Considerable research has been performed on persistent-anomaly structures for the Northern Hemisphere winter. However, atmospheric blocking structures during the warm season also have a considerable impact on weather and climate, as manifested through heat waves, floods, and droughts. In particular, atmospheric blocked flow has a profound impact on anomalously-dry regimes over the central North American continent. In order to provide a better understanding of the life cycle of the atmospheric blocking events and their relation to fast-climate phenomena, we analyse persistent height-anomaly structures derived from the National Centers for Environmental Prediction (NCEP) global reanalyses. We devise an objective criterion for the characterization of blocked flow by relating it to persistent positive height anomalies. Individual warm-season events over the North American continent are then identified and examined in case studies. This reveals a type of blocking regime, differing in structure from the Rex and Omega type blocks described in the literature, as being important in the region during summer. Moreover, changes in the statistical distribution of the event frequencies are analysed in order to detect climatic trends. We find a pronounced westward displacement of the North American anomaly event frequency maximum to be associated with the 1999-2004 drought in the Canadian Prairies.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.101659 |
| Date | January 2007 |
| Creators | Von Appen, Florian. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Atmospheric and Oceanic Sciences.) |
| Rights | © Florian Von Appen, 2007 |
| Relation | alephsysno: 002591228, proquestno: AAIMR32796, Theses scanned by UMI/ProQuest. |
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