Mesoscale circulations during vtmx
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Mesoscale Circulations during VTMX. John Horel Lacey Holland, Mike Splitt, Alex Reinecke [email protected] Overview. Temporal and spatial context for VTMX IOPs Synoptic and mesoscale conditions during IOPs. October 1999. 500 mb geopotential height. October 1999.

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Mesoscale Circulations during VTMX

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Mesoscale circulations during vtmx

Mesoscale Circulations during VTMX

John Horel

Lacey Holland, Mike Splitt,

Alex Reinecke

[email protected]


Overview

Overview

  • Temporal and spatial context for VTMX IOPs

  • Synoptic and mesoscale conditions during IOPs


October 1999

October 1999

500 mb geopotential height


October 19991

October 1999

500 mb geopotential height anomaly


October 2000

October 2000

500 mb geopotential height


October 20001

October 2000

500 mb geopotential height anomaly

Cooler and

wetter than

normal

PM-10

concentrations

half those in

October 1999


Mesowest

MesoWest

  • Data available from January 1997 to present

  • www.met.utah.edu/mesowest

  • Paper describing MesoWest submitted to BAMS

9 Oct. 0900 UTC


Diurnal temperature range fall

Diurnal Temperature Range: Fall

Alex Reinecke

MesoWest

Observations

1997-2000


Diurnal temperature range fall latitude vs elevation

Diurnal Temperature Range- FallLatitude vs. Elevation

SLC


Diurnal temperature range october 2000

Tooele

Valley

Rush

Valley

Salt Lake

Valley

Diurnal Temperature Range: October 2000


October 2000 salt lake valley

October 2000: Salt Lake Valley

Great Salt Lake: 21C- 10C

SLC

U42


Surface wind convergence in salt lake valley

Surface Wind Convergence in Salt Lake Valley

IOP 1

IOP 3

IOP 4

IOP 2

IOP 5

IOP 6

IOP 7

IOP 8

IOP 9

IOP 10

Mike Splitt- Linear regression fit


Stability and wind

Stability and Wind

  • Surface-based inversions (greater than 5C in the lowest 100 mb) observed during 15 of the 31 morning (1200 UTC) soundings at the Salt Lake City International Airport

  • Weak surface inversions with stable layers aloft below the crest of the Wasatch Mountains on 5 other mornings

  • Well-mixed conditions present during the other 11 mornings

  • Winds at 700 mb (near the crest of the Wasatch Mountains) were less than 10 m/s in 19 of the 31 morning soundings.


Iops with well developed drainage circulations

IOPs with Well-Developed Drainage Circulations

  • 5 (14-15 October)

  • 6 (15-16 October)

  • 8 (19-20 October)

  • Clear skies, weak winds aloft at crest level, strong nocturnal radiational inversions

  • Limited moisture in the boundary layer

  • Pronounced drainage flow into the Salt Lake Valley from the west, south, and east

  • Surface based inversions and drainage circulations developed after sunset  and persisted without significant interruption until sunrise


Iop 8 9 utc 20 october

IOP-8: 9 UTC 20 October

500 mb

700 mb

SLC


Iops modulated by synoptic and mesoscale systems

IOPs Modulated by Synoptic and Mesoscale Systems

  • IOP 1 ( 2-3 October)

  • Test operational procedures

  • During evening:

    • clear skies with drainage flows developing as the evening progressed

  • Synoptic-scale northerly pressure gradient developed overnight

    • Northerly winds penetrated into northern end of the Salt Lake Valley before midnight

    • Eventually  reversed the down-valley (southerly) flow through the center of the valley

    • Drainage circulations down into the valley from the Oquirrh and  Wasatch Mountains were largely unaffected


Iops modulated by synoptic and mesoscale weather systems

IOPs modulated by synoptic and mesoscale weather systems

  • IOP 4 (8-9 October), IOP 7 (17-18 October)

  • Similar boundary-layer structure to that in IOPs 5, 6, 8 until early morning

  • Prior to that time, clear skies, weak winds aloft, and strong surface-based radiational inversions

  • As a result of approaching upper-level troughs from the west, the nocturnal inversions eroded both by surface heating and by mixing due to the downward penetration of southerly winds


Iop 4 9 october

IOP-4 9 October

500 mb

Wheeler

SLC

700 mb


Iops modulated by synoptic and mesoscale systems1

IOPs Modulated by Synoptic and Mesoscale Systems

  • IOP 2 (6-7 October) and 3 (7-8 October)

  • Split flow aloft with weak upper-level short waves to the southwest and northeast of Utah

  • Strong outbreak of cold air to the east of the continental divide progressed westward after 0 UTC

  • After 1000 UTC, the depth of the cold air  to the east of the Wasatch Mountains built to sufficient height to spill over the lower terrain from Mill Creek Canyon to near the University of Utah in the northeast corner of the Salt Lake Valley

  • IOP-3 began at 2200 UTC 7 October and was terminated before midnight

  • Strong downslope conditions persisted into the evening in the northeastern corner of the Salt Lake Valley

  • Winds in the western part of the valley were turbulent


Iops modulated by synoptic and mesoscale systems2

IOPs Modulated by Synoptic and Mesoscale Systems

  • IOP 9 (20-21 October ) and IOP 10 (25-26 October)

  • Affected significantly by approaching upper-level troughs.

  • weak short-wave ridge aloft initially

  • Skies were broken to overcast

  • Weak nocturnal surface inversion and drainage circulations

  • Cold-front at 1200 UTC 21 October

  • Southerly surface winds were enhanced during IOP 10


Iop 9 3utc 21 october

IOP 9- 3UTC 21 October

500 mb

700 mb


Summary

Summary

  • Mountain/valley circulations and radiational inversions occurred on over half of the days

  • Local circulations dominated several IOPs (5, 6, 8)- but each had unique characteristics

  • Synoptic and mesoscale influenced IOPs:

    • IOP 1: interruption of drainage circulations in the north end of the Salt Lake Valley

    • IOPs 2, 3: downslope wind event

    • IOPs 4, 7: erosion of invesion from aloft

    • IOPs 9, 10: approaching weather systems


Iop 1 300 utc 3 october

IOP-1 300 UTC 3 October

6UTC


Iop 2 1200 utc 7 october

IOP 2: 1200 UTC 7 October


Iop 3 300 utc 8 october

IOP 3- 300 UTC 8 October

0Z


Iop 4 9 october1

IOP-4 9 October

500 mb

Wheeler

SLC

700 mb


Iop 5 600 utc 15 october

IOP 5 600 UTC 15 October


Iop 6 12 utc 16 october

IOP 6 12 UTC 16 October


Iop 7 600 utc 18 october

IOP 7 600 UTC 18 October


Iop 8 9 utc 20 october1

IOP-8: 9 UTC 20 October

500 mb

700 mb

SLC


Iop 9 3utc 21 october1

IOP 9- 3UTC 21 October

500 mb

0Z

700 mb


Iop 10 600 utc 26 october

IOP-10 600 UTC 26 October


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