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CalWater 2: Precipitation, Aerosols, and Pacific Atmospheric Rivers Experiment

(from CalWater2-30Nov12.pdf)
Center for Western Water and Weather Extremes
Emerging research has identified two phenomena that play key roles in the variability of the water supply and the incidence of extreme precipitation events along the West Coast of the United States. These phenomena include the role of:

  • Atmospheric rivers (ARs) in delivering much of the water vapor associated with major storms along the U.S. West Coast, and
  • Aerosols—from local sources as well as those transported from remote continents—and their modulating effects on western U.S. precipitation.

A better understanding of these two phenomena is needed to reduce uncertainties in weather predictions and climate projections of extreme precipitation and its effects, including the provision of beneficial water supply. In this white paper, we identify science gaps associated with

  1. the evolution and structure of ARs,
  2. the prediction of aerosol burdens and properties during intercontinental transport from remote source regions to the U.S. West Coast, and
  3. aerosol interactions with ARs and the impact on precipitation, including locally generated aerosol effects on orographic precipitation along the U.S. West Coast.

We propose a set of science investigations, called CalWater 2, to fill these gaps with a targeted set of aircraft and ship-based measurements and associated evaluation of data over regions offshore of California and in the central and eastern Pacific for an intensive observing period, proposed for December 2014 through March 2015. Expected outcomes for CalWater 2 include:

  • improvements in prediction systems for weather and climate,
  • distribution of an unprecedented meteorological and chemical dataset collected in
    AR environments both onshore and offshore, and
  • development of decision support tools for extreme precipitation events and water
    supply for more effective water resources management.

This assessment has been prepared by an interdisciplinary team of meteorologists, hydrologists, atmospheric chemists, and oceanographers, reflecting the breadth of processes involved and the expertise needed to make new progress. The findings described herein are largely based upon results that have emerged in the last few years from novel airborne and ground-based studies and have spawned important new questions and promising directions. The proposed observing strategy would build on these advances and employ airborne, ship-, and ground-based assets together with satellite observations to address the scientific objectives. The approach takes advantage of recent investments in new instrumentation, such as the new sophisticated instrumentation developed by UC San Diego to measure the chemical composition of nucleated aerosols, and also in observing systems, including NOAA’s Hydrometeorology Testbed, the NASA Global Hawk, and relevant satellite observing systems.