Turbulence Layer Thickness in the Stratosphere under the Presence of Viscosity and Newtonian Cooling

[摘要] Thickness of turbulence layers, strictly speaking the distance between the breaking level and the critical level, in the stratosphere is calculated numerically based on an equation representing a marginal state of internal gravity wave breakdown. The results demonstrate that the turbulence layers thinner than approximately 300m, which are frequently observed in the lower stratosphere, can be caused by the breakdown of mesoscale internal gravity waves. Kinematic viscosity and Newtonian cooling suppress the activity of turbulence depending on the horizontal wavelength of internal gravity waves and altitude. In general, long waves are more affected by such dissipative processes than short waves. Detailed inspection shows that damping due to Newtonian cooling is more effective, particularly for longer waves. Maximum eddy viscosity coefficients in the lower stratosphere are also obtained theoretically based on the turbulence layer thickness and characteristic vertical scale associated with kinematic viscosity.The relation between the turbulence layer thickness and wave amplitude provides useful information on parameters of internal gravity waves at the bottom of the middle atmosphere, which propagate upwards and break into turbulence to modify the general circulation near the mesopause.

[学科分类] 大气科学