Prsentation PowerPoint

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Université du Québec à Montréal
An Evaluation of the Surface Radiation Budget
Over North America for a Suite of Regional
Climate Models
Student Marko Markovic Director Colin Jones
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• Evaluate parameters of SRB (surface radiation
  budget) and cloud cover in RCMs against surface
  observations for North America.
• The parameters which will be evaluated are
  global solar (directdiffuse), radiation, and
  downward longwave atmospheric radiation.
• SW and LW are the main terms in surface energy
  balance that control evolution of surface
  temperature and moisture.
• Three regional models used in this study are
• 1.GEM-LAM - Limited version of
  GEM model, Canada (Coté et
  al.1998)
• 2. CRCM - The Canadian Regional
  Climate Model, (Caya and
  Laprise, 1999)
• 3. RCA3 -The Rossby Centre
  Regional Atmosphere model,
  Sweden (Jones et al.2004)
• The observation data come from the NOAA SURFRAD
  network

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Climatological mean annual cycle (2000-2004).
GEM-LAM and CRCM simulate ISR very well in winter
while overestimate in summer with 20-30W/m2
biases. RCA3 is fairly accurate in summer but
shows the biggest biases in winter and
spring. DLR is underestimated by GEM-LAM and CRCM
in winter while both models show good results for
other seasons. This underestimate has already
been seen by several studies in the past and is
related to the parametrisation of water vapor
spectra in winter conditions. CRCM gives a
systematic underestimate of 20W/m2 through the
entire annual cycle a possible cloud emissivity
problem.
PDF comparison
Probability density functions of time series,
period 15-21 UTC, season DJF
All-sky
Comparison of Probability Density Function of
Cloud Fraction
Clear Sky lt 10 of cloud cover
Models overestimate clear-sky (0 - 10), and
underestimate occurrences of cloudy-sky (90-100)
Overcasted Sky gt 90 of cloud cover
Cloud Free
Shortwave All-sky biases are mostly influenced
by biases produced in overcast conditions.
Longwave Principal errors in all-sky conditions,
for GEM-LAM and RCA3 come from clear-sky while
for CRCM from cloudy-sky biases.
Cloudy
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Differences between the models and ERA40, DJF
4-year mean, over entire N. America
SW GEM-LAM et MRCC good representation, RCA3
overestimates LW underestimate by all models CC
underestimate by all models
Summary

• - Underestimate of LW downward atmospheric
  radiation in winter, by all models
• - Cancellations of errors in cloud coverage and
  in SW clear sky radiation in RCA3 model
• - Error in diurnal cycle of clouds in all models
• Systematic underestimate of LW radiation in CRCM
• DJF LW radiation biases are due to clear-sky
  radiation in GEM-LAM and RCA3, and cloudy-sky
  radiation fluxes in CRCM.
• Comparison over entire N. America showed similar
  biases in respective models as in 6 SURFRAD
  station comparisons.