172 Assimilating Differential Reflectivity Columns into the High-Resolution Rapid Refresh Using Latent Heating Forcing

Monday, 8 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
Shawn Murdzek, The Pennsylvania State Univ., Univ. Park, PA; and D. Dowell, T. Ladwig, M. Hu, C. R. Alexander, S. Benjamin, and J. M. Brown

The High Resolution Rapid Refresh (HRRR) assimilates radar reflectivity information in order to skillfully forecast convection. This assimilation is done using an empirical relationship between reflectivity and latent heat release from hydrometeor condensation and freezing to update the temperature tendency field. The temperature tendency field then forces the HRRR to produce updrafts where the temperature tendency is large and positive. Two problems with this approach are that areas of high reflectivity are temporally and spatially offset from vertical velocity maxima. Differential reflectivity (ZDR), which is now experimentally available on a national mosaic from the Multi Radar Multi Sensor (MRMS) project, provides a possible solution to these two problems.

Vertical columns of enhanced ZDR above the environmental freezing level can be used as proxies for updrafts, so creating a two-dimensional field of ZDR column locations can focus the latent heating forcing to where convective updrafts are actively occurring. This presentation will discuss the algorithm used to detect ZDR columns and subjectively assess how well the analyzed ZDR columns match the expected locations of updrafts in convective events. The method used to create a temperature tendency field from ZDR column locations that can be assimilated into the HRRR will also be discussed. These ZDR column-derived temperature tendency fields will then be compared to the temperature tendency fields currently used by the HRRR that are derived from radar reflectivity in order to demonstrate the feasibility of assimilating ZDR columns instead of or in addition to radar reflectivity. Preliminary results from a case study in which ZDR column information is assimilated may also be presented.

- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner