CEDAR email: PhD position in geomagnetism at IPGP, Paris, France
coisson at ipgp.fr
Sat Feb 22 07:21:08 MST 2020
A PhD position is open at the Université de Paris, Institut de physique du globe de Paris (IPGP), France, please transfer this information to any suitable candidate.
The deadline for submitting a complete application is 31 March 2020.
Contact both Pierdavide Coïsson (coisson at ipgp.fr <mailto:coisson at ipgp.fr>) and Gauthier Hulot (gh at ipgp.fr <mailto:gh at ipgp.fr>) for additional details and visit: https://recrutement.cnes.fr/fr/annonce/910893-195-analysis-of-whistlers-in-the-extremely-low-frequency-elf-detected-by-swarm-75013-paris
Analysis of whistlers in the Extremely Low Frequency (ELF) detected by Swarm mission: signals of opportunity for sounding the ionosphere below Low Earth Orbits
The ESA Swarm mission comprises 3 satellites launched in 2013 on quasi-polar low-altitude orbits slowly drifting in local time, to investigate all the sources of the Earth’s. Each satellite carries an Absolute Scalar Magnetometer (ASM) under the scientific responsibility of IPGP, built by CEA-Léti and provided by CNES as a Customer Furnished Instrument. These ASM instruments nominally provide 1 Hz scalar magnetic data for both scientific investigations and the calibration of the Vector Fluxgate Magnetometers (VFM) also on board the satellites. They can, however, also be run in a so-called burst mode, when the sampling frequency is raised to 250 Hz, allowing studies of magnetic signals at frequencies so far never investigated with such precision. Initially the burst mode was tested during few sessions at the beginning of 2014, enabling to observe specific geophysical signals. Starting from 2019 the mission records now burst mode sessions of one-week duration every month. The goal of this thesis is to contribute to the exploitation of these data, along with ground-based observations, in order to improve the understanding of the electromagnetic coupling between the atmosphere and the ionosphere.
A first group of interesting signals contains whistlers, that are observed by Swarm in the Extremely Low Frequencies (ELF) range. They are generated by the strongest lightning strokes occurring in the tropospheric storm systems. These whistlers are well known, but they have not been so far studied systematically in this frequency band from Low Earth Orbits (LEO). They show that a fraction of the lightning signal energy can enter the ionosphere and propagate up to the satellites, even at frequencies normally trapped in the neutral atmosphere. Their propagation further depends on the magnetic field orientation and on the properties of the ionospheric plasma. The investigation of these signals can therefore provide important information about the distribution of lightning in the neutral atmosphere, the conditions allowing the ELF signal to penetrate the ionosphere, and the state of the ionosphere along the path of the signal between the lightning and the satellites. A feasibility study is ongoing aiming at analysing jointly data from Swarm satellites, ground ELF stations and ionosondes to constrain all this chain of phenomena. Specifically, the signals received by the satellites present a dispersion that depends strongly of the ionospheric conditions along the propagation path. A model of ELF signals propagation could be developed during this thesis work. This will provide precious information for testing and improving empirical ionospheric models, such as the International Reference Ionosphere (IRI) model, widely used for many applications. A strategy to improve such models by taking advantage of the characteristics of the whistlers detected by Swarm and the in-situ electron density measurements could thus be developed.
In addition to the investigation of whistlers, which will form the core of this PhD project, investigations of other geophysical signals could also be carried out. Complex signals have for instance been detected when crossing plasma bubbles. Such bubbles usually occur at low latitudes at night and perturb GNSS signals. The signals already detected reveal that small-scale currents can occur at the boundaries of bubbles and play a role in their development. The analysis of burst mode data could therefore contribute to our understanding of the dynamics of such phenomena. Other transitory signals (Schumann resonances, Alfvén waves... ) might also be detected in the burst mode data. All these studies would improve our understanding of the Earth space environment and its connections with the low atmosphere.
The selected candidate will join the IPGP geomagnetism team, will benefit from the experience of this team with the Swarm mission and of ASM instruments. He/She will access sophisticated software, for the processing of burst data and for the whistler propagation simulations. Last but not least, the candidate could also be involved in the development of the NanoMagSat nanosatellite project, which aims at measuring continuously the Earth magnetic field, taking advantage of a miniaturized version of the ASM instruments.
Université de Paris, Institut de physique du globe de Paris
coisson at ipgp.fr
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