MM5/VIC Modeling Evaluation of the Influence the North American Monsoon System

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 99352
cNational Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307
Hypothesis to be tested by:
(Zhu et al., J. Climate, 2005, 2007)
Winter Precipitation - Monsoon Rainfall
feedback hypothesis
Higher (lower) winter
precipitation &
spring snowpack
Weak (strong) monsoon
More (less) spring &
early summer soil
moisture
Lower (higher) spring &
early summer surface
temperature
MM5-VIC coupled model system
Precipitation
Pressure
Radiation
Wind Humidity
Air temperature
Sensible heat flux
Latent 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
PNNL
vegetation type: Single
elevation band: Single
Parameters:
Soil, veg type dependent
initialization:
Spin up 3 months
UW
Multiple
Multiple
cell dependent
Offline VIC
Domain
Regions for which winter precipitation
are related to summer monsoon in MW
and MSa in Zhu et al 2005, 2007.
150*178 grid cells at 30km resolution
in a Lambert-Conformal projection
MW
(eastern AZ and
western NM)
1
NAMS
Soil Moisture
prescribing
domain
MS
(northwestern Mexico)
(1)
(2)
MM5/VIC model setup:
● Kain-Fritsch (KF) scheme
● Rapid Radiative Transfer Model
Late
Early
(RRTM) long-wave scheme
● simple ice-explicit microphysics
● medium-range forecast (MRF)
boundary layer scheme
● NCEP/NCAR Reanalysis LBC
Experimental Design
► 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).
2
Initial soil moisture prescribed at
Field capacity
Wilting point
May 15
SM free running
June
►
July
Aug
Sep
Oct
Simulations performed on wet and dry monsoon years to
represent different atmospheric circulation conditions
Selection of wet/dry years:
MW JJAS Precipitation
1984 1990
3
2
1
0
-1
1989
1973 1979
-2
1995
-3
1950
1989
1979
1955
1960
1965
1995
1970
1975
1980
1985
1990
1995
Wet year: 1984
1993
1984
MSa JJAS Precipitation (dark) and Onset (gray)
Dry year:1989
Validation of coupled MM5/VIC modeling system
1984 wet year: Mean monthly daily precipitation
Control Simulation
Observation
June
July
June
July
Aug
Sep
Aug
Sep
1989 dry year: Mean monthly daily precipitation
Control Simulation
Observation
June
July
June
July
Aug
Sep
Aug
Sep
MM5/VIC more aggressive
in precipitating during ‘dry’
year
Positive Soil Moisture-Monsoon Rainfall Feedback ?
mean monthly precipitation difference
1984-wet minus 1984-dry
1989-wet minus 1989-dry
June
July
June
July
Aug
Sep
Aug
Sep
The reverse of the proposed negative -Winter Precipitation - Monsoon Rainfall
feedback hypothesis
1
Higher (lower) winter
precipitation &
spring snowpack
More (less) spring &
early summer soil moisture
2
Weak (strong) monsoon
3
Lower (higher) spring &
early summer surface
temperature
Begin to examine 3 links……
Soil moisture differences between the wet
and dry runs persist until mid-summer
First Layer
1984
1989
Third Layer
June
July
June
July
Aug
Sep
Aug
Sep
June
July
June
July
Aug
Sep
Aug
Sep
Land surface memory – surface thermal
conditions (1984)
Difference maps between
1984-wet and 1984-dry runs
First layer
soil moisture
June
July
Aug
Sep
June
July
Aug
Sep
+
Latent heat
June
July
-Aug
Sep
Surface skin
temperature
Difference maps between 1989-wet and
1989-dry runs
June
July
Aug
Sep
First layer
soil moisture
June
July
Aug
Sep
+
Latent heat
June
July
-Aug
Sep
Surface skin
temperature
Larger Thermal contrast– stronger monsoon
?
Difference map between 1984-wet
and 1984-dry runs:
June
July
Aug
Sep
Monthly mean surface skin
temperature
June
July
Aug
Sep
Monthly mean precipitation
Southwest surface heat low – monsoon strength
?
Difference maps between 1984wet and 1984-dry runs
Surface Skin
Temperature
June
July
Aug
Sep
June
July
Aug
Sep
500mb
Geopotential
Height
925mb Geopotential Height
June
July
Aug
Sep
In MM5-VIC increased local
surface pressure weakens the
Southwest surface heat low, but
is related to the stronger
monsoon?
Monthly mean 925 mb meridional moisture flux (QV)
averaged over longitude (107-113 oW) at 32 oN
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
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
Shallower Boundary Layer
Boundary layer height difference
between 1984-wet and 1984-dry runs
June
July
Aug
Aug
local land-atmosphere
interaction
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.
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
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 landatmospheric 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 experiments
Extreme 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 evaporation
Contribute to apparent positive soil moisture – rainfall feedback
Future Work
Explore 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 landatmosphere interaction ?
Meehl G. A., 1994:
J. Climate
shallower boundary layer
Increased convective
instability
and potential for precipitation
Schar C et al. 1999: J.Climate
Changes the surface pressure
and the flow field
Changes moisture convergence
and precipitation.
Mo K. C. and H. H. Juang, 2003: J. Geophy. Res
Monthly means of energy
components in the NAMS region
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
NAMS
(1)
(2)
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
Wet soil raises the latent
heat and reduces the
sensible heat by nearly
equal amounts, resulting
in decreased surface skin
temperature