The Behavior of the Atmospheric Boundary Layer in the Vicinity of the Gulf Stream Sea Surface Temperature Front
The Behavior of the Atmospheric Boundary Layer in the Vicinity of the Gulf Stream Sea Surface Temperature Front

Author: Hanyuan Liu

Publisher:

Published: 2023

Total Pages: 0

ISBN-13:

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The evolution of the marine atmospheric boundary layer (MABL) in the vicinity of a sea surface temperature (SST) front is of particular research interest, as the large air-sea temperature and humidity differences at the surface fuels various physical processes inside the boundary layer, causing intense heat and momentum exchange. Such processes make the mesoscale MABL an ocean-drive-atmosphere scenario. Dominant mechanisms, although having been studied intensively, are still yet to be fully understood due to the highly turbulent nature of the MABL. Previous studies often relied on satellite-derived SST and wind fields to investigate boundary layer dynamics, yet the coarse spatial and temporal resolution of such a method limits the understanding of the MABL evolution on shorter timescales. In this thesis, a combination of in situ data and model simulations is used to investigate the MABL response to the SST front in the Gulf Stream region on a timescale of one day or less. Analysis of MABL structure is divided into three categories depending on the background wind strength and its direction relative to the front: cold to warm, parallel/weak, and warm to cold. Two mechanisms identified in previous studies, vertical mixing and thermally induced pressure gradient, and their role in MABL evolution, are studied quantitatively. A comparison between observations and model simulations allows further analysis of the contribution of moist processes that were often considered to be of secondary importance in the past even over the ocean. Results show that vertical mixing is responsible for the majority of the MABL deepening, while the pressure adjustment's effect is more significant when the cross-frontal wind is weak. Sensitivity tests conducted in the Weather Research and Forecast (WRF) also show that moisture processes, including surface latent heat, boundary layer transport of moist, and cloud formation, further enhance the mixing that drives MABL changes.

The Marine Boundary Layer in the Vicinity of an Ocean Front
The Marine Boundary Layer in the Vicinity of an Ocean Front

Author: David P. Rogers

Publisher:

Published: 1989

Total Pages: 20

ISBN-13:

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Aircraft observations obtained during the Frontal Air-Sea Interaction Experiment (FASINEX) are used to investigate the structure of the marine atmospheric boundary layer in the vicinity of an ocean front. A quasi-stationary sea surface temperature (STT) discontinuity of 2 C was maintained across the frontal zone throughout the duration of the experiment. The primary response of the atmosphere to changes in the SST was observed in the surface-related turbulence fluxes. In the case of warm air flowing over cold water, the boundary layer appears to develop an internal boundary layer (IBL) in response to the sudden change in the sea surface temperature. The organized updrafts and downdrafts within this layer collapse with entrainment-detrainment processes in these cells dominating the turbulence statistics. The IBL grows in response to the wind shear in this layer, although the surface shear stress is much smaller on the colder side of the front than on the warm. The depth of the IBL, and, in the absence of the IBL, the mixed layer are found to scale with the friction velocity and the Coriolis parameter. The IBL confines the surface-related turbulent mixing and shear-driven processes to the lower layers of the atmosphere. Thus, the shallow boundary layer cloud field appears to be maintained primarily by radiative transfer within the cloud layer. Multiple cloud-capped mixed layers were frequently observed throughout the experiment. They appear to be directly related to the horizontal variation of SST with deeper boundary layers and higher cloud levels formed over warmer water. Air water interactions; Reprints. (edc).

Air-Sea Exchange: Physics, Chemistry and Dynamics
Air-Sea Exchange: Physics, Chemistry and Dynamics

Author: G.L. Geernaert

Publisher: Springer Science & Business Media

Published: 2013-04-17

Total Pages: 573

ISBN-13: 9401592918

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During the 1980's a wealth of information was reported from field and laboratory experiments in order to validate andlor modify various aspects of the surface layer Monin-Obukhov (M-O) similarity theory for use over the sea, and to introduce and test new concepts related to high resolution flux magnitudes and variabilities. For example, data from various field experiments conducted on the North Sea, Lake Ontario, and the Atlantic experiments, among others, yielded information on the dependence of the flux coefficients on wave state. In all field projects, the usual criteria for satisfying M-O similarity were applied. The assumptions of stationarity and homogeneity was assumed to be relevant over both small and large scales. In addition, the properties of the outer layer were assumed to be "correlated" with properties of the surface layer. These assumptions generally required that data were averaged for spatial footprints representing scales greater than 25 km (or typically 30 minutes or longer for typical windspeeds). While more and more data became available over the years, and the technology applied was more reliable, robust, and durable, the flux coefficients and other turbulent parameters still exhibited significant unexplained scatter. Since the scatter did not show sufficient reduction over the years to meet customer needs, in spite of improved technology and heavy financial investments, one could only conclude that perhaps the use of similarity theory contained too many simplifications when applied to environments which were more complicated than previously thought.

Properties of the Atmospheric Boundary Layer Above a Subtropical Oceanic Front
Properties of the Atmospheric Boundary Layer Above a Subtropical Oceanic Front

Author: John P. Higgins

Publisher:

Published: 1987

Total Pages: 99

ISBN-13:

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The marine atmospheric boundary layer (MABL) and synoptic-scale situation is described using rawinsonde and sea-surface temperature (SST) data collected during the 1986 Frontal Air-Sea Interaction Experiment (FASINEX). The data obtained from 14 February to 09 March 1986 are divided into eight consecutive three-day periods and analyzed. Significant changes in synoptic-scale features and flow patterns occurred during each three-day period due to movement of low pressure systems. MABL changes noted were due primarily to large scale convergence. Thirteen pairs of rawinsonde launches, seven from opposite sides of an oceanic front and six from the same side (five warm, one cold) are compared. The time difference between soundings in each pair did not exceed sixty minutes. Boundary layer height, mixed layer potential temperature and specific humidity differences between paired rawinsonde launches were larger when launches were from opposite sides of the oceanic front. A combination of both shipboard and aircraft data will be necessary to further describe the conditions of the MABL and synoptic-scale situation.

Synthetic Aperture Radar
Synthetic Aperture Radar

Author: Christopher R. Jackson

Publisher: National Environmental Satellite, Data, & Information Service

Published: 2004

Total Pages: 464

ISBN-13: 9780160732140

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Describes the types of information available from spaceborne images of the ocean.