4.2 WRF forecast sensitivity of wave-turbulence interactions to initialization strategy and PBL physics in the stable boundary layer

Suarez, Astrid, David R. Stauffer, Brian J. Gaudet, Aijun Deng, Penn State University, Larry Mahrt, Oregon State University, and Nelson L. Seaman, Penn State University

The forecast sensitivity of gravity wave-turbulence interactions to initialization strategy and PBL physics are examined through a combined observation and modeling study over Central Pennsylvania. Terrain-induced gravity waves can generate intermittent bursts of turbulence in the stable boundary layer (SBL) through the modification of momentum and thermal fluxes and nonlinear phenomena. To further investigate the impact of these interactions on the SBL, high-resolution (0.444-km-horizontal grid spacing, 10 vertical layers in lowest 50 m AGL) WRF forecasts of six gravity-wave events, producing resonant-lee-wave and hydraulic-jump-type rotors, are verified against observations from a special data network located at Rock Springs, PA. Three initialization strategies are tested: a 12-h forecast cold-started from GFS at 0000 UTC; a 24-h forecast initialized from GFS 12 h earlier; and a 12-h forecast preceded by a 12-h, data-assimilation, pre-forecast period that includes local observations. Pre-forecast data assimilation reduces temperature forecast errors within the network. This configuration is used to test four PBL parameterizations: MYJ, YSU, QNSE, and MYNN. The forecasts of wave parameters, such as wavelength, phase and amplitude, show some sensitivity to initialization strategy and PBL physics. Overall, improvements in the forecast of wave-turbulence interactions in the SBL are noted when using pre-forecast data assimilation. TKE-based schemes appear to forecast larger amplitude fluctuations in low-level wind and temperature than YSU; thus they can produce more realistic structures but larger statistical errors due to phase errors.