The global picture of aerosol layers formation in the stratosphere and in the mesosphere under the influence of gravito-photophoretic and magneto-photophoretic forces

Abstract

[1] Photophoretic forces act on a particle which has an inhomogeneous surface, especially with respect to the accommodation coefficient. Gas molecules incident on it leave the surface after more or less accommodation, resulting in a force and torque on the particle. Due to Brownian rotation of the particle the net force is zero. If the particle is also exposed to an orientating torque, the photophoretic force points in a preferred direction resulting in net photoporetic force. The orienting torque can be caused by gravity or by the earth magnetic field. Photophoretic forces are important if the mean free path of the gas molecules is larger than the size of the particles. This is the case for all particles found in the stratosphere and mesosphere. The direction of the photophoretic force can be opposite to gravity and it can exceed the weight of the particle. In that case the particle is lifted upwards, until it reaches conditions where the two forces are equal. The stratification of the stratospheric and mesospheric aerosol is given fact. The temperature profile of the atmosphere, the incoming solar flux density, and the emitted terrestrial infrared radiation, are used to investigate systematically the role of photophoresis in the formation of aerosol layers at specific altitudes for various types of particles around the globe. Photophoresis can be responsible for aerosol layer formation at altitudes of 20, 30, 50, 70 and 85 km. The layers form in specific geographic regions and at certain seasons.