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Schedule of Presentations and Abstracts: Updated May 21, 2012

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Schedule of Presentations and Abstracts: Updated May 21, 2012 Fourth International Workshop on Extratropical Transition (IWET4) Mont Gabriel Lodge St.-Adèle, Québec Canada May 20-25, 2012 Schedule of presentations and abstracts: Updated May 21, 2012 Monday, May 21: 0815: Welcome and Introduction 0830 Session 1 (ET Climatology) Chair: Shawn Milrad Kimberly M. Wood and Elizabeth A. Ritchie The University of Arizona Title: A 40-year climatology of extratropical transition in the eastern North Pacific. Part I: General characteristics. Extratropical transition has been frequently observed in many tropical basins around the world, including the western North Pacific, the northern Atlantic, and the southwestern Pacific. Conversely, only rare cases have been documented in the eastern North Pacific. This presentation will showcase a climatology of extratropical transition in this basin from 1970 to 2010, including cases which complete ET over open ocean and cases which begin ET but then make landfall before completing the process. This study utilizes 6-hourly reanalysis data from the European Centre for Medium-Range Weather Forecasts at a nominal resolution of 0.703 degrees from 1979 onward (ERA-Interim) and a nominal resolution of 1.125 degrees before 1979 (ERA-40) to produce cyclone phase space plots as well as examine the large-scale features present during extratropical transition in the eastern North Pacific. This presentation will also discuss the structure of ET in the eastern North Pacific. It will cover the average structural changes that occur during ET in this basin as well as explore how these changes differ from those seen elsewhere in the tropics. 0900 Elizabeth A. Ritchie and Kimberly M. Wood The University of Arizona Title: A 40-year climatology of extratropical transition in the eastern North Pacific. Part II: Structure and common large-scale circulation patterns. 1 The extratropical transition of tropical cyclones has been documented in many basins worldwide, including the western North Pacific, the north Atlantic, and the southwest Pacific. However, very few cases have been documented in the eastern North Pacific, and certainly no climatology has been presented thus far. This presentation will continue to explore extratropical transition in this basin from 1970 to 2010. In part II of this study, the structural changes associated with ET in the eastern North Pacific are explored. The data used in the analysis are the 6-hourly reanalysis data from the European Centre for Medium-Range Weather Forecasts at a nominal resolution of 0.703 degrees from 1979 onward (ERA-Interim) and a nominal resolution of 1.125 degrees before 1979 (ERA-40). Cyclone phase space is used to both define a common “ET time” around which to composite the analyses, and also to describe the passage of the ET-ing system as it transitions into an extratropical cyclone. This presentation will discuss the composite large-scale circulation features and structural changes that occur during ET in this basin and also explore how these changes differ from those seen elsewhere in the tropics. 0930 Chris Fogarty Canadian Hurricane Centre Title: A summary of recent notable ET events over Eastern Canada A number of significant ET events have impacted the region over the past number of years – almost twice as many as the longer-term average. This is partly a result of heightened tropical cyclone activity in the Atlantic Basin. Recent events will be presented including particular forecast challenges and successes associated with each. 1000 Health Break 1030 Discussion and Summary of Session 1 1045 Session 2 (Ensemble prediction, and data assimilation) Chair: Elizabeth R. Sanabia Sim D. Aberson NOAA/AOML/Hurricane Research Division Altug Aksoy University of Miami/CIMAS and NOAA/AOML/Hurricane Research Division 2 Kathryn Sellwood University of Miami/CIMAS and NOAA/AOML/Hurricane Research Division Title: The Transition of Hurricane Earl (2010) from a Category Four Hurricane to a Large Extratropical Cyclone The Transition of Hurricane Earl (2010) from a Category Four Hurricane to a Large Extratropical Cyclone The National Oceanic and Atmospheric Administration is in the midst of a multi- year field program, the Intensity Forecasting Experiment to improve the understanding and prediction of hurricane intensity change (Rogers et al. 2006). The experiment is conducted by the Hurricane Research Division of the Atlantic Oceanographic and Meteorological Laboratory, the Aircraft Operations Center, the Environmental Modeling Center and the National Hurricane Center. The goal is to collect observations to aid in the improvement and development of operational models during all stages of the tropical cyclone lifecycle from genesis to decay. One particular emphasis is to gather observations during the extratropical transition (ET) of tropical cyclones that are not being impacted by land. As part of the effort to improve the operational numerical guidance, an ensemble- based data assimilation system was developed (Aksoy et al. 2012). The system, named the Hurricane Ensemble Data Assimilation System (HEDAS), is based on a serial implementation of the square root ensemble Kalman filter. It is configured with a horizontal grid spacing of 9/3 km on the outer/inner domains, with the latter about 1000 km square centered near the storm center. The largest data volume assimilated are wind radials from the Airborne Doppler radar aboard the NOAA P-3 aircraft (Aberson et al. 2006). Additional sources are dynamic and thermodynamic dropwindsonde and high-level flightlevel and surface wind-speed data from NOAA and Air Force research and reconnaissance aircraft. HEDAS was run for all cases in which Airborne Doppler Radar data are available from 2008-2011. One set of cases is from Hurricane Earl (2010) as it moved northward just off the United States east coast and began its ET. A series of six missions were conducted every 12 h from about 0800 UTC 01 September to 0400 UTC 04 September in the core of Earl as it strengthened into a Category 4 Hurricane and then began its ET. During this period, the NOAA G-IV aircraft obtained environmental dropwindsonde data once daily, and six operational reconnaissance missions were conducted by the United States Air Force C-130 aircraft. This series of 15 flights represents an unprecedented data set with which to explore the ET of a major hurricane over open water. An example of the type of analyses available are shown in Fig. 1, a series of north-south cross sections of HEDAS analyses through the center of Earl. During the first mission (A), a low- to midlevel double wind-speed maximum is seen on the west, north, and east sides (only north shown), suggesting an eyewall replacement cycle. The radius of maximum wind speed contracts (B), and then the wind field broadens (C), and another secondary wind-speed maximum develops 3 (D). As Earl begins moving over cool water north of the Gulf Stream (E), the wind field becomes relatively shallow and broadens, though some vestiges of the double-wind-speed maximum remain, and the asymmetry shifts so that the wind- speed maximum is to the south rather than the north. By the final mission before land interaction (F), the wind field is relatively shallow and very broad, and the highest wind speeds are now near 600 hPa. Concurrent with this process is a cooling of the mid- to upper-levels by more than 10K (not shown), signaling that transition to an extratropical cyclone is nearly complete. This analyses represent the first time the inner-core structure of a major hurricane undergoing ET away from land interaction has been sampled and studied. The presentation will include further research on the HEDAS analyses, both in terms of dynamic and thermodynamic quantities, and also of the high-resolution model runs initialized with these analyses. Figure 1: North-south cross sections in Hurricane Earl of tangential (shaded) and radial (contoured) wind speeds (ms-1) from HEDAS analyses of aircraft data. Analyses are valid every 12 h from 1200 UTC 01 September (A) to 0000 UTC 04 September (F) 2010. The thick vertical line represents the location of the 850 hPa wind center, and the thin vertical lines represent one degree longitude north and south of that center. References Aberson, S. D., M. L. Black, R. A. Black, J. J. Cione, C. W. Landsea, F. D. Marks, Jr., and R. W. Burpee, 2006: Thirty years of tropical cyclone research with the NOAA P-3 aircraft. Bull. Amer. Met. Soc., 87, 1039-1055. Aksoy, A., S. Lorsolo, T. Vukicevic, K. J. Sellwood, S. D. Aberson, and F. Zhang, 2012: The HWRF Hurricane Ensemble Data Assimilation System (HEDAS) for high- resolution data: The impact of airborne Doppler radar observations in an OSSE. Mon. Wea. Rev., in press. Rogers, R., S. Aberson, M. Black, P. Black, J. Cione, P. Dodge, J. Gamache, J. Kaplan, M. Powell, J. Dunion, E. Uhlhorn, N. Shay, and N. Surgi, 2006: The Intensity Forecasting Experiment: A NOAA multiyear field program for improving tropical cyclone intensity forecasts. Bull. Amer. Met. Soc., 4 87, 1523-1537. 1115 Heather M. Archambault, Patrick A. Harr, Richard W. Moore DEPARTMENT OF METEOROLOGY NAVAL POSTGRADUATE SCHOOL MONTEREY, CA 93943 Title: The Interaction Between Recurving Western North Pacific TC Chaba (2010) and the Extratropical Flow: A Diagnostic and Modeling Study In late October 2010, a complex interaction between recurving western North Pacific tropical cyclone (TC) Chaba and the extratropical flow helped to initiate a Rossby wave train that dispersed rapidly downstream to North America. The subsequent establishment of a high- amplitude ridge–trough pattern over North America provided favorable synoptic conditions for record-breaking heat over western North America and heavy rain over eastern North America. The objective of this study is to identify the physical and dynamical mechanisms linking the interaction between TC Chaba and the extratropical flow to the large-scale flow reconfiguration and high-impact weather that occurred downstream.
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