The role of midlatitude mixing barriers in creating the annual variation of total ozone in high northern latitudes

Abstract

Data from the HIgh Resolution Dynamics Limb Sounder (HIRDLS), the Microwave Limb Sounder (MLS), and the Whole Atmosphere Community Climate Model (WACCM) are used to investigate the annual variation of total column ozone in high northern latitudes. Downward transport of ozone-rich air by the residual mean circulation during autumn and winter bends ozone isopleths down and increases the high-latitude ozone amounts, leading to an ozone maximum at the end of the winter. During the summer months eddy mixing acts to restore pre-fall distributions of ozone. In this study the large-scale mixing in the lower stratosphere is analyzed using Nakamura's (1996) equivalent length formulation with observed and simulated ozone. The analysis of ozone mixing is performed in the tracer equivalent latitude-potential temperature coordinate system. Steep latitudinal gradients of ozone isopleths below about 500 K occur during the winter, where there are minima in the equivalent length, indicating barriers to mixing at 30°N-40°N. This transport barrier allows large ozone maxima to develop poleward of it. The barrier disappears over the summer, permitting latitudinal mixing of the high ozone air. Above 500 K mixing is more effective during the winter, so a large winter maximum does not occur. In both midlatitude and high latitude the lower stratospheric layer from 330 to 500 K doubles its ozone content from autumn to spring, compared with much smaller changes in the layer from 500 to 650 K. Our results confirm that the presence of the winter transport barrier in the lower stratosphere controls the seasonal variation of total ozone.

Overview and update of the SPARC Data Initiative: comparison of stratospheric composition measurements from satellite limb sounders

“…The Polar Ozone and Aerosol Measurement II (POAM II) was launched aboard the SPOT-3 spacecraft in September 1993 (Glaccum et al, 1996). The spacecraft occupied a Sunsynchronous orbit, crossing the descending node at 10:30 LT, that allowed for observations in two latitude bands at 88 to 62 • S and 65 to 71 • N. The POAM II instrument used broadband radiometry to observe trace gases and aerosols in the spectral range of ∼ 350-1070 nm.…”

“…Limb observations, and merged products thereof, are also becoming increasingly important for the detection and attribution of climate change and potential feedback mechanisms, including the role of stratospheric water vapor and aerosol trends and variability in radiative forcing of climate (e.g., Solomon et al, , 2011Gilford et al, 2016;Schmidt et al, 2018). More generally, limb observations are used for the study of stratospheric dynamics and transport (e.g., Gray and Pyle, 1986;Solomon et al, 1986;Holton and Choi, 1988;Funke et al, 2005a;Manney et al, 2009), empirical studies of stratospheric climate and variability (e.g., Randel et al, 2006Randel et al, , 2010Randel and Thompson, 2011;Manney et al, 2008;Bourassa et al, 2010;Stiller et al, 2012;Gille et al, 2014), data merging, and trend evaluation activities (e.g., Randel and Wu, 1999;Hegglin et al, 2014;Shepherd et al, 2014;Froidevaux et al, 2015;Harris et al, 2015;Davis et al, 2016;Arosio et al, 2019;SPARC, 2019), with merged datasets also being used as forcing databases in climate models (e.g., Cionni et al, 2011, for ozone; Thomason et al, 2018, for aerosol) and for the validation of the representation of transport and chemistry in numerical models (e.g., Eyring et al, 2006;Gettelman et al, 2010;Hegglin et al, 2010;Strahan et al, 2011;Kolonjari et al, 2018;Froidevaux et al, 2019).…”

Interannual variability in effective diffusivity in the upper troposphere/lower stratosphere from reanalysis data

“…Other work has used tracer measurements to derive the effective diffusivity (e.g. Nakamura and Ma, ; Gille et al , ). Here we compare the equivalent length obtained with the full tracer advection calculations with the results obtained directly from PV and ozone fields from the EI reanalysis.…”

“…Nakamura and Ma, ) and ozone (e.g. Gille et al , ). Using EI ozone, we have compared the results from the hemispheric calculation (not shown) with those obtained by carefully selecting the monotonic bands.…”

Level 2 processing for the imaging Fourier transform spectrometer GLORIA: derivation and validation of temperature and trace gas volume mixing ratios from calibrated dynamics mode spectra

“…Chen, 1995;Berthet et al, 2007). Especially during summer, when the jet is weak, the UTLS over Europe consists of a cascade of small filaments (Postel and Hitchman, 1999;Ungermann et al, 2013;Gille et al, 2014).…”