lecture 1: tropical wave dynamics · be bounded . as. y substituting (2) into (1) and eliminate u...
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Tropical wave dynamics and Heat- induced steady response
Bin Wang
Department of Meteorology andIPRC, University of Hawaii
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Outline
I Equatorial wave motionII. Heat‐induced steady motionIII How mean flow affect wave and responses
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Reference reading
• Matsuno, T., 1966: Quasi‐geostrophic
motion in the equatorial area, JMSJ, 44, 25‐43.
• Gill, AE, 1980: Some simple solutions for heat‐induced tropical motion. Quart. J. Roy. Met. Soc., 449, 447‐462.
• Wang, B. 2003, Kelvin Waves, Encyclopedia of Meteorology. ED. J. Holton et al. Academic Press,.
pp.
1062‐1067.• Wang, B., and X. Xie, 1996:
Low‐Frequency equatorial
waves in vertically shear flow. Part I: Stable waves. J. Atmos. Sci., 53, 449‐467.
• Hoskins, B., and B. Wang, 2006: Large scale dynamics, in “The Asian Monsoon”
ED. B. Wang, Springer/Praxis
Publishing. New York, pp 357‐415.
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I. Equatorial wave motion
What types of free wave motion are possible in the deep tropics? What are their fundamental
causes and properties?
Observation and theories
I‐1. Vertical modes and Shallow water model I‐2. Equatorial Kelvin waves
I‐3. General dispersion relation
I‐4. Equatorial Rossby
waves and Yanai
waves
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I‐1. Vertical modes and the shallow water model
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Philips two‐level model
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0P
1P
2
0
111 ,, vu
s
p 1q
p
2P
3P
sP
3q333 ,, vu
1.3 Philips 2‐level model
xyvt
u
yyut
v
0
pyv
xu
0)(
pSpt
Consider the simplistic 2‐level approximation. The model structure
Write the equations for
the dry, adiabatic and
frictionless motion as an
example.
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Vertical difference equations
1 11
u yvt x
1 11
v yut y
21 1 0uu vx y p
3 33
u yvt x
3 33
v yut y
3 3 2 0su vx y p
3 1 2 2( ) 0S pt
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Define barotropic
& baroclinic
component
3 1 3 1 3 11 1 1( ), ( ), ( )2 2 2
u u u v v v
3 1 3 1 3 11 1 1( ), ( ), ( )2 2 2
u u u v v v
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Equations for the barotropic
and baroclinic
modes
u yvt x
v yut y
20 ( ) 0u vc
t x y
u yvt x
v yut y
1 ( ) 02 s u
u vx y p
2 20 2
12
c S p Where
Baroclinic
mode Barotropic
mode
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Vertical modes in continuously stratified atmosphere
Why vertical modes? How to determine vertical modes?‐‐with an idealized model in which the vertical structure of the motion can be
expressed as a sum of infinite vertical eigenmodes; the corresponding horizontal
motion can be described by simple equations.
Further Assumptions:‐‐Frictionless, dry, adiabatic and small amplitude perturbation motion in a quiescent
environment, so that Eqs. Become a two‐parameter system (1.1):
xyvt
u
yyut
v
0
pyv
xu
0)(
pSpt
(1.1)
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Specify basic state stratification
22)( pCpS s
21)( sss pSpC
Cs=70 m/s)
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)( pW
The solutions of (1.1) can be expressed as (1.2)
)(),,(),,( pdpdWVUvu
0)(2
22 WpS
dpWdC
xyV
tU
yyU
tV
0)(20
yV
xUC
x
)()( 2/122/1 mmm bbu
bm pppAmpW m=1,2,3…
)/(ln usm ppimb
2/120 )4/1()( ms bCmC
Substitute (1.2) to (1.1): Vertical structure W(p)
satisfies
Each vertical mode satisfies
Structure of each vertical modes satisfying boundary conditions are
Shallow water equation
(1.4), with Co,
a
separation constant
(1.2)
(1.3)
(1.4)
(1.5)
(1.6)
(1.7)
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Structure of Vertical modes
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Shallow water modelLarge‐scale tropical motion stimulated by deep convective heating
can
be well described by the lowest baroclinic
mode
(m=1) (C0
=50 m/s). Thus, the shallow water model
that describes this most important
vertical mode can be used to discuss basic equatorial wave dynamics.
ut
yvx
vt
yuy
020
yv
xuC
t
The two parameters, β and C0
, which reflect the Earth’s rotational and gravitational effects, respectively, determine an equatorial trapped length
scaleRc=(C0
/ β)1/2
‐‐‐equatorial Rossby
radius
of deformation. A value of C0
=50 m/s
corresponds to an equatorial Rossby
radius of deformation of about 15 degrees of latitude.
What limitation
does this model subject to?
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Nondimensionalization
ut
y vx
vt
y uy
0
yv
xu
t
21
/0 CRc
21
0 C
20C
Length scale: equatorial Rossby
radius
of deformation
Time scale (wave propagation)
Geopotential
height scale (ageostrophic)
( , ) ( , )x yC
x y 0
t t C / 0 ( , ) ( , )u v C u v 0 C02
Write
Non‐dimensional shallow water equation
Intrinsic scales
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I‐2. Equatorial Kelvin waves
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Coastal Kelvin waves
Large scale wave motion that is of great practical importance in O/A.
Discovered by Williams Thompson (later named Lord Kelvin) in 1879.
Kelvin wave is a special gravity waves affected by rotational effects
and trapped near coast
or mountain range.
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Matsuno
(1966) found Kelvin waves can trapped near the equator, named as equatorial Kelvin waves.
• The resultant solution of the Kelvin wave is given in dimensional form by
02 2/
00 )(/ CyetCxFCu
v 0
Equatorial Kelvin wave
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Assume meridional
velocity vanishes or the motion is exactly in the along‐equator
direction. The system of nondimensional
equation becomes
ut x
yuy
tux
0
(K1a) plus (K1c) yields a wave equation, which has a general solution,
(K.1a)
(K.1b)
(K.1c)
)()( yYtxFu
F is an arbitrary function. From (K1a),
uUsing (K1b), one can obtain
Y y Y e y( ) ( ) / 02 2
Only the minus sign is valid because the other choice leads to an unbounded solution
for large .
(K2)
(K3)
(K4)
Mathematical solution
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Horizontal Structure of EKW
• No meridional
flows.
• Zonal flows are in geostrophic
balance: Pressure gradient force balances the Coriolis
force.
• The high pressure is in phase with westerly flows.
• The flow and pressure perturbations decay with latitude evanescently.
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Properties of the EKW
• Equatorial trapping: The flow and pressure perturbations decay with latitude evanescently.
• Unidirectional propagation: Always propagate eastward. The fact that the equatorial trapping demands that the pressure and westerly flow are in
phase means that it works only for the eastward propagating gravity wave.
• Non‐dispersive waves as for non‐rotating gravity waves.
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Cause of EKW
• Equatorial Kelvin wave is a special type of gravity wave that is affected by the Earth’s rotation and trapped at the Equator.
• The existence of the equatorial Kelvin wave relies on (i) gravity and stable stratification
for sustaining a gravitational oscillation, (ii) significant Coriolis
acceleration, and (iii) the
presence of the Equator. Change of the sign of Coriolis
force at the equator makes the
equator functioning as a wall to support Kelvin waves.
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I‐3. General dispersion equation for tropical waves
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General dispersion relation (GDR)
Dispersion relation describes the fundamental property of the wave motion
by relating the wave
frequency and zonal wavenumber
k. It is a mean of distinguishing different type of waves.
For EKW, = kCo,.
In addition to the EKW, other equatorial wave solutions possibly exist.
Looking for a GDR for all other types of waves holds a key for identifying different wave motions.
Mathematically, GDR yields eigenvalues describing wave and energy propagation and the
corresponding eigenfunction
describing wave structure.
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Derivation of General dispersion relation (GDR)
0)( 2222
2
Vykk
dyVd
Since the coefficients of the governing equation (1) only depend on y, the solution for zonally propagating wave disturbance can be expressed as the form of normal modes:
( , , ) Re( ( ), ( ), ( )) ( ) u v U y V y y ei kx t
All meridional structure functions are assumed to be bounded as y Substituting (2) into (1) and eliminate U and Geopotential height leads to an equation for V(y):
(2)
(3)
Note, 22 k was used and thus Kelvin wave was excluded.Eq. (3) and bounded boundary condition for V(y) pose an eigenvalue problem, which is the same as the Schrödinger equation for a simple harmonic oscillator. Solutions exist if and only if
2, 1, 0, n ,12/22 nkk (4)
Eq (4) is the dispersion relation.
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3, 2, 1, n ,)12(4/121 22 nkn
(6)Cwk
kkgx
2 1
2 2 /
Exact dispersion relation is given by
Discussion of the dispersion relation
For real wavenumber (Neutral propagating waves),
211221 nn 211or
Differentiating the dispersion equation, (A.2.5) with respect to , one finds that the group speed in the x-direction is
(5)
These features are useful for constructing the dispersion diagram.
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The special Kelvin wave is represented by the straight line in the k>0 domain.
The GDR reflects an infinite family of meridional modes, each associated with an integer index n.
Two distinct groups of high and low frequency waves (period shorter than 1.26 days and loner than 7.3 days).
The zero group velocity line divides the eastward and westward propagation of the energy.
Mixed Rossby-gravity wave is the n=0 mode.
Dispersion relation diagram for all types of equatorial waves Matsuno (1966).
Wave number
Frequency
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2, 1, 0, n ),()()( 2/2
yHeyDyV ny
n
]2/[
0
2)2()!2(!!)1()(
n
l
lnl
n ylnl
nyH
,Re ])/1[(2/0
2 txiy eev ,Re ])/1[(2/
00
2 txiy yeeiu
Horizontal wave structuresThe meridional structures of V(y) are described by Weber-Hermite functions
For instance, the solution for the n=0 mode (the mixed Rossby-gravity waves), 1k
the structure is given by
The full horizontal structure are given by Eq. (2)
( , , ) Re( ( ), ( ), ( )) ( ) u v U y V y y ei kx t
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I‐4. Equatorial Rossby
wave and Mixed Rossby‐Gravity waves (Yanai waves
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Equatorial Rossby
waves
Rossby waves are low-frequency waves. For low frequency waves, it is shown that the dimensional dispersion equation (5) can be approximated by
02**
*
)12( Cnkk
This is the same dispersion relation as a Rossby wave in a beta-plane channel except that the quantized y-wavenumber has a slightly different form due to the meridional boundary conditions.
These low-frequency modes are, therefore, called equatorial Rossby waves.
They occur because f varies with latitude. The higher the index of the meridional mode n, the lower the frequency .
n=1,2,3,…
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For n=1 mode, zonal wind and geopotential
height are symmetric about the equator, while for n=2 mode the two fields are antisymmetric.
At the equator, there is no meridional
motion for the n=1 mode, while no zonal motion for n=2
mode.
The maximum convergence/divergence are located at y=1.25 for the
n=1 mode and y=1.75 for the n=2 mode.
ERW structures: n=1 and n=2 modes
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ERW are characterized by a geostrophic
relationship between pressure and the meridional
as well as the zonal wind.
Strong zonal winds are found near the equator for the n=1 mode, which is expected from approximate balance between pressure gradient and Coriolis
forces (both of them approach
zero as approaching to the equator ). Equatorial Rossby
waves always propagate westward, in
contrast to the equatorial Kelvin waves,
ERW is a dispersive waves. The group speed, which represents the speed at which wave energy propagates, can be either
eastward or westward, depending on wavelength
Properties of ERW
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The energy associated with long Rossby
waves
propagates westward while the energy associated with short Rossby
waves
propagates eastward.
Long Rossby
waves are approximately non‐dispersive. The dimensional westward phase speed is 1/(2n+1) times the long
gravity wave speed . Thus, the fastest long Rossby
wave (n=1) speed is about one‐third of the Kelvin wave speed (and in the opposite direction).
Properties of ERW (Continue)
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Mixed Rossby-Gravity Wave
When n=0, the dispersion equation yields only one meaningful root. This mode is unique in the equatorial
region. This particular mode is called the (Mixed) Rossby‐gravity wave?
Why?
The crossover point from k positive to negative, corresponds to a dimensional period of about 2.1 days and represents a stationary wave in the y direction; the
waves with periods shorter than 2.1 days propagate eastward while waves with periods longer than 2.1 days
propagate westward. The energy
associated with the Rossby‐gravity
waves always propagates eastward..
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The pressure and zonal velocity are antisymmetric
about the equator while the meridional
component is symmetric.
The largest meridional
flow occurs at the equator (cross‐ equatorial flow).
The largest convergence/divergence occurs at y=1.
Horizontal distribution
of velocity and pressure
for a westward moving
Rossby‐Gravity waves.
Horizontal structure of the Rossby‐Gravity waves
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Inertio‐gravity waves
The high frequency waves (large ω) are inertio‐gravity waves. These are almost symmetric in their eastward and
westward propagation.
The behavior of these waves is not discussed here. Interested readers are referred to Matsuno
(1966).
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(a)
Comparison of EKW, ERW (n=1 and n=2), Yanai waves
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II Heat‐induced atmospheric motion
II‐1 Gill Theory: Wave perspectiveII‐2Vorticity perspectiveII‐3 Response to more realistic
monsoon heating
Given a convective (latent heat) source, how would a resting tropical atmosphere
respond?
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II‐1 Gill Theory
Given a convective (latent heat) source, how would a resting tropical atmosphere respond?
Remarks:The latent heat released during convection drives the
atmospheric circulation. But the strength and the location of convection depends on large scale circulation. This is an
interactive process.In Gill theory, this complex interaction is simplified to a
one‐way problem: how the tropical atmospheric circulation responds to a given
heat source (pattern and strength).
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xyvu
yyu
Qyv
xu
)(
Gill Model Single vertical mode, shallow water equation model on an E‐beta ‐plane .Major Assumptions:1.
The forced motion is sufficiently weak: linear dynamics.
2.
The friction: Raleigh damping (a linear drag to wind speed) 3.
Thermal damping: Newtonian cooling (a heating rate proportional to the
temperature perturbation from its basic equilibrium state).4.
The momentum and thermal damping rates have the samemagnitude.
5.
Taking long wave approximation. The nondimentional
governing equations:
(1a,b,c,)
Q
is nondimensional
heating rate. A positive Q
gives u, v,
phi at the low‐level. The
vertical velocity is given by
Qyv
xu )(
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What will physically happen to the system described by Eq. (1)?
The free wave solutions of (1) consist of equatorial Kelvin waves, long Rossby
waves and the long Rossby‐gravity wave. (can you prove it?)
These types of waves will adjust the geopotential
and winds toward the imposed diabatic
heating and reach a steady state under the damping.
Derivation of analytical solutionEliminate
u
and phi from (1) leads to a single equation for v:
yQ
xQyvy
xv
yv
2
2
2(3)
Series solution can be expressed in terms of the weber‐Hermite
function Dm
(y)
)()(),(1
yDxvyxv mm
m
)()(),(1
yDxQyxQm
mm
(4a)
(4b)
)()()( 2/2
yHeyDyV ny
nRecall: ,
n
= 0, 1, 2,…
,
Wave perspective
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0
12
121)12(
111
11
mmm
mmmm
QmQ
QmQdxdvm
dxdv
)()()(),( 22
0 xFexFyDyxQy
s
)(2)()(),( 22
11 xFyeyDxQyxQy
as
The coefficients vm
(x)
can be solved from the following equation by assuming the coefficients for each order of m vanish
(5)
Gill designed two types of basic heating forcing
(6)
(7)
)(,cos)( LxkxxF
)(,0)( LxxF
Here
A mixed forcing is the sum of (6) and (7)
Note: Damping scale is 2.5 days!
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Gill’s solution for (a) heating symmetric about the equator, (b) heating
antisymmetric
about the equator.
Gill’s solution
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The ascent region basically coincides
with the imposed heating
Kelvin and n=1 Rossby
wave
propagation
in the presence of the
damping.
The zonal wind due to the Rossby
waves is balanced by the integrated
zonal wind associated with the Kelvin
waves.
The damping distance of the Kelvin
waves is about three times larger than
the damping distances of the Rossby
waves.
The zonal wind associated with Rossby
waves must be stronger than the zonal
winds associated with Kelvin waves.
0dxdxua2
0 x
a2
0
/'
0ux ' Y=0
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The major ascent and descent regions
tend to coincide with imposed heating
and cooling.
There is a cyclonic circulation in the
heated hemisphere and anticyclonic
circulation in the cooled hemisphere
at low‐levels.
The excited Rossby‐gravity waves are
confined within the forcing region,
and the Rossby
waves propagate
westward.
No response to the east of the heat
source.
Along the equator there are northerly
(southerly) cross equatorial winds in
the lower (upper) level.
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A circulation pattern more
relevant to the Asian
summer monsoon
The imposed heating
The low‐level cyclonic
circulation‐RW; the flow
pattern to the east: KW
The cross equatorial flows,
weak near‐equatorial
trough and an anticyclone
poleward.
Walker cell has a dominant
component is the Pacific
branch,.
The “Hadley cell” with a
secondary low pressure
just south of the equator
results from Qas. Gill’s solution for an asymmetric heating which is the sum
of the symmetric and antisymmetric
heatings
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II‐2 Vorticity perspective
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H w (vχ
) ξ θ
Analysis of Large-Scale Dynamics for Specified Heating (H)
1. Thermodynamic equation N2
w = H
1 2 3
2. Vorticity
equation
3. Thermal wind balance g θ'/θ0
= f əξ/əz N2H2/f 2L2 > 1
Vorticity
perspective
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Equator
warmβv = fəw/əz
LH H
Steady state supported by low level sensible heating
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EQ
EQ
(a) Initial tendency (b) Equilibrium solution
zwfv
t
QwN 2
zwfv
zQfv
z
Response to an isolated imposed heating
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EQ
EQ
(b)
Equilibrium solution: These circulations again tend to drift westwards to
give Sverdrup
balance with, in the cooling region, poleward
components of the
winds in the upper troposphere (to the east of the heating region). Damping in
the vorticity
equation would act to reduce the westward drift of all the
circulations.
(a) Initial tendency : Small, uniform cooling at other longitudes, compensating
the local convective heating, leads to descent in this region, and vortex
stretching at upper levels and shrinking at lower levels. The initial tendency is
given in (a).
Response to a heating with compensating cooling
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II‐3 Response to more realistic heating
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Atmospheric response to TP heating200 hPa 850 hPa
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Strengthening of WNPSH ~30N
Generalized Sverdrup
Balance:zQfv
z
)(
Hoskins and Wang 2006
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Trenberth et al. 2006
Circulation associated with monsoon heating
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(b) MNTNS
ONLY
(a) OBS
(c) MNTNS +
ASIAN HTNG
The Asian monsoon heating
forcing alone induces some very
realistic low‐level circulation
features (c),
The response to only orographic
forcing shows much weaker
subtropical anticyclones .
Addition of the South Asian
monsoon heating strengthens the
descent associated with the North
Pacific subtropical anticyclone by ~
70%.
The interactions between
topography and thermal response
are found to be important for
realistic simulation of the low‐
level monsoon inflow.
Rodwel
and Hoskins 1996
Processes determining the summer monsoon and subtropical anticyclones
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III. Impacts of mean state on equatorial waves and atmospheric
responseHow do “basic flows”
alter the wave
properties and atmospheric response? III‐1 Effects of vertical shear on the Rossby
wave structure and propagationIII‐2 Why does an equatorial symmetric
heating can induce asymmetric Rossby wave response?
II‐3 How can equatorial heating induce extratropical
barotropic
teleconnection?
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III‐1 Effects of vertical wind shear
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)1a.3.A(x
yvpu
xuu
tu
)1b.3.A(y
yuxvu
tv
)1c.3.A(0
pyv
xu
)1d.3.A(0
S
puyv
pxu
pt
(A.3.22,2 3131 AAAAAA
Model for study of effects of Vertical sheared flow
Model formulation including vertical sheared flow
Introduce
The two‐level model represents two vertical modes, a barotropic
mode and a
baroclinic
mode (A.3.2), which are governed by
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yxuUv
xyU
xDtD
TT
2
2
2
2
22 2
where
(A.3.3a)x
UtDt
D
(A.3.3b) 2,2 3131 uuUuuU T
xuU
xyv
DtDu
T
xvU
yyu
DtDv
T
TUyvyv
xu
x
The baroclinic
mode is governed by (A.3.4).
(A.3.4a)
(A.3.4b)
(A.3.4c)
The barotropic
mode is essentially a
Rossby
wave modified by a forcing
arising from the baroclinic
mode
acting on the vertical shear.
The barotropic
mode is governed by (A.3.3).
The baroclinic
mode is governed by a
modified shallow water equation
including the feedback from the
barotropic
mode.
The forcing terms on the RHSs
of Eqs.
(A.3.3) and (A.3.4) indicate interactions
between the barotropic
and baroclinic
modes in the presence of vertical shear.
Vertical mode interaction under mean vertical shear
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(a) Baroclinic
Rossby
mode (b) Barotropic
Rossby
mode
Meridional
structures of the geopotential
(thickness) field of the barotropic
(baroclinic)
modes for the n=1 (most equatorial trapped) Rossby
waves. Here a westerly vertical
shear means that westerly wind increases with height or easterly
wind decreases with
height.
Spherical Coordinatesmodel
In the presence of the vertical shear, the baroclinic
mode remains equatorially
trapped. In contrast, the barotropic
mode extends poleward
with geopotential
extremes occurring in the extratropics
around three Rossby
radii of deformations
away from the equator.
Vertical shear affects two vertical modes differently
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No mean flow
Westerly vertical
shear
Easterly
vertical shear
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Vertical wind shear changes the structure of RW
In a westerly (easterly) shear, the Rossby
waves have larger amplitude at the upper (lower)
troposphere. This is particularly evident in the tropical regions. Poleward
about two Rossby
radii of deformation, the barotropic
mode dominates and the sign of the geopotential
perturbation there tends to be out of phase with that in the tropical region.
Westerly
vertical shear
Easterly
vertical shear
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ESH
WSH
Wang and Xie
(1996)
The baroclinic and barotropic modes are nearly in phase (180o out of phase) in the westerly (easterly) shear. Therefore, an easterly (westerly) shear leads to the amplification of Rossby wave responses in
the lower (upper) level.
+ =
Easterly shear Barotropic TotalBaroclinic
+ =
Westerly shear
How vertical wind shear Changes structure of the ERW
Coupling of baroclinic and barotropic modes in the presence of vertical shear
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Vertical shears slow down the westward propagation
The presence of vertical shears also slow down the westward propagation
of the
Rossby waves regardless of the sign of the vertical shear.
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Without boundary layer friction the Rossby wave instability does
not depend on the
sign of the vertical shear. However, in the presence of a boundary layer, easterly
(westerly) shears enhance (suppress) the moist Rossby wave instability considerably.
Easterly Vertical Shear favors rapid growth of the moist Rossby waves
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Rossby waves will be enhanced in the vicinity of the
latitudes where the vertical shear is strengthened.
Vertical easterly shear sets in NH only
Monsoon Easterly Vertical Shear can change the horizontal structure of ERW dramatically
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Monsoon easterly vertical wind shear enhances ENSO teleconnection
JJA
Response Vertical shear DJF
JJA
DJF
Vertical shearResponseAsymmetric response to equatorial symmetric heating
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How can equatorial heating generate extratropical
response?
An equatorial internal heating first directly generate baroclinic
Rossby
mode.
Barotropic
Rossby
wave motion is then generated by barocnic
mode through
barotropic‐baroclinic
interaction in the presence of vertical wind shear of the mean flow :
The barotropic
Rossby
waves have maximum amplitudes in the extratropics
.
Vertical wind shear can provide a mechanism by which equatorial heating generates extratropical
teleconnection
patterns.
xyDUv
DtD
T
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END
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Wave energy accumulation in the equatorial westerly duct
One of the important impacts of the vertical shear on equatorial
Rossby
waves is that the westerly (easterly) shear favors trapping wave kinetic energy to the upper (lower) troposphere (Fig. 9.13).
This may be pertinent to interpretation of the in‐phase relationship between the transient kinetic energy and the equatorial mean flow in the
upper
troposphere as observed by Arkin
and Webster (1985), which is also known as accumulation of wave energy
in the upper tropospheric
westerly duct (a zonal
flow with westerly vertical shear).
On the other hand, in a region of easterly vertical shear (monsoon regions), the Rossby
waves tend to be trapped in the lower troposphere, which also agree
with the behavior of perturbations in the summer monsoon trough region.
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2)2(2 KDD
yuvDf
t To
2K
yDuvDf
t To
DKuf
tD
o22
DKuf
tD
o22
22
02
0 )1()1( KDBcDIcvuft To
mbPs 1000
mbPe 900
mbP 5002
mbP 10000
1
2
3
4
mbP 3001
mbP 7003
u1
,v1
,
u3
,v3
,
1
3
2w
Bw
00 w
PBL
uB
,vB
2)( 31 AAA
2)( 31 AAA
D
ppp
ppw
yv
xu
yfEE
eses
BBB 2)(2
2
20
2
Effects of vertical shear of zonal wind
A 2‐D version of 21/2 Layer Model by Wang and Xie
(1996)
BL equations
Free troposphere