Effects of atmospheric river landfalls on the cold season precipitation in California

Effects of atmospheric river (AR) landfalls in the California coast on the cold-season precipitation in California are examined for the cold seasons of 10 water years (WYs) 2001–2010 using observed data and regional modeling in conjunction with AR-landfall inventory based on visual inspections of precipitable water vapor (PWV) from remote sensing and reanalysis. The PWV in the SSM/I and SSMIS retrievals and the ERA-Interim reanalysis shows 95 AR-landfall days in the California coast that are almost evenly split between the northern and southern coasts across 37.5N. The CPC/NCEP gridded daily precipitation analysis shows that 10–30% of the cold-season precipitation totals in California have occurred during these AR landfalls. The analysis also reveals that the percentage of precipitation and the precipitation intensity during AR landfalls in California are characterized by strong north-to-south gradient. This north–south contrast in the AR precipitation is reversed for the non-AR precipitation in the coastal range. The frequency of AR landfalls and the cold-season precipitation totals in the Sierra Nevada region are only marginally correlated. Instead, AR landfalls are closely related with the occurrence of heavy precipitation events. The freezing-level altitudes are systematically higher for AR wet days than non-AR wet days indicating warmer low-troposphere during AR storms. Cold season simulations for the 10 WYs 2001–2010 show that the Weather Research and Forecast (WRF) model can reasonably simulate important features in both the seasonal and AR precipitation totals. The daily pattern correlation coefficients between the simulated and ERA-Interim upper-air fields exceed 0.9 for most of the period. This suggests that the simulated temporal variations in the atmospheric circulation agree reasonably with the reanalysis over seasonal time scales, characteristics critical for reliable simulations of regional scale hydrologic cycle. The simulated seasonal and AR precipitation totals also agree reasonably with the CPC/NCEP precipitation analysis. The most notable model errors include the overestimation (underestimation) of the season-total and AR precipitation in the northern (southern) California region. The differences in the freezing-level altitudes during the AR- and non-AR wet days in the simulation agree with those from the ERA-Interim reanalysis. The freezing level altitudes are systematically overestimated in the simulations, suggesting warm biases in the low troposphere. Overall, WRF appears to perform reasonably in simulating the key features in the cold season precipitation related with AR landfalls, an important capability for assessing the impact of global climate variations and change on future hydrology in California.

[1]  H. Wernli,et al.  A Lagrangian Climatology of Tropical Moisture Exports to the Northern Hemispheric Extratropics , 2009 .

[2]  C. Davis.  Mesoscale Model Simulations of Coastal Fog , 1998 .

[3]  G. Powers,et al.  A Description of the Advanced Research WRF Version 3 , 2008 .

[4]  J. Bao,et al.  Interpretation of Enhanced Integrated Water Vapor Bands Associated with Extratropical Cyclones: Their Formation and Connection to Tropical Moisture , 2006 .

[5]  F. Martin Ralph,et al.  Meteorological Characteristics and Overland Precipitation Impacts of Atmospheric Rivers Affecting the West Coast of North America Based on Eight Years of SSM/I Satellite Observations , 2008 .

[6]  Eric J. Fetzer,et al.  Extreme snowfall events linked to atmospheric rivers and surface air temperature via satellite measurements , 2010 .

[7]  Y. Qian,et al.  Atmospheric rivers induced heavy precipitation and flooding in the western U.S. simulated by the WRF regional climate model , 2009 .

[8]  M. Dettinger,et al.  Atmospheric Rivers, Floods and the Water Resources of California , 2011 .

[9]  Jinwon Kim,et al.  Simulation of a heavy wintertime precipitation event in California , 1996 .

[10]  Yongti Zhu,et al.  Atmospheric rivers and bombs , 1994 .

[11]  M. Dettinger,et al.  Flooding on California's Russian River: Role of atmospheric rivers , 2006 .

[12]  E. Brin,et al.  AIRS impact on the analysis and forecast track of tropical cyclone Nargis in a global data assimilation and forecasting system , 2009 .

[13]  Jinwon Kim,et al.  The Impact of the Sierra Nevada on Low-Level Winds and Water Vapor Transport , 2007 .

[14]  G. Wick,et al.  Satellite and CALJET Aircraft Observations of Atmospheric Rivers over the Eastern North Pacific Ocean during the Winter of 1997/98 , 2004 .

[15]  Jung‐Eun Lee,et al.  A Multiyear Regional Climate Hindcast for the Western United States Using the Mesoscale Atmospheric Simulation Model , 2003 .

[16]  Yong Zhu,et al.  A Proposed Algorithm for Moisture Fluxes from Atmospheric Rivers , 1998 .

[17]  James W. Hurrell,et al.  Elevation Dependency of the Surface Climate Change Signal: A Model Study , 1997 .

[18]  Ying-Hwa Kuo,et al.  Diagnosis of an Intense Atmospheric River Impacting the Pacific Northwest: Storm Summary and Offshore Vertical Structure Observed with COSMIC Satellite Retrievals , 2008 .

[19]  R. Arritt,et al.  Impacts of Increased Atmospheric CO2 on the Hydroclimate of theWestern United States , 2002 .

[20]  Jinwon Kim.  Precipitation and snow budget over the southwestern United States during the 1994–1995 winter season in a mesoscale model simulation , 1997 .