Assessment of ICESat-2 ice surface elevations over the Chinese Antarctic Research Expedition (CHINARE) route, East Antarctica, based on coordinated multi-sensor observations

We present the results of an assessment of ice surface elevation measurements from NASA's Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) along the CHINARE (CHINese Antarctic Research Expedition) route near the Amery Ice Shelf in East Antarctica. The validation campaign was designed and implemented in cooperation with the 36th CHINARE Antarctic expedition from December 2019 to February 2020. The assessment of the ICESat-2 geolocated photon product (ATL03) and land ice elevation product (ATL06) was performed based on coordinated multi-sensor observations using two roof-mounted kinematic global navigation satellite system (GNSS) receivers, two line arrays of corner cube retroreflectors (CCRs), two sets of retroreflective target sheets (RTSs), and two unmanned aerial vehicles (UAVs) with cameras. This systematic validation of the ICESat-2 data covered a variety of Antarctic ice surface conditions along the 520 km traverse from the coastal Zhongshan Station to the inland Taishan Station. This comprehensive investigation is complementary to the 750 km traverse validation of flat inland Antarctica containing a 300 km latitude traverse of 88∘ S by the mission team (Brunt et al., 2021). Overall, the validation results show that the elevation of the ATL06 ice surface points is accurate to 1.5 cm with a precision of 9.1 cm along the 520 km CHINARE route. The elevation of the ATL03 photons has an offset of 2.1 cm from a GNSS-surveyed CCR and is accurate to 2.5 cm with a precision of 2.7 cm as estimated by using RTSs. The validation results demonstrate that the estimated ICESat-2 elevations are accurate to 1.5–2.5 cm in this East Antarctic region, which shows the potential of the data products for eliminating mission biases by overcoming the uncertainties in the estimation of mass balance in East Antarctica. It should be emphasized that the results based on the CCR and RTS techniques can be improved by further aggregation of observation opportunities for a more robust assessment. The developed validation methodology and sensor system can be applied for continuous assessment of ICESat-2 data, especially for calibration against potential degradation of the elevation measurements during the later operation period.

UNMANNED AERIAL VEHICLE DERIVED 3D MODEL EVALUATION BASED ON ICESAT-2 FOR ICE SURFACE MICRO-TOPOGRAPHY ANALYSIS IN EAST ANTARCTICA

Modelling of ice sheet micro-topography based on Unmanned Aerial Vehicle (UAV) is meaningful for the understanding of interactions between local ice mass and climate. 3D reconstruction based on UAV has advantages that satellite remote sensing cannot replace. Here, the surface micro-topography measurement was performed during the China's 36th Antarctic expedition (CHINARE) in 2019–2020, using an UAV platform composed of a DJI Phantom 4 and a D-RTK GNSS mobile station around Zhongshan Station of China. Then, four partly overlapped models were obtained by the SfM-MVS technology. Affected by the complex environment factors, the performance of this technology sometimes is challenged over the marginal Antarctic Ice Sheet. Satellite altimetry is one of the most essential technologies for land ice surface elevation measurements, widely used in regional or global ice mass balance estimations.We use the land ice surface heights with high accuracy derived from the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) to compare with the UAV-derived models. Combined with the high precision and space-time resolution of ICESat-2 satellite altimetry, the results of the model were evaluated under different terrain conditions. It has been certified that the derived models without extra GCPs were capable of detecting the surface micro-topographic features if considering the potential factors, which can be popularized and developed in polar research.

FIELD VALIDATION OF ICESAT-2 DATA ALONG CHINARE ROUTE IN EAST ANTARCTICA

A field validation of the ICESat-2 elevation data has been conducted along the CHINARE (CHINese Antarctic Research Expedition) route near the Amery Ice Shelf in East Antarctica from December 2019 to February 2020. The study area covers a 520 km traverse from the coastal Zhongshan Station to the inland Taishan Station. We deployed two roof-mounted GNSS receivers to collect elevation data along the traverse and reduced them to the ice surface height with measured boresight parameters. The comparison of the ICESat-2 data (Release 003) with the high-precision ground-based GNSS along the traverse shows that the elevations of ATL06 ice surface products are accurate to 1.5 cm with 9.1 cm precision, and the elevations of ATL03 photon events are accurate to 4.3 cm with 8.5 cm precision. The validation results indicated high accuracy of 1.5–4.3 cm of ICESat-2 data, which provides the potentials to observe and evaluate the low-level mass changes in East Antarctica. The methodology and hardware system can be improved to execute a continuous assessment of ICESat-2 data in the following mission period.

The sensitivity of landfast sea ice to atmospheric forcing in single-column model simulations: a case study at Zhongshan Station, Antarctica

Single-column sea ice models are used to focus on the thermodynamic evolution of the ice. Generally these models are forced by atmospheric reanalysis in absence of atmospheric in situ observations. Here we assess the sea ice thickness (SIT) simulated by a single-column model (ICEPACK) with in situ observations obtained off Zhongshan Station for the austral winter of 2016. In the reanalysis the surface air temperature is about 1 °C lower, the total precipitation is about 2 mm day−1 larger, and the surface wind speed is about 2 m s−1 higher compared to the in situ observations, respectively. Using sensitivity experiments we evaluate the simulation bias in sea ice thickness due to the uncertainty in the individual atmospheric forcing variables. We show that the unrealistic precipitation in the reanalysis leads to a bias of 14.5 cm in sea ice thickness and of 17.3 cm in snow depth. In addition, our data show that increasing snow depth works to gradually inhibits the growth of sea ice associated with thermal blanketing by the snow due to changing the vertical heat flux. Conversely, given suitable conditions, the sea ice thickness may grow suddenly when the snow load gives rise to flooding and leads to snow-ice formation. A potential mechanism to explain the different characteristics of the precipitation bias on snow and sea ice is discussed. The flooding process for landfast sea ice might cause different effect compared to pack ice, thus need to be reconsidered in ICEPACK. Meanwhile, the overestimation in surface wind speed in reanalysis is likely responsible for the underestimation in simulated snow depth, however this had little influence on the modelled ice thickness.

Spatial Variability of Glaciochemistry along a Transect from Zhongshan Station to LGB69, Antarctica

The spatial glaciochemical variability of snow samples collected along a transect from Zhongshan Station to Lambert Glacier Basin 69 (LGB69) in Antarctica was investigated. Sea-salt ion concentrations exponentially decreased with increasing distance from the coast and/or altitude. The observed high sea-salt ion concentrations within 20.6 km of the coast may be related to preferential wet or dry deposition of sea-salt aerosols. Methanesulfonic acid (MSA), non-sea-salt sulfate (nssSO42−), and calcium (Ca2+) concentrations decreased along the transect. The mean MSA/nssSO42− value of the surface snow samples (0.34 ± 0.08) indicates that coastal sea areas are their likely source regions. The non-sea-salt Ca2+ (nssCa2+)/Ca2+ percentages of the surface snow and LGB69 snow pit samples reveal that continental dust is the primary Ca2+ source. The δD and δ18O values decreased from the coast inland. The variation of deuterium excess (d-excess) along the transect was stable and d-excess values in the two snow pit samples were low and similar, which indicates that the moisture source region between Zhongshan Station and LGB69 is a coastal sea area. These results reveal the spatial distribution patterns and sources of ions and stable isotopes, as well as factors that influence the deposition of ions and the composition of stable isotopes, which provide important insight for further studies of ice cores drilled in Antarctic coastal regions.

Transient cusp ionospheric disturbances caused by a solar wind dynamic pressure enhancement

<p>Interplanetary (IP) shock driven sudden compression produces disturbances in the polar ionosphere. Various studies have investigated the effects of IP shock using imagers and radars. However, very few studies have reported the plasma flow reversal and a sudden vertical plasma drift motion following a CME driven IP shock. We report on the cusp ionospheric features following an IP shock impingement on 16 June 2012, using SuperDARN radar and digisonde from the Antarctic Zhongshan Station (ZHO). SuperDARN ZHO radar observed instant strong plasma flow reversal during the IP shock driven sudden impulse (SI) with a suppression in the number of backscatter echoes. Besides, we also report on a “Doppler Impulse” phenomenon, an instant and brief downward plasma motion, were observed by the digisonde in response to the SI and discuss the possible physical causes. Geomagnetic disturbance and convection patterns indicate the flow reversal was generated by the downward field-aligned current (FAC). We speculate that sudden enhancement in ionization associated with SI is responsible for generating the Doppler Impulse phenomenon.</p>