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P. Anil Rao
and
Henry E. Fuelberg

Abstract

A three-dimensional numerical simulation of land–water circulations near Cape Canaveral, Florida, is performed using the Advanced Regional Prediction System. The role of Kelvin–Helmholtz instability (KHI) in determining the time and location of convection behind the sea-breeze front is examined. The model configuration attempts to improve upon limitations of previous work (e.g., resolution, surface characteristics, initial state). It provides a detailed and realistic simulation of the desired features.

The simulation exhibits a single precipitating storm that forms behind the sea-breeze front. This postfrontal storm develops when an outflow boundary intersects a deep layer of upward motion above the marine air. The region of ascent initially is the remnant of a cell that formed along the sea-breeze front, but before the cell decays, a portion of its upward motion is intensified and displaced. The modification of the ascent is a product of KHI that is occurring on top of the sea-breeze interface in the form of billows. The region of enhanced ascent then moves backward with the billow until the outflow boundary arrives. Thus, KHI can be critical in determining the location and time of storm development that occurs behind the Cape Canaveral sea-breeze front.

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P. Anil Rao
,
Henry E. Fuelberg
, and
Kelvin K. Droegemeier

Abstract

The Advanced Regional Prediction System is used to perform a three-dimensional numerical simulation of land–water circulations near Cape Canaveral, Florida. Three two-way nested grids having spacings of 1.6, 0.4, and 0.1 km are employed. Results show that the structures of both the sea and river breezes compare well with observation and theory.

Horizontal convective rolls (HCRs), Kelvin–Helmholtz instability (KHI), and their interactions with the sea and river breezes also are investigated. HCRs form over the heated land surface at periodic intervals. The HCRs have two preferred spatial scales: large and small. Inclusion of both the large and small HCRs yields aspect ratios that are smaller than most previous observations. However, when considering only the larger HCRs, agreement is better. The smaller HCRs eventually dissipate or merge with their larger HCR counterparts. These mergers intensify the vertical motion within the larger circulations.

The HCRs are observed to tilt upward in advance of the Indian River breeze (IRB), and then advect over and behind the land–water circulation. There is evidence that an HCR advects 2.5 km behind the surface front. The orientation of the IRB causes its interaction with an HCR to change from an intersection to a merger. This produces positive vertical vorticity that causes the IRB to rotate counterclockwise. The detailed physiography and surface characteristics used in this research allow these complex asymmetric interactions to be simulated.

In addition, the configuration of this simulation allows an even smaller-scale feature, KHI, to be observed on top of and behind the Indian River breeze front. It appears as vortices or billows that grow in amplitude and propagate backward relative to the front. The structure of the billows agrees well with previous theoretical and modeling results. Local regions of upward motion associated with the billows may be a preferred area for postfrontal convection.

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