112 research outputs found
Cross-shelf overturning in geostrophic-stress-dominant coastal fronts
No full textCompared to the dynamics of the predominantly geostrophic along-shelf current, our understanding of the cross-shelf dynamics in the Sea of Okhotsk is inadequate despite their importance in water mixing and nutrient entrainment. We investigated the cross-shelf overturning circulation along the East Sakhalin Current, which is a source of nutrients such as iron for the western North Pacific. Here, we reveal that the cross-shelf circulation during winter is characterised by a nearshore upwelling and a shelf-break downwelling under a downwelling-favourable monsoon wind, contrary to a classical Ekman overturning (EOT). This reverse EOT is driven by the internal water stress, which is caused by intensive vertical mixing and geostrophic vertical shear in the shelf-break front produced by riverine discharges from the far-eastern Eurasian Continent. The EOT blocks the Ekman onshore transport from the open ocean, thereby producing a deep mixed layer at the shelf break. Scaling analyses indicate the applicability of this mechanism to various other shelf-break fronts
Cross-shelf overturning in geostrophic-stress-dominant coastal fronts
No full textCompared to the dynamics of the predominantly geostrophic along-shelf current, our understanding of the cross-shelf dynamics in the Sea of Okhotsk is inadequate despite their importance in water mixing and nutrient entrainment. We investigated the cross-shelf overturning circulation along the East Sakhalin Current, which is a source of nutrients such as iron for the western North Pacific. Here, we reveal that the cross-shelf circulation during winter is characterised by a nearshore upwelling and a shelf-break downwelling under a downwelling-favourable monsoon wind, contrary to a classical Ekman overturning (EOT). This reverse EOT is driven by the internal water stress, which is caused by intensive vertical mixing and geostrophic vertical shear in the shelf-break front produced by riverine discharges from the far-eastern Eurasian Continent. The EOT blocks the Ekman onshore transport from the open ocean, thereby producing a deep mixed layer at the shelf break. Scaling analyses indicate the applicability of this mechanism to various other shelf-break fronts
Subtropical Western Boundary Currents over Slopes Detaching from Coasts with Inshore Pool Regions: An Indication to the Kuroshio Nearshore Path
No full textAbstract
The dynamics of subtropical western boundary currents over slopes detaching from coasts with inshore pool regions, where the water of the subtropical gyre does not enter and the velocity is small, are investigated. This study is intended to understand the dynamics of the nearshore path of the Kuroshio, which has a distinct boundary between the boundary current and the coastal water. Numerical experiments under idealized conditions are made. The results show flow patterns with pool regions similar to the Kuroshio under simple conditions. A deep countercurrent is present on the lower bottom slope, which represents observed deep currents. This is part of a deep cyclonic recirculation north of the jet, which extends to the lower bottom slope despite steep topography. This extension can be explained by the geostrophic contours. In this region, the upper boundary current feels the bottom slope and the westward intensification is blocked. In the other region, where the bottom-layer velocity is very small, the upper boundary current is free from the bottom slope and westward intensification occurs at the coast. The sensitivity to the volume transport of the boundary current is investigated by case studies. The pool regions are broken in cases with large volume transports. It is indicated that these unsteady inshore regions are produced by instability caused by an outcrop of the upper isopycnal, which is led by a large baroclinic volume transport.</jats:p
Dense shelf water formation process in the Sea of Okhotsk based on an ice‐ocean coupled model
No full textPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95161/1/jgrc11630.pd
Modeling low-level clouds over the Okhotsk Sea in summer: Cloud formation and its effects on the Okhotsk high
No full textIn summer the Okhotsk Sea is often covered by low-level clouds, which occasionally co-occur with the Okhotsk high. We investigate the formation of low-level clouds and their effects on the Okhotsk high in July using reanalysis, satellite data, and a regional climate model. Statistical analysis suggests that the amount of low-level clouds over the Okhotsk Sea has a positive relationship with the strength of the Okhotsk high; however, the formation processes of the Okhotsk high and low-level clouds are not dependent on each other. A simulation focusing on July 2003, when the Okhotsk high was the strongest in the past decade, showed low-level cloud formation and resulting strong cooling over most of the Okhotsk Sea, which can be attributed to longwave radiation. Sensitivity experiments with reduced cloud amounts reveal that this radiative flux results in the cooling of the cloud top boundary layer (CBL), thereby reinforcing the Okhotsk high within the CBL. Trajectory analyses show that unsaturated air reaches saturation mainly because of the downward sensible heat flux. After cloud formation, radiative cooling causes an upward sensible heat flux below the clouds. Such cooling and heating roughly balance with the cooling due to evaporation of drizzle and cloud water and the heating due to condensation. Eventually, the CBL achieves a low-temperature steady state over the Okhotsk Sea. Although the latent heat flux is positive over the Okhotsk Sea irrespective of the presence or absence of low-level clouds, associated moisture flux is insignificant for achieving saturation. This positive latent heat flux is enhanced under cloudy conditions and compensates for the loss of water vapor due to condensation
Rotating Stratified Barotropic Flow over Topography : Mechanisms of the Cold Belt Formation off the Soya Warm Current along the Northeastern Coast of Hokkaido
No full textThe Soya "Warm Current" (SWC) flows through a shallow strait between the Japan Sea and the Sea of Okhotsk. The SWC has a jet structure downstream of the strait along the northern coast of Hokkaido with a maximum speed exceeding 1 m s^[-1] at its axis in summer and fall. A surface cold belt with a subsurface doming structure forms offshore of the SWC axis. Mechanisms of the cold belt formation are discussed from a point of view of resonant interaction between a barotropic stratified flow and a shallow sill and subsequent baroclinic adjustment along the SWC. When a stratified current rides a slope upstream, the thermocline displaces upward greatly and outcrops owing to resonant generation of internal Kelvin waves if the upper layer is thinner than the lower layer. The control section, where a Froude number is unity, occurs "upstream" from the sill crest when the ambient inflow has a barotropic flow component. These upwelling features closely resemble those along the southwestern coast of Sakhalin Island. The SWC then flips from an upwelling-type to a downwelling-type structure; in doing so, it transits from the west coast of Sakhalin to the east coast of Hokkaido. It is this transition that leads to the offshore doming structure, which propagates downstream as a vorticity wave, manifesting the cold belt at the surface
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