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Algorithms
Algorithm for Surface Air-Sea Fluxes:
We used the COARE 3.0b algorithm to compute bulk air-sea fluxes,
including latent and sensible heat flux, net heat flux, and other
associated fluxes such as evaporation, evaporation minus precipitation,
and wind stresses.
These flux data are available for display and delivery at
hourly, daily, 5-day, monthly, and quarterly resolution from
this website
The COARE 3.0b algorithm is detailed in the following article
by Fairall et al. (2003),
"Bulk Parameterization of Air-Sea Fluxes: Updates and
Verification for the COARE Algorithm", C. W. Fairall,
E. F. Bradley, J. E. Hare, A. A. Grachev, and J. B. Edson,
J. Climate, 16, pp 571-591
We downloaded the fortran version of the software from
the following FTP site
Implementation of this algorithm by the TAO Project
of NOAA/PMEL was guided by the recommendations in the
paper by Cronin et al. (2006),
"An assessment of
buoy-derived and numerical weather prediction surface
heat fluxes in the tropical Pacific", JGR, Vol. 111,
C06038,doi:10,1029/2005JC003324
Daily Fluxes:
When computing daily fluxes, the wind speed
input to the bulk algorithm is relative to the surface
current, using in situ current observations where available,
and
OSCAR
currents elsewhere. To minimize biases in flux estimates
from using daily rather than high resolution wind speeds,
the daily wind speeds were further corrected prior to input
into the bulk algorithm using an estimate of
mesoscale gustiness computed from high resolution data
(Cronin et al. 2006).
Daily Net Surface Heat Flux:
Daily net heat flux is computed using the the sensible and latent
heat fluxes from the COARE 3.0b algorithm as well as
observations of shortwave and longwave radiation.
The equation used for computing the net surface heat flux is
qnet = swnet - qlat - qsen - lwnet
where qlat is latent heat flux, qsen is sensible heat flux,
swnet is shortwave radiation corrected for albedo, i.e.,
and lwnet is net longwave radiation defined as
lwnet = epslw * (sbc * (sst + rkel)^4 - lw)
where sst is sea surface temperature, lw is the observed
longwave radiation, epslw = 0.97, sbc = 5.67e-8, and rkel = 273.15.
High Resolution Fluxes:
For computing high resolution fluxes, Cronin et al. (2006)
recommend using hourly averages for all input data, and also using the
warm-layer and cool-skin corrections which are built into
the COARE 3.0b algorithm. To provide the best
possible estimates of the high resolution surface fluxes, we
compute them only at times when there is a complete set of
data inputs, rather than using parameterizations to replace
unavailable data. As with daily data, the wind speed input to
the COARE algorithm is relative to the surface current. In
addition, we also provide high resolution fluxes where
the current is assumed to be zero, to allow fluxes to
be computed at several mooring sites where all of the required
data except currents are available. Both of these high
resolution flux data sets are available from our website
listed above.
High Resolution Net Surface Heat Flux:
High resolution net heat flux is computed the same way as the
daily net heat flux, except that the net shortwave radiation
and net longwave radiation are outputs from the COARE v3.0b
algorithm. This is done so that the net heat flux includes
the effects of the warm layer and cool skin corrections of
the COARE 3.0b algorithm.
Evaporation:
Evaporation in millimeters per hour is computed from the latent
heat flux using the relation
Wind Stresses:
Daily wind stress vector components are computed from the
wind stress magnitude returned from the COARE 3.0b algorithm
(tau) using the following,
where u and v are the zonal and meridinal wind vector components
ad s is the wind speed corrected for gustiness using wg from
the COARE algorithm
Note u and v are relative to the surface sea current.
Input Data Quality:
For all of the flux calculations, we use only data with the
highest two levels of data quality from the TAO, TRITON,
PIRATA, and RAMA arrays.
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