Engineering topics

Andre, Mats

Publications and source records attributed to Andre, Mats.

7 records

NASA NTRS2016

Cold Ion Demagnetization near the X-line of Magnetic Reconnection

Although the effects of magnetic reconnection in magnetospheres can be observed at planetary scales, reconnection is initiated at electron scales in a plasma. Surrounding the electron diffusion region, there is an Ion-Decoupling Region (IDR) of the size of the ion length scales (inertial length and gyroradius). Reconnection at the Earths magnetopause often includes cold magnetospheric (few tens of eV), hot magnetospheric (10 keV), and magnetosheath (1 keV) ions, with different gyroradius length scales. We report observations of a subregion inside the IDR of the size of the cold ion population gyroradius (approx. 15 km) where the cold ions are demagnetized and accelerated parallel to the Hall electric field. Outside the subregion, cold ions follow the E x B motion together with electrons, while hot ions are demagnetized. We observe a sharp cold ion density gradient separating the two regions, which we identify as the cold and hot IDRs.

Toledo-Redondo, Serio↗

NASA NTRS2005

Analysis of plasmaspheric plumes: CLUSTER and IMAGE observations and numerical simulations

Plasmaspheric plumes have been routinely observed by CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. Total electron density profiles can be derived from the plasma frequency and/or from the spacecraft potential (note that the electron spectrometer is usually not operating inside the plasmasphere); ion velocity is also measured onboard these satellites (but ion density is not reliable because of instrumental limitations). The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 RE every 10 minutes; such images acquired near apogee from high above the pole show the geometry of plasmaspheric plumes, their evolution and motion. We present coordinated observations for 3 plume events and compare CLUSTER in-situ data (panel A) with global images of the plasmasphere obtained from IMAGE (panel B), and with numerical simulations for the formation of plumes based on a model that includes the interchange instability mechanism (panel C). In particular, we study the geometry and the orientation of plasmaspheric plumes by using a four-point analysis method, the spatial gradient. We also compare several aspects of their motion as determined by different methods: (i) inner and outer plume boundary velocity calculated from time delays of this boundary observed by the wave experiment WHISPER on the four spacecraft, (ii) ion velocity derived from the ion spectrometer CIS onboard CLUSTER, (iii) drift velocity measured by the electron drift instrument ED1 onboard CLUSTER and (iv) global velocity determined from successive EUV images. These different techniques consistently indicate that plasmaspheric plumes rotate around the Earth, with their foot fully co-rotating, but with their tip rotating slower and moving farther out.

Darouzet, Fabien↗

NASA NTRS1992

Electron acceleration by low frequency electric field fluctuations - Electron conics

Electron conics can be generated by fluctuations at roughly one Hz in a parallel electric field accelerating auroral electrons at altitudes of several thousand kilometers. The results from simulations including such time-varying electric fields are in good agreement with observed electron distributions. The simulation parameters are consistent with the ion beams and broadband waves associated with electron conics. Calculations are used to predict for example oscillations in the low altitude electron fluxes. These results can be used to compare different possible mechanisms for the generation of electron conics.

Andre, Mats↗

NASA NTRS1991

Convection of ion cyclotron waves to ion-heating regions

Results are presented on calculations of the convection, to lower altitudes, of low-frequency ion cyclotron waves generated in the central plasma sheet. In the calculations, ion cyclotron waves generated in the equatorial plane by a proton temperature anisotropy are considered, and the computed growth rates are used to create a model wave distribution. Spectral densities are then mapped along the magnetic field lines, using phase space methods of Ronnmark and Larsson (1988). It was found that, even in the absence of growth associated with a plasma instability, the electric fields of ion cyclotron emissions from the equatorial region will increase substantially as the waves propagate to higher latitudes. It is shown that ion cyclotron waves propagating down the field lines may contribute to the waves observed together with ion conics.

Ronnmark, Kjell↗

NASA NTRS1990

Ion heating by broadband low-frequency waves in the cusp/cleft

Ion heating via a cyclotron resonance process involving waves near the ion gyrofrequency is studied using data from two cusp/cleft crossings of the polar-orbiting DE 1 satellite. Observed cool O(+) distributions and wave intensities from one orbit are used as input to a Monte Carlo simulation. The results show that cyclotron resonance heating by broadband low-frequency waves can cause a major part of the ion heating observed in the cusp/cleft.

Andre, Mats↗

NASA NTRS1990

Heating of ion conics in the cusp/cleft

Ion conic distributions are often observed in the cusp/cleft region of the dayside magnetosphere. These ions can be heated by resonant interaction with broadband low-frequency (near the ion gyrofrequency) waves. Data from one cusp/cleft crossing of the polar orbiting DE-1 satellite is studied in detail. Observed cool O(+) distributions and observed wave intensities are used as input to a Monte Carlo simulation. The theoretically obtained hot O(+) distributions are in good agreement with the corresponding observed distributions. This resonant heating by broadband low-frequency waves is important for the outflow of ionospheric ions into the magnetosphere.

Andre, Mats↗

NASA NTRS1989

Equatorially generated ULF waves as a source for the turbulence associated with ion conics

Consideration is given to the possible source of low frequency turbulence on closed field lines in the central plasma sheet, which is used to explain ion heating and conic formation. Observations show that ion distributions in the equatorial region are often anisotropic and that these distributions excite ion cyclotron waves below the proton gyrofrequency and near the harmonics of the hydrogen cyclotron frequency. It is suggested that downcoming right-hand circularly polarized waves acquire a left-hand circularly polarized component at the crossover frequency and may tunnel through a stop zone to altitudes where they contribute to ion heating.

Johnson, Jay R.↗