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Assimilation of Doppler Weather Radar Radial Velocity and Reflectivity Observations in WRF-3DVAR System for Short-Range Forecasting of Convective Storms

Abhilash, S and Sahai, AK and Mohankumar, K and George, JP and Das, S (2012) Assimilation of Doppler Weather Radar Radial Velocity and Reflectivity Observations in WRF-3DVAR System for Short-Range Forecasting of Convective Storms. Pure and Applied Geophysics, 169 (11). pp. 2047-2070.

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Abstract

In this paper the impact of Doppler weather radar (DWR) reflectivity and radial velocity observations for the short range forecasting of a tropical storm and associated rainfall event have been examined. Doppler radar observations of a tropical storm case that occurred during 29-30 October 2006 from SHARDWR (13. 6° N, 80. 2° E) are assimilated in the WRF 3DVAR system. The observation operator for radar reflectivity and radial velocity is included within latest version of WRF 3DVAR system. Keeping all model physics the same, three experiments were conducted at a horizontal resolution of 30 km. In the control experiment (CTRL), NCEP Final Analysis (FNL) interpolated to the model grid was used as the initial condition for 48-h free forecast. In the second experiment (NODWR), 6-h assimilation cycles have been carried out using all conventional (radiosonde and surface data) and non-conventional (satellite) observations from the Global Telecommunication System (GTS). The third experiment (DWR) is the same as the second, except Doppler radar radial velocity and reflectivity observations are also used in the assimilation cycle. Continuous 6-h assimilation cycle employed in the WRF-3DVAR system shows positive impact on the rainfall forecast. Assimilation of DWR data creates several small scale features near the storm centre. Additional sensitivity experiments were conducted to study the individual impact of reflectivity and radial velocity in the assimilation cycle. Radar data assimilation with reflectivity alone produced large analysis response on both thermodynamical and dynamical fields. However, radial velocity assimilation impacted only on dynamical fields. Analysis increments with radar reflectivity and radial velocity produce adjustments in both dynamical and thermodynamical fields. Verification of QPF skill shows that radar data assimilation has a considerable impact on the short range precipitation forecast. Improvement of the QPF skill with radar data assimilation is more clearly seen in the heavy rainfall (for thresholds >7 mm) event than light rainfall (for thresholds of 1 and 3 mm). The spatial pattern of rainfall is well simulated by the DWR experiment and is comparable to TRMM observations.

Item Type: Article
Additional Information: Copyright of this article belongs to Springer
Uncontrolled Keywords: Control experiments; Convective storms; Data assimilation; Doppler radar observation; Doppler weather radars; Dynamical fields; Global telecommunication systems; Heavy rainfall; Horizontal resolution; Initial conditions; Model physics; Observation operator; Radar data assimilation; Radar reflectivities; Radial velocity; Radial-velocity observations; Rainfall event; Rainfall forecasts; Short-range precipitation forecast; Small-scale features; Spatial patterns; Surface data; Tropical storms, Data processing; Doppler radar; Experiments; Meteorological radar; Rain gages; Reflection; Storms; Tropics; Velocity; Weather forecasting, Rain, convective system; data assimilation; Doppler radar; rainfall; reflectivity; storm; weather forecasting
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 18 Jan 2014 06:11
Last Modified: 18 Jan 2014 06:11
URI: http://moeseprints.incois.gov.in/id/eprint/434

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