Representation of the Sierra Barrier Jet in 11 years of a high‐resolution dynamical reanalysis downscaling compared with long‐term wind profiler observations

Abstract

We investigate the representation of the Sierra Barrier Jet (SBJ) in four numerical models at different resolutions, primarily documenting its representation within a high‐resolution (6 km), 11‐year WRF reanalysis downscaling (WRF‐RD). A comprehensive validation of this dynamical downscaling is undertaken during 11 cool seasons (water years 2001–2011, October to March) using available wind profiler data at Chico, CA (CCO). We identify SBJ cases in the observed CCO wind profiler data, as well as in WRF‐RD at the closest grid point. WRF‐RD's representation of the SBJ at CCO is compared with that of other reanalysis products with coarser horizontal resolutions (i.e., the North American Regional Reanalysis (NARR), the California Reanalysis downscaling, and the NCEP/NCAR Reanalysis) to assess whether downscaling is necessary to correctly capture this topographically induced low‐level jet. Detailed comparisons across California between WRF‐RD and NARR suggest downscaling is necessary: Only WRF‐RD at 6 km resolution is well‐capturing this dynamical feature. A catalog of modeled SBJ events that have significant timing overlap with observations is created and used to further assess WRF‐RD's representation of SBJ events. In addition, observation‐model comparisons of other meteorologically important variables (e.g., precipitation melting level, wind profiles, temperature, and relative humidity) are performed in order to evaluate WRF‐RD's ability to capture the dynamical evolution of the SBJ. The detailed, case‐by‐case comparisons reveal WRF‐RD accurately represents 56 percent of the 256 observed SBJ cases occurring during these 11 cool seasons, albeit with a weak wind bias that increases with jet maximum wind strength.

The Regional Influence of an Intense Sierra Barrier Jet and Landfalling Atmospheric River on Orographic Precipitation in Northern California: A Case Study

“…Regional to synoptic-scale meteorological context was provided by gridded precipitation datasets, the operational landocean surface network, the 32-km resolution NARR, and SSM/I satellite imagery. This study extends the early SBJ research results from SCPP (e.g., Parish 1982; Marwitz 1983Marwitz , 1987Smutz 1986) and from the recent AR-SBJ results borne out of NOAA's HMT efforts and the California Energy Commission's CalWater program (e.g., Hughes et al 2012;Kingsmill et al 2013;Neiman et al 2013a).…”

“…Landfalling extratropical cyclones along the U.S. West Coast are often accompanied by ARs, which are long (.2000 km), narrow (,1000 km) plumes of enhanced horizontal water vapor flux embedded within the broader region of generally poleward heat transport in the cyclone warm sector (Zhu and Newell 1998;Ralph et al 2004Ralph et al , 2006Ralph et al , 2011Neiman et al 2008aNeiman et al ,b, 2013bSmith et al 2010;Sodemann and Stohl 2013). SBJs, which were first documented during the Sierra Cooperative Pilot Project (SCPP; Reynolds and Dennis 1986) and have since been studied extensively (e.g., Parish 1982;Marwitz 1983Marwitz , 1987Smutz 1986;Hughes et al 2012;Kingsmill et al 2013;Neiman et al 2013a), form in response to the deceleration of stably stratified flow as it approaches the western Sierra foothills. This deceleration leads to a weakened Coriolis force, causing the flow to turn leftward toward the north end of the CV in response to the (no longer balanced) pressure gradient force.…”

Sensitivity of Mountain Hydroclimate Simulations in Variable‐Resolution CESM to Microphysics and Horizontal Resolution

“…Understanding the physical processes that affect precipitation and snowpack accumulation in U.S.‐west mountainous regions and how they may be altered with anthropogenic climate change necessitates the use of climate models that can properly characterize land surface heterogeneity and synoptic‐scale storm systems (Huning & Margulis, ). An accurate representation of U.S.‐west orography is particularly important to realistically simulate the capture and storage of available precipitable water from the atmosphere (Ashfaq et al, ; Chen et al, ; Hughes et al, ; Ikeda et al, ; Liu et al, ; Musselman et al, ; Pierce et al, ; Rasmussen et al, ; Walton et al, ). This is due to the importance of mountain range orientation, the mountain slope variation impacts on orographic uplift, the corresponding alterations in the precipitation phase, the resultant transport and location of surface precipitation, the snow‐albedo feedback, and the life cycle of stored mountain snowpack.…”

High-Resolution Downscaled Simulations of Warm-Season Extreme Precipitation Events in the Colorado Front Range under Past and Future Climates*

“…The spatial structure of a given RCM's past and future precipitation are more similar to one another than to that of other models or that of NARR, indicating that each model's preferred regional precipitation pattern is reasonably sampled by 10 events. NARR may also have difficulty representing large precipitation amounts in mountainous terrain and has other known limitations and errors that have been documented as well (e.g., Mesinger et al 2006;Bukovsky and Karoly 2007;West et al 2007;Dominguez et al 2012;Hughes et al 2012). Thus, the comparison is offered here as a basic benchmark against a proxy for observations, but deviations between NARR and the RCM top 10 events not only reflect model bias in pattern and magnitude but also the independence of the events considered.…”