MM5/VIC Modeling Evaluation of the Influence of Antecedent Soil Moisture on Variability of
the North American Monsoon System
Chunmei Zhua, Yun Qianb, Ruby Leungb, David Gochisc,
and Dennis P. Lettenmaiera
aDepartment of Civil and Environmental Engineering Box 352700, University of Washington, Seattle, WA 98195
bPacific Northwest National Laboratory, Richland WA 99352cNational Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307
Winter Precipitation - Monsoon Rainfall feedback hypothesis
Higher (lower) winter precipitation & spring snowpack
More (less) spring & early summer soil moisture
Lower (higher) spring & early summer surface temperature
Weak (strong) monsoon
Hypothesis to be tested by:(Zhu et al., J. Climate, 2005, 2007)
PNNL UWvegetation type: Single Multiple elevation band: Single Multiple Parameters: Soil, veg type dependent cell dependent initialization: Spin up 3 months Offline VIC
MM5-VIC coupled model system
Precipitation PressureRadiationWind HumidityAir temperature
Sensible heat fluxLatent heat fluxes…
First coupled by Drs. Ruby Leung at PNNL and Xu Liang at University of California, Berkeley
Modification of coupled MM5/VIC modeling system by UW
Domain
Late Early
Regions for which winter precipitation are related to summer monsoon in MW and MSa in Zhu et al 2005, 2007.
MW
MS
1
MM5/VIC model setup:
150*178 grid cells at 30km resolution in a Lambert-Conformal projection
NAMS
(2)
(1)
● Kain-Fritsch (KF) scheme ● Rapid Radiative Transfer Model (RRTM) long-wave scheme ● simple ice-explicit microphysics ● medium-range forecast (MRF) boundary layer scheme ● NCEP/NCAR Reanalysis LBC
(eastern AZ and western NM)
(northwestern Mexico)
Soil Moisture prescribing domain
Experimental Design
Initial soil moisture prescribed at
OctSepAugJulyJune
SM free runningMay 15
Field capacity Wilting point
► Simulations performed on wet and dry monsoon years to represent different atmospheric circulation conditions
2
► The initial soil wetness condition on May 15 is a surrogate for previous winter precipitation condition.
► Control simulation s. moisture prescribed from offline VIC LDAS (3 mo spin-up, Mar-Apr-May).
1984
19891995
1979
1993
MSa JJAS Precipitation (dark) and Onset (gray)
-3
-2
-1
0
1
2
3
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995
MW JJAS Precipitation1984 1990
199519791973
Wet year: 1984
Dry year:1989
Selection of wet/dry years:
1989
Validation of coupled MM5/VIC modeling system
1984 wet year: Mean monthly daily precipitation
Control Simulation Observation
June July
Aug Sep
June July
Aug Sep
1989 dry year: Mean monthly daily precipitation
Control Simulation Observation
June July
Aug Sep
June July
Aug Sep
MM5/VIC more aggressive in precipitating during ‘dry’year
Positive Soil Moisture-Monsoon Rainfall
Feedback ?
1984-wet minus 1984-dry 1989-wet minus 1989-dry
June July
Aug Sep
June July
Aug Sep
mean monthly precipitation difference
Winter Precipitation - Monsoon Rainfall feedback hypothesis
Higher (lower) winter precipitation & spring snowpack
More (less) spring & early summer soil moisture
Lower (higher) spring & early summer surface temperature
Weak (strong) monsoon
The reverse of the proposed negative --
1
2
3
Begin to examine 3 links……
Soil moisture differences between the wet and dry runs persist until mid-
summer
1984
1989
First Layer Third Layer
June July
Aug Sep
June July
Aug Sep
June
July
Aug Sep
June July
Aug Sep
Land surface memory – surface thermal conditions (1984)
First layer soil moisture
Latent heat
Surface skin temperature
+
--
Difference maps between 1984-wet and 1984-dry runs
June
June
June
July
July
July
Aug
Aug
Aug Sep
Sep
Sep
Difference maps between 1989-wet and 1989-dry runs
First layer soil moisture
Latent heat
Surface skin temperature
+
--
June
June
June July
July
July
Aug
Aug
Aug
Sep
Sep
Sep
Larger Thermal contrast– stronger monsoon
June July
Aug Sep
June July
Aug Sep
Monthly mean surface skin temperature
Monthly mean precipitation
Difference map between 1984-wet and 1984-dry runs:
?
Difference maps between 1984-wet and 1984-dry runs
500mb Geopotential Height
Surface Skin Temperature
925mb Geopotential Height
In MM5-VIC increased local surface pressure weakens the Southwest surface heat low, but is related to the stronger monsoon?
Southwest surface heat low – monsoon strength ?
June
June
June
July
July
JulyAug
Aug
Aug
Sep
Sep
Sep
June July August September
1984-Wet 0.0047 0.0133 0.0150 0.0090
1984-Dry 0.0020 0.0134 0.0101 0.0088
1989-Wet 0.0054 0.0053 0.0033 0.0100
1989-Dry 0.0033 0.0030 0.0036 0.0087
Monthly mean 925 mb meridional moisture flux (QV) averaged over longitude (107-113 oW) at 32 oN
Weakening of the thermal low in MM5/Vic sims results in greater moisture flux into the interior of the NAMS region, likely from increased moisture availability due to increased regional evaporation instead of increased low level winds
Monthly mean planetary boundary layer height (PBL) in the NAMS domain
June July August September
1984-Wet 1354.2 1165.5 1060.9 1386.8
1984-Dry 1812.9 1552.1 1377.3 1436.5
1989-Wet 1704.1 1252.1 1332.0 1143.3
1989-Dry 2148.8 1647.3 1594.8 1264.0
Boundary layer height difference between 1984-wet and 1984-dry runs
Shallower Boundary Layer
Wet soil moisture conditions reduce
the depth of the boundary layer, therefore increase the boundary
layer moist static energy and the frequency and magnitude of
rainfall from local convective storms.
local land-atmosphere interaction
June July
Aug Aug
Summary and Conclusions
● The MM5-VIC control sims reproduce reasonable monsoon precipitation for 1984 and 1989 over northwestern Mexico (1989 somewhat wet vs. obs)
● The model land surface has memory of the initial soil wetness that lasts for several months (until August). This land memory has a negative relationship with surface thermal conditions over the NAMS domain and its larger adjacent area.
● In contrast to the original hypothesis, the wet year 1984 and dry year 1989 experiments exhibit similar positive soil moisture – rainfall feedbacks over the NAMS domain. In essence, it appears that local-regional recycling of moisture dominates in sustaining increased precipitation in the model. However magnitude of imposed anomaly likely imparts excessive influence.
● In nature, both the large-scale circulation changes and local land-atmospheric interactions in response to soil moisture conditions likely play important roles in the soil moisture – monsoon precipitation feedback. The symbiosis of these features needs to be studied in more detail.
Limitations of the experimentsExtreme wet and dry soil conditions in the sensitivity experiments
extreme surface temperature anomalies exaggerated surface low (not the optimal strength and location to start monsoon)
very intense local evaporationContribute to apparent positive soil moisture – rainfall feedback
Future WorkExplore the relationship between antecedent soil moisture and monsoon rainfall under less extreme soil conditions, and to identify the relative importance of large-scale circulation and local evaporation.
Large-scale circulation or local land-atmosphere interaction ?
shallower boundary layer
Increased convective instabilityand potential for precipitation
Changes moisture convergence and precipitation.
Changes the surface pressure and the flow field
Meehl G. A., 1994: J. Climate
Schar C et al. 1999: J.Climate
Mo K. C. and H. H. Juang, 2003: J. Geophy. Res
SM1 Tgrd LH SH
June
1984-Wet 0.262 302.8 83.8 61.8
1984-Dry 0.229 306.2 57.4 88.4
1989-Wet 0.240 304.2 78.4 65.4
1989-Dry 0.182 307.7 47.6 94.0
July
1984-Wet 0.281 301.6 85.2 51.4
1984-Dry 0.258 305.4 66.1 72.0
1989-Wet 0.273 303.8 85.4 58.2
1989-Dry 0.257 307.5 66.5 74.9
August
1984-Wet 0.282 300.2 85.9 44.3
1984-Dry 0.266 302.6 78.8 56.1
1989-Wet 0.265 301.6 77.9 55.5
1989-Dry 0.258 305.0 67.1 65.2
September
1984-Wet 0.259 299.2 86.7 35.7
1984-Dry 0.260 299.5 83.6 37.4
1989-Wet 0.280 298.8 68.6 37.5
1989-Dry 0.267 299.6 66.1 40.3
NAMS
(2)(1)
Monthly means of energy components in the NAMS
region
Wet soil raises the latent heat and reduces the sensible heat by nearly equal amounts, resulting in decreased surface skin temperature