HR: 1340h
AN: A13B-0922    [Abstracts]
TI: Tropical Climate Regimes in a Simple Setting
AU: * Barsugli, J
EM: joseph.barsugli@noaa.gov
AF: NOAA-CIRES Climate Diagnostics Center, 325 Broadway, R/CDC1, Boulder, CO 80305 United States
AU: Shin, S
EM: Sangik.Shin@noaa.gov
AF: NOAA-CIRES Climate Diagnostics Center, 325 Broadway, R/CDC1, Boulder, CO 80305 United States
AU: Sardeshmukh, P D
EM: prashant.d.sardeshmukh@noaa.gov
AF: NOAA-CIRES Climate Diagnostics Center, 325 Broadway, R/CDC1, Boulder, CO 80305 United States
AB: Multiple tropical climate regimes are found in a global atmospheric general circulation model (AGCM) couŠpled to a global slab ocean when the model is forced by different values of globally uniform insolation. Even in this simple setting, convection organizes into an Intertropical Convergence Zone (ITCZ) solely due to the effect of planetary rotation, as was found in Kirtman and Schneider (2000) for a single value of insolation. Here the response to a range of insolation values is explored and surprisingly, multiple climate regimes characterized by radically different ITCZ structures are found. In order from the coldest to warmest climates these are: a symmetric double ITCZ, a near-symmetric equatorial ITCZ, a transient asymmetric ITCZ, and a stable, strongly asymmetric ITCZ. The model exhibits hysteresis in the transition from the near-symmetric to the strongly asymmetric ITCZ regimes when insolation is increased and then decreased. The initial transition away from symmetry can occur in the absence of air-sea coupling; however, the coupling is essenŠtial for the establishment and maintenance of the strongly asymmetric ITCZ. Wind-evaporation-SST feedback as well as the longwave radiative effects of clouds and water vapor on SSTs all appear to be important in maintaining the asymmetric regime. The existence of multiple regimes in a single AGCM, and the dependence of these regimes on SST feedbacks, may have a bearing on the ITCZ simulation errors of current coupled climate models. The sensitivity of the global mean surface temperature generally decreases with increasing insolation, a consequence primarily of increasingly negative shortwave cloud forcing. Climate sensitivity measured across a regime transition can be much larger than the sensitivity within a single regime.
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
DE: 3314 Convective processes
DE: 3319 General circulation (1223)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005