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Mesoscale Circulations during VTMX. John Horel Lacey Holland, Mike Splitt, Alex Reinecke jhorel@met.utah.edu. 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

Mesoscale Circulations during VTMX

John Horel

Lacey Holland, Mike Splitt,

Alex Reinecke

jhorel@met.utah.edu


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 4 9 october1
IOP-4 9 October

500 mb

Wheeler

SLC

700 mb





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



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