Subinertial to interannual transport variations in the Korea Strait and their possible mechanisms

Abstract

The voltage‐derived transport in the Korea Strait from March 1998 to April 2002 reveals various temporal variations such as subinertial, monthly, seasonal, and interannual variations. The driving mechanisms of these temporal variations in the flows through the straits and the mean sea level of the East Sea (Sea of Japan) are investigated using a simple analytical barotropic model. The East Sea is simplified as a flat‐bottomed semienclosed basin, and it is forced by the atmospheric pressure, the along‐strait wind stress, and the sea level differences along the straits. Despite its simplicity this model explains most variations and helps us understand dominant driving forces on each timescale. At the subinertial periods of 2–10 days the atmospheric pressure dominantly drives the flows into or out of the East Sea due to a Helmholtz resonance, whose period is about 3 days, and the mean sea level cannot respond isostatically. The effects of the atmospheric pressure on the transport variations become weak at long periods because there is enough time for the East Sea to be drained or filled through the strait flows as its mean sea level responds isostatically. On the other hand, the changes in the adjusted sea levels outside the straits of the East Sea cause the pressure gradient forces along the straits and induce most of variations in the strait flows and the mean sea level at the monthly to interannual periods.

The Annual Cycle of the Japan Sea Throughflow

“…Since the model conserves mass, the SSH in the open ocean will have an opposite sign on the spatial average but weaker signal because the spatial domain is much larger. The mass balance is roughly achieved by the flows through the straits, as expected for time scales longer than the subinertial period (Lyu and Kim 2005). The change of SSH is also not due to buoyancy forcing since the model is forced only by wind stress.…”

“…The amplitude of seasonal cycle in transport is about 0.8-1.7 Sv (Isobe et al 2002;Teague et al 2002;Takikawa et al 2005), and the transport in the western half of the strait appears to show a more robust annual cycle (Fukudome et al 2010). Long-term estimates based on the sea level differences across the Tsushima Strait indicate a similar annual cycle (Lyu and Kim 2003;Takikawa and Yoon 2005), although these estimates may contain errors from baroclinic effects (Lyu and Kim 2003). Observations at the Tsugaru and Soya Straits, on the other hand, are much limited but nevertheless show a similar annual cycle in transport with a magnitude of about 0.4 ( Fig.…”

“…Nonetheless, the two-layer model was successful at illuminating the role of barotropic adjustment in the Japan Sea. The barotropic response within marginal seas has been assumed (Lyu and Kim 2005) or suggested in the past for a relatively short time-scale variability (Fukumori et al 2007;Kim and Fukumori 2008), but it is a feature that is often overlooked and the process needs to be further explored from observational data as well. Do barotropic dynamics also matter for the interannual and decadal variability of the Japan Sea Throughflow?…”

“…Observations of the total integrated Kuroshio transport south of Japan show the minimum in fall and maxima in winter and early summer (Isobe and Imawaki 2002), which does not correlate well with the Tsushima Current. By using the time series of the Tsushima Current transport based on submarine cable and sea level height at tidal stations around Japan and Korea, Lyu and Kim (2005) suggest the importance of the sea level changes induced on the Pacific side of the Tsushima Strait for the seasonal to interannual time scales. How this sea level change is related to various forcing and to transports through the Soya Strait is still uncertain.…”

Some High-Frequency Variability of Currents Obtained by "GeoDrifters" in the Tsushima Current Region

“…However, it is unlikely that the second mode has a particle excursion length scale much larger and current much stronger than the first mode. In this respect, the 51 hoursperiod motions may be associated more likely with barotropic basin oscillations with periods around three days arising from Helmholtz resonance that manifest themselves in volume transport through the Korea Strait (Lyu and Kim 2005). Further discussion is beyond the scope of present study.…”