Diagnosing behavior of the Hadley Cell and subtropical jet in idealized atmospheric models (in revision)


Recent work has shown that variability of the subtropical jet’s (STJ) latitude, phiSTJ is not coupled to that of the Hadley Cell (HC) edge, phiHC, but the reason for this disconnect has not been examined in detail. Here, we use meteorological reanalysis, comprehensive climate models, and an idealized atmospheric model to examine the cause of the distinct behavior of the STJ and HC. We find that a decoupling of phiHC and phiSTJ can occur in a dry general circulation model, indicating that large-scale dynamical processes are sufficient to reproduce the metrics' relationship without explicit variability in the zonal structure, convective processes, or sea surface temperature variability. With that said, a phiHC and phiSTJ disconnect is dependent on the model simulating an accurate climatological basic state. Comparison of model configurations reveals that a strong coupling between the two features is the result of the eddy momentum convergence being the dominant contribution to meridional flow balance. When angular momentum advection relevantly impacts meridional flow in the subtropical upper troposphere, phiSTJ is disconnected from phiHC. This result confirms the long-held acceptance that the STJ’s behavior is connected to angular momentum advection by the HC while rejecting the assumption that the phiHC and phiSTJ must therefore co-vary.

Journal of Atmospheric Science