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Large-and-Sparse-particle Clouds (LSC), characterized by large particle size (radius > 50 μm) and small number concentration (<104 m−3), were observed with the space-borne lidar, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and with the space-borne 94-GHz cloud profiling radar (CPR). CALIOP was found to be less sensitive to the LSC as compared to CPR because of the particle size distribution of LSC; hence, the cloud type is different from usual ones because CALIOP is generally more sensitive to clouds as compared to CPR when there is no lidar attenuation. An empirical criterion was introduced to identify the LSC from CALIOP and CPR data. The data analysis showed that the LSC tend to appear at high latitudes. The lifetime of LSC would be in the order of hours, because the terminal velocity of LSC particles exceeded 1 km h−1. LSC would not be fallstreak because no cloud existed above. LSC appeared to destroy supercooled clouds (SC) because their cloud top heights were higher as compared to SC, and because LSC and SC did not tend to coexist. Because of their thin optical depth, LSC did not directly impact radiative forcing; however, LSC may indirectly influence radiative forcing through changes in the distribution of SC. [ABSTRACT FROM AUTHOR]

In this study, ion drift velocities measured by Digisonde instruments over Zhongshan Station (ZHS, geog. 69.38°S, 76.38°E), Antarctica, are compared with measurements from Super Dual Auroral Radar Network (SuperDARN) HF radars. For SuperDARN Syowa East (SYE) and Kerguelen (KER) radars that intersect with ZHS, a data set comprised of adjacent range gates from nearest radar beams is used. Digisonde ion drift measurements were projected onto the direction of co-located and concurrent line-of-sight SuperDARN velocities. A comparison of the velocities shows a clear correlation (R = 0.92) between the two data sets. Projected Digisonde velocity was found to be, on average, larger than the line-of-sight SuperDARN radar velocities by a factor of 1.7. Time dependence distributions of Digisonde-SuperDARN SYE radars showed that the larger velocity discrepancies are more located at the dawnside convection cell. Considering the known features of the high-latitude convection patterns at cusp latitude, the statistical results imply the velocity discrepancies are related to the differences in the temporal and spatial evolution of plasma structures. [ABSTRACT FROM AUTHOR]

A total of 15 glaciers in the Ny-Ålesund region were studied for their glacier radar zones vis-à-vis ELA over the period 2016–2020, using the multi-seasonal SAR data. All the glaciers were comprised of three zones, namely middle percolation/wet snow, lower percolation/wet snow, and clean ice. Using the anomalies of temperature and precipitation derived from Ny Ålesund meteorological station, it is observed that the ELA for most of the glaciers shifted to a higher altitude during 2016–2018 when the temperature was slightly high as compared to the long term mean, while it shifted down the glacier due to heavy accumulation and low temperature during 2019–20. The maximum shift of ±25 (with an uncertainty of ±6.85 m arising out of remote sensing data) in ELA, was detected during 2016–2020. These results obtained using geospatial technology-based analysis are provided for assessing the impact of climate change on the behaviour of the glaciers. [ABSTRACT FROM AUTHOR]

This Polar Science special issue, "SuperDARN/Studies of Geospace Dynamics - Today and Future," originated from an international SuperDARN (Super Dual Auroral Radar Network) annual workshop held in Japan in June 2019, and is focused on studies of geospace dynamics particularly related to SuperDARN. Its purpose is to overview recent wide and active research, new scientific results and future perspectives mainly through, but not limited to, the scientific papers presented at the workshop. This special issue is an opportunity to commemorate a quarter century since the establishment of SuperDARN in 1995 and to contribute to the further development of geospace sciences and relevant technology. Thirteen valuable papers have been published covering a wide variety of scientific and technical topics. [ABSTRACT FROM AUTHOR]

In this paper, echo occurrence rates for the Dome C East (DCE) and the new Dome C North (DCN) radars are studied. We report the ionospheric and ground scatter echo occurrence rates for selected periods around equinoxes and solstices in the final part of the solar cycle XXIV. The occurrence maps built in Altitude Adjusted Corrected Geomagnetic latitude and Magnetic Local Time coordinates show peculiar patterns highly variable with season. The comparisons of the radar observations with the International Reference Ionosphere model electron density and with ray tracing simulations allow us to explain the major features of observed patterns in terms of electron density variations. The study shows the great potential of the DCE and DCN radar combination to the Super Dual Auroral Radar Network (SuperDARN) convection mapping in terms of monitoring key regions of the high-latitude ionosphere critical for understanding of the magnetospheric dynamics. [ABSTRACT FROM AUTHOR]

We report the history and progress of the Japanese contribution to the Super Dual Auroral Radar Network (SuperDARN) project; especially focusing on the initial stage of SENSU (S yowa South and E ast HF Radars of N IPR for SU perDARN) project. The SENSU Syowa South HF radar operated by NIPR was one of the starting members of the initial SuperDARN radar operating at Syowa Station in Antarctica in 1995. It provided bi-directional common-volume observations with the Halley radar. In 1997 the SENSU Syowa East radar was installed. The King Salmon radar organized by NICT was installed in Alaska, USA in 2001. The Hokkaido East radar organized by Nagoya University was installed in Hokkaido, Japan in 2006, and the Hokkaido West radar began operation in 2014. The Japanese group has also contributed to SuperDARN by hosting three SuperDARN workshops in Japan namely: 1) in Tokyo in 1998 hosted by NIPR, 2) in Hokkaido in 2007 hosted by Nagoya University and 3) at Yamanashi in 2019 hosted by NICT. [ABSTRACT FROM AUTHOR]

We have been operating remote high frequency (HF) wave receivers for the SuperDARN Hokkaido East radar in Nagoya (1092 km away from the radar) and Rikubetsu (a few tens of m away from the radar antenna) since 2014 to monitor the ionospheric environment and its changes. One receiver set consists of a USRP-N210 receiver unit, Ubuntu Linux PC and dipole/loop antenna. Using the remote receiver data it is possible to monitor the upward/downward motion of the ionosphere at the ionospheric reflection point of the HF radar backlobe beams emitted toward the Nagoya area. The usage of the SuperDARN (backlobe) beams has the following advantages over other instruments such as HF Doppler systems: (1) SuperDARN Backlobe beams also have high directivity, so that it is possible to observe strong echoes at the remote area more than 1000 km away from the radar. (2) Since the SuperDARN radars emit pulse waves instead of continuous waves, it is possible to identify the travel time from the radar to the receiver. The initial results of the observation of ionospheric perturbations using the remote HF wave receiver of the SuperDARN Hokkaido East radar are described. [ABSTRACT FROM AUTHOR]

A medium-scale travelling ionospheric disturbance (MSTID) was observed concomitantly by SANAE and Halley SuperDARN HF radars during the period 02–06 UT 17 March 2013. The event occurred during a geomagnetically quiet time where no substorm or storm activities were observed. Both radars (at similar geomagnetic latitudes of 61.80S (SANAE) and 62.10S (Halley)) are well placed for observing the sporadic E (Es) region associated with the ionospheric trough around midnight during quiet geomagnetic conditions. F region electrodynamics and electrical coupling between E and F regions are one of the important mechanisms for the generation of nighttime MSTIDs. This is thought to be the generation mechanism in this study. We analysed the radar data using multitaper method (MTM). Multiple windowing mitigates spectral leakage and bias. The orthogonality of the tapers allows for confidence levels of peaks to be determined. The results from both radars show an MSTID with a period of approximately 23 min propagating at a speed ~280 ms−1 (SANAE) and 178 ms−1 (Halley) in the Southeast direction. An upper limit of ~55 kW was estimated to be dissipated by Joule heating due to the MSTID over an area where it was detected by both radars with more than 90% confidence. [ABSTRACT FROM AUTHOR]

The high frequency radars in the Super Dual Auroral Radar Network (SuperDARN) estimate the elevation angles of returned backscatter using interferometric techniques. These elevation angles allow the ground range to the scattering point to be estimated, which is crucial for the accurate geolocation of ionospheric measurements. For elevation angles to be accurately estimated, it is important to calibrate the interferometer measurements by determining the difference in the signal time delays caused by the difference in the electrical path lengths from the main array and the interferometer array to the point at which the signals are correlated. This time delay is known as t diff. Several methods have been proposed to estimate t diff using historical observations; these methods are summarised in this paper. Comparisons of the t diff estimates from the different calibration methods are presented and sources of uncertainty discussed. The effect of errors in the estimated t diff value on the accuracy of geolocation is evaluated and discussed. The paper concludes with a series of recommendations for both scientific SuperDARN data users and SuperDARN radar operators. [ABSTRACT FROM AUTHOR]

A review of researches related to ultra low frequency (ULF) waves studied using a midlatitude coherent decameter radar located near Ekaterinburg (EKB), Russia is presented. The radar was constructed similar to SuperDARN radars. During the experiment conducted in 2013–2015 three of its beams were surveyed successively with the integration time of 6 s providing time resolution of 18 s at each beam. In a few cases, data received in the nighttime ionosphere showed signatures of the drift compressional mode. In one of them, the wave exhibited clear dependence of frequency on azimuthal wave number m , which corresponds with the theory of drift compressional waves. In another case, merging of the drift compressional and Alfvén modes at some critical value of m was shown. A number of the observed waves' frequencies were compared with the Alfvén ones inferred from the spacecraft data. The results showed that in a large part of cases waves had sub-Alfvénic frequencies. This finding complies with the assumption that at least a part of the waves observed with the radar should be identified with the drift compressional mode, whose frequency can be lower than frequency of field line resonance (FLR). Additionally, a case of simultaneous spacecraft and radar wave observation was presented. As the wave had poloidal structure, diamagnetic properties, and its frequency was considerably lower than the minimal frequency of the FLR, it was assumed that it was some kind of compressional mode, apparently the drift compressional wave. [ABSTRACT FROM AUTHOR]

The method for calibrating elevation measurements at EKB ISTP SB RAS radar obtained for the period 20/09/2019–18/11/2019 is presented. The calibration method is a modernization of the method for calibrating radar by meteor trails. The main difference of the method is the use of not a statistically processed FitACF data, but the full waveform of the signals scattered on the meteor trails. Using the full waveform makes it possible to more reliably distinguish meteor scattering from other possible scattered signal sources, and to determine meteor heights from the trail lifetime using the NRLMSIS-00 model. A comparison of the results with the results of E-layer calibration method shows a good agreement. The first examples of regular elevation observations at the EKB ISTP SB RAS radar are presented, and their preliminary interpretation is given. [ABSTRACT FROM AUTHOR]

An all-digital agile dual auroral radar network (AgileDARN) was developed by the National Space Science Center, Chinese Academic of Sciences (NSSC, CAS). AgileDARN can achieve higher performance and greater flexibility based on highly digitized hardware and its distributed digital signal processing system. Multiple receiving beams can be created within the transmitting beam pattern better to determine the direction of arrival (DOA). In each beam, seven real-time azimuthal sub-beams are synthesized simultaneously with 16 main digital receiver channels. Each sub-beam detects the echo around the transmitting boresight with an angular separation of 0.46°. Comparing the echoes from different sub-beams, the azimuthal geolocation of the irregularities can be improved when their volume is smaller than the beamwidth. Furthermore, the Chebyshev window enables the control of the sidelobes and antenna pattern, effectively suppressing interference. To implement multi-beam forming, extra processing resources of the field-programmable gate array (FGPA) are required. This paper introduces the signal processing procedure and analyzes the requirements on the FPGA resources，and the technique is validated with meteor echoes received by the AgileDARN radar. The azimuthal geolocation of echoes increases by seven times compared with the single beamforming SuperDARN radar. • Applied and implemented the multi-beam forming technique to the AgileDARN radar. • Creat seven receiving beams to better determine the direction of arrival (DOA). • Employ the Chebyshev weighting to suppress the sidelobes of the array pattern. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]