Group seminar on 18. June, 14:15

Indices of Walker circulation strength

Katarina Kosovelj

The Walker circulation is an integral part of the tropical atmospheric circulation that influences weather patterns globally. Due to its importance, especially over the Pacific, many indices have been used historically to quantify the Pacific Walker circulation strength and its variability, such as indices based on surface pressure, surface zonal winds, mid-tropospheric vertical velocity and stream function, upper-tropospheric velocity potential, etc.

My talk will consist of two parts. In the first part, I will summarize a paper by Kosovelj and Zaplotnik (2023). We reviewed and compared ten different Pacific Walker circulation indices for the 1951-2020 period using ERA5 reanalysis data.

In the second part, I will discuss my current research in collaboration with Nedjeljka Žagar and Yuan-Bing Zhao from the University of Hamburg. I will explain the new Walker circulation index, KIWI, based on global Kelvin wave energy, compare the KIWI index from three different reanalyses (ERA-5, ERA-20C, and NOAA's 20CRv3), and discuss its sensitivity to vertical resolution. I will also compare KIWI to different (Pacific) Walker circulation indices.