Polar front jet waveguide, teleconnections, and temperature extremes in the boreal summer.

Abstract:

By using a linear barotropic dynamical framework of the mid-latitude circulation, it is known that the tropospheric subtropical jet (STJ) can act as a waveguide to allow the zonal propagation of Rossby wave, known as the “circumglobal teleconnection” (CGT). The CGT pattern gradually gains its popularity in recent years among the climate community, since many high-impact weather events in the middle latitudes are argued to be related to the abnormal behavior of the CGT. However, in addition to the STJ, it is found that the Eurasian polar front jet (PFJ) can also as a waveguide to trap the Rossby wave activities when the background atmospheric stratification effect is considered. In contrast to the STJ waveguide that is strongest in the wintertime, the strength of PFJ waveguide peaks in the summertime. The stronger guiding effect of PFJ in the boreal summer indicates more stagnant and large-amplitude Rossby wave activities will be easily trapped in the middle and high latitudes of Eurasia, and could potentially lead to the local high temperature extremes there. Therefore, a thorough investigating about the PFJ waveguide dynamics and associated trapped teleconnections will be helpful to deepen our understanding about the atmospheric low-frequency variabilities over the Eurasia, and its relation to regional high-impact weather extremes.

This talk will be three-fold. The first part will discuss how the climatological PFJ waveguide is formed and maintained. The second part will discuss the dominant waveguide teleconnection trapped by the PFJ, which is a new identified teleconnection pattern: the British-Baikal Corridor (BBC) pattern. In contrast to many other well-known teleconnections that can be explained by linear dynamics, we will provide evidences that the life cycle of BBC pattern is primarily determined by the nonlinear eddy-eddy interactions. The last part will be a case study. We will illustrate how the abnormal activity of BBC pattern could be related to an extraordinary temperature extreme event in Europe during June 2019, which is the hottest June on record for Europe.