Atmosphere Ocean Science Colloquium
What causes atmospheric blocks? - A new perspective using the finite amplitude wave activity theory
Speaker: Pragallva Barpanda, CIRES/ NOAA PSL, University of Colorado, Boulder
Date: Wednesday, April 28, 2021, 3:30 p.m.
The atmospheric jet stream is an eastward river of wind in the midlatitudes that steers and meanders across the globe due to planetary waves and eddies . However, under certain conditions these jet meanderings become stationary and disrupt the eastward flow of eddies causing extreme temperature conditions that can persist from a few days to more than a week. Such phenomena are known as atmospheric blockings. Despite decades of research there has been no consensus on the mechanisms that lead to atmospheric blocks. In my talk I will show that atmospheric blocks are persistent events with anomalously large wave activity whose dynamics can be explained by the finite-amplitude local wave activity framework. Using the wave activity budget and a feature tracking algorithm, we perform a careful analysis of all the major persistent anomalies of the jet stream during the Northern Hemisphere winter. Almost all of these persistent events are found to occur in clusters collocated with the quasi-stationary ridge over the Euro-Atlantic sector and the Pacific sector as predicted by local wave-activity theory. Despite substantial variations among individual events, on an average these persistent events exhibit a strong non-linear relationship between the wave activity and wave activity flux - a characteristic traffic jam behavior in the atmosphere.