The Maintenance of the Longitudinal Subtropical Jet Structure During Austral Winter

The austral winter subtropical jet maintenance is analyzed by comparing the observed upper tropospheric zonal momentum budget with an idealized aquaplanet model simulation with localized tropical heating in the summer hemisphere. The model and observations show great similarity, demonstrating the dominant role of localized tropical convection in shaping the longitudinal jet structure. In both observations and the model, localized tropical convection drives a meridional flow toward the winter pole, which advects angular momentum to the upstream side of the subtropical jet, while the downstream side is maintained by zonal advection. Angular momentum is approximately conserved up to 20 (Formula presented.) S in the poleward flow region, which is the Indian Ocean sector in the observations. The subtropical jet is in geostrophic balance with a stationary Rossby wave driven by tropical convection, with an anticyclone northwest of the subtropical jet, and a cyclone southeast of it.