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Problems of HIRLAM in wintertime stable boundary layer - analysis of forecasts and observations. Timo Vihma, Evgeni Atlaskin, and Laura Rontu. Model validation against Sodankylä sounding data Periods: January and March 2005 - PowerPoint PPT Presentation
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Problems of HIRLAM in wintertime stable boundary layer
- analysis of forecasts and observations
Timo Vihma, Evgeni Atlaskin, and Laura Rontu
Model validation against Sodankylä sounding data
Periods: January and March 2005
Model versions: H635E (Gollvik-Rodriques soil-snow-forest schema), H637 and H640
Model product validated: 24 h forecasts
In 2005,
January was very mild in Sodankylä
but March was colder than usually
Results for January 2005: focus on the errors in the air temperature
- At the heigths of 30 and 90 m, HIRLAM has a large positive bias in cold conditions.
- In warm conditions, the bias is often negative but much smaller in magnitude
- H635N with the snow schema does not produce better results
- The largest errors in the lowermost 100 m occur under conditions of a strong inversion, as estimated from the temperature difference between 30 and 1100 m
- The temperature error at the heights of 30 and 90 m depends much more on T(170-30m) than on T(1100-170m), i.e., large errors are related to near-surface-based inversions, but not so much to clearly elevated inversions.
The largest temperature errors at the height of 30 are not associated with saturation (neither observed nor modelled).
- Near the surface, HIRLAM has a positive bias in cold conditions and a negative bias in warm conditions. This bias in q is qualitatively similar to that in T, but now magnitudes of the positive and negative bias are approximately equal.
Errors in the air specific humidity
Errors in q occur also without any temperature inversion, but in conditions of a large T(170-30m), the bias in q(30m) is always positive
The largest errors in q(30m) typically occur when the observed RH(30m) = 0.85-0.95.
H335N yields much lower values of RH than H640
March 2005
Everything told before holds also for March 2005, except:
- the error in specific humidity at the heights of 30 and 90 m depends neither on T nor on RH
- considering the spoecific humidity, H635N performs better than H637
Conclusions
- largest temperature errors occur in cold conditions with a large T(170-30m)
- in conditions of a large T(170-30m), the bias in q(30m) is always large
- the largest errors in temperature and humidity were typically not related to saturation
- the presence of solar radiation does not have a large effect on the temperature error in HIRLAM
- Although January 2005 was mild and March 2005 was cold, the differences in the model performance with respect to the air temperature were small
- H635N with the new snow-forest scheme does not show improvement, but this may also be related to problems in snow analysis and the digital filter initialization
- much more analyses are needed: next application of the tower data, then analysis on the relative importance of factors controlling T2m (a) in reality and (b) in HIRLAM.