The article is dedicated to the 100th anniversary of Vladimir Georgievich Snopkov (1924– 1992) – a participant in the Great Patriotic War, a veteran of the Shirshov Institute of Oceanology of RAS, one of the most honored researchers of atmospheric processes in the World Ocean, who worked on 28 expeditions on flagship research vessels: the legendary “Vityaz”, “Academician Kurchatov”, “Dmitry Mendeleev”. For these merits, Vladimir Georgievich was deservedly awarded the Order of the Red Banner of Labor. Brief information is provided about his difficult childhood and adolescence, military service, desire to obtain a good professional education as a meteorological engineer at the Higher Arctic Maritime School (HAMS) – later renamed the Leningrad Higher Marine Engineering School named after Admiral S. O. Makarov (LHMES), scientific and creative path. A significant place in the research of V.G. Snopkov is occupied by the largest hydrophysical experiments of the 70s and 80s of the last century (Polygon-70, MEGAPOLIGON-90, etc.), in which he participated. The results of the analysis of actual observations in these experiments are reflected in the list of selected works.

The modern climate is the climate of the current century with its characteristic features. The ocean and the atmosphere, however, are considered as two of the most important components of the climate system. The dynamics and thermodynamics of these spheres reflect the current perturbations of the planetary environment on intra-decadal (2–8 years) and multi-decadal (20– 60 years) time scales. Quasisynchrony and globality of the phenomena occurring in the modern climate system are provided and accompanied by planetary scale structures identified both in the atmosphere and in the ocean: respectively, the Global Atmospheric Oscillation (GAO) and the Multi-decadal Oscillation of the Heat content in the Ocean (MOHO). A characteristic feature of the modern climate dynamics is its observed multidecadal rhythm with a period of about 60 years. The rhythm of 1940–1999 was a two-phase structure, in which the initial phase (1940–1974) was essentially continental, and the final one (1975-1999) was relatively wet. The transition of the climate from the continental phase to the humid phase in the mid-1970s turned out to be “sudden” and was recognized as a climate shift. The search for the source of the observed variability of the modern climate made it possible to establish that the heat content of the active upper layer (AUL) of the World Ocean (WO) demonstrates multidecadal phases of heat accumulation and heat discharge, consistent with multi-decadal phases of climate disturbances. It should be noted that the heat accumulation phase of the WO AUL corresponds to a continental climate, and its thermal discharge corresponds to a relatively humid one. The mechanism of the observed multidecadal phase variability of the modern climate is the planetary intrasystem redistribution of heat between WO and continents, in which the general circulation of the atmosphere plays the role of a mediator.

The article is dedicated to the 100th anniversary of the birth of a former employee of the Shirshov Institute of Oceanology of RAS, an active participant in the Great Patriotic War, head of the Cabinet of Hydrochemistry of the IO RAS, Doctor of geographical sciences Vladimir Nikolaevich Ivanenkov (1922–1991). The main milestones of his military biography are mentioned and the key stages of scientific activity as one of the leading specialists of the Institute of Oceanology in the field of ocean biohydrochemistry in the 60s–80s of the last century are noted.

One of the most remarkable peculiarities of the modern climate, undoubtedly, should be recognized as the climatic shift observed in the mid-70s of the last century. The reasons for this phenomenon for a long time, despite the activation of climatologists from all over the world, remained a mystery that requires its disclosure. First of all, this was due to the fact that the shift that took place turned out to be unexpected for scientists and was accompanied by rapid qualitative changes in the planetary climate. To date, thanks to the efforts of scientists using the results of rapidly developing numerical modeling, diagnostic calculations and observational data in large hydrophysical experiments in various regions of the World Ocean (WO), an understanding of the role of the ocean factor in the variability of the current climate has developed. It became clear that climatic shifts are an important feature of the internal dynamics of the climate system. The most obvious evidence of intrasystemic processes should be considered the discovered planetary structures in the atmosphere – Global Atmospheric Oscillation (GAO) and in the ocean – Multi-decadal Oscillation of the Heat content in the Ocean (MOHO), which are quasi-synchronous accompanying variations in the modern climate. GAO, its structure and features have been discussed in detail earlier in a number of studies. As for the MOHO, its structure and features are discussed in the proposed work. It is characteristic that the MOHO is located in the layer of the main thermocline (100-600 m). In a quasi-uniform layer (0–100 m), and in a deep layer (600-5500 m), the thermodynamic regime differs from the regime in the layer of the main thermocline. Probably, it is precisely this circumstance that did not allow earlier to draw attention to such an important detail in the structure of the WO thermodynamic variability. The presence of extreme multi-decadal temperature field disturbances at intermediate levels (200, 300, 400, 500, 600 m) should be noted as an important characteristic feature of the oscillation. Large-scale hydrophysical experiments (POLYGON-70, POLYMODE, etc.) made it possible to reveal the vortex structure in the dynamics of WO waters and to discover that the vortices of the open ocean have maxima of kinetic energy precisely in the layer of the main thermocline. This allows us to assume a connection between synoptic eddy activity and MOHO. However, the latter remains to be studied.

Multi-decade rhythmicity is one of the most important features of the dynamics of the modern climate. The rhythm of 1940–1999 was a two-phase structure in which the initial phase (1940–1974) was essentially continental, and the final phase (1975–1999) was relatively wet. The transition of the climate from the continental phase to the humid one in the mid-70s of the twentieth century was “sudden” and recognized as a climate shift. A certain globality and quasi-synchronicity of multi-decade climate changes is realized with the participation of planetary thermodynamic structures both in the ocean and in the atmosphere of two the most important components of the climate system. The presence of a Global atmospheric oscillation was discovered and studied in detail. This paper offers the first attempt to consider the content and features of the planetary multi-decadal oscillation of the heat content of the World Ocean. The analysis of ocean oscillation is based on the results of numerical simulation of the World Ocean water circulation in the period from 1948 to 2007 using the model of the Marchuk Institute of Numerical Mathematics of Russian Academy of Sciences. The differences in the average water temperature fields in the upper 1200-meter layer, calculated for two opposite phases of the oscillation, revealed the main features of its structure.

“In the last quarter of the ХХ-th century, our country has implemented several major programs of experimental research of the World ocean. Among them, a special place was occupied by the huge in its scale and scientific significance the project SECTIONS aimed at studying the climatic interaction of the ocean and atmosphere. Currently, systematic research in this field has gained new momentum through regular Hydrophysical monitoring of the energy-active region in the North Atlantic in the annual expeditions by Shirshov Institute of Oceanology of RAS (Gladyshev et al., 2017). The results of some special Russian ocean expeditions of the past years, one of which is described for the first time in this article, can serve as a certain historical background for modern studies of the ocean climate evolution”. In 1990 Russian oceanographers carried out a comprehensive hydrophysical study of the Newfoundland energy-active zone in the Northern Atlantic ocean, as part of the national project “Sections” included in the international program WOCE. Three research vessels (R/V) of the Shirshov Institute of Oceanology (SIO): “Vityaz“(cruise 19), “Professor Stockman“( cruise 26) and “Academician Kurchatov“ (cruise 50) together with additional 4 vessels of other institutions were engaged in the field study. Scientific management for general programme of the expedition, dubbed “ATLANTEX-90”, was carried out by Professor Yu. A. Ivanov. The main objective of the program was to study the space-time short-period variability of water dynamics in the large – scale ocean circulation system of Gulfstream–North Atlantic Current. To this aim, in May–June 1990 R/V “Academician Kurchatov” performed several sections crossing the main hydrological fronts of the Newfoundland energy-active zone (45–53°N., 36–45°W). Observations were conducted using the cable probe with sensors of temperature, conductivity and pressure (CTD) and expendable bathythermograph (XBT). All this equipment was special made and passed metrological certification in the design Bureau of Oceanological Engineering (BOE) of SIO. The equipment metrology fitted in whole with international standards at that time. The sea surface temperature (SST) was recorded along the RV route as well. The current velocity was measured during about one month at 14 moorings deployed on a section along meridian 36°W, from 47 to 53°N. The measurements were conducted using electronically operated current meters of POTOK type of the BOE of SIO production. The meters were installed on the each mooring at the horizons of 100, 200, 1000, 2000, 3500 m. In addition to the data of own measurements, facsimile maps of SST from the nearest hydrometeorological observatories were received by radio communication channel during the whole period of observations. Analysis of the obtained data showed that during the field study period the North Atlantic Current (NAC) divided into two branches (Central and Southern) roughly in the neighborhood of 47.5–48°N, where isobath 4500 m turned to the East at right angle to isobath 4000 m. After point of the bifurcation, the Central branch initially maintained a Northerly direction, then turned North-West along the isobath of 4000 m, and farther, turning East, crossed the meridian of 36°W between 51° and 52°N. Prior that stage, the Central branch sometimes approached the meridian 36°W at about 50°N, then deviated to the North–Northwest and finally turned North-East about 51,5°N. The Southern branch of NAC after a split of the main NAC flow followed approximately to isobath 4500 m, and crossed the meridian of 36°W at about 48°North latitude. East of 36°W it could be at times of East-North-East direction, but usually this branch unfolded to the South-South-West, forming the high ridge of the ocean surface dynamic height on the Eastern flank of the NAC. Three return flows were observed in the section of 36°W. One of the flows is marked between the Central and Southern branches of the NAC, while the other two were recorded on the Northern and Southern edges of the section. This structure of the velocity field in fact remained unchanged through all June 1990. The basic zonal flow was observed in the entire water column within the depths from 100 m to 3500 m. The highest current speeds were typical for the upper part of this layer. At depths of 1000–2000 m the velocities were noticeably weakened, increasing again in some places near the bottom. The distribution of meridional components of flow speed according to the measurements on the buoys allowed us to detect the presence of large-scale divergence, which was located along the section on 36°W. Direction of the meridional component of the current to the North and South of 49°N turned out to be the opposite, forming that divergence in the field of the velocity. Under the analysis of the observations it was taken into account that an important role in the formation of the structure of ocean circulation in the area of research could play a seamount (>2600 m), registered by the sounders of R/V “Academician Kurchatov” near 49°N, 36°W. The results of measurements and calculations showed that the average over the entire observation period water transport of the Central branch of NAC through the 36°W section accounted for 62.4 Sv. This value is comparable to the transfer of NAC, assessed four years later by Lazer (1994) 50±23 Sv for approximately the same area where we conducted our work in 1990. Approximately the same average transfer (46,5 Sv) was found in two return flows (presumably North and South recirculations of the NAC Southern branch). In whole, the average water transport in the Eastern direction through the section on 36°W was as high as 111 Sv., and it was 60.9 Sv after subtracting reverse fluxes.

Discovery of the global atmospheric and oceanic oscillations was regarded as an essential addition to the wide range of multi-scale processes characterizing the variability of the global climate system short-term dynamics. Interannual global atmospheric oscillation (GAO) was found during the study of a physical mechanism and indices of the well-known events of El Niño (Byshev et al., 2012.). The first report on the multi-decadal oscillation of the of the ocean upper active layer heat content (MOHO) was published in 2016 (Byshev et al., 2016 ). Subsequent heat content evolution studies of these intra-century processes in the atmosphere and in the ocean allowed to propose a new realistic approach to improvement a theory and methods of the modern climate variability evaluating (Byshev et al., 2017; Byshev et al., 2018; Serykh et al., 2019). The article provides a brief annotated review of the main publications devoted to the substantiation and analytical description of the basic concepts of short-period variability of the modern climate associated with the global effects of inter-annual atmospheric oscillation (GAO) and multi-decadal oscillation of the ocean upper active layer heat content of the world ocean (MOHO).

Multi-decadal variability of the modem climate (fluctuations of 50-70 years) is one of the most urgent current problems in the earth Sciences. The actual oscillation consists of two phases, each of which is 25-35 years: the phase when the upper active layer (UAL) of the world ocean, giving sensitive and latent heat to the atmosphere, makes a kind of its thermal discharge, and the phase of a continental climate, when the ocean UAL accumulates heat, seeking to restore its initial state. There is reason to believe that the variability under consideration reflects the internal dynamics of the ocean-atmosphere-continent climate system. The presence of planetary structures in the GAO atmosphere (global atmospheric oscillation) and in the MOSTOK ocean (multi-decadal oscillation of ocean heat content) allows us to understand the reproduction of the observed rhythm of the climate system. The most sensitive to the climate system are changes in the phases of climate, as a result of which there are sudden qualitative shifts, accompanied by a certain restructuring of the General circulation of the ocean and the atmosphere. So in the ocean, when the climate phase changes, either deep convection intensifies (with the thermal unloading of the ocean UAL), or it weakens, and possibly stops (with the accumulation of heat of the UAL). In the atmosphere of the changing phases of a climate impact on monsoon circulation: a more continental climate phase corresponds to a strengthening of the monsoon circulation with all accompanying this process features. The forecast of climate phase changes is therefore important for the economic, social and political life of society. In turn, the quality of the forecast is associated with an understanding of the nature of the observed variability and the representation of the mechanism of this phenomenon. In the work for some areas of the world ocean the evolution of the thermal structure of the UAL with the dynamics of the steric mode of oscillations of the level determined by satellite altimetric observations is compared. It was found that the sea level rise between the time phases of 1993-1999 and 2000-2015 it was 4-6 cm and corresponded to the increase in the level that would occur with the observed increases in the heat content of the ocean UAL. It is concluded that on inter-decadal time scales, along with ocean surface temperature (SST) data, altimetric satellite observations can be used in the future to identify regional sources and heat sinks in the ocean.

Interadapted fields of main hydrophysical characteristics in the vicinity of hydrological sections carried out in 1997–1998 in the Barents Sea are obtained on the basis of model computations. The complex analysis of these materials and atmospheric situation in the region during 1997–1998 enabled to estimate quantitatively the variations of significant hydrodynamic conditions: the decrease in the inflow of rather warm and salty North Atlantic waters and the compensation inflow of polar waters, the decrease in total heat content and the weakening of water dynamics in the system of the general cyclonic circulation, and the increase in the ice coverage of the Barents Sea in anomalously cold winter 1997/98. It is revealed with a high degree of the confidence probability that the significant deviations from the normal conditions occur in response to the global El Niño disturbance which took place in the same years with the maximum values of the Southern Oscillation Index in January–March 1998.

On the basis of model calculations, mutually fitted fields were obtained for the key hydrophysical properties in the vicinity of the hydrological sections executed in the Barents Sea during 1997–1998. Integrated analysis of these data allowed us to evaluate the variability of crucial hydrodynamic conditions: the decrease of supply of relatively warm and saline North Atlantic waters with compensatory inflow of Arctic waters; the decrease of total heat content and increase of thermal convection; the weakening of water dynamics in the system of general cyclone circulation; and the abnormally cold winter in 1997–1998 with the increase in the ice covering of the Barents Sea. With a high confidence probability, it was found that considerable deviations from the mean weather conditions took place in response to the El Niño global disturbance of the same period, with the maximum southern oscillation index (SOI) in January–March 1998. The El Niño signal in the baric field of the Arctic basin, noted even in November–December 1997 as a crest of increased pressure, reached its maximum development in April–June 1998 in the form of a well-pronounced atmospheric anticyclone. Recognizing the natural correlation of this phenomenon and the maximum SOI value, one may state that the Barents Sea responds to an El Niño event in about three months. This circumstance should be used as an important parameter for climate forecasting.