UW-AOS Department Seminar - April 1, 2024 - Libby Orr

Speaker: Libby Orr, AOS graduate student

Title: Characteristics of The Northern Hemisphere Warm-Season
Tropopause-Level Jet & Associated Trends as Revealed By 3 Reanalysis Datasets

Abstract: A calendar-year analysis of the isentropic housing of Northern Hemisphere tropopause-level jets is undertaken using the JRA-55, ERA5, and NCEP reanalysis datasets from
1979 - present. The analysis recreates a result of Christenson et al. (2017) which clearly shows a bimodal distribution of jet frequency of occurrence in the cold season (November – March) with the two peaks corresponding to the polar and subtropical jets, respectively. The analysis reveals that the vast majority of the warm season (May – October) is characterized by a unimodal
distribution suggestive of a single tropopause-level jet during these months. The waviness of this unimodal warm season NH tropopause-level jet is considered from the perspective of the average latitudinal displacement (ALD) diagnostic of Martin (2021). Trends in the various characteristics of the warm season jet over the past 60-plus years are also described.