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A satellite-based study of ocean-atmosphere heat fluxes in the vicinity of John Brewer Reef, Queensland

Michael, Kelvin John (1988) A satellite-based study of ocean-atmosphere heat fluxes in the vicinity of John Brewer Reef, Queensland. PhD thesis, University of Tasmania.

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Abstract

This study investigates the use of satellite observations for determining the
exchange of radiation and turbulent heat fluxes between the ocean and atmosphere.
Meteorological observations and radiation fluxes were collected for 45 weeks at John
Brewer Reef (18° 38' S, 147° 4 'E), approximately 70 km north-northeast of
Townsville, Australia. Estimates of the mean weekly radiation and turbulent heat
fluxes through the ocean surface were derived from concurrent satellite observations,
and compared with surface-based estimates.
The net radiation flux was separated into four components. The downwelling
shortwave radiation flux was derived from GMS-3 visible image data, initially on a
daily basis, using a model of atmospheric shortwave transmittance. The weekly
average downwelling shortwave radiation flux was estimated with a root mean square
accuracy of 14.3 Wm-2. The upwelling shortwave radiation flux was parameterised
as a simple function of season. Downwelling longwave radiation flux was estimated
with a complex scheme. A radiative transfer model (LOWTRAN 6) was employed to
calculate downwelling longwave radiation fluxes under clear and totally overcast skies
with atmospheric profiles derived from NOAA-9 TOYS sounding data. The cloud
fraction, as determined from GMS-3 visible images, was used to produce a weighted
average of the two downwelling longwave radiation fluxes. The weekly average
downwelling longwave radiation flux was produced with a rms accuracy of
9.1 Wm-2. The upwelling longwave radiation flux was provided primarily by the sea
surface temperature, which was obtained on a weekly basis from a product which
combined multi-channel satellite-derived temperatures with surface measurements from
ships-of-opportunity. The rms accuracy of the resulting weekly average upwelling
longwave radiation flux was 3.0 Wm-2. The weekly average net radiation flux was
reproduced with arms accuracy of 18.9 Wm-2.
The turbulent heat flux was dominated by the latent heat flux, which was
modelled according to the bulk aerodynamic approach. The weekly-averaged specific humidity difference between the sea surface and the ten metre level was derived as a
simple function of the weekly-averaged precipitable water vapour in the atmosphere, as
estimated by NOAA-9 TOVS data. Wind speeds were obtained from a standard
meteorological wind analysis which included the region of John Brewer Reef. The
weekly-averaged values of the latent heat flux were reproduced with arms accuracy of
39.6 W m-2. The sensible heat flux, which was in general a small term, was estimated
as a fraction of the latent heat flux. The total turbulent heat flux was modelled with a
rms accuracy of 45.4 Wm-2.
The heat balance of a hypothetical column of water near John Brewer Reef was
considered. A comparison was drawn between the radiation and heat fluxes through
the upper surface of the column and the variations in the heat content of the column as
evidenced by temporal changes in its sub~surface temperature profile. A limited
quantity of information on the current fields and the spatial distribution of sub-surface
water temperatures allowed the discussion of oceanic advection of heat on an order-of
magnitude basis only. It was determined that advection made a significant contribution
to the heat balance of the column in winter only.
The satellite-derived radiation and turbulent heat flux estimates were extended
to form spatial averages over a mesoscale region and temporal averages for five
weekly periods. The fluxes were calculated for the corresponding area and period with
data extracted from marine weather reports, representing the traditional source of
mesoscale, mean monthly ocean-atmosphere heat fluxes. Differences between the
fluxes derived from the marine observations and those estimated by satellite were
larger than, expected, considering the accuracy displayed by the satellite estimates in the
neighbourhood of John Brewer Reef. The implication is that the superior temporal and
spatial resolution of satellite observations allows better reproduction of the surface heat
and radiation fluxes than the traditional approaches.

Item Type: Thesis (PhD)
Keywords: Ocean-atmosphere interaction, Oceanography
Copyright Holders: The Author
Copyright Information:

Copyright 1988 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)-University of Tasmania, 1989. Bibliography: leaves 273-303. Map on folded leaf in pocket

Date Deposited: 03 Feb 2015 03:03
Last Modified: 10 Nov 2017 04:02
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