Master Thesis Defense by Weiji Hu
Title: Impact of Greenland’s Summer Ice Melt on the North Atlantic Oscillation
Abstract:
This study provides a comprehensive analysis of the Greenland Ice Sheet’s (GIS) summer melt and its subsequent influence on the North Atlantic Oscillation (NAO), as well as how it relates to sea surface temperature (SST) variations, using various data sets and methodologies, holding significance for predicting climate changes in the North Atlantic region.
Initially, we found no significant correlation between the annual total mass loss of the GIS and the NAO. This may be due to the inability of the mass loss from ice sheet calving to significantly influence atmospheric circulation in the subsequent months. Thus, considering the total annual mass loss of the GIS could introduce errors due to the mass of ice lost, which might disrupt the influence of melting on the NAO. Additionally, our analysis of sea ice, which could potentially have similar effects as ice sheet calving, revealed no direct significant correlation with the NAO.
A visible negative correlation between Greenland’s summer melt and the NAO in November was consistently observed in both the GRACE data and HIRHAM data, highlighting the substantial impact of meltwater on atmospheric circulation patterns. Moreover, the HIRHAM runoff data revealed a pattern where the initial negative correlation between melt volumes and the NAO shifts positively before dissipating, suggesting the temporal spread of meltwater effects over several months.
Furthermore, to explore whether the melt also affects other atmospheric circulation patterns, we performed EOF decomposition on 500 hPa geopotential height data and extracted principal component time series, which showed no significant relationships with components other than the NAO. Temperature is considered the primary factor influencing melting; however, our preliminary investigation found difficulties in using direct temperature data to predict the NAO due to challenges in obtaining a temperature series that represents the entire ice cap melting. Nevertheless, this study leverages detailed temperature data from multiple Greenland stations to further explore regional impacts.
Notably, this paper discusses the primary potential factor influencing atmospheric circulation due to melt: sea surface temperature (SST). The mediating role of SST is considered the primary pathway through which melt affects atmospheric circulation. An EOF analysis of SST was conducted to identify the main patterns and their relationship with Greenland melt data, revealing correlations between Greenland’s summer melt and subsequent major SST patterns, thereby enhancing our understanding of the complexities of ocean-atmosphere interactions. However, no clear correlation has yet been observed between these autumn SST principal component sequences and the subsequent November NAO. This may require further analysis of more data to better understand these interactions.
Supervisor: Jens Hesselbjerg Christensen
Censor: Martin Drews, DTU