Transcript Dynamically Downscaled Regional Reanalysis for the

Dynamical Downscaling of Climate
for the Southeast United States
Lydia Stefanova
Center for Ocean-Atmosphere Prediction Studies (COAPS)
Florida State University
With contributions from Tim LaRow (FSU/COAPS) and
Michelle M. Irizarry-Ortiz and Jayantha Obeysekera (SFWMD)
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Outline
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La Florida climate downscaling experiments
Available data
Regional model configuration
Results from downscaling of reanalysis: CLARReS
data set
• Preliminary results from a climate change scenario
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Downscaling Experiments
• 20 century: 1979-2000 for reanalyses (R2 and ERA-40), 1969-2000 for models
(CCSM, GFDL, HadCM3)
• 21 century: A2 scenario 2039-2070
• Blue (reanalyses) and Green (climate scenarios): completed
• Yellow: pending
20 century
Historic
veg
Current
veg
21 century (A2)
Future
veg
Historic
veg
Current
veg
Future
veg
R2
ERA-40
CCSM
GFDL
HadCM3
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Vegetation Scenarios
Historical
Present
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What is a Reanalysis?
A retroactive "best guess" for the state of the atmosphere based on all
available observations and knowledge.
The observations (relatively sparse, and possibly containing errors and thus not
necessarily mutually consistent) are assimilated into a dynamical forecast model
which is run for a very short time (essentially creating a now-cast) to produce a
best estimate for the state of the atmosphere (including variables that are not
available from observations, but are derived through the model equations (based
on fluid dynamics and physics)) as a spatially and physically consistent gridded
data set.
In summary, a reanalysis is our best guess about the atmospheric fields of the recent
weather and climate, based on a combination of a) observations and b) modeling
knowledge of the physics and dynamics of the atmosphere.
To obtain dynamically downscaling regional reanalysis, the global reanalysis is used to
force a regional model
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Model, Input, and Output
• Regional Model: National Centers for Environmental
Prediction (NCEP)/Experimental Climate Prediction Center
(ECPC) Regional Spectral Model (RSM)
• Input: Global reanalysis (NCEP’s R2 or ECMWF’s ERA-40),
atmospheric winds, temperature, humidity, and surface
pressure at 6-hourly intervals as lateral boundary conditions.
• Output: Regionally downscaled reanalysis: COAPS LandAtmosphere Regional Reanalysis for the Southeast (CLARReSR2 or CLARReS-ERA40), hourly 2-D variables, 3-hourly 3-D
variables
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Available Data
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ftp://ftp.coaps.fsu.edu/pub/Southeast/CLARReS10/
Subdirectories: Documentation; ERA-40; R2
Data uploaded in netCDF format
Request additional variables by emailing [email protected]
Date
10/21/2010
10/26/2010
Frequency
Field
Precipitation
Specific humidity at 2m
U, V winds at 10m
10/29/2010
Hourly
11/17/2010
1/25/2011
Daily
Temperature 2m
Downward shortwave flux at surface
Latent heat flux at surface
Snowfall rate water equivalent
Ground heat flux
Surface roughness
Sensible heat flux
Surface pressure
Daily maximum temperature at 2m
Daily minimum temperature at 2m
Name
pratescf
spfh2m
ugrd10m,
vgrd10m
tmp2m
dswrfsfc
lhtflsfc
srwegsfc
gfluxsfc
sfcrsfc
shtflsfc
pressfc
tmin2m
tmax2m
Units
kg m-2 s-1
kg kg-1
m s-1
K
W m-2
W m-2
kg m-2 s-1
W m-2
m
W m-2
Pa
K
K
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Domain and Model Configuration
Chattanooga
Augusta
Charleston
Macon
Montgomery
Savannah
Tallahassee
Daytona
Tampa
Melbourne
West Palm Beach
Miami
Dynamics: hydrostatic primitive equations
with spectrally transformed onto
Fourier basis functions, Juang and
Kanamitsu (1994)
10-km horizontal resolution; 28 vertical
layers; 4-min resolution orography
Planetary boundary layer processes, Hong
and Pan (1996)
Shortwave and longwave radiation, Chou
and Lee (1996)
Shallow convection, Slingo (1987)
Deep convection: Simplified ArakawaSchubert Scheme, Pan and Wu (1995)
Boundary forcing: scale selective bias
correction, Kanamaru and Kanamitsu
(2007)
Land surface: Noah; 4 soil layers, Ek et al
(2003)
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Precipitation
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Mean: wet bias outside of Florida; wet bias in CLARReSERA40 over Everglades; Dry bias over southeast Florida
Seasonal cycle: summer precipitation overestimated
outside Florida
Interannual variability: generally proper sign
JJA frequency of rainy days: frequency of precipitation days
is generally underestimated in Florida, and overestimated
for Georgia, Alabama and South Carolina. The frequency of
light events is generally underestimated, while that of heavy
events is generally overestimated. Precipitation from
tropical cyclones is realistic, provided the storms are
present in the global model.
Diurnal cycle: Good agreement with observations
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Climatology
How well is the AVERAGE year represented?
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Annual Precipitation Rate
Global Reanalysis
(R2)
Downscaled Reanalysis
(CLARReS-R2)
Observations
(PRISM)
mm/day
[PRISM: Oregon State Climate Group data set, gauge-based, uses intelligent
interpolation, 4km resolution]
• Note grid size of global vs downscaled reanalysis: amount of detail
• Comparable magnitudes. Note different spatial structure and bias.
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Summer Precipitation Rate
R2
CLARReS-R2
PRISM
mm/day
Very wet bias in the global reanalysis; reduced but not eliminated in downscaled
version; Florida bias less than remainder of domain;
Note that rainfall is not directly downscaled; Instead, the regional model produces its
own rain from the atmospheric circulation generated from the
winds/temperature/humidity forcing
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Interannual Variability
How well is the DIFFERENCE between two years
captured?
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Difference of dry and wet winter month,
(Jan 1988-Jan1987) (mm/day)
R2
CLARReS-R2
OBS (UDel)
ERA-40
CLARReS-ЕRА40
OBS (PRISM)
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Difference of dry and wet summer month
(Jun 1988-Jun1987) (mm/day)
R2
CLARReS-R2
OBS (UDel)
ERA-40
CLARReS-ЕRА40
OBS (PRISM)
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0.25
Normalized Annual Cycle
(Area averages)
0.2
CLARReS10/R2
0.15
CLARReS10/ERA40
R2
0.1
Central
Florida
North
Georgia
NE Florida
South Florida
0.05
0.25
0.25
0.25
0.25
ERA40
PRISM
0
1
2
3
4
5
6
7
8
9
10
11
12
0.2
0.2
0.2
0.2
0.15
0.15
0.15
0.1
0.1
0.1
0.05
0.05
0.05
0
0
0
1
1
1
2
2
2
3
3
4
4
5
5
6
6
7
7
7
8
8
8
9
9
9
10
10 11
11 12
12
10 11 17
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Normalized Annual
Cycle (Stations)
CLARReS10/R2
0.15
CLARReS10/ERA40
R2
0.1
0.05
0.25
0.25
0.25
ERA40
COOP Station
PRISM
Tampa
Tallahassee
Miami
0
1
2
3
4
5
6
7
8
9
10
11
12
0.2
0.2
0.2
0.15
0.15
0.1
0.1
0.05
0.05
0
0
11
22
33
44
55
66
77
88
99
10
10
11
11
12
12
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Frequency of JJA Precipitation
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Percent JJA days with Prate > 20mm/day
CLARReS-R2
CLARReS-ERA40
Observations
(CPC Unified)
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Probability of exceeding a given precipitation
threshold on any summer day
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Diurnal Cycle of JJA Precipitation
How is precipitation distributed
throughout a typical summer day?
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Time of diurnal maximum, GMT
CLARReS-R2
CLARReS-ЕRА40
(EDT=GMT-4)
OBS
• Earlier maxima along the coasts (~18-20
GMT = ~2-4PM EDT); later inland (~22-24
GMT=6-8pm EDT)
• Sea breeze convergence in peninsular
Florida
• Land breeze signature over the water
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Correlation of modeled mean daily
cycle with observations
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
CLARReS10-R2
CLARReS10-ERA40
MERRA
station
WES
MIA
DAY
CHAR
SAV
MEL
CHAT
TAL
MON
MAC
TAM
AUG
ASH
CFSR
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Tropical and Extratropical Storms
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Tropical Cyclone Associated Precipitation
(inches)
Global Reanalysis
Global Reanalysis
CLARReS
CLARReS
Observation
Observation
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Tropical Cyclone Associated Precipitation
(inches)
Global Reanalysis
Global Reanalysis
CLARReS
Observation
CLARReS
Observation
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Hurricane Andrew [1992] Associated
Precipitation (inches)
Global Model
CLARReS
Observation
Observations from HPC
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Opal [1995] Wind Field (kts)
CLARReS-ERA40 (21UTC04Oct1995)
10m Wind Speed
Observed H*Wind
850hPa Wind Speed
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12-15 March 1993 “Storm of the Century”
… was an extratropical storm of unusual intensity affecting the Eastern US.
Areas as far south as central Alabama and Georgia received 6 to 8 inches of
snow. The Florida Penninsula recorded hurricane-force wind gusts and recordlow barometric pressure.
Satellite Image
Observed
Snow Cover
CLARReS-R2 (12UTC 13 March 1993)
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Seasonal Cycle for Daily Average, Minimum
and Maximum 2-m Temperatures
(Assessment limited to Florida)
Daily average temperature (Tave) is captured very well in both models.
Daily maximum temperature (Tmax):
• Both models overestimate Tmax across the state especially from Feb-Oct.
• In both models Lake Okeechobee and areas very close to the coast show
lower Tmax than interior areas (not evident in gridded observations). The
models are probably correct.
Daily minimum temperature (Tmin):
• In general, Tmin is overestimated across the state, especially in northern
Florida and in the Panhandle area.
• In both models LOK and areas very close to the coast show higher Tmin
than interior areas (higher Tmin over LOK not seen in
PRISM or USGS). Models are probably correct.
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Interannual Signal in Daily
Tmin and Tmax
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Interannual variability in the statistical distribution of daily minimum and
maximum temperatures
Large-scale control from El Nino and La Nina: On average, El Nino winters
are colder and wetter than La Nina years.
Standard deviation and anomalies
Skewness and kurtosis
Comparison with COOP station data
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Daily Tmin
El Nino (avg. cold and wet)
La Nina (avg. warm and dry)
CLARReS
Station Observations
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Daily Tmax
El Nino (avg. cold and wet)
La Nina (avg. warm and dry)
CLARReS
Station Observations
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Higher moments, daily Tmin
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Higher moments, daily Tmax
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Downscaling of Regional Reanalises:
Summary
Precipitation
• Downscaled reanalysis precipitation has wet bias outside of Florida; wet
bias in CLARReS-ERA40 over Everglades; Dry bias over southeast Florida.
• In Florida, the frequency of heavy rainfall is generally overestimated.
• The shapes of annual and diurnal cycles are simulated well.
• The interannual variability is simulated well.
• Tropical storm precipitation is simulated well provided the storm is well
inside the regional domain.
Temperature
• Tmax and Tmin generally overestimated; Average T generally OK.
• Interannual variability and higher statistical moments simulated well.
Hourly downscaled data available from
ftp://ftp.coaps.fsu.edu/pub/Southeast/CLARReS10/
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Preliminary results from
downscaling of climate projections
• Regional model forced with boundary conditions from the National
Center from Environmental Prediction (NCEP) Community Climate
System Model (CCSM) simulations.
• Seasonal means for 1969-1999 subtracted from the seasonal means for
2039-2069.
• Maximum and minimum daily temperatures (Tmin and Tmax), average
daily temperature (Tave), precipitation rate (Prate, mm/day)
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Downscaling of Climate Projections
Summary
Compared to the 20th century, the 21st century Florida is warmer and drier.
• Tmax is up by 2-3⁰C in winter, ~3⁰C and more the rest of the year
• Tmin is up by 1.5-2⁰C
• Prate is down by 0.25-1 mm/day (3-12 inches/month). (NB: The regionally
downscaled CCSM has a strong dry bias, therefore probably
underestimates the drying)
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