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Transient Mountain Waves and Their Interaction with Large Scales

Transient Mountain Waves and Their Interaction with Large Scales. Chih-Chieh Chen, Gregory J. Hakim and Dale R. Durran Department of Atmospheric Sciences University of Washington, USA May 26, 2005. Momentum Budget Perspective. Forcing for Zonal Mean Flow h = 1.5 km.

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Transient Mountain Waves and Their Interaction with Large Scales

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  1. Transient Mountain Waves and Their Interaction with Large Scales Chih-Chieh Chen, Gregory J. Hakim and Dale R. Durran Department of Atmospheric Sciences University of Washington, USA May 26, 2005 ICAM/MAP2005

  2. Momentum Budget Perspective ICAM/MAP2005

  3. Forcing for Zonal Mean Flow h = 1.5 km ICAM/MAP2005

  4. Global Response for h = 1.5 km ICAM/MAP2005

  5. The dynamics of the large-scale flow is well known • in the absence of a mountain. Spatial Response 2. We may define “difference fields” as ICAM/MAP2005

  6. Difference fields t = 25 hours z = 1.5 km ICAM/MAP2005

  7. Difference fields z = 1.5 km ICAM/MAP2005

  8. Difference fields t = 50 hours z = 1.5 km ICAM/MAP2005

  9. Difference fields t = 50 hours z = 3.5 km ICAM/MAP2005

  10. Can the flow response be explained by balanced dynamics? QGPV difference is inverted by using geostrophic balance as the balance constraint. ICAM/MAP2005

  11. u difference vs balanced u t = 50 hours z = 1.5 km ICAM/MAP2005

  12. u difference vs balanced u t = 50 hours z = 3.5 km ICAM/MAP2005

  13. Implication of PV Inversion • What is the effect of GWD? • Can we recover the spatial response by using a GWD parameterization scheme? ICAM/MAP2005

  14. GWD Parameterization Experiment Assuming: Gravity wave drag is deposited in the mountainous region (area = ) only. ICAM/MAP2005

  15. (exact) (GWD Exp.) -6 m/s -1 m/s GWD Parameterization Experiment 72 km t = 50 hours z = 3.5 km ICAM/MAP2005

  16. Summary • For highly nonlinear cases, the wave packet accumulation mechanism to induce low-level mean flow acceleration is absent due to severe wave dissipation. • A broad region of flow deceleration extends far downstream from the mountain with patches of flow acceleration north and south of it. • Despite the small scales of PV anomalies generated by wave breaking, QGPV inversion recovers most of the actual response. • The experiment with a “perfect” GWD parameterization fails to produce enough spatial flow deceleration/acceleration. ICAM/MAP2005

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