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Precipitation over Narrow Mountain Ranges

Precipitation over Narrow Mountain Ranges. Ethan Gutmann Roy Rasmussen, Greg Thompson, David Gochis , Kyoko Ikeda, Changhai Liu, Jimy Dudhia , Martyn Clark. Problem Definition. Precipitation: snow Narrow: ~10km (the physics apply to all ranges) Mountain: >1km high. The Question?.

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Precipitation over Narrow Mountain Ranges

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  1. Precipitation over Narrow Mountain Ranges Ethan Gutmann Roy Rasmussen, Greg Thompson, David Gochis, Kyoko Ikeda, Changhai Liu, JimyDudhia, Martyn Clark

  2. Problem Definition Precipitation: snow Narrow: ~10km (the physics apply to all ranges) Mountain: >1km high

  3. The Question? Why are PRISM and WRF different, and which is correct? Wind

  4. The Question? Or is the Linear Theory model correct? (Smith and Barstad 2004) Wind

  5. The Question? Or is the Linear Theory model correct? (Smith and Barstad 2004) Wind With unrealistic parameters

  6. The hypothesis Strong updrafts on the upwind side of the mountain carry snow to the downwind side, where opposing downdrafts hurry the snow to the ground. … but no solid evidence

  7. For Reference: Enhanced Model precipitation in lee Enhanced RADAR reflectivity in lee Colle et al., 2000; Medina et al., 2004; Garvert et al., 2007 … but no solid evidence

  8. Stepping back…

  9. The Test Measurements of snow in the Sangre de Cristo Mountains 10km wide, 1.5km high, ~100km upwind fetch

  10. Modeling W (m/s) Updrafts in WRF reach >4m/s Terminal velocity of snow is ~1m/s Note: stronger downdrafts

  11. The Test In the trees : ~3400m NCAR Snow depth SNOTEL Snow depth

  12. The Test NCAR Snow depth SNOTEL Snow depth Wind

  13. Site Photos NCAR Site SNOTEL Site

  14. Initial Data

  15. Initial Data

  16. Wind direction

  17. Wind direction

  18. The Test Wind

  19. Other Mountains Wind

  20. Future Climate? Apparent decrease in the future (relatively more on upwind). NOTE: PGW is rescaled to match NARR mean, it increases everywhere

  21. Conclusions Snow preferentially falls in the lee of narrow mountain ranges. This effect is likely to decrease in the future, but this decrease is relatively small. This may lead to more water in upwind watersheds.

  22. Thanks Photo:Greg Thompson

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