Arctic Stratosphere Circulation Changes in the 21st Century in Simulations of INM CM5

Simulations of Institute of Numerical Mathematics (INM) coupled climate model 5th version for the period from 2015 to 2100 under moderate (SSP2-4.5) and severe (SSP5-8.5) scenarios of greenhouse gases growth are analyzed to investigate changes of Arctic polar stratospheric vortex, planetary wave propagation, Sudden Stratospheric Warming frequency, Final Warming dates, and meridional circulation. Strengthening of wave activity propagation and a stationary planetary wave number 1 in the middle and upper stratosphere, acceleration of meridional circulation, an increase of winter mean polar stratospheric volume (Vpsc) and strengthening of Arctic stratosphere interannual variability after the middle of 21st century, especially under a severe scenario, were revealed. March monthly values of Vpsc in some winters could be about two times more than observed ones in the Arctic stratosphere in the spring of 2011 and 2020, which in turn could lead to large ozone layer destruction. Composite analysis shows that “warm” winters with the least winter mean Vpsc values are characterized by strengthening of wave activity propagation from the troposphere into the stratosphere in December but weaker propagation in January–February in comparison with winters having the largest Vpsc values.

Comparison of Key Characteristics of Remarkable SSW Events in the Southern and Northern Hemisphere

<p>An exceptionally strong sudden stratospheric warming (SSW) in the Southern Hemisphere (SH) during September 2019 was observed. Because SSW in the SH is very rare, comparison with the only recorded major SH SSW is done. According to World Meteorological Organization (WMO) definition, the SSW in 2019 has to be classified as minor. The cause of SSW in 2002 was very strong activity of stationary planetary wave with zonal wave-number (ZW) 2, which reached its maximum when the polar vortex split into two circulations with polar temperature enhancement by 30 K/week and it penetrated deeply to the lower stratosphere and upper troposphere. On the other hand, the minor SSW in 2019 involved an exceptionally strong wave-1 planetary wave and a large polar temperature enhancement by 50.8 K/week, but it affected mainly the middle and upper stratosphere. The strongest SSW in the Northern Hemisphere was observed in 2009. This study provides comparison of two strongest SSW in the SH and the strongest SSW in the NH to show difference between two hemispheres and possible impact to the lower or higher layers.</p>

Comparison of Key Characteristics of Remarkable SSW Events in the Southern and Northern Hemisphere

An exceptionally strong sudden stratospheric warming (SSW) in the Southern Hemisphere (SH) during September 2019 was observed. Because SSW in the SH is very rare, comparison with the only recorded major SH SSW is done. According to World Meteorological Organization (WMO) definition, the SSW in 2019 has to be classified as minor. The cause of SSW in 2002 was very strong activity of stationary planetary wave with zonal wave-number (ZW) 2, which reached its maximum when the polar vortex split into two circulations with polar temperature enhancement by 30 K/week and it penetrated deeply to the lower stratosphere and upper troposphere. On the other hand, the minor SSW in 2019 involved an exceptionally strong wave-1 planetary wave and a large polar temperature enhancement by 50.8 K/week, but it affected mainly the middle and upper stratosphere. The strongest SSW in the Northern Hemisphere was observed in 2009. This study provides comparison of two strongest SSW in the SH and the strongest SSW in the NH to show difference between two hemispheres and possible impact to the lower or higher layers.

Migrating and non-migrating tides observed in the stratosphere from FORMOSAT-3/COSMIC temperature retrievals

Formosa Satellite-3 and Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) temperature data during October 2009–December 2010 are analysed for tides in the middle atmosphere from ∼10 to 50 km. COSMIC is a set of six micro-satellites in near-Sun-synchronous orbits with 30∘ orbital separations that provides good phase space sampling of tides. Short-term tidal variability is deduced by considering ±10 d data together. The migrating diurnal (DW1) tide is found to peak over the Equator at 30 km. It maximises and slightly shifts poleward during winters. Over middle and high latitudes, DW1 and the non-migrating diurnal tides with wavenumber 0 (DS0) and wavenumber 2 (DW2) are intermittent in nature. Numerical experiments in the current study show that these could be a result of aliasing as they are found to occur at times of a steep rise or fall in the mean temperature, particularly during the sudden stratospheric warming (SSW) of 2010. Further, the stationary planetary wave component of wavenumber 1 (SPW1) is found to be of very large amplitudes in the Northern Hemisphere, reaching 18 K at 30 km over 65∘ N. By using data from COSMIC over shorter durations, it is shown that aliasing between stationary planetary wave and non-migrating tides is reduced and thus results in the large amplitudes of the former. This study clearly indicates that non-linear interactions are not a very important source for the generation of non-migrating tides in the middle- and high-latitude winter stratosphere. There is also a modulation of SPW1 by a ∼60 d oscillation in the high latitudes, which was not seen earlier.

Migrating and Non-Migrating Tides Observed in the Stratosphere from FORMOSAT-3/COSMIC Temperature Retrievals

FORMOSAT-3/COSMIC temperature data during 2009 to 2010 are analysed for tides in the middle atmosphere from ~ 10 to 50 km. COSMIC is a set of six micro satellites in near sun synchronous orbits with 30° orbital separations and provides good phase space sampling of tides. Short term tidal variability is deduced by considering ± 10 days' data together. The DW1 tide is found to peak over the equator at 30 km. It maximises and slightly shifts poleward during winters and thus is attributed to ozone absorption. Over mid and high latitudes, DW1 and the non-migrating tides DS0 and DW2 are intermittent in nature. Numerical experiments in the current study show that these could be a result of aliasing as they are found to occur at times of steep rise or fall in the mean temperature, particularly during the SSW of 2010. Further, stationary planetary wave components are found to be of very large amplitudes in the northern hemispheres reaching 18 K at 30 km over 65° N. By using data from COSMIC over shorter durations, aliasing between SPW and non-migrating tides is reduced and thus results in the large amplitudes of the former. This study clearly indicates that non-linear interactions are not a very important source of generation of the non migrating tides in the high latitude winter hemisphere. There is also a modulation of SPW1 by ~ 60 days in the high latitudes, which was not seen earlier.

Statistics on Nonmigrating Diurnal Tides Generated by Tide-Planetary Wave Interaction and Their Relationship to Sudden Stratospheric Warming

The nonmigrating diurnal tide, DW2, is known to have a source from the stationary planetary wave with wavenumber 1 (SPW1) and the migrating diurnal tide (DW1) interaction. Recent research has shown that DW2 time evolution in the equatorial mesopause tracks very well with SPW1 in the polar stratosphere for the winter of 2009–2010, which contains a sudden stratospheric warming (SSW) vortex split event. This paper extends previous research and investigates the relationship between these two waves for 31 winters from 1979 to 2010 with the extended Canadian Middle Atmosphere Model (eCMAM) through correlation and composite analysis. Significant correlations are present between the two waves in 20 out of 31 winters (65%). We separate the 31 winters into four categories: SSW-displacement, SSW-split, minor-SSW, and no-SSW. Our results show that there is no significant difference among the four categories in terms of correlations between the two waves. Although SPW1 is usually stronger during a SSW-D winter, this does not warrant a stronger interaction with DW2.

On the origin of the mesospheric quasi-stationary planetary waves in the unusual Arctic winter 2015/2016

The midwinter 2015/2016 was characterized by an unusually strong polar night jet (PNJ) and extraordinarily large stationary planetary wave (SPW) amplitudes in the subtropical mesosphere. The aim of this study is, therefore, to find the origin of these mesospheric SPWs in the midwinter 2015/2016 study period. The study duration is split into two periods: the first period runs from late December 2015 until early January 2016 (Period I), and the second period from early January until mid-January 2016 (Period II). While the SPW 1 dominates in the subtropical mesosphere in Period I, it is the SPW 2 that dominates in Period II. There are three possibilities explaining how SPWs can occur in the mesosphere: (1) they propagate upward from the stratosphere, (2) they are generated in situ by longitudinally variable gravity wave (GW) drag, or (3) they are generated in situ by barotropic and/or baroclinic instabilities. Using global satellite observations from the Microwave Limb Sounder (MLS) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) the origin of the mesospheric SPWs is investigated for both time periods. We find that due to the strong PNJ the SPWs were not able to propagate upward into the mesosphere northward of 50∘ N but were deflected upward and equatorward into the subtropical mesosphere. We show that the SPWs observed in the subtropical mesosphere are the same SPWs as in the mid-latitudinal stratosphere. Simultaneously, we find evidence that the mesospheric SPWs in polar latitudes were generated in situ by longitudinally variable GW drag and that there is a mixture of in situ generation by longitudinally variable GW drag and by instabilities at mid-latitudes. Our results, based on observations, show that the abovementioned three mechanisms can act at the same time which confirms earlier model studies. Additionally, the possible contribution from, or impact of, unusually strong SPWs in the subtropical mesosphere to the disruption of the quasi-biennial oscillation (QBO) in the same winter is discussed.

On the origin of the mesospheric quasi-stationary planetary waves in the unusual Arctic winter 2015/16

The mid winter 2015/16 was characterized by an unusually strong polar night jet (PNJ) and by extraordinarily large stationary planetary wave (SPW) amplitudes in the subtropical mesosphere. The aim of this study is to find the origin of these mesospheric SPWs in mid winter 2015/16. The time period studied here is split into two time periods. The first period runs from late December 2015 until early January 2016 and the second period from early January until mid January 2016. While the SPW 1 dominates in the subtropical mesosphere in Period I, it is the SPW 2 that dominates in Period II. There are three possibilities how SPWs can occur in the mesosphere: 1) they propagate upward from the stratosphere, 2) they are in situ generated by longitudinally variable gravity wave (GW) drag, or 3) they are in situ generated by barotropic and/or baroclinic instabilities. Using global satellite observations from the Microwave Limb Sounder (MLS) and from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) the origin of the mesospheric SPWs is investigated for both time periods. We found that due to the strong PNJ the SPWs were not able to propagate upward into the mesosphere northward of 50°N but were deflected upward and equatorward into the subtropical mesosphere. We show that the SPWs observed in the subtropical mesosphere are the same SPWs as in the mid-latitudinal stratosphere. At the same time we found evidence that the mesospheric SPWs in polar latitudes were in situ generated by longitudinally variable GW drag and that there is a mixture of in situ generation by longitudinally variable GW drag and by instabilities in mid latitudes. Our results based on observations show that every three mechanisms, upward propagating SPW and in situ generated SPWs by longitudinally variable GW drag and instabilities can act at the same time which confirms earlier model studies. Additionally, a possible contribution or impact of the unusually strong SPWs in the subtropical mesosphere to the disruption of the QBO in the same winter is discussed.

Influence of the sudden stratosphere warming on quasi-2 day waves

The influence of the sudden stratosphere warming (SSW) on quasi-2 day wave (QTDW) with westward zonal wavenumber 3 (W3) is investigated using the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). The summer easterly jet below 90 km is strengthened during an SSW, which results in a larger refractive index and thus more favorable condition for the propagation of W3. In the winter hemisphere, the Eliassen Palm (EP) flux diagnostics indicate that the strong instabilities at middle and high latitudes in the mesopause region are important for the amplification of W3, which are weakened during SSW periods due to the deceleration or even reversal of the winter westerly winds. Nonlinear interactions between the W3 and the wavenumber 1 stationary planetary wave produce QTDW with westward zonal wavenumber 2 (W2). The meridional wind perturbations of the W2 peak in the equatorial region, while the zonal wind and temperature components maximize at middle latitudes. The EP flux diagnostics indicate that the W2 is capable of propagating upward in both winter and summer hemispheres, whereas the propagation of W3 is mostly confined to the summer hemisphere. This characteristic is likely due to the fact that the phase speed of W2 is larger, and therefore its waveguide has a broader latitudinal extension. The larger phase speed also makes W2 less vulnerable to dissipation and critical layer filtering by the background wind when propagating upward.