Dynamical Processes of Equatorial Atmospheric Angular Momentum (formerly paper P2.23)

The dynamical processes that drive intraseasonal equatorial atmospheric angular momentum (EAAM) fluctuations are examined with National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis data. The primary methodology involves the regression of relevant variables including the equatorial bulge, mountain, and friction torques, surface pressure, streamfunction, and outgoing longwave radiation, against the time derivative of the two components and the amplitude of the EAAM vector.

The results indicate that the observed 10-day westward rotation of the EAAM vector corresponds to the propagation of a zonal wavenumber one, antisymmetric, Rossby wave normal mode. Additional findings suggest that fluctuations in the amplitude of the EAAM vector are driven by poleward propagating Rossby waves excited by the latent heating within equatorial mixed Rossby-gravity waves and also by wave-wave interaction amongst planetary waves. Both of these processes can induce surface pressure anomalies that amplify the EAAM vector via the equatorial bulge torque. The Greenland mountain torque was also found to drive large fluctuations in the amplitude of the EAAM vector. Both the friction torque and wave/zonal mean flow interaction were shown to dampen the EAAM amplitude fluctuations.

A comparison of the EAAM dynamics in the atmosphere with that in an aquaplanet GCM suggests that the mountain torque also drives fluctuations in the phase speed of the atmospheric wave field associated with the EAAM vector, and it confines the wave-wave interaction to planetary scales.