A dynamic link between high-intensity precipitation events in southwestern North America and Europe at the Last Glacial Maximum


Marcus Lofverstrom


Both hydroclimate proxies and modeling studies alike present compelling evidence for abundant precipitation in southwestern North America and Europe at the Last Glacial Maximum (LGM). However, model simulations exhibit an apparent disagreement between changes in precipitation and the orientation of the midlatitude jet streams relative to modern. This is surprising, as it is well known from modern observations that the jet streams and storm tracks closely follow one another in the time mean. The present study shows that a substantial fraction (between 35 and 50%) of the precipitation along the western seaboards of the Northern Hemisphere continents at the LGM is due to short lived high-intensity events, rather than a permanent rearrangement of the circulation. Moreover, these precipitation events are shown to be dynamically linked by a wavenumber-5 stationary wave packet that is trapped in a midlatitude waveguide. When the wave energy is concentrated in the eastern North Pacific, an atmospheric river is excited that makes landfall along the North American west coast. 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. Understanding the dynamics of this teleconnection pattern is not only key for interpreting proxy-data signals in past climates, but may also be important for improving predictions of storm track dynamics and water resources availability in the face of climate variability and change.


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