Transcript Relationship between Antecedent Land Surface Conditions and

Relationship between Antecedent Land Surface Conditions and Precipitation in the North American Monsoon Region
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Chunmei Zhu , Dennis P. Lettenmaier , and Tereza Cavazos
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Department of Civil & Environmental Engineering, Box 352700, University of Washington, Seattle, WA 98195
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Department of Physical Oceanography, Centro de Investigacion Cientifica de Educacion, Superior de Ensenada, Ensenada, Mexico
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Winter Precipitation - JJAS Monsoon West Rainfall
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Winter precipitation – spring soil moisture link
Introduction
We explore possible links between North American Monsoon System (NAMS) seasonal (Jun-Jul-AugSep) precipitation and pre-monsoon (previous autumn, winter, and spring) land surface conditions,
including precipitation, temperature, soil moisture and snow cover anomalies. We hypothesize land and
sea surface feedback mechanisms associated with NAMS precipitation, and we propose an approach
for determining their dynamical links. Following previous investigators, we partitioned the NAMS
region into four sub-regions (Monsoon West, South, North and East) based on the seasonality and
variability of JJAS monsoon precipitation from 1961-1990, and evaluated the possible effects of
previous land surface conditions in various subcontinental “predictor regions” on Monsoon West (MW)
monsoon precipitation. Data for the study were monthly aggregates from the retrospective Land Data
Assimilation System (LDAS) archive for the period 1950 to 1999 (Maurer et al, 2002). The
retrospective LDAS archive includes gridded precipitation (P), mean surface air temperature (SAT),
and Variable Infiltration Capacity (VIC) land surface model-derived soil moisture (Sm), and snow
water equivalent (SWE). We outline future work that will construct an exploratory seasonal monsoon
precipitation predictive model based on antecedent conditions.
Figure 2a: Monsoon West winter predictor region.
Figure 2b: 15-year moving average correlation of JJAS
MW precipitation with winter precipitation in predictor
region
● The statistically significant negatively related region includes southern California, Nevada, Utah,
Arizona, western Colorado and New Mexico, which is the potential winter predictor region for
Monsoon West monsoon rainfall (figure 2a).
● This negative relationship varies in strength. It is strong during the 1965-1990 period, but weak
otherwise.
The figures show apparent relationships between strong and weak MW monsoon precipitation and soil
moisture in the preceding spring. The left figure shows the strong (weak) monsoons are associated with
dry (wet) antecedent soil moisture. Note that the left figure appears similar to Figure 2c, and indicates
that spring soil moisture in the Southwest is a reflection of winter precipitation. The right figure is is for
June, and confirms that in much of the Southwest, soil moisture anomalies persist from winter through
the following spring (immediately prior to the monsoon). Note that the Great Plains and Southwest show
reverse signals.
Soil moisture – surface temperature link
●This negative signal is especially strong during extreme years (Figure 2c).
The figure at left shows that April soil moisture
has a negative, but not very strong correlation
with May and June surface air temperature.
References:
Comrie A.C. and E.C. Glenn, 1998: Principal components-based regionalization of precipitation regimes across the southwest United
States and northern Mexico, with an application to monsoon precipitation variability. Clim. Res., 10, 201-215.
Guzler D.S., 2000: Co variability of spring snowpack and summer rainfall across the southwest United States. J. Climate, 13, 4018-1027.
Gutzler D.S. and J.W. Preston, 1997: Evidence for a relationship between spring snow cover in North America and summer precipitation
in New Mexico. Geophys. Res. Lett., 24, 2207-2210.
Higgins R.W. and W.Shi , 2000: Dominant factors responsible for interannual variability of the summer monsoon in the Southwestern
United States. J. Climate, 13, 759-776.
Hu Q. and F. Song, 2002: Interannual rainfall variations in the North American Summer Monsoon Region: 1900-98. J. Climate, 15, 11891202.
Liang, X., D. P. Lettenmaier, E. F. Wood, and S. J. Burges, 1994: A Simple hydrologically Based Model of Land Surface Water and
Energy Fluxes for GSMs, J. Geophys. Res., 99(D7), 14,415-14,428.
Lo F. and M.P. Clark, 2002: Relationships between spring snow mass and summer precipitation in the Southwestern United States
associated with North American monsoon system. J. Climate, 15, 1378-1385.
Matsui T, V. Lakshml and B. Small, 2003: Links between snow cover, surface skin temperature, and rainfall variability in the North
American Monsoon system. J. Climate, 16, 1821-1829.
Maurer E.P., A.W. Wood, J.C. Adam, D.P. Lettenmaier, and B. Nijssen, 2002: A long-term hydrologically-based data set of land surface
fluxes and states for the conterminous United States. J. Climate, Vol. 15, 3237–3251.
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Figure 2c: Monsoon West JFM
relative precipitation anomaly
composite for wet and dry years.
Period: 1965-1999.
Snow – surface temperature link
April SWE (in the region shown in Figure 3a) shows a
strong negative correlation with May and June surface
air temperature in the Four Corners region.
3 Snow-monsoon Relationship
Pre-monsoon SAT – monsoon precipitation
Antecedent June surface air temperature (SAT) in Northern AZ and
in the Southern Rockies is positively correlated with July MW
precipitation. It seems that in the core of the monsoon the
relationship is negative, possibly because rainfall there comes
earlier. The land –surface mechanisms associated with SAT and
precipitation remain unclear, and need further investigation
Study Domain
Figure 3a: Monsoon West snow index area
Monsoon West
Monsoon South
Figure 3b: 15-year moving average correlation of
Monsoon West snow index versus JJAS monsoon rainfall
● A snow index equal to April SWE in the mountainous part of the U.s. Southwest (blue area in Figure 3a)
and JJAS MW precipitation shows a negative correlation.
● This negative relationship is especially strong during 1965 – end of 1980s.
Monsoon North
Monsoon East
Monsoon regions are defined as in Comrie & Glenn paper (1998) based on the seasonality
and variability of JJAS monsoon precipitation from 1961-1990. In the following section we
evaluate the possible effects of previous land surface conditions in various subcontinental
“predictor regions” on Monsoon West (MW) monsoon precipitation.
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Winter Precipitation-monsoon rainfall feedback hypothesis
Higher (lower) winter precipitation
and spring snowpack
lower (higher) spring and early
summer surface temperature
More (less) spring or
early summer soil moisture
Weak (strong) monsoon
Conclusions:
● For the Monsoon West region (here referring to eastern AZ and western NM), land
surface-monsoon relationships are not stable in time. The strength of land surface
teleconnections in MW seems to be strongest for 1965-1990. JJAS (monsoon) precipitation
is MW appears to be negatively related to the previous winter’s precipitation in the U.S.
Southwest, and to spring snow accumulation in the mountainous part of the Southwest.
● The antecedent land surface link that we propose related to SWE, soil moisture, and air
temperature) is stronger in the Southwest mountainous area and the Four Corners source
areas. This is a mountainous area, where snow plays a strong role in land surface
processes, however it is not yet clear that the apparent land memory mechanism is related
to snow per se. Furthermore, the surface temperature – monsoon links remain unclear, and
need further investigation.