Two Very Low Frequency (VLF) AWESOME remote sensing systems located at Algiers, Algeria (36.45°N, 3.28°E) and Sebha, Libya (27.02°N, 14.26°E) monitor VLF signal perturbations for evidence of ionospheric disturbances. During the EuroSprite‐2007 campaign a number of Transient Luminous Events (TLEs) were captured over the Mediterranean Sea by cameras at Pic du Midi (42.94°N, 0.14°E) and at Centre de Recherches Atmosphériques (CRA) in southwestern France (43.13°N, 0.37°E). The cameras observations are compared to collected VLF AWESOME data. We consider early VLF perturbations observed on 12–13, 17–18 October and 17–18 December, 2007. The data from the two VLF receivers confirm the association between TLEs and early VLF signal perturbations with the perturbations amplitudes dependent on the observation configuration i.e. whether the TLE is near the receiver, near the transmitter, or far from both and the scattering process. The results also reveal that the early VLF perturbations can occur in the absence of a TLE.

[1] Lightning strokes are capable of initiating disturbances in the lower ionosphere, whose recoveries persist for many minutes. These events are remotely sensed via monitoring subionospherically propagating very low frequency (VLF) transmitter signals, which are perturbed as they pass through the region above the lightning stroke. In this paper we describe the properties and characteristics of the early VLF signal perturbations, which exhibit long recovery times using subionospheric VLF transmitter data from three identical receivers located at Algiers (Algeria), Tunis (Tunisia), and Sebha (Libya). The results indicate that the observation of long recovery events depends strongly on the modal structure of the signal electromagnetic field and the distance from the disturbed region and the receiver or transmitter locations. Comparison of simultaneously collected data at the three sites indicates that the role of the causative lightning stroke properties (e.g., peak current and polarity), or that of transient luminous events may be much less important. The dominant parameter which determines the duration of the recovery time and amplitude appears to be the modal structure of the subionospheric VLF probe signal at the ionospheric disturbance, where scattering occurs, and the subsequent modal structure that propagates to the receiver location.

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The study presented in this paper investigated the performance of a proposed system constructed from Brayton, two parallel inverse Brayton and Rankine cycles. It has been carried out by varying the Brayton cycle pressure ratio for different values of expansion pressures of the two inverse Brayton cycles using variable inlet pressures, above atmospheric. The results revealed that the best theoretical performance could be achieved when the system was simulated with a high value of expansion pressure of the second inverse Brayton cycle. Also, it was shown that, as a result of altering the expansion pressure of the second inverse Brayton cycle, the range of the upper cycle pressure ratio increased and the system attained a high thermal efficiency (54 per cent).