Abstract:

Atmospheric rivers (ARs), long and narrow filaments of intense moisture transport, are responsible for at least 90% of the poleward moisture transport in the atmosphere over midlatitude regions. ARs serve as an important source of freshwater or the cause of weather hazards for many regions around the world. Thus, understanding what controls the interannual variability of ARs and how ARs have responded to anthropogenic forcing in the past few decades become increasingly important. In this talk, I will first present the leading modes of boreal winter AR variability over both the North Pacific and North Atlantic Ocean basins in observations and climate models. Using an ensemble of AMIP models from CMIP6, I will then quantify the roles of internal variability versus sea surface temperature/sea ice forcing in driving the interannual variability of these leading modes. These results indicate that AR activities over the North Pacific are more predictable compared to those over the North Atlantic. In the second part of this talk, I will shift the focus from the Northern Hemisphere to the Southern Hemisphere and present the poleward shift of ARs in the Southern Hemisphere in recent decades. I will elucidate the roles of anthropogenic forcing versus internal variability in shaping the observed poleward shift of ARs using two large model ensembles. These results highlight the forced versus unforced variabilities of ARs at different time scales.