transient mountain waves and their interaction with large scales
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Transient Mountain Waves and Transient Mountain Waves and Their Interaction with Large ScalesTheir Interaction with Large Scales
Chih-Chieh Chen,Chih-Chieh Chen, Gregory J. Hakim and Dale R. DurranGregory J. Hakim and Dale R. Durran
Department of Atmospheric SciencesDepartment of Atmospheric SciencesUniversity of Washington, USAUniversity of Washington, USA
May 26, 2005May 26, 2005
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Momentum Budget PerspectiveMomentum Budget Perspective
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Forcing for Zonal Mean FlowForcing for Zonal Mean Flow h = 1.5 km h = 1.5 km
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Global Response for h = 1.5 kmGlobal Response for h = 1.5 km
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Spatial ResponseSpatial Response
1.The dynamics of the large-scale flow is well known in the absence of a mountain.
2. We may define “difference fields” as
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Difference fieldsDifference fieldst = 25 hours z = 1.5 km
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Difference fieldsDifference fieldsz = 1.5 km
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Difference fieldsDifference fieldst = 50 hours z = 1.5 km
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Difference fieldsDifference fieldst = 50 hours z = 3.5 km
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Can the flow response be explained by balanced dynamics?
QGPV difference is inverted by using geostrophic balance
as the balance constraint.
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u difference vs balanced uu difference vs balanced ut = 50 hours z = 1.5 km
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u difference vs balanced uu difference vs balanced ut = 50 hours z = 3.5 km
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Implication of PV InversionImplication of PV Inversion
What is the effect of GWD? Can we recover the spatial response by using
a GWD parameterization scheme?
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GWD Parameterization ExperimentGWD Parameterization ExperimentAssuming:Gravity wave drag is deposited in the mountainous region (area = ) only.
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GWD Parameterization Experiment GWD Parameterization Experiment 72 km
(exact) (GWD Exp.)
t = 50 hours z = 3.5 km
-6 m/s -1 m/s
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SummarySummary
For highly nonlinear cases, the wave packet accumulation For highly nonlinear cases, the wave packet accumulation mechanism to induce low-level mean flow acceleration is mechanism to induce low-level mean flow acceleration is absent due to severe wave dissipation.absent due to severe wave dissipation.
A broad region of flow deceleration extends far downstream A broad region of flow deceleration extends far downstream from the mountain with patches of flow acceleration north and from the mountain with patches of flow acceleration north and south of it.south of it.
Despite the small scales of PV anomalies generated by wave Despite the small scales of PV anomalies generated by wave breaking, QGPV inversion recovers most of the actual breaking, QGPV inversion recovers most of the actual response.response.
The experiment with a “perfect” GWD parameterization fails to The experiment with a “perfect” GWD parameterization fails to produce enough spatial flow deceleration/acceleration.produce enough spatial flow deceleration/acceleration.