Orographic effects of the subtropical and extratropical Andes on upwind precipitating clouds

The orographic effect of the Andes (30°S–55°S) on upwind precipitating clouds from midlatitude frontal systems is investigated using surface and satellite data. Rain gauges between 33°S and 44°S indicate that annual precipitation increases from the Pacific coast to the windward slopes by a factor of 1.8 ± 0.3. Hourly gauges and instantaneous satellite estimates reveal that the cross-barrier increase in annual precipitation responds to an increase in both the intensity and frequency of precipitation. CloudSat satellite data indicate that orographic effects of the Andes on precipitating ice clouds increase gradually from midlatitudes to subtropics, likely as a result of a reduction of synoptic forcing and an increase of the height of the Andes equatorward. To the south of 40°S, the thickness of clouds slightly decreases from offshore to the Andes. The total ice content increases substantially from the open ocean to the coastal zone (except to the south of 50°S, where there is no much variation over the ocean), and then experience little changes in the cross-mountain direction over the upstream and upslope sectors. Nevertheless, the maximum ice content over the upslope sector is larger and occurs at a lower level than their upwind counterparts. In the subtropics, the offshore clouds contain almost no ice, but the total and maximum ice content significantly increases toward the Andes, with values being much larger than their counterparts over the extratropical Andes. Further, the largest amounts of cloud ice are observed upstream of the tallest Andes, suggesting that upstream blocking dominates there.

[1]  Robert A. Houze,et al.  Air motions and precipitation growth in Alpine storms , 2003 .

[2]  C. Mass,et al.  Multiscale Mountain Waves Influencing a Major Orographic Precipitation Event , 2007 .

[3]  J. Evans,et al.  Orographic Precipitation and Water Vapor Fractionation over the Southern Andes , 2006 .

[4]  S. Matrosov Characteristics of Landfalling Atmospheric Rivers Inferred from Satellite Observations over the Eastern North Pacific Ocean , 2013 .

[5]  Daniel J. Gottas,et al.  A water vapour flux tool for precipitation forecasting , 2009 .

[6]  J. Minder,et al.  Mesoscale Variations of the Atmospheric Snow Line over the Northern Sierra Nevada: Multiyear Statistics, Case Study, and Mechanisms , 2013 .

[7]  R. Houze Orographic effects on precipitating clouds , 2012 .

[8]  B. Colle Sensitivity of Orographic Precipitation to Changing Ambient Conditions and Terrain Geometries: An Idealized Modeling Perspective , 2004 .

[9]  P. Forster,et al.  Global cloud condensation nuclei influenced by carbonaceous combustion aerosol , 2011 .

[10]  C. Schär,et al.  A PRECIPITATION CLIMATOLOGY OF THE ALPS FROM HIGH-RESOLUTION RAIN-GAUGE OBSERVATIONS , 1998 .

[11]  B. Barrett,et al.  Effect of the Andes Cordillera on Precipitation from a Midlatitude Cold Front , 2009 .

[12]  R. Garreaud,et al.  Summer Precipitation Events over the Western Slope of the Subtropical Andes , 2014 .

[13]  Graeme L. Stephens,et al.  Retrieval of ice cloud microphysical parameters using the CloudSat millimeter‐wave radar and temperature , 2009 .

[14]  Gerald G. Mace,et al.  Global hydrometeor occurrence as observed by CloudSat: Initial observations from summer 2006 , 2007 .

[15]  R. Marchand,et al.  Hydrometeor Detection Using Cloudsat—An Earth-Orbiting 94-GHz Cloud Radar , 2008 .

[16]  J. Rutllant,et al.  Synoptic aspects of the central chile rainfall variability associated with the southern oscillation , 2007 .

[17]  J. Coen,et al.  Influences of Storm-Embedded Orographic Gravity Waves on Cloud Liquid Water and Precipitation , 2000 .

[18]  M. Rojas,et al.  Large-Scale Control on the Patagonian Climate , 2013 .

[19]  Marius Schaefer,et al.  Extreme Precipitation and Climate Gradients in Patagonia Revealed by High-Resolution Regional Atmospheric Climate Modeling , 2014 .

[20]  M. Biasutti,et al.  Observed frequency and intensity of tropical precipitation from instantaneous estimates , 2013 .

[21]  R. Rotunno,et al.  Mechanisms of Intense Alpine Rainfall , 2001 .

[22]  R. Houze,et al.  Modification of Precipitation by Coastal Orography in Storms Crossing Northern California , 2005 .

[23]  L. A. Rasmussen,et al.  Hydrology of the North Cascades Region, Washington: 1. Runoff, precipitation, and storage characteristics , 1976 .

[24]  F. Martin Ralph,et al.  Modification of Fronts and Precipitation by Coastal Blocking during an Intense Landfalling Winter Storm in Southern California: Observations during CALJET , 2004 .

[25]  B. Hoskins,et al.  A new perspective on southern hemisphere storm tracks , 2005 .

[26]  Radar observations of precipitation and airflow on the Mediterranean side of the Alps: Autumn 1998 and 1999 , 2001 .

[27]  S. Matrosov Observations of Wintertime U.S. West Coast Precipitating Systems with W-Band Satellite Radar and Other Spaceborne Instruments , 2012 .

[28]  J. Gironás,et al.  Spatial estimation of daily precipitation in regions with complex relief and scarce data using terrain orientation , 2014 .

[29]  Prashant Kumar,et al.  On the effect of dust particles on global cloud condensation nuclei and cloud droplet number , 2011 .

[30]  R. Houze,et al.  Vertical Structures of Precipitation in Cyclones Crossing the Oregon Cascades , 2007 .

[31]  M. Nuñez,et al.  Climatology of Winter Orographic Precipitation over the Subtropical Central Andes and Associated Synoptic and Regional Characteristics , 2011 .

[32]  G. Roe OROGRAPHIC PRECIPITATION , 2005 .

[33]  R. Marchand,et al.  A description of hydrometeor layer occurrence statistics derived from the first year of merged Cloudsat and CALIPSO data , 2009 .

[34]  R. Houze,et al.  Upstream Orographic Enhancement of a Narrow Cold-Frontal Rainband Approaching the Andes , 2013 .

[35]  Raymond T. Pierrehumbert,et al.  Upstream Effects of Mesoscale Mountains , 1985 .

[36]  Robert A. Houze,et al.  Turbulence as a Mechanism for Orographic Precipitation Enhancement. , 2005 .

[37]  P. Neiman,et al.  The statistical relationship between upslope flow and rainfall in California's coastal mountains: Observations during CALJET , 2002 .

[38]  O. Bousquet,et al.  Observations and impacts of upstream blocking during a widespread orographic precipitation event , 2003 .

[39]  Rodrigo E. Bürgesser,et al.  Lightning in Western Patagonia , 2014 .

[40]  D. Durran,et al.  Mesoscale Controls on the Mountainside Snow Line , 2011 .

[41]  C. Daly,et al.  A Statistical-Topographic Model for Mapping Climatological Precipitation over Mountainous Terrain , 1994 .

[42]  B. Colle,et al.  The Impact of Varying Environmental Conditions on the Spatial and Temporal Patterns of Orographic Precipitation over the Pacific Northwest near Portland, Oregon , 2011 .

[43]  D. Winker,et al.  Overview of the CALIPSO Mission and CALIOP Data Processing Algorithms , 2009 .

[44]  B. Barrett,et al.  Multiday Circulation and Precipitation Climatology during Winter Rain Events of Differing Intensities in Central Chile , 2011 .

[45]  Steven D. Miller,et al.  Rainfall retrieval over the ocean with spaceborne W‐band radar , 2009 .

[46]  E. O'connor,et al.  The CloudSat mission and the A-train: a new dimension of space-based observations of clouds and precipitation , 2002 .

[47]  Chialin Wu,et al.  Cloud profiling radar for the CloudSat mission , 2005, IEEE International Radar Conference, 2005..

[48]  René D. Garreaud Warm Winter Storms in Central Chile , 2013 .

[49]  M. Falvey,et al.  Wintertime Precipitation Episodes in Central Chile: Associated Meteorological Conditions and Orographic Influences , 2007 .