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Aeronomy and Astrophysics

The polar regions have been called Earth's window to outer space. Originally, this term applied to aurora and other dynamic events staged as incoming solar plasmas encountered the Earth's geomagnetic fields. Because of its unique properties, the polar upper atmosphere becomes a virtual screen on which the results of such interactions can be viewed (and through which evidence of other processes can pass). More recently, this concept has been extended to refer to the "ozone hole" in the polar atmosphere. As scientists have verified an annual loss of ozone in the polar stratosphere, a window previously thought "closed" (stratified ozone blocking
the sun's ultraviolet rays) is now known to "open" in certain seasons.

For astronomers and astrophysicists, the South Pole presents unique opportunities. Thanks to the relative lack of environmental pollution and anthropogenic "noise," the unique pattern of light and darkness, and the geomagnetic force field properties, scientists staging their instruments here can probe the structure of the sun and the universe with unprecedented precision. Studies supported by the Aeronomy and Astrophysics program probe three regions:

The stratosphere and the mesosphere: In these lower regions, current research focuses on stratospheric chemistry and aerosols, particularly those implicated in the ozone cycle.

The thermosphere, the ionosphere, and the magnetosphere: These higher regions derive many characteristics from the interplay between energetically-charged particles (ionized plasmas in particular) and geomagnetic/geoelectric fields. The upper atmosphere, particularly the ionosphere, is the ultimate sink of solar wind energy transported into the magnetosphere just above it. This region is energetically dynamic, with resonant wave-particle interactions, and Joule heating from currents driven by electric fields.

The universe beyond, for astronomical and astrophysical studies: Many scientific questions extend outside the magnetosphere, including a particular interest in the sun and cosmic rays. Astrophysical studies are primarily conducted at Amundsen-Scott South Pole Station or on long-duration balloon flights launched from McMurdo.

All research projects sponsored by this program benefit from (indeed most require)
the unique physical conditions found only in the high latitudes, yet their ramifications extend far beyond Antarctica. High-latitude astrophysical research contributes to the understanding of Antarctica's role in global environmental change, promotes interdisciplinary study of geosphere/biosphere interactions in the middle and upper atmosphere, and improves understanding of the critical processes of solar energy in these regions. Life exists on earth in a balance not only because of the critical distance from the sun but also because of numerous chemical and atmospheric phenomena peculiar to our atmosphere. The 20th century expansion of traditional astronomy to the science of astrophysics, coupled with the emerging discipline of atmospheric science (See also the Ocean and Climate Systems program), is nowhere better exemplified than in Antarctica.

AMANDA - Antarctic Muon and Neutrino Detector Array.
Robert Morse, University of Wisconsin.

Neutrinos are elementary particles. They are believed to have very little or no mass, no electrical charge, and can take any of three forms. Coursing through the universe, they interact only rarely with other particles. AMANDA's primary objective is to discover the sources - both within our galaxy and beyond - of the shower of very-high-energy neutrinos descending on (and usually passing through) the Earth.

AMANDA uses an array of photomultiplier tubes (embedded between 1 and 2 kilometers into the ice) near the South Pole to create a Cherenkov detector out of the natural ice. Originally, 20 strings were installed in the ice, and last season 6 more strings known as the AMANDA-2 detector were added. This system detects high-energy neutrinos originating off the planet that have passed through Earth. Such sources of origin could be diffuse, made up of contributions from many active galactic nuclei (AGNI); or they could be point sources of neutrinos - coming from supernova remnants (SNRs), rapidly rotating pulsars, neutron stars, individual blazars, or other extragalactic point sources.

Recently, new sources of high-energy gamma rays have been discovered, such as the source Mrk-421, discovered by NASA's Compton Gamma-Ray Observatory (CGRO) and Mt. Hopkins Observatory. AMANDA is designed to study just such objects, which are believed to emit high-energy neutrinos copiously. To date, neutrino astronomy has been limited to the detection of solar neutrinos, plus one brief, spectacular burst from the supernova that appeared in the Large Magellanic Cloud in February 1987
(SN-1987a). Only now is it becoming technically feasible to build large neutrino telescopes. As one of the first-generation detectors, AMANDA promises to make seminal contributions to this new branch of neutrino astronomy. (AA-130-O)

Long-duration balloon project.
Steven Peterzen, NASA/National Scientific Balloon Facility.

Free-flying balloons possess many advantages as a means of high-altitude exploration; compared to satellites they remain much longer in a specific location, and cost a fraction to launch. The National Scientific Balloon Facility's (NSBF) effort in Antarctica, known as the Long-Duration Balloon (LDB) program, launches high-altitude balloons carrying scientific payloads into the stratosphere.

This season during a launch window from 15 December to 10 January, the LDB program will support two stratospheric flights from its facility at Williams Field (the Top Hat and ATIC projects). The balloons have a volume of 792.756 cubic meters (28.42 million cubic feet) and will ascend at a rate of approximately 275 meters per minute (900 feet per minute) to a float altitude between 3-4 mb (approximately 125kft). The launches will reach float altitude, circumnavigate the continent between 77S and 80S latitude (average) and are anticipated to terminate on the Ross Ice Shelf or polar plateau. In advance of these two major launches, up to five "pathfinder" balloons equipped with GPS transponders will be sent up to help determine the stratospheric conditions.

TopHat: This experiment (AO-147-O) will help researchers estimate the mass of the Universe (to at least the 10-percent level) by measuring variations in the cosmic microwave background radiation (CMBR). Instrument data will also provide a high precision map of the sky in the far-IR range for use in galactic studies.

Advance Thin Ionization Calorimeter (ATIC): This project (AO-149-O) involves a series of balloon flights from Antarctica (each from 10-14 days duration) to investigate the composition and energy spectra of galactic cosmic rays (GCR) at the highest energies accessible from balloon platforms. (AB-145-O)

Long-duration balloon program: TopHat 2000-2001 antarctic campaign.
Stephan S. Meyer, University of Chicago, Enrico Fermi Institute.

The CMBR (cosmic microwave background radiation) is the name given to a class of radiation first detected in 1965, which, according to the big bang theory, provides evidence of the Universe's origin. About 15 x 109 years ago, the entire Universe is believed to have consisted only of dense, glowing, hot matter; thus, with no empty space, the seminal explosion was of "space" itself. As the echo of this event, the CMBR proves that the Universe is expanding along with the volume of matter and radiation within it.

This project will conduct a program of complementary balloon-borne experiments to measure the anisotropy on certain angular scales. Such measurements have become increasingly important for providing information on the initial conditions from which the large-scale structure of the Universe has evolved. Measurements detected by COBE on large angular scales (and the results of our FIRS experiment) help to define the outer boundaries for CMBR anisotropy studies. We now enter a detailed measurement phase, which promises quantitative answers to some of the fundamental questions about how the structure of the Universe evolved.

To take advantage of new opportunities for long-duration circumpolar ballooning (LDB), we have developed TopHat. A novel instrument concept designed to provide reliable, quantitative measurements of the CMBR anisotropy, the TopHat instruments are optimized to reject both systematic and foreground spurious signals. By placing the telescope on top of the balloon, we can use an observing environment unequaled in any sub-orbital CMBR experiment performed to date; The entire sky above the instrument will be free from supporting structures that could scatter radiation into the sidelobes of the optics, which has been a critical source of systematic uncertainty for anisotropy measurements at the 10-6 level of sensitivity. We expect to achieve unprecedented spectral coverage of a significant portion of the sky. Not only does this yield an excellent check of systematic errors which can plague any experiment of this sensitivity, it also will enable us to understand as never before the nature of the far-infrared foreground spectrum in high-galactic latitudes. (AB-147-O)

Long-duration balloon program: Advance thin ionization calorimeter (ATIC) science balloon payload.
John P. Wefel, Louisiana State University.

Galactic cosmic rays (GCR) - electrons and the nuclei of hydrogen and some other atoms - provide the only direct sample of matter from outside the solar system, as they reach the Earth's atmosphere traveling nearly the speed of light. Since they have electric charge, they are deflected by any magnetic fields they encounter on their journey from beyond the solar system. These events, as well as collisions with the nuclei of the atoms making up the tenuous gas throughout the Universe, build valuable scientific information into the GCRs, which scientists on Earth are eager to extract.

Previous, pioneering experiments have indicated differences in the spectra of hydrogen, helium, and the heavier nuclei, based on the energy they posess. Also, when you look at the total overall spectrum and composition of the full ("all-particle") GCR spectrum, you will find changes in the energy regime approaching the well-known spectral "knee" at 1015-1016 electronvolts (eV).

The ATIC Balloon Experiment will use NASA's Long Duration Ballooning program for a series of balloon flights from Antarctica in December 2000 (each lasting 10-14 days) to investigate the composition and energy spectra of galactic cosmic rays (GCR) at the highest energies accessible from a balloon platform, the region up to ~1014 eV. Our goal is to apply new experimental techniques to the study of these very high-energy particles and to verify some previous reports. We also undertake the search for GCR behavior that might be expected if (as is widely believed) supernovae remnants are the "cosmic accelerators" for the GCR. (AB-149-O)

Magnetometer data acquisition at McMurdo and Amundsen-Scott South Pole Stations.
Louis Lanzerotti, University of Alaska Geophysical Institute, and Alan Wolfe,
New York City Technical College.

The magnetosphere is that region of space surrounding a celestial object (such as the Earth or the sun) where the object's magnetic field is strong enough to trap charged particles. Magnetometers have been installed at selected sites in both polar regions to measure changes in the magnitude and direction of Earth's magnetic field. The unique climatic conditions in Antarctica also permit scientists to view the atmosphere optically (see project AO-104-O) and to correlate such hydromagnetic-wave phenomena with particle-precipitation measurements.

In this project we are measuring such variations with magnetometers installed at conjugate sites in both hemispheres; at McMurdo Station and Amundsen-Scott South Pole Station, Antarctica, and at Iqaluit, in the Northwest Territories in Canada. The antarctic systems gather unique data related to the coupling of the interplanetary medium into the dayside magnetosphere, including the magnetospheric cusp region. The data also shed light on the causes and propagation of low-frequency hydromagnetic waves throughout the magnetosphere.

The antarctic magnetometers continue to measure the magnitude and direction of variations in Earth's magnetic field in the frequency range from 0 to about 0.1 hertz, with resolution of about one nanoTesla. These data are being analyzed in the context of other concurrent data acquired by the six automatic geophysical observatories
(AGOs) that are a part of the Polar Experiment for Geophysical Upper Atmosphere Investigations (PENGUIn) program (project AO-112-0); and the data will also be ranged against data obtained from magnetometers operated by Bell Laboratories in the continental United States. (AO-101-O)

High-latitude magnetic pulsations.
Mark Engebretson, Augsburg College, and Roger Arnoldy,
University of New Hampshire.

The Earth's magnetic field arises from its mass and motion around the polar axis, but it creates a powerful phenomena at the edge of space known as the magnetosphere, which has been described as a comet-shaped cavity or bubble around the Earth, carved in the solar wind. When that supersonic flow of plasmas emanating from the Sun encounter the magnetosphere, the result is a long cylindrical cavity, flowing on the lee side of the Earth, fronted by the blunt nose of the planet itself . With the solar wind coming at supersonic speed, this collision produces a "bow shock" several Earth radii in front of the magnetosphere proper.

One result of this process are fluctuations in Earth's magnetic field, called "micropulsations," which can be measured on time scales between 0.1 second and 1,000 seconds. It is known that magnetic variations can significantly affect power grids and pipelines. We plan to use magnetometers (distributed at high latitudes in both the antarctic and arctic) to learn more about how variations in the solar wind can affect the Earth and manmade systems.

We will study these solar-wind-driven variations and patterns at a variety of locations, and over periods of time up to a complete solar cycle. Since satellite systems are now continuously observing solar activity and also monitoring the solar wind, it is becoming feasible to develop models to predict the disruptions caused by such magnetic anomalies. And while our work is geared specifically toward a better understanding of the world and its manmade systems behavior, it will also involve space weather prediction. (AO-102-O)

Antarctic auroral imaging.
Stephen Mende, Lockheed Palo Alto Research Laboratory.

Scientists are only beginning to essay quantitative studies on the dynamic behavior of the magnetosphere. In the past, detail-oriented explorations with space satellites have enabled them to map the average distribution of magnetospheric energetic particle plasma content. But the dynamics of auroral phenomena - when particles from the magnetosphere precipitate into the atmosphere, producing fluorescence - have been hard to quantify through optical means. Amundsen-Scott South Pole Station is uniquely situated to observe aurora because the darkness of polar winter permits continuous optical monitoring; at most other sites, the sky becomes too bright near local mid-day.

The aurora can actually be regarded as a two-dimensional projection of the three-dimensional magnetosphere, because particles tend to travel along the magnetic field line. By observing the dynamics and the morphology of the aurora, scientists get a reliable glimpse into the dynamics of the region of the three-dimensional magnetosphere associated directly with it. This method relies on knowledge relating the type of aurora to both specific energies of precipitation as well as to specific regions of the magnetosphere.

We are deploying an intensified optical, all-sky imager (operating in two parallel wavelength channels, 4,278 and 6,300 Angstroms) to record digital and video images of auroras in the winter darkness. These wavelength bands allow us to discriminate between more- and less-energetic electron auroras and other precipitation. The South Pole Station observations of the polar cap and cleft regions entail measuring auroral-precipitation patterns and then interpreting the results in terms of the coordinated observations of (magnetic) radio-wave absorption images as well as (high-frequency) coherent-scatter radar measurements.

We expect this work to provide insight into the sources and energization mechanisms of auroral particles in the magnetosphere, as well as other forms of energy inputs into the high-latitude atmosphere. (AO-104-O)

Global thunderstorm activity and its effects on the radiation belts and the lower ionosphere.
Umran Inan, Stanford University.

Tracking dynamic storms is a challenge, but lightning associated with thunderstorms can provide scientists an indirect way of monitoring global weather. This project employs very-low-frequency (VLF) radio receivers at Palmer Station, Antarctica, operated in collaboration with the British and Brazilian Antarctic Programs, both of which operate similar receivers. All are contributors to the Global Change Initiative.

The VLF receivers measure changes in the amplitude and phase of signals received from several distant VLF transmitters. These changes follow lightning strokes because radio (whistler) waves from the lightning can cause very energetic electrons from the Van Allen radiation belts to precipitate into the upper atmosphere. This particle precipitation then increases ionization in the ionosphere, through which the propagating VLF radio waves must travel. Because the orientations to the VLF transmitters are known, it is possible to triangulate the lightning sources that caused the changes. Once the direction of the lightning source is known, it can be subjected to waveform analysis and used to track - remotely - the path of the thunderstorms. The data will also be correlated with data from the antarctic Automatic Geophysical Observatory network, and will be used by scientists engaged in magnetospheric and ionospheric research. (AO-106-P)

Extremely-low-frequency/very-low-frequency waves at the South Pole.
Umran Inan, Stanford University.

Atmospheric scientists orient their studies around different strata, or regions, and the boundaries and interactions between these regions are of particular interest. How are the upper atmosphere regions coupled electrodynamically? What can we learn by measuring the energy that is being transported between the magnetosphere and the ionosphere? These are but two of the questions the U.S. Antarctic Program's automatic geophysical observatory (AGO) program is designed to explore.

Plasmas occur in the magnetosphere and the ionosphere, and they can be transported and accelerated by a variety of different wave-particle interactions. One important dynamic in this system is particle precipitation that is driven by extra-low-frequency/very-low-frequency (ELF/VLF) waves. Thus, measuring ELF/VLF waves from the multiple sites of the AGO network provides a powerful tool for remote observations of magnetosphere processes.

This project maintains a system at Amundsen-Scott South Pole Station to measure magnetospheric ELF/VLF phenomena, and to correlate the data with measurements made by the AGO system. This season provides an acid test for the reliability of the new digital recording system (compared to the reel-to-reel analog system), which provides higher quality data. (AO-106-S)

Study of polar stratospheric clouds by lidar.
Alberto Adriani, Instituto De Fisica Dell'Atmosfere, Rome, Italy.

The appearance each spring of the stratospheric ozone hole above Antarctica is driven by chlorine compounds interacting on the surfaces of clouds that formed the previous polar winter, known as polar stratospheric clouds (PSCs). This is one explanation for why ozone depletion is much more severe in polar regions than elsewhere.

This project uses light detection and range finding (lidar or a "light detection and rangefinding" instrument) to study the PSCs, stratospheric aerosol, and the thermal behavior and dynamics of the atmosphere above McMurdo Station. Continuous lidar observations provide insight on the formation, evolution, and other peculiar characteristics of these PSCs. These data provide a complement to the information gained from balloon-borne instruments in project AO-131-O, and thus collaborative activities are being coordinated with the University of Wyoming. (AO-107-O)

South Pole Air Shower Experiment-2.
Thomas Gaisser, University of Delaware.

Cosmic rays consist of protons and other atomic nuclei, accelerated (scientists believe) to high energy levels in such distant astrophysical sources as supernova remnants. As cosmic rays from space arrive at the Earth, they interact in the upper atmosphere. The South Pole Air Shower Experiment-2 (SPASE-2) is a sparsely filled array of 120 scintillation detectors spread over 15,000 square meters at South Pole. This array detects the charged particles (primarily electrons) that are produced by interactions of these very high energy cosmic rays.

A nine-station subarray called VULCAN has been constructed to detect the Cherenkov radiation (light emitted by a charged particle moving through a medium at a higher speed than the speed of light within that material, analogous to the shock wave produced by objects moving faster than the speed of sound) produced high above the ground in the same showers. The SPASE array is located less than half a kilometer from the top of AMANDA and is designed to complement AMANDA's neutrino detecting capacity. (See project AA-130-OO). SPASE-2 has two goals -

First, to investigate the high-energy primary (galactic in origin) cosmic radiation, by determining the relative contribution of different groups of nuclei at energies above approximately 100 teraelectronvolts. This can be done by analyzing coincidences between SPASE and AMANDA. Such coincident events are produced by high-energy cosmic-ray showers with trajectories that pass through SPASE (on the surface) and AMANDA (buried 1.5 to 2 kilometers beneath it). AMANDA detects the high-energy muons penetrating the Earth in those same showers for which SPASE detects the low-energy electrons arriving at the surface. The ratio of muons to electrons depends on the mass of the original primary cosmic ray nucleus. The VULCAN detector further permits the calculation of two other ratios that also depend on primary mass in readings from the showers it detects.

Second, to use the coincident events as a tagged beam. This construction permits us to investigate and calibrate certain aspects of the AMANDA response. This project cooperates with the University of Leeds in the United Kingdom. (AO-109-O)

High-latitude Antarctic neutral mesospheric and thermospheric dynamics and thermodynamics.
Gonzalo Hernandez, University of Washington.

South Pole is a unique and interesting spot from which to observe the dynamical motion of the atmosphere. The fact that it is on the axis of Earth's rotation strongly restricts the types of wave motion that can occur there, as compared to lower latitude sites. Antarctica attracts atmospheric scientists for many reasons; a primary draw is that neutral winds perforce can only blow across the Earth's rotational axis. This simple condition has a profound influence on the large-scale dynamics of the atmosphere at high latitude, as only zonal wave-number one mode horizontal motions are possible.

The resulting simplifications may help in understanding the behavior of the global atmosphere. For example, how do scientists measure the wind speed of the atmosphere? One direct method is by determining the Doppler shift of naturally occurring emissions in the upper atmosphere as they flow along at predictable heights. Hydroxyl radicals (OH), for example, are confined to a fairly narrow band near 90 kilometers altitude.

This study uses a high-resolution Fabry-Perot interferometer (located at Amundsen-Scott South Pole Station) to make simultaneous azimuthal observations of the individual line spectra of several upper atmospheric trace species, most importantly the hydroxyl radical (OH) and atomic oxygen. The observed Doppler shift of the emission lines provides a direct measure of the line-of-sight wind speed, while the wind field structure can also be derived from these multi-azimuth measurements. The simultaneously observed line widths also provide a direct measurement of kinetic temperature. (AO-110-O)

Riometry in Antarctica and conjugate regions.
Theodore J. Rosenberg and Allan T. Weatherwax, University of Maryland at College Park.

The University of Maryland continues to conduct research into upper atmospheric processes; using photometry to take auroral luminosity measurements and riometry to make high-frequency cosmic noise absorption measurements. A primary focus of our analysis activities over the next several years will include coordinated ground- and satellite-based studies and Sun/Earth comparisons.

The latest work also involves extensive collaboration with other investigators using complementary data sets. Continuing science activities in the 1998-2001 time frame - as we enter the next solar maximum period - will enable us to participate in, and contribute to, several major science initiatives, including the GEM, CEDAR, ISTP/GGS, and National Space Weather programs

Riometers measure the relative opacity of the ionosphere. This work employs a new imaging riometer system called IRIS (imaging riometer for ionospheric studies). The first two IRISs were installed at Amundsen-Scott South Pole Station and Sondre Stromfjord, Greenland. A third IRIS has been installed at Iqaluit, Northwest Territories, Canada - the magnetic conjugate to South Pole. Broadbeam riometers also operate at several frequencies at South Pole, McMurdo, and Iqaluit; auroral photometers operate at South Pole and McMurdo. This array of instruments constitutes a unique network for the simultaneous study of auroral effects in both magnetic hemispheres.

The focus of all of this work is to enhance understanding of the relevant physical processes and forces that drive the observed phenomena; this includes both internal (such as magnetospheric/ionospheric instabilities) and external forces, such as solar wind/IMF variations. From such knowledge may emerge an enhanced capability to forecast; many atmospheric events can have negative technological or societal impact, and accurate forecasting could ameliorate these impacts. (AO-111-O)

Polar experiment network for geophysical upper-atmosphere investigations (PENGUIN).
Theodore Rosenberg, University of Maryland at College Park.

The data obtained from automatic geophysical observatories (AGO) help researchers understand the Sun's influence on the structure and dynamics of the Earth's upper atmosphere. The ultimate objective of this research into how the solar wind couples with the Earth's magnetosphere, ionosphere, and thermosphere is to be able to predict solar/terrestrial interactions that can interfere with long-distance phone lines, power grids, and satellite communications.

A consortium of U.S. and Japanese scientists are working with a network of six AGOs, established on the east antarctic polar plateau and equipped with suites of instruments to measure magnetic, auroral, and radiowave phenomena. The AGOs are totally autonomous, operate year-round, and require only annual austral summer service visits.

When combined with measurements made at select manned stations, these arrays facilitate studies on the energetics and dynamics of the high-latitude magnetosphere, on both large and small scales. The research will be carried out along with in situ observations of the geospace environment by spacecraft, in close cooperation with other nations working in Antarctica and in conjunction with conjugate studies performed in the Northern Hemisphere. PENGUIn AGO data will be sent to Augsburg College in Minnesota, and there processed and distributed to PENGUIn investigators. (AO-112-O)

Auroral dynamics by the all-sky-imager at Amundsen-Scott South Pole Station.
Masaki Ejiri, National Institute of Polar Research, Japan.

The South Pole is a unique platform for observing aurora during austral winter season; as a point on the earth's rotational axis, the pole provides a unique vantage to observe the airglow and to discern the characteristics of acoustic gravity waves in the polar region, as they vary in altitude/wavelength.

We can observe aurora continuously throughout the 24 hours in a day, which allows us to collect data on -

the dayside polar cusp/cleft aurora (due to the direct entry of the solar wind);

afternoon aurora that are closely associated with the night side magnetospheric storm/substorm activities; and

on the polar cap aurora, which is dependent on the polarity of the interplanetary magnetic field. Research has shown that these auroras come from the precipitation of low-energy particles entering the magnetosphere in the solar wind.

Since 1965, data have been acquired at the South Pole using a film-based, all-sky-camera system. With the advance of technology, we are now able to obtain digital images and process large amounts of information automatically. The current technology is known as the all-sky-imager (ASI), a digital CCD imager monitored and controlled by the Japanese NIPR (National Institute of Polar Research) using a satellite internet system and modern telescience techniques. ASI is equipped with interference filters for auroral emissions of 427.8 nm, I 557.7 nm and I 630.0nm; an OH (hydo-oxide 730 nm) filter is also available, while a panchromatic image can be obtained without the filter.

These international collaborations should enhance knowledge of the magnetosphere, the ionosphere and of upper/middle atmosphere physics. The HF (high frequency) radars at Halley Bay, Sanae and Syowa Station yield the vector velocity of ionospheric plasma over the South Pole. These studies should provide further insight into the physics of the magnetosphere, the convection of plasma in the polar cap, and solar wind effects; specifically dayside auroral structure, nightside substorm effects, and polar-cap arcs. (AO-117-O)

Solar and heliosphere studies with antarctic cosmic-ray observations.
John Bieber, University of Delaware.

Cosmic rays - penetrating atomic nuclei and electrons from outer space that move at nearly the speed of light - continuously bombard the Earth. Colliding with air nuclei in the upper atmosphere, they create a cascade of secondary particles that shower down through the atmosphere. Neutron monitors deployed in Antarctica provide a vital three-dimensional perspective on this shower and how it varies along all three axes. Accumulated neutron-monitor records (begun in 1960 at McMurdo Station and in 1964 at Amundsen-Scott South Pole Station) provide a long-term historical record that supports efforts to understand the nature and causes of solar/terrestrial and cosmic-ray variations, as they are discerned occurring over the 11-year sunspot cycle, the 22-year Hale cycle, and even longer time scales.

This project continues a series of year-round observations at McMurdo and Amundsen-Scott South Pole Stations, recording cosmic rays with energies in excess of 1 billion electronvolts. These data will advance our understanding of a number of fundamental plasma processes occurring on the Sun and in interplanetary space. At the other extreme, we will study high time-resolution (10-second) cosmic-ray data to determine the three-dimensional structure of turbulence in space, and to elucidate the mechanism by which energetic charged particles scatter in this turbulence. (AO-120-O)

Antarctic miniature lidar/automatic weather station lidar.
Jonathan Rall, NASA Goddard Space Flight Center.

As radar is to electromagnetic energy, lidar (light detection and rangefinding device) is to light. After sending an intense pulse of light (usually from a laser) through the particles and molecules suspended in the air along the propagation line, lidar system detectors are able to analyze the density, structure, and composition of target atmospheric regions based on how the light is scattered and reflected.

One vital object of study for this new technology are the Type 1a (nitric acid trihydrate) polar stratospheric clouds (PSCs) implicated in the annual austral springtime destruction of stratospheric ozone over Antarctica. These clouds play a crucial role in the atmospheric degradation of ozone by freeing up of the chlorine radical from the stable reservoir compounds. Scientists are trying to detect, profile and monitor these PSCs in hopes of better understanding their origin (natural vs. anthropogenic) and evolution (spatial as well as temporal). Ultimately, the goal is an enhanced ability to predict the magnitude of future ozone holes.

The first fully autonomous lidar was deployed to automated geophysical observatory (AGO) P1 on the polar plateau in January of 1999. This instrument operated continuously until the AGO platform failed in July 1999. This instrument will be removed from AGO P1, refurbished at Goddard Space Flight Center and redeployed to an automatic weather station in the 2000-2001 season. Given the limited number of AGO platforms and their fixed locations, we decided to collocate the lidar instruments with established automatic weather stations (AWS). The AWS project (see OO-283-M) has nearly 50 stations at various locations on and around the continent.

This project, meanwhile, is developing and testing a robust, low-power consumption, atmospheric lidar instrument that can operate autonomously yet still establish a long-term data record of the temporal and spatial evolution of polar stratospheric clouds (PSC). The other primary science objective is to continuously monitor the long-term atmospheric optical thickness from the surface to an altitude of 30 kilometers. This data will be compiled into a database that will provide statistics on atmospheric conditions that can be used by future space altimetry missions such as ICEsat. (AO-126-O)

Rayleigh and sodium lidar studies of the troposphere, stratosphere, and mesosphere at the Amundsen-Scott South Pole Station.
George Papen, University of Illinois.

The Earth's atmosphere is described by several stratified layers, each with distinctive structure, dynamics and characteristics. The stratosphere begins about 11 kilometers (km) above the surface; the mesosphere runs from about 50 km to its upper boundary, the menopause, where atmospheric temperature reaches its lowest point (about -80C), before beginning to rise as altitude increases through the outer layer, the thermosphere, which runs from 80 km to outer space.

This research deploys a sodium-resonance lidar at the South Pole to study the atmosphere's vertical structure and dynamics, from the lower stratosphere up to the menopause. As the project enters its fourth year, scientists will be able to better study the mesopheric temperature using an iron-resonance lidar (added last year), which extends our ability to measure the air dynamics and temperature structure even higher, to about 100 km. An airglow imaging camera aids in studies of the horizontal structure.

This final complement of instrumentation, used in conjunction with the normal balloon-borne radiosondes flown regularly from South Pole, will provide extensive data on:

the temperature structure from the surface to 100 km altitude;

the nature of the polar stratospheric clouds (PSCs), which are important to ozone chemistry;

the variability and frequency of metallic layers in the mesosphere, which play roles in communications as well as atmospheric chemistry;

gravity waves in the troposphere, lower stratosphere and menopause regions; and

many other phenomena, some of which are unique to the South Pole. (AO-127-O)

High-latitude electromagnetic wave studies using antarctic automatic geophysical observatories.
James LaBelle, Dartmouth College.

Aurora are light shows (streamers and arches of light) created when electrons, accelerated along Earth's magnetic field lines, excite atoms in the atmosphere. Many people are familiar with pictures of the aurora's optical effects, but it turns out that the aurora also generates radio signals, invisible to the human eye, but easily detectable with radio receivers tuned to frequencies between 0.05 and 5.0 megahertz (MHz).

Scientists understand the phenomenon of auroral hiss that causes broadband noise at frequencies below 1 MHz. But two other radio phenomena attributable to auroras remain unexplained - narrowband emissions near 2.8 and 4.2 MHz and broadband noise bursts in the frequency range of 1.4 to 4.0 MHz. Although these radio emissions constitute a small fraction of the total energy of the aurora, they may provide important clues to the more energetic processes; this possibility would mirror the use of radio emissions from the Sun to infer processes taking place in the solar corona.

Taking advantage of radio-quiet antarctic conditions, this project uses low-frequency/
middle-frequency/high-frequency receivers in hopes of developing insights about these emissions from antarctic auroral zone and polar cap sites. The receivers have been installed at Amundsen-Scott South Pole Station, in five U.S. automatic geophysical observatories, and in two British automatic geophysical observatories. (AO-128-O)

Spectroscopic and interferometric studies of airglow and auroral processes in the antarctic upper atmosphere over the South Pole Station.
Gulamabas Sivjee, Embry-Riddle Aeronautical University.

While the aurora tend to dominate the optical sky and researchers' interest, other, weaker emissions know as airglow (like aurora) provide indications of solar scattering by various species, and also reveal other phenomena. At Amundsen-Scott South Pole Station, we study the dynamics and chemistry of the upper atmosphere - airglow occurs above 60 kilometers) with an infrared spectrophotometer, an eight-channel photon-counting photometer, and an infrared Michelson interferometer.

By measuring the variations in the brightness and temperature of airglow band emissions, researchers can detect planetary, gravity, and tidal waves. The horizontal wave structures can be elucidated by looking in several directions while making these measurements at several wavelengths (which vary at different heights in the atmosphere) and will also provide information on the vertical extent of the wave activity. Also, viewing the different altitude auroral emissions with the spectrophotometer provides insight into the nature of the sources of the auroral precipitating electrons, and how these different sources vary over time. (AO-129-O)

Measurements of polar stratospheric clouds, condensation nuclei, and ozone during the austral winter and spring.
Terry Deshler, University of Wyoming.

Ozone depletion in the antarctic stratosphere, in a general sense, is quite well understood; however, questions remain concerning the character of particles in polar stratospheric clouds (PSCs) and which observations may provide the first indications of ozone recovery. This project will contribute to our understanding of these phenomena by continuing balloon-borne measurements based at McMurdo Station, Antarctica.

There are still many uncertainties about PSCs; it is clear, however, that the heterogeneous chemistry - which activates chlorine to destroy ozone - occurs on the surface of these particles. We will continue our PSC-size distribution measurements during the early- and mid-winter period (when PSC activity is greatest), and during late winter, when ozone loss begins.

Mid-winter measurements will be completed by science technicians from the civilian support contractor. We will make 15 aerosol flights between June and September, measuring the concentration of condensation nuclei and particles between 0.15 and 10.0 _m radius. The fundamental measurements from these instruments provide estimates of the size of the particles that form in PSCs. From these measurements the surface areas and volumes within PSCs can be estimated. The particle size estimates help scientists calculate denitrification/dehydration rates, the surface area necessary to quantify chlorine activation models, and volume parameters to estimate particle composition. Further estimates of particle composition will involve methods to infer particle index of refraction, which is a function of composition. That effort involves our continuing collaboration with Alberto Adriani, Instituto di Fisica Dell'Atmosfera, Rome (AO-107-O), where researchers compare optical scattering by measuring aerosol size distributions, either by ground-based lidar or in situ by a balloon-borne laser backscattersonde.

In addition to the aerosol measurements, we will maintain annual late winter/spring measurements of ozone, taken about every 3 days. These measurements have been approved for inclusion in the data base of the Network for the Detection of Stratospheric Change. At a minimum, this will continue to provide a measurement base to detect the first signs of ozone recovery. Stratospheric chlorine levels are now peaking, following which the lessening of ozone depletion is expected to be altitude-dependent. Measurements like these, of vertical ozone profiles, provide one of the crucial tools needed to observe the first signs of recovery following the decline in stratospheric chlorine. (AO-131-O)

Trace gas measurements over the South Pole using millimeter-wave spectroscopy.
Robert L. de Zafra, State University of New York at Stony Brook.

Many atmospheric gases radiate millimeter-length radio waves, but each species has its own unique spectrum. These fingerprints not only identify the gas, but also provide information on its temperature and pressure. These properties enable scientists to use the millimeter-wave spectrum of the atmosphere to determine how abundantly and at what altitudes a number of trace species can be found.

This research (over the course of a full year) monitors the atmosphere above South Pole, Antarctica, with a millimeter spectroscope for ozone, carbon monoxide, nitrous oxide, nitric acid, water vapor, and nitrogen dioxide. Several of these gases have important roles in the formation of the annual antarctic ozone hole. Others - particularly water vapor and carbon monoxide - can provide information about the vertical transport and other dynamics of the upper stratosphere and the mesosphere. (AO-138-O)

Dynamics of the mesophere and lower thermosphere using ground-based radar and TIMED instruments.
Susan K. Avery, University of Colorado, Boulder.

We will study the dynamics of the mesosphere and lower thermosphere over Antarctica using measurements from instruments on NASA's TIMED satellite and a meteor radar to be installed at Amundsen-Scott South Pole station. Specific science objectives include the space-time decomposition of wave motions; delineation of the spatial climatology over Antarctica with emphasis on the structure of the polar vortex; dynamical response to energetic events; and interannual variability.

The proposed meteor radar is a VHF system that will be able to measure the spatial structure and temporal evolution of the horizontal wind field over the South Pole. We will also use the existing ground-based radars at Davis Station, Syowa Station, Rothera Station, and Scott Base to determine spatial climatology. Wind and temperature measurements to be made by NASA's TIMED satellite during orbits over the South Pole will provide opportunities for combined ground-based, space-based experiments and validation activities. (AO-284-O)

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