Large scale atmospheric drivers of intraseasonal snowfall variability on Kilimanjaro's glaciers

Due to the thermal homogeneity of the tropics, the rapidly retreating glaciers in Eastern Africa, such as at the summit of Kilimanjaro, are predominantly influenced by moisture and precipitation variability. Several case studies have shown that significant snowfall events with durations of just a few days can lead to deep snow cover that can persist for several months on the glaciers, with significant impacts on their long-term mass balance. However, the large-scale phenomena that influence this intraseasonal variability at high elevations remain poorly understood. Here, we use a unique dataset of daily surface height observations from Kilimanjaro’s Northern Ice Field and the ERA5 reanalysis to investigate the large-scale weather patterns that are associated with snowfall at the summit of Kilimanjaro from 2000-2022. We highlight that over 50% of surface height increase on the glacier was associated with the recently identified phenomenon known as westerly moisture transport events (WMTEs), atmospheric river like features that bring moisture into Eastern Africa from the Congo basin and can lead to enhanced precipitation in Eastern Africa. This work develops understanding of the processes that influence the mass balance of East Africa’s glaciers, which will help to improve the interpretation of these glaciers’ unique proxy record of the sparsely observed tropical mid-troposphere.