Chapter 10: Polar Processes

• Main Authors: Santee, Michelle L., Lambert, Alyn, Manney, Gloria L., Lawrence, Zachary D., Chabrillat, Simon, Hoffmann, Lars, Palmer, Sean P., Minschwaner, Ken
• Format: Book Part
• Language: English
• Published: SPARC Office 2022
• Subjects: FOS: Earth and related environmental sciences; Antarctic; Arctic; Antarc*; Antarctica
• Online Access: https://juser.fz-juelich.de/record/906514; https://juser.fz-juelich.de/search?p=id:%22FZJ-2022-01493%22

This chapter focuses on microphysical and chemical processes in the winter polar lower stratosphere, such as polar stratospheric cloud (PSC) formation; denitrification and dehydration; heterogeneous chlorine activation and deactivation; and chemical ozone loss. These are “threshold” phenomena that depend critically on meteorological conditions. A range of diagnostics is examined to quantify differences between reanalyses and their impact on polar processing studies, including minimum lower stratospheric temperatures; area and volume of stratospheric air cold enough to support PSC formation; maximum latitudinal gradients in potential vorticity (a measure of the strength of the winter polar vortex); area of the vortex exposed to sunlight each day; vortex break-up dates; and polar cap average diabatic heating rates. For such diagnostics, the degree of agreement between reanalyses is an important direct indicator of the systems’ inherent uncertainties, and comparisons to independent measurements are frequently not feasible. For other diagnostics, however, comparisons with atmospheric observations are very valuable. The representation of small-scale temperature and horizontal wind fluctuations and the fidelity of Lagrangian trajectory calculations are evaluated using observations obtained during long-duration superpressure balloon flights launched from Antarctica. Comparisons with satellite measurements of various trace gases and PSCs are made to assess the thermodynamic consistency between reanalysis temperatures and theoretical PSC equilibrium curves. Finally, to explore how the spatially and temporally varying differences between reanalyses interact to affect the conclusions of typical polar processing studies, simulated fields of nitric acid, water vapour, several chlorine species, nitrous oxide, and ozone from a chemistry-transport model driven by the different reanalyses for specific Arctic and Antarctic winters are compared to satellite measurements.