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Lodovica C. Illari. Marino, Garrett P Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences. Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences 2010-03-25T15:01:50Z 2010-03-25T15:01:50Z 2009 2009 http://hdl.handle.net/1721.1/53106 502999866 Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009. Includes bibliographical references (leaves 45-47). Atmospheric blocking events disturb synoptic-scale features from their normal eastward progression, causing anomalous weather conditions for the duration of the blocking event. The essence of blocking can be captured by variation of potential temperature ([theta]trop) on the dynamically-defined tropopause, considered as the 2 potential vorticity unit (PVU) surface. A climatology is constructed on winter ERA-40 data (DJFM 1957/58-2001/02) of [theta]trop and wind. The climatology reveals a maximum in blocking activity over the eastern Atlantic. Long-lasting (> 10 days) Atlantic sector (0-45°W) blocks are then identified using a blocking index developed by Pelly and Hoskins (2003), which detects reversals of the usual meridional [theta]trop gradient. A composite of the 32 cases identified reveals that a blocking precursor signal, serving as an indicator of meridional flow preceding the onset of persistent Atlantic blocking episodes, can first be identified over the Pacific two weeks prior to genesis. The composite shows the precursor signal to be consistent with a transitioning positive-to-negative phase PNA, while the composite mature phase of Atlantic blocking resembles the negative phases of the NAO and AO. The results suggest that non-ephemeral blocking is a global, rather than localized, phenomenon. by Garrett P. Marino. S.M. 53 leaves eng Massachusetts Institute of Technology M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 Earth, Atmospheric, and Planetary Sciences. Precursors to atmospheric blocking events Thesis application/pdf Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="7e3cb497-2a48-4505-ab86-cdd444c74973"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Precursors to atmospheric blocking events</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2009</PublicationDate> <Authors> <Author> <DisplayName>Marino, Garrett P</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Earth, Atmospheric, and Planetary Sciences.</Keyword> <Abstract>Atmospheric blocking events disturb synoptic-scale features from their normal eastward progression, causing anomalous weather conditions for the duration of the blocking event. The essence of blocking can be captured by variation of potential temperature ([theta]trop) on the dynamically-defined tropopause, considered as the 2 potential vorticity unit (PVU) surface. A climatology is constructed on winter ERA-40 data (DJFM 1957/58-2001/02) of [theta]trop and wind. The climatology reveals a maximum in blocking activity over the eastern Atlantic. Long-lasting (&gt; 10 days) Atlantic sector (0-45°W) blocks are then identified using a blocking index developed by Pelly and Hoskins (2003), which detects reversals of the usual meridional [theta]trop gradient. A composite of the 32 cases identified reveals that a blocking precursor signal, serving as an indicator of meridional flow preceding the onset of persistent Atlantic blocking episodes, can first be identified over the Pacific two weeks prior to genesis. The composite shows the precursor signal to be consistent with a transitioning positive-to-negative phase PNA, while the composite mature phase of Atlantic blocking resembles the negative phases of the NAO and AO. The results suggest that non-ephemeral blocking is a global, rather than localized, phenomenon.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>