Bi-hemispheric Correspondence Among Mid-latitude Glacier Equilibrium Line Altitudes, Atmospheric Temperatures, and Westerly Wind Fields

Abstract:

Glaciers acutely respond to their ambient climate. However, the extent to which glaciers capture local, regional, or hemispheric climate processes is less clear. Here we explore the relationships between global climate variables and end of summer snowlines (EOSS) of mountain glaciers on opposite sides of the planet: in the Southern Alps of New Zealand and in the European Alps. We performed EOF analyses on EOSS observations for the past several decades from glaciers in these two antipodal mountain ranges. We then correlate these EOF timeseries with relevant variables from the ERA5 climate reanalysis, including summer (ablation) season temperature and tropospheric wind speeds at several different geopotential heights, as well as sea-level pressure. We find that for each study area, glacier EOSS: (1) show a significant and positive correlation with mid-latitude summer atmospheric temperatures from sea-level to ~100 mbar in the troposphere; and (2) a significant positive (negative) correlation with the poleward (equatorward) position of the summertime westerlies again extending from sea-level to ~100 mbar in the troposphere. Our results suggest that glaciers in the Southern and European Alps monitor the temperature and position of air masses associated with their respective westerly wind belts. We also find that glacier EOSS show a stronger relationship with regional-scale tropospheric temperature variability than thermometers, highlighting the sensitivity of temperate mid-latitude mountain glacier EOSS to regional, and potentially hemispheric, atmospheric temperature.