Axial Angular Momentum: Vertical Fluxes and Response to Torques

摘要

The horizontally averaged global angular momentum μ at a certain height reacts only to the vertical divergence of the angular momentum flux at least above the crest height of the earth's orography. The flux is tied to the torques at the surface. Data are used to evaluate the flux and the response of μ to the torques. It is shown that the accuracy of the data is sufficient for an investigation of this interaction. It is found that the horizontally averaged angular momentum in the upper troposphere and lower stratosphere tends to be negative before an event of positive friction torque. Downward transports of negative angular momentum from these layers allow the angular momentum to further decrease near the ground, even shortly before the event although the friction torque is positive at that time. The impact of the mountains during this process is demonstrated. The ensuing positive response to the friction torque is felt throughout the troposphere. The final decay of this reaction involves downward transports of μ with typical velocities of ～1-2 km day~(-1). The angular momentum in the lower troposphere tends to be negative before an event of positive mountain torque. There is a short burst of rapid upward transport of positive angular momentum during the event itself, which reaches the stratosphere within 1-2 days. A phase of decay follows with slow downward transport of positive angular momentum.