Том 55, № 6 (2019)

A review of the results of Russian studies of the middle atmosphere in 2015–2018 prepared by the Commission on the Middle Atmosphere of the Association of Meteorology and Atmospheric Sciences National Geophysical Committee for the National Report on Meteorology and Atmospheric Sciences to the 27th General Assembly of the International Union of Geodesy and Geophysics (Canada, 2019) is presented.

The most significant results of Russian studies in the field of atmospheric electricity in 2015–2018 are reviewed. The review is a part of the Russian National Report on Meteorology and Atmospheric Sciences to the International Association of Meteorology and Atmospheric Sciences (IAMAS). It was presented and approved at the 27th General Assembly of the International Union of Geodesy and Geophysics (IUGG)¹. The review is followed by a list of the main Russian works on atmospheric electricity published in 2015–2018.

The modern climate of our planet is characterized not only by a trend caused by an increase in the concentration of greenhouse gases in the atmosphere, but also by fluctuations covering a wide range of frequencies and scales. The global climate variability based on the modeling results of the Coupled Model Intercomparison Project Phase 5 of the World Climate Research Program is characterized by significant differences between models. In particular, for the decadal-scale anomalies of the global and hemispheric temperatures, the standard deviation differences between models are as high as fourfold. However, in contrast to the differences in climate sensitivity between models, the causes of a wide range of the estimates of climate variability are still not entirely understood. The research in this paper is based on two-component energy-balance stochastic model. We analyze the sensitivity of interannual and interdecade variability of the mean global surface temperature (GST) to the feedback and thermal inertia of the atmosphere–ocean system under the assumption that the main external forcing factor is random fluctuations of the radiation balance at the upper boundary of the atmosphere. We estimate the influence of thermal inertia and feedback in the climate system on the interannual and interdecade variability (variance) of the GST and the spectrum of its fluctuations using the absolute and relative sensitivity functions derived in the research.

The existence of relationships between the kinematic characteristics of wind (maximum velocity and its acceleration) in a tropical cyclone (TC) and the values of gravity anomalies (vertical and horizontal components, respectively, vertical components of gravity anomalies (VGAs) and horizontal components of the gravity anomalies (HGAs)) along the paths of movement of TCs is established. It is shown that the changes in VGA and wind velocity are in general close in antiphase and to a certain extent correlate qualitatively. An analysis of wind accelerations and the corresponding values of VGA has not revealed a clear correspondence in their comparison. Changes in HGA values are close to changes in wind velocity and correlate well at the qualitative level, except for the entry of a TC to dry land and the movement of a TC across a highly anomalous region. A comparison of changes in maximum velocity and acceleration of wind to changes in HGA values is performed for the first time.

The meridional structure of climatic trends and anomalies of potential temperature and salinity in the North Atlantic waters in different periods of the Atlantic Multidecadal Oscillation (AMO) in 1948–2017 are studied based on the EN4 and WOA2013 objective analyses data. An analysis of these different data sets allowed us to reveal almost identical patterns of variability of the thermohaline fields of the North Atlantic, which increases the reliability of the results. Long-term temperature and salinity trends calculated over the period 1948–2017 show that warming and salinization of water occur in the upper ~1 km layer of the North Atlantic. On the contrary, cooling and freshening of deep waters are observed, which is associated with the melting of the Greenland ice sheet, transport of fresher waters from the Arctic Ocean, and deepening of these cold and fresher waters into the deeper layers. Composite analysis of the zonally averaged temperature and salinity anomalies of the North Atlantic waters after removing the trends showed that in the warm AMO periods warming and salinization of waters are observed in the upper 1-km layer of the North Atlantic when compared to the cold periods based both on the EN4 and WOA2013 data. Below the 1-km layer, significant regions of cooling and freshening are observed; this distribution is more pronounced in the EN4 data. Analysis of the dynamics of zonally averaged temperature and salinity anomalies in the successive periods associated with the temporal variability of the AMO index revealed that these anomalies propagate along the zonally averaged meridional thermohaline circulation. To show this using the Institute of Numerical Mathematics Ocean Model (INMOM), the stream function of the Atlantic Meridional Overturning Circulation (AMOC) was simulated. It is shown that positive and negative anomalies of both temperature and salinity circulate along the water motion in the AMOC around its core, descending down into the deep ocean layers approximately at 60° N and ascending to the surface at 25° N, replacing each other with a period of about 60 years. It can be assumed that due to this process both the warm and cold phases of the AMO are formed.

We consider the problem of the propagation of a localized internal perturbation in the form of an oscillating wave packet (breather) of the first mode in a three-layer fluid with an uneven bottom in the form of a smooth step. The study is carried out using a method of numerical simulation within a fully nonlinear two-dimensional (in the vertical plane) set of Navier–Stokes equations. A set of calculations has been performed for different widths and heights of the bottom step. Inhomogeneity of the medium leads to the transformation of the internal wave field with the formation of weak reflected waves of the lowest modes and one or two first-mode breathers that propagate to the region of shallower depths. It is found from the analysis of linear stability in the terms of Richardson and Froude numbers that potentially unstable regions appear at the smallest values of the step width. An amplitude and energy analysis of secondary reflected nonlinear waves has been performed. The vertical mode composition of the fully nonlinear wave field has been analyzed. It is shown that the first mode makes the largest contribution to the vertical structure of the full-nonlinear packet, though the fourth, second, and third modes also make a noticeable contribution.

The anomalous transport of passive admixture is studied when unsteady chains of wave structures with closed streamlines are excited in a barotropic jet flow that models the zonal flows in the Earth’s atmosphere and ocean, as well as in the laboratory experiments. The analysis is performed within a dynamical model describing saturation of the barotropic instability of the jet current in a plane channel with rigid parallel walls with account for the beta effect and external friction. The equations of a barotropic current are solved numerically using the pseudospectral approach. It is found that the generation of high modes in a jet with a “two-hump” velocity profile leads to the accelerated transition to the complex dynamics. A multiharmonic regime with a discrete spectrum appears in the initial stage of this motion. The exponents of the power dependence on the time of the average (over the ensemble) displacement of tracer particles and its dispersion are found for the basic generation regimes of the wave structure, which confirm the occurrence of the anomalous diffusion of the admixture. A self-similar probability density function of tracer displacements has been found and the dependence of the transition to the complex dynamics on the number of vortices in the chain and on the intensity of the beta effect has been revealed. Numerical estimates are presented which confirm the possibility of generating unsteady vortex chains and the related anomalous transport of the passive admixture.