The Hunga Tonga‐Hunga Ha'apai (HTHH) eruption on 15 January 2022 was one of the most explosive volcanic events of the 21st century so far. According to satellite‐based measurements, 0.4 Tg of sulfur dioxide (SO2) was injected into the stratosphere during the eruption. By using observations and model simulations, here we investigate changes in the chemical compositions of the stratosphere 1 year after the HTHH eruption and examine the key physical and chemical processes that influence the ozone (O3) concentrations. Injected SO2 was oxidized into sulfate during the first 2 months, and transported from the tropics to the Antarctic by the Brewer‐Dobson circulation within 1 year. In mid‐to‐low latitudes, enhanced sulfate aerosol increased O3 concentrations in the middle stratosphere but declined in the lower stratosphere. In addition to the chemical processes, sulfate aerosols also reduced polar low‐stratospheric O3 concentrations through enhanced Antarctic upwelling anomalies.

Tropical cold point tropopause temperature (CPT) anomalies determine lower stratospheric water vapor (LSWV) variations, leading to a high correlation between variations in tropical average CPT and changes in tropical average LSWV. However, this high correlation is only found in winter and spring. This work revisits the factors controlling LSWV variations using observations and simulations over the past~40 years. It is found that the first and second empirical orthogonal function (EOF) modes of tropical CPT variations together explain the tropical average LSWV changes much better than the tropical average CPT variations. The high correlation between the first and second EOF modes of tropical CPT variations and tropical average LSWV changes holds in all four seasons. A further analysis shows that the first and second EOF modes of tropical CPT variations are related to canonical El Niño-Southern Oscillation (ENSO) activity and sea surface temperature (SST) variations in the central Pacific Ocean, respectively. ENSO Modoki is also an important factor that affects LSWV variations by influencing the vertical velocity at the tropopause. The quasi-biennial oscillation (QBO) affects the CPT, and is the third process modulating the LSWV changes. The simulations also support the results.

In this work we investigate interannual variations in lower stratospheric ozone from 1984 to 2016 based on a satellite‐derived data set and simulations from a chemical transport model. An empirical orthogonal function (EOF) analysis of ozone variations between 2000 and 2016 indicates that the first, second, and third EOF modes are related to the quasi‐biennial oscillation (QBO), canonical El Niño–Southern Oscillation (ENSO), and ENSO Modoki events, respectively; these three leading EOFs capture nearly 80% of the variance. However, for the period 1984–2000, the first, second, and third modes are related to the QBO, ENSO Modoki, and canonical ENSO events, respectively. The explained variance of the second mode in relation to ENSO Modoki is nearly twice that of the third mode for canonical ENSO. Since the frequency of ENSO Modoki events was higher from 1984 to 2000 than after 2000, the Brewer‐Dobson circulation anomalies related to ENSO Modoki were stronger during 1984–2000, which caused ENSO Modoki events to have a greater effect on lower stratospheric ozone before 2000 than after. Ozone anomalies associated with QBO, ENSO Modoki, and canonical ENSO events are largely caused by dynamic processes, and the effect of chemical processes on ozone anomalies is opposite to that of dynamic processes. Ozone anomalies related to dynamic processes are 3–4 times greater than those related to chemical processes.

This study investigates the effects of global and regional sea surface temperature (SST) warming from the Industrial Revolution to the present on the stratosphere using a climate model, and estimates the relative contributions of SST warming in different regions. The observed global SST warming is found to cause colder and stronger stratospheric zonal circulations in the high latitudes of both hemispheres, and a colder lower stratosphere in the tropics and ozone depletion. This occurs because the warming in the tropical Atlantic and in the north Indian Ocean and North Pacific strongly cool the stratosphere in the southern and northern high latitudes, respectively. The cooling in the lower stratosphere at lower and midlatitudes is mainly caused by SST warming in the tropical Pacific and north Indian Ocean. The changes in stratospheric temperature are related to changes in circulation and ozone. In addition, we investigate the effects on the stratosphere of ideal 1-K uniform warming of SST in different oceans and compare these effects with those caused by the realistic SST warming. The observed global SST warming and 1-K uniform global SST warming have opposite effects on the high-latitude stratosphere in both hemispheres: 1-K uniform global SST warming results in warmer and weaker stratospheric zonal circulations and a corresponding increase in ozone. This is because the 1-K uniform increase in SST in the tropical Pacific causes extremely strong warming and weakening stratospheric zonal circulations. The contribution of a 1-K uniform increase of SST in the tropical Pacific to stratospheric temperature, circulation, and ozone anomalies overwhelms that of a 1-K uniform increase of SST in other regions.