All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 295 81 12
PDF Downloads 225 64 3

Large-Scale Antecedent Conditions Associated with the 12–14 March 1993 Cyclone (“Superstorm '93”) over Eastern North America

Lance F. BosartDepartment of Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by Lance F. Bosart in
Current site
Google Scholar
PubMed
Close
,
Gregory J. HakimDepartment of Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by Gregory J. Hakim in
Current site
Google Scholar
PubMed
Close
,
Kevin R. TyleDepartment of Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by Kevin R. Tyle in
Current site
Google Scholar
PubMed
Close
,
Mary A. BedrickDepartment of Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by Mary A. Bedrick in
Current site
Google Scholar
PubMed
Close
,
W. Edward BrackenDepartment of Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by W. Edward Bracken in
Current site
Google Scholar
PubMed
Close
,
Michael J. DickinsonDepartment of Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by Michael J. Dickinson in
Current site
Google Scholar
PubMed
Close
, and
David M. SchultzDepartment of Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by David M. Schultz in
Current site
Google Scholar
PubMed
Close
Full access

Abstract

The results of a multiscale analysis of the 12–14 March 1993 superstonn (SS93) over eastern North America are presented. A time sequence of overlapping 10-day time-mean 5OO-hPa geopotential height and anomaly composites shows that the Northern Hemisphere (NH) flow pattern from 18 February to 15 March 1993 is characterized by 1) three persistent troughs situated over eastern Asia and the northwestern Pacific, over eastern North America, and over northwestern Africa and southwestern Europe eastward to central Russia; and 2) a massive blocking anticyclone located over the central and eastern Atlantic. Beginning 8–9 March 1993 the planetary-scale flow amplifies substantially. The explosive SS93 cyclogenesis and the transport of cold air to very low latitudes occurs a few days later as the NH available potential energy content, after peaking on 9 March 1993, decreases by about 6%–7%.

A dynamical tropopause analysis is used to track coherent transient potential vorticity (PV) anomalies and show their qualitative interaction with the planetary-scale flow. SS93 is attributed to the interaction and eventual merger of strong PV anomalies embedded in the northern and southern branches of the westerlies in a background confluent northwesterly flow associated with an amplifying positive-phase Pacific–North American flow pattern. The northern PV anomaly originates in southwestern Canada on 18 February and circumnavigates the NH at relatively high latitudes, a track that permits it to maintain arctic characteristics prior to merger. The southern PV anomalies, tracked from Europe and western Asia eastward across the Pacific, reach North America by 11 March 1993 where they become associated with widespread convention over southern Texas and the northwestern Gulf of Mexico beginning 12 March 1993.

The unique aspects of SS93 are attributed to 1) the near simultaneous amplification of the planetary-scale flow and the lateral and vertical interaction of individual PV anomalies cast of the Rockies during the merger process, and 2) the lag of the northern PV anomaly relative to the southern anomaly so that a baroclinic zone containing lower-tropospheric air of significant conditional instability is allowed to remain in place over southern Texas and the northwest Gulf of Mexico in the cyclogenetic environment ahead of the northern PV anomaly.

Abstract

The results of a multiscale analysis of the 12–14 March 1993 superstonn (SS93) over eastern North America are presented. A time sequence of overlapping 10-day time-mean 5OO-hPa geopotential height and anomaly composites shows that the Northern Hemisphere (NH) flow pattern from 18 February to 15 March 1993 is characterized by 1) three persistent troughs situated over eastern Asia and the northwestern Pacific, over eastern North America, and over northwestern Africa and southwestern Europe eastward to central Russia; and 2) a massive blocking anticyclone located over the central and eastern Atlantic. Beginning 8–9 March 1993 the planetary-scale flow amplifies substantially. The explosive SS93 cyclogenesis and the transport of cold air to very low latitudes occurs a few days later as the NH available potential energy content, after peaking on 9 March 1993, decreases by about 6%–7%.

A dynamical tropopause analysis is used to track coherent transient potential vorticity (PV) anomalies and show their qualitative interaction with the planetary-scale flow. SS93 is attributed to the interaction and eventual merger of strong PV anomalies embedded in the northern and southern branches of the westerlies in a background confluent northwesterly flow associated with an amplifying positive-phase Pacific–North American flow pattern. The northern PV anomaly originates in southwestern Canada on 18 February and circumnavigates the NH at relatively high latitudes, a track that permits it to maintain arctic characteristics prior to merger. The southern PV anomalies, tracked from Europe and western Asia eastward across the Pacific, reach North America by 11 March 1993 where they become associated with widespread convention over southern Texas and the northwestern Gulf of Mexico beginning 12 March 1993.

The unique aspects of SS93 are attributed to 1) the near simultaneous amplification of the planetary-scale flow and the lateral and vertical interaction of individual PV anomalies cast of the Rockies during the merger process, and 2) the lag of the northern PV anomaly relative to the southern anomaly so that a baroclinic zone containing lower-tropospheric air of significant conditional instability is allowed to remain in place over southern Texas and the northwest Gulf of Mexico in the cyclogenetic environment ahead of the northern PV anomaly.

Save