Atmosphere Ocean Science Colloquium

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Suppression of Arctic air formation, and enhanced frequency of Sudden Stratospheric Warming events in warm climates

Speaker: Eli Tziperman, Harvard

Location: Warren Weaver Hall 1302

Date: Wednesday, March 21, 2018, 3:30 p.m.

Synopsis:

First, we consider the process of Arctic air formation currently occurring over northern North America during the winter season's polar night, and leading to extreme cold outbreaks further south. We propose that such Arctic air formation may be suppressed in a warmer climate by a low-cloud feedback. This may explain the existence of freeze intolerant animals and trees such as crocodiles and palm trees that thrived in northern North America 50 Million years ago (Eocene), where current temperatures could be as low as -40C. We further show that the proposed mechanism also explains recent climate observations and future climate projections, both showing an unexplained enhanced and surface-intensified warming over high-latitude continental areas.

Second, it is proposed that in a warmer, higher CO2 world, the expected strengthening of the equatorial Madden-Julian Oscillation (MJO) can lead to more frequent sudden stratospheric warming (SSW) events. This may, in turn, affect tropospheric weather and extreme events. The SSW proposed enhancement mechanism involves two main elements. First, a direct propagation of MJO-forced planetary waves to the Arctic stratosphere. Second, an interaction of these waves with the mid-latitude tropospheric jet that amplifies its zonal asymmetry and therefore the stationary waves generated at the mid-latitudes and propagating to the Arctic Stratosphere, triggering additional SSW events.