meeting review Eighth Cyclone Workshop Scientific Summary, Val Morin, Quebec, Canada, 12-16 October 1992 Rainer Bleck,* Howard Bluestein,+ Lance Bosart,@ W. Edward Bracken,@ Toby Carlson,++ Jeffrey Chapman,@ Michael Dickinson,@ John R. Gyakum,++ Gregory Hakim,@ Eric Hoffman,@ Haig lskenderian,@ Daniel Keyser,@ Gary Lackmann,@ Wendell Nuss,@@ Paul Roebber,@ Frederick Sanders,*** David Schultz,@ Kevin Tyle,@ and Peter Zwack+++ Abstract in the Washington, D.C., area in October 1978. Donald Johnson chaired a preliminary planning meeting (at- The Eighth Cyclone Workshop was held at the Far Hills Inn and tending were Lance Bosart, John Cahir, John Conference Center in Val Morin, Quebec, Canada, 12-16 October Hovermale, Carl Kreitzberg, Chester Newton, Norman 1992. The workshop was arranged around several scientific themes Phillips, Frederick Sanders, Phillip Smith, Ronald Tay- of current research interest. The most widely debated theme was the applicability of "potential vorticity thinking" to theoretical, observa- lor, Dayton Vincent, and Johnson) in which it was tional, and numerical studies of the life cycle of cyclones and the generally agreed that a focused research effort on the interaction of these cyclones with their environment on all spatial extratropical cyclone should be initiated and carried and temporal scales. A combination of invited and contributed talks, out, and the findings debated at periodic scientific with preference given to younger scientists, made up the workshop. workshops. Johnson agreed to serve as the chair of the informal Extratropical Cyclone Project Steering Com- 1. Workshop background mittee (other steering committee members included David Baumhefner, Bosart, Hovermale, Smith, Taylor, Working scientists and students interested in cy- and Vincent), which would arrange and organize the clone-related research problems have used the venue workshops. of periodic cyclone workshops to exchange ideas and Table 1 lists the eight cyclone workshops that have information from observational, theoretical, and nu- been held to date. The first meeting was held at the merical studies of cyclogenesis and the life cycle of National Meteorological Center (NMC) during 30 May- cyclones. This article reports on the most recent cy- 1 June 1979. Subsequent meetings alternated be- clone workshop gathering, held at the Far Hills Inn and tween a location at or near NMC (to encourage partici- Conference Center in Val Morin, Quebec, Canada, pation by operational meteorologists and modelers) during 12-16 October 1992. and elsewhere. After the seventh gathering, at the The idea to conduct cyclone workshops was first Drexel Lodge in Newton Square, Pennsylvania, in explored during the American Meteorological Society's October 1988, a brief hiatus occurred before the most (AMS) Weather Analysis and Forecasting Conference recent workshop, in October 1992. Smith took the lead in rekindling interest in the cyclone workshop by chair- ing an informal gathering of interested participants at *Rosenstiel School of Marine and Atmospheric Science, University the AMS Annual Meeting in Atlanta, Georgia, in Janu- of Miami, Miami, Florida +School of Meteorology, The University of Oklahoma, Norman, ary 1992. A new steering committee was formed (mem- Oklahoma bers were Bosart, Daniel Keyser, Johnson, Patricia @Department of Atmospheric Science, State University of New York Pauley, Donald Perkey, Melvyn Shapiro, and Smith) to at Albany, Albany, New York oversee the effort. Bosart was "elected" (by virtue of **Department of Meteorology, The Pennsylvania State University, being absent from the discussion—he was elsewhere University Park, Pennsylvania ++Department of Atmospheric and Oceanic Sciences, McGill in the hotel attending another meeting) as workshop University, Montreal, Quebec, Canada coordinator and convenor of the Eighth Cyclone Work- @@Department of Meteorology, Naval Postgraduate School, shop, held during October 1992. Preference was given Monterey, California to younger scientists and graduate students in the ***Marblehead, Massachusetts scheduled talks, and younger scientists were also +++Department of Physics, University of Quebec at Montreal, Montreal, Quebec, Canada invited to give some of the theme talks. A principal ©1993 American Meteorological Society driving force behind the workshop was a desire by Bulletin of the American Meteorological Society 1361 Unauthenticated | Downloaded 10/08/21 10:14 PM UTC ing upward from the surface (stalagmites) TABLE 1. Cyclone Workshop Meeting History and of stratospheric anomalies extending downward from the tropopause (stalactites). Workshop He expressed hope that his method of com- Number Date Location bining the two classical ingredients of extrat- ropical cyclogenesis in a single picture will aid 1 30 May-1 June 1979 Washington, D.C. (NMC) the understanding of baroclinic instability and 2 9-11 July 1980 University Park, Pennsylvania will allow the operational and theoretical com- 3 9-11 March 1982 Washington, D.C. (NMC) munities to describe this process in mutually 4 2-4 November 1983 Madison, Wisconsin understandable terms. 5 22-25 April 1985 Port Deposit, Maryland 6 16-20 February 1987 Pacific Grove, California Baroclinic instability in the Eady model is 7 18-21 October 1988 Newtown Square, Pennsylvania characterized by zero interior PV gradients 8 16-20 October 1992 Val Morin, Quebec, Canada and is driven entirely by boundary tempera- ture gradients. Consistent with this behavior, plots showing the evolution of an Eady mode depicted isentropic absolute vorticity stalag- participants to debate the value of "potential vorticity mites and stalactites growing into the interior of the domain. (PV) thinking." Sanders challenged the group to show Finally, Bleck speculated on the causes of our inabil- how much more has been learned about the structure ity to predict intensity changes in hurricanes. He sur- and behavior of cyclones through "PV thinking" than mises that diabatic heating in the ascending air leads to through the established "omega equation thinking" or an accumulation of anticyclonic PV in the upper part of "Sutcliffe development thinking." The challenge (bait?) a hurricane. Unless the surrounding atmosphere has was taken up eagerly by other scientists. similar PV values, this air will be dynamically con- The workshop review appears in session order. Two strained from flowing out to the sides, and the hurricane authors are listed for each session: the session chair weakens "under its own weight." Bleck asserts that first and the session note taker second. successful prediction of hurricane intensification will not be possible until PV can be measured reliably both in the upper part of the vortex and in the surrounding 2. Workshop overview environment. Presently, no prospects exist for obtain- ing the required data. a. "PV thinking"—Daniel Keyser and Gary Lackmann Next, Christopher Davis discussed various aspects This session began with a presentation by Rainer regarding the application of PV thinking to the real Bleck entitled "Who Needs Potential Vorticity?" This atmosphere. A broad topic was that of "direct" versus question rapidly crystallized into one of the main themes "indirect" effects. As an example, Davis considered an of the workshop. Bleck's hypothesis is that PV can be interior diabatic heat source. A direct effect is the used to remove misconceptions and to replace need- diabatic alteration of PV due to the heating; an indirect lessly complicated dynamical theories with simpler effect is the alteration of the background PV field ones. As an example of a (common) misconception, he through advection by the flow induced by these showed a newspaper weather map that explained diabatically generated anomalies. Another significant weather events as being caused by high or low atmo- topic dealt with inversion of individual PV anomalies. spheric pressure. An example of a needlessly compli- Three possible ways to define PV anomalies are in cated dynamical theory that still does not penetrate to terms of 1) a departure from a spatial or a temporal the heart of the matter, in his opinion, is the one dealing mean, 2) the difference between two instantaneous with secondary circulations associated with the defor- states ascertained, for example, from parallel model mation of the mass field near jet streaks. integrations in which particular physical processes are Bleck proceeded to point out links between jet streaks. included or excluded (i.e., the sensitivity approach), Petterssen type B cyclogenesis, the Eady model, and and 3) changes in PV due to advection and non- PV thinking. As a means of depicting the linkage conservative processes determined through explicit between PV and cyclogenesis graphically, Bleck pre- integration of PV conservation equations. In order sented three-dimensional wire-mesh plots illustrating to isolate net differences in PV due to diabatic pro- the phase relationship between upper- and lower- cesses, an adiabatic mesoscale model simulation was tropospheric PV perturbations during extratropical cy- contrasted with a full-physics run. An explicit PV inte- clogenesis. Bleck stated that representation in isen- gration was used in conjunction with the full-physics run tropic space allows depiction of surface-trapped PV to isolate the portion of the total PV difference due to anomalies in terms of absolute vorticity spikes protrud- direct diabatic PV alteration. The full-physics run exhib- 1362 Vol. 74, No. 7, July 1993 Unauthenticated | Downloaded 10/08/21