An Analysis of Atmospheric Teleconnection Patterns, Their Interactions and Associated Boundary Forcing

Download or read book An Analysis of Atmospheric Teleconnection Patterns, Their Interactions and Associated Boundary Forcing written by Nicholas Soulard and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "The goal of the work presented herein is to advance our understanding of the role that tropical heating has on the extratropical seasonal climate. The fact that tropical forcing can influence the extratropical Northern Hemisphere is well known and well documented; however, interactions amongst low-frequency patterns of atmospheric variability forced by the tropics is complicated and needs further investigation. The response to tropical forcing over the extratropical Northern Hemisphere is further complicated by the fact that the background climate state is changing due to global climate change. This then has impacts on how the tropics influence the extratropics. Finally, newly discovered low-frequency patterns of atmospheric variability demand that we investigate how/whether they can be forced. These three issues are the basis for the three manuscripts that comprise this thesis.There is a documented sporadic relationship between the Pacific-North American pattern (PNA) and the North Atlantic Oscillation (NAO) during the boreal winter months. Using inter-annual running correlation for every three-month mean of the year, we show that not only is there a sporadic correlation between the PNA and NAO during the boreal winter months, but that they are consistently correlated during the spring and early summer months.We show that when the tropics have a weaker than normal influence on the extratropics (such as when the phase of the Pacific Decadal Oscillation (PDO) changes phase), the PNA and NAO are correlated. This same principle applies to both the winter months, and the spring/early summer, the only difference being that the tropics rarely have an impact on the extratropics during the spring/early summer months, which is why the correlation between the PNA and NAO is consistent during that time of the year.We next document the changing relationship between El Niño and its two extratropical response patterns, the PNA and the Tropical Northern Hemisphere pattern (TNH), which, like the PNA, affects conditions over North America. Several studies have aimed to clarify which one of these patterns best represents El Niño’s influence on the extratropical Northern Hemisphere. Further studies have taken this line of inquiry a step further and have split El Niño events into two categories: East Pacific (EP) and Central Pacific (CP) events. Using a novel tracking algorithm, we show that the correlation between El Niño and the PNA is stronger the further west El Niño’s sea-surface temperature (SST) anomaly is located. The relationship between El Niño and the TNH appears to be less dependent on the location of the SST anomaly, but rather depends on the phase of the Atlantic Multidecadal Oscillation. Finally, the strength and position of the jet also influence both teleconnections, as under different El Niño states the jet will differ.In the final results chapter, we examine a relatively new low-frequency pattern called the circumglobal teleconnection pattern (CGT). This pattern is a wavenumber 5 Rossby wave centered along the jet, which completely circumscribes the globe. The goal of this chapter is to analyse to what extent tropical forcing can influence long range teleconnections through understanding whether the CGT can be forced by tropical heating anomalies. Using a simple general circulation model (GCM) we show that the CGT, in the model, is preceded by heating anomalies in the equatorial Indian Ocean and western tropical Pacific. We then show that this is also the case in reanalysis.Each of these chapters addresses a different aspect of the impact of tropical forcing on the extratropical Northern Hemisphere"--