30 September 2023, Volume 34 Issue 3

    

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  Contents

  Advances in Polar Science. 2023, 34(3): 155.

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Editorial Note
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  Persistently explore new understandings of Greenland Ice Sheet ablation

  XIAO Cunde, ZHANG Tong

  Advances in Polar Science. 2023, 34(3): 155-157. https://doi.org/10.12429/j.advps.2023.0108

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Reviews
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  Overview of China Polar Climate Change Annual Report (2022)

  LUO Yingyan, DING Minghu

  Advances in Polar Science. 2023, 34(3): 158-164. https://doi.org/10.12429/j.advps.2023.0020

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  The China Meteorological Administration recently released China Polar Climate Change Annual Report (2022) in Chinese, with the following main conclusions. Using the China Reanalysis-40 dataset (CRA-40), rapid warming has been observed in the Antarctic Peninsula and West Antarctica since 1979, with some parts of East Antarctica also experiencing warming. In 2022, the regional average temperature in Antarctica based on observational data was close to the long-term average (1991–2020). The Arctic, on the other hand, has experienced a warming trend at a rate of 0.63 °C per decade from 1979 to 2022 based on CRA-40, which is 3.7 times the global mean during the same period (0.17 °C per decade). In 2022, the overall temperature in the Arctic, using station data, was 1.10 °C above the long-term average (1991–2020). In recent years, both the Antarctic and Arctic regions have witnessed an increase in the frequency and intensity of extreme weather events. In 2022, based on the sea ice extent from National Snow and Ice Data Center, USA, Antarctic sea ice reached its lowest extent on record since 1979, and on 18 March, the most rapid surface warming event ever recorded on Earth occurred in the Antarctic, with a temperature increase of 49 °C within 3 d. This report has been integrated into China’s National Climate Change Bulletin system, to contribute to raising public awareness of polar climate change and providing valuable scientific references to address climate change.
Articles
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  Analysis of the record-breaking August 2021 rainfall over the Greenland Ice Sheet#br#

  DOU Tingfeng, XIE Zuowei, Jason E. BOX, YANG Qing, YANG Yifan, TENG Shiwen, XU Gaojie, LIU Chao, LI Xichen, Derek HOUTZ, GONG Xun, DU Zhiheng, DING Minghu, YU Yongqiang, XIAO Cunde

  Advances in Polar Science. 2023, 34(3): 165-176. https://doi.org/10.12429/j.advps.2022.0016

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  Rainfall was witnessed for the first time at the highest area of the Greenland Ice Sheet on 14 August, 2021. The thermodynamic mechanisms supporting the rainfall are revealed by ERA5 reanalysis, in-situ and satellite data. We find that a strong southward intrusion of the polar vortex favored the maintenance of a deep cyclone over Baffin Island and an amplification of anticyclonic circulation over the southeastern ice sheet, which pumped warm and moist air toward Greenland from anomalously warm waters south of Greenland. Across a wide swath of the ice sheet, atmospheric uplift maintained above-melting and rainfall conditions via condensation and enhanced downward infrared irradiance. Without the low-level liquid clouds, the spatial extent and duration of the rainfall would have been smaller. Over the ice sheet topographic summit, the air temperature from the ground to 250 hPa level was ~2 °C higher than the previous record set on 12 July, 2012. Such events may occur more frequently with the decreased temperature contrast between the Arctic and the mid-latitude regions that drives highly amplified jet streams. Thus, this extreme event serves as a harbinger of a more likely wet surface condition across all elevations of the ice sheet.
  
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  Assessment of Greenland surface melt algorithms based on DMSP and SMOS data#br#

  LI Qian, WANG Che, ZHANG Tong , CHENG Wei, DING Minghu

  Advances in Polar Science. 2023, 34(3): 177-189. https://doi.org/10.12429/j.advps.2022.0010

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  Satellite-borne microwave radiometers provide essential measurements to study the surface melt state of ice sheets. Therefore, selecting suitable microwave radiometer data is critical to characterize the spatial distribution of surface melt. In this study, we investigated the Greenland Ice Sheet and evaluated the usefulness, as climate indicators, of data acquired by microwave radiometers onboard the F17 satellite of the United States of America Defense Meteorological Satellite Program (DMSP) and the Soil Moisture and Ocean Salinity (SMOS) satellite of the European Space Agency. First, surface melt was simulated using the DMSP dataset as input for a brightness temperature threshold algorithm, the Microwave Emission Model of Layered Snowpacks (MEMLS2), and the SMOS dataset as input for the L-band Specific MEMLS (LS-MEMLS). For accuracy evaluation, the simulation results were then compared with surface melt estimates derived from air temperature measurements at Automatic Weather Stations and from ice surface temperature measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite-borne instrument. Our results show that global (over Greenland) MEMLS2 simulation performance (overall accuracy 83%) was higher than that of LS-MEMLS (overall accuracy 78%). However, in southeastern Greenland, MEMLS2 omission error was markedly higher than that of LS-MEMLS, whereas LS-MEMLS could detect longer-lasting surface melt than MEMLS2. This analysis showed that DMSP-based surface melt simulations are more accurate than SMOS-based simulations, thereby providing a data selection reference for surface melt studies of the Greenland Ice Sheet.
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  Performance of surface radiation products of Greenland Ice Sheet using in-situ measurements

  CHE Jiahang, HUAI Baojuan, SUN Weijun, DING Minghu, WANG Lei, ZHANG Qinglin, WU Jiake, KANG Limin, TENG Xinru, YANG Xiaohong, YAN Jinpei, ZHAO Shuhui

  Advances in Polar Science. 2023, 34(3): 190-219. https://doi.org/10.12429/j.advps.2023.0002

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  Radiation is the direct energy source of the surface natural environment and the main driving force of climate change. It has increasingly become an important meteorological factor affecting the surface heat exchange and glacier mass balance, especially in the glacier changes of the Greenland Ice Sheet (GrIS). Due to the harsh climatic conditions of GrIS and sparse observed data, it has become an important way to obtain radiation data from reanalysis datasets. However, the applicability of these radiation data on GrIS is uncertain and worth exploring. In this work, we evaluate five reanalysis datasets (the fifth generation of European Centre for Medium-Range Weather Forecasts (ERA5), European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-Interim), Japanese 55-year Reanalysis (JRA55), National Centers for Environmental Prediction Reanalysis II (NCEP2) and Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2)) during 1997–2022 using observations from 26 Program for Monitoring the Greenland Ice Sheet (PROMICE) automatic weather stations (AWSs) and 3 K-transect AWSs on GrIS. The conclusions are as follows: ERA5 has the best performances in downward shortwave radiation (SWD) as well as downward and upward longwave radiation (LWD and LWU), but the performance is not the best in upward shortwave radiation (SWU).Based on the radiation budget analysis with ERA5 during 1979–2022, the fluctuation of longwave radiation is greater than that of shortwave radiation. The seasonal variation of shortwave radiation is obvious, while that of longwave radiation is small. The increasing trend of longwave radiation may result from global warming, in which ice sheets absorb more solar radiation and the surface heats up significantly, emitting more LWU.
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  Marginal weakening promoted rift propagation of the Petermann Ice Shelf in northwestern Greenland from 2016 to 2022

  LI Daan, JIANG Liming, HUANG Ronggang, LU Xi

  Advances in Polar Science. 2023, 34(3): 220-231. https://doi.org/10.12429/j.advps.2023.0015

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  Ice-shelf rifts are precursors of glacier calving, and thus they serve as indicators of ice shelf instability, especially under oceanic and atmospheric warming conditions. Therefore, understanding the dynamic processes underlying rift propagation and the associated damage mechanisms is essential to evaluate ice-shelf instability and to predict glacier calving. In this study, we investigated the effect of marginal weakening on rift propagation on the ice shelf of the Petermann Glacier, among the largest in Greenland, during 2016–2022. First, we analyzed satellite optical images to monitor rift growth (length and width) by tracking the tip trajectory of three large rifts identified on the Petermann Ice Shelf. Then, we estimated rift depth using ArcticDEM and ICESat-2 data. Our results indicated consistent increases of the rift widths and depths over the study period, with mean values of 133 m·a⁻¹ and 0.3 m·a⁻¹, respectively. We also combined remote-sensing observations with an ice-sheet numerical model to calculate the stress and damage fields on the Petermann Ice Shelf and to assess the ice shelf margin stability and strength. We determined that damage and lateral shear in the fracture zone degraded ice shelf integrity by decreasing the contact length with the fjord wall. In conclusion, marginal weakening effectively promoted rift propagation on the Petermann Ice Shelf, increasing the risk of future glacier calving.
Letter & Trend
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  Vibrocorer for undisturbed sampling of firn aquifer layers in Greenland: general concept

  Pavel TALALAY, XIAN Tao, FAN Xiaopeng, LI Bing, LI Yazhou, GONG Da

  Advances in Polar Science. 2023, 34(3): 232-235. https://doi.org/10.12429/j.advps.2023.0001

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  The firn aquifer beneath the Greenland Ice Sheet may play a significant role in rising sea level. Both traditional mechanical drilling and electric thermal drilling are poorly adapted for effective, low-disturbance sampling in firn aquifers. We propose using a vibrocoring technique for the undisturbed sampling of dry firn and firn aquifer layers. A remote-controlled vibrocorer is designed to obtain 1-m-long cores with a diameter of 100 mm. The depth capacity of the system is approximately 50 m. The total weight of the vibrocoring system with the surface auxiliary equipment is approximately 110 kg, and corer assembly itself weighs ~60 kg.