Unprecedented atmospheric conditions (1948–2019) drive the 2019 exceptional melting season over the Greenland ice sheet
Year: 2020
Type: article
Abstract: . Understanding the role of atmospheric circulation anomalies on the surface mass balance of the Greenland ice sheet (GrIS) is fundamental for improving estimates of its current and future contributions to sea level rise. Here, we show, using a combination of remote sensing observations, regional climate model outputs, reanalysis data and artificial neural networks, that unprecedented atmospheric conditions (1948–2019) occurring in the summer of 2019 over Greenland promoted new records or close-to-record values of SMB, runoff and snowfall. Specifically, runoff in 2019 ranked second within the 1948–2019 period (after 2012) and first in terms of surface mass balance negative anomaly for the hydrological year September 1, 2018–August 31, 2019. Summer of 2019 was characterized by an exceptional persistence of anticyclonic conditions that, in conjunction with low albedo associated with reduced snowfall in summer, enhanced the melt-albedo feedback by promoting the absorption of solar radiation and favored advection of warm, moist air along the western portion of the ice sheet towards the North, where the surface melt has been the highest since 1948. The analysis of the frequency of daily 500 hPa geopotential heights obtained from artificial neural networks shows that the total number of days with the most frequent atmospheric pattern that characterized the summer of 2019 was 5 standard deviations above the 1981–2010 mean, confirming the exceptional nature of the 2019 season over Greenland.
Source: The cryosphere
Authors: Marco Tedesco, Xavier Fettweis
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $1,574
Awards: G1116492890, G2198400075, G2260578362, Collaborative Research: Refreezing in the firn of the Greenland ice sheet: Spatiotemporal variability and implications for ice sheet mass balance, Collaborative Research: Closing the Gaps in Climate Models' Surface Albedo Schemes of Processes Driving the Darkening of the Greenland Ice Sheet, G353390944, COMBINING ALTIMETRY WITH ELECTROMAGNETIC AND REGIONAL-CLIMATE MODELS FOR IMPROVED ESTIMATION OF GREENLAND ICE SHEET MASS BALANCEWE PROPOSE TO GENERATE IMPROVED LONG-TERM ESTIMATES OF GREENLAND MASS BALANCE BETWEEN 2003 AND 2019 (AND BEYOND) BASED ON A COMBINATION OF ALTIMETRY GRAVIMETRY AND IN-SITU DATASETS USED IN CONJUNCTION WITH ELECTROMAGNETIC AND REGIONAL CLIMATE MODELING. AMONG THE PRODUCTS OF THIS WORK THERE WILL BE MAPS OF SPECIFIC MASS BALANCE (I.E. THE MASS BALANCE PER UNIT AREA OF THE ICE SHEET EXPRESSED IN WATER-EQUIVALENT ELEVATION CHANGE) AS PARTITIONED BETWEEN CHANGES DRIVEN BY SURFACE MASS BALANCE AND BY ICE DYNAMICS OF FIRN-THICKNESS CHANGE AND OF THE BIAS EXPECTED FOR CRYOSAT-2 BASED ON THE FIRN MODEL AND ALSO IMPROVED GRACE ESTIMATES OF TOTAL MASS CHANGES. WE PROPOSE TO ACCOMPLISH THESE TASKS BY USING THE DIFFERENT DATASETS TO IMPROVE A REGIONAL CLIMATE MODEL TO BETTER CAPTURE THE TIMING AND MAGNITUDE OF SNOW AND ICE ACCUMULATION AND ABLATION SIGNALS. WE WILL THEN USE THE IMPROVED CLIMATE-MODEL OUTPUT COMBINED WITH A FIRN MODEL TO PREDICT ELEVATION CHANGES FOR THE ICE SHEET AND WILL FURTHER ADJUST THE FIRN MODEL TO MATCH MEASURED DENSITY PROFILES AND TO MATCH ELEVATION CHANGES IN DYNAMICALLY STABLE PARTS OF THE ICE SHEET. LAST WE WILL TRANSLATE THE ADJUSTED FIRN-MODEL OUTPUT INTO AN ELECTROMAGNETIC MODEL OF THE SURFACE TO CALCULATE HOW KU-BAND RADAR ENERGY PENETRATES THE SURFACE OF THE ICE SHEET AND TO PREDICTED BIASES AND BIAS CHANGES FOR CRYOSAT-2 DATA UNDER DIFFERENT RETRACKING STRATEGIES. THE OUTPUTS OF THE IMPROVED SMB MODEL WILL ALSO BE USED TO GENERATE IMPROVED GRACE SOLUTIONS OVER GREENLAND AT REGIONAL SCALES (E.G. MASCON SOLUTIONS). THE SYNERGIC APPROACH PROPOSED IN THIS PROJECT OFFERS A UNIQUE AND TO OUR KNOWLEDGE UNPRECEDENTED WAY TO ADDRESS CRUCIAL KNOWN ISSUES CONCERNING THE ESTIMATES OF MASS CHANGES FROM ALTIMETRY DATA AS WELL AS THEIR INTER-MISSION CALIBRATION. THE COMBINATION OF THE DIFFERENT TOOLS (E.G. REGIONAL AND ELECTROMAGNETIC MODELS) OVERCOMES THE LIMITATIONS OF THE SINGLE APPROACHES ADDRESSING ONE OF THE LARGEST PROBLEMS IN ALTIMETRY (AND ICE SHEET REMOTE SENSING IN GENERAL) ON HOW TO RELATE THE KNOWLEDGE OF SNOW/FIRN PARAMETERS TO THE ELECTROMAGNETIC QUANTITIES THAT ARE DRIVING THE SIGNAL RECORDED BY THE REMOTE SENSING INSTRUMENTS. THE FINAL PRODUCT WILL CONSIST OF COHERENT IMPROVED SPATIALLY DISTRIBUTED AND LONG-TERM ESTIMATES OF MASS AND ELEVATION CHANGES WHICH WILL BENEFIT FROM THE PROCESSORIENTED VISION AND TOOLS OF THE PROJECT S TEAM HENCE SUPPORTING NOT ONLY THIS SPECIFIC PROJECT BUT ALSO THE GROWTH OF THE ALTIMETRY COMMUNITY IN ANTICIPATION OF THE ICESAT-2 LAUNCH., ICE SHEETS AND GLACIERS PLAY A CRUCIAL ROLE ON THE EARTH'S CLIMATE SYSTEM AFFECTING ATMOSPHERIC CIRCULATION FRESHWATER FLUXES AND CRUCIALLY SEA LEVEL CHANGE. THE SURFACE ENERGY AND MASS BALANCE IS A CRUCIAL MEDIATOR OF THESE EFFECTS AND IMPROVING THE REALISM OF THESE PROCESSES IN MODEL SIMULATIONS HAS IMPORTANT CONSEQUENCES FOR MODEL PROJECTIONS OF FUTURE CLIMATES. SPECIFICALLY CHANGES IN ALBEDO OVER TIME (SEASONALLY AND ON CLIMATE TIME SCALES) PLAY A KEY ROLE IN SURFACE MELT VARIABILITY. THE DEPOSITION OF ANTHROPOGENIC AND NATURAL AEROSOLS CAN ALSO DIRECTLY MODULATE THE SURFACE ALBEDO. FRESH SNOW ACCUMULATION INCREASES ALBEDO OVER PERMANENTLY ICE COVERED AREAS WHILE DURING SUMMER ALBEDO DECREASES AS A RESULT OF THE MELTING. IN THIS PROJECT WE PROPOSE TO INVESTIGATE THE RELATIONSHIPS BETWEEN ALBEDO AND SURFACE MASS BALANCE OVER THE GREENLAND AND ANTARCTIC ICE SHEETS AND OTHER GLACIATED AREAS OF THE GLOBE ON ATMOSPHERIC AND SURFACE MASS BALANCE. WE EXAMINE NATURAL SEASONAL VARIABILITY AND THE FORCED VARIABILITY OF FUTURE PROJECTIONS USING A NEW PHYSICALLY CONSISTENT METHOD FOR DETERMINING DYNAMIC ICE ALBEDO SCHEME IN THE NASA GISS-E2 GLOBAL CLIMATE MODEL. WE AIM AT ADDRESSING THE FOLLOWING SCIENCE QUESTIONS: WHAT IS THE RELATIONSHIP OF ALBEDO OVER THE ICE SHEETS TO ATMOSPHERIC FLUXES? HOW WELL CAN THE NASA GISS-E2 MODEL REPRODUCE EXTREME EVENTS SUCH AS THE HIGH EXTREME MELTING YEAR OF 2012 (WHEN MELTING EXTENDED UP TO 95 % OF THE ICE SHEET) AND THE LOW MELTING YEAR OF 1992 (DUE TO THE MOUNT PINATUBO ERUPTION)? WHAT IS THE IMPACT OF A DYNAMIC ALBEDO ON SURFACE MASS BALANCE AND THE ROLE OF NATURAL AND ANTHROPOGENIC AEROSOLS. UP TO RECENTLY THE BROADBAND ALBEDO FOR ICE SHEETS IN THE NASA GISS-E2 MODEL WAS STATIC AND SET TO THE OBSERVED MEAN VALUE OF 0.8 FOR ALL MONTHS AND REGIONS. THIS LIMITED THE QUALITY OF THE SIMULATION OF SURFACE MASS BALANCE QUANTITIES (SUCH AS RUNOFF MELTWATER PRODUCTION ETC.) AND OF ICE-ATMOSPHERE COUPLING. IN THIS PROJECT WE WILL MAKE USE OF A NEW ALBEDO SCHEME FOR THE NASA GISS-E2 MODEL THAT HAS BEEN DEVELOPED AND IS BEING REFINED AT NASA GISS. THIS WILL LEVERAGE CURRENT FUNDING OF POSTDOCTORAL RESEARCHER DR. ALEXANDER (NASA GISS) WHO IS EVALUATING A REGIONAL MODEL SIMULATION OF SNOW DENSITY'S MODULATION OF SURFACE ALBEDO DR. FISCHER WHO IS DEVELOPING METHODS OF COUPLING GISS-E2 AND ICE SHEET MODELS AND PI TEDESCO (LDEO COLUMBIA AND NASA GISS) WHO IS EXAMINING THE EFFECT OF LIGHT-ABSORBING IMPURITIES ON THE SNOW/ICE SURFACES AND THE EVOLUTION OF GRAIN SIZE ASSOCIATED WITH MELTING AND REFREEZING CYCLES. WE WILL ALSO USE AEROSOL DEPOSITION FROM THE MODEL TO INCLUDE THE CHANGING IMPACT OF LIGHT ABSORBING IMPURITIES IN THE NEW ALBEDO SCHEME AND THE ASSOCIATED IMPACT ON GRAIN SIZE EVOLUTION. WE WILL ALSO MAKE USE OF A SUB-GRID-SCALE SCHEME OF ELEVATION CLASSES THAT ALLOWS FOR HIGHER RESOLUTION SIMULATION OF ICE SHEET SURFACE PROCESSES ON ELEVATION CLASSES. WE WILL ASSESS THE ALBEDO SCHEME THROUGH THE COMPARISON WITH SATELLITE DATA (E.G. MODIS AVHRR) IN-SITU MEASUREMENTS RE-ANALYSIS PRODUCTS (E.G. MERRA-2) AND THE OUTPUTS OF A REGIONAL CLIMATE MODEL (E.G. MAR). MODEL SIMULATIONS WILL BE STUDIED IN COMPARISON WITH PRESENT-DAY REMOTE SENSING AND IN SITU OBSERVATIONS AND WITH THE ATMOSPHERIC OUTPUTS OF REGIONAL CLIMATE MODELS FORCED AT THE LATERAL BOUNDARIES WITH GISS-E2 OUTPUTS. WE WILL USE MODIS LAND SURFACE TEMPERATURE; MELT EXTENT AND DURATION FROM PASSIVE AND ACTIVE MICROWAVE DATA; CALIPSO AND CLOUDSAT DATA FOR CLOUD COVER VERTICAL PROFILE RADIATIVE FLUXES; CERES FOR RADIATIVE FLUXES; AIRS FOR TEMPERATURE AND WATER VAPOR PROFILES. OUR PROJECT ADDRESSES THE FOLLOWING RESEARCH THEMES 'COUPLING IN THE EARTH SYSTEM' 'EXTREMES IN EARTH SYSTEMS' AND 'CONSTITUENTS IN CLIMATE SYSTEM' AND THE FOLLOWING PROGRAMMATIC PRIORITIES: 'CHARACTERIZE AND/OR HELP REDUCE UNCERTAINTIES IN THE MODELS AND PRODUCTS' 'EXTEND THE RANGE OF MODEL OR PRODUCT VALIDITY BY USING NEW COMPONENTS'., G53398864, G5769078035, CIF: Small: Robust Sparse Recovery for Highly Correlated Data, G6289226862, N/A, G7452998910, G7664062879
OpenAlex ID: W2991298899