AbstractBoth hydroclimate proxies and modeling studies show compelling evidence for a southward shift in precipitation over western North America and western Europe at the Last Glacial Maximum. The latitude band where extratropical cyclones preferably make landfall in the modern climate appear drier than today, whereas the now arid southwestern North America and western Mediterranean regions experienced comparatively wetter conditions. The causes of this hydroclimate shift remains debated, and several competing explanations have been proposed. In southwestern North America, the change has been linked to an increased frequency of atmospheric rivers, whereas the European signal is thought to be more strongly linked to a zonalisation of the extratropical jet stream and storm track. Here we show modeling evidence that these phenomena may be dynamically linked by a wavenumber-5 stationary wave packet that is trapped in a midlatitude waveguide. An atmospheric river is excited (due to anticyclonic Rossby wave breaking) when the wave energy is concentrated in the eastern North Pacific. A few days later, when the wave packet has reached Europe, the North Atlantic jet stream assumes a zonally oriented state that brings abundant precipitation to the western Mediterranean sector. The dynamics of this hemispheric scale teleconnection are therefore key to interpreting proxy-data signals in past climates, and for improving predictions of storm track dynamics and water resource availability in the face of climate variability and change.
Dr. Marcus Lofverstrom completed his M.Sc. and Ph.D. degrees in meteorology (2009, 2014) at Stockholm University where he completed dissertation research on the interaction between ice sheets and the large-scale atmospheric circulation over the last glacial cycle. From 2015-2018, he was engaged in postdoctoral research at NCAR's Climate and Global Dynamics Division in Boulder, Colorado. Lofverstrom was appointed Assistant Professor with the University of Arizona's Department of Geosciences in Fall 2018. His primary research interests include dynamic meteorology, paleo-climatology, and numerical modeling. He teaches undergraduate and graduate courses in Earth-system modeling, atmosphere and ocean circulation through time, and Python programming. You can read more about his research at his website.