Preliminary results of the expedition of the marine hydrophysical institute of the ukrainian national academy of sciences on the R/V Éksperiment in the northwest part of the black sea in May 2007

In May 2007, the Marine Hydrophysical Institute of the Ukrainian National Academy of Sciences carried out an oceanographic expedition in the northwest sector of the Black Sea. This expedition originates a series of surveys scheduled for this region. It was realized within the framework of national and international projects, such as Climate, Ecoshelf, Stable Ecosystem, SESAM, ECOOP, and Oceanography. We present the data on the works carried out in this expedition and perform a brief analysis of the process of subduction of waters on the northwest shelf. It is shown that, despite the abnormally warm preceding autumn–winter period, the wellpronounced subduction of waters formed in the process of autumn–winter cooling was still observed over the drop of depth along the isopycnic surfaces σt = 14.0 and σt = 14.5–14.6 in May 2007. New data on the intensity of vertical turbulent exchange over the continental slope in the northwest part of the Black Sea are obtained.     

Atlantic multidecadal oscillation and its manifestations in the Atlantic-European region

We present a brief survey of the works devoted to the investigation of the Atlantic Multidecadal Oscillation, i.e., of the quasiperiodic variations of sea-surface temperature in the North Atlantic with typical time scales of 50–100 yr. This oscillation is a manifestation of the natural variability in the ocean-atmosphere system. The characteristic scale of the Atlantic Multidecadal Oscillation is determined by the speed of the meridional oceanic circulation in the North Atlantic. The analyzed oscillation affects various climatic characteristics: air temperature, river discharge in the European and North-American regions, the number and intensity of tropical cyclones in the Atlantic Ocean, and the parameters of mid-latitude cyclones and anticyclones in the Atlantic-European region. The main mechanism by which the Atlantic Multidecadal Oscillation affects the climatic characteristics of the regions neighboring with the North Atlantic is the atmospheric response to the thermal anomalies in the ocean leading to a shift of the centers of atmospheric action and to the changes in the intensity and predominant directions of propagation of atmospheric cyclones and anticyclones. By using the results of long-term instrumental observations carried out in Eastern Europe and the data array of reconstructed temperature in the Alpine region, it is shown that the Atlantic Multidecadal Oscillation is responsible for a significant part of low-frequency variations of temperature in Europe. This fact confirms the potential predictability of the regional atmospheric manifestations of the Atlantic Multidecadal Oscillation on the decadal-scale. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 69–79, July–August, 2008.     

Comparative characteristics of the global manifestations of five El Niño events

On the basis of the statistical analysis of the global fields of outgoing long-wave radiation, surface temperature of the ocean, and components of the wind velocity, we analyze five El Niño events observed in 1963–1983. We study the dependence of the global circulation in the lower atmosphere on the behaviour of the temperature of the surface waters and outgoing long-wave radiation in the west part of the tropical zone of the Pacific Ocean. General regularities and specific features of different El Niño events are also analyzed.     

Meridional heat transport in the North Atlantic and the trends of its variations in the second half of the 20th century

The meridional heat transport in the ocean is computed according to the data of zonal sections of the World Ocean Circulation Experiment made in the North Atlantic in 1992–1998. We perform the generalized analysis of the estimates of meridional heat transport obtained by different authors by direct methods on the basis of the data of sections made between 7.5 and 48°N in the second half of the last century. The meridional heat transport averaged over the entire period of observations attains its maximum (1.38 ± 0.19 PW) in the Subtropical Atlantic. The meridional heat transport is characterized by fairly intense seasonal variability. Its maximum (about 1.9 PW) is observed in the Subtropical Atlantic at the end of summer and its minimum (about 0.8 PW) is attained at the end of winter. A significant trend toward the intensification of meridional heat transport is revealed near 36°N in 1959–1993 (from 0.75 to 1.1 PW). This is an indication of the intensification of meridional oceanic circulation in the North Atlantic. Dedicated to the 75th birthday of N. A. Timofeev, Honored Scientist of the Ukraine, Doctor of Geographical Sciences __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 45–58, January–February, 2007.     

Evaluation of the meridional heat transport in the Subtropical Atlantic

By using the data of a standard section made along 24.5°N in the Subtropical Atlantic within the framework of the World-Ocean-Circulation Experiment, we compute the meridional heat transport. In agreement with the major part of published estimates obtained according to the data of direct oceanographic measurements, it is approximately equal to 1.1 PW. The meridional heat transport along 24.5°N is caused mainly by the quasistationary meridional circulation with fairly stable structure. At the same time, we discovered the intense seasonal variability of some components of the meridional heat transport. The contribution of eddy heat flows to the integral transport is insignificant. Dedicated to the jubilee of Prof. Viktorina Fedorovna Sukhovei __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 3–15, January–February, 2006.     

On the Mechanism of Decadal Oscillations in the Ocean–Atmosphere System

The aim of the work is to check the hypothesis that quasiperiodic oscillations of meridional heat transport intensified by a positive feedback existing in the ocean–atmosphere system in subtropical regions is one of the principal factors governing the decadal variability of various hydrophysical fields in the North Atlantic. We use a simple three-box model of the North Atlantic with one lower and two upper boxes and meridional circulation for typical parameters of the ocean–atmosphere system. It is assumed that the decadal anomalies of sea-level pressure are proportional to the anomalies of sea-surface temperature. The deduced system of ordinary differential equations for the temperature of the upper two boxes with quadratic nonlinearity and the behavior of the solution in the vicinity of the stationary point are analyzed by using standard procedures for the investigation of linearized equations for small perturbations. It is shown that, for typical parameters of the ocean–atmosphere system, oscillating solutions for the sea-surface temperature with periods of 10–20yr can be realized even without taking salinity into account.     

On the Statistical Structure of Hydrometeorological Fields in the North Atlantic

We study the possibility of detection of statistically significant trends as a characteristic of low-frequency variability of hydrometeorological fields in the North Atlantic on the basis of relatively short time series. We use the monthly data of the Russian Hydrometeorological Center for 1957–1990 and analyze their statistical structure. It is shown that significant linear and quadratic trends can be detected in the fields of most hydrometeorological characteristics of the North Atlantic. The residual signal is approximated by using the first-order autoregressive model. Typical values of the coefficient of autoregression vary within the range 0.3–0.6 (for different hydrometeorological characteristics of the North Atlantic). The maximum correlation is observed for the fields of sea-surface temperature and humidity, whereas the minimum correlation is typical of the fields of wind velocity and the difference between the temperatures of water and air.