Download Fred Sanders` Contributions to Synoptic Meteorology

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