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Lidar and radar observations of persistent atmospheric wave activity in the Antarctic atmosphere motivate investigation of generation of acoustic‐gravity waves (AGWs) by vibrations of ice shelves and exploiting their possible ionospheric manifestations as a source of information about the ice shelves' conditions and stability. A mathematical model of the waves radiated by vibrations of a finite area of the lower boundary of the atmosphere is developed in this paper by extending to AGWs an efficient, numerically exact approach that was originally developed in seismology and underwater acoustics. The model represents three‐dimensional wave fields as Fourier integrals of numerical or analytical solutions of a one‐dimensional wave equation and accounts for the source directionality, AGW refraction and diffraction, and the wind‐induced anisotropy of wave dissipation. Application of the model to the generation of atmospheric waves in Antarctica by free vibrations of the Ross Ice Shelf reveals a complex three‐dimensional structure of the AGW field and elucidates the impact of various environmental factors on the wave field. The intricate variation of the wave amplitude with altitude and in the horizontal plane is shaped by the spatial spectrum of the ice surface vibrations and the temperature and wind velocity stratification from the troposphere to the mesosphere. It is found that the waves due to the low‐order modes of the free oscillations of the Ross Ice Shelf, which have periods of the order of several hours, can transport energy to the middle and upper atmosphere in a wide range of directions from near‐horizontal to near‐vertical. Plain Language Summary: This research paper paves the way to infer the conditions and stability of ice shelves in Antarctica by looking at unusual wave activity in the atmosphere. The researchers have developed a mathematical model to understand how these waves, called acoustic‐gravity waves (AGWs), are created by the vibrations of ice shelves. The model is based on a method previously used in seismology and underwater acoustics and accounts for various factors that affect the waves, such as the properties of the source, the way the waves bend and spread due to wind, and how they dissipate. The researchers applied this model to study the atmospheric waves generated by vibrations of the Ross Ice Shelf in Antarctica. The results show a complex 3D structure of the AGW field, highlighting the impact of different environmental factors on the wave activity. The variation in wave amplitude depends on the ice surface vibrations and the temperature and wind conditions at different heights in the atmosphere. The study found that waves with periods of several hours can transfer energy from the ice shelf to the middle and upper atmosphere in various directions. This new approach could help scientists better understand the conditions and stability of ice shelves in the future. Key Points: Vibrations of large ice shelves radiate atmospheric waves that can travel in a wide range of directions from near‐horizontal to near‐zenithSimple, numerically efficient model is developed of atmospheric wave generation by finite sources at the ground levelWith the surface vibrations' spectrum as the input, the model quantifies atmospheric perturbations from the troposphere to the thermosphere [ABSTRACT FROM AUTHOR]

Atmospheric electricity parameters (AEP) measurements from Antarctica predominantly feature either the potential gradient (PG) and/or air‐Earth current (AEC) density. We report for the first time simultaneous measurements of the bipolar ions concentration/conductivity, PG, and AEC density. AEP measurements were carried out at Maitri (70.8°S, 11.8°E) from December 2018 to November 2019. We formulated a few criteria, irrespective of the weather conditions, to select the electrically quiet days and some additional criteria based on the conductivity measurements to discern globally representative data (GRD) from such days. The measurements of the PG and AEC density over the Antarctic plateau demonstrated the diurnal curves similar to the Carnegie pattern, which represents the global thunderstorms and electrified shower clouds (ESCs) occurring on different continents and oceans, we regard the data having such trend as GRD. We found significant variability in the concentration of small bipolar ions/conductivity in the austral summer which in turn affects GRD. However, the concentration of bipolar ions is nearly consistent at ∼250 negative ions cm−3 and ∼300 positive ions cm−3 in winter and enhances the probability of GRD. Such differences can arise out of the prevalent planetary boundary layer processes in the two seasons. When the PG varied between ∼50 Vm−1 and ∼150 Vm−1 and the maximum range of conductivity variations was ∼0.2 × 10−14 ℧ m−1, the AEPs represented the signatures of the global thunderstorm and ESC activities. Plain Language Summary: Monitoring of the atmospheric electricity parameters is a simple technique to monitor global thunderstorm activity and electrified shower clouds. For this, the data need to be free from local disturbances. Obtaining such data in Antarctic Plateau was found to be successful. On the other hand, the coastal Antarctic stations, experience local or regional contributions in it. This paper attempts to provide some techniques to obtain globally representative data (GRD). This paper suggests that the diurnal variation of the concentration of bipolar small ions strongly impacts the GRD. Therefore a day free from the diurnal variation of the concentration of bipolar ions is essential to discern the global signals. The winter season appears to be a better season for this as the summer season experiences mild convection activity that causes local and regional electrical signals that contaminate the data. Key Points: Atmospheric electrical conductivity is the key parameter to discern globally representative data (GRD) over the Maitri, AntarcticaGRD is discernible on a day when conductivity is consistent, and such days are most common in local winterIn the austral summer, the planetary boundary layer (PBL) processes produce local electrical signals that interfere with the global signals [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]

Atmospheric rivers (ARs) that reach the Antarctic Ice Sheet (AIS) transport anomalous moisture from lower latitudes and can impact the AIS via extreme precipitation and increased downward longwave radiation. ARs contribute significantly to the interannual variability of precipitation over the AIS and thus are likely to play a key role in understanding future changes in the surface mass balance of the AIS. Dronning Maud Land (DML) is one of four maxima in AR frequency over coastal East Antarctica, with AR precipitation explaining 77% of the interannual variability in precipitation for this region. We employ a 16‐node self‐organizing map (SOM) trained with MERRA‐2 sea‐level pressure anomalies to identify synoptic‐scale environments associated with landfalling ARs in and around DML. Node composites of atmospheric variables reveal common drivers of precipitation associated with ARs reaching DML including anomalous high‐low surface pressure couplets, anomalously high integrated water vapor, and coastal barrier jets. Using a quasi‐geostrophic framework, we find that upward vertical motion associated with the occlusion process of attendant cyclones dominates atmospheric lift in AR environments. We further identify mechanisms that explain the variability in AR precipitation intensity across nodes, such as the lift associated with the occlusion process of attendant cyclones and the spatial coincidence of ascent induced by the occlusion process and frontogenesis. The latter suggests that ARs making landfall during the mature phase of cyclogenesis result in higher precipitation intensity compared to landfalling ARs that occur during the occluded phase. Plain Language Summary: Atmospheric Rivers (ARs) that reach the Antarctic Ice Sheet (AIS) transport moisture in the atmosphere from lower latitudes and can result in significant precipitation on the ice sheet. Around Dronning Maud Land, East Antarctica, the precipitation associated with ARs has a substantial impact on the year‐to‐year variability in the amount of water stored by the ice sheet. As the climate warms, changing AR impacts may modulate future global sea level changes as more or less water is stored in the AIS. We assess the environmental factors driving AR precipitation from 1980 to 2020 around Dronning Maud Land, and find that the amount of moisture and the strength of the cyclone associated with an AR do not significantly impact the intensity of precipitation an AR produces. We also identify atmospheric conditions that lift moist air to produce precipitation. We find that ARs reaching Antarctica in the middle of a cyclone's life cycle result in stronger precipitation intensities compared to ARs reaching Antarctica toward the end of a cyclone's life cycle. Key Points: Atmospheric Rivers (ARs) that reach Dronning Maud Land (DML) control the interannual variability of precipitation in the regionAR environments near DML feature an anomalous surface pressure couplet, anomalously high moisture, and sometimes a coastal barrier jetThe occlusion process dominates the quasi‐geostrophic forcing for lift in DML ARs, which modulates the intensity of AR precipitation [ABSTRACT FROM AUTHOR]

We present a novel method to discriminate atmospheric electric field (AEF) variations originating from the global electrical circuit and local meteorological‐induced AEF variations. By comparing the AEF values measured at two different heights, the method identifies the AEF data including disturbances caused by charged blowing snow particles, and provides the fair‐weather AEF data. The intense positive (fair‐weather direction) apparent AEF was measured during strong winds because of the collision of negatively charged blowing snow particles into the sensor electrode of the electric field mill. In general, the volume density of blowing snow particles rapidly decreases with increasing height. Therefore, measured AEF values at the two heights were different. The difference between AEF values measured at the two heights increased at a wind speed of 6 m/s or more. Meanwhile, the statistical analysis showed that the AEF with and without clouds was less than approximately 1 V/m at Syowa Station, which is negligible. In addition, this case study at Syowa Station found no relationship between cloud extension/dissipation and AEF. Accordingly, we propose a practical method to identify the fair‐weather conditions by the AEF values at two heights and wind speed observed in the polar region, such as at Syowa Station. When we employ criteria that the difference between the AEF observed at the 1.4 and 10 m heights was within ±20 V/m under the wind speed with less than 6.0 m/s to the whole data at Syowa Station, 24% of them were identified as fair‐weather data. Plain Language Summary: Under the fair‐weather conditions on the ground, there is an atmospheric electric field (AEF) of about 100 V/m in the positive polarity from the upper atmosphere to the ground. In the polar regions, the AEF measurements have been often conducted, because there are a small number of aerosols which are a source of noise in AEF measurements under the fair‐weather conditions. However, blowing‐snow that frequently occurs in the polar regions are the major source of noise in AEF measurements due to the electrified snow particles. We have shown that the use of two different height AEF observations and wind speed data allows us to identify the noisy period originating from the electrified snow. In general, the AEF measurements, clouds are also a source of electric disturbance for the fair‐weather AEF. However, at Showa Station in Antarctica, the influence of clouds on the AEF measurements was found to be negligible. Thus, we conclude that this method, which can identify the fair‐weather period without various optical observation, would contribute to the study of global electric circuits. Key Points: A novel fair‐weather identification of atmospheric electric field (AEF) in polar region for the study of global electrical circuit is proposedTwo different height observations of AEF with the wind speed data identify snow‐origin signal [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]

This study focuses on methods to estimate dry marine aerosol surface area (SA) from bulk optical measurements. Aerosol SA is used in many models' ice nucleating particle (INP) parameterizations, as well as influencing particle light scattering, hygroscopic growth, and reactivity, but direct observations are scarce in the Southern Ocean (SO). Two campaigns jointly conducted in austral summer 2018 provided co‐located measurements of aerosol SA from particle size distributions and lidar to evaluate SA estimation methods in this region. Mie theory calculations based on measured size distributions were used to test a proposed approximation for dry aerosol SA, which relies on estimating effective scattering efficiency (Q) as a function of Ångström exponent (å). For distributions with dry å < 1, Q = 2 was found to be a good approximation within ±50%, but for distributions with dry å > 1, an assumption of Q = 3 as in some prior studies underestimates dry aerosol SA by a factor of 2 or more. We propose a new relationship between dry å and Q, which can be used for −0.2 < å < 2, and suggest å = 0.8 as the cutoff between primary and secondary marine aerosol‐dominated distributions. Application of a published methodology to retrieve dry marine aerosol SA from lidar extinction profiles overestimated aerosol SA by a factor of 3–5 during these campaigns. Using Microtops aerosol optical thickness measurements, we derive alternative lidar conversion parameters from our observations, applicable to marine aerosol over the SO. Plain Language Summary: The Southern Ocean (SO) surrounding Antarctica is one of the few places where aerosol concentrations and composition are similar to pre‐industrial values. This makes data collected in this region important for improving and understanding climate model simulations. However, direct observations of aerosols are rare because of the remoteness, frequent storms, and high winds and waves common to the SO. In this study, we use some of these rare aerosol observations to test methods for estimating important aerosol quantities using other measurements that are easier to collect. The improvements presented here may increase the availability of key data for improving climate models by replacing rare measurements with ones that can be collected continuously and autonomously. Key Points: Methods to estimate dry marine aerosol surface area (SA) from bulk optical measurements were tested for the Southern Ocean regionA new relationship between effective scattering efficiency and dry Ångström exponent is proposed for nephelometer measurementsOverestimation of aerosol SA from previous methods is reduced by derivation of new lidar backscatter conversion parameters [ABSTRACT FROM AUTHOR]

This study performs a comprehensive evaluation of the simulated cloud phase in the U.S. Department of Energy, Energy Exascale Earth System Model, atmosphere model version 2 (EAMv2), and version 1 (EAMv1). Enabled by the CALIPSO (Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation) simulator, EAMv2 and EAMv1 predicted cloud phase is compared against the GCM‐Oriented CALIPSO Cloud Product (CALIPSO‐GOCCP) at high latitudes where mixed‐phase clouds are prevalent. Our results indicate that the underestimation of cloud ice in simulated high‐latitude mixed‐phase clouds in EAMv1 has been significantly reduced in EAMv2. The increased ice clouds in the Arctic mainly result from the modification on the WBF (Wegner‐Bergeron‐Findeisen) process in EAMv2. The impact of the modified WBF process is moderately compensated by the low limit of cloud droplet number concentration in cloud microphysics and the new dCAPE_ULL trigger used in deep convection in EAMv2. Moreover, it is found that the new trigger largely contributes to the better cloud phase simulation over the Norwegian Sea and Barents Sea in the Arctic and the Southern Ocean where large errors are found in EAMv1. However, errors in simulated cloud phase in EAMv1, such as the overestimation of supercooled liquid clouds near the surface in both hemispheres and the underestimation of ice clouds over Antarctica, persist in EAMv2. This study highlights the impact of deep convection parameterizations, which has received little attention, on high‐latitude mixed‐phase clouds, and the importance of continuous improvement of cloud microphysics in climate models for accurately representing mixed‐phase clouds. Key Points: EAMv2 largely improves cloud ice phase at high latitude regions, while biases in liquid phase shown in EAMv1 remainUpdated tuning parameters in Wegner‐Bergeron‐Findeisen process and deep convection are important for reduced negative bias in ice phase cloudsThe new dCAPE_ULL trigger in deep convection is responsible for the better cloud phase simulation over high‐latitude oceans [ABSTRACT FROM AUTHOR]

Satellite lidar remote sensing of the atmosphere has been ongoing for more than a decade providing the opportunity to study atmospheric processes in great detail. Here we use 12 years of Cloud‐Aerosol Lidar with Orthogonal Polarization measurements to derive a climatology of blowing snow layer height, optical depth, and frequency over Antarctica for the period 2006–2017. Limited to the vertical resolution of the Cloud‐Aerosol Lidar with Orthogonal Polarization data, our climatology includes all blowing snow layers greater than about 30 m in thickness for clear or optically thin cloud regions. Our results show that blowing snow occurs over 50% of the time over large regions with frequencies often exceeding 70%. The overall pattern of blowing snow frequency is fairly consistent from year to year, but there are regional differences. We examined the data for temporal trends in blowing snow properties and found significant trends only in blowing snow frequency. A small area of East Antarctica with generally low blowing snow frequency shows a statistically significant increase in blowing snow frequency ranging from 10% to 100% per decade. No significant trends in frequency were found in regions of high (>50%) blowing snow frequency, and only isolated small areas exhibited a decrease in frequency through the study period. Plain Language Summary: During the last decade a new satellite remote sensing tool has become available for atmospheric research. The technique, called lidar (light ranging and detection), uses short (laser) pulses of visible light to probe the vertical structure of the atmosphere. The Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations mission launched in 2006 has greatly increased our knowledge of atmospheric structure over the polar region. One of the important discoveries made by this satellite is the ubiquitous nature of blowing snow episodes over Antarctica. Blowing snow occurs when the surface wind exceeds a threshold value (about 5–7 m/s) and snow is carried aloft and transported downwind. Once aloft, the snow particles can be carried great distances and even blown off the continent. In this paper we use Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation data to detect the occurrence of blowing snow over Antarctica and construct a 12‐year climatology of its frequency of occurrence, layer depth, and particle density. We have discovered that many regions of Antarctica experience blowing snow over 70% of the time and that blowing snow storms can last for days, cover areas as large as the state of Texas, and reach heights of 400 m or more. Key Points: A first satellite‐derived climatology of blowing snow over Antarctica is presentedBlowing snow frequency exceeds 70% over large regions of East AntarcticaSome areas of East Antarctic show a statistically significant increasing trend in blowing snow frequency [ABSTRACT FROM AUTHOR]

We report the first lidar observations of vertical fluxes of sensible heat and meteoric Na from 78 to 110 km in late May 2020 at McMurdo, Antarctica. The measurements include contributions from the complete temporal spectrum of gravity waves and demonstrate that wave‐induced vertical transport associated with atmospheric mixing by non‐breaking gravity waves, Stokes drift imparted by the wave spectrum, and perturbed chemistry of reactive species, can make significant contributions to constituent and heat transport in the mesosphere and lower thermosphere (MLT). The measured sensible heat and Na fluxes exhibit downward peaks at 84 km (−3.0 Kms−1 and −5.5 × 104 cm−2s−1) that are ∼4 km lower than the flux peak altitudes observed at midlatitudes. This is likely caused by the strong downwelling over McMurdo in late May. The Na flux magnitude is double the maximum at midlatitudes, which we believe is related to strong persistent gravity waves in the MLT at McMurdo. To achieve good agreement between the measured Na flux and theory, it was necessary to infer that a large fraction of gravity wave energy was propagating downward, especially between 80 and 95 km where the Na flux and wave dissipation were largest. These downward propagating waves are likely secondary waves generated in‐situ by the dissipation of primary waves that originate from lower altitudes. The sensible heat flux transitions from downward below 90 km to upward from 97 to 106 km. The observations are explained with the fully compressible solutions for polarization relations of primary and secondary gravity waves with λz > 10 km. Plain Language Summary: The upper atmosphere is filled with waves that originate in the lower atmosphere from storm systems and airflow over mountainous terrain, and then propagate upward. These waves play key roles in establishing the composition and temperature structures by mixing the upper atmosphere and by perturbing chemical reactions of important reactive species like atomic oxygen and ozone. By using meteoric sodium (Na) that is injected between 78 and 110 km altitude by the vaporization of cosmic dust, as a tracer, and exciting the Na atoms to fluorescence using a lidar system located at McMurdo Station, Antarctica, we directly measured the vertical transport of heat and Na induced by the full spectrum of waves. A surprising discovery is the positive heat flux in the lower thermosphere (97–106 km), which contradicts conventional thinking but demonstrates the importance of the fully compressible solutions for polarization relations of primary and secondary gravity waves. By comparing the measured Na transport with theory, we also show that many of the waves between 80 and 95 km are propagating downward, which are likely generated in this region when upward propagating waves become unstable and break, much like ocean waves behave when breaking over a shoal. Key Points: We report the first observations of vertical fluxes of sensible heat & Na induced by the complete temporal spectrum of gravity wavesMcMurdo sensible heat and Na fluxes exhibit large downward peaks near 84 km and large upward sensible heat fluxes occur at ∼97–106 kmSensible heat & Na flux measurements support theories and show significant impacts of wave‐induced vertical transport and secondary waves [ABSTRACT FROM AUTHOR]

Observations at McMurdo Station, Antarctica from 24 November 2015 through 3 January 2017 were used to characterize the physical relationships between boundary layer stability and atmospheric state and fluxes. The basis of this analysis was self‐organizing maps (SOMs), a neural network algorithm, used to identify the range of potential temperature profiles present in the twice‐daily radiosonde data during the ARM (Atmospheric Radiation Measurement) West Antarctic Radiation Experiment (AWARE) campaign. The SOM identified profiles ranging from strongly stable to weakly stable regimes over the lowest 500 m of the atmosphere. It was found that in the winter (MJJA), moderate and strongly stable regimes occur most frequently (61%), while weakly stable regimes dominate in the summer (DJ, 83.4%). The mechanisms responsible for the dominance of different stability regimes in each season were analyzed to determine why these regimes occur with varying frequency throughout the year. This analysis found that wind speed variations and radiative cooling are responsible for the stability observed in the winter, radiative warming, as well as weaker wind speeds, are responsible for summer weak stability, and stability variations in the transition seasons (FMA, SON) are characterized by a change in sign of net radiation with increasing stability, as wind speed changes little across stability regimes. Low‐level jets were observed to occur about 50% of the time below areas of enhanced stability aloft and were observed most frequently in the transition seasons. The boundary layer depth, as determined by the Bulk Richardson number, was found to decrease with increasing stability. Key Points: Self‐organizing maps are used to examine the range of boundary layer conditions at McMurdo Station, AntarcticaA strong seasonal cycle of boundary layer stability regimes exists, forced by varying net radiation and wind speedLow‐level jets occur about 50% of the time below areas of enhanced stability aloft [ABSTRACT FROM AUTHOR]

Recent studies have suggested that water isotopologues in snow pits from remote East Antarctica can be influenced by the input of stratospheric water, which has anomalously high 17O‐excess values. However, it remains unclear whether the 17O‐excess records preserved in snow and ice from this region can be used to reconstruct stratosphere‐troposphere exchange (STE). In this study, we present high‐resolution 17O‐excess records from two snow pits at Dome A, the highest point of the Antarctic ice sheet. The 17O‐excess records show a significant positive correlation with the strength of the Brewer‐Dobson circulation (BDC), the hemispheric‐scale troposphere‐stratosphere overturn circulation. Stronger BDC leads to more stratospheric water input over Antarctica and higher 17O‐excess, and vice versa. In addition, the 17O‐excess records also have a significant positive correlation with the Southern Annular Mode (SAM) index, because SAM modulates Antarctic precipitation, which has a dilution effect on the stratospheric water input. The 17O‐excess records do not show significant correlations with local temperature and relative humidity in the moisture source region. These results suggest the dominant effect of BDC on 17O‐excess and indicate the potential for using 17O‐excess records in ice cores from remote sites in East Antarctica for reconstructing long‐term variations of STE, and understanding their mechanisms and climate effects. Plain Language Summary: Previous studies suggest the influence of stratospheric water on 17O‐excess variations in snow pits from the inland Ppateau of East Antarctica, and the potential for using ice‐core 17O‐excess to trace historical stratosphere‐troposphere exchange. However, it remains unclear whether ice‐core 17O‐excess records from this remote part of East Antarctica can be used as a proxy for stratosphere‐troposphere exchange. In this study, we presented high‐resolution 17O‐excess records from two snow pits at Dome A, the highest point of the Antarctic ice sheet. We found that the 17O‐excess variations over the past several decades were mainly controlled by the strength of the Brewer‐Dobson circulation. This discovery could open up an opportunity for new methods to reconstruct long‐term variations of the Brewer‐Dobson circulation. Key Points: The 17O‐excess records in snow pits at Dome A show a significant correlation with the strength of the Brewer‐Dobson circulation (BDC)Stronger BDC leads to more stratospheric water input over Antarctica and higher 17O‐excess, and vice versaThe 17O‐excess records are also significantly correlated with the Southern Annular Mode, which dilutes the stratospheric water input [ABSTRACT FROM AUTHOR]

Prominent excursions in the number of cosmogenic nuclides (e.g., 10Be) around 774 CE/775 document the most severe solar proton event (SPE) throughout the Holocene. Its manifestation in ice cores is valuable for geochronology, but also for solar‐terrestrial physics and climate modeling. Using the ECHAM/MESSy Atmospheric Chemistry (EMAC) climate model in combination with the Warning System for Aviation Exposure to SEP (WASAVIES), we investigate the transport, mixing, and deposition of the cosmogenic nuclide 10Be produced by the 774 CE/775 SPE. By comparing the model results to the reconstructed 10Be time series from four ice core records, we study the atmospheric pathways of 10Be from its stratospheric source to its sink at Earth's surface. The reconstructed post‐SPE evolution of the 10Be surface fluxes at the ice core sites is well captured by the model. The downward transport of the 10Be atoms is controlled by the Brewer‐Dobson circulation in the stratosphere and cross‐tropopause transport via tropopause folds or large‐scale sinking. Clear hemispheric differences in the transport and deposition processes are identified. In both polar regions the 10Be surface fluxes peak in summertime, with a larger influence of wet deposition on the seasonal 10Be surface flux in Greenland than in Antarctica. Differences in the peak 10Be surface flux following the 774 CE/775 SPE at the drilling sites are explained by specific meteorological conditions depending on the geographic locations of the sites. Plain Language Summary: During large solar storms, high energy particles are hurled with enormous force toward Earth by the Sun. As these particles collide with atmospheric constituents (such as oxygen or nitrogen) unique nuclides of cosmogenic origin are formed in the higher atmosphere. From there they are transported downwards and finally precipitate at the surface due to different sink processes. Their imprints can be conserved over thousands of years within natural archives, such as ice cores or tree rings. Analysis of these natural archives around the globe indicates that the strongest solar storm over the last 10.000 years happened around 774 CE/775. This event is estimated to have been up to two orders of magnitude stronger, than the strongest known events documented for the satellite era. In this study, we model and analyze the transport and deposition of the cosmogenic nuclides produced by the extreme 774 CE/775 event, by applying a new experimental setup. Our results might help to interpret the fingerprints of historical extreme events with respect to the prevailing atmospheric conditions. Key Points: The modeled transport and deposition of the cosmogenic nuclide10Be produced by the 774/775 solar proton event was compared to 10Be ice core recordsHemispheric differences in stratospheric and cross‐tropopause transport, and deposition were identified, with polar summertime maxima of 10Be surface fluxDifferences in reconstructed10Be surface fluxes are explained by the local ratio of wet to dry deposition maximizing inthesummertime [ABSTRACT FROM AUTHOR]

The oxygen and hydrogen isotopic composition in snow and ice have long been utilized to reconstruct past temperatures of polar regions, under the assumption that post‐depositional processes such as sublimation do not fractionate snow. In low‐accumulation (<0.01 m yr−1) areas near the McMurdo Dry Valleys in Antarctica, surface snow and ice samples have exceptionally low deuterium excess values (d‐excess ≡ δD – 8*δ18O)—sometimes as negative as −5‰—an uncommon phenomenon that is not fully understood. Here we use both an isotope‐enabled general circulation model and an ice physics model and establish that such exceptionally low d‐excess values can only arise from precipitation if the majority of the moisture is sourced from the Southern Ocean (south of 55°S). However, the model results show that moisture sourced from oceans north of 55°S contributes significantly (>50%) to precipitation in Antarctica today. We thus propose that sublimation must have occurred to yield the low d‐excess values in snow observed in and near the Dry Valleys, and that solid‐phase‐diffusion in ice grains is sufficiently fast to allow Rayleigh‐like isotopic fractionation in similar environments. We calculate that under present‐day conditions at the Allan Hills outside the Dry Valleys, 3%–24% of the surface snow is lost due to sublimation. Because the magnitude of sublimation may be nonstationary (i.e., it could vary in time) during past cold periods, we suggest that sublimation‐induced fractionation can alter the relationship between the snow isotopic composition and polar temperatures. Plain Language Summary: Earth's past temperatures in the polar regions are often calculated from the relative abundances of heavy hydrogen or oxygen atoms (isotopes) in the polar ice. Implicit to this approach is the assumption that once the snow has fallen from the sky, its isotopic composition no longer changes. Yet, this conventional notion is incompatible with some observations. In and near the McMurdo Dry Valleys in Antarctica, for example, the surface snow and ice show an unusually large depletion in heavy hydrogen isotopes relative to heavy oxygen isotopes. Deficits of such a magnitude are rare in precipitation and therefore hint at sublimation causing the ice to change its isotopic composition (to "fractionate") after deposition; if true, this process would challenge the conventional wisdom about snow and ice as paleoclimate indicators. Here, we investigate whether these unusual heavy‐isotope deficits could originate from Antarctic precipitation. We determine that the moisture arriving at Antarctica today does not have these deficits. Sublimation of the snow that falls, however, can quantitatively explain the observed range of heavy‐hydrogen depletions. We conclude that sublimation does fractionate isotopes in and near the Dry Valleys, and may affect the past temperatures reconstructed from the hydrogen and/or oxygen isotopes. Key Points: Exceptionally low deuterium excess values exist in surface snow in the McMurdo Dry Valleys and Allan Hills Blue Ice Area, East AntarcticaTo yield such low deuterium excess in Antarctic precipitation, unrealistic moisture contributions from high‐latitude oceans are requiredSublimation fractionation lowers deuterium excess in relatively dry, windy, and warm conditions [ABSTRACT FROM AUTHOR]

The calving of Antarctic ice shelves remains unpredictable to date due to a lack of understanding of the role of the different climatic components in such events. In this study, the role of atmospheric forcing in the calving of the Brunt Ice Shelf (BIS) in February 2021 is investigated using a combination of observational and reanalysis data. The occurrence of a series of extreme cyclones around the time of the calving induced an oceanward sea‐surface slope of >0.08° leading to the calving along a pre‐existing rift. The severe storms were sustained by the development of a pressure dipole on both sides of the BIS associated with a La Niña event and the positive phase of the Southern Annular Mode. Poleward advection of warm and moist low‐latitude air over the BIS area just before the calving was also observed in association with atmospheric rivers accompanying the cyclones. Immediately after the calving, strong offshore winds continued and promoted the drift of the iceberg A‐74 in the Weddell Sea at a speed up to 700 m day−1. This study highlights the contribution of local atmospheric conditions to ice‐shelf dynamics. The link to the larger scale circulation patterns indicates that both need to be accounted for in the projections of Antarctic ice shelf evolution. Plain Language Summary: A calving event is the process by which a large block of ice gets separated from an ice shelf or glacier and forms an iceberg. Large calving events from marine‐terminating ice shelves around Antarctica remain to date highly unpredictable. This process is typically associated with the glaciological cycle of the ice shelves as well as ocean dynamics. However, atmospheric forcing in triggering such events has been largely overlooked. This is investigated for the calving of iceberg A‐74 from the Brunt Ice Shelf (BIS) in February 2021. We found that strong near‐surface winds associated with intense cyclones promoted the event via an increased sea‐surface slope toward the open ocean, which amplified the stress on the pre‐existing rift and led to the calving. After the calving, the iceberg drifted westwards in the Weddell Sea at a speed of 700 m day−1 aided by strong offshore winds. The extreme weather conditions leading to the calving were associated with an alternation of a series of high (blockings) and low (troughs) pressure systems around the BIS region. Key Points: An intense and stationary cyclone around the ice shelf, which was part of a wave train occurred at the time of the calvingStrong near‐surface winds associated with the cyclone promoted the calving of the Brunt Ice Shelf via oceanward sea‐surface slopeCalving occurred on 26 February when the ice accelerated significantly in a westward direction from a velocity of 4–6 to 700 m day−1 [ABSTRACT FROM AUTHOR]

We report the results of a high‐sensitivity sulfur‐isotope (δ34S) analysis of samples from shallow ice core DF01 from Dome Fuji, East Antarctica, and present chronological profiles of the data with an annual resolution covering the entire nineteenth century. In the δ34S and non‐sea‐salt (nss)‐sulfate ([SO42−]nss) profiles, the signals of five well‐known nineteenth century volcanic eruptions were confirmed: Krakatau 1883 (and Tarawera 1886), Makian 1861, Cosiguina 1835, Tambora 1815, and Unknown 1809. Due to large influence of sulfate caused by volcanic eruptions in the first half of the nineteenth century, the averages of nss‐sulfur‐isotope composition (δ34Snss) and [SO42−]nss for the second half (+14.6‰ and 67.6 μg/L), calculated after excluding these prominent signals, were found to differ from those of the first half century (+9.1‰ and 84.1 μg/L). We also examined anomalous variations other than the five major volcanic signals in the δ34S and [SO42−]nss profiles based on not only variations in δ34S and [SO42−]nss but also variations in the concentrations of other ions. We then identified the presence of three additional volcanic signals: Babuyan 1831, Galunggung 1822, and an unknown volcanic eruption around 1807. The latter two signals confirmed for the first time in Antarctic ice cores. Other δ34S and [SO42−]nss anomalies may be related to an influx of coastal air masses, a nonstratospheric volcanic eruption near Antarctica or an increase in the relative contribution of a stratospheric component to the precipitation in inland Antarctica. These demonstrate the importance of obtaining the annually resolved, continuous δ34S profile over a certain period. Plain Language Summary: We analyzed δ34S and several ion concentrations, such as SO42−, in ice core samples from Antarctica (DF01 core) with approximate annual resolutions for an entire period of the nineteenth century. On the profiles of δ34S and SO42−, we found several singular fluctuations other than the prominent volcanic eruptions. Some of them may be unknown volcanic eruption signals in the Antarctic ice cores, but there were also singular points that implied some unique meteorological conditions that are not volcanic eruptions. Key Points: We performed high‐sensitivity sulfur‐isotope (δ34S) analyses for the samples from the shallow ice core DF01, corresponding to the period 1799–1900Singular fluctuations were found on the temporal profiles of δ34S and sulfate ion concentration except for prominent volcanic eruptionsSome of the singular points imply volcanic signals not confirmed in Antarctic ice cores and signals of short‐term meteorological changes [ABSTRACT FROM AUTHOR]

In the follow‐up of the Australian "Black Summer" event that persisted from August 2019 to March 2020, we present the optical properties of the stratospheric aerosols injected into the atmosphere by these wildfires. The outbreak of pyrocumulonimbus (PyroCb) activity triggered between 2019/12/29 and 2020/01/04 has raised the stratospheric aerosol load of the Southern Hemisphere to unprecedented levels. Long‐range transport brought some of the plumes down to the Antarctic region, where general circulation patterns kept them circling around the continent. The 532 nm Rayleigh/Mie/Raman ground‐based lidar of the French Antarctic station Dumont d'Urville (66.6°S–140°E) acquired unprecedented time series of these carbonaceous aerosols starting approximately 20 days after the injection and up to the most recent measurements in October 2019 where local radiosonde reported anomalous ozone depletion as compared to the decadal average. The lidar provides a first and unique time series at high vertical and temporal resolution, complemented by satellite measurements from Ozone Monitoring Instrument, Ozone Mapping and Profiler Suite, and Microwave Limb Sounder. Aerosol backscatter ratio decreases from 1.9 to 1.2 between January and June 2020. Aerosol origin and persistence are characterized, as well as their optical properties and vertical distribution over several months. Plain Language Summary: Major wildfires are now known to significantly contribute to the stratospheric aerosol load, which in turn may have consequences at the global scale. The deep convection and radiative uplift processes that they can spark, now colloquially referred to as pyroconvection, can inject significant quantities of aerosols into the stratosphere. The major wildfires that raged in Australia at the end of 2019 are a case in point: they injected an unprecedented amount of material into the stratosphere. After some weeks and due to the general circulation patterns, a part of this material ended up trapped above the Antarctic region. The lidar located at the French Antarctic station Dumont d'Urville had a unique opportunity to probe these stratospheric aerosols for an extended time period, allowing to observe the evolution in time of their optical properties over months. This study presents these valuable measurements which contribute to our knowledge of biomass‐originated stratospheric aerosols and highlights the importance of operational ground‐based instrumental capabilities and coverage at high latitudes. Key Points: 2019–2020 Australian bushfires injected an unprecedented amount of aerosol into the stratosphere with impact at polar latitudesLongest ground‐based lidar smoke aerosol record acquired at Dumont d'Urville with persistent 532 nm scattering ratio throughout the year 2020Simultaneous presence of polar stratospheric clouds and smoke aerosols were observed during the wintertime [ABSTRACT FROM AUTHOR]

Climate models exhibit major radiative biases over the Southern Ocean owing to a poor representation of mixed‐phase clouds. This study uses the remote‐sensing dataset from the Measurements of Aerosols, Radiation and Clouds over the Southern Ocean (MARCUS) campaign to assess the ability of the Weather Research and Forecasting (WRF) model to reproduce frontal clouds off Antarctica. It focuses on the modeling of thin mid‐level supercooled liquid water layers which precipitate ice. The standard version of WRF produces almost fully glaciated clouds and cannot reproduce cloud top turbulence. Our work demonstrates the importance of adapting the ice nucleation parameterization to the pristine austral atmosphere to reproduce the supercooled liquid layers. Once simulated, droplets significantly impact the cloud radiative effect by increasing downwelling longwave fluxes and decreasing downwelling shortwave fluxes at the surface. The net radiative effect is a warming of snow and ice covered surfaces and a cooling of the ocean. Despite improvements in our simulations, the local turbulent circulation related to cloud‐top radiative cooling is not properly reproduced, advocating for the need to develop a parameterization for top‐down convection to capture the turbulence‐microphysics interplay at cloud top. Plain Language Summary: Among the major shortcomings of climate models is a poor representation of clouds over the Southern Ocean. Thanks to new measurements from the Measurements of Aerosols, Radiation and Clouds over the Southern Ocean campaign that took place aboard the Aurora Australia ice breaker, we can now better assess the ability of models to represent clouds off Antarctica. In particular, we focus here on clouds that are mostly composed of ice crystals but that are topped by a thin layer of so‐called "supercooled" liquid droplets that form at temperatures below zero Celsius. While the standard version of the model produces clouds composed only of ice, we show that by adapting the formulation of ice crystal formation to the very pristine atmospheric conditions peculiar to the Southern Ocean it is possible to successfully reproduce thin layers of supercooled liquid droplets observed in mixed‐phase clouds. The latter significantly changes how much sunlight these clouds reflect to space, which is critical to understanding the climate. Compared to ice crystals, liquid droplets tend to reflect more solar energy toward space and at the same time, they enhance the cloud infrared emission toward the surface of the Antarctic ice sheet. Key Points: Weather Research and Forecasting‐observation comparison during Measurements of Aerosols, Radiation and Clouds over the Southern Ocean shows the inability of the model in standard configurations to simulate austral mixed‐phase cloudsA parameterization of ice nucleation based on new ice nucleating particle measurements improves the simulation of supercooled liquid water near cloud topFurther parameterization developments targeting the convection at cloud top are needed to reproduce the turbulence‐microphysics interplay [ABSTRACT FROM AUTHOR]

We analyze the long‐range transport to high latitudes of a smoke particle filament originating from the extratropics plume after the Australian wildfires colloquially known as "Black Saturday" on 7 February and report the first Antarctic stratospheric lidar characterization of such aerosols. Using a high‐resolution transport/microphysical model, we show that the monitoring cloud/aerosol lidar instrument operating at the French Antarctic station Dumont d'Urville (DDU, 66°S to 140°E) recorded a signature of those aerosols. The 532 nm scattering ratio of this filament is comparable to typical moderate stratospheric volcanic plume, with values between 1.4 and 1.6 on the first and third days of March above DDU station at around the 14 and 16 km altitude, respectively. A dedicated model is described and its ability to track down fine optical signatures is validated against Antarctic lidar elastic aerosol and DIAL ozone measurements. Using 1 month of tropical Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) data to support a relatively simple microphysical scheme, we report modeled aerosol presence above DDU station after advection of the aerosol size distribution. In situ measurements also report associated positive ozone anomaly. This case study provides evidence that biomass burning events injecting significant amounts of material up to stratospheric altitudes can be transported toward high latitudes. We highlight a potential imprint of smoke particles on the Antarctic atmosphere over larger time scales. Any underestimation of the global impact of such deep particle transport will lead to uncertainties in modeling the associated chemical or radiative effects, especially in polar regions, where specific microphysical and chemical processes take place. Plain Language Summary: A series of bushfires ignited in the Australian state of Victoria on 7 February 2009 and ended up being the most devastating fire hazard in Australia before the recent 2019/2020 fires. Active remote sensing monitoring instruments are deployed on the French Antarctic station Dumont d'Urville. For the first time, the station recorded presence of aerosols having originated from this biomass burning event at stratospheric altitudes using the atmospheric laser sounding technique (lidar). We combine model calculations to space‐borne and ground‐based measurements to track the long‐range transport of a small filament of the aerosol plume down to the Antarctic station to highlight the possible global impact of such events. Key Points: In 2009, the DDU Antarctic Lidar reported an unusual backscatter ratio of 1.4 above 13 km, first signature of the Australian wildfiresA microphysical transport model using CALIOP data as constraints successfully models the optical properties of the Antarctic lidar overpassPositive ozone anomaly is reported using lidar measurements [ABSTRACT FROM AUTHOR]

A reanalysis data set produced by the Copernicus Atmosphere Monitoring service (CAMS reanalysis, 2003 to present day) augmented by ERA5 data for the years before 2003 is used to describe the evolution of the 2020 Arctic ozone season and to compare it with years back to 1979. Ozone columns over large parts of the Arctic reached record low values in March and April 2020 because of an exceptionally strong, cold, and persistent Arctic polar vortex. Minimum ozone columns were below 250 DU for most of March and the first half of April, with the lowest values of 211 DU in the CAMS reanalysis found on 18 March. Such low values are extremely unusual for the Arctic. The previous years with similarly strong Arctic ozone depletion were 2011 and 1997 with minimum values of 232 and 217 DU, respectively. The performance of the CAMS ozone analysis is assessed by comparison with ozonesonde data and found to agree well with the independent observations. We find a clear sign of chemical ozone destruction with ozone severely depleted in a layer between 80 and 50 hPa in late March and early April when partial pressure values below 2 mPa were observed. Profiles from the limb sounders Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer (ACE‐FTS) and Microwave Limb Sounder (MLS) show clear signs of chlorine activation and the presence of polar stratospheric clouds. Monthly mean ozone columns in March 2020 were up to 180 DU or 40% lower than the CAMS climatology (2003–2019) while values for 2011 and 1997 were lower by 31% and 35%, respectively. Plain Language Summary: The stratosphere is the layer of the atmosphere between about 15 and 50 km where most of the ozone resides. Usually, Arctic ozone reaches maximum values in the stratosphere during boreal spring. However, in spring 2020 the Arctic stratosphere was exceptionally cold, and ozone transport from the midlatitudes was inhibited. Because of the low temperatures, polar stratospheric clouds could form over the Arctic region and lead to stratospheric ozone destruction. This led to record low ozone columns in the Arctic at the end of March and the beginning of April 2020, with minimum values of 211 DU. This is lower than in 1997 and 2011, the previous two years that had exceptionally low ozone columns over the Arctic during spring. In spring 2020, the Arctic ozone layer showed clear signs of chemical ozone depletion with ozone almost completely destroyed in a layer around 18 km in a way that is usually only seen over the Antarctic during the austral spring, when the ozone hole forms. Key Points: Arctic ozone columns in spring 2020 were the lowest since 1979 because the Arctic polar vortex was unusually strong, cold, and long lastingWe see evidence of chlorine activation and the presence of polar stratospheric clouds over the Arctic in March 2020The CAMS reanalysis captures the 2020 Arctic stratospheric ozone well [ABSTRACT FROM AUTHOR]

Potential sources of inertia‐gravity waves (IGWs) in the lower stratosphere (z = 15–22 km) at Jang Bogo Station, Antarctica (74°37′S, 164°13′E) are investigated using 3‐year (December 2014 to November 2017) radiosonde data, including the 25‐month result (December 2014 to December 2016) analyzed in Yoo et al. (2018, https://doi.org/10.1029/2018JD029164, Part 1). For this investigation, three‐dimensional backward ray tracing calculations are conducted using the Gravity wave Regional Or Global RAy Tracer. Among 248 IGWs, 112, 68, and 68 waves are generated in the troposphere (z < 8 km), tropopause (z = 8–15 km), and lower stratosphere (z = 15–18.5 km), respectively. These waves mainly propagate from the northwestern and southwestern regions of Jang Bogo Station dominated by the prevailing westerlies between the upper troposphere and lower stratosphere. Potential sources of IGWs are categorized into orography, fronts, convection, and the flow imbalance including the upper‐tropospheric jet stream. In the troposphere, relatively large numbers of waves are associated with fronts (37) and orography (35) compared with convection (28). In the tropopause (stratosphere), 36 (42) waves, including 11 cases associated with the upper‐tropospheric jet stream, are excited by the flow imbalance. Waves related to the flow imbalance are characterized by low intrinsic frequency (1–2f), short vertical wavelength (1–2 km), and longer horizontal wavelength (50–1000 km), whereas the waves induced by the tropospheric sources have wider ranges of intrinsic frequency (1–20f) and vertical wavelengths (1–15 km) with relatively shorter horizontal wavelengths (less than 500 km). Key Points: Propagation and sources of inertia‐gravity waves (IGWs) are investigated using the Gravity wave Regional Or Global RAy Tracer (GROGRAT)Orography, fronts, convection, and the flow imbalance including the jet stream are suggested as potential sources for the observed IGWsRelationships between the observed IGWs and their sources are examined [ABSTRACT FROM AUTHOR]

More than 2,000 analyses of beryllium‐10 (10Be) and sulfate concentrations were performed at a nominal subannual resolution on an ice core covering the last millennium as well as on records from three sites in Antarctica (Dome C, South Pole, and Vostok) to better understand the increase in 10Be deposition during stratospheric volcanic eruptions. A significant increase in 10Be concentration is observed in 14 of the 26 volcanic events studied. The slope and intercept of the linear regression between 10Be and sulfate concentrations provide different and complementary information. Slope is an indicator of the efficiency of the draining of 10Be atoms by volcanic aerosols depending on the amount of SO2 released and the altitude it reaches in the stratosphere. Intercept gives an image of the 10Be production in the stratospheric reservoir, ultimately depending on solar modulation. The Samalas event (1257 CE) stands out from the others as the biggest eruption of the last millennium with the lowest positive slope of all the events. We hypothetize that the persistence of volcanic aerosols in the stratosphere after the Samalas eruption has drained the stratospheric 10Be reservoir for a decade, meaning that solar reconstructions based on 10Be should be considered with caution during this period. The slope of the linear regression between 10Be and sulfate concentrations can also be used to correct the 10Be snow/ice signal of the volcanic disturbance. Key Points: Beryllium‐10 deposition on polar ice sheets is influenced by stratospheric volcanic eruptionsThe biggest volcanic eruption of the last millennium, the Samalas (1257 CE), probably drained out the polar stratospheric 10Be reservoir over a decadeSolar reconstructions based on 10Be ice core records must take into account volcanic disturbance [ABSTRACT FROM AUTHOR]

In central Antarctica, where accumulation rates are very low, summer sublimation of surface snow is a key element of the surface mass balance, but its fingerprint in isotopic composition of water (δD, δ18O, and δ17O) remains unclear. In this study, we examined the influence of summer sublimation on δD, δ18O, and δ17O in precipitation using data sets of isotopic composition of precipitation at various sites on the inland East Antarctica. We found unexpectedly low δ18O values in the summer precipitation, decoupled from surface air temperatures. This feature can be explained by the combined effects of weak or nonexistent temperature inversion and moisture recycling associated with sublimation‐condensation processes in summer. Isotopic fractionation during the moisture‐recycling process also explains the observed high values of d‐excess and 17O‐excess in summer precipitation. Our results suggest that the local cycle of sublimation‐condensation in summer is an important process for the isotopic composition of surface snow, water vapor, and consequently precipitation on inland East Antarctica. Key Points: Isotopic composition in summer precipitation on inland East Antarctica is more depleted than expected from the range of surface air temperatures during precipitationThe strong depletion of isotopic composition in summer precipitation are caused by the combined effects of weak or nonexistent temperature inversion and moisture recycling associated with snow sublimationIsotopic fractionation occurs during the moisture recycling process [ABSTRACT FROM AUTHOR]

Predicted changes in Southern Hemisphere (SH) precipitation and Antarctic ice mass correspond to variations in the meridional moisture flux (MMF). Thirty‐five years of ERA‐Interim reanalysis data are combined with an extratropical cyclone (ETC) identification and tracking algorithm to investigate factors controlling SH MMF variability in the midlatitudes and near Antarctica. ETC characteristics which exert the strongest control on ETC MMF are determined thus identifying which ETCs contribute most to SH moisture transport. ETC poleward propagation speed exerts the strongest control on the ETC MMF across the Antarctic coastline. In SH winter, ETCs with the largest poleward propagation speeds transport 2.5 times more moisture than an average ETC. In the midlatitudes, ETC genesis latitude and poleward propagation speed have a similar influence on ETC MMF. Surprisingly, ETC maximum vorticity has little control on ETC MMF. Cyclone compositing is used to determine the reasons for these statistical relationships. ETCs generally exhibit a dipole of poleward and equatorward MMF downstream and upstream of the cyclone center, respectively. However, ETCs with the largest poleward propagation speeds resemble open frontal waves with strong poleward moisture transport downstream of the cyclone center only and thus result in the largest MMF. These results suggest that inhomogeneous trends and predicted changes in precipitation over Antarctica may be due to changes in cyclone track orientation, associated with changes to the large‐scale background flow, in addition to changes in cyclone number or intensity. Plain Language Summary: We investigate how large‐scale weather systems transport moisture from low latitudes (which are very moist) to high latitudes (which are much drier) in the Southern Hemisphere. Of special interest is how these weather systems transport moisture to Antarctica. For snow (and rain) to occur, there needs to be moisture present in the atmosphere. If the amount of moisture transported from low latitudes to high latitudes changes, the amount of snow falling over Antarctica will also change. This changes the amount of water stored as ice and snow in the Antarctic ice sheet. Changes to the Antarctic ice sheet could have drastic impacts on global sea levels. We study how the amount of moisture transported depends on the type, or characteristics, of weather systems. Weather systems which move the fastest from low latitude or midlatitude toward Antarctic can move 2.5 times more moisture than an average weather system. Surprisingly, the strongest weather systems do not move much more moisture than the average weather system. These results tell us that we should consider how the track of weather systems will change in the future in addition to how the strength or number of these large‐scale weather systems will change. Key Points: Moisture transport by extratropical cyclones (ETC) in the Southern Hemisphere is investigated using 35 years of ERA‐Interim reanalysis dataThe amount of moisture transported poleward by an ETC depends strongly on the ETC poleward propagation speed and weakly on ETC intensityChanges to storm track latitude and tilt may explain observed trends in SH precipitation better than changes in ETC intensity [ABSTRACT FROM AUTHOR]

Knowledge of black carbon (BC) concentrations and size distributions within surface snow in Antarctica is limited. However, these measurements are important to understanding global aerosol transport from combustion sources, and BC contributes to positive radiative forcing. This study analyzed the concentrations and size distributions of BC and inorganic ions in snow samples collected at the Syowa station in Antarctica from April to December 2011 and along a traverse route to an inland (Mizuho) station. The BC size distributions in snow were bimodal with mass median diameters of ~140 and ~690 nm. We also estimated the mass median diameter from unimodal distributions and found smaller diameters than were reported by other studies. The mass concentrations of BC in snow were higher in inland samples than in Syowa samples. Among Syowa samples, the BC concentrations in December (2117.3 ng L−1 on average) were higher than in other periods (288.2 ng L−1 on average). The December samples experienced ambient temperatures above 0 °C, and the atmospheric BC concentrations did not increase simultaneously. Inorganic ions originated from the ocean and decreased with increasing distance from the coastal area. We conclude that the BC concentrations in surface snow increased mainly by postdeposition processes through the loss of water mass due to melting, evaporation, and sublimation. Our study is the first to report detailed BC concentrations and size distributions in eastern Antarctica, and the results will help to evaluate BC global transport, the snow albedo estimations in this region, and the climate impacts of BC. Key Points: BC concentrations and size distributions in snow samples were measured during a 9‐month observation period in AntarcticaBC in our snow samples showed bimodal mass size distributions and smaller diameters than those in other regionsThe snow samples that experienced temperatures above 0 degrees had the highest BC concentrations, possibly due to postdeposition processes [ABSTRACT FROM AUTHOR]