Hybrid power generation system for aircraft electrical emergency network

A whole structure and two management strategies are proposed here for hybridisation of a Ram air turbine (RAT) by means of supercapacitors. Such hybrid structure is dedicated to an aircraft emergency network. The structure consists in coupling, through a 270 V DC bus, a controlled source (RAT) with a storage device interfaced through a bidirectional DC–DC converter. Both the energy-management strategies are described and analysed: the first one is to assign the ‘high-frequency harmonics’ of the load power to the storage which is current controlled, whereas the RAT controls the bus voltage and then only feeds the average power, losses and low-frequency harmonics of the load. The second one proposes an energy optimised operation of the system: the RAT, being current controlled, is able to maximise the supplied power (maximum power point tracking), as for classical wind turbines. For such a strategy, the bus voltage is regulated from the storage device. The RAT sizing and its mass can then be strongly reduced by means of this hybrid structure controlled with optimised management strategies. Experiments on a lab test-bench confirm analyses presented

Statistical properties of flux closure induced by solar wind dynamic pressure fronts

peer reviewedWe present a statistical study of flux closure intervals induced by solar wind dynamic pressure fronts. We consider that a dynamic pressure front reaches the Earth when a dayside subauroral proton flash is observed in the SI2 channel of the IMAGE-FUV experiment. This pragmatic criterion selects both weak and strong pressure fronts. It is found that the preconditioning of the magnetosphere prior to the pressure pulse arrival mainly governs the magnetospheric response to a weak solar wind dynamic pressure front. This preconditioning includes the amount of open magnetic flux available in the magnetosphere prior to the pressure front arrival and the size of the magnetospheric cavity. However, in the case of a strong pressure pulse, the magnetospheric response is more sensitive to the solar wind properties characterizing the dynamic pressure front. The pressure jump is not the only one important, but also the variation of the solar wind velocity and IMF magnitude. In overall terms, we find that a strong dynamic pressure front is typically characterized by a dynamic pressure increase larger than Ë 2.8 nPa that takes place on timescales of the order of a few minutes

Solar wind control of auroral substorm onset locations observed with the IMAGE-FUV imagers

peer reviewedThe FUV imagers on board the IMAGE satellite provide multispectral snapshots of the polar region every 2 min. The combination of the Wide-Angle Imaging Camera (WIC) with SI12 (Doppler shifted Lyman-alpha) and SI13 (135.6 nm) spectral imagers is used to discriminate between the electron and the proton aurora. We describe a statistical study of the location of 78 substorms observed close to the 2000-2001 winter solstice. The latitudinal distribution of the onsets observed with WIC is asymmetric with a median at 65.6° MLAT and a full width at half maximum (FWHM) of 3.5°. Their local time distribution is concentrated between 2000 and 0200 MLT with a median at 23.4 +/- 0.3 hours MLT and a FWHM of 1.8 hours. No statistically significant difference is found in the spatial distribution of the proton and electron onsets. All onsets take place within a region of preexisting proton precipitation, indicating that substorm initiation occurs in regions of stretched but dipole-like field lines that cross the equatorial plane close to the Earth. Latitudes of substorm onsets are located at a variable distance from the poleward FUV auroral boundary but remain at a nearly constant distance from the equatorward limit of both proton and electron auroral ovals. The magnetic latitudes of the onsets are correlated with some of the solar wind plasma properties measured by the ACE satellite prior to the substorm breakup. In particular, a clear anticorrelation is found between the onset MLAT and the 1-hour averaged solar wind dynamic pressure. A decrease of the onset latitude is also observed for larger B intensity values. No dependence of the onset MLT on the solar wind speed is observed, in contrast to the relationship expected from the thermal catastrophe model for substorm initiation. Our results are in agreement with models locating the initial instability in the near magnetosphere such as the near-Earth current disruption models

Potential of TIMED/GUVI limb observations for medium-scale traveling ionospheric disturbances study at mid-latitudes

At mid-latitudes, medium-scale traveling ionospheric disturbances (MSTIDs) are the most recurrent type of ionospheric irregularities. During daytime, the common source of MSTIDs is the propagation of atmospheric gravity waves whose origin is generally found in the lower atmosphere. In the nighttime hours, the Perkins instability induces another type of MSTIDs that is correlated with the appearance of sporadic E layers, sometimes leading to spread-F signatures in ionograms. MSTIDs climatology and characterization have been extensively described during the last two decades, mainly using GNSS measurements. However, only few studies are devoted to the description of their vertical structure and the monitoring of their propagation into the ionosphere, which is helpful to understand their dissipation processes and their physical origin. The NASA’s TIMED mission was launched in December 2001 on a 74° inclination low-Earth orbit at an altitude of 625 km, which allowed to cover both low and high-latitude regions. The Global Ultraviolet Imager (GUVI) instrument aimed at remotely sense, among others, the ionospheric ion and electron densities. GUVI performs disk observations and limb scans in five FUV wavelength channels, making it an ideal tool to characterize the vertical structure of the ionosphere as well as to contextualize the study. The purpose of this work is to use GUVI limb scans to characterize MSTIDs preliminary detected by GNSS in mid-latitudes before December 2007, after which the instrument exclusively supplied disk observations. We first select a few MSTID cases during solar maximum conditions that were observed in the Total Electron Content (TEC) by GNSS ground stations. Then, we combine our dataset with GUVI limb observation of the OI-135.6 nm emission to characterize the vertical structure of the MSTIDs. At last, concurrent observations from ionosondes located in the vicinity of the region where the GNSS and GUVI data were obtained will also provide an interesting cross-comparison dataset