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