Environmental Engineering Reference
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the algorithm error (Zeng et al.
1998
;Brunkeetal.
2002
,
2003
). Brunke et al. (
2011
)
evaluate six reanalysis (MERRA, ERA-40, ERA-Interim, NCEP/NCAR, NCEP/DOE,
and CFSR), four satellite-based flux products (GSSTF2, GSSTF2b, J-OFURO2, and
HOAPS), and the merged product (OAFlux) by comparison with direct covariance
LHF and SHF and inertial-dissipation wind stress measurements from cruises over the
tropics and mid- and high latitudes. The biases range from
3.0to20.2Wm
2
for
10
3
Nm
2
for wind stress. The
ranges of the biases are small for moderate wind speeds but diverge for strong wind
speeds (10-20 m s
1
). The bulk variable-caused uncertainty dominates SHF and wind
stress biases of many products. MERRA is found to be the “best performing” among all
three reanalysis-based fluxes. Of the satellite-based products, GSSTF2b is among “best
performing” for LHF and SHF.
1.4 to 6.0Wm
2
for SHF, and
LHF,
7.6to7.9
11.6 Summary and Outlook
Satellite-based ocean surface turbulent flux products have been improved in recent
years with better understanding of the mechanisms of air-sea exchange leading to
improved bulk flux algorithms. The improved algorithms are complemented by
more accurate satellite retrievals of input meteorological and oceanic variables.
Discrepancies among these products are mostly due to different input variables.
“Trends” in these products have been noted (Chiu et al.
2008
) and can mostly be
attributed to satellite attitude and inter-satellite calibrations. More accurate satellite
attitude calculations (Hilburn and Shie
2011
) and efforts to recalibrate all SSM/I
satellites, such as the development of the “fundamental climate data record” by
NOAA (Kummerow
2009
), will lead to more homogeneous microwave data sets
that will be applicable for climate studies.
Accurate turbulent air-sea flux estimates are crucial for advancing our under-
standing of the dynamics of air-sea interactions at the mesoscale to global scale.
Assessment of the trends and variabilities will help quantify the relative role of the
atmosphere and ocean in global change. At the basin and regional scales, LHF has
shown to impact monsoons and hurricanes (Gautam et al.
2005
; Gao and Chiu
2010
), and the inclusion of LHF derived from the OAFlux merged products has a
significant impact on the prediction of typhoon intensity (Gao and Chiu
2012
). The
major limitations of satellite-based flux products for tropical cyclone studies are
their relatively coarse spatial and temporal resolution or limited coverage. High-
resolution (0.25
) ocean surface turbulent flux data sets aimed at the regional to
hurricane scales have been or are being produced (Shie et al.
2009
; Liu et al.
2011
).
From these new data sets, improved understanding of the dynamics of air-sea
interactions at global to regional scales will emerge, and their impact on operational
applications and climate studies will soon be realized.
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