A traveling atmospheric disturbance generated by a soil colour change in a high-resolution climate model experiment

Abstract

The climate model CESM-WACCM is used to study the way a soil colour change of the eastern region of the Sahara affects the dynamics of the troposphere. The soil colour is darkened for 5 days. The difference between the perturbed model run and the control model run is used to isolate the soil colour change-induced atmospheric perturbation from random atmospheric waves which are stronger by an order of magnitude or more. The perturbation generates a circular wave radially propagating away from the Sahara on the first day of the simulation. After nine hours, the wave front reaches the convection zone in Brazil where a secondary wave is generated and can be clearly seen until 23:00 UT. The mean wave velocities of the traveling atmospheric disturbances are 〈v〉=200±50 m/s for the primary wave and 〈v〉=220±40 m/s for the secondary wave. The mean horizontal wavelengths are 〈λ〉=3000±500 km for the primary wave and 〈λ〉=2600±600 km for the secondary wave. The mean wave periods are 〈p〉=4±1 h for the primary wave and 〈p〉=3±1 h for the secondary wave. Since the perturbed model run diverges from the control run with the passage of time, the attribution of cause and effect becomes difficult after a few days. Analysis of the simulation data of the first day leads to a deeper understanding of global teleconnections, radiative transfer and wave-coupling processes between the surface and the atmospheric layers.