Prof.  Andrey  Koval
the Department of Atmospheric Physics, St. Petersburg University,  Russia

Title: Atmospheric teleconnections: natural tropical oscillations and nonlinear interactions of global atmospheric waves

Abstract:

The report is dedicated to the latest achievements of the scientific group representing St. Petersburg University and Russian Hydrometeorological University in the modeling of large-scale atmospheric dynamic processes. The response of the global atmospheric extratropical circulation at heights of the middle and upper atmosphere to tropical oscillations namely the equatorial stratospheric quasi-biennial oscillation (QBO) and El Niño Southern Oscillation (ENSO) is investigated. For this purpose, a three-dimensional numerical nonlinear model of general circulation of the middle and upper atmosphere (MUAM) is used. Not only the conventional (easterly and westerly) QBO phases are considered but also two transitional ones: westerly-shear (wsQBO, from easterly to westerly) and easterly-shear (esQBO, from westerly to easterly) in order to reveal the QBO-induced changes in global circulation and interactions of planetary waves (PWs) with the mean flow. The interpretation of obtained results is carried out through the residual meridional circulation, Eliassen-Palm fluxes and meridional temperature gradients calculated using MUAM ensemble simulations for the four QBO phases and two ENSO phases. The simulation results demonstrate the manifestation of the teleconnection mechanism: changes in thermal and dynamic regimes of the extratropical winter stratosphere associated with QBO and ENSO influence. It is shown in particular that esQBO transition phase is characterized by the strongest temperature and zonal wind changes, which can be explained by both: direct PW influence (through changes in Eliassen-Palm flux and associated heat fluxes) and indirect PW influence (through modifications in the meridional circulation). The simulation results were confirmed by the reanalysis data. Changes in the extratropical stratospheric circulation under different QBO-ENSO combinations are also studied. Part of the report is also focused on the study of the generation processes of secondary PWs as a result of nonlinear interactions in the atmosphere. The importance of such studies uncovering teleconnection patterns between the Earth's equatorial and extratropical dynamic systems is explained, in particular, by their impact on the frequency and intensity of sudden stratospheric warmings – events that lead to extreme cold waves at mid-latitudes in the troposphere of Northen Hemisphere, as well as to the formation of ozone anomalies. The presented research is carried out with the support of St. Petersburg University (grant No. 116234986).

Biography:

Andrey Koval, Doctor of Physical and Mathematical Sciences (PhD habil.), Professor of the Department of Atmospheric Physics at St. Petersburg University. His research interests include numerical modeling of the circulation of the middle and upper atmosphere, analysis of satellite and ground-based observations in order to study various aspects of atmospheric dynamics, including wave interactions of various scales. In 2021, at the age of 37, he performed PhD habilitation on the topic "Interactions of hydrodynamic waves in the middle and upper atmosphere". Winner of the St. Petersburg University Academic Council awards for publication activity and scientific achievements for young scientists. He has published more than 50 works in scientific journals, including a large number of articles in first quartile journals. Main achievements in recent years: Developed a method for calculating the residual meridional circulation (RMC) up to thermosphere heights based on the 3-dimensional nonlinear circulation model of the middle and upper atmosphere MUAM, performed RMC calculations at different stages of sudden stratospheric warming in the Northern and Southern Hemispheres, as well as at different phases of natural tropical oscillations (QBO/ENSO). Studied the features of propagation and reflection of planetary waves (PWs) at different levels of solar activity up to the thermosphere, demonstrated the effect of PW reflection in the lower thermosphere at high solar activity, leading to circulation changes in MLT area. Developed a new approach to diagnostics of nonlinear interactions of PWs, demonstrated the process of generation of secondary 16-day PW by internal atmospheric sources.