A%20comparison%20of%20the%20down%20valley%20flow%20for%20the%20MAP%20IOP8%20and%20IOP3%20with%20the%20numerical%20laboratory%20Mesonh%20model.

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A comparison of the down valley flow for the MAP
IOP8 and IOP3 with the numerical laboratory
Mesonh model.
Nicole Asencio, Joël Stein and Michel Chong
CNRM Météo-France and Laboratoire dAérologie.
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Presentation

• Introduction and numerical set-up.
• IOP3 and IOP8 rain and wind validations.
• Mesonh numerical laboratory to compare IOP8 and
  IOP3 reversal flow origins.
• conclusion

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Numerical Set-up
Non-hydrostatic MESONH model Two-way interactive
grid-nesting models Microphysics with
ice. Turbulence 1D BL89. Arpege analyses for the
initialization and the coupling every 6 hours.
2.5km model
10km model
10km model convection scheme KAFR 2.5km model
explicit cold microphysics
54 hours
22/10/99 for IOP8 27/09/99 for IOP3
20/10/99 25/09/99
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Synoptic presentation
H
500hPa
L
20 October 1999 1200UTC
L
A
D
H
D
Surface
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IOP3 Daily Rain validation
25 September
26 September
Rain gauges
2.5km model
Correlation coefficient first day second
day IOP3 0.63
0.81
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IOP8 Daily Rain validation
20 October
21 October
Rain gauges
2.5km model
Correlation coefficient first day second
day IOP8 0.75
0.58
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Wind vectors and Potential temperature at 450m
ASL
K
Cold pool
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zoom Wind vectors and Potential temperature
at 450m ASL
K
DOW
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IOP8 and IOP3 comparison meridional wind at the
valleys outflow
IOP8
IOP3
W
E
E
W
Thin layer maximum 200-400 meters
Deep layer maximum 1km-2km
ToceTicino valleys
ToceTicino Valleys
Como Valley
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Presentation

• Introduction and numerical set-up.
• IOP3 and IOP8 rain and wind validations.
• Mesonh numerical laboratory to compare IOP8 and
  IOP3 reversal flow origins.
• conclusion

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IOP3 diagnostics
Upper-level wind intesity
rain
Outflow
RAIN 0-450m WIND DIRECTION 2.8-6km WIND INTENSITY
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IOP8 diagnostics
Upper-level wind intesity
rain
Outflow
RAIN 0-450m WIND DIRECTION 2.8-6km WIND INTENSITY
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Sensitivity experiments
10km model
during a short period associated to reversal
flow duration 30 hours for IOP3 24 hours for
IOP8
2.5km model
Inside a small area associated to accumulated
rain location Nev no evaporation cooling
Nmt no melting and no evaporation
cooling Slope no melting and no evaporation
cooling above relief
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IOP3 Sensitivity experiments
NEV EXPERIMENT NMT EXPERIMENT
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IOP3 Main Origin
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IOP8 Sensitivity experiments
NEV NMT SLOPE
RAIN REF 0-450m WIND DIRECTION 2.8-6km WIND
INTENSITY
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conclusion
IOP8

• IOP8
• The reversal flow within the Toce valley mainly
  originates from the subsidence induced by the
  melting over the orography.
• The diabatic effects over the plain contribute
  to maintain the cold low-level airmass which
  spreads over the western part of the Po valley .
• The reverse flow extension over the plain is
  driven by the cold pool intensity.

• The reversal flow at the regional scale is not
  sensitive to the diabatic
• effects, the down-valley flow inside the Toce
  valley is linked to diabatic mechanisms above the
  relief.
• The upstream flow intensity inducing the
  transition from blocked
• to unblocked regime drives the duration of the
  reverse flow.

IOP3
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