MODELING OF A BORE OBSERVED ON JUNE 04

MODELING OF A BORE OBSERVED ON JUNE 04 DURING IHOP 2002 Mariusz Pagowski NOAA Research - Forecast Systems Laboratory CIRA, Colorado State University Steven E. Koch NOAA Research - Forecast Systems Laboratory J. -W. Bao NOAA Research - Environmental Technology Laboratory IHOP Workshop, Toulouse, June 14 -18, 2004

Outline u Mesoscale Model Simulations u Comparison with Observations u Analysis u ° Bore Origin ° Bore and the PBL Conclusions

Model Setup Nested MM 5 model (18, 6, 2, 0. 666 km) initialized at 00 Z 4 June 02 u Initial / boundary conditions from hourly RUC-20 km analyses u 44 vertical levels (22 below 1500 m) u Ensemble based convective parameterization (Grell and Devenyi 2002) in two lower resolution domains u Different Mellor-Yamada based 1. 5 -order closures (Burk-Thompson 1989, Eta Janjic 1994, QL with prognostic mixing length Mellor and Yamada 1982) u Reisner microphysics and Smirnova land-surface model u

NWS Surface Reports and Model Results (6 km) 0500 UTC 1000 UTC

S-POL Radar Reflectivity and Model Results (6 km) 0500 UTC 0730 UTC

S-POL Radar Reflectivity and Model Results (2 km) Convergence / Divergence pattern

FM-CW , MAPR and Model Results (. 6 km) Structure function Potential temperature Vertical velocity

Bore Origin Divergence / convergence movie Front-relative velocity / relative humidity movie

Bore Origin cont’d Front-relative velocity Relative humidity

Bore Origin cont’d u u u Wave trapping when Scorer parameter decreases with height (lee waves, Holton 1992, Crook 1988) Wave dispersion (Mahapatra et al. 1991) Wave generation by pressure disturbances (Simpson 1987, Baines 1995)

Bore Origin cont’d Vertical velocity / Scorer parameter movie

Bore and the PBL TKE/Shear production movie

Bore and the PBL cont’d AERI Sounding and Model Results (. 6 km) Potential temperature Mixing ratio

Bore and the PBL cont’d Surface temperature Surface relative humidity / mixing ratio

Bore and the PBL cont’d U-advection V-advection W-advection Turbulence

Conclusions u u MM 5 simulations show some realism in reproducing a second bore observed on June 4, 2002 during IHOP. Simulations show sensitivity to initial conditions and small sensitivity to TKE based PBL parameterizations. Bore in the model is generated when wind/pressure perturbations induced by precipitation reach a surface front. This result cannot be verified since there are no observations. The bore developed into a wave-train. Modeled wave amplitude and length is close to the observed. Origin of the wave-train is related to the nonhydrostatic(dynamic) pressure disturbances on the frontal head but cannot be verified. Cooling and moistening of the mixed in the bore’s wake is reproduced by the model and can be easily explained. Surface warming and drying also occurs in the model due to advection. The warming is smaller than observed.