18A.4 Development and testing of improved radar-data assimilation techniques for the Rapid Refresh and HRRR

Friday, 30 September 2011: 9:45 AM
Monongahela Room (William Penn Hotel)
Curtis R. Alexander, NOAA/ESRL, Boulder, CO; and D. C. Dowell, M. Hu, S. S. Weygandt, T. G. Smirnova, S. G. Benjamin, J. M. Brown, E. P. James, and P. Hofmann

In this presentation, we will describe ongoing work to improve the radar-data assimilation capabilities for the Rapid Refresh (RR) and associated High-Resolution Rapid Refresh (HRRR). Currently, the RR and HRRR rely on a diabatic-digital filter initialization (DFI)-based radar reflectivity assimilation procedure within the RR. This procedure, first coded within the RUC and used successfully since November 2008 in the NCEP operational RUC, has since been ported to the Rapid Refresh (RR). The RR (including the radar-DFI assimilation procedure) is slated (as of May 2011) to replace the RUC at NCEP in September 2011. A companion presentation (Weygandt et al.) describes a quantitative and case study assessment of the forecast improvement from this radar-data assimilation within the RUC and RR, as well as for HRRR runs nested within the RUC and RR.

A major drawback of assimilating the radar data only within the RR model, which employs 13-km horizontal grid spacing, is the inability to continuously cycle explicit convection within the HRRR. Thus, work to improve the HRRR convective forecast skill is ongoing through experimentation with cycled 3-km radar-data assimilation techniques. We are evaluating a number of methods to apply the radar-DFI technique in a cycled way at 3-km (including a forward only 15-min update cycle). At the conference, we will present preliminary results, including an assessment of the 3-km forecast improvement from adding a cycled 3-km radar assimilation. Special attention will be given to storm-scale spin-up and balance (including an evaluation of the cold-pool evolution) along with continuity of convective-scale structures, originating from an accurate storm-scale analysis (initial condition), during much of the free forecast period (several hours).

A second focus of work to improve HRRR radar assimilation is on the use of radial velocity within the HRRR. Here, we will examine the forecast impact from assimilation of these data and evaluate sensitivity to variations in the assimilation configuration (assumed correlation length scale, data quality control, use of clear-air data, etc.). Finally, time permitting, we will describe some more experimental work, in which ensemble Kalman filter techniques have been applied to the storm-scale radar data assimilation problem.

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