The long-term variability of sea level and surface flows in the Gulf of Mexico (GOM) is studied using global monthly sea level reconstruction (RecSL) for 1900–2015. The study explored the long-term relation between the dynamics of the GOM and inflows/outflows through the Yucatan Channel (YC) and the Florida Straits (FS). The results show a century-long trend of increased mean velocity and variability in the Loop Current (LC); however, no significant upward trend was found in the YC and FS flows, only increased variability. Empirical orthogonal function (EOF) analysis of sea surface height found spatial patterns dominated by variations in the LC and temporal variations on time scales ranging from a few months to multidecadal. The time evolution of each EOF mode of sea level is correlated with the velocity of either the LC, the YC, or the FS or some combination of the different flows. The mean sea level difference between the GOM and the northwestern Caribbean Sea was found to be influenced by the North Atlantic Oscillation (NAO), with unusually high differences during the 1970s when the NAO index was low and the Atlantic Ocean circulation was weak. Extreme peaks in SL difference coincide with the extension of the LC and the seasonal eddy shedding pattern. The observed seasonal cycle in the extension area of the LC as obtained from 20 years of altimeter data is significantly correlated (R = 0.63; confidence level = 98%) with the seasonal YC flow obtained from 116 years of the RecSL data. However, the same LC extension record had lower correlation (R = 0.45; confidence level = 90%) with the observed YC transport obtained from direct moored measurements over ~ 5 years, indicating the need for much longer measurements, since the LC extension and the YC flow are strongly affected by interannual and decadal variations. The study demonstrates the usefulness of even a coarse-resolution reconstruction for studies of regional ocean variability and climate change over longer time scales than current direct observations allow.
Long-term hydrographic temperature and salinity transect data in the East China Sea from June 1955 to November 2001 are analyzed
in order to examine the geostrophic velocity and the structure of the Kuroshio current. The structure of the Kuroshio Current
is divided into three basic forms, a single-core structure, a double-core structure and a multi-core structure; the appearance
percentage of the three forms are 53.1%, 31.4%, and 15.4%, respectively. The analysis suggests that multi-core structures
have significant seasonal and interannual variabilities that are not fully understood but may relate to variations in transport
and associated flow instabilities. The Kuroshio's spatial character is also analyzed in detail by applying a simplified model
of motion instability into this multi-core structure of the East China Sea Kuroshio. The theoretical results are found to
be consistent with the observations, suggesting that the instability of the Kuroshio in the East China Sea may bring forth
the formation of the observed multi-core structure. 相似文献
A wetting and drying (WAD) algorithm is implemented in a baroclinic three-dimensional ocean circulation model of Cook Inlet,
Alaska, where large tidal ranges (≈10 m) regularly expose extensive mudflats. The model includes tides and wind- and buoyancy-induced
flows. In the upper Inlet, the model successfully simulates large amplification of tides and propagation of fast (3 ∼ 4 m
s−1) tidal bores over shallow mudflats. The simulated return flows during ebb expose large areas (∼100 km2) of the mudflats. Medium-resolution (250- and 500-m) images obtained from the moderate resolution imaging spectroradiometer
(MODIS) instruments aboard the Terra and Aqua satellites were used to verify the model results by identifying the location,
extent, and temporal changes of the exposed mudflat regions. The results demonstrate the value of operational, medium-resolution
remote sensing data in evaluating the WAD model. Sensitivity tests show that WAD produces approximately 20% larger tidal amplitude
and 10% slower phase than the corresponding experiment without WAD. In the deep channel of the central Inlet, the confluence
of saline water of the lower Inlet with brackish water from rivers and melting ice from land around the upper Inlet produces
a salinity front. At the simulated front, strong vertical circulation cells and surface convergence and currents develop,
especially during the flood. The characteristics resemble those of “rip tides” often observed in this region. 相似文献