We review the characteristics of sea level variability at the coast focussing on how it differs from the variability in the nearby deep ocean. Sea level variability occurs on all timescales, with processes at higher frequencies tending to have a larger magnitude at the coast due to resonance and other dynamics. In the case of some processes, such as the tides, the presence of the coast and the shallow waters of the shelves results in the processes being considerably more complex than offshore. However, 'coastal variability' should not always be considered as 'short spatial scale variability' but can be the result of signals transmitted along the coast from 1000s km away. Fortunately, thanks to tide gauges being necessarily located at the coast, many aspects of coastal sea level variability can be claimed to be better understood than those in the deep ocean. Nevertheless, certain aspects of coastal variability remain under-researched, including how changes in some processes (e.g., wave setup, river runoff) may have contributed to the historical mean sea level records obtained from tide gauges which are now used routinely in large-scale climate research.

Influence of the Kuroshio in the East China Sea on the baiu rainband is examined using satellite observations, a reanalysis dataset, and a regional atmospheric model from 2003 to 2008. Satellite observations and reanalysis data reveal that precipitation over the Kuroshio is the highest in early summer (June), when the baiu rainband covers the East China Sea. The high rainfall is collocated with the warm sea surface temperature (SST) tongue of the Kuroshio. This locally enhanced precipitation is embedded in the large-scale baiu rainband, so that the amplitude of precipitation over the Kuroshio is twice as large as that in its surrounding area. The Kuroshio is also accompanied by high surface wind speed, energetic evaporation, and wind convergence. This wind convergence likely results from the SST influence on atmospheric pressure through not only temperature changes, but also humidity changes. Furthermore, the Kuroshio anchors the ascent motion and large diabatic heating with a peak in the midtroposphere, suggesting that the influence of the Kuroshio extends to the upper troposphere. It is also found that the East China Sea in June is the region of the strongest deep atmospheric response to western boundary currents along with the Gulf Stream region in summer. The observational results are well reproduced by the regional atmospheric model. The model indicates that when the SST tongue of the Kuroshio is smoothed, the enhanced precipitation, the energetic evaporation, and the wind convergence over the Kuroshio disappear, although the large-scale structure of the baiu rainband is not essentially changed.

This study examines interannual to decadal variability of the Kuroshio Extension (KE) jet using satellite altimeter observations from 1993 to 2010. The leading empirical orthogonal function (EOF) mode of sea level variability in the KE region represents the meridional shift of the KE jet, followed by its strength changes with a few month lag. This shift of the KE jet lags atmospheric fluctuations over the eastern North Pacific by about three years. Broad sea level anomalies (SLAs) emerge in the eastern North Pacific 3-4 years before the upstream KE jet shift, and propagate westward along the KE jet axis. In the course of the propagation, the meridional scale of the SLAs gradually narrows, and their amplitude increases. This westward propagation of SLAs with a speed of about 5 cm s 21 is attributed to the westward propagation of the meridional shift of the jet, consistent with the thin-jet theory, whose importance has been suggested by previous numerical studies. In addition, the westward-propagating signals tend to conserve their quasigeostrophic potential vorticity anomaly, which may explain the characteristic changes of SLAs during the propagation. After the westwardpropagating signals of positive (negative) SLAs reach at the east coast of Japan, the upstream KE jet strengthens (weakens) associated with the strength changes of the northern and southern recirculation gyres. Interestingly, this strength change of the KE jet propagates eastward with a speed of about 6 cm s 21 , suggesting an importance of advection by the current.

The propagation of density‐compensated (warm/salty or cool/fresh) spiciness anomalies in the North Pacific thermocline is investigated using Argo profiles for the period 2001–2008. A cool/fresh spiciness anomaly on 25 < σθ < 25.5 kg m−3 isopycnals appears in the eastern subtropical North Pacific at 120°W–150°W in 2003–2004 with a salinity anomaly of about −0.15 PSS‐78. This spiciness anomaly migrates southwestward, and arrives in the western tropical North Pacific at 145°E–175°W in 2008 with the salinity anomaly decreasing to about −0.043 PSS‐78. Two warm/salty anomalies are observed to propagate along the same path from 2003 to 2005, and after 2005. The propagation path and speed of the anomalies are in good agreement with advection by the mean geostrophic current. In the course of propagation, the anomalies are diffused and are subject to high frequency injection of spiciness anomalies, especially in the eastern subtropical North Pacific.

many of the coupled ocean-atmosphere global circulation models in the coming decade will represent oceanic fronts reasonably well, and it is hoped that this review along with the table of metrics will provide a useful benchmark for evaluating these models.