Performance of surface radiation products of Greenland Ice Sheet using in-situ measurements

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(Gr IS).Due to the harsh climatic conditions of Gr IS 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 Gr IS 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 Gr IS.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.

Persistently explore new understandings of Greenland Ice Sheet ablation

Greenland and Antarctic ice sheets are the largest potential contributors to global sea level rise(GSLR),amounting to more than 64 m of sea level equivalence(SLE).Between the two,Greenland Ice Sheet(GrIS)alone comprises about 7 mSLE,with a much faster speed of ablation than the Antarctic Ice Sheet.

Analysis of the record-breaking August 2021 rainfall over the Greenland Ice Sheet

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℃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.

Greenland Ice Sheet Contribution to Future Global Sea Level Rise based on CMIP5 Models

Sea level rise （SLR） is one of the major socioeconomic risks associated with global warming. Mass losses from the Greenland ice sheet （GrIS） will be partially responsible for future SLR, although there are large uncertainties in modeled climate and ice sheet behavior. We used the ice sheet model SICOPOLIS （Simulation COde for POLythermal Ice Sheets） driven by climate projections from 20 models in the fifth phase of the Coupled Model Intercomparison Project （CMIP5） to estimate the GrlS contribution to global SLR. Based on the outputs of the 20 models, it is estimated that the GrIS will contribute 0-16 （0-27） cm to global SLR by 2100 under the Representative Concentration Pathways （RCP） 4.5 （RCP 8.5） scenarios. The projected SLR increases further to 7-22 （7-33） cm with 2~basal sliding included. In response to the results of the multimodel ensemble mean, the ice sheet model projects a global SLR of 3 cm and 7 cm （10 cm and 13 cm with 2~basal sliding） under the RCP 4.5 and RCP 8.5 scenarios, respectively. In addition, our results suggest that the uncertainty in future sea level projection caused by the large spread in climate projections could be reduced with model-evaluation and the selective use of model outputs.

Accumulation over the Greenland Ice Sheet as Represented in Reanalysis Data

Annual precipitation,evaporation,and calculated accumulation from reanalysis model outputs have been investigated for the Greenland Ice Sheet （GrIS）,based on the common period of 1989-2001.The ERA-40 and ERA-interim reanalysis data showed better agreement with observations than do NCEP-1 and NCEP-2 reanalyses.Further,ERA-interim showed the closest spatial distribution of accumulation to the observation.Concerning temporal variations,ERA-interim showed the best correlation with precipitation observations at five synoptic stations,and the best correlation with in situ measurements of accumulation at nine ice core sites.The mean annual precipitation averaged over the whole GrIS from ERA-interim （363 mm yr 1） and mean annual accumulation （319 mm yr 1） are very close to the observations.The validation of accumulation calculated from reanalysis data against ice-core measurements suggests that further improvements to reanalysis models are needed.

Some recent advances in remote sensing-based monitoring of changes in the Greenland Ice Sheet

The mass balance of the Greenland Ice Sheet(GrIS)plays a crucial role in global sea level change.Since the 1960s,remote sensing missions have been providing extensive and continuous observation data for change monitoring of the GrIS.In this paper,we present our recent research results from remote sensing-based GrIS change monitoring.First,historical satellite data are processed and used to fill data gaps and are combined with existing partial maps,completing an ice velocity map of the GrIS from the 1960s to 1980s.This map provides valuable data for estimating the historical mass balance of Greenland.Second,the monthly gravimetry-based mass balance of the GrIS from 2002 to 2020 is estimated by combining Gravity Recovery and Climate Experiment(GRACE)and GRACE Follow On(GRACE-FO)data.It is found that the GrIS has lost a total mass of approximately 4443±75 Gt during this period.Third,based on Global Land Ice Measurements from Space(GLIMS),an updated Greenland glacier inventory is achieved utilizing data collected between 2006 and 2020.This inventory provides more detailed and up-to-data glacier boundaries of Greenland.Overall,these advances provide essential data support for estimating the mass balance of the GrIS,contributing to the advancement of research on global sea level change.

Assessment of Greenland surface melt algorithms based on DMSP and SMOS data

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.

Vibrocorer for undisturbed sampling of firn aquifer layers in Greenland: general concept

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.

Evaluation of vertical crustal movements and sea level changes around Greenland from GPS and tide gauge observations

To better monitor the vertical crustal movements and sea level changes around Greenland,multiple data sources were used in this paper,including global positioning system(GPS),tide gauge,satellite gravimetry,satellite altimetry,glacial isostatic adjustment(GIA).First,the observations of more than 50 GPS stations from the international GNSS service(IGS)and Greenland network(GNET)in 2007–2018 were processed and the common mode error(CME)was eliminated with using the principal component analysis(PCA).The results show that all GPS stations show an uplift trend and the stations in southern Greenland have a higher vertical speed.Second,by deducting the influence of GIA,the impact of current Gr IS mass changes on GPS stations was analysed,and the GIA-corrected vertical velocity of the GPS is in good agreement with the vertical velocity obtained by gravity recovery and climate experiment(GRACE).Third,the absolute sea level change around Greenland at 4 gauge stations was obtained by combining relative sea level derived from tide gauge observations and crustal uplift rates derived from GPS observations,and was validated by sea level products of satellite altimetry.The results show that although the mass loss of Gr IS can cause considerable global sea level rise,eustatic movements along the coasts of Greenland are quite complex under different mechanisms of sea level changes.