UAP Science Programs at Antarctic Stations
The Upper Atmosphere Physics (UAP) science projects that operate at South Pole
and McMurdo Stations, Antarctica, are described in the Science Program Plan
published annually by the United States Antarctic Program (USAP).
Another excellent reference is Upper Atmosphere Research in
Antarctica, L.J. Lanzerotti and C.G. Park, editors, published by the
American Geophysical Union as Volume 29 in the Antarctic Research Series.
The Review issue of the Antarctic Journal of the United States,
published annually by the National Science Foundation (NSF), contains articles
for general readers, which describe current scientific activities at all
Antarctic stations, and span all scientific disciplines funded by the
NSF. For more general information about the influence of solar activity on
the terrestrial environment, consult Sun, Weather, and Climate, by
J. R. Herman and R. A. Goldberg (NASA SP 426, 1978).
The principal investigators (PI) for the University of Maryland's
Upper Atmosphere Physics research in Antarctica are Professor T.J. Rosenberg
and Dr. Al Weatherwax,
Institute for Physical Science and Technology, University of Maryland,
College Park, MD 20742-2431, firstname.lastname@example.org, email@example.com.
(Graphic courtesy of NASA)
The projects that operate
from instrumentation in the Skylab Building at South Pole Station, and
at the Arrival Heights Laboratory at McMurdo Station,
examine natural phenomena occuring in the earth's atmosphere and
magnetosphere. The broad focus of these science programs is toward
improved understanding of the mechanisms that couple solar processes
into the terrestrial environment; these include investigations of phenomena
associated with short-term environmental effects (auroras, induced
electrical currents, radiowave communications interference), as
well as those associated with longer-term effects (changes in the ozone
layer, atmospheric composition studies, stratospheric winds, weather,
and even climate). Instruments for these tasks include
optical and radio devices for remote sensing, as well as sensors that
monitor changes in the electric and magnetic fields at the station; the
instruments that measure local fields (including VLF receivers) are
sensitive to perturbations that propagate from remote generation
Instruments Used for Upper Atmosphere Studies
- Riometers, Prof. T.J. Rosenberg and Dr. A.T. Weatherwax, PI
- Photometers, Prof. T.J. Rosenberg and Dr. A.T. Weatherwax, PI
- Fluxgate Magnetometer,
Dr. L.J. Lanzerotti, PI
- Searchcoil Magnetometer,
Prof. R.L. Arnoldy, PI
- LF/MF/HF Receiver,
Prof. J. LaBelle, PI
For many investigations, South Pole represents a unique site for
studying environmental phenomena. In the case of atmospheric studies
this must be obvious, because of the location remote from contaminating
sources; in addition to monitoring current atmospheric parameters,
ice-coring experiments provide information about past atmospheres.
However, the station is also uniquely situated for investigations
associated with magnetospheric phenomena. An important region of the
earth's magnetosphere separates processes associated with polar cap
environments, from those normally related with auroral activity.
Polar cap effects are associated with magnetic field lines that connect
almost directly with the solar magnetic field on the dayside (cusp/cleft),
and with the deep tail of the magnetosphere on the nightside.
The boundary between the polar cap and those regions of the magnetosphere
associated with closed magnetic field lines is coincident with the
auroral oval, so-named because of the frequent occurrence of auroral
arcs inside a narrow band around the magnetic pole.
The 'polar cap' designation is normally
applied to phenomena that occur poleward of the oval, so that the
dayside cusp/cleft is regarded as a separate region with properties
distinct from either the polar cap or auroral/sub-auroral regions.
McMurdo Station, at invariant magnetic latitude of about 80 degrees, lies
inside the polar cap at all local times.
Since the magnetic pole is displaced from the geographic pole, South Pole
Station is located at an invariant latitude (74.25 degrees)
that places the station equatorward of the nominal undisturbed auroral
oval on the dayside, and poleward of the oval (in the polar cap) on the
consequently at dawn and dusk the station passes underneath the oval.
Under disturbed magnetic conditions the characteristics of the oval,
and indeed the entire magnetosphere, experience dramatic changes, so that
this simplistic picture does not hold during the most interesting times
for scientific investigation.
The variety of observational details
during disturbed magnetospheric conditions ranges across not only
different instrument regimes, but also encompasses time scales ranging
from seconds to hours, and spatial scales from meters to nearly global.
Consequently the investigation of the environment during disturbed times
involves coordinated observations using instruments at widely spaced
fixed observatories on the earth, as well as satellite instruments
in the solar wind and inside the magnetosphere. At the Antarctic
signals from many of the instruments are recorded together on a common
data logger, and the data are shared among the Principal Investigators
(PI's) providing the data, as well as with colleagues operating elsewhere.
Since the beginning of the IGY (International Geophysical Year -
1957-1958), the collaboration in Antarctic research has been on an
The brief discussions presented below are intended to describe
the basic objectives of the science
experiments involved in studies of solar/magnetospheric/ionospheric
coupling processes. More detailed discussions should be sought from
the PI's responsible for the science programs.
Digital Data Acquisition System
The scientific instruments operated at the Antarctic observatories provide
analog signals that are digitized and recorded by the Digital Data
Acquisition Systems (DAS). These were designed and built
at the University of Maryland, and have been in continuous use at the stations
since December, 1981. The original DASes recorded to 9-track magnetic tape,
and operated nearly flawlessly until 1994 at South Pole, and 1995 at McMurdo.
These were replaced with PC-based systems, recording to magneto-optical disk.
The data acquisition systems are operated as station facilities, and record
data from many experiments, including,
- Riometers, University of Maryland
- Photometers, University of Maryland
- Searchcoil Magnetometer, University of New Hampshire
- Fluxgate Magnetometer, Bell Laboratories
- Electric Field, Stanford University
- Very-Low-Frequency (VLF) Radiowaves, Stanford University
- Cosmic Rays, Bartol Research Foundation
- Wind Speed, Stanford University
Riometers are usually operated with broad-beam antennas, with
beamwidth on the order of 60 degrees. These integrate absorption
activity over a large portion of the ionosphere, so small scale
details of the actual physical distribution of electron density
enhancements are lost. Narrow beam antennas, with beamwidths of
10 to 20 degrees, are sensitive to smaller scale features of ionization,
but are generally limited in the ionospheric area which can be
examined at one time. The data from several riometers operated at
different frequencies, but examining the same sky with broadbeam
antennas, show effects which have been interpreted as being due
to small scale spatial structure in the electron precipitation region
which does not completely fill the antenna beam. Results analyzed
from narrow beam and multiple frequency riometer data, in conjunction
with optical data from all-sky cameras and photometers, indicate that
the spatial scale of ionospheric electron density perturbations can be
very small, on the order of a few kilometers.
(Photo courtesy of T.J. Rosenberg)
A recent trend in riometry is toward the use of antennas providing
several narrow beams, which examine different parts of the sky. Some
of these systems have been constructed to provide several fixed beams,
and others scan the ionosphere in a linear path with one or more
steerable beams. The IRIS system was designed to operate as a fast-scan
multiple-beam instrument to examine the entire ionospheric sky, out
to about 45 degrees from the zenith. The IRIS antenna is a sophisticated
phased-array which produces 49 narrow beams, on the order of 12 degrees
beamwidth, all of which are sampled once a second. This system is
capable of examining ionospheric electron density perturbations in
fine time scale, as well as small spatial scale.
At South Pole Station, the University of Maryland operates broadbeam
riometers at 20.5, 30, 38.2, and 51.4 MHz. The signals from these
instruments are digitized and recorded at 1-Hz resolution by the station
data acquisition system. The broadbeam antennas are located in a group
about 1-km from the Cusp Lab. For the 20.5, 30 and 51.4 MHz systems,
the broadbeam antenna comprises two adjacent parallel horizontal dipoles;
the antenna for the 38.2 MHz system is a single element identical to those
used with the IRIS phased array, including a chicken-wire ground plane
located a quarter-wavelength below the horizontal dipole element plane.
The antenna beam projects a nearly circular -3 dB locus onto the
ionosphere, where the absorption of cosmic radio noise occurs; the
-3 dB beamwidth is approximately 60-degrees, so the diameter of the
typical ionospheric absorption region at 90 km altitude is about 100 km.
Both the sun and the earth have magnetic fields, generated by electrical
currents flowing inside the respective bodies. In addition to electromagnetic
radiation (e.g., light, radiowaves, x-rays), the sun emits an
electrically-charged gas (solar wind plasma) which carries the 'frozen-in'
solar magnetic field along with it as it streams away from the sun.
The plasma is composed almost entirely of electrons and protons.
Perturbations in the plasma density/magnetic field propagate as
Alfven waves. At 1-AU (astronomical unit - the mean distance of the
earth from the sun) the solar wind plasma density is about ten particles
per cubic centimeter, the solar wind speed is about 400 km/s, and the
magnitude of the interplanetary magnetic field (IMF) is about 10 nT.
(Graphic courtesy of NASA)
If there were no solar wind, the earth's magnetic field would be dipolar,
but the pressure of the solar wind causes the simultaneous distortion of
the earth's magnetic field, and deflection of the solar wind around
the earth. Not surprisingly, the steady-state configuration resembles
the 'bow shock' around the prow of a moving boat, so that designation
has been used in the identification of the magnetospheric analog.
The complicated steady-state configuration contains several distinct
regions, as shown in the figure. This picture represents merely an
'average' view of the conditions that prevail in globally-defined
regions during quiet conditions. The steady-state environment represents
an equilibrium balance between the energy input from the solar wind, and
processes which transfer energy within the magnetosphere, including
energy deposition into the atmosphere. Because of the tilt of the earth's
magnetic dipole axis (about 11.5 degrees), the magnetic pole performs a
diurnal rotation around the geographic pole. This causes distortions in
the steady-state magnetosphere, and these effects are accentuated by
the seasonal tilt of the rotational axis with respect to the solar ecliptic
plane (about 23 degrees). The picture during disturbed times
is extremely dynamic, and the physical processes involved in the transfer
of energy under these conditions are not well understood.
The investigation of solar/magnetic storm-time phenomena is the
single principal purpose of much of the upper atmosphere research at South
Pole Station. Magnetic substorms are responsible for the creation of
various dynamic processes in the magnetosphere, including
flux transfer events associated with magnetic merging regions
in the boundary layer between the solar wind and the inner magnetosphere;
precipitation of solar wind/boundary layer plasma directly into the
atmosphere through the polar cusp/cleft; plasmoids in the
magnetospheric tail which are associated with the energization and
precipitation of energetic electrons into the nightside atmosphere,
creating westward travelling surges, among other effects;
pulsating auroras in the
morningside auroral oval, caused by large-scale precipitation modulations
with periods on the order of several minutes; expansion of the
auroral oval to lower magnetic latitudes; mid-afternoon
poleward surges of auroral structures into the polar cap from the
auroral oval, etc. All of these phenomena are accompanied by
perturbations in the terrestrial magnetic field; the surface magnetic
field strength at auroral latitudes is about 60,000 nT, and perturbations
of about 1000 nT are common during disturbed times, sometimes lasting for
several days, but usually with time scales of only minutes or hours.
Variations in the magnetic field at South Pole Station
are studied using two different magnetometers. Rapid fluctuations
in the geomagnetic field (with periods a fraction of a second)
are measured with a
searchcoil magnetometer, or micropulsation detector, consisting
of a mu-metal core surrounded by many thousands of turns of wire. The
detector for a single axis is about 6-feet long, and about eight inches in
diameter; two perpendicular axes measure the horizontal components
of dB/dt at South Pole and McMurdo Stations. The project is S-102,
and the PI is Dr. R.L. Arnoldy, University of New Hampshire.
Slow variations of the terrestrial magnetic field
are measured with the fluxgate magnetometer (DC to the Nyquist
frequency of 0.5 Hz, at 1-Hz sampling rate); the sensor itself comprises
three small mutually perpendicular coils of wire.
The fluxgate magnetometer can
measure fluctuations as small as 0.03 nT, although magnetic storm effects
often are associated with perturbations of 1000 nT or more.
the fluxgate magnetometer can be found in the University of Maryland's
Data Acquisition System Manual. The science project is S-101, and
the PI is Dr. L.J. Lanzerotti, Lucent Technologies/Bell Laboratories.
The solar wind plasma that becomes trapped inside the
magnetosphere is confined by the structure of the magnetic field to
various regions, such as the Van Allen radiation belts, and even extending
into the tail of the magnetosphere. In the absence of solar flare
activity, the magnetospheric plasma achieves a steady-state balance
between source and loss mechanisms. Some of the plasma is lost
through the tail because the magnetic field lines are not believed to
close on the nightside high-latitude magnetosphere; other processes
include electromagnetic wave-particle interaction mechanisms which
cause the precipitation of plasma into the atmosphere. During magnetic
substorms, horizontal ionospheric electric currents flow in the
E-region ionosphere; these currents are possible because in this altitude
range (about 85-140 km) the electrons remain constrained against motion
perpendicular to the magnetic field, while the protons are 'un-magnetized'
because collisions with the neutral atmosphere occur with a frequency
greater than the cyclotron gyrofrequency. Consequently, atmospheric
tidal motions as well as electric fields lead to currents.
The measurement of slowly-varying (or DC) electric fields
is very difficult, and the experimental practice sometimes resembles
artistry more than science.
The measurement of the surface electric field includes wind-related
static electricity, which is particularly bothersome in the cold, dry
A variety of optical instruments operate at South Pole
Station during the austral winter season. Instruments which examine
natural phenomena in the D- and E-region ionosphere include photometers
and all-sky cameras operated by the University of Maryland,
Lockheed/Martin's Advanced Technology Center (formerly Palo Alto Research
Laboratory), and Utah State University. The optical instruments
are located on the top floor of the Skylab Building at South Pole Station,
and operate through domes projecting through the roof of the building.
Other optical experiments include interferometers and lidars, which
examine phenomena in the neutral atmosphere as well as the ionosphere.
The Science Program Plan published by USAP describes these projects
briefly. Since the riometer program is directed toward ionospheric
phenomena associated with the precipitation of auroral electrons
into the atmosphere, the principal optical instruments that provide
complementary measurements are the photometers and all-sky cameras.
At both South Pole and McMurdo Stations, photometers measure ionospheric
optical emissions at 630 nm and 427.8 nm. The field of view of the
photometers (60 degrees) was designed to match that of the broadbeam
riometers, in order to make useful comparisons between data from the
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