HR: 0800h
AN: A51A-0025    [Abstracts]
TI: The role of antecedent land surface conditions in North American Monsoon warm season precipitation
AU: * zhu, c
EM: chunmei@hydro.washington.edu
AF: Department of Civil & Environmental Engineering, University of Washington, Seattle, WA 98195 United States
AU: Lettenmaier, D P
EM: dennisl@u.washington.edu
AF: Department of Civil & Environmental Engineering, University of Washington, Seattle, WA 98195 United States
AU: Cavazos, T
EM: tcavazos@cicese.mx
AF: Department of Physical Oceanography, Centro de Investigacion Cientifica de Educacion Superior de Ensenada , Ensenada, 22800 Mexico
AB: North American Monsoon (NAM) warm season precipitation strongly affects the semiarid regions of the southwestern U.S. and northwestern Mexico. A first step in developing useful prediction capabilities for NAM precipitation is to explore links between the NAM seasonal (JJAS) precipitation and the antecedent pre-monsoon (previous autumn, winter, and spring) land surface conditions, such as precipitation, surface air temperature, soil moisture, and snow cover. We define two monsoon regions: western in Arizona and eastern in New Mexico which exhibit a "pure" monsoon signal, and northwestern Mexico as the core NAM region. Land surface data for the east and west regions are monthly aggregates from the extended retrospective North American Land Data Assimilation System (N-LDAS) archive for the period 1950 to 1999, which includes gridded precipitation (P), mean surface air temperature (Ts), and Variable Infiltration Capacity (VIC) land surface model-derived soil moisture (Sm), and snow water equivalent (SWE). For northwestern Mexico three different sources of station data are combined and gridded to be analogous to the N-LDAS archive: Servicio MeterorolOgico Nacional (SMN) daily data (pre-1940 - 2003), SMN daily historical precipitation data (1995 - near real-time), and northwestern Mexico NAME Event Raingage Network (NERN) precipitation daily data (2002 - ). Long-term (1950-2003) retrospective VIC model runs were then performed to produce derived data (soil moisture, snow) analogous to those in the N-LDAS archive. Through correlation and composite analysis, we find that the two southwest US regions and northwestern Mexico exhibit somewhat different land surface feedback mechanism. For the U.S, regions, we previously proposed a land surface feedback hypothesis and found that while NAM precipitation is correlated with the previous winter's precipitation, the corresponding soil moisture anomaly contributes little to the predictability of NAM precipitation. For northwestern Mexico, the previous winter and spring's precipitation influences spring soil moisture enough to explain a negative relationship with pre-monsoon early summer surface air temperature, and hence the strength of the NAM precipitation. However, these relationships are not strong enough to provide a reliable predictor of NAMS precipitation at seasonal lead times. Also, compared to land surface conditions, atmospheric circulation conditions seem to play a more important role in NAM precipitation anomalies.
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
DE: 1866 Soil moisture
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005