The role of stratospheric minor warmings in producing the total ozone deficiencies over Europe in 1992 and 1993

During 1992 and 1993, record low total ozone values were observed over the middle and high northern latitudes. The ozone data from the long-operating station at Belsk, Poland, have been used to examine their departures from climatological behaviour in 1992 and 1993. It seems that not only do the exceptionally low ozone amounts recorded over the northern mid-latitudes need an explanation but also their occurrence for two years in a row. One of the possible mechanisms which may be responsible for this event is suggested to be connected with the occurrence of stratospheric minor warmings. They occur without a breakdown of the polar vortex but only with the displacement of very cold air towards lower latitudes (as in January 1992 and February 1993). It is known that air masses in the polar vortex have been chemically disturbed and, when they arrive over the sunlit middle latitudes, chemical destruction of ozone is likely to occur. During the periods under study, the strongest negative total ozone deviations correspond to strong negative temperature deviations at 30 hPa and to large potential vorticity values; this points to the presence over Europe of air masses of polar vortex origin. It has been shown that the characteristics of mid-winter stratospheric warmings and the interannual variability of winter-spring total ozone averages at Belsk are associated with each other.     

Some features of the vertical ozone distribution from millimeter wave measurements at Pushchino and Onsala observatories

A number of features of the stratospheric ozone distribution were revealed by joint millimeterwave observations of ozone emission lines at 142,175 and 110,836 GHz carried out during the winter periods of 1988–1989 and 1989–1990 at the Radioastronomical Observatory of the P.N. Lebedev Physical Institute of the Russian Academy of Sciences and at the Onsala Space Observatory of Chalmers University of Technology, Sweden. It is shown that vertical ozone variations observed at the two observatories were connected with large scale dynamical processes that occurred in the stratosphere. When the stratosphere was relatively undisturbed the ozone profiles obtained at both observatories were close to the ozone reference model given by Keating and Pitts. There were periods during a stratospheric warming when the ozone content measured at the two observatories in the 25–40 km altitude range was higher by a factor ~ 1.5 than the model values. Dynamical processes in the stratosphere also gave rise to rapid (4 h duration) and large deviations from the model ozone profile. An ozone layer depletion was observed in the 27–55 km altitude range. The observed ozone variations illustrate the sensitivity of the ozone distribution to stratospheric disturbances including stratospheric warmings.     

Modelling of ozone reduction by stratospheric aircraft

Using a two-dimensional model of the atmospheric circulation and composition, different scenarios of the effects of stratospheric aircraft on ozone layer destruction were calculated. It is shown that the ozone loss depends strongly on the altitude and composition of engine emissions from high-speed civil transport aircraft. The inclusion in the two-dimensional model of the effects of chemical eddies results in significantly reduced ozone losses in the high latitudes of the northern hemisphere during wintertime, when the dynamics of the stratosphere are strongly disturbed by planetary waves. This result can be connected with the increase of stratosphere/troposphere exchange.     

1987–1989 total ozone and ozone sounding observations in Northern Scandinavia and Antarctica,and the climatology of the lower stratosphere during 1965–1988 in Northern Finland

The total ozone observations of Tromsö (Northern Norway), Sodankylä (Northern Finland) and Murmansk (Northwestern Soviet Union) for 1987–1989 have been studied. Comparisons of the total ozone with stratospheric temperatures observed at Sodankylä have been made. These values have also been compared with the long-term mean total ozone at Tromsö and the long-term means of stratospheric temperatures at Sodankylä. No severe ozone depletions were observed. The exceptionally high total ozone values at these stations in February 1989 were connected to abnormally high stratospheric temperatures. The comparison of total ozone observed at roughly the same southern latitudes revealed great differences in the springtime.The 1989 ozone sounding observations of Sodankylä, Bear Island and Ny Ålesund (Spitzbergen) did not reveal any indications of pronounced ozone depletion. A comparative study of ozone, temperature and relative humidity indicated that the springtime variability of ozone in the lower stratosphere was clearly connected to meteorological variability. The lower tropospheric ozone had two distinct maxima, one in spring with large-scale photochemical causes and the other in summer connected with the emissions of hydrocarbons and oxides of nitrogen in Europe.Temperature observations made at Sodankylä over 24 yr revealed the existence of a potential for polar stratospheric cloud formation in the lower stratosphere in winter and early spring. A trend analysis of 50 hPa temperature revealed a negative trend of −0.16 K/yr in January and a positive trend of 0.15 K/yr in April; the annually-averaged trend was only −0.02 K/yr for this 24-yr period. When the January–February mean temperatures are separated according to the phase of the QBO in the tropical stratosphere, correlations between temperatures and sunspot numbers are found.     

Climatology of the middle atmosphere of the Southern hemisphere

Main features of spatial distribution and time variations of meteorological parameters in the Southern hemisphere at altitudes 25–80 km are reviewed on the basis of zonal empirical models revised in 1982. Meridional distribution and seasonal variations are analysed. For comparison purposes with the Northern hemisphere, a model developed by Cole and Kantor in 1978 is used. It is revealed that the compilation of new models of the Southern hemisphere atmosphere has not resulted in substantial revision of hemispheric-structure outlined earlier in studies conducted in the Central Aerological Observatory. Meridional distribution of the parameters in summer is characterized by higher values of temperature, pressure and density gradients in the stratosphere of the Southern hemisphere than in that of the Northern hemisphere. This resulted in greater advancement of the core of the summer-time easterly (low towards the equator in the Southern hemisphere than in its northern counterpart. In winter, meridional temperature gradients in the middle stratosphere are greater in the Southern hemisphere than those in the Northern hemisphere, however, rapid attenuation of the gradients with height is observed in the Southern hemisphere, and above 35–40 km they become negative near 50–60°S, in contrast to positive values typical for the Northern hemisphere stratosphere. In the wind field, specific features of the Southern hemisphere westerly flow are high intensity and relatively low altitude of the maximum speed (as compared to the Northern hemisphere).The phases of the annual temperature wave at low latitudes are similar south and north of the equator; south of 30°S a reversal of the phase is observed. The semi-annual oscillation of temperature and wind is less pronounced in middle and high latitudes of the Southern hemisphere than in the Northern hemisphere.The origin of the primary differences between the hemispheres is related mainly to lower intensity of large-scale stratospheric processes in the Southern hemisphere as compared to those in the Northern hemisphere, which is confirmed by values of the standard deviation of the parameters in the two hemispheres.In summer, temperature and pressure fields based on satellite data are symmetric relative to the poles in both hemispheres. In winter, the distortion of the mean pressure field in the mesosphere may be as great in the Southern as in the Northern hemisphere.     

Radiative perturbation due to the eruption of El Chichón: Effects on ozone

The ozone depletion over the Antarctic region is now attributed to processes involving heterogeneous chemistry on polar stratospheric clouds. Similar mechanisms are probably working also in the Northern hemisphere high latitudes [Douglass and Stolarski (1989) Geophys. Res. Lett. 16, 131] and may be important in explaining the secular trend of ozone in the last twenty years above 50° North [Pitari and Visconti (1991) J. geophys. Res. 96, 10,931]. Hofmann and Solomon [(1989) J. geophys. Res. 94, 5029] have shown that the local observed decrease in the ozone amount following the eruption of El Chichón could be explained in terms of heterogeneous chemistry on the volcanic aerosol surface. In this paper we use a two dimensional model to study the effects on ozone introduced by the El Chichón aerosols through a perturbation in the radiation field; both the temperature and the photolysis rates are affected. We show that up to half of the observed decrease may be attributed to radiative effects at mid latitudes.     

Influence of latitudinal and longitudinal variations of ozone and water vapour on the solar semidiurnal tide

A new tidal source model, based on climatological global ozone and water vapour distributions, has been obtained for January, April, July and October. The source model is used for modelling the solar semidiurnal tide in the lower thermosphere within the framework of the classical tidal theory. The observed phase quasibimodality of the semidiurnal tide at middle latitudes is possibly formed, to a great extent, by two types of hemispheric asymmetry (changing sharply near the equinox) of the ozone distribution. Near 95 km at middle latitudes, the ozone and water vapour distribution nonzonality yields typical values ~2 m/s for maximum longitudinal variations of the zonal and meridional wind amplitudes, and the range ~0.2–0.5 h for maximum longitudinal phase variations in the Northern hemisphere, while they can reach ~10 m/s and ~1.5 h in the Southern hemisphere. The hemispheric asymmetry is mainly caused by the effect of the water vapour tidal source.     

An observational study of the D-region winter anomaly in lower latitudes during sudden stratopsheric warmings

An observational study of the D-region winter anomaly of HF radio wave absorption in lower latitudes has been made during the period of a sudden stratospheric warming of the 1967/1968 winter. By means of large-scale isopleth analysis of the absorption index, ƒ_min, and of meridional winds near 70 km height along 60°N, it is found that there exists a winter anomaly in lower latitudes which is comparable in order to that in middle latitudes, resulting from a nitric oxide (NO) increase due to southward transport from higher latitudes by well-developed planetary wave winds. From the daily changes of absorption in the equatorial region, it is found that the enhanced absorption reveals an oscillation with a period of about 2 weeks and has its maximum in the region south of 20°N. The period is similar to that of planetary wave amplitudes in the winter stratosphere and mesosphere, suggesting that an effect of planetary waves could contribute to the equatorial anomaly of the absorption in the D-region.     

An observational study of the D-region winter anomaly and sudden stratospheric warmings

An observational study of the link between the winter anomaly in ionospheric absorption and sudden stratospheric warmings for the 1967/1968 winter has been made. On the basis of the daily large-scale distributions of the absorption index, f_min, it is found that the winter anomaly during sudden warming could result from a NO increase induced by southward transport from the polar region, where NO is most abundant associated with a well-developed vortex in the D-region (large amplitude planetary wave).     

Tidal winds from the MLT global radar network during the first LTCS campaign—September 1987

Winds and tides were measured by a number of MLT (Mesosphere, Lower Thermosphere) radars with locations varying from 43–70°N, 35–68°S, during the first LTCS (Lower Thermosphere Coupling Study) Campaign, 21–25 September 1987. The mean winds were globally westerly, consistent with early winter-like (NH) and late winter (SH) circulations.The semi-diurnal tide had vertical wavelengths near or less than 100 km at most locations, with some latitudinal variation (longer/shorter at lower latitudes in the NH/SH)—amplitudes decreased at high latitudes. The global tide was closer to anti-symmetric, with northward components being in phase at 90 km. Numerical model calculations [Forbes and Vial (1989), J. atmos. lerr. Phys. 51, 649] for September have rather similar wavelengths and amplitudes; however, the global tide was closer to symmetric, and detailed latitudinal trends differed from observed.The diurnal tide had similar wavelengths in each hemisphere, with short values (~30 km) at 35°, long (evanescence) at 68–70°, and irregular phase structures at mid-latitudes. The tide was neither symmetric nor anti-symmetric. Model calculations for the equinox [Forbes. S and Hagan (1988), Planet. Space Sci. 36, 579] were by nature symmetric, and showed the short wavelengths extending to mid-latitudes (43–52°). Southern hemisphere phases were significantly (6–8 h) different from observations. Amplitudes decreased at high latitudes in model and observation profiles.     

A SIMPLIFIED MODEL OF THE GLOBAL INTERACTION OF THE ATMOSPHERE,OCEAN, AND CONTINENTS

The authors outline a model, based on interacting cells which simulate conditions at high and low latitudes, to describe and predict energy and other flows occurring between the atmosphere, oceans, and continents. They propose that this model is more accurate and efficient (in terms of the use of computer time) than conventional hydrodynamic models based on the Navier-Stokes and other equations. Tests of the model for conditions in the Southern Hemisphere provided results, in terms of annual swings in air temperature (and in another case, also for water vapor pressure and precipitation regimes), which corresponded generally with actual observations (translated by Andrew R. Bond).     

Effects of geomagnetic storms in the lower ionosphere,middle atmosphere and troposphere

Geomagnetic storm effects at heights of about 0–100 km are briefly (not comprehensively) reviewed, with emphasis being paid to middle latitudes, particularly to Europe. Effects of galactic cosmic rays, solar particle events, relativistic and highly relativistic electrons, and IMF sector boundary crossings are briefly mentioned as well. Geomagnetic storms disturb the lower ionosphere heavily at high latitudes and very significantly also at middle latitudes. The effect is almost simultaneous at high latitudes, while an after-effect dominates at middle latitudes. The lower thermosphere is disturbed significantly. In the mesosphere and stratosphere, the effects become weaker and eventually non-detectable. There is an effect in total ozone but only under special conditions. Surprisingly enough, correlations with geomagnetic storms seem to reappear in the troposphere, particularly in the Northern Hemisphere. Atmospheric electricity is affected by geomagnetic storms, as well. We essentially understand the effects of geomagnetic storms in the lower ionosphere, but there is a lack of mechanisms to explain correlations found deeper in the atmosphere, particularly in the troposphere. There seem to be two different groups of effects with possibly different mechanisms—those observed in the lower ionosphere, lower thermosphere and mesosphere, and those observed in the troposphere.     

The El Chichon volcanic cloud in the stratosphere: lidar observation at Fukuoka and numerical simulation

The stratospheric volcanic cloud from the eruption.of El Chichon, Mexico, on 4 April 1982 was observed routinely by a Nd: YAG lidar system from 18 April 1982 at Kyushu University, Fukuoka, Japan. The observed layers of the cloud above 20 km were in the easterly wind region and those below 20 km were in the westerly region. The main part of the cloud mass was in the upper layer. This upper layer broadened slowly until September 1982, then broadened rapidly and merged with the lower layer as the easterly wind changed to the westerly wind. The vertical eddy diffusion coefficient estimated from the broadening of the upper layer was much smaller than the value usually used in the one-dimensional model calculation of chemical components until September and subsequently remained at about the same value. The increase of the integrated backscattering coefficient (IBC) was about two orders of magnitude larger than the largest increase after volcanic injections for the last 10 years. The IBC reached a maximum value on 3 May and gradually decreased until August 1982, then re-increased until December 1982. The IBC between December 1982 and February 1983 was about the same value as in May 1982. Using the one-dimensional stratospheric sulfate aerosol model simulations it was concluded that to explain the broadening of the upper layer an eddy diffusion coefficient of about 10²cm²s^-1 would be needed in the easterly wind region in summer. It was also concluded that the IBC re-increase was caused after advective horizontal transport from lower to higher latitudes by chemical reactions within the upper layer without meridional diffusion during summer and that the transport was controlled by nucleation, which gives rise to small particles, a decreasing settling velocity of the volcanic cloud and then the cloud being less affected by horizontal transport.     

Middle atmosphere abundances of water vapor and ozone during MAP/WINE

Water vapor and ozone concentrations measured at mid and high latitudes above Europe during the MAP/WINE Campaign in the winter 1983/1984 are presented. Both water vapor and ozone distributions are found to be variable and structured. On two occasions strong enhancements of mesospheric ozone were recorded, which were probably caused by dynamic effects. The assumption of a photochemical equilibrium for ozone at high latitudes in winter does not appear justified according to the variations measured during MAP/WINE. Water vapor mixing ratios determined in the stratosphere and mesosphere above Scandinavia yield average mixing ratios of near 4 ppmv.     

On the problem of a connection between ozone dynamics at high latitudes and magnetospheric processes

Two data sets of ozone density measurements over a wide latitudinal range in the Arctic during summer and winter seasons arc presented. It is shown that geophysical effects manifest themselves in the O₃ dynamics in the high latitude region under various circumstances. Therefore a type of total ozone content diurnal variation is a distinctive feature in the auroral oval as well as the polar cap and must be taken into account in any full model of ozone dynamics in the polar regions.     

On the Antarctic ozone hole

Some key observational evidence, that throws light on current ³ questions regarding the Antarctic ozone hole, is discussed. Together with dynamical theory and high-resolution numerical modelling results, the observed facts indicate that the problem has a very high degree of spatio-temporal structure in that sharp distinctions need to be made, for instance, between September and October behaviour, between behaviour near 50mb and near 100mb, and between soundings taken well inside, near the edge of, and outside the polar vortex. In winter and early spring the interior of the vortex probably behaves as an isolated material entity (at least on isentropic surfaces above about 70mb), while outside the vortex the ozone column is being increased in the classical, transport related manner, including the effect of relatively strong diabatic descent. Statistical constructs that blur these distinctions may miss important clues. The weight of evidence (as of August 1987) makes it difficult to escape the conclusion that substantial chemical destruction of ozone takes place inside the vortex in September, as originally postulated by Farmanet al.Nature315, 207 (1985).     

Maps of Upper Air Currents Above the Earth

Maps have been compiled for the zonal and meridional components of the resultant velocities of upper air currents in January and July. The principal features of these maps are described and analyzed, and the winter and summer situations of the Northern and Southern Hemispheres are compared.     

Large-scale irregularities of electron concentration in the southern magnetic anomaly area according to Intercosmos 19 satellite data

Using Intercosmos 19 satellite topside sounding data, a type of complex ionogram for which the lowest frequency of the radio-wave which has passed through the ionosphere is smaller than the greatest frequency of the radio-wave reflected from the ionosphere is considered. (Under normal conditions these frequencies are identically equal.) A mechanism is suggested by which radio-waves transmitted by the satellite propagate over 3000 km in the topside ionosphere in the presence of inclined large-scale plasma structures, which can explain the main features of such ionograms.The space-time distribution of this phenomenon on a global scale is analysed. It is shown that it manifests itself mainly in the local winter, in the daytime and in the Southern Hemisphere. It is hypothesized that these large-scale irregularities are formed in the vicinity of the South Atlantic magnetic anomaly and then move westward.     

Mid-latitude rocket measurements op plasma irregularities associated with topside density depletion

A plasma irregularities spectrum analyzer and a Langmuir probe experiment on a rocket experiment conducted at mid-latitudes during quiet night-time winter conditions revealed the existence of an isolated plasma density depletion between 700 and 1100 km. A substantial enhancement of intensity of the irregularities coinciding with the depletion was observed over a broad band of irregularity sizes ranging from tens of meters to several kilometers. The power spectral index was equal 0.84∓0.17 as compared to 1.71∓0.56 for the irregularities outside the plasma depletion.