Transcript Slide 1

On HRM3 (a.k.a. HadRM3P, a.k.a.
PRECIS) North American simulations
Bill Gutowski (on behalf of Richard Jones, Simon Tucker
and Wilfran Moufouma-Okia)
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Contents
• Results from the HadCM3-driven climate
(change) simulation
• Results from the NCEP-driven climate
simulation
• Comparison of NCEP and ERA-Interim
simulations and boundary conditions
• Concluding remarks
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Results from the HadCM3-driven
climate simulations
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Experimental Set-up
• The 50km resolution HadRM3P
was nested within the HadCM3
GCM, and run in two time-slices:
1968-2000 and 2038-2070 under
SRES A2 emission scenario
• Domain size is 171x146 - the
interior domain corresponds to the
NARCCAP region
• The outer 8 grid boxes were
discarded along with the first two
years of the model output data
whilst the interior solution was
spinning up
• The simulations provided 30 year
baseline and future periods for
analysis
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How to assess the RCM performance in
simulating the current climate
HadRM3P
consistency
realism
HadCM3
realism
Observations
• Compare like with like
• RCM only has skill at spatial scales resolved by its grid
• Aggregate or interpolate RCM or observed data
• Can not compare individual RCM years with corresponding
observed years when GCM-driven (same reason as with GCM)
• Errors are a combination of three errors:
• 1) Physical errors in the GCM affecting the LBCs
• 2) RCM/GCM consistency errors
• 3) Physical errors in the RCM
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Large-scale consistency between
HadRM3P and HadCM3
Mean sea level pressure
700 hPa advection of humidity
HadRM3P
HadCM3
These results are computed for mean JJA 1971-2000, and on the GCM grid
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The realism of HadRM3P and HadCM3
• Models realistically
capture the mean winter
precipitation
• Similarities between
HadRM3P and HadCM3
biases
• Important differences
occurs in areas of
complex orography
Mean DJF 1971-2000 precipitation and anomalies
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•
Summer mean precipitation is also well captured
by the two models
HadRM3P biases are
largely reduced over
domain,
Mean JJA 1971-2000 precipitation and anomalies
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There is a consistency in the anticipated temperature
change signal of HadRM3PvsHadCM3
RCM
GCM
DJF
MAM
JJA
Projected seasonal changes in temperature, between 1971-2000 and 2041-2070
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Results from the NCEP and ERAInterim driven climate simulation
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HadRM3P precipitation compared to CRU
climatology – NCEP boundary conditions
Winter
Summer
CRU
NCEP-driven RCM
RCM bias
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1981-2000 Mean seasonal precipitation and biases
HadRM3P JJA/
DJF temperature
biases:
Top – ERA-In
boundaries
Bottom – NCEP
boundaries
Bias pattern similar
– magnitude much
greater with NCEP
boundaries
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Difference in DJF surface temperature
simulation when using NCEP rather
than ERA-Interim boundaries
HadRM3P DJF
temperature bias
reduced by >5K when
using ERA-Interim
boundary conditions
Similar signal seen in
summer
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1000hPa
200hPa
1000hPa
NCEP–ERA-Interim temperature (left and middle) and Rh
925hPa
150hPa
925hPa
NCEP warmer and moister on western inflow boundary
850hPa
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100hPa
850hPa
Summary of reanalysis
downscaling analysis
• HadRM3P-NCEP has by far the largest seasonal
temperature biases (see BAMS article)
• HadRM3P has no systematic tendency for significant
positive temperatures biases (Xu et el., 2006 over China,
Marengo et al., 2009 over South America, Kamga et
Buscalet, 2006, over Africa)
• Previous studies have used ECMWF boundary conditions,
ERA-15, ERA-40 or ERA-Interim reanalyses
• HadRM3P-ERA-Interim data produces significantly lower
(5K) temperature biases - and similar in magnitude to the
other RCMs.
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Some reasons for differences
in the downscaled reanalyses
• At the boundary of the NARCCAP domain the NCEP data
are both warmer and moister in the lower troposphere and
in the upper troposphere/stratosphere – directly increasing
temperature and increasing downward longwave radaiation
(from higher atmospheric humidities and, in winter, by
increased cloud cover)
• In winter the warmer temperatures lead to reduced snow
cover thus enhanced solar radiation absorption at the
surface and in spring/summer lead to drier soils, lower
evaporative cooling and lower cloud amounts enhancing
surface solar radiation
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Concluding remarks on GCM
downscaling
• HadRM3P model successfully downscaled the climate
projection from HadCM3 over North America
• HadRM3P-HadCM3 simulates realistically the mean
surface features of the twentieth century climate
• The regional climate shows a good agreement with the
large-scale driving fields and adds value to the GCM
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Concluding remarks on
reanalysis downscaling
• It is important not to base strong conclusions on a model's
performance (either good or bad) on the basis of
simulations driven by a single set of reanalyses.
• The quality of a reanalysis should be assessed before
using it to validate an RCM (Cerezo-Mota et al concluded
the NCEP reanalyses were deficient for assessing RCM
reliability in southern N. America)
• HadRM3P is the only non-North American model in
NARCCAP and would have been reformulated if it had
been developed using NCEP boundary conditions
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