This work considers a series of numerical experiments to identify the direct role of the sea ice reduction process in forming climatic trends in the northern hemisphere. We used two more or less independent mechanisms of ice reduction. The first is traditionally associated with increasing the concentration of carbon dioxide in the atmosphere from the historic level of 360 ppm to the level corresponding to the maximum concentration in implementing the mildest scenario RCP 2.6 - 450 ppm. Due to this growth, the average air temperature in the Arctic increases, and, by this, the ice volume decreases. The second mechanism is associated with a decrease in the reflectivity of ice and snow. As a result, the amount of solar radiation absorbed by the ice increases while the ice volume decreases. We assume that comparing the results of these two experiments allows us to judge the direct role of ice reduction, regardless of the reasons that caused this reduction.
The stratospheric polar vortex strength in spring determines to a great extent the duration and intensity of ozone depletion in the polar regions. A temperature increase in the lower subtropical stratosphere in spring leads to an increase in the stratospheric equator-to-pole temperature gradient and the subsequent strengthening of the Antarctic polar vortex, accompanied by severe springtime ozone depletion. At the same time, the unusual weakening of the Antarctic polar vortex was observed in the spring of 2019. An abnormal temperature decrease in the lower subtropical stratosphere was recorded in the same time period and probably led to a decrease in the stratospheric equator-to-pole temperature gradient and the subsequent weakening of the polar vortex.
The stratospheric polar vortex strength in spring determines to a great extent the duration and intensity of ozone depletion in the polar regions. The size of the Antarctic ozone hole usually reaches its maximum in September and then drops off during October and November. However, in 2015, a significant increase in the ozone hole area relative to climatological mean values was observed in October under the strong polar vortex conditions, and in 2002 its abnormal decrease was recorded as a result of the splitting of the polar vortex in September. A significant increase and decrease in temperature of the lower subtropical stratosphere in the spring of 2015 and 2002, which contributed to a corresponding increase and decrease in the stratospheric meridional temperature gradient during these years, was considered as a possible cause for the polar vortex strengthening in 2015 and its weakening in 2002.
In a number of works, it is shown that the reaction of extratropical circulation to strong eruptions of tropical volcanoes is the strengthening of the Northern polar vortex. The observations show that at the winter following after the autumn eruptions of volcanoes in the tropical belt there is a positive anomaly in the intensity of the polar vortex. In this paper, the reaction of the Northern polar vortex to tropical volcanic eruptions is numerically investigated. The possible mechanism of vortex amplification is shown.
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