Southern Hemisphere Storm Tracks Research Articles

The effect of a regional increase in ocean surface roughness on the tropospheric circulation: a GCM experiment

The sensitivity of the atmospheric circulation to an increase in ocean surface roughness in the Southern Hemisphere storm track is investigated in a paired general circulation model experiment. Such a change in sea roughness could be induced by ocean waves generated by storms. Two extended permanent-July runs are made. One with standard sea surface roughness, the other with ten times as a large surface roughness over open sea poleward of 40° S. The regional increase in ocean surface roughness significantly modifies the tropospheric circulation in the Southern Hemisphere. The strongest effect is the reduction of tropospheric winds (by 2 m/s or 10%) above the area with increased roughness. The poleward eddy momentum flux is reduced in the upper troposphere and the meridional eddy sensible heat flux is reduced in the lower troposphere. Zonal mean and eddy kinetic energy are consistently reduced.

The Geographical Locations of Southern Hemisphere Storm Tracks: Linear Theory

The instability properties of a three-dimensional climatological January Southern Hemisphere flow field are examined using a five-level spherical quasi-geostrophic spectral model. The growth rates, phase frequencies, disturbance streamfunctions and eddy momentum and heat fluxes are studied for the eight fastest growing modes, all of which we monopole cyclogenesis modes. There is reasonable agreement between instability theory and observations as far as the geographical locations of the storm tracks and eddy fluxes are concerned. The principal storm track is located in the eastern part of the hemisphere slightly downstream and poleward of the jet stream maxima. The usual vertical structure problem of instability theory occurs with the theoretical disturbance streamfunctions and eddy fluxes being relatively too large at the surface compared with values at the tropopause.