Interdecadal Oscillation of the Ocean Heat Content as a Contribution to Understanding of Physical Aspects of the Present-Day Climate

Abstract

A Specific feature of the present-day climate dynamics consists in its multidecadal oscillations with a period of about 20–60 years, and intradecadal disturbances with time scales of 2–8 years. The period of 1940–1999 was distinctive due to the two–phase structure in which the initial phase (1940–1974) was substantially dry, and the final one (1975–1999) was relatively humid. The transition of the climate from the dry to the humid phase in the mid-1970s was recognized as a climatic shift. The certain globality and quasisynchronism of multidecadal climate changes occur involving planetary thermodynamic structures in the two most important components of the climate system, namely, the ocean and the atmosphere. The search for the origin of the observed present-day climate variability revealed the World Ocean (WO) active upper layer (AUL) heat content to demonstrate sequential multidecadal phases of heat accumulation and discharge consistent with multidecadal phases of climate disturbances. Thus, the WO AUL heat accumulation phase corresponds to a dry climate, and its thermal discharge corresponds to a relatively humid one. The mechanism of the observed multidecadal phase variability in the present-day climate consists of the planetary intrasystemic redistribution of heat between WO and continental air masses, where the general circulation of the atmosphere plays the role of an intermediary.

Multidecadal Phase Changes in the Thermodynamic State of the System: Ocean–Atmosphere–Continent

“…In each of the regions under consideration, frontal zones are observed, which form horizontal boundaries of propagation and interaction of subarctic and central oceanic water masses, thereby determining their regional climatic significance. Of particular interest is the time interval 1975-1999, limited by the two climate shifts (mid-1970s and the eve of the 21st century) and characterized by the WO thermal discharge [4,29]. Noteworthy are specific differences in the cellular structure of quasi-homogeneous waters in the near-surface 200 m ocean layer during the indicated period and beyond it.…”

“…Large-scale hydrophysical experiments "Megapolygon" (subarctic frontal zone of the northwestern PO, July-October 1987) and "Atlantex-90" (Newfoundland energetic zone, May-July 1990) were carried out in the two key areas of the WO during the multidecadal rhythm of the present-day climate . Unprecedented observations during the implementation of these two projects made it possible to obtain extremely important comprehensive instrumental evidence of thermodynamic processes during multidecadal oscillation of the heat content of the WO during the phase of its thermal discharge [4,5]. These observations made it possible to establish the characteristic anomalous thermodynamic states of the named water areas.…”

“…The following RVs took part in the hydrological surveys and comprehensive observations of the thermodynamic state of the Gulf Stream-NA Current system: the weather RVs "Viktor Bugaev" (voyage 54); "Musson" (voyages 61 and 62); "Volna" (voyages 51 and 52); RVs IO RAS "Vityaz" (voyage 19); "Professor Stockman" (voyage 26); "Akademik Kurchatov" (voyage 50); scientific and fishing vessel PINRO "Persey-III". The experiment allowed us to obtain important evidence on the features concerning the thermodynamic state of the system Gulf Stream-NA Current, large-scale and synoptic dynamics of the ocean and its interaction with the atmosphere, and the evolution of atmospheric pressure formations over the ocean in the climate phase characterized by the WO thermal discharge [4].…”

“…The most significant of them are climate shifts [1][2][3] constituting unexpected and rapid transitions from the phase of the observed (for 25-35 years) relatively humid global climate into the phase of its essentially continental state, and then (after 25-35 years) its subsequent transition to a humid phase, etc. The search for the source of multidecadal phase changes in the global climate [4] made it possible to consider this process as an intrasystem-one supported by oscillations in the World Ocean (WO) heat content localized in the layer of the main thermocline. Thus, a feature of the present climate dynamics is episodic rapid (for 2-3 years) phase transitions of the global climate from one qualitative state to another.…”

“…Establishing signs of the MOHO [5] in the main thermocline layer [4] made it possible to use the features of the WO dynamics as a new approach. Since the main thermocline layer is characterized by the main current systems of the WO, a joint consideration of the two most important of them-the Kuroshio and the Gulf Stream-is of natural interest.…”