Kinematic structure of an Atlantic cloud cluster during GATE and its time variation

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SIKDAR, DHIRENDRA N. ; HENTZ, STEVEN J. (2011)

This study uses the GATE (GARP Atlantic Tropical Experiment) upper air network in the tropics combined with high resolution SMS-1 (Synchronous Meteorological Satellite) derived winds at low levels, to identify the time-varying kinematics, and mass flux within the region of an intense cloud cluster on September 5, 1974. Satellite data was stored, displayed, and processed on the Man-Computer Interactive Data Access System (McIDAS). Measurements of cloud area expansion covering 20 h determined the cloud cluster stages. Quantitative measurements of the mass flux and kinematic properties of the cluster are given for the growth, growth-mature, and mature-dissipating stages of the cluster. In the growth phase of the cluster strong convergence exists below 900 mb. Relative winds show that the mass inflow to the cluster comes from the west-southwest below 950 mb within the subcloud layer. During the growth-mature stage deep convective system dominates the cluster. Strong low level convergence decreases as divergence at 250 mb becomes dominant. In the growth stage downward motion exists above 600 mb, which becomes strongly upward as the cluster matures. Maximum vertical motion shifts from 800 to 300 mb in the mature-dissipating stage. A mass budget quantitatively describes the horizontal and vertical mass exchanges in and around the cluster. In the growth stage subcloud layer air is horizontally transported from distances greater than 300 km from the cluster center, transported upward in the cluster, and exits in the 800–600 mb layer. The growth-mature stage, characterized by wide-spread deep convection shows that mass is raised at the 200–250 mb layer, where it is transported northward. Most of this mass is supplied by the large scale flow of warm moist air below 950 mb. Relative winds show that deep convection in the cluster is responsible for the upward transport of equatorial air to higher latitudes, supporting the view that cloud clusters are an integral part of the Hadley circulation cell.DOI: 10.1111/j.2153-3490.1980.tb00971.x
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