Field-aligned scale length of depleted structures associated with post-sunset equatorial plasma bubbles

In this study we make use of the Swarm counter-rotation constellation for estimating typical scale length post-sunset equatorial plasma bubbles (EPBs) along fluxtubes. The close approaches between spacecraft near equator occurred in September and October 2021, covering magnetic local time from 19:00 to 23:00, which is favorable occurrence EPBs. It first show quasi-simultaneously samplings by A/C B same fluxtube but at different altitude. observations frequently reveal density depletions only one altitude, confirming that EPBs extend over finite parts fluxtube. Based on a statistical analysis double single EPB detections fluxtube, our results imply field-aligned depletion structures associated with order 550 km. Our are lower part depleted fluxtubes, they coincide well latitudes ionization anomaly. upper equator, estimation technique does not work because too large separation satellites.