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F-BURST – mapping of Field -aligned currents in the ionosphere and BURSTYbulk flows in the magnetotail.



FBURST aims at better understanding the ionosphere-magnetosphere coupling based on multi-spacecraft observations that can monitor the status of the high latitude ionospheric field aligned current system (FAC) and the conditions in the geomagnetic tail.

In particular, this project focusses on the fast plasma jets detected at more than 60000 km from the Earth in the geomagnetic tail, called Bursty Bulk Flows (or BBFs). These BBFs are easily recognisable in in-situ data from ESA’s Cluster mission and NASAs MMS (Magnetospheric Multi-Scale) since they are characterised by velocities exceeding 300 km/s and highly structured magnetic field perturbations, consisting typically of a dipolar variation of the magnetic field component perpendicular to the current sheet (Bz). It has been established that BBFs are responsible for most of the plasma transport from the magnetotail to the inner magnetosphere, playing a pivotal role in the global magnetospheric energy budget. Therefore, advancing our understanding of how BBFs couple to the ionosphere is of critical importance to obtaining a complete understanding of ionosphere-magnetosphere coupling.

The FACs, which are the oldest known manifestation ionosphere-magnetosphere coupling, connect the F2 ionospheric layer (150 – 200 km altitude) with the outer magnetosphere, including also the geomagnetic tail. The main distribution of FACs consists of two concentric rings in the high-latitude ionosphere in proximity of the auroral oval, which is the region where visible polar aurorae are observed. FAC intensity and location are directly connected with the level of geomagnetic activity since they strongly intensified and expands to lower latitudes during geomagnetic substorms.

The current knowledge of BBFs-ionosphere link comes from a number of single-case studies reported in scientific literature, with simultaneous observations of BBFs and FAC in the nightside Region1. FBURST project envisages instead a statistical approach combining together the long-term Swarm observations to monitor FAC in synergy with long-term data from Cluster and MMS to detect BBFs in the geomagnetic tail. This approach, which is currently missing in literature, would allow to: 1- establish a measurable statistical link between BBFs and perturbations in FACs; 2- identify the physical mechanism that connects the BBFs with planarity and spatial scale of FAC filaments. In order to link Swarm and magnetospheric observations and therefore map the BBFs into the ionosphere, FBURST would rely on Tsyganenko field-line model. The project also envisages a statistical connection between MMS/Cluster magnetotail observations and Swarm ionospheric observations, not relying on one-to-one MMS-Cluster-Swarm mapping, that will maximise the use of both statistical datasets.

This will provide a deeper insight into the behaviour of FACs in terms of the variations in current density, the distortion of their structure, and also quantification of the spatial scales. This will simultaneously contribute to a better characterisation of FACs but also shed significant light on a key magnetosphere-Ionosphere coupling mechanism (BBFs), which is not completely understood.



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