Transient Mountain Waves and Their Interaction with Large Scales
description
Transcript of Transient Mountain Waves and Their Interaction with Large Scales
ICAM/MAP2005ICAM/MAP2005 11
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
ICAM/MAP2005ICAM/MAP2005 22
Momentum Budget PerspectiveMomentum Budget Perspective
ICAM/MAP2005ICAM/MAP2005 33
Forcing for Zonal Mean FlowForcing for Zonal Mean Flow h = 1.5 km h = 1.5 km
ICAM/MAP2005ICAM/MAP2005 44
Global Response for h = 1.5 kmGlobal Response for h = 1.5 km
ICAM/MAP2005ICAM/MAP2005 55
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
ICAM/MAP2005ICAM/MAP2005 66
Difference fieldsDifference fieldst = 25 hours z = 1.5 km
ICAM/MAP2005ICAM/MAP2005 77
Difference fieldsDifference fieldsz = 1.5 km
ICAM/MAP2005ICAM/MAP2005 88
Difference fieldsDifference fieldst = 50 hours z = 1.5 km
ICAM/MAP2005ICAM/MAP2005 99
Difference fieldsDifference fieldst = 50 hours z = 3.5 km
ICAM/MAP2005ICAM/MAP2005 1010
Can the flow response be explained by balanced dynamics?
QGPV difference is inverted by using geostrophic balance
as the balance constraint.
ICAM/MAP2005ICAM/MAP2005 1111
u difference vs balanced uu difference vs balanced ut = 50 hours z = 1.5 km
ICAM/MAP2005ICAM/MAP2005 1212
u difference vs balanced uu difference vs balanced ut = 50 hours z = 3.5 km
ICAM/MAP2005ICAM/MAP2005 1313
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?
ICAM/MAP2005ICAM/MAP2005 1414
GWD Parameterization ExperimentGWD Parameterization ExperimentAssuming:Gravity wave drag is deposited in the mountainous region (area = ) only.
ICAM/MAP2005ICAM/MAP2005 1515
GWD Parameterization Experiment GWD Parameterization Experiment 72 km
(exact) (GWD Exp.)
t = 50 hours z = 3.5 km
-6 m/s -1 m/s
ICAM/MAP2005ICAM/MAP2005 1616
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.