HR: 17:00h
AN: GC54B-06    [Abstracts]
TI: COMPARING MECHNISMS OF SUBTROPICAL DRYING IN CLIMATE-CHANGE PROJECTION WITH THOSE CONTRIBUTING TO HISTORICAL DROUGHTS
AU: Seager, R
EM: rich@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: * Kushnir, Y
EM: kushnir@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Kelley, C
EM: colinkelley@mac.com
AB: Climate models display considerable agreement in their projection of future drying in subtropical regions, the Southwest US included, under common emission scenarios. The dynamical mechanisms leading to future droughts are a combination of thermodynamic effects related to the increase moisture carrying capacity of the atmosphere and a circulation change consistent of a broadening of the Hadley Cells, a related poleward shift in the location of the subtropical jets and a warming and increases static stability of the tropical troposphere. These mechanisms are distinctly different from the one responsible for droughts in the 19th and 20th century and, to the best of our knowledge, to the megadroughts that plagued the Southwest US in the medieval period. In the latter, a ?La Ni?a like? state in the tropical Pacific, with cold SST in the eastern equatorial Pacific and a cold tropical troposphere, lead to a similar, poleward displacement of the subtropical jet. We assert that only models that can simulate both kinds of mechanisms can be trusted in future climate projections. We also assert that it is important to identify which of these mechanisms dominate in the climate at any given time for reasons of attribution and prediction. In this presentation we contrast these two types of drought as they affect the Southwest US and the global circulation and attempt to determine which of these types dominates the present.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1620 Climate dynamics (0429, 3309)
DE: 1622 Earth system modeling (1225)
DE: 1626 Global climate models (3337, 4928)
DE: 1637 Regional climate change
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting