Total Column Ozone Trends from the NASA Merged Ozone Time Series 1979 to 2021 Showing Limited Recovery to 1979 Amounts after Declining into the Mid 1990s

Abstract. Monthly averaged total column ozone data Ω_MOD from the Merged Ozone Data set (MOD) were examined to show that the latitude-dependent ozone depletion turnaround dates T_A(θ) range from 1994 to 1998. Ω_MOD used in this study was created by combining data from Solar Backscattered Ultraviolet instruments (SBUV/SBUV-2) and the Ozone Mapping and Profiler Suite (OMPS-NP) from 1979 to 2021. T_A(θ) is defined as the date when the zonally average ozone ceased decreasing. The new calculated systematic latitude-dependent T_A(θ) shape should appear in atmospheric models that combine the effects of photochemistry and dynamics in their estimate of ozone recovery. Trends of zonally averaged total column ozone in percent per decade were computed before and after T_A(θ) using two different trend estimate methods that closely agree, Fourier Series Multivariate Linear Regression and linear regression on annual averages. During the period 1979 to T_A(θ) the most dramatic rates of SH ozone loss were P_D = −10.9 ± 3 % per decade at 77.5° S and −8.5 ± 0.9 % per decade at 65° S, which is about double the NH rate of loss of P_D = −5.6 ± 4 %/decade at 77.5° N and 4.4 ± 1 %/decade at 65° N for the period 1979 toT_A(θ). After T_A(θ), there has been an increase at 65° S of P_D = 1.6 ± 1.4% per decade with smaller increases from 55° S to 25° S and a small decrease at 35° N of −0.4 ± 0.3 %/decade. Except for the Antarctic region, there only has been a small recovery in the Southern Hemisphere toward 1979 ozone values and almost none in the Northern Hemisphere.