Year: 2024
Type: article
Abstract: Over the last four decades (1980–2020), the summer westerlies that prevail in South Asia along the monsoon trough region have weakened by about 25% based on multiple reanalysis datasets. Trends in a range of climate model simulations suggest that the weakening is driven by multiple anthropogenic forcings. Over the period, sea-level pressure has increased by 0.6–1.0 hPa over South Asia’s northwestern regions, induced by cooling due to aerosol emission and changes in land use and land cover, and has decreased over the Arabian Peninsula mainly due to warming by greenhouse gases. These changes in temperature and pressure act to weaken the regional pressure gradient, deflecting the subtropical westerlies from South Asia toward the Arabian Peninsula and weakening the winds in the monsoon trough and its adjacent region. The slowing down of winds appears to result in an anomalous moisture loading and increase in rainfall over the semi-arid northwestern South Asia. This weakening and its associated changes in regional climate are highly relevant to policymaking across South Asia.
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $3,390
Awards: Department of Energy (DoE) Support of the National Center for Atmospheric Research Activities, G5477578438, G6313549709, SEA LEVEL CHANGE IS AN IMPORTANT INDICATOR OF HOW THE EARTH IS RESPONDING TO CLIMATE CHANGE BUT IT IS ALSO IMPORTANT TO UNDERSTAND ITS SOCIOECONOMIC IMPACTS. THEREFORE UNDERSTANDING HOW MUCH SEA LEVEL WILL RISE IN THE FUTURE AND HOW IT WILL IMPACT COASTAL POPULATIONS CENTERS AND INFRASTRUCTURE IS A PROBLEM OF PARAMOUNT IMPORTANCE FOR SCIENTISTS TO ADDRESS. WE RELY ON COUPLED CLIMATE MODELS AND SEMI-EMPIRICAL MODELS TO PROJECT FUTURE SEA LEVEL CHANGES BUT THE PROJECTIONS VARY WIDELY AND THE ERRORS ARE POORLY UNDERSTOOD. HERE WE PROPOSE TO USE NASA OBSERVATIONAL DATASETS TO EVALUATE PRESENT-DAY SEA LEVEL CHANGE IN THE CMIP6 ENSEMBLE AND ICE SHEET MASS BALANCE IN THE ISMIP6 MODEL ENSEMBLE AND OTHER MODELS AND PROJECTIONS AS THEY BECOME AVAILABLE OVER THE PERIOD FOR WHICH WE HAVE OBSERVATIONS (THE LAST 2-3 DECADES). THERE ARE A VARIETY OF SATELLITE AND AIRBORNE MEASUREMENTS THAT CAN HELP US EVALUATE DIFFERENT PROJECTIONS OF SEA LEVEL CHANGE AND ICE MASS LOSS INCLUDING RADAR ALTIMETRY (TOPEX/POSEIDON JASON-1 2 3) SATELLITE GRAVITY (GRACE GRACE FOLLOW-ON) LASER ALTIMETRY (ICESAT ICESAT-2) AND OPERATION ICEBRIDGE (OIB). THE MULTI-MODEL EVALUATION WILL PROVIDE AN ASSESSMENT OF THE MODEL QUALITY IN REPRESENTING SEA LEVEL CHANGE AND ICE SHEET MASS LOSS. THE BEST MODEL(S) WILL BE CHOSEN TO BE USED FOR SEA LEVEL IMPACT STUDIES USING DIFFERENT CLIMATE CHANGE SCENARIOS. TO REPRESENT PROJECTION UNCERTAINTY WE PROPOSE TO EXTRAPOLATE MODEL UNCERTAINTY AS WELL AS THE DIFFERENCE BETWEEN MODEL AND OBSERVATIONS OF THE PRESENT-DAY INTO THE FUTURE. WE PROPOSE TO USE THESE PROJECTION ASSESSMENTS TO STUDY THE IMPACTS OF SEA LEVEL RISE ON COASTAL POPULATIONS AND INFRASTRUCTURE. SUCH STUDIES CAN ONLY BE CONDUCTED AT LOCATIONS WHERE PRESENT-DAY SEA LEVEL IS ACCURATELY KNOWN RELATIVE TO THE LAND USUALLY AT TIDE GAUGES. HOWEVER THERE ARE MANY LOCATIONS IN THE WORLD WHERE WE HAVE NEITHER TIDE GAUGES OR A PRECISE DIGITAL ELEVATION MODEL (DEM). WE PROPOSE TO USE SATELLITE MEASUREMENTS TO DETERMINE A PRECISE DEM AND PRESENT-DAY RELATIVE MEAN SEA LEVEL FOR THE PURPOSES OF EVALUATING THE IMPACTS OF FUTURE SEA LEVEL RISE. THE PRECISE DEM WILL BE DETERMINED USING STEREO IMAGERY FROM THE WORLDVIEW SATELLITE VIA THE STRUCTURE FROM MOTION (SFM) TECHNIQUE. THIS DEM CAN BE TIED INTO A PRECISE TERRESTRIAL REFERENCE FRAME USING ICESAT (AND SOON ICESAT-2) LASER ALTIMETER MEASUREMENTS. PULSE-LIMITED RADAR ALTIMETRY DOESN T REACH CLOSER TO THE COAST THAT 7-10 KM SO WE WILL ALSO USE ICESAT AND ICESAT-2 MEASUREMENTS TO EXTEND TRADITIONAL MEAN SEA SURFACES UP TO THE COAST. IN THIS WAY WE WILL BE ABLE ESTIMATE PRESENT-DAY MEAN SEA LEVEL RELATIVE TO THE LAND USING ONLY SATELLITE MEASUREMENTS. WE WILL TEST OUR METHODS AT APPROXIMATELY A HALF DOZEN SITES AROUND THE WORLD THAT ARE PARTICULARLY VULNERABLE TO SEA LEVEL CHANGE. IN ORDER TO FULLY UNDERSTAND THE IMPACTS OF FUTURE SEA LEVEL RISE WE ALSO NEED TO UNDERSTAND LOCAL VERTICAL LAND MOTION (VLM). WHILE WE NOW HAVE MAPS OF VLM IN MANY LOCATIONS DETERMINED FROM GLOBAL GNSS NETWORKS AND INSAR IMAGING THESE HAVE BEEN DETERMINED FROM VERY SHORT MEASUREMENT TIME SPANS AND THUS REFLECT MANY DIFFERENT GEOPHYSICAL PROCESSES. FOR LONG-TERM SEA LEVEL PROJECTIONS WE NEED LONG-TERM ESTIMATES OF VERTICAL LAND MOTION (E.G. DUE TO GIA TECTONIC PROCESSES LONG-TERM SUBSIDENCE ETC.) SO THAT WE CAN ESTIMATE HOW MUCH ACCUMULATED LAND MOTION WE MIGHT SEE IN THE FUTURE (2050 2100 ETC.). THEREFORE WE ALSO PROPOSE TO DEVELOP A MODEL (GIA+TECTONICS) OF LONG-TERM VLM FROM THE OBSERVED GNSS AND INSAR VLM RATES. WE ALSO CONTINUE TO PRODUCE REGIONAL VLM ESTIMATES FROM THE AVAILABLE GEODETIC DATA. WE PLAN TO CONDUCT THIS INVESTIGATION IN CONCERT WITH THE NASA SEA LEVEL CHANGE TEAM (N-SLCT) AND MAKE OUR RESULTS AVAILABLE THROUGH THE NASA SEA LEVEL WEB PORTAL.
OpenAlex ID: W4404513794