Meridional temperature gradient and the midlatitude storm track
The southern hemisphere’s atmospheric circulation experiences several annual and seasonal changes that are well documented and studied. The teleconnections between different variables are verified and used to explain variability in everyday climate and weather. Theories using physics are taught and published in textbooks to help us understand the connectivity and complexity of such a system. One theory is the meridional temperature gradient has a direct impact on the storm track. This thesis investigates that theory using the ERA-Interim dataset. The temperature gradient is a direct result of the temperature field, and depending on the latitudes you decide in which to constrain your gradient, the gradient experiences several changes. In the high latitudes, the southern annual oscillation created a two peaked pattern; the mid-latitudes display the expected seasonal mono peak pattern. The strong correlations seen in the high latitudes means that the gradient is driven by the patterns experienced at higher latitudes. The independence of behaviours displayed by the ocean sectors led to the research investigating the influences, looking at not just the hemisphere, but also each basin separately. The Pacific and Indian Ocean showed in several results to act independently from one another, in temperature gradients, wind field, and storm track position. The strong correlations between the temperature gradient and the wind field, as well as the storm track field show that the two are connected, as the theory suggests. If temperatures rise in the tropics, or decrease in the poles, then the temperature gradient will steepen. The pressure gradient force increases which pushes the thermal wind balance poleward, shifting the position of the westerlies. The area with the largest variation in the wind speed becomes the storm track, which would also shift poleward. Climatic factors such as the southern oscillation index, southern annular mode or Indian Ocean dipole show slight correlations with the temperature field, but have little to no influence on the temperature gradient itself. Precipitation levels in New Zealand are highly variable due to the nature of the countries location and topography. What was found was little connection between the northern part of the country and the storm track. However, closer proximity to the storm track, such as the south of the country, do experience a small amount of variation due to the storm tracks influence.