The impact of the crop area vegetation and soil properties on the biases was investigated in a series of numerical experiments. The biases were largely caused by the erroneous prescription of crop vegetation phenology in the surface model of the GCM. The prescribed crop soil properties also contributed to the biases. Based upon these results, the crop model has been improved and the systematic errors in the U.S. summer simulations have been reduced.
The numerical experiments also revealed that land surface effects on the atmospheric variables at and near the surface during the North American summer are very pronounced and persistent, but are limited to the area of the anomalous land surface forcing. In this regard, the mid-latitude land surface effects described here are similar to those previously found for tropical regions.
last update: 31 August 1995
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