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Title: ARM Cloud Aerosol Precipitation Experiment (ACAPEX) Science Plan

The western U.S. receives precipitation predominantly during the cold season when storms approach from the Pacific Ocean. The snowpack that accumulates during winter storms provides about 70-90% of water supply for the region. Understanding and modeling the fundamental processes that govern the large precipitation variability and extremes in the western U.S. is a critical test for the ability of climate models to predict the regional water cycle, including floods and droughts. Two elements of significant importance in predicting precipitation variability in the western U.S. are atmospheric rivers and aerosols. Atmospheric rivers (ARs) are narrow bands of enhanced water vapor associated with the warm sector of extratropical cyclones over the Pacific and Atlantic oceans. Because of the large lower-tropospheric water vapor content, strong atmospheric winds and neutral moist static stability, some ARs can produce heavy precipitation by orographic enhancement during landfall on the U.S. West Coast. While ARs are responsible for a large fraction of heavy precipitation in that region during winter, much of the rest of the orographic precipitation occurs in post-frontal clouds, which are typically quite shallow, with tops just high enough to pass the mountain barrier. Such clouds are inherently quite susceptible to aerosol effects on both warmmore » rain and ice precipitation-forming processes.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [3] ;  [1] ;  [1] ;  [3] ;  [1] ;  [6] ;  [7] ;  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  2. Scripps Institution of Oceanography, La Jolla, CA (United States)
  3. National Oceanic and Atmospheric Administration, Washington, DC (United States)
  4. The Hebrew University of Jerusalem (Israel)
  5. Science and Technology Corporation (STC), Hampton, VA (United States)
  6. Colorado State Univ., Fort Collins, CO (United States)
  7. National Aeronautics and Space Administration (NASA), Washington, DC (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
DOE Contract Number:
Resource Type:
Program Document
DOE ARM Climate Research Facility, Pacific Northwest National Laboratory; Richland, Washington
Research Org:
DOE Office of Science Atmospheric Radiation Measurement (ARM) Program (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Contributing Orgs:
Pacific Northwest National Laboratory
Country of Publication:
United States