Atmospheric boundary layer over the central and western equatorial Pacific Ocean observed during COARE and CEPEX

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Abstract

The present study is based on aircraft data collected in the western and central equatorial Pacific as a part of the Coupled Ocean-Atmosphere Response Experiment (COARE) and the Central Equatorial Pacific Experiment (CEPEX). The purpose of this discussion is to provide some insight into the coupling of the atmosphere to the ocean in regions of light winds and high humidity, as well as near deep organized convection, and to compare and contrast these climatically important tropical regions. The results presented use both the aerial extent of cold cloud top temperatures and surface layer similarity to highlight the variation of the surface fluxes as a function of convective regimes. A wide range of convective conditions were encountered during the 5 months of COARE and CEPEX, ranging from deep, towering anvils to shallow trade cumuli. The variety of conditions sampled has provided a unique set of turbulence data over open ocean, which are compared to fundamental spectral forms. Results suggest that assumptions regarding surface layer processes based on a large-scale assessment of the convective conditions are likely to be inaccurate. For example, during free convective conditions, where buoyancy production dominates over mechanical production of turbulence in the boundary layer, surface heat and buoyancy fluxes are enhanced for the given wind conditions, compared to those observed for forced convection, due to transport by buoyant plumes. This highlights the importance of considering the effect of the buoyancy flux on the vertical velocity variance in light winds in the parameterization of the surface fluxes. For forced convective conditions, where cloud circulations cause enhanced mechanical turbulence and reduced buoyancy in the boundary layer, surface fluxes are enhanced, as are the scales of turbulent eddies, drawing surface heat and moisture away from the surface. As with buoyant plumes, this process needs to be considered by surface flux parameterizations early enough in the convective process in order to accurately represent the role of the surface in the development of convection. While the temperature of the warm pool region in COARE is found to be largely independent of local conditions measured by the aircraft, we observe that the warmest temperatures (>30°C) coincide exclusively with the lightest winds, which highlights the importance of wind-driven mixing in determining the thermal structure of the upper ocean.

Original languageEnglish (US)
Pages (from-to)23217-23237
Number of pages21
JournalJournal of Geophysical Research: Space Physics
Volume102
Issue numberC10
StatePublished - 1997
Externally publishedYes

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atmospheric boundary layer
Atmospheric boundary layer
Pacific Ocean
surface flux
oceans
boundary layer
buoyancy
atmospheres
atmosphere
ocean
turbulence
convection
Fluxes
Buoyancy
experiment
Experiments
surface layer
parameterization
aircraft
plume

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)
  • Atmospheric Science
  • Geochemistry and Petrology
  • Geophysics
  • Oceanography
  • Space and Planetary Science
  • Astronomy and Astrophysics
  • Earth and Planetary Sciences(all)
  • Environmental Science(all)

Cite this

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title = "Atmospheric boundary layer over the central and western equatorial Pacific Ocean observed during COARE and CEPEX",
abstract = "The present study is based on aircraft data collected in the western and central equatorial Pacific as a part of the Coupled Ocean-Atmosphere Response Experiment (COARE) and the Central Equatorial Pacific Experiment (CEPEX). The purpose of this discussion is to provide some insight into the coupling of the atmosphere to the ocean in regions of light winds and high humidity, as well as near deep organized convection, and to compare and contrast these climatically important tropical regions. The results presented use both the aerial extent of cold cloud top temperatures and surface layer similarity to highlight the variation of the surface fluxes as a function of convective regimes. A wide range of convective conditions were encountered during the 5 months of COARE and CEPEX, ranging from deep, towering anvils to shallow trade cumuli. The variety of conditions sampled has provided a unique set of turbulence data over open ocean, which are compared to fundamental spectral forms. Results suggest that assumptions regarding surface layer processes based on a large-scale assessment of the convective conditions are likely to be inaccurate. For example, during free convective conditions, where buoyancy production dominates over mechanical production of turbulence in the boundary layer, surface heat and buoyancy fluxes are enhanced for the given wind conditions, compared to those observed for forced convection, due to transport by buoyant plumes. This highlights the importance of considering the effect of the buoyancy flux on the vertical velocity variance in light winds in the parameterization of the surface fluxes. For forced convective conditions, where cloud circulations cause enhanced mechanical turbulence and reduced buoyancy in the boundary layer, surface fluxes are enhanced, as are the scales of turbulent eddies, drawing surface heat and moisture away from the surface. As with buoyant plumes, this process needs to be considered by surface flux parameterizations early enough in the convective process in order to accurately represent the role of the surface in the development of convection. While the temperature of the warm pool region in COARE is found to be largely independent of local conditions measured by the aircraft, we observe that the warmest temperatures (>30°C) coincide exclusively with the lightest winds, which highlights the importance of wind-driven mixing in determining the thermal structure of the upper ocean.",
author = "Yolande Serra",
year = "1997",
language = "English (US)",
volume = "102",
pages = "23217--23237",
journal = "Journal of Geophysical Research: Space Physics",
issn = "2169-9380",
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