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 The Fred Sanders Symposium, Seattle 2004 Eliassen 80th Birthday Party, March 1996 Endicott House, Dedham, Massachusetts

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) n Fronts are strongest at the surface and weaken with altitude (cf. Hoskins and Bretherton 1972). n A narrow plume of rising warm air exists above the surface frontal position (cf. Keyser and Anthes 1982). n 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) n A surface pressure trough and wind shift (prefrontal trough) often precedes the temperature gradient (front). n The relationship between the trough and the front is important for frontogenesis/frontolysis.

Sanders (1967) Sanders (1999a)

1200 UTC 4 March0000 UTC 5 March 1200 UTC 8 March 0000 UTC 9 March

PREFRONTAL WIND SHIFT FRONT FORT SILL, OKLAHOMA (FSI) 17–18 APRIL 1953 TEMPERATURE AND DEWPOINT (°C) SEA LEVEL PRESSURE (hPa) PRESSURE TEMPERATURE DEWPOINT the front analyzed by Sanders (1955)

Sanders (1955) MM5 Simulation (Paul Roebber) 1800 UTC 17 April UTC 18 April UTC 18 April 1953 FSI Kansas Oklahoma Texas L L L red lines: 1000-hPa geopotential height (every 10 m) green arrows: 1000-hPa winds yellow surface:  < 293 K L= center of 1000-hPa circulation COLD AIR FSI

“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 n 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 n 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)

“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