Soho Observations of Density Fluctuations in Coronal Holes

In recent UVCS/SOHO White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes at heliocentric distances of 1.9 to 2.45 solar radii. The motivation for the observation is the 2.5D MHD model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes. In February 1998 we performed new observations using the UVCS/WLC in the coronal hole and obtained additional data. The new data corroborate our earlier findings with higher statistical significance. The new longer observations show that the power spectrum peaks in the 10–12 minute range. These timescales agree with EIT observations of brightness fluctuations in polar plumes. We performed preliminary LASCO/C2 observations in an effort to further establish the coronal origin of the fluctuations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Radio observations of Venus and the interpretations

The radio observations of Venus are reviewed and compared with theoretical microwave spectra computed for a variety of models of the Venusian environment. The models considered are (a) a CO₂-N₂ atmosphere, (b) an atmosphere of dust (the aeolosphere model), and (c) a cloud model with various loss mechanisms in the cloud. The effect of polarization on the surface emissivity has been included in all the computations. It is shown how the radio observations place limits upon the acceptable models, for example, the density and size of dust particles required in the aeolosphere model. It is shown how some models place severe restrictions on radar observations at short centimeter wavelengths, thereby emphasizing the importance of such experiments. These same models show that the Mariner II observations can not be interpreted in terms of surface phenomena and provide a new interpretation for the microwave phase effect.This work was supported in part by the U.S. Army, Navy and Air Force under Contract DA36-039-AMC-03200(E); and in part by the National Aeronautics and Space Administration (Grants NsG-250-62 and NsG-419).     

Space Radiation Damage Measurements in the Earth Synchronous Orbit

For direct measurement of the integrated radiation dose experienced in Earth synchronous orbit, p-i-n diodes were flown as radiation dosimeters on LES-6. The diode, which has a lifetime of 10-4 seconds in the intrinsic region, was originally developed as a neutron dosimeter, but can detect 1-MeV electron fluences as low as 1013 e·cm-2. Observations over three years in orbit are presented.     

Modified Generalized Sign Test Processor for 2-D Radar

The modified generalized sign test processor is a nonparametric, adaptive detector for 2-D search radars. The detector ranks a sample under test with its neighboring samples and integrates (on a pulse-to-pulse basis) the ranks with a two-pole filter. A target is declared when the integrated output exceeds two thresholds. The first threshold is fixed and yields a 10-6 probability of false alarm when the neighboring samples are independent and identically distributed. The second threshold is adaptive and maintains a low false-alarm rate when the integrated neighboring samples are correlated and when there are nonhomogeneities, such as extraneous targets, in the neighboring cells. Using Monte Carlo techniques, probability of false-alarm results, probability of detection curves, and angular accuracy curves have been generated for this detector. The detector was built and PPI photographs are used to indicate the detector's performance when the radar is operated over land clutter.     

Angle-of-Arrival Estimation Using an Adaptive Antenna Array

A direction-finding technique is presented that is capable of simultaneously estimating the arrival angles of multiple signals. Pulsed as well as continuous signals can be handled with the signal form only approximately specified. An adaptive antenna array is used as a processing device in the estimation technique. The effect of input signal and feedback loop parameters upon estimate bias is discussed.     

7. Dynamics,winds, circulation and turbulence in the atmosphere of venus

With the possible exception of the lowest one or two scale heights, the dominant mode of circulation of Venus' atmosphere is a rapid, zonal, retrograde motion. Global albedo variations in the ultraviolet may reflect planetary scale waves propagating relative to the zonal winds. Other special phenomena such as cellular convection in the subsolar region and internal gravity waves generated in the interaction of the zonal circulation with the subsolar disturbance may also be revealed in ultraviolet imagery of the atmosphere. We discuss the contributions of experiments on the Orbiter and Entry Probes of Pioneer Venus toward unravelling the mystery of the planet's global circulation and the role played by waves, instabilities and convection therein.     

Initial observations of low energy charged particles near the Earth's bow shock on ISEE-1

We report initial measurements from the ULECA sensor of the Max-Planck-Institut/University of Maryland experiment on ISEE-1. ULECA is an electrostatic deflection — total energy sensor consisting of a collimator, deflection analyzer and an array of solid state detectors. The position of a given detector, which determines the energy per charge of an incident particle, together with the measured energy determine the particle's charge state. We find that a rich variety of phenomena are operative in the transthermal energy regime (10 keV/Q to 100 keV/Q) covered by ULECA. Specifically, we present observations of locally accelerated protons, alpha particles, and heavier ions in the magnetosheath and upstream of the Earth's bow shock. Preliminary analysis indicates that the behavior of these locally accelerated particles is most similar at the same energy per charge.     

Relationship Between Substorm Auroras and Processes in the Near-Earth Magnetotail

Although the auroral substorm has been long regarded as a manifestation of the magnetospheric substorm, a direct relation of active auroras to certain magnetospheric processes is still debatable. To investigate the relationship, we combine the data of the UV imager onboard the Polar satellite with plasma and magnetic field measurements by the Geotail spacecraft. The poleward edge of the auroral bulge, as determined from the images obtained at the LHBL passband, is found to be conjugated with the region where the oppositely directed fast plasma flows observed in the near-Earth plasma sheet during substorms are generated. We conclude that the auroras forming the bulge are due to the near-Earth reconnection process. This implies that the magnetic flux through the auroral bulge is equal to the flux dissipated in the magnetotail during the substorm. Comparison of the magnetic flux through the auroral bulge with the magnetic flux accumulated in the tail lobe during the growth phase shows that these parameters have the comparable values. This is a clear evidence of the loading–unloading scheme of substorm development. It is shown that the area of the auroral bulge developing during substorm is proportional to the total (magnetic plus plasma) pressure decrease in the magnetotail. These findings stress the importance of auroral bulge observations for monitoring of substorm intensity in terms of the magnetic flux and energy dissipation.