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Processes affecting historical variations and future projections in GCM simulations of the central and southeast U.S. climate

PI: Kenneth Kunkel
Institution: Illinois State Water Survey
Additional Investigators: Xin-Zhong Liang
The central and southeast U.S. is one of the few locations globally that has not experienced at least some warming during the 20th Century. The causes for this remain the subject of active research; one recent paper hypothesized that the temporal pattern of SST anomalies in the tropical Pacific observed in the latter half of the 20th Century can induce an atmospheric response leading to decreased temperature, increased cloud cover, and increased precipitation in this region. We propose to undertake an analysis of the AR4 GCM simulations, focusing on this observed regional feature of little or no warming. The overarching question is this: To what extent can GCMs reproduce this feature of the 20th Century climate and what are the implications of the answer for confidence in their 21st Century projections?

Our specific objectives are:
(1) to determine whether any 20th Century CGCM simulation can reproduce the observed central and southeast U.S variations of temperature and precipitation;
(2) to determine through process-oriented studies why models produce certain variations in the central U.S. with a particular, though non-exclusive, focus on processes related to SSTs; and
(3) to determine to what extent the models project changes in these forcing processes in the 21st Century. This analysis will complement ongoing work at our institution in which we are performing 21st Century regional climate model simulations using PCM and HadAM3 data as the lateral boundary conditions.

The AR4 data sets needed are:
(1) time series of 20th Century simulations, including the following specific variables: surface climate (temperature, precipitation, humidity, cloud cover, sea level pressure, wind speed and direction) for the U.S., upper air data (height, wind, temperature, specific humidity) at standard levels for North America and adjacent ocean areas, and global SSTs; and
(2) time series of the same data for 21st Century simulations for the A1B, A2, and B1 emissions scenarios.
  • Kunkel, K.E., X.-Z. Liang, J. Zhu, and Y. Lin, 2006: Can CGCMs simulate the Twentieth Century “warming hole” in the central United States. J. Climate, 19, 4137–4153. Abstract. Edit.

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