Do supersonic aircraft avoid contrails?

[摘要] The impact of a potential future fleet of supersonic aircraft oncontrail coverage and contrail radiative forcing is investigated bymeans of simulations with the general circulation modelECHAM4.L39(DLR) including a contrail parameterization. The modelsimulations consider air traffic inventories of a subsonic fleet andof a combined fleet of sub- and supersonic aircraft for the years2025 and 2050, respectively. In case of the combined fleet, part ofthe subsonic fleet is replaced by supersonic aircraft. The combinedair traffic scenario reveals a reduction in contrail cover atsubsonic cruise levels (10 to 12 km) in the northern extratropics,especially over the North Atlantic and North Pacific. At supersonicflight levels (18 to 20 km), contrail formation is mainlyrestricted to tropical regions. Only in winter is the northernextratropical stratosphere above the 100 hPa level cold enough forthe formation of contrails. Total contrail coverage is onlymarginally affected by the shift in flight altitude. The modelsimulations indicate a global annual mean contrail cover of 0.372%for the subsonic and 0.366% for the combined fleet in 2050. Thesimulated contrail radiative forcing is most closely correlated tothe total contrail cover, although contrails in the tropical lowerstratosphere are found to be optically thinner than contrails in theextratropical upper troposphere. The global annual mean contrailradiative forcing in 2050 (2025) amounts to 24.7 mW m⁻²(9.4 mW m⁻²) for the subsonic fleet and 24.2 mW m⁻²(9.3 mW m⁻²) for the combined fleet. A reduction of thesupersonic cruise speed from Mach 2.0 to Mach 1.6 leads to adownward shift in contrail cover, but does not affect global meantotal contrail cover and contrail radiative forcing. Hence thepartial substitution of subsonic air traffic leads to a shift ofcontrail occurrence from mid to low latitudes, but the resultingchange in contrail-induced climate impact is almost negligible.

[学科分类] 大气科学