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The paper presents climatology of the poorly known, particularly at high latitudes, short-period (8- and 6-h) tides observed by meteor radars at high latitudinal stations Tromso (70°N, 19°E) and Svalbard (78°N, 16°E) based on 16 years (2003–2018) and 18 years (2001–2018) of measurements, respectively. The main focus of this study is to clarify the seasonal variability and vertical structure of the two tides observed at both sites. It is found that at the two not very distant high-latitude stations Tromso and Svalbard both tides have not only different seasonal variability but also some distinction in the altitude structure as well. In general the short-period tides at both sites are vertically upward propagating waves but with seasonally depending vertical wavelength. The two tides at Tromso and the 8-h one at Svalbard reveal some inter-annual variability with a period of quasi-2 years. An assessment of the solar heating as the main mechanism for the generation of the 8- and 6-h tides simulated by the model WACCM6 is presented as well. The results could be used as benchmarks for model simulations and for understanding better the forcing mechanisms of these short-period tides at high latitudes.

Neutral air temperatures at 90 km altitude over Svalbard (78°N, 16°E) for the period 2002 to 2019 inclusive have been estimated from observations by the Nippon/Norway Svalbard Meteor Radar (NSMR). The data are presented per se and we shall not attempt to identify contributions from extra-terrestrial or anthropogenic driving. On the other hand, comparison with the corresponding period of solar UV flux notably fails to exhibit similarities. Moreover, there is indeed evidence of systematic temporal changes, possibly with a breakpoint around 2012. Selecting winter and summer months and years before and after 2012 and fitting trend-lines, we see strong evidence for cooling during summer. An apparent winter cooling prior to 2012 lacks statistical significance. A suggestion of reversal to winter warming after 2012 is also very uncertain. The summer cooling is found to be 9.9 ± 2.9 K decade−1 between 2002 and 2012, and 4.3 ± 1.2 K decade−1 between 2002 and 2019. Importantly, there is a suggestion (although lacking statistical significance) that summer cooling alleviated after 2012, and even reversed in winter.

Balloon-borne observations of lower stratospheric water vapor were conducted with the Cryogenic Frostpoint Hygrometer (CFH) in July, September, and November 2013 at Syowa Station (69.0oS, 39.6oE) in the Antarctic. High-precision and high vertical resolution data of water vapor concentration up to an altitude of about 28 km were obtained successfully except for a contamination in the observation of July 2013. A comparison between the CFH and coincident satellite (i.e., Aura/MLS) observations showed a good agreement within their uncertainty. A position of Syowa Station relative to the stratospheric polar vortex edge varied depending on both the observation date and altitude. Temperature and pressure histories of the observed air parcels were examined by 10-day backward trajectories. These analyses clearly demonstrated that most air parcels observed in the lower stratosphere above Syowa Station experienced final dehydration inside the polar vortex. On the other hand, a clear signature of rehydration or incomplete dehydration was also observed around a 25 hPa pressure level in the observation of July 2013.

The PANSY radar is the first Mesosphere–Stratosphere–Troposphere/Incoherent Scatter (MST/IS) radar in the Antarctic region. It is a large VHF monostatic pulse Doppler radar operating at 47 MHz, consisting of an active phased array of 1045 Yagi antennas and an equivalent number of transmit–receive (TR) modules with a total peak output power of 500 kW. The first stage of the radar was installed at Syowa Station (69°00′S, 39°35′E) in early 2011, and is currently operating with 228 antennas and modules. This paper reports the project's scientific objectives, technical descriptions, and the preliminary results of observations made to date. The radar is designed to clarify the role of atmospheric gravity waves at high latitudes in the momentum budget of the global circulation in the troposphere, stratosphere and mesosphere, and to explore the dynamical aspects of unique polar phenomena such as polar mesospheric clouds (PMC) and polar stratospheric clouds (PSC). The katabatic winds as a branch of Antarctic tropospheric circulation and as an important source of gravity waves are also of special interest. Moreover, strong and sporadic energy inputs from the magnetosphere by energetic particles and field-aligned currents can be quantitatively assessed by the broad height coverage of the radar which extends from the lower troposphere to the upper ionosphere. From engineering points of view, the radar had to overcome restrictions related to the severe environments of Antarctic research, such as very strong winds, limited power availability, short construction periods, and limited manpower availability. We resolved these problems through the adoption of specially designed class-E amplifiers, light weight and tough antenna elements, and versatile antenna arrangements. Although the radar is currently operating with only about a quarter of its full designed system components, we have already obtained interesting results on the Antarctic troposphere, stratosphere and mesosphere, such as gravity waves, multiple tropopauses associated with a severe snow storm in the troposphere and stratosphere, and polar mesosphere summer echoes (PMSE).

A new meteor radar on Bear Island (74.5°N, 19.0°E) has been conducting horizontal wind observations on a regular basis since completion of its installation on 1 November 2007. We have analyzed wind data obtained with the meteor radar between 80 and 100 km over 42 months from November 2007 to April 2011, and presented seasonal variations as well as year-to-year variations in mean winds, diurnal and semidiurnal tides based on 1-month averaged wind data. We also presented seasonal variations in quasi-2 day wave (Q2DW). Obtained results are compared with those from Tromso (69.6°N, 19.2°E) MF radar for the same interval. There is a good agreement in the mean zonal wind, meridional diurnal tide, and semidiurnal tides. In particular, the agreement is excellent for the semidiurnal tides, suggesting the same mode is dominant between 70° and 75° between 82 and 91 km in the northern Scandinavia sector. Seasonal variations in the Q2DW at both sites are similar, but the intervals of intermittent activity were not correlated well at the two sites except for the meridional component in summer. In general, the results obtained at Bear Island agree with published results at other high latitude stations in the northern hemisphere. We also showed variations in the mean winds and the semidiurnal tide during the January 2009 Sudden Stratospheric Warming event.

This study assesses the relation between the year-to-year variability of the semidiurnal tides (SDT) observed at high latitudes of both hemispheres and the global stratospheric stationary planetary wave (SPW) with zonal wavenumber S=1 (SPW1) derived from the UKMO temperature data. No significant positive correlation can be identified between the interannual variability of the Northern Hemisphere (NH) SDT and the Southern Hemisphere (SH) SPW1 for austral late-winter months. In contrast, a good consistency is evident for the interannual variations between the SDT observed at Rothera (68°S, 68°W) and the Arctic SPW1 for NH mid-winter months. Since it has been observed that during austral summer the non-migrating SDT often plays a significant role at the latitude of Rothera, a physical link between the SH SDT and the NH SPW is suggested. This asymmetry in the interhemispheric link is also noted in a recent study.

Kinetic energy dissipation rates for the auroral MLT have been obtained from the Tromso middle frequency radar (MFR) and compared with simultaneous measurements of neutral wind-shears obtained from the Nippon/Norway Tromso meteor radar (NTMR). Since wind-shears can drive dynamic instabilities which in turn result in turbulent dissipation of kinetic energy, we would expect these parameters to be correlated, and this is indeed the case. Having established this correlation we quantitatively combine the results from each radar to estimate the turbulent diffusion coefficient for momentum; considering the tentative nature of this approach, we find the agreement with previous estimates to be surprisingly good.

Seasonal variations of activity and horizontal propagation direction of gravity waves in the MLT region at mid-latitude over Shigaraki, Japan (35 N) are investigated for various time and spatial scales using the MU radar observations and recent airglow imaging observations. Semiannual variation with solsticial maxima and equinoctial minima are generally observed for short period (

An all-sky optical imager is in routine observation at the South Pole. Monochromatic images of aurora and air glow at N 2 + 427.8nm, OI 557.7nm, OI 630nm and OH 730nm are supplying significant information on the magnetospheric process in the polar cap and cusp/cleft region along with atmospheric wave signature at this particular point. SuperDARN radars in Antarctica make observations over the South Pole. At Syowa Station, Antarctica, a multi-instrumental observation project is now being implemented for the study of the polar upper atmosphere from the mesosphere to the thermosphere, where complex physical and chemical processes take place making the region very attractive for scientific research. Two HF radars, which are part of SuperDARN radars, have been already installed and started observations. By the end of 1999, all-sky imagers, photo meters, a Na temperature Lidar, an MF radar and a Fabry-Perot interferometer will be introduced and start collecting various physical parameters on a routine basis. In the Arctic region, we are planning to deploy coordinated ground-based observations with optical, radio and radar sensing of the polar middle and upper atmosphere in conjunction with EISCAT radars. Scientific goals are versatile to shed light on the tangled coupling processes in response to magnetospheric disturbances from above and bi-lateral interactions with high-density lower atmospheric layers. These are outlined in this paper.

The MU radar (middle and upper atmosphere radar) has been used since 1984 to study the dynamics of the mesosphere and lower thermosphere (MLT) as well as the dynamics of the lower atmosphere and the ionosphere. Gravity waves in the mesosphere have been studied extensively over various time and vertical scales during the daylight hours using backscatter from turbulent irregularities. Scatter from meteor trails can be used during day or night to study the dynamics of the MLT, and techniques to apply the MU radar for meteor scatter observations have been developed and recently improved. The meteor observation mode of the MU radar can detect about 15,000–20,000 echoes/day and 10,000 echoes/day are from underdense trails with arrival angle determination. This high meteor echo rate enables us to determine the wind velocities and molecular diffusion coefficient with the time/height resolutions of 30 min × 1 km at 80–100 km for 24 hours a day. From the horizontal distribution of the meteor echoes, horizontal gradients of the wind fields can also be detected, as well as vertical shears of horizontal winds. These high resolution meteor echo observations were made simultaneously with OH spectrometer observations. These combined observations yielded information on both the horizontal and vertical structure of the gravity waves. Comparisons were made between the temperature variations determined by OH airglow and determined by the diffusion coefficient of the meteor echoes and excellent agreement was found. Cooperative observations with sodium lidars, FPI, airglow imagers, and an MF radar are also being carried out.

We attempt to find the northern hemisphere zonal wavenumber for a striking quasi-2-day wave “event” or “burst” observed near 90 km altitude in the summer of 1992. A unique set of data on the upper atmosphere from nine radar sites is analysed (spacings ∼400– ∼ 12,000 km), and compared with expectations from models. The 2-day wave phase comparison, which finds zonal wavenumber m = 4, is conclusive. Determination of n, which defines the meridional wave amplitude structure, is not attempted, as the sites here have only a small latitude spread (21°N to 55°N). Also the amplitude seems to be unstable showing some sort of modulation which is not simultaneous at all sites. Finally, the radars have not been “calibrated” against each other in terms of wind speed. This calibration would have to be done before small differences in wave amplitude could be believed. A similar event in 1991 for which fewer sites are available is also discussed. Here the choice between m = 3 and 4 is not as clear.