HR: 1340h
AN: A53B-0885    [Abstracts]
TI: Regional Atmospheric Moisture Cycling over the Southwestern US
AU: * Anderson, B T
EM: brucea@bu.edu
AF: Boston University Geography Dep't., 675 Commonwealth Ave., Rm. 460, Boston, MA 02215-1401 United States
AU: Kanamaru, H
EM: hkanamaru@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD-0224, La Jolla, CA 92093-0224 United States
AU: Roads, J O
EM: jroads@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD-0224, La Jolla, CA 92093-0224 United States
AB: In this talk we use a suite of regional model simulations and surface and upper-air based observations to examine the summertime hydrologic cycle over the southwestern United States. At the climatological scale, it is found that seasonal precipitation is balanced predominantly by evaporation; in addition, this evaporation also supports a net vertically integrated moisture flux divergence from the region of the same magnitude as the precipitation itself. This vertically-integrated large-scale moisture flux divergence is the result of an offsetting balance between convergence of low-level moisture and divergence of moisture aloft (above 800mb). Based upon the balances found in this region, we develop a new "recycling" metric for precipitation (which is defined as the ratio of locally-derived precipitation to total precipitation) to better quantify the contributions of these various budget terms to the climatological rainfall as seen in both model simulations and observations. While traditional methods for estimating the recycling rate give a ratio of about 0.25, the new metric suggests a recycling rate of 0.80. This indicates that about 75-85 percent of the area-averaged precipitation is the result of evaporative processes, indicating a much greater importance of locally-derived rainfall in generating climatological precipitation than previously thought. As part of this talk we will discuss how the newly-developed regional moisture-cycling metric differs from traditional metrics and how estimates derived from both models and observations may provide greater insight into the regional feedback mechanisms that affect the response of seasonal rainfall variability to local and external forcing factors.
DE: 9350 North America
DE: 3359 Radiative processes
DE: 1655 Water cycles (1836)
DE: 1833 Hydroclimatology
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting