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Subglacial lakes have been mapped across Antarctica with two methods, radio‐echo sounding (RES) and ice‐surface deformation. At sites where both are coincident, these methods typically provide conflicting interpretations about the ice‐bed interface. With a single exception, active subglacial lakes identified by surface deformation do not display the expected flat, bright, and specular bed reflection in RES data, characteristic of non‐active lakes. This observational conundrum suggests that our understanding of Antarctic subglacial hydrology, especially beneath important fast‐moving ice streams, remains incomplete. Here, we use an airborne RES campaign that surveyed a well‐characterized group of active subglacial lakes on lower Mercer and Whillans ice streams, West Antarctica, to explore inconsistency between the two observational techniques. We test hypotheses of increased scattering and attenuation due to the presence of an active subglacial lake system that could suppress reflected bed‐echo power for RES observations in these locations, finding that entrained water is most plausible. Plain Language Summary: The bottom of an ice sheet is insulated from cold air temperatures, often warm enough to melt and pond liquid water into lakes. These lakes beneath the ice sheet have been identified by two independent measurements, first with radar methods and second with changes in height of the ice surface (altimetry). Interestingly, the two methods rarely identify the same lakes: radar generally detects lakes in the ice‐sheet interior, whereas altimetry detects active lakes near the ice‐sheet margins that fill and drain within the time series of repeated measurements (∼years). In this study, we investigate a group of active subglacial lakes at which both radar and altimetry data sets are available. We demonstrate that the radar returns from active lake reflections are much dimmer than expected based on non‐active lake signatures and investigate the physical processes controlling those dim reflections. We argue that water moves into the ice when the lake fills or drains and that is the most plausible explanation for the observational discrepancy. Key Points: Active subglacial lakes, identified by surface deformation, do not create the expected bright and specular radar reflectionEntrained water in basal ice suppresses radar power by scattering and attenuation, and it also likely alters the basal ice mechanicsUnderstanding the radar expression of subglacial water on Earth provides context for investigations of subsurface water on planetary bodies [ABSTRACT FROM AUTHOR]

The morphology and motion of auroras have been widely studied due to their indications on magnetospheric processes. Here, we report a new kind of "auroral curls," which have wavelengths in the mesoscale (∼100 km) and propagate azimuthally. Utilizing data from the Chinese Antarctic Zhongshan Station (the all‐sky imager and the high‐frequency radar), the Active Magnetosphere and Planetary Electrodynamics Response Experiment and the Defense Meteorological Satellite Program, we analyze an event occurred on 23 April 2019. We find these curls are fine structures in the poleward boundary of multiple arcs. Corresponding field‐aligned currents manifest as a series of longitudinally arranged pairs, while ionospheric flow velocities nearby oscillate with periods in the Pc 5 band. Observational evidence suggests these curls are connected with ultra‐low frequency (ULF) waves, which opens the possibility of using auroras to globally image ULF waves. Plain Language Summary: Auroras caused by precipitation of magnetospheric particles contain information about physical processes happened in the magnetosphere. In this letter, we report a new kind of auroral dynamic forms observed in Antarctica. These structures present both spatial and temporal periodic characteristics, which have similar scales with those of magnetospheric ultra‐low frequency (ULF) waves. We propose these auroral forms are connected with ULF waves, which provides a potential method to globally image ULF waves by analyzing properties of these auroras. Key Points: Azimuthally propagating "auroral curls" with mesoscale wavelengths were observed in AntarcticaThese curls are fine structures in the poleward boundary of multiple arcs formed by longitudinal‐arranged field‐aligned current pairsIonospheric flow velocities nearby oscillate with periods in the Pc 5 band, indicating connections with ultra‐low frequency waves [ABSTRACT FROM AUTHOR]

It has recently been suggested that clay minerals, which are widespread on the Martian surface, could be the possible source of the basal bright reflections detected by MARSIS at Ultimi Scopuli, instead of briny water. This hypothesis is based on dielectric measurements on a wet Ca‐Montorillonite (STx‐1b) sample conducted at 230 K, which reported permittivity values (apparent permittivity of 39 at 4 MHz) compatible with the median value of 33 retrieved by MARSIS 4 MHz data inversion in the high reflectivity area. These experimental results are, however, incompatible with well‐established dielectric theory and with laboratory measurements on clays, at MARSIS frequency and Martian temperatures, reported in the literature. Here, we replicate the experiment using a setup to precisely control the rate of cooling/warming and the temperature inside and outside the clay sample. We found that the rate of cooling, the position of the temperature sensor and, consequently, the thermal equilibrium between the sample and the sensor play a fundamental role in the reliability of the measurements. Our results indicate that even for a large water content in the clay sample, at 230 K and 4 MHz, the apparent permittivity is only 8.4, dropping to 4.1 at 200 K, ruling out clays as a possible source of the bright reflections detected by MARSIS at the base of the SPLD. Plain Language Summary: The recent discovery of bright basal reflections below the South polar ice cap at Ultimi Scopuli (Mars) by MARSIS has sparked an intense debate on their origin. Because bright radar reflections detected below the ice sheets in Antarctica and Greenland usually indicate the presence of basal water, and based on additional data processing methods, these anomalies were interpreted to be caused by liquid briny water. Recent laboratory measurements questioned this hypothesis and instead suggested that the presence of clay could explain the observed results. According to these measurements, the dielectric properties of wet clay at 230 K (−43°C) mimic the high reflectivity of briny water. Here, we replicate the experiment, making sure to reach thermal equilibrium during each measurement run to guarantee that the temperature is correctly evaluated when the dielectric properties of the sample are measured. This was accomplished using a dedicated setup to precisely control the thermal cycle and to carefully check the internal and external temperatures of the wet clay sample. Our experimental results clearly show that the dielectric properties of clay at 230 K are incompatible with the observed MARSIS anomalies and thus briny water remains the most plausible explanation for the bright basal reflections detected by MARSIS. Key Points: Anomalous bright basal reflections have been detected by MARSIS at Ultimi Scopuli, MarsDielectric measurements of wet clays at low temperature show that they cannot generate strong basal reflectionsReliable measurements of dielectric behavior of planetary analogs require a careful control of the temperature inside the sample [ABSTRACT FROM AUTHOR]

In polar regions, blowing snow (BLSN) can play a substantial role in regional thermodynamics and radiation properties. The extent of the impact depends upon the depth of the BLSN layer, a property that is difficult to measure and not well understood. The West Antarctic Radiation Experiment (AWARE) Field Campaign saw the deployment of a large suite of observational instruments to McMurdo Station, Antarctica, allowing for in‐depth investigation of BLSN. During the year of the campaign, BLSN occurred ∼7.4% of the time. In this study, additional remote sensing observations are used to supplement an existing ceilometer‐based BLSN characterization algorithm creating a multi‐instrument (MI) depth estimation algorithm to yield layer depths with more certainty. Backscatter coefficient and linear depolarization ratios from the micropulse and high spectral resolution lidar (HSRL) are incorporated along with color ratio derived from HSRL backscatter and Ka‐band radar reflectivity observations. This provided estimates of BLSN depth that were less impacted by noise/artifacts in any one set of observations. When applied to the data from AWARE, the MI algorithm yielded an average depth of 168.2 m with ∼60% of plumes less than 200 m in depth. Events occurring with precipitation saw the most value in the additional instruments, with the suite of observations allowing for more separation of BLSN particles from fallstreaks. Plain Language Summary: This study used multiple lidar and radar instruments to identify the height of blowing snow (BLSN) layers at McMurdo Station in Antarctica. This information can be used to evaluate and improve BLSN models which have had minimal verification above ground. Results of this study compare well to prior studies, however, the suite of instruments demonstrate that agreement is partially due to compensating errors within single instrument (ceilometer) studies. Key Points: Inclusion of additional lidars and radar improve estimates of blowing snow layer heightsCeilometer only algorithms are prone to offsetting height errors due to extinction and fallstreaksFuture in situ observations are paramount to improving and validating this experimental algorithm [ABSTRACT FROM AUTHOR]

The characteristics of the horizontal wind in the mesosphere and lower thermosphere (MLT) at King Sejong Station (KSS) in the Antarctic Peninsula are investigated using approximately 15‐year (March 2007–November 2021) meteor radar (MR) observations. The 15‐year climatology and variability of the MLT winds at KSS are analyzed for the first time, and comparisons with the observations at other Antarctic stations are performed. The short‐period oscillations (periods between 2 hr and 10 days) of the winds, including tides and several planetary wave components, are examined for each month. Temporal and altitudinal variations in the amplitudes of the semidiurnal and diurnal tides, the two largest short‐period components, are analyzed. Annual and semiannual oscillations of the wind are distinct below and above z = 90 km, respectively. The long‐term trend of the zonal wind is estimated through a multiple linear regression analysis. Statistically significant trends of the zonal wind of ∼0.5–0.8 m s−1 yr−1 appear above z = 90 km in July. To understand observed MLT wind trends, the gravity‐wave momentum flux and gravity‐wave drag (GWD) in the MLT region are estimated from the MR observations at KSS for the 15 years. Similar seasonal variations are found between the trends of the zonal winds and zonal GWDs, especially above z = 94 km. In July where a strong positive zonal wind trend appears, positive correlation between the zonal wind and zonal GWDs is found to be statistically significant above z = 94 km. Plain Language Summary: The mesosphere and lower thermosphere (MLT) is the atmospheric layer between the Earth's lower atmosphere and space. A meteor radar (MR) can be used to observe the horizontal winds in the MLT region. In this study, we analyze the characteristics of the MLT winds using the recent 15‐year MR observations at King Sejong Station (KSS; 62.22°S, 58.78°W) located in the Antarctic Peninsula. We find that the zonal and meridional components of the MLT wind at KSS exhibit temporal variability on various timescales. Statistically significant trends of the zonal wind appear above z = 90 km in July. To understand the observed MLT wind trends, we calculated the gravity‐wave momentum flux and gravity‐wave drag (GWD) using the MR observations at KSS for 15 years, which are quite unique data for such a long time period. A similar seasonal pattern between the zonal wind and the zonal GWD suggests that the positive zonal wind trend observed from the MR at KSS in July is likely related to that of the GWD. Key Points: Horizontal winds in the mesosphere and lower thermosphere at King Sejong Station are investigated using 15‐year meteor radar observationsThe 15‐year climatology, short‐ and long‐period variability, and long‐term trends of the observed winds are examinedSignificant positive zonal wind trends above 90 km are, to a certain degree, associated with zonal gravity wave drag trends [ABSTRACT FROM AUTHOR]

A new 36.17 MHz all‐sky meteor radar was installed at McMurdo Station Antarctica (77.8°S, 166.7°E) in February 2018 to provide wind measurements in the mesosphere and lower thermosphere (MLT) region (70–120 km). This instrument is the highest latitude meteor radar currently in operation in the southern hemisphere; it joins two other meteor radars within the Antarctic Circle. The radar will provide long‐term continuous wind measurements of the polar region, and contribute to a greater understanding of MLT dynamics. This work describes the radar hardware and its context with other instruments in the region. The paper provides an overview of the spatial and temporal variation in meteor echoes over the observation period of March 2018 through October 2021. It also provides an analysis of the mean winds and solar tides over the first three years of operation; including a description of an observed 12 hr summertime wind oscillation consistent with previously documented observations of a westward propagating 12 hr non‐migrating tide of zonal wavenumber 1. Key Points: A new 36.17 MHz all‐sky meteor radar was installed at McMurdo Station Antarctica (77.8°S, 166.7°E) in February 2018The radar provides hourly wind measurements in the mesosphere and lower thermosphere region (70–120 km)The work introduces the radar hardware, a summary of mean winds and tides, and an abundance of atmospheric wave activity for ongoing study [ABSTRACT FROM AUTHOR]

The sparse distribution of the observing network over the high latitudes of the Southern Hemisphere reduces the accuracy of regional atmospheric circulation (re)analysis and weather forecasting. Using operational medium‐range ensemble forecasts, we compared the forecast skill among forecast centres regarding a midlatitude cyclone close to western Australia on 17 December 2017. At forecast day 4.5, a large ensemble spread in an upper‐level trough over western Australia, which had travelled from coastal Antarctica, caused large uncertainty and error in the predicted position of the midlatitude cyclone. Using an ensemble data assimilation system and the Atmospheric General Circulation Model for the Earth Simulator and the Local Ensemble Transform Kalman Filter Experimental Ensemble Reanalysis version 2 (ALERA2), we conducted an operational forecast experiment to investigate the impact on ALERA2 and its forecast result of assimilation of 1‐hourly horizontal wind speed observational data from the PANSY radar located at the Japanese Syowa Station in Antarctica. An observing system experiment revealed that incorporation of PANSY radar data improved the reproducibility of atmospheric parameters in the troposphere and lower stratosphere as initial conditions for forecasting. To investigate the impact of PANSY radar data on forecast skill regarding the midlatitude cyclone, 63‐member ensemble forecast experiments were conducted using analysis data both with and without PANSY data as initial conditions. Comparison of the forecast results from the ensemble forecast experiments confirmed that incorporation of PANSY radar data reduced the ensemble spread and error in the upper troposphere over the Antarctic region as initial conditions, which enhanced the accuracy of the prediction of the positions of the upper‐level trough and surface cyclone over western Australia at forecast day 4.5. These experiments suggest that the PANSY radar represents an observing system suitable for continuous improvement in forecast skill of the atmospheric circulation in the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

The persistent Southern Ocean (SO) shortwave radiation biases in climate models and reanalyses have been associated with the poor representation of clouds, precipitation, aerosols, the atmospheric boundary layer, and their intrinsic interactions. Capitalizing on shipborne observations collected during the Clouds Aerosols Precipitation Radiation and atmospheric Composition Over the Southern Ocean 2016 and 2018 field campaigns, this research investigates and characterizes cloud and precipitation processes from synoptic to micro scales. Distinct cloud and precipitation regimes are found to correspond to the seven thermodynamic clusters established using a K‐means clustering technique, while less distinctions are evident using the cyclone and (cold) front compositing methods. Cloud radar and disdrometer data reveal that light precipitation is common over the SO with higher intensities associated with cyclonic and warm frontal regions. Multiple lines of evidence suggest the presence of diverse microphysical features in several cloud regimes, including the likely dominance of ice aggregation in deep precipitating clouds. Signatures of mixed phase, and in some cases, riming were detected in shallow convective clouds away from the frontal conditions. Two of the K‐means clusters with contrasting cloud and precipitation properties are observed over the high‐latitude SO and coastal Antarctica, suggesting distinct physical processes therein. Through a single case study, in‐situ and remote‐sensing data collected by an overflight of the Southern Ocean Clouds Radiation Aerosol Transport Experimental Study were also evaluated and complement the ship‐based analysis. Plain Language Summary: The current generation of climate models and reanalyses products have difficulties in properly representing the radiative balance over the Southern Ocean (SO), which can be traced to the poor understanding of clouds and precipitation processes in this region. The remote location of the SO is a key factor for the lack of field observations that allow the scientific community to address the above‐mentioned problem. However, recent coordinated field campaigns have collected an unprecedented amount of data, offering new opportunities to explore this understudied region. This research paper aims to study clouds and precipitation processes over the SO using shipborne data collected from two field campaigns in 2016 and 2018. Using different synoptic classification techniques, we identify unique macro and micro cloud and precipitation behaviors that correspond to the various weather patterns across a wide range of latitudes. In addition, we use aircraft observations collected from an overflight to evaluate and complement our analysis of the shipborne data. The study offers a framework that may help better understand the nature of the model biases over the SO. Key Points: Distinct cloud and precipitation regimes correspond to the Southern Ocean synoptics, defined using a sounding K‐means clustering techniqueEvidence suggests diverse microphysical features, like mixed phase in shallow convection and ice aggregation in deep precipitating cloudsTwo unique synoptic patterns have unique cloud and precipitation properties over the high‐latitudes, where climate models have large biases [ABSTRACT FROM AUTHOR]

Surface, upper‐air, and radar observations are used to assess the performance of the Antarctic Mesoscale Prediction System (AMPS) in simulating the mesoscale aspects of a wind and precipitation event over the Ross Island region of Antarctica that spanned January 16–20, 2016. The observations, collected during the Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE), provide a unique dataset for evaluating AMPS, especially the radar observations that facilitate a three‐dimensional depiction of winds and precipitation. Comparisons of AMPS forecast data with surface meteorology, balloon‐sounding, and profiling radar observations at and above sites near McMurdo Station reveal a mixture of similarities and differences. A generally southerly flow is evident at low levels in both the AMPS simulations and observed Doppler radial velocities. AMPS winds are comparable to those observed at the surface and aloft in terms of magnitude, direction, and timing but the strongest simulated southerly flow is displaced eastward relative to the observations. AMPS‐simulated reflectivity over the broader Ross Island region is more limited in areal extent and smaller in magnitude than observed by a scanning Doppler radar. Three episodes of surface precipitation are observed near McMurdo Station over the five‐day event with peak rates of ∼3 mm h−1 and a total accumulation of ∼22 mm. However, AMPS produces no surface precipitation at that location over the five‐day event due to a low‐level dry bias in the forecasts. The results show the first observationally based three‐dimensional understanding of meteorology in the Ross Island region. [ABSTRACT FROM AUTHOR]

Random‐noise‐induced biases are inherent issues to the accurate derivation of second‐order statistical parameters (e.g., variances, fluxes, energy densities, and power spectra) from lidar and radar measurements. We demonstrate here for the first time an altitude‐interleaved method for eliminating such biases, following the original proposals by Gardner and Chu (2020, https://doi.org/10.1364/ao.400375) who demonstrated a time‐interleaved method. Interleaving in altitude bins provides two statistically independent samples over the same time period and nearly the same altitude range, thus enabling the replacement of variances that include the noise‐induced biases with covariances that are intrinsically free of such biases. Comparing the interleaved method with previous variance subtraction (VS) and spectral proportion (SP) methods using gravity wave potential energy density calculated from Antarctic lidar data and from a forward model, this study finds the accuracy and precision of each method differing in various conditions, each with its own strengths and weakness. VS performs well in high‐SNR, yet its accuracy fails at lower‐SNR as it often yields negative values. SP is accurate and precise under high‐SNR, remaining accurate in worse conditions than VS would, yet develops a positive bias under low‐SNR. The interleaved method is accurate in all SNRs but requires a large number of samples to drive random‐noise terms in covariances toward zero and to compensate for the reduced precision due to the splitting of return signals. Therefore, selecting the proper bias removal/elimination method for actual signal and sample conditions is crucial in utilizing lidar/radar data, as neglecting this can conceal trends or overstate atmospheric variability. Plain Language Summary: Second‐order statistics like atmospheric wave‐induced variances or fluxes of physical parameters calculated from lidar or radar data would have positive biases if detection‐noise‐induced variances or fluxes were not properly eliminated. If such biases remained, not only would atmospheric variances be overestimated, implying unrealistic wave activity and growth rates, but certain phenomena could be concealed, presenting misleading pictures of the atmospheric observations. While various methods have been developed to account for this, all have limitations to their use. This study summarizes the development, theory, and application procedures for three different methods, namely conventional variance subtraction, the spectral proportion method, and the interleaved method, which can be used to correct such biases. The newest of these methods is adapted from operating on the data time‐wise into an altitude‐wise approach, improving its applicability. The performances of the three methods are compared by calculating the variance‐based gravity wave potential energy density derived from lidar data taken at McMurdo, Antarctica. Their accuracies are assessed by using a forward model. This study aims to guide future research by providing information on how and when to apply each of these methods in order to enhance the outcomes of existing and future lidar/radar systems and datasets. Key Points: We demonstrate for the first time an altitude‐interleaved method for eliminating random‐noise‐induced biases from second‐order statisticsThe interleaved method is compared to the spectral proportion and variance subtraction methods to reveal strengths and limitations of eachLidar data from Antarctica & a forward model are used to assess accuracies and precisions of the three methods under different conditions [ABSTRACT FROM AUTHOR]

A phase‐sensitive radar (ApRES) was deployed on Totten Ice Shelf to provide the first in situ basal melt estimate at this dynamic East Antarctic ice shelf. Observations of internal ice dynamics at tidal time scales showed that early arrivals from off‐nadir reflectors obscure the true depth of the ice shelf base. Using the observed tidal deformation, the true base was found to lie at 1,910–1,950‐m depth, at 350–400 m greater range than the first reflection from an ice‐ocean interface. The robustness of the basal melt rate estimate was increased by using multiple basal reflections over the radar footprint, yielding a melt rate of 22 ± 2.1 m a−1. The ApRES estimate is over 40% lower than the three existing satellite estimates covering Totten Ice Shelf. This difference in basal melt is dynamically significant and highlights the need for independent melt rate estimates using complementary instrumentation and techniques that rely on different sets of assumptions. Plain Language Summary: Observations of the rate of melting at the base of ice shelves are needed to model accurately ice sheet evolution. Local measurements are scarce, yet necessary for validation of satellite products and ocean models. We deployed a phase‐sensitive radar in the proximity of grounding zone of Totten Ice Shelf in East Antarctica, to measure basal melt in this dynamic region where uncertainties on melt rate estimates are high. We developed a method that accounts for basal geometry complexities and derived a melt rate estimate of ∼22 m per year, which is lower than previous estimates, but it confirms that the basal melt rate Totten Ice Shelf experiences is unusually high for East Antarctica. Key Points: First in situ radar‐derived basal melt estimate on Totten Ice Shelf yields 22 ± 2.1 m a−1, at least 40% lower than existing satellite estimatesRadar‐derived observation of tidal ice dynamics constrains estimate of ice thickness for a complex baseThe use of multiple basal reflections in melt derivation increases robustness of the estimate when early off‐nadir returns are present [ABSTRACT FROM AUTHOR]

From 2015 to 2017, the ROSETTA‐Ice project comprehensively mapped Antarctica's Ross Ice Shelf using IcePod, a newly developed aerogeophysical platform. The campaign imaged the ice‐shelf surface with lidar and its internal structure with ice‐penetrating radar. The ROSETTA‐Ice data was combined with pre‐existing ice surface and bed topography digital elevation models to create the first augmented reality (AR) visualisation of the Antarctic Ice Sheet, using the Microsoft HoloLens. The ROSETTA‐Ice datasets support cross‐disciplinary science that aims to understand 4D processes, namely the change of 3D ice‐shelf structures over time. The work presented here uses AR to visualise this dataset in 3D and highlights how AR can be simultaneously a useful research tool for interdisciplinary geoscience as well as an effective device for science communication education. [ABSTRACT FROM AUTHOR]

Ice shelves fringe much of the Antarctic continent, and, despite being up to 2 km thick, are vulnerable to climate change. Owing to their role in helping to control the ice sheet contribution to sea level change there is great interest in measuring the rate at which they are melting into the ocean. This study describes the development and deployment of an icepenetrating phase-sensitive FMCW radar, sufficiently robust and with sufficiently low-power consumption to be run through the Antarctic winter as a standalone instrument, yet with the stability and mm-precision needed to detect the very slow changes in ice shelf thickness in this exceptionally demanding environment. A number of elegant processing techniques are described to achieve reliable, high-precision performance and results presented on field data obtained from the Larsen-C ice shelf, Antarctica. [ABSTRACT FROM AUTHOR]