Improved understanding of the stratospheric response to very different climate including the cold climate of the Last Glacial Maximum (LGM) will broaden the perspective and provide insight when assessing the stratospheric response to anthropogenically-induced climate changes in the 21st century. The spatial distributions of stratospheric ozone, stratosphere-to-troposphere ozone flux, and ultraviolet radiation reaching to the lower troposphere under various climate states obtained from the project will become available to the tropospheric chemistry modeling community. The research results will be disseminated to the broader atmospheric and climate research community through scientific publications. The proposal will support a Ph.D. student and a postdoc and provide interdisciplinary training in atmospheric dynamics and chemistry to the graduate student and postdoc. The research team is committed to public outreach, including developing educational videos and other outreach materials for grades K-12; giving public lectures on the research.
The Brewer-Dobson circulation (BDC) is the stratospheric meridional circulation that links the tropics and pole in the winter hemisphere. The BDC couples the troposphere and the stratosphere through the transporting of ozone-depleting gases from tropical troposphere to the stratosphere and then from the stratosphere to the troposphere in the mid- and high-latitudes, influencing the lifetime of trace gases such as methane. By transporting stratospheric ozone from the tropics where it is produced to the poles, the BDC also determines the spatial distribution of the ozone column abundance that is the primary control on ultraviolet radiation penetration into the lower troposphere, playing an important role for driving atmospheric chemistry. During the cold climate of the LGM, both temperature and Brewer-Dobson circulation could be very different from the present day, because of different concentrations of radiative and chemical constituents (e.g., CO2, H2O, CH4, N2O, CFC), surface boundary conditions (colder sea surface temperatures, larger latitudinal temperature gradients and large ice sheets) and tropospheric circulations.
Recent work using ice core observations shows higher tropospheric ozone concentrations in cold climates relative to warm climates, indicative of the potential importance of stratosphere-troposphere ozone transport. However, there are very few studies on the BGC and ozone during the cold climate and there is no study so far quantifying the stratosphere-to-troposphere ozone flux and surface ultraviolet radiation during that time. Motivated by the recent findings from ice core observations, this research project will fill this knowledge gap by investigating the BDC and stratospheric ozone and quantifying the stratosphere-to-troposphere ozone flux and ultraviolet radiation and their impact on the tropospheric chemistry during the cold climate of the LGM. They researchers will apply the most recent version of the Whole Atmosphere Community Climate Model with interactive stratospheric chemistry, and the ice age chemistry and proxy tropospheric chemistry-climate model to explain the high concentration of tropospheric ozone in cold climates.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
