of 250 Inn using Dynamics. Explon_r 2 (DE 2) data from the ion drift meter. (IDM) ..... serial number of the individual ob_rvaxious. ..... _'_--127.5. ' _--1274_. _*_.
JOURNAL
OF GEOPHYSICAL
NASA-CR-20692
VOL.
100, NO. A12, PAGES 23,993--24,002,
DECEMBER
waves
S. Johnson,
near
W.
300
B. Hanson,
km
over
1 R. R. Hedges,
the
and
polar
W.
caps
R. Coley
Center for Space Sciences, The University of Texas at Dalhs, Richardson G.
l, 1995
1
Gravity F.
RESEARCH,
03#"
'"
R. Carignan
The University of Michigan, Ann Arbor
N.
W.
Spencer
NASA Cs_dard Space Flight Centea-, Greenbelt, Maryland
Abstract. a_
Distinctive
wave
particles,
and ions
neut_, ve z_.
tan over
propagaang 500
kin.
of the order They
indicate
that
the horizontal must
recognizable neutral
caps.
propagate
phase
are interpreted
calculated
the entire
neutral
as being
cap.
lengths
but
velocity
neutral
they
along
calculated from little attenuation
of about
Vertical of 103 s.
clearly By combining
and mmpea-atm-e
the
with the
of the order of 0.04 erg/cm2-s total solar ultraviolet heat observations on orbital with altitude.
passes
at at
The observation of internalgravity waves at altitudesas
The purpose
of this paper is to descrfl_ Explon_r
(IDM)
[Heelis
eta/.,
(RPA)
[Hanson
spectrometer atmosphere al., 1981].
in excess
of 250
Inn
2 (DE 2) data from the ion drift meter
1981],
the
et a1.,1981], (WATS)
motions
some wave
over the polar caps at altitudes
using Dynamics
internal
path
perturbations
to be of the order
and ion temperature.
concenlration
Introduction
observed
thesatellite
are most
waves
velocity
temperatx_
usually
of
alfin,des
gravity
to the dayside.
vertical component of the neutral velocity, an upward energy flux 250 km has been calculated, which is about equal to the maximum input above that altitude. Upward energy fluxes altitudes from 250 to 560 km indicate relatively
at
by vertical
The associated
the nightside
atmosphere,
2
due to internal
are characterized
is from
the observed
and temperature
Explorer
of 10 inn and the periods
of ion vertical
from
velocity
Dynamics
wave
polar
progression
in the
from
The disturbances
to be of the order
in the observations
pressure
These
across
of vertical
.observed
of 100 m/s and horizontal
are inferred
waves
in the distributions
are frequently
atmosphere.
often extend
displacements The
me polar
in the neutral
penmbations
forms
retarding
the wind
[Spencer
eta/.,
potential
analyzer
and temperature
mass
1981], and the neutral
composition spectrometer (NACS) [Carignan The waveforms are interpreted as being due
gravity
waves
propagating
The motions are seen as well-formed, of vertical velocity (both ion and
in the neuwal
et to
high as the exoba_se was unexpected because of anticipated strong attcnuaticmabove 120 km due to viscosityand thermal conduction. The expectation of strongabsorptionisbased on the work of P/noway and Hines [1963],Mid&Icy and Liemohn [1966], and Hod&e_ [1969]. Wave forms are illastxated in Figun: 1 for propagating and standing waves; it will be useful to keep these patterns in mind in the subsequent discussion of the observations. The displacements
atmosphere.
quasi-sinusoidal patterns neutral) with associated
temperature and composition perturbations that permit evaluadon of some properties of the waves; these patterns indicate that the horizontal phase progression of the waves is
from
equilibrium
positions
and the
velocities
associated with the changing displacements are portrayed. In the present context the displacements and velocities are the components
in the
vertical
direction.
From
satellites,
neither
the displacements nor the time variations at fixed Points in space can be observed directly because of the motion of the
from the nightside to the dayside and that the waves transport significant amounts of energy upwards, even at altitudes as
satellite.
high
as the base
been
observed
high compared to the wave propagation velocity; that is, the observations are essentially of spatial variations. The vertical displacement perturbations can be inferred from the
of the exosphere.
Waves
of this sort have
over much of the Earth by Potter
et al. [1976],
snapshot
The
satellite
at a fixed
observations
time
because
constitute
the satellite
nearly
velocity
a
is so
who described theirdistributionwith latitudeand possible causes. Gross and lluan& [1985] have observed waves of
temperature
similarwavelength atlow tomiddle ladmdes and altitudes near 250 km.
displacements and velocity perturbations are in phase quadrature in time for both propagating and standing waves.
I_ed Copyright
or from composition
For propagating waves the perturbations quadrature in space, and the displacement
September il, 1994. 1995 by the Aazaican C,_ytical
perturbations
the axis
UaioQ.
velocity
profiles
depending
is in the direction
In the case of standing Paper numbca-95JA02858 0 !4 8-0227/95/95JA-02858505.00
half
the
perturbations 23,993
time
and
occur
waves of
propagation
the spatial phase
at the nodes,
half
The
are also in phase profdes lead or lag
upon whether
of wave out
changes.
the coordinate or opposed
profdes the
as illustrated
to it.
are in phase time,
and
in Figure
!.
no
JOHNSON
23,994
Pr_opaqatin
9
El" AL.: GRAVITY
WAVES
NEAR
300 KM
Standing
Wave
Wove
t=O
0.5
0.5
0.0
/
0.0
-0.5 -0.5 _ -t.Ot 0
/ J
0.5
1 .o
-I .111 o
o.5
1.0 t=n/4
0.5 /
0.5_/
"\
/
\ //
-0.5
-0.5 0.0_ -t .0 0
\
/
-I .0
Arrows
indicate
O.5
o
1.0
0.5 Dlstonco
1 .o
t=./2
di?eetion
of
,,"
0.5
propagation
"
1
/ 0.0
/ \
Displacement
-0.5[-1.0
Velocity
--
/
"" "- _
/
/
o
t.0
0.5 t=3n/4
0.5 0.0 t.O_ -0.5
-t.O o
0.5
t.o t=TT
0.5 0.0
--
-0.5 -1.0 0 Figure waves
I. The spatial distribution at five selected time intervals.
waves
are
either
in phase
(e.g.,
of displacements and velocities At selected instants in time the
for
_r/2 < t < a') or in antiphase
Figure
polar
cap. are
in each
cases
the the
magnetic
shown,
index.
the
segments
observed
IDM
on
22
not
initial
portion are
during
of
the
the
over
verucal
passes
over
a polar
interplanetary
out of 40
passes
interplanetary field dam
m/s; other records show in Figure
smaller
cap.
in the
_r/'2)
direction
with
one
of
satellite
for standing for standing
another.
motion
or opposed
to
(In
field
was
on which were
thlce
The
and
the
Kp
Kp
directed
waves
vary from about 100
in each case, and the horizontal wave
3 shows
data
8303
on
253
kin.
the
entire
for
IDM
ion
February The
data
for
ion velocity
:emperaturcs 1,
and
1983;
the
oscillations
in
components
concentrations
spacecraft
question
and
from
altitude
extend
orbit
was
about
ritually
across
local
polar
magnetic
MLT,
at
terms
of
the
field
is
almost
severely wave
cap.
The
noon,
at
1621:09
UT.
vertical
satellite
The
ion
UT,
waves
ion
the
and
are
velocities,
vertical,
consu-ained motions can
entered
1613:35
seen
vy.
motions
and it is no be seen in
polar
exited most
Because in
the
surprise that the horizontal
cap
near
near
0300
clearly
in
the magnetic horizontal
are
no evidence of ion velocity
were
available. The
amplitudes.
RPA
being chosen
is no obvious
waves
2, velocity-correlated
perturbauous were present used m determine whctber
times been
then=
these
Figure a
orbital
is missing.)
panel; of
sta_ have
segm©m
in each
occurrence
33
intervals
located
shown
between
and
shown
m the
selected
time
vertical velocity pcrtui'bation amplitudes to 300
seen orbital
(15-rain)
arbitrarily the
are
However,
southward
perturbations
the
panel;
indices
relationship
wave
by
Seven-thousand-kilometer
indicated that
the
observed
segments
so
for 0 < t
