Radiative forcing by contrails

[摘要] A parametric study of the instantaneousradiative impact of contrails is presented using three different radiativetransfer models for a series of model atmospheres and cloud parameters.Contrails are treated as geometrically and optically thin plane parallelhomogeneous cirrus layers in a static atmosphere. The ice water content isvaried as a function of ambient temperature. The model atmospheres includetropical, mid-latitude, and subarctic summer and winter atmospheres. Opticallythin contrails cause a positive net forcing at top of the atmosphere. At thesurface the radiative forcing is negative during daytime. The forcing increaseswith the optical depth and the amount of contrail cover. At the top of theatmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to0.5 causes about 0.01 to 0.03 Wm^-2 daily mean instantaneous radiativeforcing. Contrails cool the surface during the day and heat the surface duringthe night, and hence reduce the daily temperature amplitude. The net effectdepends strongly on the daily variation of contrail cloud cover. The indirectradiative forcing due to particle changes in natural cirrus clouds may be of thesame magnitude as the direct one due to additional cover.

Key words. Atmospheric composition and structure(aerosols and particles) · Meteorology and atmospheric dynamics (climatology ·radiative processes)

[学科分类] 地球科学(综合)