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Mcfadden, J.

Publications and source records attributed to Mcfadden, J..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Recovery Timescales of the Dayside Martian Magnetosphere to IMF Variability

In this work we revisit an event observed by Mars Atmosphere and Volatile Evolution MissioNin the solar wind where the interplanetary magneticfield (IMF) rotates around the Mars‐Sun axis during∼6 min. Based on a time‐dependent LATMOS Hybrid Simulation, we determine recovery timescales of thedayside Martian magnetosphere normalized by the IMF variability timescale. Particularly, wefind thatsuch recovery timescales range between 8 s and 11 min for an∼90° IMF rotation that lasted 50 s (observed aspart of the 6‐min time interval), depending on the considered magnetospheric region. We alsofind thatthe O+plume recovery timescales range between 40 and 120 s, taking greater values for further downstreamdistances (at least up to 1RMdownstream from the terminator plane). This range is on the order of themagnetosheath O+gyroperiod, showing the kinetic nature of the plume recovery process.

Romanelli, N.↗
NASA NTRS1992

Mars Observer magnetic fields investigation

The magnetic fields experiment designed for the Mars Observer mission will provide definitive measurements of the Martian magnetic field from the transition and mapping orbits planned for the Mars Observer. The paper describes the instruments (which include a classical magnetometer and an electron reflection magnetometer) and techniques designed to investigate the nature of the Martian magnetic field and the Mars-solar wind interaction, the mapping of crustal magnetic fields, and studies of the Martian ionosphere, which are activities included in the Mars Observer mission objectives. Attention is also given to the flight software incorporated in the on-board data processor, and the procedures of data processing and analysis.

Acuna, M. H.↗
NASA NTRS1986

Production of flickering aurora and field-aligned electron flux by electromagnetic ion cyclotron waves

Recent observations have suggested that flickering aurora is produced by a modulation of the field-aligned component of the electron flux within an auroral arc. It is proposed that a portion of the field-aligned electrons are of ionospheric origin and that these electrons are accelerated and their flux modulated by electromagnetic ion cyclotron waves that occur below the main acceleration region on auroral arc field lines. A model of the electromagnetic ion cyclotron wave shows that the parallel phase velocity of the wave increase as the wave propagates toward the ionosphere. A test particle calculation shows that ionospheric electrons trapped or reflected by the wave are accelerated to energies of several keV and that their flux is modulated at the wave frequency. The relative amplitudes of the model wave electric fields are consistent with the observations of small-scale low-frequency ionospheric and magnetospheric electric fields near auroral arcs of approximately 10 mV/m and 100 mV/m, respectively. The large-amplitude ion cyclotron waves also produce a ponderomotive force and a self-consistent ambipolar electric field. Energy considerations show that the downward energy flux in the electromagnetic ion cyclotron wave can be several percent of the total downward auroral electron energy flux.

Temerin, M.↗
NASA NTRS1984

Observations of double layer-like and soliton-like structures in the ionosphere

Two types of large electric field signatures, individual pulses and pulse trains, were observed on a sounding rocket launched into the afternoon auroral zone on January 21, 1982. The typical electric fields in the individual pulses were 50 mV/m or larger, aligned mostly parallel to B, and the corresponding potentials were at leat 100 mV (kT approximately 0.3 eV). A lower limit of 15 km/sec can be set on the velocity of these structures, indicating that they were not ion acoustic double layers. The pulse trains, each consisting of on the order of 100 pulses, were observed in close association with intense plasma frequency waves. This correlation is consistent with the interpretation of these trains as Langmuir solitons. The pulse trains correlate better with the intensity of the field-aligned currents than with the energetic electron flux.

Boehm, M. H.↗
NASA NTRS1974

A remote sensing study of Pacific hurricane Ava

Aircraft, Skylab, NOAA-2, ATS-3, and NIMBUS-5 recently obtained a variety of measurements of Pacific hurricane Ava. These measurements are unusually broad in scope and include satellite observed passive microwave emissivities at 13.9 and 19.5 GHz, active microwave scattering cross-sections at 13.9 GHz, and near infrared and visible images. Essentially simultaneous aircraft measurements of wind speed, waves, whitecaps, 1.4 and 13-15 GHz passive microwave emissivities, 1.4 GHz active microwave images, sea surface temperatures, pressure fields, and aerosol size distributions were also obtained. A brief description of sensors and platforms is presented along with some in-depth details of results obtained.

Ross, D.↗