Atmospheric stability
; General circulation model
; Land surface change
; Medieval Climate Anomaly (MCA)
; Model experiments
; Palmer drought severity indices
; Pdsi reconstruction
; Sea surface temperature (SST)
; Aerosols
; Atmospheric temperature
; Boundary conditions
; Drought
; Experiments
; Surface measurement
; Uncertainty analysis
; Dust
; aerosol
; bare soil
; boundary condition
; climate forcing
; drought
; dust
; general circulation model
; land surface
; reconstruction
; regional climate
; sea surface temperature
; tree ring
; North America
; Pacific Ocean
; Pacific Ocean (Tropical)
英文摘要:
Tree-ring-based reconstructions of the Palmer drought severity index (PDSI) indicate that, during the Medieval Climate Anomaly (MCA), the central plains of North America experienced recurrent periods of drought spanning decades or longer. These megadroughts had exceptional persistence compared to more recent events, but the causes remain uncertain. The authors conducted a suite of general circulation model experiments to test the impact of sea surface temperature (SST) and land surface forcing on the MCA megadroughts over the central plains. The land surface forcing is represented as a set of dune mobilization boundary conditions, derived from available geomorphological evidence and modeled as increased bare soil area and a dust aerosol source (328-448N, 1058-958W). In the experiments, cold tropical Pacific SST forcing suppresses precipitation over the central plains but cannot reproduce the overall drying or persistence seen in the PDSI reconstruction. Droughts in the scenario with dust aerosols, however, are amplified and have significantly longer persistence than in other model experiments, more closely matching the reconstructed PDSI. This additional drying occurs because the dust increases the shortwave planetary albedo, reducing energy inputs to the surface and boundary layer. The energy deficit increases atmospheric stability, inhibiting convection and reducing cloud cover and precipitation over the central plains. Results from this study provide the first model-based evidence that dust aerosol forcing and land surface changes could have contributed to the intensity and persistence of the central plains megadroughts, although uncertainties remain in the formulation of the boundary conditions and the future importance of these feedbacks.
NASA Goddard Institute for Space Studies, New York, and Lamont-Doherty Earth Observatory, Palisades, NY, United States; Lamont-Doherty Earth Observatory, Palisades, NY, United States; NASA Goddard Institute for Space Studies, Department of Applied Physics and Applied Math, Columbia University, New York, NY, United States; University of Wisconsin-Madison, Madison, WI, United States
Recommended Citation:
COOK B.I.,Seager R.,Miller R.L.,et al. Intensification of north american megadroughts through surface and dust aerosol forcing[J]. Journal of Climate,2013-01-01,26(13)