8.6 Evaluation of HRRR boundary layer structure via high-resolution radiosondes.
Fovell, Robert, University at Albany, SUNY
Along with the
surface layer treatment, the planetary boundary layer (PBL) scheme represents
one of the most important parameterizations in a numerical weather prediction
(NWP) model. Among other things, PBL schemes are responsible for determining
the depth, stability and vertical profiles of humidity and horizontal wind in
the boundary layer. These are subject to observational uncertainty and also the
validity of assumptions that can vary widely among parameterizations.
NOAA's operational High Resolution Rapid Refresh (HRRR) model is run at
convection-permitting (3 km) horizontal resolution and utilizes the
Mellor–Yamada–Nakanishi–Niino level 2.5 (MYNN2) PBL scheme. This is a
state-of-the-art treatment that has been substantially upgraded and expanded in
recent years. HRRR forecasts of boundary layer wind, temperature, and specific
humidity are being evaluated using 60 high-resolution radiosondes across the
contiguous US (CONUS) that can provide roughly 5 m vertical resolution near the
surface. Challenges in employing this underutilized resource have been
mitigated or overcome and the spatially- and temporally-averaged composites are
revealing shortcomings in the forecasts that can be addressed with further
improvements to the scheme.