The dynamic barrier of the polar vortex prevents the penetration of air masses into the vortex and contributes to the preservation of extremely low temperatures inside the vortex. The melting of polar stratospheric clouds in winter occurs as a result of the dynamic barrier weakening in the lower stratosphere. The dynamic barrier exists when the wind speed over the entire edge of the polar vortex is more than 20, 26 and 30 m/s respectively at the 50, 20 and 10 hPa levels. We studied the dynamics of the Arctic polar vortex in the winter-spring of 2017/2018 before and after its splitting on 10 February at the 50, 20 and 10 hPa levels by the vortex delineation method using geopotential. In the middle stratosphere, since 15 February, an irreversible breakdown of the polar vortex was observed (the dynamic barrier weakening and the vortex area decrease below 10 million km2 ), and in the lower stratosphere at the 50 hPa level, a short-term recovery of the dynamic characteristics of the polar vortex was observed from 9 to 17 March. The case of 2017/2018 is one of the exceptions, when the collapsing cyclone experienced a short-term recovery of the polar vortex characteristics in the lower stratosphere in spring after the vortex area decreased below 10 million km2 and the dynamic barrier weakened.
Volcanic eruptions can contribute to polar ozone depletion when volcanic aerosol propagates into the tropical or polar stratosphere. During the period from 1850 to the present, none of the eruptions of extratropical volcanoes in the Northern Hemisphere was observed in the tropical stratosphere and, therefore, could not contribute to the polar vortex strengthening in the conditions of an increase of the stratospheric equator-to-pole temperature gradient as a result of an increase of the tropical stratospheric temperature. However, this is possible during mid-latitude volcanic eruptions with VEI ≥ 6 and during high-latitude volcanic eruptions with VEI ≥ 7. During the period from 1980 to the present, none of the eruptions of extratropical volcanoes in the Northern Hemisphere influenced the intensity of Arctic ozone depletion, since in some cases the ejection of eruption products was outside the polar vortex, and in other cases the height of the ejection was insufficient and the volcanic aerosol was removed from the stratosphere as a result of sedimentation even before the polar vortex formation. However, the effect of extratropical volcanic eruptions on Arctic ozone depletion is possible when the eruption products enter the polar vortex, or when a volcanic aerosol propagates into the polar region before the polar vortex formation with a sufficient lifetime in the stratosphere, determined, in particular, by the height of the ejection.
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 Arctic stratospheric polar vortex usually forms in autumn, reaches its peak intensity in mid-winter and decays from late winter to spring. In most cases, the polar vortex breakdown occurs as a result of the penetration of vertically propagating planetary waves into the stratosphere and is accompanied by the occurrence of sudden stratospheric warmings. In the winter of 2018/2019, the vortex breakdown occurred in late December after increased wave activity for more than 10 days in the first half of winter. In this work, we examined the unusual dynamics of the Arctic polar vortex in the lower stratosphere in the winter of 2018/2019 using a new method based on the vortex delineation.
The stratospheric aerosol layer is mainly composed of sulfuric acid aerosol particles, which are microdroplets of a 75 % aqueous solution of sulfuric acid H2SO4. The most powerful source of stratospheric aerosol particles is large volcanic eruptions that inject significant amounts of sulfur dioxide SO2 into the stratosphere. Sulfur dioxide is oxidized to a sulfuric acid aerosol in the stratosphere within two weeks. The concentration of sulfuric acid aerosol in the lower stratosphere can increase by 1–2 orders of magnitude as a result of large volcanic eruptions. In this work, we presented a list of volcanic eruptions with the possible injection of aerosols into the stratosphere from 1800 to 2020.
The polar vortex strength and persistence from December to January play an important role in Arctic ozone depletion from late winter to spring. The short-term elongation or displacement of the Arctic polar vortex in midwinter, occurring under the influence of vertically propagating planetary waves, can lead to the local weakening of the dynamical barrier of the vortex edge. The weakening of the vortex edge in winter, accompanied by short-term complete melting of polar stratospheric clouds (PSCs), leads to the fact that the springtime ozone destruction was not observed even under the conditions of the strong polar vortex (in the presence of PSCs). In this work, we showed that complete or almost complete melting of PSCs in midwinter is observed during the local weakening of the dynamic barrier of the Arctic polar vortex edge in the lower stratosphere, characterized by a decrease in zonal and meridional winds below 20 m/s for at least 3 hours in a small section of the vortex edge determined by the geopotential values of about 19.5⋅104 m2/s2 at the 50 hPa pressure level.
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.
The polar vortex strengthening leads not only to a temperature decrease in the lower stratosphere, but also to its increase in the upper stratosphere inside the vortex. Over the Antarctic, this dependence is observed from autumn to spring: in the upper stratosphere high temperatures are observed inside the polar vortex, and low temperatures occur outside, especially in spring. Over the Arctic, a temperature increase in the upper Arctic stratosphere is observed under conditions of the strengthening of the northern polar vortex. Temperature variations in the upper polar stratosphere are determined by the ozone concentration and depend on the dynamics of the polar vortex: with a decrease in the ozone content inside the strong vortex in the upper stratosphere, a temperature increase is observed.
The influence of the phase of the quasi-biennial oscillation (QBO) on the period of stratospheric ozone depletion over the Arctic is considered. The list of Arctic ozone depletion events from 1979 to 2019 is given. Most of the Arctic ozone depletion events have been well researched and extensively referenced. In this work, we examined ozone depletion observed in the winter of 1983, 1986 and 1987. Arctic ozone depletion occurring during the easterly and westerly phases of the QBO are usually observed in January and from February to April, respectively.
The influence of the stratospheric polar vortex on the tropospheric vortex begins to appear in November, is significantly enhanced from December to February and decreases in March. The strong stratospheric polar vortex centered over the North Pole enhances the tropospheric one, which largely repeats the shape and location of the stratospheric vortex during this period. The strong stratospheric polar vortex displaced relative to the pole can lead to the splitting of the tropospheric vortex. And finally, the splitting of the stratospheric vortex in winter leads to a significant weakening of the tropospheric one.
The Arctic stratospheric polar vortex usually forms in autumn, reaches its peak intensity in mid-winter and decays in spring. The earlier breakdown of the polar vortex (from January to March) occurs due to the upward propagation of planetary waves from the troposphere into the stratosphere, leading to the occurrence of sudden stratospheric warmings (SSWs). SSWs are accompanied by a strong displacement or splitting of the polar vortex. In most cases, SSWs occur from late January to March. In this study, we analyze the effects of one of the earliest SSWs which occurred on 18 December 1998. The Arctic polar vortex recovered in February 1999 after its splitting in December 1998 and decayed in late February after the second splitting of the polar vortex.
One of the most prominent features of the Arctic polar vortex is its large interannual variability associated with a high frequency of occurrence of sudden stratospheric warmings (SSWs). SSWs appear due to the breaking and dissipation of planetary Rossby waves, propagating from the troposphere into the stratosphere, as a result of interaction with the westerly zonal flow (i.e. the stratospheric polar vortex). In this study, we analyze the dynamics of the Arctic polar vortex under the influence of the anomalous upward wave activity flux in the winter 2012/2013.
Black carbon (BC) aerosol particles, when being in sufficient amount in the Earth’s atmosphere, significantly influence its radiation balance and intensively deplete ozone by heterogeneous chemical reactions. There are many sources of BC in the troposphere: bio- and fossil-fuel burning, forest and bush fires, power generation and industrial processes, engines, etc. Aircraft emissions are widely assumed to be the principal source of BC nanoparticles in the stratosphere. In this paper, we make a hypothesis that Plinian eruptions with VEI ≥ 5 are a strong occasional source of long-lived BC in the stratosphere and suggest a possible mechanism of BC formation in volcanic conduits during the eruptions. Based on this hypothesis, and using the 1991 Pinatubo eruption (VEI = 6) as an example, we roughly estimate CBC and number concentration of BC particles NBC, which are required to cause ozone depletion events in the tropical stratosphere (at altitudes where ozone depletion cannot occur due to the presence of volcanic sulfuric acid aerosols). For this purpose, we use vertical ozone profiles obtained over the tropical station Hilo (19.72° N, 155.11° W; Hawaii) in September and November 1992. The September CBC and NBC values, we calculated for BC particles of mean radius 120 nm at an altitude of ~20.5 km, are 35.4 ±30.6 ng/m3 and (2.2±1.9)×106 particles/m3, respectively. The November CBC and NBC values for BC particles of mean radius 40 nm at an altitude of ~30 km are 25.3 ±7.8 ng/m3 and (4.2±1.3)×107 particles/m3, respectively.
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