Abstract. The quasi-stationary asymmetry of total ozone over Antarctica during spring is studied by TOMS data during the period . Statistics on the amplitude and longitudinal position of zonal anomalies are obtained from the distribution of total ozone along seven individual latitudes at 5-degree intervals between 50 • S and 80 • S. As shown by the September-November means, the mid-latitude collar of ozone-rich stratospheric air has a sub-Antarctic maximum with a mean location in the quadrant 90 • E-180 • E and a total ozone level of about 380 DU between 50 • S and 60 • S. The steady displacement and elongation of the ozone hole under the influence of planetary waves causes a zonal anomaly of low ozone in the sector 0 • -60 • W with total ozone levels of about 200 DU between 70 • S and 80 • S. Climatologically, the highest amplitude of the zonal anomaly is 57.2±13.5 DU (relative asymmetry of 32% between high and low ozone levels) at 65 • S latitude.A significant eastward shift of approximately 45 • in longitude is observed in the total ozone minimum over the Weddell Sea -South Atlantic sector during 1979-2005, whereas the zonal maximum is relatively stable in location. Also apparent is a long-term shift in tropopause temperature distribution in the region.The geographical distribution of the zonal extremes in total ozone for the seven latitudes shows that (i) the extremes exhibit sensitivity to the shape of the Antarctic continent, (ii) the stationarity of the extremes increases poleward above the edge of continent and (iii) the positions of the extremes at the higher latitudes tend to follow the meridionally oriented elements of orography. It is suggested that the radiative influence of Antarctica contributes to the formation of this pattern. Anomalies in the horizontal structure of the tropopause, which appear related to orography, support this view.Correspondence to: G. P. Milinevsky (gmilin@univ.kiev.ua) Mechanisms involved in the formation and decadal change in the total ozone asymmetry, as well as possible influences of the asymmetry on the stratospheric thermal regimes and regional UV irradiance redistribution are discussed.

On 11 December 2016 at 00:12:30 UT, Van Allen Probe‐B, at the equator and near midnight, and AC6‐B, in the ionosphere, were on magnetic field lines whose 100 km altitude foot points were separated by 600 km. Van Allen Probe‐B observed a 30 s burst of lower band chorus waves (with maximum amplitudes >1 nT) at the same time that AC6‐B observed intense microburst electrons in the loss cone. One second averaged variations of the chorus intensity and the microburst electron flux were well correlated. The low‐altitude electron flux expected from quasi‐linear diffusion of the equatorial electrons by the equatorial chorus is in excellent agreement with the observed, 1 s averaged, low‐altitude electron flux. However, the large‐amplitude, <0.5 s duration, low‐altitude electron pulses require nonlinear processes for their explanation.

Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-angle scattering of non-thermal electrons by whistler waves at Earth’s bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvén Mach number ∼11 and a shock angle ∼84°. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-thermal (0.5–2 keV) electron flux, correlated with high-frequency (0.2–0.4 , where is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1 ms cadence) showed fluctuations with the same frequency. These features indicate that non-thermal electrons were pitch-angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear.

We present surprising observations by the NASA Van Allen Probes spacecraft of whistler waves with substantial electric field power at harmonics of the whistler wave fundamental frequency. The wave power at harmonics is due to a nonlinearly steepened whistler electrostatic field that becomes possible in the two-temperature electron plasma due to the whistler wave coupling to the electron-acoustic mode. The simulation and analytical estimates show that the steepening takes a few tens of milliseconds. The hydrodynamic energy cascade to higher frequencies facilitates efficient energy transfer from cyclotron resonant electrons, driving the whistler waves, to lower energy electrons.

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