Stratospheric Ozone in the Last Glacial Maximum

Susan Solomon,Mingcheng Wang,Becky Alexander,Rachel H. White,Qiang Fu

doi:10.1029/2020jd032929

Abstract

AbstractUsing the Whole Atmosphere Community Climate Model version 6, stratospheric ozone in the Last Glacial Maximum (LGM) is investigated. It is shown that, compared with preindustrial (PI) times, LGM modeled stratospheric temperatures are increased by up to 8 K, leading to faster ozone destruction rates for gas phase reactions, especially via the Chapman mechanism. On the other hand, stratospheric hydroxyl radical (OH) and nitrogen oxides (NOx) concentrations are decreased by 10–20%, which decreases catalytic ozone destruction, thereby decreasing ozone loss rates. The net effect of these two compensating mechanisms in the upper stratosphere (above 15 hPa) is a vertically integrated 1–3 Dobson unit (DU) decrease during the LGM. In the lower stratosphere (tropopause to 15 hPa), changes in the stratospheric overturning circulation and resulting transport dominate changes in ozone. Consistent with a weakening of the residual circulation in the LGM, lower stratospheric ozone is increased by 2–5 DU in the tropics and decreased by 5–10 DU in the extratropics, but the latter is partly compensated by ozone increases due to a lower tropopause. It is found that tropospheric ozone is decreased by about 5 DU in the LGM versus PI. Combined changes in stratospheric and tropospheric ozone lead to a decrease in total ozone column everywhere except over the northeast North America, equatorial Indian and West Pacific Oceans. Surface ultraviolet radiation in the LGM versus PI is increased over the Northern Hemisphere middle and high latitudes, especially over the ice caps, and over the Southern Hemisphere near 60°S.

Highlights

As a key component of the Earth system, stratospheric ozone protects life on Earth from hazardous ultraviolet (UV) radiation, and has a crucial impact on the tropospheric chemistry. Rohrer and Berresheim (2006) showed that tropospheric hydroxyl radical (OH) is linearly correlated with UV radiation based on 5 years of measurements in Germany. Murray et al (2014) found that stratospheric ozone, via its impact on surface UV radiation, is an important factor controlling variability in tropospheric OH over glacial‐interglacial periods in a chemistry‐climate model
Such temperature changes agree with previous studies (Rind et al, 2001, 2009) and have a significant impact on stratospheric ozone concentration in the Last Glacial Maximum (LGM), as will be shown later
We have investigated stratospheric ozone in the LGM using Whole Atmosphere Community Climate Model version 6 (WACCM6)

Summary

Introduction

As a key component of the Earth system, stratospheric ozone protects life on Earth from hazardous ultraviolet (UV) radiation, and has a crucial impact on the tropospheric chemistry. Rohrer and Berresheim (2006) showed that tropospheric hydroxyl radical (OH) is linearly correlated with UV radiation based on 5 years of measurements in Germany. Murray et al (2014) found that stratospheric ozone, via its impact on surface UV radiation, is an important factor controlling variability in tropospheric OH over glacial‐interglacial periods in a chemistry‐climate model. Compared to the rich literature on stratospheric ozone for the current and future climates, there are only a few studies on stratospheric ozone in the LGM (Crutzen & Brühl, 1993; Martinerie et al, 1995; Murray et al, 2014; Noda et al, 2018; Rind et al, 2009). Rind et al (2009) examined stratospheric ozone in the LGM using the 3‐D GISS Global Climate Middle Atmosphere model (4° × 5° and 53 layers) with linearized ozone chemistry (McLinden et al, 2000). Geng et al (2017) hypothesized that higher tropospheric ozone in the extratropics could be due to increased transport of stratospheric ozone to the surface driven by an enhanced BDC in the glacial climate (Rind et al, 2001, 2009).

Model Description

Model Simulations

Temperature Changes

Ozone Change

UV Radiation Change

Conclusion and Discussion