ALBERT

Beschreibung: High-energy electrons have been measured systematically in a low-altitude (520 x 675 km), nearly polar (inclination = 82 deg) orbit by sensitive instruments onboard the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX). Count rate channels with electron energy thresholds ranging from 0.4 MeV to 3.5 MeV in three different instruments have been used to examine relativistic electron variations as a function of L-shell parameter and time. A long run of essentially continuous data (July 1992 - July 1993) shows substantial acceleration of energetic electrons throughout much of the magnetosphere on rapid time scales. This acceleration appears to be due to solar wind velocity enhancements and is surprisingly large in that the radiation belt 'slot' region often is filled temporarily and electron fluxes are strongly enhanced even at very low L-values (L aprroximately 2). A superposed epoch analysis shows that electron fluxes rise rapidly for 2.5 is approximately less than L is approximately less than 5. These increases occur on a time scale of order 1-2 days and are most abrupt for L-values near 3. The temporal decay rate of the fluxes is dependent on energy and L-value and may be described by J = Ke-t/to with t(sub o) approximately equals 5-10 days. Thus, these results suggest that the Earth's magnetosphere is a cosmic electron accelerator of substantial strength and efficiency.

Beschreibung: Rocket data have been used to evaluate the characteristics of precipitating relativistic electrons and their effects on the electrodynamic structure of the middle atmosphere. These data were obtained at Poker Flat, Alaska, on May 13 and 14, 1990, during a midday, highly relativistic electron (HRE) precipitation event. Solid state detectors were used to measure the electron fluxes and their energy spectra. An X ray scintillator was included on each flight to measure bremsstrahlung X rays produced by energetic electrons impacting on the upper atmosphere. However, these were found the be of negligible importance for this particular event. The energy deposition by the electrons has been determined from the flux measurements and compared with in situ measurements of the atmospheric electrical response. The electrodynamic measurements were obtained by the same rockets and additionally on May 13, with an accompanying rocket. The impact flux was highly irregular, containing short-lived bursts of relativistic electrons, mainly with energies below 0.5 MeV and with fluxes most enhanced between pitch angles of 0 deg - 20 deg. Although the geostationary counterpart of this measured event was considered to be of relatively low intensity and hardness, energy deposition peaked near 75 km with fluxes approaching an ion pair production rate in excess of 100/cu cm s. This exceeds peak fluxes in relativistic electron precipitation (REP) events as observed by us in numerous rocket soundings since 1976. Conductivity measurements from a blunt probe showed that negative electrical conductivities exceeded positive conductivities down to 50 km or lower, consistent with steady ionization by precipitating electrons above 1 MeV. These findings imply that the electrons from the outer radiation zone can modulate the electrical properties of the middle atmosphere to altitudes below 50 km. During the decline and activity minimum of the current solar cycle, we anticipate the occurence of similar events but with fluxes 1-2 orders of magnitude above that reported here, based on studies of earlier solar cycles (e.g., Baker et al., 1993).

Beschreibung: The International Sun-Earth Explorer 3 (ISEE-3) magnetic field and plasma electron data from Jan - March 1983 have been searched to study thin current sheets in the deep tail region. 33 events were selected where the spacecraft crossed through the current sheet from lobe to lobe within 15 minutes. The average thickness of the observed current sheets was 2.45 R(sub E), and in 24 cases the current sheet was thinner than 3.0 R(sub E); 6 very thin current sheets (thickness lambda less than 0.5 R(sub E) were found. The electron data show that the very thin current sheets are associated with considerable temperature anisotropy. On average, the electron gradient current was about 17% of the total current, whereas the current arising from the electron temperature anisotropy varied between 8-45% of the total current determined from the lobe field magnitude.

Beschreibung: The particle scattering and current sheet stability features in the geomagnetic tail during the phase of substorm growth were investigated using Tsyganenko's (1989) magnetic field model. In a study of four substorm events which were observed both in the high-altitude nightside tail and in the auroral ionosphere, the model magnetic field was adjusted to each case so as to represent the global field development during the growth phase of the substorms. The model results suggest that the auroral brightenings are connected with processes taking place in the near-earth region inside about 15 earth radii. The results also suggest that there is a connection between the chaotization of the electrons and the auroral brightenings at substorm onset.

Beschreibung: The scientific objective of the NASA Small-class Explorer Mission SAMPEX is summarized. A brief history of the Small Explorer program is provided along with a description of the SAMPEX project development and structure. The spacecraft and scientific instrument configuration is presented. The orbit of SAMPEX has an altitude of 520 by 670 km and an 82 deg inclination. Maximum possible power is provided by articulated solar arrays that point continuously toward the sun. Highly sensitive science instruments point generally toward the local zenith, especially over the terrestrial poles, in order to measure optimally the galactic and solar cosmic ray flux. Energetic magnetospheric particle precipitation is monitored at lower geomagnetic latitudes. The spacecraft uses several innovative approaches including an optical fiber bus, powerful onboard computers, and large solid state memories (instead of tape recorders). Spacecraft communication and data acquisition are discussed, and the space- and ground-segment data flows are summarized. A mission lifetime of 3 years is sought with the goal of extending data acquisition over an even longer portion of the 11-year solar activity cycle.

Beschreibung: The theory of magnetospheric recirculation for cyclic electron energization and transport may apply in part to heliospheric transport of Jovian electrons if enhanced cross-IMF propagation occurs at heliospheric altitudes near and below the solar wind transition region. Low altitude, ecliptic-to-polar transport would short-circuit conventional interplanetary diffusion, facilitate rapid access to the polar heliosphere with minimal adiabatic energy losses, and provide a seed population for acceleration to 100-1000 MeV energies at the solar wind termination shock and in the heliomagnetotail.

Beschreibung: High quality multilayers with 2d spacings as short as about 44 A have been used successfully for astronomical observations. Observation of both the sun and cosmic X-ray sources (for which radiation longward of the carbon edge at about 44 A is strongly attenuated by interstellar matter) are possible at wavelengths shorter than 40 A with current multilayer technology, if mirrors are used at nonnormal angles of incidence. We discuss several configurations which are suitable for high resolution solar imaging observations in the wavelength interval between 0.5 and 50 A. We also describe the design and anticipated performance of a multilayer optical system we are currently developing for a rocketborne solar observatory.

Beschreibung: This paper will discuss the optical testing of extreme grazing incidence mirror systems and normal incidence high-precision mirror systems during fabrication processing of the optical substrates. The optical metrology is closely coupled with an advanced material removal process which will be discussed in terms of the optical metrology. Interferometric data will be presented of the optical surfaces. Surface roughness data will be shown and discussed.

Beschreibung: We have designed, analyzed, and are now fabricating an All-Reflecting H-Lyman-alpha Coronagraph/Polarimeter for solar research. This new instrument operates in a narrow bandpass centered at 215.7 A - the neutral hydrogen Ly-alpha line. It is shorter and faster than the telescope which produced solar Ly-alpha images as a part of the MSSTA payload that was launched on May 13, 1991. The Ly-alpha line is produced and linearly polarized in the solar corona by resonance scattering, and the presence of a magnetic field modifies this polarization according to the Hanle effect. The Lyman-alpha Coronagraph/Polarimeter instrument has been designed to measure coronal magnetic fields by interpreting, via the Hanle effect, the measured linear polarization of the coronal Ly-alpha line. Ultrasmooth mirrors, polarizers, and filters are being flow-polished for this instrument from CVD silicon carbide substrates. These optical components will be coated using advanced induced transmission and absorption thin film multilayer coatings to optimize the reflectivity and polarization properties at 1215.7 A. We describe some of the solar imaging results obtained with the MSSTA Lyman-alpha coronagraph. We also discuss the optical design parameters and fabrication plans for the All-Reflecting H-Lyman-alpha Coronagraph/Polarimeter.

Beschreibung: We discuss and analyze the possible sources of observational and instrumental uncertainty that can be encountered in measuring magnetic fields of the solar corona through polarimetric observations of the Hanle effect of the coronal Ly-alpha line. The Hanle effect is the modification of the linear polarization of a resonantly scattered line, due to the presence of a magnetic field. Simulated observations are used to examine how polarimetric measurements of this effect are affected by the line-of-sight integration, the electron collisions, and the Ly-alpha geocorona. We plan to implement the coronal magnetic field diagnostics via the Ly-alpha Hanle effect using an all-reflecting Ly-alpha coronagraph/polarimeter (Ly-alphaCoPo) which employs reflecting multilayer mirrors, polarizers, and filters. We discuss here the requirements for such an instrument, and analyze the sources of instrumental uncertainty for polarimetric observations of the coronal Ly-alpha Hanle effect. We conclude that the anticipated polarization signal from the corona and the expected performance of the Ly-alphaCoPo instrument are such that the Ly-alpha Hanle effect method for coronal field diagnostics is feasible.