Plan for U.S. Participation in the GARP Atlantic Tropical Experiment (1971) / Chapter Skim
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SCIENTIFIC OBJECTIVES
SCIENTIFIC OBJECTIVES
Pages 4-12
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From page 4... ...
The first approach requires detailed knowledge of the internal structure of convection and how it responds to changes in the synoptic-scale environment, while the second approach is mainly concerned with relating the bulk properties of convective ensembles to the synoptic-scale fields. Both approaches are consistent with the overall objectives of GARP, yet each suffers from inherent shortcomings.
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From page 5... ...
Here, as in the field of atmospheric turbulence, a coordinated effort to understand both the internal structure and the bulk properties represents the path to progress. Thus, an experiment is envisioned that will provide simultaneous measurements of: (a)
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From page 6... ...
In fact, it appears that many of the Pacific systems can be traced backward across the Atlantic to an origin over Africa. Synoptic systems of the tropical North Atlantic summer season have been classed in four categories: 1.
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From page 7... ...
When the westward moving ITCZ and tradewind disturbances come under the influence of the upper-tropospheric trough, in the region of the Antilles, a sudden flareup of the convective activity is often observed. At the present time, considerable uncertainty exists regarding the structure and energetics of all three types of disturbance mentioned above and the nature of the interactions that take place between them because of the lack of radiosonde data.
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From page 8... ...
Gusty surface winds and cool temperatures associated with downdrafts cause a local enhancement of sensible heat flux from the sea surface, which results in a rather rapid modification of the downdraft air. Organized cloud groups apparently originate when the low-level mixed layer attains a thickness such that it extends above the condensation level of the air within it, over a distance roughly 10 km on a side.
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From page 9... ...
Many of the following statistics represent averages of many individual systems obtained from these studies. Disturbed weather tends to occur near or slightly east of the low-level troughs in "cloud clusters" with dimensions on the order of 2-10° of latitude on a side.
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From page 10... ...
The problem is that in order to make use of this concept in numerical prediction models, it is necessary to make additional assumptions in order to relate the subcloud layer convergence to the synoptic-scale motion field and to parameterize the collective effects of the convection upon the synoptic motions. At present, we are lacking a sound physical basis for these assumptions.
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From page 11... ...
It has been mentioned that much of the convergence of mass and moisture into regions of disturbed weather takes place above the subcloud layer. The vertical profile of synoptic-scale divergence may represent the superposed effects of three types of internal circulation; buoyant updrafts, which carry subcloud air upward to near the 200-mbar level; entrainment into updrafts; and evaporatively cooled downdrafts, which replace some of the loss from the subcloud layer with air that has entered the region from above.
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From page 12... ...
While no one hypothesis is presently capable of explaining the complicated convective phenomena of the tropics, existing hypotheses, such as CISK, at least focus attention on events in the subcloud and frictional boundary layers as deserving of concerted observation.
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