Topic: The role of stratosphere-troposphere interaction in seasonal predictability

Speaker: Researcher Wang Lei

Time: 10:00-12:00, May 8, 2023 (Monday)

Venue: S927, Mong Man Wai Technology Building, Tsinghua University

Introduction to the Lecture:

Stratosphere-troposphere interaction has drawn extensive attention from the academic community in recent years. This report intends to demonstrate, through two examples, the important position of stratosphere-troposphere interaction in large-scale atmospheric circulation at middle and high latitudes in the northern hemisphere.

In recent years, many studies have uncovered the close connection between the frequent occurrence of extreme cold events in Eurasia in winter and the rapid melting of Arctic sea ice. However, the causal relationship between them is still a matter of dispute. Previous studies have shown that the decrease of Arctic sea ice can weaken the stratospheric polar vortex, which can help cold air from the Arctic invade into the south, thus causing the cooling of Eurasia. Our latest research shows that El Nino-Southern Oscillation (ENSO) and Quasi-Biennial Oscillation (QBO), as two important interannual variability signals in tropical areas, also play an important role in modulating the polar vortex in the Arctic stratosphere, which is an important factor causing the unstable relationship between the Barents-Kara Sea (BKS) sea ice in autumn and the near-surface temperature in Europe and Asia in winter. This means that the comprehensive effects of Arctic sea ice and tropical factors should be considered at the same time when predicting the winter weather and climate in Eurasia.

The North Atlantic Oscillation (NAO), as the most important atmospheric mode in the middle and high latitudes in the northern hemisphere, exerts an important influence on the surface climate in the northern hemisphere. For example, its abnormal phase in summer often corresponds to frequent high-temperature heat waves in the corresponding areas. Great breakthroughs have been made in the NAO's winter forecast in recent years, but the mainstream numerical model has almost no techniques for the NAO's summer forecast. We found a new forecasting factor, which can accurately forecast the summer North Atlantic Oscillation Index more than two months in advance. This predictability is mainly achieved through the trans-seasonal dissemination and evolution of abnormal signals of troposphere-stratosphere-troposphere atmospheric circulation. This work challenges the traditional idea that stratosphere-troposphere interaction does not work in summer, highlights the bridge function of the stratosphere process, and provides a new approach for summer season forecast.

Profile of the Speaker:

Wang Lei, Young Researcher at the Institute of Atmospheric Sciences of Fudan University, Part-time Associate Researcher at the Lamont-Doherty Earth Observatory of Columbia University, Editor of Advances in Atmospheric Sciences, Secretary-General of the Chinese Committee of the International Association of Meteorology and Atmospheric Sciences (IAMAS), and Young Member of the Special Committee on Oceanic Research (SCOR);

In 2010, he graduated from the Department of Physics of the University of Toronto, engaged in the study of stratospheric atmospheric circulation;

From 2011 to 2013, he worked in the Department of Earth and Planetary Sciences, Johns Hopkins University, engaged in research on atmospheric chemistry-stratospheric climate coupling;

From 2013 to 2017, he worked at Columbia University, engaged in research on atmospheric circulation, seasonal and intra-seasonal climate predictability of Arctic sea ice and long-term climate change in stratosphere;

Since December 2017, he has been working at the Institute of Atmospheric Sciences of Fudan University, mainly engaged in the research of weather-climate prediction and predictability at middle and high latitudes and of stratospheric dynamics.