Summer Climate Dynamics Defenses

Two Climate Dynamics students defended doctoral theses this summer that extended our understanding of the predictability of weather and climate.

Ralph Getzandanner, working closely with advisor and AOES faculty member David Straus, examined the relationship between mid-latitude regime transitions and tropical diabatic heating. Regimes are atmospheric circulation patterns that affect weather conditions over large geographical areas. These regimes are persistent and frequently reoccur over the same region. Getzandanner identified a set of four regimes by performing a k-mean cluster analysis on wintertime circulation features (500 hPa geopotential height) in the Euro-Atlantic region. The research showed that tropical diabatic heating appears to be a precursor in many of the regime transitions in the Euro-Atlantic region. By knowing when a transition from one regime to another will occur, weather forecasts could be extended beyond the normal deterministic limit into the sub-seasonal time frame.

Nick Lybarger, advised by AOES faculty member Cristina Stan, examined the joint effect of ENSO and MJO on predictability.

Understanding El Niño-Southern Oscillation (ENSO) is one of the keys to understanding the global climate. The spread of hot West Pacific water, which overtakes the normally cool East Pacific, affects weather patterns throughout the globe. Accurately predicting El Niño allows more accurate prediction of those subsequent weather patterns, giving time for precautionary measures against drought or flooding. The Madden-Julian Oscillation (MJO) is a shorter-term pattern of tropical atmospheric convection that also occurs over the Pacific Ocean. Because both of these phenomena are of such large spatial scale, understanding their interactions should prove quite useful in understanding the mechanisms which drive both.

Nick Lybarger’s thesis work quantified their interactivity by developing an index which takes into account the shifting ocean currents associated with both El Niño and wind patterns related to the MJO. Experiments carried out on a simple model of the Pacific Ocean showed that the MJO can have a strong affect on El Niño development when oceanic waves are simultaneous with MJO winds, but that those winds are not the primary mechanism which initiates El Niño. This relationship was then shown to have some ability to predict the occurrence of El Niño, outperforming the more typical measures of El Niño such as central Pacific ocean temperatures. When MJO winds are simultaneous with strong oceanic waves, El Niño is both more likely to occur and more likely to be a strong event.