Climate variability
; ENSO
; Model evaluation/performance
; Multidecadal variability
; North America
; Paleoclimates
; Atmospheric pressure
; Climate models
; Climatology
; Drought
; Nickel
; Soil moisture
; Computer simulation
; atmosphere-ocean coupling
; atmospheric general circulation model
; climate variation
; computer simulation
; decadal variation
; drought
; hydrometeorology
; oceanic general circulation model
; paleoclimate
; reconstruction
; North America
英文摘要:
Simulated hydroclimate variability in millennium-length forced transient and control simulations from the ECHAM and the global Hamburg Ocean Primitive Equation (ECHO-G) coupled atmosphere-ocean general circulation model (AOGCM) is analyzed and compared to 1000 years of reconstructed Palmer drought severity index (PDSI) variability from the North American Drought Atlas (NADA). The ability of the model to simulate megadroughts in the North American southwest is evaluated. (NASW: 25°-42.57°N, 125°-105°W). Megadroughts in the ECHO-G AOGCM are found to be similar in duration and magnitude to those estimated from the NADA. The droughts in the forced simulation are not, however, temporally synchronous with those in the paleoclimate record, nor are there significant differences between the drought features simulated in the forced and control runs. These results indicate that model-simulated megadroughts can result frominternal variability of the modeled climate systemrather than as a response to changes in exogenous forcings. Although the ECHO-G AOGCM is capable of simulating megadroughts through persistent La Ni~na-like conditions in the tropical Pacific, other mechanisms can produce similarly extreme NASW moisture anomalies in the model. In particular, the lack of low-frequency coherence between NASW soil moisture and simulated modes of climate variability like the El Ni~no-Southern Oscillation, Pacific decadal oscillation, and Atlantic multidecadal oscillation during identified drought periods suggests that stochastic atmospheric variability can contribute significantly to the occurrence of simulated megadroughts in the NASW. These findings indicate that either an expanded paradigm is needed to understand multidecadal hydroclimate variability in the NASW or AOGCMs may incorrectly simulate the strength and/or dynamics of the connection between NASW hydroclimate variability and the tropical Pacific.
资助项目:
NOAA, National Oceanic and Atmospheric Administration
; NSF, National Science Foundation
; NOAA, National Oceanic and Atmospheric Administration
; NSF, National Science Foundation
Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, Palisades, United States; Department of Earth and Environmental Science, Columbia University, New York, NY, United States; NASA Goddard Institute for Space Studies, New York NY, United States; Instituto de Geociencias (UCM-CSIC) Facultad de Ciencias Fĺsicas, Universidad Complutense, Madrid, Spain
Recommended Citation:
Coats S.,Smerdon J.E.,Seager R.,et al. Megadroughts in southwestern North America in ECHO-G millennial simulations and their comparison to proxy drought reconstructions[J]. Journal of Climate,2013-01-01,26(19)