Transcript Boundary Layer Parameterization Issues in the MM5

Boundary Layer Parameterization
Issues in the MM5 and Other
Models.
Cliff Mass, Eric Grimit, Jeff Baars,
David Ovens, University of
Washington
Apparent Problems
During the past years a number of issues
have become evident with the MM5 (and
other) boundary layers, with the unproven
implication that the PBL schemes or land
surface schemes are to blame.
Basic Infrastructure
• MM5 36, 12, and 4-km real-time runs over
the Northwest
• UW data collection effort (roughly 24networks over the region)
• UW Verification System
Some Observations
• 10-m Winds are too geostrophic.
• Positive wind biases (~2-3 knots) exist
when all wind speeds are considered and
turn negative for winds greater than three
knots.
• Difficult to maintain shallow pools of cold
air or shallow cloud layers.
Domain-Wide Biases
24h Forecast, Valid 12Z, all wind speeds-Night
12-h Forecast, Valid 00 UTC-DAY
Less Positive Bias at 00 UTC than 12 UTC
Questions
• Does this error vary with wind speed?
• Might part of it derive from wind sensor
errors at slow speeds?
Instrument
start threshold spd
Met One 014A
1.0 mph
Met One 034B
0.9
RM Young 05103
2.2
RM Young 05106 "Marine"
2.2
RM Young 03001 "air quality"
1.1
RM Young 03101 "air quality"
1.1
Climatronics CS800
<1.0
ASOS's F420 (company: n/a)
2.3
Vaisala WM30
<0.9
Vaisala WA15/WA25
<1.1
start threshold dir
- mph
0.9
2.4
2.4
1.8
1.8
<1.0
2.3
2.2
0.9
Looks like many networks are using the RM Young 05103. Agrimet does,
the fixed/drifting buoy data does along with Vaisala,
Schoolnet and RAWS show a picture of one on their website although
Schoolnet mentions that stations installed prior to 1997 used a white
cup/vane type.
Wind Direction
• Winds generally too geostrophic by 5-10
degrees
Looks Worse for higher wind speeds… 4km is best
But things changed this year
• Winds speeds developed a significant
negative bias.
• We changed the source of surface
verification data…from using the lowest
sigma and surface data to using the PBL
scheme output directly.
Wind Speed Bias Valid at 12 UTC for 24 h Forecast
Less Change at 00UTC-- still generally underforecast.
Wind Direction…00UTC
12 UTC
4-km MM5 is best by far!
Temperature Biases
• Large temperature biases can occur at
certain times:
• When there is a shallow layer of cold air
(few hundred m deep) that is mixed out.
• During transition season (particularly
spring, when land surface conditions are
problematic)
• During summer during warm periods.
00 UTC
12 UTC
Problems with Shallow Cold Air
January 6,
2004
Well-Forecast Snow Event
2-4 inches
…but not the
Freezingdays
rain…because
Several
of freezing mixed
Out coasted
the coldPortland
air
rain
in a
sheath of ice….PDX
closed for THREE days
Shallow Fog…Nov 19, 2005
• Held in at low levels for days
• MM5 held in the inversion…generally
without the shallow mixed layer of cold air
a few hundred m deep
• MM5 could not maintain the moisture at
low levels
Where are the problems?
• PBL parameterizations?
• Land surface models or surface specifications?
• Dynamical models themselves (too much
diffusion, etc)?
• What happens at 1-10 km resolution when some
PBL structures are beginning to be resolved?
• Lack of verification/evaluation data/
Who is working on PBL
parameterizations and evaluating
current ones?
• Generally a hollowing out of the U.S. efforts (e.g.,
UW Energy Transfer Group)
• For MM5/WRF mainly Korean effort (Yonsei
University)
• Still activity in Europe…mainly Dutch?
• Some interest in UW; Forest Service sponsored
effort, Chris’s group.
• No one at NCEP actively working on PBL
parameterizations for mesoscale models.
Computer forecast models were
nearly perfect for the onset and
amount of snow over Puget Sound.
The End
They did not do a good job for the
freezing rain over the east side and
around Portland…. and we know
why.