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Quantifying the Stable Boundary Layer Structure and Evolution during T-REX 2006

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Final rept. 1 Sep 2009-31 Aug 2014

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A comprehensive study integrating surface observations, data from in-situ measurements, and a nested numerical model with two related topics was conducted in this project. the WRF PBL schemes are very much sensitive to complex terrain regions. No single parameterization can represent all events i.e., weather conditions and all mountainous terrain regions e.g., Sierra-Nevada. The use of high-resolution i.e., grid spacing at 4 km or less modeling is essential to advance our understanding of mountain-valley flows in association with stable boundary layer conditions. Observations and model results suggest that the T-REXEOP4 event never quite achieves a truly steady-state down-valley flow condition near the surface, as fluctuations in the jet strength and the near surface mean valley wind direction appeared to occur throughout the event. The simulation results also suggest that adding two additional nests an outer 13.5 km and an inner 500 m can produce a much better evolution of the nocturnal low-level jet and especially in terms of the speed max. It also appears as if the addition of the outer 13.5 km nest was far more critical then the addition of the inner 500 m nest, lending support to the idea that accurately capturing the synoptic condition was a critical player in this valley low-level jet event. Overall, the low-level nocturnal down-valley jet is fairly well resolved by the simulations in terms of timing, spatial location, and height above the valley floor.

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  • Atmospheric Physics
  • Meteorology

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