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

  2. Overview • Temporal and spatial context for VTMX IOPs • Synoptic and mesoscale conditions during IOPs

  3. October 1999 500 mb geopotential height

  4. October 1999 500 mb geopotential height anomaly

  5. October 2000 500 mb geopotential height

  6. October 2000 500 mb geopotential height anomaly Cooler and wetter than normal PM-10 concentrations half those in October 1999

  7. MesoWest • Data available from January 1997 to present • www.met.utah.edu/mesowest • Paper describing MesoWest submitted to BAMS 9 Oct. 0900 UTC

  8. Diurnal Temperature Range: Fall Alex Reinecke MesoWest Observations 1997-2000

  9. Diurnal Temperature Range- FallLatitude vs. Elevation SLC

  10. Tooele Valley Rush Valley Salt Lake Valley Diurnal Temperature Range: October 2000

  11. October 2000: Salt Lake Valley Great Salt Lake: 21C- 10C SLC U42

  12. 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

  13. 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.

  14. 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

  15. IOP-8: 9 UTC 20 October 500 mb 700 mb SLC

  16. 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

  17. 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

  18. IOP-4 9 October 500 mb Wheeler SLC 700 mb

  19. 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

  20. 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

  21. IOP 9- 3UTC 21 October 500 mb 700 mb

  22. 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

  23. IOP-1 300 UTC 3 October 6UTC

  24. IOP 2: 1200 UTC 7 October

  25. IOP 3- 300 UTC 8 October 0Z

  26. IOP-4 9 October 500 mb Wheeler SLC 700 mb

  27. IOP 5 600 UTC 15 October

  28. IOP 6 12 UTC 16 October

  29. IOP 7 600 UTC 18 October

  30. IOP-8: 9 UTC 20 October 500 mb 700 mb SLC

  31. IOP 9- 3UTC 21 October 500 mb 0Z 700 mb

  32. IOP-10 600 UTC 26 October

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