THE AMERICAN MONSOONS

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THE AMERICAN MONSOONS AND THEIR ROLE IN THE
WATER CYCLE E. Hugo Berbery, Estela Collini,
Viviane Silva Department of Meteorology
University of Maryland with thanks to Julia
Nogués-Paegle, Lee Byerle, Brant Liebmann, Rong
Fu PACS PI Meeting - Boulder
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• Outline
• 1. The North American monsoon and the low-level
  jets
• 2. The South American monsoon
• a. Advective processes
• b. Surface processes
• Keywords
• Low-level Jet
• Sources of moisture
• Land surface atmosphere feedbacks
• Hydrologic Cycle

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Summer Monsoons LLJs MCCs Impact on large
basins LS-A feedbacks
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Great Plains
Gulf of California
Berbery and Fox-Rabinovitz (2003)
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Byerle and Paegle
LLJ and Precipitation Response to Ambient Zonal
flow and Orography Deviations from
Climatology
wet
U200 hPa
Forcing
Response
dry
LLJ
correlation coefficients shown (JJA 1951-2000)
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Byerle and Paegle
LLJ and Precipitation Response to Ambient Zonal
flow and Orography Deviations from
Climatology
LLJ
wet
U200 hPa
Forcing
dry
Response
correlation coefficients shown (DJF 1951-2000)
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The mechanical blocking of the upstream zonal
winds by Andes has a strong control on SALLJ,
especially on seasonal and intraseasonal scales
Strong northerly SALLJ
Strong westerly upstream westerly wind to the
west of Andes
Wang and Fu, 2003, J. Climate
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Berbery and Barros, 2002 JHM
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Liebmann et al.
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Annual cycle of precipitation (mm/day) as a
function of the latitude.
From Berbery and Barros 2002, JHM.
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The Eta model

• Model Configuration
• Horizontal resolution
• 80 km and 22 km
• (tests at 48, 25, 15)
• Vertical resolution
• 38 lyrs (tests w/ 45 lyrs)
• Initial and boundary conditions
• AVN NCEP Reanalyses
• Further online information and forecasts
  http//www.atmos.umd.edu/berbery/etasam

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While there is an excess of model precipitation
over the Monsoon region, the Eta model
successfully reproduces the day to day
variability. In the southern region, the model
reproduces the variability and magnitude of the
precipitation.
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The structure of the summer LLJ estimated from
the Eta at two resolutions 80 km and 22 km
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Composites based on P gt Pm 1.5 Psd
Moisture flux at 925 hPA
V. Silva
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Precipitable Water
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Theta-e
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Precipitation
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Runoff
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The South American monsoon region
Precipitation
Runoff
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Land surface - atmosphere processes
Drier land surface (lower surface latent flux and
higher Bowen ratio) during dry and early
transition seasons appears to be the cause of
strong delay (gt 1.5 months) of the wet season
onset.
1979 Early onset
1984 late onset
1986 late onset
1990 normal
Fu and Li, 2003, J. Theor. obs. Clim., LBA
special issue
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Land surface ? Precipitation
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Austral Summer
Latent heat
Sensible heat
Soil Moisture vs Surface variables
Precipitation
Bowen Ratio
Each dot represents a 15-day average
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Schematic of the precipitation-soil moisture
feedback
Increased Soil Moisture (time scales of 2 weeks
or longer)
Decreased Sensible Heat
Increased Latent Heat
Decreased Bowen Ratio (and increased Evaporative
Fraction)
Increased Precipitation
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Eta model simulations - October 1983
IC SM() -45, -30, -15, 15, 30, 45
E. Collini
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• Summary
• The role of advective and local processes was
  discussed and their impact on precipitation and
  runoff was assessed.
• Two precipitation regimes whose centers form a
  dipole pattern were discussed their
  active/break periods seem to be associated with
  lateral shifts of the Low-level Jet east of the
  Andes.
• The precipitation-soil moisture interactions
  over SAM reveal a positive feedback at time
  scales larger than 2 weeks.

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The Eta model (2)
Alternative settings Large domain for seasonal
simulations Higher resolution domain for
studies of hydrologic impacts
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VIC Hydrologic Model
Input Runoff baseflow at each grid
cell Output River discharge at the basins
exit point
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River routing model resolution 1/8 degrees