Showing papers by "Tobia Carozzi published in 2001"

First results of electric field and density observations by Cluster EFW based on initial months of operation

Abstract: Highlights are presented from studies of the electric field data from various regions along the CLUS- TER orbit. They all point towards a very high coherence for phenomena recorded on four spacecraft that are sepa- rated by a few hundred kilometers for structures over the whole range of apparent frequencies from 1 mHz to 9 kHz. This presents completely new opportunities to study spatial- temporal plasma phenomena from the magnetosphere out to the solar wind. A new probe environment was con- structed for the CLUSTER electric field experiment that now produces data of unprecedented quality. Determination of plasma flow in the solar wind is an example of the capability of the instrument.

Multi-spacecraft observations of broadband waves near the lower hybrid frequency at the Earthward edge of the magnetopause

Abstract: Broadband waves around the lower hybrid frequency (around 10 Hz) near the magnetopause are studied, using the four Cluster satellites. These waves are common at the Earthward edge of the boundary layer, consistent with earlier observations, and can have amplitudes at least up to 5 mV/m. These waves are similar on all four Cluster satellites, i.e. they are likely to be distributed over large areas of the boundary. The strongest electric fields occur during a few seconds, i.e. over distances of a few hundred km in the frame of the moving magnetopause, a scale length comparable to the ion gyroradius. The strongest magnetic oscillations in the same frequency range are typically found in the boundary layer, and across the magnetopause. During an event studied in detail, the magnetopause velocity is consistent with a large-scale depression wave, i.e. an inward bulge of magnetosheath plasma, moving tailward along the nominal magnetopause boundary. Preliminary investigations indicate that a rather flat front side of the large-scale wave is associated with a rather static small-scale electric field, while a more turbulent backside of the large-scale wave is associated with small-scale time varying electric field wave packets.

LINDA – the Astrid-2 Langmuir probe instrument

Abstract: . The Swedish micro-satellite Astrid-2, designed for studies in magnetosperic physics, was launched into orbit on 10 December 1998 from the Russian cosmodrome Plesetsk. It was injected into a circular orbit at 1000 km and at 83 degrees inclination. The satellite carried, among other instruments, a double Langmuir Probe instrument called LINDA (Langmuir INterferometer and Density instrument for Astrid-2). The scientific goals of this instrument, as well as the technical design and possible modes of operation, are described. LINDA consists of two lightweight deployable boom systems, each carrying a small spherical probe. With these probes, separated by 2.9 meters, and in combination with a high sampling rate, it was possible to discriminate temporal structures (waves) from spatial structures. An on-board memory made it possible to collect data also at times when there was no ground contact. Plasma density and electron temperature data from all magnetic latitudes and for all seasons have been collected. Key words. Ionosphere (plasma temperature and density; plasma waves and instabilities; instruments and techniques)

Full polarimetry measurements of stimulated electromagnetic emissions: First results

Abstract: A theory and technique for the measurement of the full state of polarization (SOP) for wideband electromagnetic HF emissions from the ionosphere are introduced. The technique was employed in a recent experiment at the Sura ionospheric HF pumping facility near Nizhniy Novgorod, Russia, to measure the full SOP of stimulated electromagnetic emissions (SEE) in their steady state. Measurements were made for O-mode polarized pump waves at two different frequencies: one below and one slightly above the fourth electron gyroharmonic frequency. The wideband spectral parameters measured in this experiment include the horizontal intensity, the degree of horizontal circular polarization, the degree of horizontal polarization and the tilt angle of the horizontal polarization ellipse. Evaluation of the data collected demonstrates that the technique can be used for HF polarimetry and that, in particular, such measurements provide useful new diagnostics for SEE. Among the most important results regarding the polarimetry of SEE were low degrees of circular polarization in the frequency range between the peak of the broad upshifted maximum and the pump; some SEE features had degree of circularity and tilt angle values that were consistent with slightly oblique waves indicative of a distributed SEE source region; and the pump was found to have changed from an initial left-handed polarized state to a right-handed polarized state during steady state.

en Waves Observed by Cluster at the Magnetopause

Abstract: We analyze ELF turbulence (∼0.03-10 Hz) ob- served by Cluster at the magnetopause layer during multi- ple, 120 magnetopause crossings on a single event, Decem- ber 31, 2000, 09-16 UT. Waves below the proton gyrofre- quency (fci ≈ 0.3 Hz) are identified as kinetic Alfvwaves, while waves (0.3-10 Hz) between the ion gyrofrequency and the lower hybrid frequency are consistent with drift-Alfv ´ waves driven by strong density gradients. These waves ex- hibit an electrostatic character and from their dispersive prop- erties we infer that they may have perpendicular scales less than ion gyroradius. Due to rapid convective flows at the magnetopause boundary the short wavelength structures are Doppler shifted and appear as broadband waves in satellite data. The Cluster observations show that the dispersive Alfv ´ waves at the magnetopause layer have electric field magni- tudes of 5 mV/m and spectral peak power of 10 −6 (V/m) 2 /Hz. These waves are expected to play an important role in the processes of energy/mass transport and diffusion across the magnetopause.