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Fred Sanders’ Contributions to Synoptic Meteorology: Perspectives on his Cold-Frontal Research David M. Schultz Cooperative Institute for Mesoscale Meteorological Studies, University of Okalhoma, and NOAA/National Severe Storms Laboratory, Norman, Oklahoma Eliassen 80th Birthday Party, March 1996 Endicott House, Dedham, Massachusetts The Fred Sanders Symposium, Seattle 2004 MIT and the Green Building Fred Sanders’ Three Major Achievements in Synoptic Meteorology Fred Sanders, and some of his students and grandstudents (1997 Cyclone Workshop) 1. Explosive Cyclogenesis 2. Shortwave Troughs 3. Cold Fronts “A perusal of the titles of the more than 100 articles in the Compendium would leave the uninitiated reader with the impression that there are no such things as fronts and air masses.” – Taljaard et al. (1961), writing about the Compendium of Meteorology (1951) “Sometimes I wonder whatever happened to fronts? . . . Fronts have passed through a sort of Dark Age of neglect in which only a loyal few worried very much about them.” – Sanders (1967) Significant Conclusions of Sanders (1955) Fronts are strongest at the surface and weaken with altitude (cf. Hoskins and Bretherton 1972). A narrow plume of rising warm air exists above the surface frontal position (cf. Keyser and Anthes 1982). Warm air is entrained into the frontal zone near the ground (i.e., the front is not a material surface). (Sanders 1955, Fig.10) Further Study of Cold Fronts: Sanders (1967, 1999a,b) Sanders (1999a,b) covers Principal Conclusions of Sanders (1967, 1999a,b) A surface pressure trough and wind shift (prefrontal trough) often precedes the temperature gradient (front). The relationship between the trough and the front is important for frontogenesis/frontolysis. Sanders (1967) Sanders (1999a) 1200 UTC 4 March 0000 UTC 5 March 1200 UTC 8 March 0000 UTC 9 March 30 1030 20 15 10 5 0 PRESSURE PRESSURE FRONT PREFRONTAL WIND SHIFT 25 1020 T EMPERAT URE TEMPERATURE 1010 DEW POINT DEWPOINT -5 1000 SEA LEVEL PRESSURE (hPa) TEMPERATURE AND DEWPOINT (°C) FORT SILL, OKLAHOMA (FSI) FORT SILL, OKLAHOMA (FSI) -10 990 17/00 17/03 17/06 17/09 17/12 17/15 17/18 17/21 18/00 18/03 18/06 18/09 18/12 18/15 18/18 18/21 17 – 18 APRIL APRIL 1953 17–18 1953 the front analyzed by Sanders (1955) COLD AIR Kansas Oklahoma Texas L Sanders (1955) MM5 Simulation (Paul Roebber) • FSI COLD AIR 1800 UTC 17 April 1953 L • FSI COLD AIR 0000 UTC 18 April 1953 • FSI L red lines: 1000-hPa geopotential height (every 10 m) green arrows: 1000-hPa winds yellow surface: q < 293 K L= center of 1000-hPa circulation 0600 UTC 18 April 1953 “It often appears, however, that one or more wind shifts precede the zone of temperature contrast in cold fronts. . . . The origins of such lines are not typically well known and they may arise from more than one source.” – Sanders and Doswell (1995) Mechanisms for Prefrontal Troughs External to the front – – – – – Synoptic-scale forcing Interacting lower and midtropospheric fronts Lee troughs, drylines, or topographic effects Translating axis of dilatation Inhomogeneities in the prefrontal air Internal to the front – – – – – – Along-front temperature gradients (proposed by Sanders) Moist processes Prefrontal descent of air Ascent of air at the front Mixing at the front Prefrontal bores or gravity waves (from Schultz 2004, submitted) AMS CONFERENCES ON MESOSCALE PROCESSES: PRESENTATIONS ON "FRONTS AND FRONTOGENESIS" 300 20 250 15 200 TOTAL NUMBER OF PRESENTATIONS 150 10 100 5 50 NUMBER OF PRESENTATIONS ON FRONTS 0 0 1985 1990 1995 YEAR 2000 PERCENTAGE TOTAL NUMBER OF PRESENTATIONS and NUMBER OF PRESENTATIONS ON FRONTS PERCENTAGE “This complexity should not be cause for despair! It is what is there and to deny it cannot benefit forecast accuracy.” – Sanders (1999a) Sailing in Boston Harbor, August 1999