Abstract: The evolution of total ozone and surface UV radiation over some stations in the southern region of South America and in Antarctica in relationship with polar vortex occurrences is analyzed using Total Ozone Mapping Spectrometer total ozone measurements and local surface UV data for the 1997–2003 period. The data are classified as a function of the position of the stations with respect to the polar vortex using equivalent latitude at 550 K isentropic level. The study of vortex occurrences showed that Ushuaia station (54.9°S) was located ?40% of the cases in the edge of the vortex and 5% inside the vortex core during the winter-spring period. Concerning the Marambio (62.2°S) and Dumont d'Urville (66.4°S) stations, located on the shore of the Antarctic continent, the analysis shows a zonal asymmetry with respect to the center of the vortex. Marambio is located around 60% of the time inside the vortex, while Dumont d'Urville is predominantly at the edge of or outside the vortex. The evolution of the equivalent latitude of the stations in the anomalous 2002 winter presents a different behavior with respect to other years in the 1997–2003 period. The persistence of the vortex core above the stations is in average 1.8 days over Ushuaia and 7.1 days over Marambio in October during the 1997–2003 period with corresponding mean total ozone columns of 208.2 and 181.4 Dobson units, respectively. When the stations are inside the vortex, the total ozone columns are generally larger at Ushuaia than at Marambio in October during the 1997–2003 period. Finally, the impact of ozone-depleted air mass occurrences on ultraviolet radiation is evaluated by relating total ozone and UV erythemal dose measured at the stations. Twofold or threefold UV dose increases were reached in the 55°–65° southern latitude region during vortex overpasses, reaching maximum UV dose around 5 kJ/m2. The average increase of UV dose could be computed at the stations considered in the study when the measurement sampling and the number of vortex occurrences was sufficient. An average increase of 67.6% of the erythemal UV dose was found in October at Ushuaia over the years 1997, 1998, and 2000. This value is strongly weighted by vortex occurrences over the station in 2000. At Marambio an average UV increase of 47.4% was found over the years 1999 and 2000. Midlatitude stations like Comodoro Rivadavia (45.8°S) are generally little affected by vortex intrusions. Nevertheless, the maximum UV dose can increase by more than 50% when the vortex passes over the station.

Abstract: We have used new spaceborne (elevation) and airborne (ice thickness) data to constrain a 2D1/2 model of snow accumulation and ice flow along the Ridge B-Vostok station ice flow line (East Antarctica). We show that new evaluations of the ice flow line geometry (from the surface elevation), ice thickness (from low-frequency radar data), and basal melting and sliding change significantly the chronology of the Vostok ice core. This new Vostok dating model reconciles orbital and glaciological timescales and is in good agreement with the Dome Fuji glaciological timescale. At the same time, the new model shows significantly older ages than the previous GT4 timescale for the last glacial part, being thus in better agreement with the GRIP and GISP2 chronologies.

Abstract: The upper atmosphere dynamics in the polar cap is mainly driven by ion-drag momentum sources imposed by the mapping of magnetosphere convection into the thermosphere/ionosphere and by Joule and auroral particle heating. Auroral particles also enhance conductivity particularly in the middle and lower ionosphere. Changes in the magnetospheric energy and momentum sources can significantly modify the wind circulation during geomagnetic storms. To observe these effects, a Michelson interferometer has been installed in Svalbard to measure winds in the thermosphere. Prior to 30 October 2003, cloud cover over Svalbard rendered the conditions unfavorable for optical observation. However, meteorological conditions improved after this date to enable the thermospheric response to the 28 October coronal mass ejection to be made. During quiet geomagnetic conditions measured wind velocities were in good agreement with those predicted by the Horizontal Wind Model (HWM). During disturbed geomagnetic conditions, HWM tended to underestimate the observed velocities. Comparison of the wind observations with a physical model tended to show reasonable agreement during both the strongly driven and recovery phase of the storm. Although the physical model did not always capture the timing of the rapid changes in the wind response in the early phase of the storm, the amplitudes of the fluctuations were in good agreement. After the initial phase the physical model agreed well with both the timing and amplitude of the meridional and zonal wind fluctuations. The meridional wind component was also derived from the EISCAT Svalbard Radar ion velocity and was found to be in close agreement with the optical winds observations.

Abstract: A flare on 2003 October 28 produced a relativistic particle event at Earth, although the active region AR 10486 was located to the east of the central meridian of the Sun. The paper considers features related to the acceleration at the Sun and the propagation to the Earth of energetic particles in this event, which occurred on a disturbed interplanetary background caused by preceding activity on the Sun and a corotating high-speed solar wind stream. From a study of the onset times of the event at different neutron monitors, we conclude that the earliest arriving solar particles were neutrons. The first relativistic protons arrived a few minutes later. Among relativistic solar protons (RSP), two populations could clearly be distinguished: prompt and delayed ones. The prompt solar protons caused an impulse-like increase at a few neutron monitor stations. The delayed solar protons arrived at Earth 0.5 hours later. Both prompt and delayed relativistic protons arrived at Earth from the antisunward direction. On the other hand, subrelativistic electrons that were traced by their radio emission from meter waves (Nançay Radioheliograph and Decametric Array) to kilometer waves (Wind/WAVES) are accompanied by metric radio emission in the western solar hemisphere, far from the flaring active region. We propose a scenario that reconciles the unusual features of energetic particles at the Earth with the observed structure of the interplanetary magnetic field, which suggests the Earth is at the interface between an interplanetary coronal mass ejection (ICME) and a corotating stream during the event. In this scenario the high-energy protons and electrons are accelerated in the flaring active region, injected into the eastern leg of an ICME loop rooted in the active region, and reach the Earth from the antisunward direction after passing through the summit of the loop. We attribute the promptly escaping subrelativistic electrons to acceleration in the western solar hemisphere and propagation along the nominal Parker spiral.

Abstract: The diurnal and semidiurnal variations of the geomagnetic field are investigated at 18 observatories using long series of hourly values (up to 97 years at Sitka). The seasonal variations of amplitude of the 12-hour and 24-hour lines are obtained for the H and Z components using a 28-day sliding window. The Fourier analysis is performed using either all days within the window or only the five quietest days. At midlatitudes a strong lack of symmetry about the summer solstice is observed for both lines and both components. This effect is enhanced when selecting quiet days. When averaged over the entire series, the sign of this seasonal asymmetry is the same at 9 out of 10 midlatitude observatories for both lines and for a given component; it is opposite for the H and Z components. Such a coherent seasonal asymmetry is not found at low and high latitudes. At high latitudes a strong annual variation is found inside the polar caps, while a strong semiannual variation is found in the auroral zones. When selecting quiet days, these two effects are weaker, and the seasonal asymmetry becomes comparable to that at midlatitudes. At all latitudes the year-to-year variations of the seasonal asymmetry are uncorrelated with solar activity. It is suggested that lower thermospheric winds may have a similar seasonal asymmetry between spring and autumn equinoxes. Such an asymmetry is present in the published literature but has been overlooked. Possible causes for this wind asymmetry are reviewed.