USGCRP Home National Assessment Background Information Scenarios & Data Guidance on When to Use the VEMAP Data   Search 
Updated
12 October, 2003

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National Assessment of


Options (monthlies and dailies):Observations:
Future (monthlies and dailies):
Circumstances:General: The VEMAP monthly dataset is probably fine for monthly/interannual variability examinations; the problem is with the dailies. To look at daily extremes, you are better off using the HCN data for the historical period and the HCN data combined with model deltas for the future.
Notes on Tmin, Tmax, Tmean calculations:The atmospheric GCM computations occur at time steps on the order of 2030 mintues, even though the actual values are saved only several times daily at most. Temperature is computed as an instantaneous value at each model time step. The minimum and maximum temperatures are therefore the minimum and maximum (screen) temperature values that occur amongst all the time steps between 0Z and 24Z at a given grid point. The mean screen temperatures are the mean of the temperatures at each time step within this 24 hour period (in the case of CCCma, provided as two values between 0Z and 12Z and 12Z and 24Z). Therefore the mean screen temperatures will not equal the mean of the minimum and maximum temperatures, even though this is the case in the real world where records of minimum and maximum temperatures are the primary temperature observations. The average monthly temperatures (minimum, maximum, and mean) are calculated by averaging these daily values. References:Mearns, L. O., Rosenzweig, C., and R. Goldberg. 1997). Mean and variance change in climate scenarios: methods, agricultural applications, and measures of uncertainty. Climatic Change. 35(4): 367. Mearns, L. O., Rosenzweig, C., and R. Goldberg. (1996). The effect of changes in daily and interannual climatic variability on CeresWheat. a sensitivity study. Climatic Change. 32(3): 257. 
