Fred Sanders’ Contributions to

Synoptic Meteorology:

Perspectives on his Cold-Frontal Research

David M. SchultzCooperative Institute for Mesoscale

Meteorological Studies, University of Okalhoma, and NOAA/National Severe Storms Laboratory, Norman, Oklahoma

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

MIT and the Green Building

Fred Sanders’ Three Fred Sanders’ Three Major Achievements in Major Achievements in Synoptic MeteorologySynoptic Meteorology

Fred Sanders, and some of his students and grandstudents(1997 Cyclone Workshop)

1. Explosive Cyclogenesis1. Explosive Cyclogenesis

2. Shortwave Troughs2. Shortwave Troughs

3. Cold Fronts3. Cold Fronts

““A perusal of the titles of the more than 100 articles in A perusal of the titles of the more than 100 articles in the the Compendium Compendium would leave the uninitiated reader with would leave the uninitiated reader with

the impression that there are no such things as fronts the impression that there are no such things as fronts and air masses.”and air masses.”

– Taljaard et al. (1961), – Taljaard et al. (1961), writing about the writing about the Compendium of MeteorologyCompendium of Meteorology (1951) (1951)

“Sometimes I wonder whatever happened to fronts? . . . “Sometimes I wonder whatever happened to fronts? . . . Fronts have passed through a sort of Dark Age of Fronts have passed through a sort of Dark Age of neglect in which only a loyal few worried very much neglect in which only a loyal few worried very much

about them.”about them.”

– Sanders (1967)– Sanders (1967)

Significant Conclusions of Significant Conclusions of Sanders (1955)Sanders (1955)

Fronts are strongest at the surface and Fronts are strongest at the surface and weaken with altitudeweaken with altitude (cf. Hoskins and (cf. Hoskins and Bretherton 1972).Bretherton 1972).

A narrow plume of rising A narrow plume of rising warm warm air exists above the air exists above the surface surface frontal position frontal position (cf. (cf. Keyser and Keyser and Anthes 1982).Anthes 1982).

Warm air is entrained into the frontal zone Warm air is entrained into the frontal zone near the ground (i.e., the front is not a near the ground (i.e., the front is not a material surface). material surface).

(Sanders 1955, Fig.10)

Further Study of Cold Fronts: Further Study of Cold Fronts: Sanders (1967, 1999a,b)Sanders (1967, 1999a,b)

Sanders (1999a,b)covers

Principal Conclusions of Principal Conclusions of Sanders (1967, 1999a,b)Sanders (1967, 1999a,b)

A surface pressure trough and wind A surface pressure trough and wind shift (shift (prefrontal troughprefrontal trough) often precedes ) often precedes the temperature gradient (the temperature gradient (frontfront).).

The relationship between the trough The relationship between the trough and the front is important for and the front is important for frontogenesis/frontolysis.frontogenesis/frontolysis.

Sanders (1967)

Sanders (1999a)

1200 UTC 4 March 0000 UTC 5 March

1200 UTC 8 March 0000 UTC 9 March

PR

EF

RO

NT

AL

WIN

D S

HIF

T

FR

ON

T17/00 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

-10

-5

0

5

10

15

20

25

30

990

1000

1010

1020

1030

17 – 18 APRIL 1953

TEMPERATURE

DEWPOINT

PRESSURE

FORT SILL, OKLAHOMA (FSI)FORT SILL, OKLAHOMA (FSI)

17–18 APRIL 1953

TE

MP

ER

AT

UR

E A

ND

DE

WP

OIN

T (

°C)

SE

A L

EV

EL

PR

ES

SU

RE

(hP

a)

PRESSURE

TEMPERATURE

DEWPOINT

the front analyzed by Sanders (1955)

Sanders (1955) MM5 Sanders (1955) MM5 Simulation Simulation (Paul Roebber)(Paul Roebber)

1800 UTC 17 April 1953

0000 UTC 18 April 1953

0600 UTC 18 April 1953

•FSI

Kansas

OklahomaTexas

L

L

Lred lines: 1000-hPa geopotential height (every 10 m) green arrows: 1000-hPa windsyellow surface: < 293 KL= center of 1000-hPa circulation

COLD AIR

COLD AIR

COLD AIR

•FSI

•FSI

““It often appears, however, that one or It often appears, however, that one or more wind shifts precede the zone of more wind shifts precede the zone of

temperature contrast in cold fronts. . . . temperature contrast in cold fronts. . . . The origins of such lines are not typically The origins of such lines are not typically well known and they may arise from more well known and they may arise from more

than one source.”than one source.”

– Sanders and Doswell (1995)– Sanders and Doswell (1995)

Mechanisms for Prefrontal TroughsMechanisms for Prefrontal Troughs External to the frontExternal to the front

– Synoptic-scale forcingSynoptic-scale forcing– Interacting lower and midtropospheric frontsInteracting lower and midtropospheric fronts– Lee troughs, drylines, or topographic effectsLee troughs, drylines, or topographic effects– Translating axis of dilatationTranslating axis of dilatation– Inhomogeneities in the prefrontal airInhomogeneities in the prefrontal air

Internal to the frontInternal to the front– Along-front temperature gradients Along-front temperature gradients (proposed by Sanders)(proposed by Sanders)

– Moist processesMoist processes– Prefrontal descent of airPrefrontal descent of air– Ascent of air at the frontAscent of air at the front– Mixing at the frontMixing at the front– Prefrontal bores or gravity wavesPrefrontal bores or gravity waves

(from Schultz 2004, submitted)

0

50

100

150

200

250

300

0

5

10

15

20

1985 1990 1995 2000

AMS CONFERENCES ON MESOSCALE PROCESSES:PRESENTATIONS ON "FRONTS AND FRONTOGENESIS"

TOTAL NUMBER OF PRESENTATIONS and NUMBER OF PRESENTATIONS ON FRONTS

PERCENTAGE

PERCENTAGE

TOTAL NUMBER OF PRESENTATIONS

NUMBER OF PRESENTATIONSON FRONTS

YEAR

““This complexity should not be cause for despair! It is what This complexity should not be cause for despair! It is what is there and to deny it cannot benefit forecast accuracy.”is there and to deny it cannot benefit forecast accuracy.”

– Sanders (1999a)– Sanders (1999a)

Sailing in Boston Harbor, August 1999