Associations between the 11-year solar cycle,the QBO and the atmosphere. Part I: the troposphere and stratosphere in the northern hemisphere in winter

Linear correlations between the three solar cycles in the period 1956–1987 and high-latitude stratospheric temperatures and geopotential heights show no associations. However, when the data are stratified according to the east or west phase of the quasi-biennial-oscillation (QBO) in the equatorial stratosphere significant correlations result: when the QBO was in its west phase the polar data were positively correlated with the solar cycle while those in middle and low latitudes were negatively correlated. The converse holds for the east phase of the QBO. Marked relationships existed throughout the troposphere too.No major mid-winter warming occurred in the west phase of the QBO during a minimum in the three solar cycles. In the east phase major warmings tended to take place in the minima of the cycle. Thus the signal of the quasi-biennial-oscillation in the extratropical stratosphere tends to be strengthened in solar minima, and weakened in solar maxima.     

Theoretical models of polar-cap convection under the influence of a northward interplanetary magnetic field

The unexpected patterns of high-latitude auroral luminosity and ionospheric convection that are observed when the interplanetary magnetic field (IMF) has a northward orientation have inspired a variety of theoretical interpretations. The existing models, all referring to steady-state conditions, can be classified according to the topology of the polar magnetic field lines and of the polar-cap convection streamlines. The classes of model include: (1) a closed magnetosphere model, (2) a conventional open model with a distorted, but topologically unchanged, polar-cap boundary, (3) a conventional open model with distorted, but topologically unchanged, polar-cap convection cells, (4) a modified open model with ‘lobe convection cells’ contained wholly on open magnetic-field lines, and (5) a modified open model with a bifurcated polar cap. The third and fourth types require significant regions of sunward flow on open polar-cap field lines, a concept that presents serious theoretical difficulties. The other three types appear equally viable from a theoretical point of view, and the comparison against observations is an ongoing enterprise. Outstanding theoretical questions include (a) how do observed structures in the polar ionosphere map along magnetic field lines into the magnetosphere?, (b) what is the mechanism that drives the observed sunward convection at highest latitudes on the day side?, and (c) what role does time dependence play in the observed phenomena?     

Boundary populations in the polar caps

The morphology of precipitating particles, measured at low altitude in the polar regions, varies systematically with the strength and direction of IMF B_z and with solar wind speed V_sw. We use particle data taken onboard the DMSP satellites to determine these variations. Both individual satellite passes during the storm/quieting period of 26 and 27 August 1990, and statistical maps compiled from a data base over 4.5 yr are presented. We focus attention on those magnetospheric populations that have magnetosheath characteristics, the boundary populations. We show that the precipitating ion boundary population, whose down-coming spectra can be fitted to streaming Maxwellians, expands from a region confined near the dayside cusp for southward IMF, to a thick, annular region, including the dayside cusp, for northward IMF. The expansion in local time is inhibited by increasing solar wind speed. Boundary electrons behave somewhat differently. They have easier access to the polar regions and their variations have shorter spatial/temporal scale lengths than the boundary ions. For strongly northward IMF, intense, agitated boundary electrons can be found over all or part of the polar cap. Broad regions (up to ~ 100 km) of strongly accelerated electrons (several keV) that produce visible arcs are embedded in this population. Two features of the ion boundary population help identify its source. (1) The spectra of the boundary ions expanding into the polar cap exhibit field-aligned streaming, which, downtail, is toward the Earth. (2) The region into which the boundary ions expand best maps magnetically to a dawn-dusk cut across the neutral sheet, rather than to the low-latitude boundary layer. Therefore, we conclude that the immediate source for boundary ions in the polar regions during northward IMF is the plasma sheet boundary layer. These ions reach tail lobe field lines by convection whose direction when mapped to the ionosphere is sunward. Significant change in the topology of the magnetospheric magnetic field, and, in particular, the closing of high-latitude field lines, is not required to explain the data.     

Simulations of the behaviour of the polar thermosphere and ionosphere for northward IMF

The dynamics and structure of the polar thermosphere and ionosphere within the polar regions are strongly influenced by the magnetospheric electric field. The convection of ionospheric plasma imposed by this electric field generates a large-scale thermospheric circulation which tends to follow the pattern of the ionospheric circulation itself. The magnetospheric electric field pattern is strongly influenced by the magnitude and direction of the interplanetary magnetic field (IMF), and by the dynamic pressure of the solar wind. Previous numerical simulations of the thermospheric response to magnetospheric activity have used available models of auroral precipitation and magnetospheric electric fields appropriate for a southward-directed IMF. In this study, the UCL/Sheffield coupled thermosphere/ionosphere model has been used, including convection electric field models for a northward IMF configuration. During periods of persistent strong northward IMF B_z, regions of sunward thermospheric winds (up to 200 m s⁻¹) may occur deep within the polar cap, reversing the generally anti-sunward polar cap winds driven by low-latitude solar EUV heating and enhanced by geomagnetic forcing under all conditions of southward IMF B_z. The development of sunward polar cap winds requires persistent northward IMF and enhanced solar wind dynamic pressure for at least 2–4 h, and the magnitude of the northward IMF component should exceed approximately 5 nT. Sunward winds will occur preferentially on the dawn (dusk) side of the polar cap for IMF B_y negative (positive) in the northern hemisphere (reverse in the southern hemisphere). The magnitude of sunward polar cap winds will be significantly modulated by UT and season, reflecting E-and F-region plasma densities. For example, in northern mid-winter, sunward polar cap winds will tend to be a factor of two stronger around 1800 UT, when the geomagnetic polar cusp is sunlit, then at 0600 UT, when the entire polar cap is in darkness.     

Empirical convection models for northward IMF

It is clear that polar cap convection during times of northward IMF is more structured and of lower mean speed than at times of southward IMF. This, coupled with the fact that the polar cap is smaller, means that empirical models are more difficult to construct with certainty. It is also clear that sunward flow deep in the polar cap is often observed, but its connection with the rest of the flow pattern is controversial.At present, empirical models are of three types: ‘statistical’ models wherein data from different days but with similar IMF conditions are averaged together; ‘pattern recognition’ models, which are built up by examining individually hundreds of passes to derive a ‘typical’ pattern which embodies features frequently observed; and ‘assimilative’ models, which use data of different types and from as many locations as possible, but all taken at the same time, in order to derive a snapshot (or series of snapshots) of the entire pattern.Each type of model has its own difficulties. Statistical models, by their very nature, smooth out flow features (e.g. the convection reversal, and the locus of sunward flow deep in the polar cap) which are not found at precisely the same invariant latitudes and magnetic local times on different days. Pattern recognition models are better at reproducing small-scale features, but the large-scale pattern can be a matter of interpretation. Assimilative models (such as AMIE) hold out the best hope for creating instantaneous, global convection patterns; however, the analysis technique tends to be most irregular (and least reliable) in the regions which are not well covered by in situ data. It appears that, at least at times, a four cell model with sunward flow at the highest and lowest latitudes, and antisunward flow in between, is consistent with the observations. At other times, the observations may be consistent with a two-cell convection pattern, but which includes significant meanders within the polar cap.     

On the structure and circulation of the polar thermosphere under magnetically quiet conditions

A theoretical study is presented bearing on the thermospheric circulation and composition at polar latitudes. The observed motions and density perturbations in N₂, O and He have signatures which may be understood in terms of two different source mechanisms. We consider electric field momentum coupling and Joule heating as well as interactions between both processes. A spectral model in terms of vector spherical harmonics (with magnetic coordinates) is used, delineating the diurnal and mean (time independent) components. The important non-linearities are evaluated in configuration space. The electric field model of Volland and the global average density and temperature variations of Hedin (MSIS) are adopted as input. Our analysis leads to the following conclusions. (1) The vortex type double cell polar circulation (zonal wave number m = 1) is primarily driven by collisional momentum transfer from electric field induced ion convection. (2) Because of the thermospheric low pass filter, a large time independent component (zonal wave number m = 0) is produced by Joule heating; the heavier species (N₂) being concentrated where the lighter ones (O, He) are depleted, and vice versa due to wind induced diffusion (3) The electric field driven vortex circulation redistributes the mass and energy in the time independent density and temperature variations (from Joule heating), producing primarily diurnal variations (m = 1) in the temperature and composition near the pole and at auroral latitudes, again the heavier and lighter species varying out of phase. The above results are in substantial agreement with observations. It is worth noting that momentum rectification associated with the diurnally varying electric field and conductivity induces a weak zonally symmetric (single cell) prograde polar vortex. However, this motion is partially compensated by a retrograde vortex from geostrophic balance due to Joule heating, which dominates near the pole. These motions are small compared with the diurnally varying component in the polar circulation.     

Simulations of the seasonal variations of the thermosphere and ionosphere using a coupled,three-dimensional,global model,including variations of the interplanetary magnetic field

The University College London Thermospheric Model and the Sheffield University Ionospheric Convection Model have been integrated and improved to produce a self-consistent coupled global thermospheric/high latitude ionospheric model. The neutral thermospheric equations for wind velocity, composition, density and energy are solved, including their full interactions with the evolution of high latitude ion drift and plasma density, as these respond to convection, precipitation, solar photoionisation and changes of the thermosphere, particularly composition and wind velocity. Four 24 h Universal Time (UT) simulations have been performed. These correspond to positive and negative values of the IMF BY component at high solar activity, for a level of moderate geomagnetic activity, for each of the June and December solstices. In this paper we will describe the seasonal and IMF reponses of the coupled ionosphere/thermosphere system, as depicted by these simulations. In the winter polar region the diurnal migration of the polar convection pattern into and out of sunlight, together with ion transport, plays a major role in the plasma density structure at F-region altitudes. In the summer polar region an increase in the proportion of molecular to atomic species, created by the global seasonal thermospheric circulation and augmented by the geomagnetic forcing, controls the plasma densities at all Universal Times. The increased destruction of F-region ions in the summer polar region reduces the mean level of ionization to similar mean levels seen in winter, despite the increased level of solar insolation. In the upper thermosphere in winter for BY negative, a tongue of plasma is transported anti-sunward over the dusk side of the polar cap. To effect this transport, co-rotation and plasma convection work in the same sense. For IMF BY positive, plasma convection and co-rotation tend to oppose so that, despite similar cross-polar cap electric fields, a smaller polar cap plasma tongue is produced, distributed more centrally across the polar cap. In the summer polar cap, the enhanced plasma destruction due to enhancement of neutral molecular species and thus a changed ionospheric composition, causes F-region plasma minima at the same locations where the polar cap plasma maxima are produced in winter.     

On the association between the QBO and the extratropical stratosphere

Although diagnostic studies and mechanistic model experiments have found that, on average, the polar vortex in northern winter is stronger and colder in the west than in the east years of the equatorial Quasi-Biennial Oscillation (QBO), we show with an expanded data base that the results are not statistically significant. The reason for the insignificance is that in 36% of the winters (13 out of 36) the vortex was warm and weak in the west, and cold and strong in the east years. Only at low activity in the 11-yr solar cycle did the difference between the west (cold) and the east (warm) years become statistically significant. At high solar activity the west years had a warm and the east years a cold polar vortex in the mean. We show this association with the 11-yr solar cycle also in terms of the geostrophic wind.     

Electric field generation at the magnetospheric boundary for northward IMF

We discuss three different processes which generate electric fields at the magnetopause during northward interplanetary magnetic field (IMF) conditions. These are (1) Petschek-type magnetic field reconnection, (2) magnetic field diffusion, and (3) viscous-like interaction resulting from the Kelvin-Helmholtz instability. For northward IMF all three processes lead to the formation of a boundary layer on closed magnetic field lines adjacent to the magnetospheric boundary. The thickness of the boundary layer depend on Petschek's parameter in the first case, the magnetic Reynolds number in the second case, and an effective Reynolds number in the third case. In each case coupling between the boundary layer and the ionosphere occurs via field-aligned currents. These field-aligned currents result from the penetration into the polar ionosphere of the electric field generated at the magnetospheric boundary. These currents are closed by a transverse current in the boundary layer and the associated Lorentz force causes a decrease of the kinetic energy of the solar wind plasma inside the boundary layer. As a result of this velocity decrease the thickness of the boundary layer increases on both flanks of the magnetosphere near the equatorial plane. The convergence of the boundary layer on the dawn and dusk sides leads to antisunward plasma flow in the magnetospheric tail.     

Characteristics of polar cap aurora

The characteristics of extremely high-latitude dayside auroras are examined by using auroral TV data obtained at Godhavn, Greenland, and simultaneous DMSP particle data. Two different kinds of aurora are found near the pre-noon sector, namely (1) the polar arc: this aurora is observed during quiet periods and originates from the dayside region. It is related to about 100 eV electron precipitation or less, and (2) the polar corona: this aurora is observed during disturbed periods and the appearence latitute of this aurora is confined within a certain region about 70–80° MLAT. It is related to a few hundred eV electrons. These results suggest that the origin of the polar arc seems to be the plasma mantle or low-latitude boundary layer, and the origin of the polar corona seems to be the low-latitude boundary layer or Boundary Plasma Sheet.     

Fabry-Perot spectrometer observations of the auroral oval/polar cap boundary above Mawson,Antarctica

Zenith observations of the oxygen λ1630 nm auroral/airglow emission (produced at an altitude of ∼220 to ∼250 km) were obtained with the Mawson Fabry-Perot Spectrometer (FPS) during three ‘zenith direction only’ observing campaigns in 1993. The data show many instances of strong (50 to 100 m s⁻¹) upwellings in the vertical wind, when the auroral oval is located equatorward of the zenith. Our data appear consistent with the existence of a region of upwelling up to ∼ 4° poleward of the poleward boundary of the visible auroral oval, rather than short duration, explosive heating events. The upwellings are probably the vertical component of wind shear produced by reversal of the zonal thermospheric winds, which occurs near the poleward boundary of the visible auroral oval. Zenith temperature was also seen to increase when the oval was equatorward of Mawson, showing rises of up to 300 K or more. However, this increase is at times unrelated to the upwellings, and seems to be caused by the expansion of the warm polar cap over the observing site.On a number of nights the boundary between the polar cap and the auroral oval was observed to pass over our site several times, occasionally showing a quasi-periodic expansion and contraction. We speculate that this quasi-periodic movement may be related to periodic auroral activity that is known to generate large-scale gravity waves.     

The Development of General Earth Science in the USSR During the Soviet Period

General earth science, or general physical geography, is viewed as one of three synthetic physical-geographic disciplines, the two others being landscape science, or regional physical geography, and paleo-geography. General earth science is concerned with the earth's geographic or landscape envelope as a whole and with its general patterns: the laws of zonality and integrity of the landscape envelope, the circulation of matter, rhythmicity, polar asymmetry and other regularities.     

北极斯瓦尔巴群岛的旅游资源

北极斯瓦尔巴群岛地区是地球最北端的陆区,那里特有的景观,如午夜的太阳、极光、海湾、冰川、极地动物、苔原生态体系、人类探索北极的足迹等都是宝贵的极地旅游资源,有待于我们开发和利用。     

IMF Bx and By dependencies of the polar cap auroral distribution for northward IMF orientation inferred from observations at Vostok station

The effects of the IMF radial (B_x) and azimuthal (B_y) components on the distribution of polar cap arcs are examined using all-sky camera data from Vostok station for the winter months of 1977–1985. We conclude that three factors control the character of the aurora distribution: the type of the sector structure, the IMF radial component, and the IMF azimuthal component. Based on the experimental results, the following scheme for the auroral distribution in the northern and southern polar caps for different signs of B_x and B_y is put forward. The ‘garden hose’ structure (B_x > 0, B_y < 0 or B_x < 0, B_y > 0) produces symmetric auroral distributions in the morning and evening sectors of both the northern and southern polar caps; the ‘orthogonal garden hose’ structure (B_x > 0, B_y > 0 or B_x < 0, B_y < 0) is evidently inefficient in the production of aurorae. The B_x component determines the intensity of aurorae in that polar cap where geomagnetic field lines are in the opposite direction to the IMF (B_x < 0 in the case of the northern cap, and B_x > 0 for the southern cap) and produces the daytime auroral belt poleward of the auroral oval and parallel to it. The B_y component affects the auroral appearance in the morning or evening sectors of the polar cap, depending on its sign, and acts asymmetrically in the opposite polar cap. The appropriate patterns of plasma filament distributions in the high-latitude tail lobes are proposed. The characteristics of auroral movements affected by the B_y component (such as the direction and speed of the arc motion and the magnitude of displacements) are examined.     

Middle atmosphere electrical structure during MAC/EPSILON

Extensive use of rocket-launched probes during the MAC/EPSILON campaign at the Andøya Rocket Range, Norway, has enabled the characterization of the region's electrical environment for all four flight series. The first rocket salvo was conducted during daylight (15 October 1987) and the subsequent three occurred at night (21 and 28 October and 12 November 1987), all of them during geomagnetically disturbed conditions. Measurements of polar electrical conductivity, ion mobility and number density are presented, and their associated structure is investigated for local auroral ionization effects. This is believed to be the first time that Gerdien condenser mobility measurements have indicated a heavy-ion presence (positively charged aerosols) in the auroral mesopause region.     

Magnetopause plasma transients: signatures in the auroral ionosphere

The magnetopause and adjacent boundary layers of the Earth's magnetosphere play important roles in transferring momentum and energy from the solar wind to the magnetosphere-ionosphere system. The details of the different boundary processes, their ionospheric signatures and relative importance are not well known at present. Particle precipitation, field-aligned current, auroral emission, ionospheric ion drift and ground magnetic perturbations are among the low-altitude parameters that show signatures of various plasma processes in the LLBL and the magnetopause current layer. Magnetic merging events, Kelvin-Helmholtz waves, and pressure pulses excited by the variable solar wind/magnetosheath plasma are examples of boundary phenomena that may be coupled to the ionosphere via field-aligned currents. In this paper, attention is focussed on a specific category of auroral activity occurring in the cusp/cleft region predominantly during the southward directed interplanetary magnetic field (IMF). Co-ordinated observations from the ground and satellites in polar orbit have been used to study the temporal/spatial development of the events in relation to the background patterns of particle precipitation and ionospheric convection as well as the field-aligned current and ion drift characteristics of the individual events. The auroral phenomenon is characterized by a sequence of elongated forms moving laterally into the polar cap. Spatial scales of major events repeating every 5–10 min are ∼200 km (N-S) times 300–1000 km (E-W). Smaller scale auroral structures with more irregular occurrence rates are observed at times. The preliminary evidence suggests that the motion pattern is regulated by the IMF orientation, that is, the direction of longitudinal motion along the polar cap boundary is determined by the IMF B_Y polarity. The examples reported here occurred within 1000–1400 MLT, near the zero point potential line separating the morning and post-noon convection cells. During nonzero IMF B_Y the auroral structures are associated with channels of enhanced zonal ionospheric ion flow and Birkeland current sheets of opposite polarity, imbedded within the larger scale IMF B_Y-related cusp-mantle current system. These characteristics are discussed in relation to model predictions of ionospheric signatures of magnetopause plasma transients, with particular emphasis placed on impulsive magnetic merging events.     

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.     

A unified view on convection and field-aligned current patterns in the polar cap

During the last two decades measurements of polar cap ionospheric electric fields and currents, field-aligned currents, and global auroral forms have been made from ground-based and space-based platforms. An attempt is made to unify these observations into a large-scale view of polar phenomena. In this view, plasma convection patterns and the corresponding electrodynamics in the polar region can consistently be ordered by the orientation of the interplanetary magnetic field (IMF). The different patterns of the electric potential and of field-aligned currents depend on where the main interaction between the terrestrial and interplanetary fields occurs, on the morning or evening side of the central polar cap, or on the dayside portion of the ‘closed’ cusp region, or on the nightside portion of the ‘open’ cusp region. One of the essential elements of this unified view is that it is possible to account for various convection patterns ranging from the four-cell pattern (during periods of strong northward IMF and B_y ~ 0), to the three-cell pattern (B_z > 0 and |B_y| 2> 0), to the conventional two-cell pattern (B_z < 0) with its possible deformation into a convection throat near the dayside cusp (during southward IMF). We also discuss the way in which the complicated field-aligned current systems can consistently be accounted for in terms of these convection patterns.     

A. E. Nordenskiöld in Swedish memory: the origin and uses of Arctic heroism

ABSTRACT

For Nordic nations scientific activities in the Polar Regions proved significant in defining national identities and shaping scientific profiles. Starting in the nineteenth century and continuing throughout the next century, polar research proved instrumental in inculcating national honour and expressing small-state colonial aspirations. It provided a source of heroes for forging collective memory and the fostering of youth by presenting the polar explorer as a model character. This study explores the ideological lineage of the nineteenth century polar hero by first relating this idol to historical archetypes of Western culture. It identifies the special traits of the Nordic polar hero and discusses how it was used for patriotic purposes. As a case in point the article looks at the career of the Finnish-Swedish mineralogist and Arctic expedition leader Adolf Erik Nordenskiöld and the ways he, with the help of others, successfully navigated not only the drift ice of polar seas but also the international republic of science, and the three national scenes of Sweden, Finland and Russia. In the process he was turned into a national hero both in Finland and Sweden, and presented as a patriotic role model for adolescents in the arts of postponing gratification and enduring hardship.     

Polar thermospheric Joule heating,and redistribution of recombination energy in the upper mesosphere

Kellogg, W. W. (1961, J. Met. 18, 373) suggested that transport of atomic oxygen from the summer into the winter hemisphere and subsequent release of energy by three body recombination, O + O + N₂→O₂ + N₂ + E, may contribute significantly to the so-called mesopause temperature anomaly (increase in temperature from summer to winter). Earlier model calculations have shown that Kellogg's mechanism produces about a 10% increase in the temperature from summer to winter at 90 km. This process, however, is partly compensated by differential heating from absorption of UV radiation associated with dissociation of O₂. In the auroral region of the thermosphere, there is a steady (component of) energy dissipation by Joule heating (with a peak near 130 km) causing a redistribution and depletion of atomic oxygen due to wind-induced diffusion. With the removal of O. latent chemical energy normally released by three body recombination is also removed, and the result is that the temperature decreases by almost 2% near 90 km. Through dynamic feedback, this process reduces the depletion of atomic oxygen by about 25% and the temperature perturbation in the exosphere from 10% to 7% at polar latitudes. Under the influence of the internal dynamo interaction, the prevailing zonal circulation in the upper thermosphere (small in magnitude) changes direction when the redistribution of recombination energy is considered. The above described effects are very sensitive to the adopted rates of eddy diffusion. They are also strongly time dependent and are significantly reduced for disturbances associated with magnetic storms.