Interannual covariability in Northern Hemisphere air temperatures and greenness associated with El Niño‐Southern Oscillation and the Arctic Oscillation

In this paper, we estimate the year‐to‐year variations in northern vegetation greenness as they relate to the dominant modes of climate variability. In particular, we analyze spatial data of Northern Hemisphere satellite‐sensed vegetation greenness, surface temperature, precipitation, and upper air data for the 1982–1998 period to isolate well correlated modes of variability between temperature and greenness and to assess their relationship to large‐scale circulation anomalies. It is found that during spring, large‐scale modes of interannual vegetation variability are strongly correlated with spatiotemporal modes of variability in the overlying temperature field. In addition, the results indicate that the two predominant hemispheric‐scale modes of covariability are related to teleconnections associated with the El Niño‐Southern Oscillation (ENSO) and the Arctic Oscillation (AO). The warm event ENSO signal is manifested as warmer and greener conditions in North America, Far East Asia, and to some extent central Europe, while the features of the positive phase AO signal include enhanced warm and green conditions over large regions in Europe and Asian Russia, with opposite anomalies in the eastern half of North America. Whether observed trends in vegetation activity over the past 20 years are also related to systematic changes in these two modes of variability is still unclear.