Evaluation of WRF PBL Schemes in the Marine Atmospheric

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Evaluation of WRF PBL Schemes in
the Marine Atmospheric Boundary
Layer over the Coastal Waters of
Southern New England
Matthew J. Sienkiewicz and Brian A. Colle
School of Marine and Atmospheric Sciences, Stony Brook
University
Stony Brook, NY
NROW XV
12 November 2014
Coastal New England’s Wind Resource
A combination of shallow coastal
bathymetry, population density,
average wind speed at turbine hub
height, and load coincidence make
the coastal waters of Southern New
England ideal for offshore wind
energy.
Winter
Spring
Summer
Fall
Offshore wind resource maps are
created using mesoscale models
to account for the sparse
observations at and above the
water surface.
Modeled Seasonal Peak Offshore Wind
Resource at 90 meters (hub height).
(Dvorak et al. 2012)
Motivation
 Offshore wind resource assessment
and operational forecasting are
dependent on mesoscale models
accurately representing coastal
processes
 Models are known to have wind speed
biases at the surface over the water
(Colle et al. 2003)
 Studies of WRF PBL scheme
performance have been conducted
using coastal and offshore towers and
wind profilers in the North Sea and
Japan
 Regional study is needed to address
model biases throughout the entire
marine boundary layer in the coastal
region of southern New England
FINO1 Tower in the North Sea
(Neumann and Nolopp 2007)
Model Wind Speed Biases at NDBC
Moored Buoy and C-MAN Stations
• Wind speed biases near
the surface vary spatially,
diurnally and seasonally
• Near-surface buoys are not
representative of above
surface winds due to
unknown stability/shear
profiles
• Accurate representation of
MABL winds is partly
dependent upon the
accuracy of the SST field
and the PBL scheme
(Ohsawa et al. 2009)
Wind Speed biases in m s-1. C-MAN Stations
are in blue and moored buoys are in red.
Wind speeds were reduced from the lowest model
level (~7.5 meters) to the buoy anemometer height
of 5 meters similar to Hsu et al. 1994.
Motivation
 Studies verifying WRF PBL schemes above the water
have mostly been limited to the North Sea and Japan.
 More validation is needed within the planetary boundary
layer above buoy height.
Research Questions
 What are the short-term forecast biases in the marine
boundary layer over the coastal waters of Southern New
England?
 How do these biases vary with height above the water
surface?
 Are there particular stability and flow regimes favoring
certain PBL wind biases?
Observational Datasets
Cape Wind
Meteorological
Mast
2003-2011
55
meters
NDBC Moored
Buoys and C-MAN
Stations
5 meters
Temperature,
Pressure
60
meters
41
meters
20
meters
10
meters
Wind
speed,
direction
Long-EZ Aircraft Flights
40 Hz measurements of
3D winds, temperature,
pressure and humidity
Combination of buoy,
tower, and aircraft
observations provides a
dataset for model
verification throughout
the entire marine
boundary layer.
Experimental Design and Model
Configuration
 WRF-ARW (version 3.4.1)
 Six PBL schemes
 Two First-order (YSU, ACM2)
 Four TKE-order (MYJ,
MYNN2.5, BouLac, QNSE)
 NARR initial and boundary
conditions (3-hourly)
 0.5° NCEP Daily SST
 38 vertical levels
 30-hour forecasts
 First 6 forecast hours are
discarded as model spin-up
4 km
12 km
36 km
90 run dates randomly selected between 2003-2011
Equally divided between warm season (APR-SEP) and cool season (OCTMAR)
Equally divided between 00z and 12z model initialization times
CW Tower Wind Speed Biases
COOL SEASON
• Largest biases
found during the
day
• Biases increase in
magnitude with
height
• BouLac scheme
shows large
biases at night
Error bars represent bootstrap 95% confidence intervals.
Cape Wind Composite Profiles
COOL SEASON
• Models are undersheared during the
day
• Super-adiabatic
lapse rates during
cool season
• Too much mixing
of lower
momentum from
below or higher
momentum from
above
CW Tower Wind Speed Biases
WARM SEASON
• Largest Biases found
at 20-meter level
during night
• Biases decrease in
magnitude with
height
• BouLac scheme
shows increasing
biases with height
during day
Error bars represent bootstrap 95% confidence intervals.
Cape Wind Tower Composite Profiles
WARM SEASON
• Models display too
much wind shear
below 40 meters
• Too little
downward mixing
of higher
momentum
• Consistently too
cool by 1-2 K
throughout lower
levels (SST errors?)
High SST Variability in the region
• Western and central Nantucket Sound
heats up in the Spring and stays warm
into the Fall
• Eastern Nantucket Sound is subjected to
strong tidal mixing of cooler water from
the Gulf of Maine
• Cold water pools over the Nantucket
Shoals
• Westward excursions of cold water south
of MV occur under certain flow regimes
CW TOWER
44020
NOAA / Rutgers University
National Data Buoy Center
Hong et al. 2009
How do the NCEP Daily SST products
perform in Nantucket Sound?
Large negative
warm season bias
• For the 5-year period spanning 2009-2013
• Gridded SST products compared with observed water
temperature at buoy location
What is the relationship between
Wind Shear and Stability?
Bin-averaged Wind Shear vs. Stability
• YSU, ACM2, MYJ
and QNSE
schemes display
too much wind
shear in neutral to
higher stabilities
• BouLac scheme is
under-sheared in
higher stabilities
• Models possibly
under-sheared in
unstable regimes
• Models oversheared in neutral
stability
What is the relationship between
Wind Speed and Wind Speed Bias?
Bin-Averaged Mean Error by Modeled Wind Speed
Low (high) wind speed biases are found at low (high) modeled wind speeds.
Aircraft Observations during
IMPOWR Campaign
Improving the Mapping and Prediction of Offshore Wind Resources (2013-2014)
• AIMMS-20 instrument
• Up to 40 Hz measurements of
temperature, pressure,
relative humidity and threedimensional winds
• Targeted Nantucket Sound,
Buzzard’s Bay and offshore
waters to the south
• Flights consisted of level
flight legs, spirals up to
1500 meters and slant
soundings below 1000
meters
Long-EZ Aircraft
AIMMS-20
Model Set-up for Long-EZ Flights
• 24-hour simulations
forced with hourly Rapid
Refresh analyses
• Prescribed NCEP 1/12th
degree SST
• One-way nested 1.333
km grid with 5-minute
output used for
interpolation of model
variables to aircraft flight
track
1.333 km
4 km
Strong Southwesterly Flow with Marine LLJ
23-JUN-2013 18z SFC ANALYSIS
• Southwesterly flow
dominated by
Bermuda High
• Land-sea
temperature
difference of 20 °F
• 40 knot LLJ
structure developed
over coastal waters
and SE
Massachusetts
Aircraft Spiral 2200 UTC 23 JUNE 2013
fhr22
Too Strong
Too Stable
Too Cool
Aircraft Cross-section
23z 23-JUN-2013
SW-NE
300
297
STABLE LAYER
294
18
>19 m s-1
16
14
12
10
RAP-WRF PBL Schemes
Winds at 300 meters at forecast hour 23
YSU
ACM2
MYJ
MYNN2
BouLac
QNSE
Most schemes display the observed extent of 18-19 m s-1 winds at 300 meters
from Buzzard’s Bay to the south shore of Long Island.
CHH Sounding 0000 UTC 24 JUNE 2013
fhr24
Too Strong
Good Agreement
Too stable, too warm
How do the initial and boundary
conditions affect the jet structure?
Winds at 300 meters and NW-SE Cross-sections for lowest 1 km at f24
RAP-WRF
NAM-WRF
GFS-WRF
NARR-WRF
• RAP-WRF correctly displays extent of strong winds to south shore of Long Island
• NARR-WRF shows weakest jet structure that is retracted to the northeast
How do the boundary conditions
affect the jet structure?
NARR-WRF best
handles lowest
level winds, but
under-predicts LLJ
Too Stable
Too Cool
How does the SST field affect the
momentum and thermal structures
below jet level?
SST Perturbation Experiment
• Better represent SST field in
Nantucket Sound by warming the
western Sound and cooling the
eastern Sound.
• Warmed upstream regions and
decreased land/sea contrast to
south while increasing it to north
• Maintained continuous SST field
SST Perturbation Experiment Results
• Perturbing the SST field only slightly affected the below-jet
thermal, moisture and momentum profiles
Summary of Results
• Lowest 60 meters are too stable and too sheared
during the Warm Season, resulting in negative
wind speed biases at the 20 meter level
• Too unstable during the Cool Season, resulting in
too much mixing of higher momentum from
above and negative wind speed biases
increasing with height
• Combination of coarse SST field and surface
layer scheme over-doing surface fluxes is most
likely the cause of misrepresented low-level
stability in models
• Different initial and boundary conditions yield
more varied results than different PBL schemes
Thank you!
[email protected]
SBU-WRF: http://itpa.somas.stonybrook.edu/LI_WRF
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