On the theory of convective jets and thermals in the atmosphere

In traditional theoretical models of convection from isolated sources, results usually depend little on their sizes: convective jets and isolated thermals rapidly “forget” the source geometry. However, new problems in which the sizes of a source are relatively large and can significantly influence results have recently become important. These are, for example, problems of the dynamics of intensive methane emissions of geologic origin. The paper generalizes some well-known integral models of thermals and jets. Although these simple schemes cannot compete with complicated numerical models in describing the spatial structure of the currents, they are shown to be able to reproduce a number of important numerical results rather well (the height and time of the rise of convective elements) and, moreover, to find clear physical laws and determine explicit dependences on parameters of the problem.     

Boltzmann statistical theory and asymptotics of the temperature distribution of spontaneous jets in the convective atmospheric surface layer

An ensemble of convective thermals is distinguished from the surface layer of penetrative turbulent convection over a heated horizontally uniform surface. A statistical model of the ensemble of convective thermals is developed that uses the idea of entropy in the Boltzmann-Jaynes form. The distribution of thermals by potential energies is shown to display an entropy maximum. On the basis of the Boltzmann distribution by potential energies, the temperature distribution of spontaneous jets is obtained and found to be consistent with known experimental data.     

热带对流性降水的逆温特征

通过对赤道辐合带降水的观测发现,热带对流性降水过程普遍存在逆温现象,为更好的解释这一现象,利用微波辐射计数据,对降水过程的大气层结进行了深入分析。结果表明:(1)强对流降水过程中普遍存在两个"暖心",暖心之间有"冷泡";(2)典型逆温过程发生在对流系统边缘,对流云云顶高度均在10 km以上;(3)逆温现象出现时存在水汽密度和液态水含量大值区。近地面"暖心"下方和第二"暖心"内部水汽密度和液态水含量较小,两个"暖心"之间存在大值中心。第二"暖心"之上水汽密度较小,液态水含量较大。     

On the problem of the formation of the Greenland sea convective gyre

The transformation of the interfaces of a rotating three-layer fluid is described through a simple hydrodynamic model using the shallow-water approximation. Using the Greenland sea gyre as an example, it is shown that a cyclonic circulation results in the oncoming deflection of the upper and lower layers, which favours the development of deep convection.Translated by Mikhail M. Trufanov.     

On similarity profiles predicted in the convective marine boundary layer

On the basis of the ideal of local scale similarity theory, the profile equations of wind, temperature and humidity for the eonvective marine boundary layer have been obtained. The marine boundary layer measurements were made over the western Pacific Ocean as past of the Tropical Ocean and Global Atmosphere (TOGA) Programme during Nov. 1986-Feb. 1987. The similarity profiles predicledfor wind. temperature and humidity in the MBL are in good agreement with the observational data.     

On the theory of hailstone growth

Analysis of the existing theories of hailstone growth has shown that there are two different approaches to the explanation of the layered structure of hailstones. L.G. Kachurin showed that the layered structure of ice on the surface of an object placed into the flux of supercooled water aerosol is controlled by the equilibrium film thickness. Another approach is based on the equation of heat balance at the hailstone surface and on the introduction of the critical water content. This paper elucidates the meaning of the critical equilibrium film thickness and establishes the relation between the two existing criteria controlling the transition from the dry regime of hailstone growth to the wet regime.     

On local and convective accelerations in steep wave events

The local and convective accelerations of steep irregular wave events have been investigated. These properties are measured by a two-camera PIV technique. Furthermore, the experiments are compared with two different theories including a fully nonlinear and a simplified analytical model. An important result is that the convective term is of the same order of magnitude and of opposite sign as the local acceleration. The convective acceleration term can therefore not be neglected in acceleration and force estimates.     

On the vertical lifting of dust in a convective unstable atmospheric boundary layer

A model for the density Q of vertical mass flux of sand (dust) in the convective atmospheric boundary layer as a function of the number density N of convective elements (including vortices), friction velocity u _*, and vertical (turbulent) buoyancy flux B is proposed. It is shown that the flux Q is proportional to the product of the square root of B and the sixth power of u _*. This finding is consistent with empirical dependences Q(u _*) reported in the literature. We discuss two methods for experimentally determining density N when the lifting of dust occurs, mainly due to (terrestrial and Martian) dust devils.     

On the theory of internal waves under ice cover

A theoretical model is contrived that describes the propagation of internal waves under ice cover. According to the results obtained in the study, the flexures of the ice surface with a frequency close to but smaller than the Brunt-Väisälä frequency can gain amplitudes sufficient for recording internal waves. A comparison of the theory with observations showed a satisfactory agreement.     

On the theory of internal surges in shallow basins

On the basis of well-known solutions, we analyse an internal surge, i.e. a sharp step-like variation of the pycnocline depth in a shallow basin. According to results obtained, in those cases where the pycnocline is situated approximately at mid-depth of the basin, the surge may have the form of a steadily moving non-linear wave (kink) governed by the combined Korteweg-de Vries equation with quadratic and cubic non-linearities. The vertical velocity component in such a wave has the form of a pulse and represents a soliton. Estimates of surge parameters obtained from real hydrologic data are in good agreement with the experimentally measured data.Translated by Vladimir A. Puchkin.     

对流风暴的移动和演变对下游地区对流降水影响的个例分析

利用加密自动气象观测站资料、多普勒天气雷达资料、葵花卫星资料及ERA5再分析资料,对2019年海上卫星发射气象保障过程中6月1日上游对流风暴的移动和演变造成山东半岛对流降水的机制进行了分析.结果表明:1)辐合线与干线重合触发新生对流单体形成潍坊风暴,潍坊风暴东移过程中强度增强和聊城风暴进入烟台后转向造成山东半岛一带出现...     

On the theory of calculation of currents in the world's ocean straits

The paper considers the statement of the problem on quasi-stationary diagnosis of currents, temperature, salinity, and density fields for multiply connected areas with fluid boundaries. The principles of self-similar parameterization over the vertical axis are applied by introducing models for the vertical substance distribution, which have two regularly varying functions. The problem is reduced to handling a set of Poisson equations, enabling the boundary conditions to be automatically determined at the island shores. A scheme is presented for calculating current velocity components at an arbitrarily oriented transect. Several examples of current velocity computation for the topographically complex oceanic areas are given which support the data collectedin situ. Translated by Vladimir A. Puchkin.     

Preliminary study on the dynamic mechanism of the deep equatorial jets

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Scarifying and fingering surfaces of plunging jets

The local surface deformation resulting from the oblique impact of a columnar water jet has been computed, using a three-dimensional large eddy simulation, as a model of the overturning jet of a breaking wave. The emergence of the secondary jet from the front face of the initial jet has been examined and the organisation of the vortices within the jet characterised. As the secondary jet emerges, the vorticity field becomes unstable under the action of the strong shear beneath the jet surface and pairs of longitudinal counter-rotating vortices stretched along the direction of the jet projection are formed. The presence of these longitudinal vortex pairs creates convergent surface flows, resulting in the formation of longitudinal scars on the rear face of the projecting jet. Following significant growth of the scars on both its upper and lower surfaces, the jet decouples into fingers. The lateral widths of the longitudinal vortices provide a minimum measure of the finger size. A horizontal Froude number Fr_h, representing a measure of strength of horizontal shear in a gravity-dominated impacting flow is defined, which characterises the organisation of the longitudinal vortices occurring in the shear flow, and the resultant formation of scars and fingers. For higher Fr_h, stronger longitudinal vortices and deeper scars are formed at longer lateral intervals, enhancing the fingering process during the splashing event. Fundamental features of material transport in the vicinity of the surface of jets (e.g. gas transfer across a sea surface) are related to the entrainment of surface fluid by the longitudinal vortices, and is thus also characterised by Fr_h.     

Southern jets of the antarctic circumpolar current in the Eastern Pacific Antarctic

The advent of the era of satellite observations of the ocean surface has resulted in a considerable complication of views on the structure of currents in the World Ocean. Up to eight jets came to be distinguished in the zone of the Antarctic Circumpolar Current (ACC). To identify these jets, it is conventional to use qualitative criteria relating a jet’s position to the isoline of a characteristic (temperature, for instance) on any near-horizantal surface. In the present work, based on data of sections and climatology of the World Ocean Circulation Experiment (WOCE) program, we examine the temperature patterns of the subsurface waters of the Southern Ocean, which are commonly used for recognition of fronts. The focus is on the southern jets of the ACC in the Eastern Pacific Antarctic. There are two groups of criteria for these jets, which imply that position of the latter is determined from a certain isotherm on the surface of the minimum (maximum) potential temperature of the Winter water (Upper Circumpolar Deep Water). However, the results of our analysis show that, in fact, the WOCE climatology data allow one to formulate temperature criteria only for the second of the above groups and only for individual sectors of the Southern Ocean-specifically, for the study area. These criteria serve as the basis for determining localization of the southern jets of the ACC in the WOCE sections in this ocean’s region. We also show that the temperature increased by about 0.1°C from the mid-1990s to the mid-2000s in the layer of maximum temperature of the Upper Circumpolar Deep Water in the zone of southern jets of the ACC.     

Airborne imagery of ocean mixed-layer convective patterns

Airborne infrared and synthetic aperture radar imagery collected over the Gulf Stream are used to examine the surface patterns of small-scale thermal convection and wind-driven Langmuir circulation. These patterns have a thermal contrast of ～0.25 °C, which is roughly an order of magnitude larger than predicted by large-eddy simulations but consistent with the effect on surface temperature of surfactant accumulations induced by mixed-layer eddies.     

Air dynamics near the soil surface and convective emission of aerosol

Asymptotics for the mass concentration of finely dispersed aerosol are obtained on the basis of in situ measurements in a desert in the Caspian region and estimates of hydrodynamic parameters in the viscous thermal boundary layer near the soil surface. In the problem under consideration, the dynamic velocity (friction speed) and the temperature drop in the thermal boundary layer are external parameters. The model of a porous soil layer, in which the air dynamics is described with the use of the Darcy equation, is considered a possible mechanism of aerosol export. The estimates of the critical parameters at which sand particles thermally roll over in soil pores are obtained.     

Coastal tidal jets and tidal fringe development around the Isles of Scilly

Tidal jets are a ubiquitous feature of the coastal environment and result from strong tidal streaming off coastal features such as promontories. Around the Isles of Scilly there exist two tidal jets which tend to propagate in a clockwise sense around the island group. Currents in excess of 90 cm s⁻¹ appear necessary for their production and the jets are characterized with a Reynolds number of about 30. It is shown that the jets indicate the direction of the maximum stream and the residual circulation around the islands. With an offshore component to the residual flow, tidal fringes may develop from the jets and such fringes were observed on the northern side of the islands.     

Effects of hydrostatic approximation and resolution on the simulation of convective adjustment

A two-dimensional non-hydrostatic ocean model and a hydrostatic version of the same model are used to simulate convective adjustment, without the use of an instantaneous adjustment parameterization. The model geometry is a domain on the vertical plane of width 40 km and depth 500 m. Model results for four cases are examined: hydrostatic and non-hydrostatic, at 0.1 and 1 km spatial resolution. The convectively adjusted stable state obtained in all four cases are qualitatively similar; thus the hydrostatic approximation does not eliminate convective adjustment. The details of the simulated convective plumes depend on resolution and whether the hydrostatic approximation is made. The adjusted state has significant stratification which cannot be captured by the conventional instantaneous adjustment or diffusion-based parameterizations. We also compare the results to the case when an instantaneous adjustment parameterization is used.