LAKE EFFECT SNOW SIMULATION John D McMillen

LAKE BONNEVILLE EFFECT SNOW

 27 Oct 2010 Event  Trevor Alcott found that the simulation and by extension, the GSLE are sensitive to the terrain around the lake  Downstream terrain is a strong positive impact on production of SWE GSLE SIMULATION

 I have replicated Trevor’s control and run several microphysics schemes  This case is also sensitive to microphysics parameterization  The most sophisticated schemes overproduce SWE GSLE SIMULATION

 This study views the additional moisture source of Lake Bonneville as a possible sensitivity  The results are compared with existing studies of the climate of the Pleistocene over Lake Bonneville LAKE BONNEVILLE SIMULATION

 Terrain raised to ~1550m  Freshwater Lake Temp K  Land Use Index, Land Use Fraction, and Landmask reset BUILDING THE LAKE

 WRF ARW  24 hour run from 18 UTC 26 Oct 2010 to 18 UTC 27 Oct 2010  Triple nested  12, 4, 1.33 km grid spacing  Lake Bonneville added in domains two and three  Physics  YSU PBL  NOAH LSM  RRTM LW radiation and RRTMG SW radiation  Simple Diffusion  Kain-Fritsch Cumulus for 12, 4 km domains.  No Cumulus for 1.33km domain  Microphysics  Thompson WRF DETAILS

 Total Accumulated Precipitation UTC 27 Oct RESULTS

 3 UTC simulated reflectivity z=2.5 km, lowest model level wind RESULTS

 5 UTC simulated reflectivity z=2.5 km, lowest model level wind RESULTS

 7 UTC simulated reflectivity z=2.5 km, lowest model level wind RESULTS

 9 UTC simulated reflectivity z=2.5 km, lowest model level wind RESULTS

 11 UTC simulated reflectivity z=2.5 km, lowest model level wind RESULTS

PALEOCLIMATE Jewell 2010 Lake circulation model and stream incision indicate surface westerlies Jewell 2007, Schofield et al 2004 Lake spits indicate strongest surface winds were from the north-northwest unlike modern southwesterly Bromwich et al 2004 Polar MM5 month- long simulations indicate <5 m/s surface easterlies in Jan; surface westerlies in Jul Laabs et al 2006, Refsnider 2008, Monroe et al 2006 Glacier signatures in Wasatch and Uintahs indicate a west to east decline in precip requires westerlies Laabs et al 2009, Glaciers in northeast Uintahs retreat earlier than in southwest Uintahs indicating shadowing by the range and southwest flow

WESTERLIES AND GLACIERS

 This event is sensitive to the addition of Lake Bonneville  Total accumulated precipitation increases in maximum amount and areal coverage  The elevated low friction lake surface intensifies a mesoscale vortex on the baroclinic trough  Precipitation increases due to this feature  Possibly decreases precip to the northeast of the lake  Paleoclimate assumptions based on Geographical proxies are highly variable  The hypothesis of glaciation in the Uintah Mountains declining eastward due to less influence of Lake Bonneville has merit based on this case and the modeling work by Hostetler and Giorgi 1992, Hostetler et al 1994 CONCLUSIONS