[1] This paper presents the first Antarctic meteor radar temperature estimates. These temperatures have been derived from meteor diffusion coefficients using two techniques: pressure model and temperature gradient model. The temperatures are compared with a temperature model derived using colocated OH spectrometer measurements and Northern Hemisphere rocket observations. Pressure model temperatures derived using rocketderived pressures show good agreement with the temperature model, while those derived using Mass Spectrometer and Incoherent Scatter (MSIS) and CIRA model pressures show good agreement in winter but poor agreement in summer. This confirms previous studies suggesting the unreliability of high-latitude CIRA pressures. The temperature gradient model temperatures show good agreement with the temperature model but show larger fluctuations than the pressure model temperatures. Meteor temperature estimates made during the Southern delta-Aquarids meteor shower are shown to be biased, suggesting that care should be taken in applying meteor temperature estimation during meteor showers. On the basis of our results we recommend the use of the pressure model technique at all sites, subject to determination of an appropriate pressure model.

The assimilative mapping of ionospheric electrodynamics technique has been used to derive the large-scale high-latitude ionospheric convection patterns simultaneously in both northern and southern hemispheres during the period of January 27-29, 1992. When the interplanetary magnetic field (IMF) B• component is negative, the convection patterns in the southern hemisphere are basically the mirror images of those in the northern hemisphere. The total cross-polar-cap potential drops in the two hemispheres are similar. When B• is positive and IB•I > B•, the convection configurations are mainly determined by B• and they may appear as normal "two-cell" patterns in both hemispheres much as one would expect under southward IMF conditions. However, there is a significant difference in the cross-polar-cap potential drop between the two hemispheres, with the potential drop in the southern (summer) hemisphere over 50% larger than that in the northern (winter) hemisphere. As the ratio of decreases (less thn one), the convection configuration in the two hemispheres may be significantly different, with reverse convection in the southern hemisphere and weak but disturbed convection in the northern hemisphere. By comparing the convection patterns with the corresponding spectrograms of precipitating particles, we interpret the convection patterns in terms of the concept of merging cells, lobe cells, and viscous cells. Estimates of the "merging cell" potential drops, that is, the potential ascribed to the opening of the dayside field lines, are usually comparable between the two hemispheres, as they should be. The "lobe cell" provides a potential between 8.5 and 26 kV and can differ greatly between hemispheres, as predicted. Lobe cells can be significant even for southward IMF, if IBl > IBI. To estimate the potential drop of the "viscous cells," we assume that the low-latitude boundary layer is on closed field lines. We find that this potential drop varies from case to case, with a typical value of 10 kV. If the source of these cells is truly a viscous interaction at the flank of the magnetopause, the process is likely spatially and temporally varying rather than steady state. New Zealand. 6491 6492 LU ET AL.: HIGH-LATITUDE IONOSPHERIC CONVECTION PATTERN Pedersen and Hall conductance models are obtained by combining the auroral conductance model of Fuller-Rowell and Evans [1987] with an empirical model of conductance produced by solar extreme ultraviolet radiation based on Chatanika radar observations. The statistical electric potential model is based on Millstone Hill radar observations [Foster et al., 1986]. Both conductance and potential models are parameterized by the hemispheric power index (HPI) [Foster e! al., 1986]. A very important feature of AMIE is its ability to give quantitative information about the uncertainty in the resultant patterns, so that features mapped reliably can LU ET AL.' HIGH-LATITUDE

A 16 month series of lidar measurements in the stratosphere and mesosphere-lower thermosphere (MLT) region over Davis Station (69 ∘ S, 78 ∘ E) in Antarctica is used to study gravity waves. The unprecedentedly large number of observations totaling 2310 h allows us to investigate seasonal variations in gravity wave activity in great detail. In the stratosphere the gravity wave potential energy density (GWPED) is shown to have a large seasonal variation with a double peak in winter and minimum in summer. We find conservative wave propagation to occur between 29 and 41 km altitude in winter as well as in summer, whereas smaller energy growth rates were observed in spring and autumn. These results are consistent with selective critical-level filtering of gravity waves in the lower stratosphere. In the MLT region the GWPED is found to have a semiannual oscillation with maxima in winter and summer. The structure of the winter peak is identical to that in the stratosphere, suggesting that the gravity wave flux reaching the MLT region is controlled by the wind field near the tropopause level. IntroductionAtmospheric gravity waves are important for vertical coupling in the atmosphere. They transport energy and momentum vertically and horizontally over large distances. At high latitudes, dissipation of these waves in the mesosphere-lower thermosphere region (hereafter MLT region) transfers momentum into the background flow, driving a global meridional circulation from the summer pole to the winter pole [Lindzen, 1981;Holton, 1983]. Associated with this circulation is the upwelling of air at the summer pole causing the strong adiabatic cooling of the summer MLT region [Andrews et al., 1987;Becker, 2012]. This gravity wave-induced cooling gives rise to observed temperatures as low as 130 K which are far from radiative equilibrium [Lübken, 1999;Lübken et al., 2014]. For this reason, phenomena like noctilucent clouds and polar mesospheric summer echoes are limited to the summer polar region [Olivero and Thomas, 1986]. Without gravity wave-induced cooling, temperatures in the summer MLT remain above the frost point [Rapp and Thomas, 2006]. The occurrence of noctilucent clouds is thus a result of gravity waves propagating from the troposphere/lower stratosphere into the MLT region.Gravity waves have been extensively studied in models [e.g., Zhang, 2004] as well as through employing observational techniques such as lidars [e.g., Rauthe et al., 2008;Yamashita et al., 2009], radars [e.g., Nicolls et al., 2010 Lue et al., 2013], radiosondes [e.g., Allen andVincent, 1995;Moffat-Griffin et al., 2011], satellite-based radiometers [e.g., Alexander et al., 2008;Wright and Gille, 2013], and Global Positioning System radio occultation [e.g., Wang and Alexander, 2010]. Among all observational techniques, lidars provide the highest temporal and vertical resolutions over a wide altitude range and observation periods up to several days.

[1] The objective of this study is to understand better the propagation of Pi 2 waves in the nighttime region. We examined Pi 2 oscillations that showed high correlation between high-and low-latitude Magnetic Data Acquisition System/Circum Pan-Pacific Magnetometer Network stations (correlation coefficient: jgj ! 0.75). For each horizontal component (H and D) we examined the magnetic local time (MLT) dependence of the delay time of high-latitude Pi 2 oscillations that corresponds to the highest correlation with the low-latitude Pi 2 oscillation. We found the delay time of the high-latitude H showed remarkable MLT dependence, especially in the premidnight sector: we found that in the premidnight sector the high-latitude H oscillation tends to delay from the low-latitude oscillation (<100 s). On the other hand, the delay time of the high-latitude D oscillation was not significant ($±10 s) in the entire nighttime sector. We propose a Pi 2 propagation model to explain the observed delay time of high-correlation highlatitude H. The model quantitatively explains the trend of the event distribution. We also examined the spatial distribution of high-correlation Pi 2 events relative to the center of auroral breakups. It was found that the high-correlation Pi 2 events tend to occur away from the center of auroral breakups by more than 1.5 MLT. The present result suggests that the high-correlation H component Pi 2 oscillations at high latitude are a manifestation of forced Alfvén waves excited by fast magnetosonic waves.

We present the first detection of thermal tides in the middle atmosphere at polar latitudes in summer. The IAP iron lidar is in operation in Davis (69°S, 78°E), Antarctica, since December 2011 and measures temperatures in the height range 84–96 km with an accuracy of 1–3 K (after 1 hour integration) with an effective altitude resolution of 1 km. Iron densities are observed from ∼75–140 km. We analyze 171 hours of observations in the period 11–28 January, 2011, and find strong tidal modulations in Fe density and temperatures. Typical amplitudes of thermal tides are 2–4 K for both the diurnal and semidiurnal component. The diurnal tide is larger (smaller) than the semidiurnal component below (above) ∼90 km. The phase of the diurnal tide decreases with altitude by ∼1.3 h/km which corresponds to a vertical wavelength of ∼30 km. A similar phase progression is observed in Fe densities extending below and above the height range of temperature measurements. The overlay of diurnal and semidiurnal components leads to tidal modulations of up to ±6 K for temperatures, and up to ±4000/ccm (=±40%) for Fe number densities. These modulations are much larger compared to most simulations and point to some missing processes in tidal modeling.

We analyze ionospheric convection pat terns over the polar regions during the passage of an interplanetary magnetic cloud on January 14, 1988, when the interplanetary magnetic field (IMF) rotated slowly in direction and had a large amplitude. Using the assirnilative mapping of ionospheric electrodynamics (AMIE) procedure, we combine simultaneous observations of ionospheric drifts and magnetic perturbations from many different instruments into consistent patterns of high-latitude electrodynamics, focusing on the period of northward IMF. By combining satellite data with ground-based observations, we have generated one of the most comprehensive data sets yet assembled and used it to produce convection maps for both hemispheres. We present evidence that a lobe convection cell was embedded within normal merging convection during a period when the IMF By and B, components were large and positive. As the IMF became predominantly northward, a strong reversed convection pattern (afternoon-to-morning potential drop of around 100 kV) appeared in the southern (

We report the first observations of polar mesosphere summer echoes (PMSE) above the high‐latitude Southern Hemisphere (SH) station Davis, Antarctica (68.6°S, 78.0°E geographic; 74.6°S magnetic). Observations were obtained using a 55 MHz atmospheric radar, the first stage of which was commissioned late in the austral summer of 2002–2003. The radar commenced mesosphere observations with approximately 20 kW of transmitted power in October 2003. PMSE were recorded from 19 November to 3 December 2003 and, after a break in radar operation, from 27 January to 21 February 2004. We present the initial seasonal and diurnal occurrence morphology from 180 hours of Davis PMSE observations. Our initial findings reveal that SH PMSE show similar backscatter echo characteristics and occurrence properties to those reported for the Northern Hemisphere (NH).

Abstract.A −190-nT negative bay in the geomagnetic X component measured at Macquarie Island (−65 • ) showed that an ionospheric substorm occurred during 09:58 to 11:10 UT on 27 February 2000. Signatures of an auroral westward flow channel (AWFC) were observed nearly simultaneously in the backscatter power, LOS Doppler velocity, and Doppler spectral width measured using the Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar. Many of the characteristics of the AWFC were similar to those occurring during a polarisation jet (PJ), or subauroral ion drift (SAID) event, and suggest that it may have been a precursor to a fully developed, intense westward flow channel satisfying all of the criteria defining a PJ/SAID. A beamswinging analysis showed that the westward drifts (poleward electric field) associated with the flow channel were very structured in time and space, but the smoothed velocities grew to ∼800 m s −1 (47 mV m −1 ) during the 22-min substorm onset interval 09:56 to 10:18 UT. Maximum westward drifts of >1.3 km s −1 (>77 mV m −1 ) occurred during a ∼5-min velocity spike, peaking at 10:40 UT during the expansion phase. The drifts decayed rapidly to ∼300 m s −1 (18 mV m −1 ) during the 6-min recovery phase interval, 11:04 to 11:10 UT. Overall, the AWFC had a lifetime of 74 min, and was located near −65 • in the evening sector west of the Harang discontinuity. The large westward drifts were confined to a geographic zonal channel of longitudinal extent >20 • (>1.3 h magnetic local time), and latitudinal width ∼2 • . Using a half-width of ∼100 km in latitude, the peak electric potential was >7.7 kV. However, a transient velocity of >3.1 km s −1 with potential >18.4 kV was observed further poleward at the end of the recovery phase. Auroral oval boundaries determined using DMSP measurements suggestCorrespondence to: M. L. Parkinson (m.parkinson@latrobe.edu.au) the main flow channel overlapped the equatorward boundary of the diffuse auroral oval. During the ∼2-h interval following the flow channel, an ∼3 • wide band of scatter was observed drifting slowly toward the west, with speeds gradually decaying to ∼50 m s −1 (3 mV m −1 ). The scatter was observed extending past the Harang discontinuity, and had Doppler signatures characteristic of the main ionospheric trough, implicating the flow channel in the further depletion of F-region plasma. The character of this scatter was in contrast with the character of the scatter drifting toward the east at higher latitude.Key words. Ionosphere (auroral ionosphere; electric fields and currents; ionosphere-magnetospehere interactions) Magnetospheric physics (storms and substorms)