Ozone research has been a hot spot in research on climate change because stratospheric ozone can directly affect the earth system and climate change by absorbing solar ultraviolet radiation.The ozone valley over the Tibetan Plateau in summer has a significant impact on local climate.Against the background of energy conservation and emissions reduction,studying the characteristics and possible mechanism of ozone change in the future can provide theoretical support for the future development of relevant policies.
To understand future ozone trends over the Tibetan Plateau in summer and their possible mechanism,version 3 of the Whole Atmosphere Community Climate Model(WACCM3),with a horizontal resolution of 1.9°×2.5°(longitude×latitude)and vertical resolution of 1.1 km in the upper troposphere and lower stratosphere region,was used to simulate three emissions scenarios of the Special Report of the Intergovernmental Panel on Climate Change(IPCC).The three emissions scenarios were A1B("[which] describes a future world of very rapid economic growth,global population that peaks in mid-century and declines thereafter,and the rapid introduction of new and more efficient technologies.Major underlying themes are convergence among regions,capacity building,and increased cultural and social interactions,with a substantial reduction in regional differences in per capita income.Direction of technological change in the energy system is a balance across all sources."),A2("[which] describes a very heterogeneous world.The underlying theme is self-reliance and preservation of local identities.Fertility patterns across regions converge very slowly,which results in continuously increasing global population.Economic development is primarily regionally oriented and per capita economic growth and technological change are more fragmented and slower than in other storylines."),and B1("[which] describes a convergent world with the same global population that peaks in mid-century and declines thereafter,as in the A1 storyline,but with rapid changes in economic structures toward a service and information economy,with reductions in material intensity,and the introduction of clean and resource-efficient technologies.The emphasis is on global solutions to economic,social,and environmental sustainability,including improved equity,but without additional climate initiatives.").
The simulation results showed that,under A1B,A2 and B1,2001-2099 global total ozone has an increasing trend,which means ozone recovery.The increasing trend of total ozone under A2 is strongest,and the increasing trend of total ozone under B1 is weakest.In the three emissions scenarios,total ozone over the Tibetan Plateau area(26-38°N,75-105°E) shows an increasing trend,but the speed of recovery is slower than that of the global total ozone;that is,the ozone valley over the Tibetan Plateau will significantly deepen.Total chlorine content over the Tibetan Plateau in summer and the chloride concentration at 70 hPa near the center of the ozone valley over the Tibetan Plateau in summer showed decreasing trends for the next 100 years.Meanwhile,the ascending branch of local Hadley Circulation over the Tibetan Plateau in summer has a decreasing trend.These two factors lead to an increase in total ozone over the Tibetan Plateau in summer in the future.On the other hand,the intensity of the South Asia high in the future will enhance,the divergence near the South Asian high will strengthen,and the ozone flux divergence near the South Asian high will strengthen too,which may be the reason for the deepening of the ozone valley over the Tibetan Plateau.
In summary,in the period 2001-2099,based on the A1B,A2 and B1 emissions scenarios,total ozone is expected to increase over the Tibetan Plateau,caused by pollutants reduction and a weakening of local Hadley Circulation;the deepening of the ozone valley over the Tibetan Plateau may be controlled by the enhancement of the South Asia high.