GOALS (Global Ocean-Atmosphere-Land System) for Predicting Seasonal-to-Interannual Climate A Program of Observation, Modeling, and Analysis (1994) / Chapter Skim
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3 LARGE-SCALE INTERACTIONS AMONG THE UPPER OCEAN, ATMOSPHERE, AND LAND
3 LARGE-SCALE INTERACTIONS AMONG THE UPPER OCEAN, ATMOSPHERE, AND LAND
Pages 21-36
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From page 21... ...
indicates that these convective clouds tend to be clustered together in large agglomerations, which are referred to here as "heat sources." There are three major localized heat sources: one is centered over the Amazon basin; one is over tropical Africa; and the largest one is over the "maritime continent," which comprises Indonesia, Malaysia, the surrounding islands, and adjacent oceanic regions. In addition to these localized heat sources, there are also the somewhat rectilinearshaped sources characteristic of the Intertropical Convergence Zones (ITCZs)
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From page 23... ...
Indeed, it is the interannual motion of this heat source that can be identified with the ENSO phenomenon. During warm phases of ENSO, the maritime-continent heat source expands eastward into the anomalously warm tropical Pacific; during cold phases, it contracts back into the warm western Pacific.
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From page 24... ...
Contour interval of 1K for SST; OLR values below 240 Wm~2, indicated by the shading, are associated with regions of enhanced deep convective clouds. SST and surface winds after Sadler et al.
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From page 25... ...
Thus, the motion of the maritime-continent heat source in the tropical Pacific due to SST variations in the tropical Pacific is only part of the puzzle. In general, climate variations in the tropics can be viewed as modulations and movements of the tropical heat sources, each affected by its underlying ocean, by combinations of ocean and land, or by land alone, and by interactions with other heat sources.
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From page 26... ...
In spite of these difficulties, the influence of the tropics on the midlatitudes has been demonstrated by numerical model experiments that show that the more realistic the simulation of tropical heat sources, the more realistic the simulation of midlatitude circulation. The western boundary ocean currents (the Gulf Stream, for example)
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From page 27... ...
Adequate initialization and assimilation procedures to specify the initial land-surface properties, including soil moisture arid snow cover, and realistic parameterizations of energy and momentum exchanges between the land surface and atmosphere need to be developed for this potential predictability to be fully understood and utilized. Finally, the question arises as to whether anomalies in midlatitude
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From page 28... ...
Subseasonal Variability Short-term climate variability is often obscured by fluctuations on the subseasonal time scale. Of particular importance in this regard are the eastward-propagating planetary waves with periods on the order of 40 to 60 days, which modulate convection and perturb the surface wind field over the tropical Indian and western Pacific sectors (Madden and Julian, 1971~.
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From page 29... ...
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From page 30... ...
In certain situations, analysis of the high-frequency variability can yield important insights into physical processes that operate across the full range of time scales. For example, Figure 3-4 shows time series of surface wind speed, insolation, and subsurface temperature at one of the TOGA TAO moorings over a 10-day period.
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From page 31... ...
An understanding of and ability to predict the interannual fluctuations that are of interest to GOALS depend on the ability to simulate and explain the annual cycle. The circulation changes associated with short-term climate variability represent relatively small distortions in the climatological mean annual cycle.
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From page 32... ...
Many such features can be understood as a direct response to the annual cycle in insolation, but some of the other features are no less difficult to explain than the ENSO cycle. For example, the observed meridional shifts in the ITCZs, which account for the single pronounced rainy season around March over much of equatorial South America, appear to be a consequence of complex interactions involving upwelling in the equatorial cold tongues, vertical mixing and evaporation, changes in the overlying stratus clouds, and changes in surface winds induced by the continental monsoons.
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From page 33... ...
The accompanying slow evolution of SST anomalies in the eastern Pacific is due to an atmosphere-ocean instability modulated by the effects of slowly propagating equatorial ocean waves and equilibrated by nonlinear processes in the atmosphere and ocean. ENSO manifests itself through the expansion of warm SSTs and heavy rainfall eastward into the Pacific, thereby modulating the annual cycle in the eastern part of the basin.
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From page 34... ...
Warm wintertime surface air temperature anomalies downstream over western Canada that occurred in association with the same atmospheric teleconnection pattern contributed to the observed warmth of the Northern Hemisphere during the 1980s relative to the previous three decades (Trenberth, 1990; Trenberth and Hurrell, 1994~. It is not clear whether this long-lived "regime shift" is rooted in the ENSO cycle itself or whether it is of extratropical origin (Trenberth, 1990~.
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From page 35... ...
Such processes include desertification, variability of the eastern and western boundary currents, the gyre circulations and their associated poleward heat fluxes, and relationships between the atmospheric circuIatiorr, sea-ice extent, salinity, and the production of bottom water in the marginal ice zones.
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