The impacts of atmospheric rivers on Antarctic ice sheet and sea ice
Atmospheric rivers(ARs)are characterized as long,narrow,and transient channels of strong horizontal water vapor transport.Previous studies have primarily focused on their impact on mid-latitudes,empha-sizing the potential risks of deleterious hazards and financial losses.However,less attention has been given to ARs in the Antarctic region,despite they account for over 90％of moisture transport into the high latitudes.ARs typically originate in the robust poleward meridional transport flank within ridges(blocking highs)and explosive extratropical cyclones in the Antarctic region,facilitating the substantial moisture transport through a vigorous low-level jet.Three widely-used metrics for characterizing the moisture intrusion state are integrated water vapor,v-component of integrated water vapor and integrated water vapor.An AR is detected when the en-closed shape of the extremely high moisture intrusion path is adequately elongated.The frequency of ARs varies across different AR detection algorithms based on diverse metrics and distinct extremity thresholds.The annual frequency of ARs decreases with latitude,exhibiting a zonally asymmetric pattern that show high-er seasonal frequencies in austral winter and spring.These spatial and temporal features are shaped by the geo-graphical environment and the distribution of synoptic systems in the Antarctic region.The annual variability of AR frequency appears to be associated with dominant atmospheric modes in southern high latitudes,such as the Southern Annular Mode.Additionally,it is also modulated by the natural variability of sea surface temperature modes,including El Nino Southern Oscillation and Indian Ocean Dipole.ARs have significant impacts on the Antarctic ice sheet and sea ice.ARs contribute both positively and nega-tively to the Antarctic ice sheet.On one hand,the intense snowfall during ARs constitutes a major portion of the total precipitation over the ice sheet,favoring its mass gain.Conversely,warm-moist air intrusions accompanying ARs induce surface melting and extremely high temperatures due to foehn winds and anomalously high net surface energy flux.Moreover,surface meltwater during ARs promotes hydraulic fracturing on the ice shelves and trigger their disintegration by removing sea ice through strong winds.These processes pose a substantial threat to the ice sheet mass balance.Mean while,the warm-moist air and strong winds during ARs thermodynamically and dynamically reduce sea ice.ARs lead to anomalously high temperatures and net surface heat flux,intensifying sea ice thermodynamically melting,especially in winter.The strong winds dynamically drift the sea ice onshore,accel-erating ice breaking through powerful waves and further enhancing lateral melting.Though ARs in the Antarctic region have been subject to various analyses,certain questions persist.The eval-uation on ARs'impact on Antarctic ice sheet and sea ice remain contingent on the chosen detection algorithm,ne-cessitating the development of a more universal and robust approach.Implementing machine learning to extract the spatial and temporal features of ARs could offer such an approach.Moreover,although the fact that most liquid precipitation is attributed to ARs,its influence on the ice sheet and sea ice is often overlooked,despite its potential to enhance melting and destabilize ice shelves.In addition,ARs may exert a profound influence on the ocean,sub-sequently providing feedback to the atmosphere.However,the interaction between ARs and the Southern Ocean is not well understood.Therefore,further research imperative to elucidate these mechanisms and evaluate the future changes in Antarctic ice sheet mass balance and sea ice influenced by ARs.
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