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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2. 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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3. Results from the HadCM3-driven climate simulations
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4. Experimental Set-up
The 50km resolution HadRM3P was nested within the HadCM3 GCM, and run in two time-slices: and 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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5. How to assess the RCM performance in simulating the current climate
HadRM3P
HadCM3
Observations
consistency
realism
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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6. 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 , and on the GCM grid
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7. 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 precipitation and anomalies
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8. Summer mean precipitation is also well captured by the two models
HadRM3P biases are largely reduced over domain,
Mean JJA precipitation and anomalies
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9. There is a consistency in the anticipated temperature change signal of HadRM3PvsHadCM3
RCM
GCM
DJF
MAM
JJA
Projected seasonal changes in temperature, between and
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10. Results from the NCEP and ERA-Interim driven climate simulation
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11. HadRM3P precipitation compared to CRU climatology – NCEP boundary conditions
Winter
Summer
CRU
NCEP-driven RCM
RCM bias
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Mean seasonal precipitation and biases

12. 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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13. 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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14. NCEP–ERA-Interim temperature (left and middle) and Rh
1000hPa
200hPa
1000hPa
NCEP–ERA-Interim temperature (left and middle) and Rh
925hPa
150hPa
925hPa
NCEP warmer and moister on western inflow boundary
850hPa
100hPa
850hPa
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15. 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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16. 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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17. 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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18. 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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