Showing papers on "Secondary circulation published in 1990"

The role of secondary circulation in boundary mixing

Abstract: Enhanced mixing near a sloping boundary reduces the stratification and hence the vertical diffusive buoyancy transport. An additional advective buoyancy flux, however, is associated with the bidirectional secondary flow driven by buoyancy forces near the boundary. Some integral relations and simple physical arguments show that, while advection increases the downslope buoyancy transport, it decreases the vertical transport; the overall effectiveness of boundary mixing involves the square of the reduction factor that would occur for the diffusive flux alone in a region of reduced stratification. The secondary circulation may increase the effectiveness of boundary mixing, indirectly, however, by restoring the stratification, and hence the diffusive fluxes, unless this restratification also suppresses the mixing. Integral relations are also derived for the along-slope flow which is part of the solution rather than arbitrary, and the relationship of the theory to Ekman layer dynamics is discussed.

Quasi-balanced dynamics in the tropics

Abstract: We propose a quasi-balance dynamical system of equations for slowly evolving, large-scale motions in the tropics. Unlike other balance schemes, equatorially trapped Kelvin waves are included. Following the lead of Gill, this system is based on the neglect of the meridional acceleration (the so-called long-wave approximation). Consistent budgets for kinetic energy and potential vorticity are derived, with those quantities appropriately redefined. Unlike the quasi-geostrophic system, vertical advection of potential vorticity as well as of potential temperature is relevant. A primary circulation is defined, involving the zonal wind, geopotential, and potential temperature, such that potential vorticity depends on latitudinal and vertical gradients of the primary circulation. A residual secondary circulation is governed by an elliptic equation for a streamfunction in the meridional plane. The invertibility principle is affected by the Kelvin waves with zero potential vorticity. The eigenfrequencies f...

A diagnostic study of an explosively deepening oceanic cyclone over the northwest pacific

Abstract: The vertical motions and secondary circulation of an explosively deepening oceanic cyclone,which oc-curred over the Northwest Pacific Ocean and was in conjunction with 200 hPa-level jet stream and hascentral pressure falls of 33.9 hPa/24h,have been computed from seven-level nonlinear balance model and Saw-yer-Eliassen-Shapiro equation for the transverse ageostrophic circulation.The vertical motions are partitionedinto contributions from large-scale latent heat release,effect of cumulus heating,thermal advection,differen-tial vorticity advection,etc.,while the secondary circulation stream function is partitioned into contributionsfrom geostrophic deformation,transfer of momentum and heat in the area of cumulus and diabatic heating.The principal results are the following.Large-scale latent heat release is very crucial to the explosive de-velopment of cyclones.If there is enough transfer of moisture,the positive feedback process between ascentof air and large-scale heating would work.The cumulus heating and the transfer of momentum and heatin the area of cumulus play an important role during the explosively deepening stage.Thermal advection isthe initial triggering condition for large-scale heating and the conditional instability for the convection ofcumulus.