Linking Jet Stream Variability and the NAO to the Terrestrial Carbon Cycle in Europe

Abstract: The terrestrial carbon cycle is a part of the global carbon cycle, where one important component is the terrestrial vegetation. Terrestrial vegetation largely controls the land surface carbon exchanges and leverage the atmospheric greenhouse gas concentrations, significantly affecting the trajectory of global warming. It is therefore important to improve the understanding of vegetation response to different climatic factors, in particular for those linked to large-scale climate variability, which is still less studied so far. Vegetation greenness is suggested to be a useful tool in order to understand vegetation response. Looking at Europe, the climate factors that affect vegetation the most are linked to the large-scale atmospheric circulation over the North Atlantic, like the jet stream, which varies in speed and latitude, and the North Atlantic Oscillation (NAO). Here, I compute monthly indices representing the variability of these atmospheric features, and correlate them with monthly vegetation greenness data (NDVI) anomalies over a period of five years. This is done both for regionally-averaged NDVI and the months April-July and as a geographical point-by-point analysis for the month of May. The results show a significant correlation between Scandinavian NDVI and the NAO as well as jet speed at multiple time lags, up until 2 months. The jet latitude, instead, showed significant correlation for three regions in mid/southwestern Europe at longer time lags of 3-4 months. This means that the position of the jet in winter can affect the spring vegetation growth in this area. The jet speed and NAO, however, works mostly at shorter timespans.