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Vertical Structure of
the Atmospheric Boundary Layerin Trade Winds
Yumin Moon
MPO 551September 26, 2005
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Papers to Present
Riehl, H., Yeh T. C., Malkus J. S., and La Seur,N. E., 1951: The Northeast Trade of the PacificOcean. Quarterly Journal of the RoyalMeteorological Society. 77, 598-626.
Augstein E., Schmidt, H., and Ostapoff, F., 1974:The Vertical Structure of the Atmospheric
Planetary Boundary Layer in Undisturbed TradeWinds over the Atlantic Ocean. Boundary LayerMeteorology, 6, 129-150.
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Riehl 1951
Analyzed observations inthe Northeast Pacific
Ocean during the dry
season (July to October).
Three weather ships, PearlHarbor, Hickam Field, both
in Honolulu, HI.
Hourly surface
observations, two
radiosonde observations
per day.
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Riehl 1951
Wind Steadiness
Air above the
Inversion Top
Inversion Layer Cloud Layer
Subcloud layer
Vm = mean speed100mV
VS
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Riehl 1951
Vertical Cross-Section of Wind Speed Mean Vertical Distribution
of Wind Speed
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Riehl 1951
Vertical Distribution of Divergence
dzvs
dzwz
zz
)()(00
Equation of Continuity,
assuming steady state
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Riehl 1951
Whereas the inversionascends downstream,
individual columns
descend, shrink
vertically and spread
horizontally. Large
masses of air, located
above the inversion at
32N have become a
part of the cloud layerwhen they reach
Honolulu, HI.
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Riehl 1951
The air that has beenincorporated in the
inversion layer
The air that has been
incorporated in thecloud layer
The air that has been
below the inversion
throughout the journey
from 32N.
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Riehl 1951
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Riehl 1951
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Riehl 1951
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Riehl 1951
0)()()()( dsPELds
z
qA
zLdsqw
zLdsqv
sL
Equation of Continuity for Latent Heat in a layer of unit thickness and cross-section
and extending over the distance ds
VerticalHorizontal Turbulent
Exchange
Source/Sink
Steady-state is assumed.
Lateral mixing is neglected compared to vertical mixing.
The vertical coordinate is attached to the trajectory of the mean
motion
w vanishes everywhere thus the second term (vertical) isdropped out, except at the top where the boundary is a horizontal
surface.
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Riehl 1951
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Riehl 1951 Rise of the inversion is
accomplished through the pickup oflatent heat by the trade in thecourse of its passage over thetropical ocean.
The bases of cumulus clouds are
nearly uniform height, but the topsare very irregular.
The tops of the cumulus cloudsbreak off and evaporate quickly.
Moisture is introduced into thelower portions of the inversion
layer. Then the air in the inversion layer
becomes gradually similar to thecharacteristics of the cloud layer.
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Riehl 1951
fsp
dtdv
1
fs
pvvdiv
t
v
)(
)(
dsdzfs
pdsdzvvdivvdsdz
t
)(
z
vz
f
0)()()(
dsz
v
z
vdzppvwdsvwdsvvdzvvdz btdu
btdu
Inflow term
upstream,
downstream
Inflow term
top, bottom
Pressure
Term
Turbulent term
top, bottom
Equation of momentum
Integrating over a volume bounded by ds, dz,
and of unit thickness in the direction normal to s
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Riehl 1951
Layer
(mb)
Inflow
Upstream
Outflow
Downstream
Net Inflow
Top
Outflow
Bottom
Net Pressure
Term
Turbulent
Term Bottom
Turbulent
Term Top
1020-
960
-0.3 -0.2 -0.1 0 0 0 -2.7 4.4 -1.6
960-
880
-0.4 -0.4 0 -0.1 0 -0.1 -2.6 1.6 1.1
880-
800
-0.4 -0.4 0 -0.1 -0.1 0 -1.2 -1.1 2.3
800-
720
-0.4 -0.3 -0.1 -0.1 -0.1 0 0 -2.3 2.4
In units of 10^8 G CM SEC^-2
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Augstein 1974
Analyzed observationscollected during the AtlanticExpedition 1965 Sep 12 toOct 11 and the Atlantic
Tradewind Experiment(ATEX) 1969 Feb 6-21.
Three ships, Planet at thenortheast, Discoverer atthe northwest, and Meteor
at the south. 8 radiosondes observations
per day, radar windmeasurements.
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Augstein 1974
Surface Layer adiabatic temperature gradient, decreaseof specific humidity with height, slight statical instability.
Mixed Layer adiabatic temperature lapse rate, nearly
constant vertical specific humidity.
Transition Layer nearly isothermal temperaturedistribution, strong upward decrease of moisture.
Cloud Layer temperature gradient slightly higher than the
moist adiabatic lapse rate, upward weak decrease of
specific humidity, conditionally unstable. Trade Inversion increasing temperature, steep decrease
of moisture.
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Augstein 1974
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Augstein 1974
Increasing cumulusconvection causes anincrease of downwardflux of inversion air intothe cloud layer, thus
pushing the inversionupward. This process iscombined with downwardheat flux which effects adiabatic warming of the
cloud layer.
Strong convective activitydestroys the tradeinversion; the organizedcloud circulation thentransports air parcels with
relatively low potentialtemperature upward andwith high potentialtemperature downward.This process results in a
diabatic warming of thelower part of the cloudregion and in a diabaticcooling of the upper part
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Augstein 1974
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Augstein 1974
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Augstein 1974