Preliminary Discussion Of The Oscillation Mechanism About Convection At Labrador Sea

Deep convective mixing provides a rare vertical connection in the meridionaloverturning circulation of the ocean. Surface cooling by the atmosphere transformssurface waters into high-density deeper waters. In the North Atlantic Ocean, thisprocess creates a link between the northward surface flow of warm waters in the gulfStream and North Atlantic Current system and the deep southward flow of cold watermasses in the Deep Western Boundary Current and interior pathways(Boweret.al.,2009).The extensive cooling of sea surface needed for such atransformation is mainly provided by turbulent fluxes of sensible and latent heat dueto a combination of strong winds and cold dry air. So study of deep convection has aprofound implication for air-sea system around the globe.Not only within mode waters but also in deep convection areas (exceptcontinental shelf), convection can be found to vary interannually. Most scientists givetheir theories on the contributions from wind stress,radiation and freshwater flux tothe variability. This paper focuses on the most recognized theories to present therelationship between buoyancy flux and deep convections process. From start, thispaper choose Mixed Layer Depth (MLD) as the representative of the strengtheningand weakening of convection. With the modification of MLD method which first iscame up with by Holte and Talley (2009),and the aid of factors at Labrador Sea, wegive a new method for estimating MLD. By comparing Buoyancy flux calculatedfrom MERRA datasets, CFSR datasets and so on with MLD estimated by usingARGO CORA3.3datasets,the result is pretty shocking. The correlation betweenBuoyancy flux and MLD is not as high as people have been thought. A newmechanism is needed to fill the gap.Jiayan Yang(1996) had combined the1.5-dimensional model of Killworth andSmith(1984) with Welander(1997) sea-ice model to study the convection process inwinter ice-covered areas. This model is forced by zero-net-gain annual cycle of winter freezing and spring melting. And it has been successful to stimulate the formation ofdichothermal layer in the Sea of Okhotsk and an interannual oscillation arises fromthis model even though the model forcing excludes an interannual variation. Thispaper provides the open-ocean convection in winter ice-free areas, which is differentfrom the Yang Model.This paper makes a connection between convection areas and boundary areas,and the salinity transport from boundary current to convection areas makes a bigdifference on interannual variation of convection.Through this relationship, this paperbuild a heat-salt ideal model to illustrate the interannual oscillation of convection.Given different assumptions about the variable in the model, we can come upwith different types of oscillation. First, we can make the assumption there is norelationship between the difference of upper layer and lower layer density with rate offlow from the lower layer in convection areas to the lower layer in boundary currentareas.Because it is not a closed equations, we make further assumption that density isa function of time during steady state, it is known,and it result an irregular oscillatordue to a discontinuous root.Second,we can make the assumption there is a relationship between thedifference of upper layer and lower layer density with rate of flow from the lowerlayer in convection areas to the lower layer in boundary current areas. And further thisrelationship is known and its function is known. By nondimensionalization theequations, we can get a result of a two-year oscillation. This result is based on amechanism as follows:In the convection areas,when winter comes,the sea surface is cooled and densityrises, the profile of this water pillar is static instability. The surface waters is movingdownward,and lower layer waters is moving upper ward. Mixing happens. Becausethe lower layer is always salty than the upper, so every winter mixing happens,theupper layer is gaining salinity until one winter, the difference between upper layersalinity with lower’s is very small, it cause the convection to move deeper than ever,and create massive horizontal flow between lower boundary current and lower layerin convection areas. And compensation current from upper boundary current to upper layer in convection areas is much more than ever. As a result, upper layer inconvection areas is being diluted. The loop is going on.