HR: 1340h
AN: A43A-0034    [Abstracts]
TI: Mechanisms of the Remote Tropical Precipitation Reduction During El Ni\~{n}o
AU: * Lintner, B R
EM: ben@atmos.berkeley.edu
AF: Department of Geography, University of California, 507 McCone Hall, Berkeley, CA 94720-4740 United States
AU: Chiang, J C
EM: jchiang@atmos.berkeley.edu
AF: Department of Geography, University of California, 507 McCone Hall, Berkeley, CA 94720-4740 United States
AB: During El Ni\~{n}o phases, negative rainfall anomalies are evident across many portions of the tropics outside of the Pacific (hereinafter ``the remote tropics''). In this paper, we make use of an intermediate level complexity model (the Quasi-equilibrium Tropical Circulation Model or QTCM) and its ``single column'' analogue (the Single Column QTCM or SCQTCM) to investigate the mechanisms underlying the remote tropical precipitation reduction during El Ni\~{n}o. Specifically, we focus on the ``equilibrated precipitation response'', i.e., the precipitation anomalies that occur after the remote tropics has adjusted to a time-invariant El Ni\~{n}o forcing. In both the QTCM and SCQTCM, widespread remote tropical precipitation reductions are simulated, although there are some differences in the magnitude and spatial patterns of the precipitation response between the two models. Using the SCQTCM---which represents the remote tropics as a set of disconnected columns in which both tropospheric temperature and horizontal circulation are imposed---we show that anomalous tropospheric temperature forcing (as opposed to anomalous horizontal circulation) accounts for the largest fraction of the precipitation reduction. Moreover, through application of spatially uniform and nonuniform anomalous tropospheric temperature forcing scenarios to the SCQTCM, we find that only the latter produces an El Ni\~{n}o-like distribution of precipitation anomalies. By contrast, the uniform forcing scenario produces a distinctly different pattern of anomalies, namely enhanced precipitation over deep convective zones and decreased precipitation elsewhere. That the SCQTCM produces an El Ni\~{n}o-like anomalous precipitation field when forced with tropospheric temperature alone points to the potentially significant role of tropospheric temperature as a generator of the equilibrium precipitation response to El Ni\~{n}o. However, it appears that nonuniformities (gradients) in tropospheric temperature, rather than the uniform warming of temperature itself, are crucial to the establishment of the remote tropical precipitation anomalies during El Ni\~{n}o.
DE: 3332 Mesospheric dynamics
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3374 Tropical meteorology
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting