The Relationship Between Convective Adjustment Hadley Circulation and Normal Modes of the ANMRC Spectral Model

Abstract By expanding model forecasts with and without convection in terms of three-dimensional normal mode functions it is shown that convective adjustment mainly influences gravity modes for vertical mode 4 of the nine-level ANMRC spectral model. It is also shown that the dominant influence of convective adjustment occurs in the lowest frequency gravity modes for all zonal wavenumbers and in particular wavenumbers 0 to 8. By applying various gravity mode filters it is shown that the Hadley circulation in this model is also dominated by these low-frequency gravity modes.