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Abstract. The number density of ozone, [O3], maximizes around 26 km in the tropics, protecting life from harmful ultraviolet (UV) light without poisoning it at the surface. Textbooks explain this interior maximum with two paradigms: (1) the source-controlled paradigm explains [O3] as maximizing where its source maximizes between abundant photons aloft and abundant [O2] below, and (2) the source / sink competition paradigm, inspired by the Chapman cycle, explains ozone as scaling with [O2] and the photolytic source / sink ratio. However, each paradigm's prediction for the altitude of peak [O3] is off by 10 km, reflecting their well-known omission of ozone sinks from catalytic cycles and transport. We present a minimal, steady-state theory for the tropical stratospheric [O3] maximum, accurate to within 1 km and formulated in terms of the dominant ozone sinks. These sinks are represented simply by augmenting the Chapman cycle with linear damping of O and O3, leading to the Chapman+2 model. The Chapman+2 model correctly simulates peak tropical [O3] at 26 km, yet this peak is not explained by either paradigm. Instead, the peak is newly explained by the transition from an O-damped regime aloft to an O3-damped regime below. An explicit analytical expression is derived for ozone under gray radiation. This theory accurately predicts an interior maximum of ozone and correctly predicts that an increase in top-of-atmosphere UV light will lead to a downward shift in the peak [O3] due to a downward shift in the regime transition, a result not even qualitatively predicted by the existing paradigms. 

Abstract In response to rising , chemistry‐climate models (CCMs) project that extratropical stratospheric ozone will increase, except around 10 and 17 km. We call the muted increases or reductions at these altitudes the “double dip.” The double dip results from surface warming (not stratospheric cooling). Using an idealized photochemical‐transport model, surface warming is found to produce the double dip via tropospheric expansion, which converts ozone‐rich stratospheric air into ozone‐poor tropospheric air. The lower dip results from expansion of the extratropical troposphere, as previously understood. The upper dip results from expansion of the tropical troposphere, low‐ozone anomalies from which are then transported into the extratropics. Large seasonality in the double dip in CCMs can be explained, at least in part, by seasonality in the stratospheric overturning circulation. The remote effects of the tropical tropopause on extratropical ozone complicate the use of (local) tropopause‐following coordinates to remove the effects of global warming. 

The ozone layer is often noted to exhibit self-healing, whereby depletion of ozone aloft induces ozone increases below, explained as resulting from enhanced ozone production due to the associated increase in ultraviolet (UV) radiation below. Similarly, ozone enhancement aloft can reduce ozone below (reverse self-healing). This paper considers self-healing and reverse self-healing to manifest a general mechanism we call photochemical adjustment, whereby ozone perturbations lead to a downward cascade of anomalies in UV and ozone. Conventional explanations for self-healing imply that photochemical adjustment is stabilizing, damping perturbations towards the surface. However, photochemical adjustment can be destabilizing if the enhanced UV disproportionately increases the ozone sink, as can occur if the enhanced UV photolyzes ozone to produce atomic oxygen, which speeds up catalytic destruction of ozone. We analyze photochemical adjustment in two linear ozone models (Cariolle v2.9 and LINOZ), finding that (1) photochemical adjustment is destabilizing above 40 km in the tropical stratosphere and (2) self-healing often represents only a small fraction of the total photochemical stabilization. The destabilizing regime above 40 km is reproduced in a much simpler model: the Chapman cycle augmented with destruction of O and O3 by generalized catalytic cycles and transport (the Chapman+2 model). The Chapman+2 model reveals that photochemical destabilization occurs where the ozone sink is more sensitive than the source to perturbations in overhead column ozone, which is found to occur when the window of overlapping absorption by O2 and O3 is optically unsaturated, i.e., when overhead slant column ozone is below approximately 10^18 molec. cm−2. 

Abstract In response to global warming, ozone is predicted to increase aloft due to stratospheric cooling but decrease in the tropical lower stratosphere. The ozone reductions have been primarily attributed to a strengthening Brewer‐Dobson circulation, which upwells ozone‐poor air. Yet, this paper finds that strengthening upwelling only explains part of the reduction. The reduction is also driven by tropospheric expansion under global warming, which erodes the ozone layer from below, the low ozone anomalies from which are advected upwards. Strengthening upwelling and tropospheric expansion are correlated under global warming, making it challenging to disentangle their relative contributions. Therefore, chemistry‐climate model output is used to validate an idealized model of ozone photochemistry and transport with a tropopause lower boundary condition. In our idealized decomposition, strengthening upwelling and tropospheric expansion both contribute at leading order to reducing tropical ozone. Tropospheric expansion drives bottom‐heavy reductions in ozone, which decay in magnitude into the mid‐stratosphere.