilation were evaluated by comparing them against the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) product 3B42 Real Time and rain gauge data.

An improvement of the forecast was observed when radar data were assimilated, showing the importance of improving the initial condition by assimilating high resolution data into the model.

The results are being analised to check if the assimilation of no-precipitation observations have success in suppress spurious convection on short forecasts and also if it can reduce noise at 1-day forecasts.

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