Relationship of Subtropical Jet and Hadley Cell in CMIP5 Model Output
Is the subtropical jet actually coupled to the Hadley Cell?
Current theory on atmospheric general circulation explains that the existence of the subtropical jet is due to the Hadley Cell’s conservation of angular moment. That is, as the upper branch of the Hadley Cell circulates from the equator to the subtropics, its radius to the axis of rotation of the Earth decreases thus the zonal flow in the circulation must increase to maintain angular momentum. In doing so, there is a maximum in upper tropospheric wind at the edge of the Hadley cell. However, analysis of the subtropical jet in output from the Coupled Model Intercomparison Project (CMIP5) do not support this theoretical explanation of the jet’s existance. Rather, the subtropical jet’s latitude does not covary with the Hadley Cell at all. This surprising result is discussed in greater detail in our GRL publication, “Disconnect Between Hadley Cell and Subtropical Jet Variability and Response to Increased CO2."