Heat Transport Components
The western boundary currents in the subtropical gyre of the North Pacific have
three branches: the major branch, Kuroshio, in the ETC; the second branch, East
Ryukyu Current (ERC), to the east of the Ryukyu Islands; the third small branch
in the Taiwan Strait between mainland China and Taiwan, with mean depth of only
60 m.
The 21-month PCM-1 measurement is too short to derive seasonal cycle of the
Kuroshio temperature transport. However, the PCM-1 results suggests robust
linear relationship between the sea level difference across the ETC and the
Kuroshio volume transport (right) and also between the Kuroshio temperature and
volume transport as for the Florida Current (left).
(a) Kuroshio volume transport in the ETC measured by the PCM-1
array and sea level difference across the Kuroshio between Keelung
and Ishigaki.
(b) Kuroshio volume transport climatology (thick dashed) derived from
the SLD of 1989-1996 with the calibration from the PCM-1 measurements;
the seasonal cycle of the temperature transport derived from the
volume transport climatology based on the linear regression of the
figure to the left, with its standard deviation show by dashed curves.
(a) The temperature transport measured by PCM-1 moored current meter
array (solid curve) and that from linear regression of the temperature
and volume transports (dashed curve). The correlation is
0.99. (b) The linear regression of the temperature and volume transport
of the Kuroshio measured by the PCM-1 array,
and that of the Florida Current,
derived from monthly climatology of Molinari et al. (1990).
The seasonal cycle of the volume transport in the Taiwan Strait. In this
shallow and well mixed strait, the temperature transport is simply the product
of the volume transport and the cross-strait mean temperature derived station
data in NODC WOD (1998).
The seasonal variation of northward volume transport in the
Taiwan Strait derived from Mariano ship drift climatology and Zhao and
Fang (1991) estimates, in comparison to the POP simulation and the
transport anomalies (right axis) from the longshore wind-forced analytical
model of Lee and Williams (1988).
According to the breakdown of (1), the total contribution of the branches
through the ETC and the Taiwan Strait to the meridional heat flux is called the
Kuroshio component, QK.
The contribution of the ERC is included in the
interior baroclinic heat flux component, QI,
similar to the treatment of
currents east of the Bahamas in the North Atlantic (e.g., Hall and Bryden,
1982). Analogous to the currents east of the Bahamas (e.g., Fillenbaum et al.,
1997), the ERC's barotropic contribution to meridional heat flux is essentially
negligible because its vertical mean potential temperature is close to the
cross-section mean potential temperature, and this approximation will be
accounted for in the error analysis.
Ekman heat fluxes calculated from four wind products and Levitus94.
Ekman heat fluxes calculated from four wind products and Levitus
climatology. The mean of all four wind estimates is also shown which
is used as the best estimate for the heat flux.
Final estimates of the three heat flux components and total meridional heat
transport across 24°N with error bar.
Final estimate of trans-Pacific heat flux at 24°N with error bar.
(a) through (c) are the Kuroshio, interior geostrophic baroclinic, and
Ekman components, with annual means: 1.58±0.07 PW,
-1.81±0.15 PW, and 0.78±0.07 PW. (d)
is the total heat flux, whose annual mean is 0.55±0.21 PW. The
error bar included the upper bound of possible barotropic correction term
(0.11 PW) related to the East Ryukyu Current.
The 21-month PCM-1 measurement is too short to derive seasonal cycle of the Kuroshio temperature transport. However, the PCM-1 results suggests robust linear relationship between the sea level difference across the ETC and the Kuroshio volume transport (right) and also between the Kuroshio temperature and volume transport as for the Florida Current (left).
(a) Kuroshio volume transport in the ETC measured by the PCM-1 array and sea level difference across the Kuroshio between Keelung and Ishigaki. (b) Kuroshio volume transport climatology (thick dashed) derived from the SLD of 1989-1996 with the calibration from the PCM-1 measurements; the seasonal cycle of the temperature transport derived from the volume transport climatology based on the linear regression of the figure to the left, with its standard deviation show by dashed curves.
(a) The temperature transport measured by PCM-1 moored current meter array (solid curve) and that from linear regression of the temperature and volume transports (dashed curve). The correlation is 0.99. (b) The linear regression of the temperature and volume transport of the Kuroshio measured by the PCM-1 array, and that of the Florida Current, derived from monthly climatology of Molinari et al. (1990).
The seasonal cycle of the volume transport in the Taiwan Strait. In this shallow and well mixed strait, the temperature transport is simply the product of the volume transport and the cross-strait mean temperature derived station data in NODC WOD (1998).
According to the breakdown of (1), the total contribution of the branches through the ETC and the Taiwan Strait to the meridional heat flux is called the Kuroshio component, QK. The contribution of the ERC is included in the interior baroclinic heat flux component, QI, similar to the treatment of currents east of the Bahamas in the North Atlantic (e.g., Hall and Bryden, 1982). Analogous to the currents east of the Bahamas (e.g., Fillenbaum et al., 1997), the ERC's barotropic contribution to meridional heat flux is essentially negligible because its vertical mean potential temperature is close to the cross-section mean potential temperature, and this approximation will be accounted for in the error analysis.
Ekman heat fluxes calculated from four wind products and Levitus94.
Final estimates of the three heat flux components and total meridional heat transport across 24°N with error bar.
