There has been renewed interest in developing commercial supersonic transport aircraft due to the increased overall demands by the public for air travel, the aspiration for more intercontinental travel, and the desire for shorter flight times. Various companies and academic institutions have been actively considering the designs of such supersonic aircraft. As these new designs are developed, the environmental impact on ozone and climate of these fleets need to be explored. This study examines one such proposed commercial supersonic fleet of 55-seater that is projected to fly at Mach 2.2, corresponding to cruise altitudes of 17-20 km, and which would burn 122.32 Tg of fuel and emit 1.78 Tg of NOx each year. Our analyses indicate this proposed fleet would cause a 0.74% reduction in global column ozone (similar to 2 Dobson Units), which is mainly attributed to the large amounts of nitrogen oxides released in the atmosphere from the supersonic aircraft. The maximum ozone loss occurs at the tropics in the fall season, with a reduction of -1.4% in the total column ozone regionally. The stratospheric-adjusted radiative forcing on climate from this fleet was derived based on changes in atmospheric concentrations of ozone (59.5 mW/m(2)), water vapor (10.1 mW/m(2)), black carbon (-3.9 mW/m(2)) and sulfate aerosols (-20.3 mW/m(2)), resulting in a net non-CO2, non-contrail forcing of 45.4 mW/m(2), indicating an overall warming effect. Plain Language Summary With the general public's increased demand for air travel, a desire for more intercontinental travel with shorter flight times, there has been renewed interest in developing commercial supersonic transport aircraft. Various companies and academic institutions have been actively considering the design of such a supersonic aircraft. As these new designs are developed, the environmental impact of these realistic fleets on ozone and climate needs to be explored. This study looked at one such supersonic fleet, expected to fly at Mach 2.2, corresponding to a cruising altitude of 17-20 km, that would burn 122.32 Tg of fuel and emit 1.78 Tg of NOx per year. Our analysis shows that this proposed fleet would result in a 0.74% reduction in global columnar ozone (approximately 2 Dobson units), mainly due to the large atmospheric release of nitrogen oxides by supersonic aircraft. The impact on climate from this fleet was derived to have a net forcing of 45.4 mW/m(2), indicating an overall warming effect.

There have been extensive studies on poleward expansion of the Hadley cells and the associated poleward shift of subtropical dry zones in the past decade. In the present study, we study the trends in the width and strength of the Hadley cells, using currently available simulation results of the Coupled Model Intercomparison Project Phase-6 (CMIP6), and compare the trends with that in CMIP5 simulations. Our results show that the total annual-mean trend in the width of the Hadley cells is 0.13 degrees +/- 0.02 degrees per decade over 1970-2014 in CMIP6 historical All-forcing simulations. It is almost the same as that in CMIP5. The trend in the strength of the Northern-Hemisphere (NH) cell shows much greater weakening in CMIP6 than in CMIP5, while the strength trend in the Southern-Hemisphere (SH) cell shows slight strengthening. Single-forcing simulations demonstrate that increasing greenhouse gases cause widening and weakening of both the NH and SH Hadley cells, while anthropogenic aerosols and stratospheric ozone changes cause weak strengthening trends in the SH cell. CMIP6 projection simulation results show that both the widening and weakening trends increase with radiative forcing. (C) 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.