The Atmospheric Boundary Layer Over Polar Marine Surfaces
EDGAR L ANDREAS
v
where τ = vectoral stress exerted on the top of the floe
INTRODUCTION
by the wind
v
The Atmospheric Boundary Layer (ABL) is the low-
τw = vectoral stress exerted on the underside of
est few hundred meters of the atmosphere, where the
the floe by the water
Earth's surface most directly influences atmospheric
vf = Coriolis parameter
processes. The vast majority of Earth's human inhabit-
v k = vertical unit vector
ants are never outside the ABL.
∇H = gradient in sea surface height
v
I cannot hope, in a few pages here, to compete with
I = internal ice forces vector.
the many good books recently published on the ABL
v
v
(Arya 1988, Stull 1988, Sorbjan 1989, Garratt 1992,
τ and τw are the only turbulence terms in eq 1. Thus,
Kaimal and Finnigan 1994)--nor do I need to. My pur-
the main concern boundary-layer meteorologists have
v
pose here is to present some of the basic concepts of
with eq 1 is evaluating τ , the surface stress on the top
v
boundary-layer meteorology, to define some of the jar-
side of the ice. The desire to know τ motivates much of
gon a relative novice might encounter in the above (and
what I will write in this monograph.
other) texts, and to describe a few of the unique prob-
The energy budget at the surface of an ice floe is
lems associated with the ABL over polar marine sur-
(e.g., Maykut 1978, Parkinson and Washington 1979,
faces.
Makshtas 1991)
This report divides into two logical parts. In the first
part, I focus on microscale processes in the so-called
B = Qs - αsQs + QL↓ - QL↑ - Hs - HL + C (3a)
Atmospheric Surface Layer (ASL). The height scale
relevant in the ASL is generally 1030 m; relevant hori-
= melting/freezing + storage/release .
(3b)
zontal scales are a few hundred meters. In the second
part, I tie surface-layer processes to the structure of the
entire ABL. Here, the relevant height scale is the height
αs = shortwave albedo
of the ABL--typically a few hundred meters over po-
lar marine surfaces. The relevant horizontal scale is on
QL↓ = incoming longwave radiation
the order of kilometers.
QL↑ = emitted longwave radiation
C = conduction to the ice surface from below
Hs = turbulent sensible heat flux (the flux driven
BASIC EQUATIONS OF AN ICE FLOE
by a difference in temperature between the
The momentum balance of a floating ice floe is (e.g.,
ice surface and the air)
Hibler 1979)
HL = turbulent latent heat flux (the flux driven
v
r
vv
v
Du v v
by a difference in water vapor density be-
= τ - τw + mf k u mg∇H + I .
m
(1)
tween the surface and the air).
Dt
v
In eq 3, my convention is that positive terms add heat
Here, m is the mass of the floe; u is the velocity vector
to the ice surface; negative terms carry heat away. Thus,
of the floe; D/Dt is the material derivative
for example, when Hs and HL are positive, turbulence
vv
is carrying heat from the surface into the air.
D
= + u⋅∇
(2)
If the seven terms on the right-hand side of eq 3a do
Dt
t
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