A Detailed, Multi‐Scale Assessment of an Atmospheric River Event and Its Impact on Extreme Glacier Melt in the Southern Alps of New Zealand

Abstract

North‐westerly airflow and associated atmospheric rivers (ARs) have been found to profoundly influence New Zealand’s west coasts, by causing flooding, landslides and extreme ablation and accumulation on glaciers in the Southern Alps. However, the response of local glacier mass balance to synoptic‐scale circulation, including events with ARs, has typically not been investigated by considering mesoscale processes explicitly. In this study, high‐resolution atmospheric simulations from the Weather Research and Forecasting model are used to investigate the mesoscale drivers of an extreme ablation event on Brewster Glacier (Southern Alps), which occurred on February 6, 2011 during the landfall of an AR on the South Island. The following processes were found to be crucial for transferring the high temperature and water vapor contained in the AR into energy available for melt on Brewster Glacier: First, the moist‐neutral character of the air mass enabled the flow to pass over the ridge, leading to the development of orographic clouds and precipitation on the windward side of the orography, and foehn winds on the leeside. These processes fueled melt through longwave radiation and strong turbulent and rain heat fluxes within the high‐condensation environment of the orographic cloud. Second, orographic enhancement occurred due to both cellular convection within the cloud and the combined effect of multiple precipitating systems by the seeder‐feeder‐mechanism. These results indicate the potential importance of AR dynamics for New Zealand’s glaciers. They also illustrate the benefit of mesoscale atmospheric modeling for advancing process understanding of the glacier‐climate relationship in New Zealand.

Increasing extreme melt in northeast Greenland linked to foehn winds and atmospheric rivers

“…Several studies have suggested a link between intense NE Greenland melt events and warm, dry downslope winds known as "foehn" descending from the GrIS plateau to the west 3,[20][21][22] . Mattingly et al 21 found evidence that atmospheric rivers (ARs) affecting northwest (NW) Greenland may lead to foehn conditions and enhanced melt in NE Greenland after the moist air mass crosses the ice divide and flows downslope, similar to warming documented on the lee side of the West Antarctic peninsula and other mountainous areas [23][24][25][26] . However, there has not been any systematic study of the role of foehn in forcing melt in northern Greenland, where the topography consists of a wide dome with a relatively gentle slope in comparison with the more narrow mountain ranges studied in other regions.…”

Modeling cloud properties over the 79 N Glacier (Nioghalvfjerdsfjorden, NE Greenland) for an intense summer melt period in 2019

“…Despite the deficiency in modeled surface albedo, the statistical performance metrics are predominantly in the range of previous model evaluations of hourly WRF simulations (e.g., Hines and Bromwich, 2008; Bromwich et al ., 2009; Collier et al ., 2018; Temme et al ., 2020; Turton et al ., 2020; Kropač et al ., 2021), suggesting sufficient model skill to use the model output in the further analyses of the cloud effect.…”

“…The model was run for 22 days, covering the period July 21 to August 10, 2019. The first 48 hr were discarded for model spin‐up in accordance with previous WRF model studies (e.g., Listowski and Lachlan‐Cope, 2017; Kropač et al ., 2021).…”

Evolution and origin of global glaciers and their impacts on the environment

“…Glacier retreats have complex impacts on the ecosystem, water cycle and underground stress. (1) The decrease of glacier reduces the ground surface stress, thus changing the balance between underground stress and surface pressure. For glaciers located in the tectonic shear zone, this may cause fault earth.…”