Identification And Analysis Of Ionospheric Plasma Bubbles

At dusk,the ionospheric F-region plasma density in the equatorial region often exhibits depletions.This structure is usually called equatorial plasma bubbles(EPBs).As a result of the plasma diamagnetic effect,the magnetic field strength inside the plasma bubble will increase,while the components perpendicular to the ambient magnetic field show variations interpreted as Alfvenic signatures accompanying the field aligned currents.However,the mechanisms underlying formation of the transverse perturbations are still not very clear.This paper uses the vector,scalar magnetic field and plasma density data of the European Space Agency Swarm constellation,to investigate the magnetic signatures related with EPBs.We find changes both in the magnetic field strength and the component parallel with the main field are all anti-correlated with the density variations inside EPBs.When using the scalar and vector(parallel component)data products of Swarm to identify EPBs,we find that the noise level of the scalar magnetometer is obviously lower than that of the vector magnetometer onboard Swarm,and using the scalar data can increase the chance to identify EPBs,especially to find EPBs with relatively lower field fluctuations.We analyze the influence of the magnetic field data quality on the automatic plasma bubble identification,and introduced other physical phenomena that may interfere the identification,including the plasma blob,medium to small-scale travelling ionospheric disturbances,and geomagnetic pulsations.Correctly identifying EPBs from the magnetic field data produced by the near Earth orbiting satellites,can help understanding the evolution of EPBs globally,and advancing scintillation forecast.On the other hand,excluding the magnetic field data affected by the plasma bubble may increase the accuracy of the geomagnetic model.