The blue jets occur when some positively charged upper part of any cloud interacts with a negatively charged layer present immediately above it. This then briefly equalizes both opposing charges which result in a bright blue discharge of static electricity. This is called blue lighting.
The blue jet that was seen over Nauru was seen through optical cameras, photometers, and an X-ray and gamma-ray detector from the International Space Station. The researchers have gone to say that the blue flashes were accompanied by UV light flashes which are also called ELVES.
As per Neubert, “Normal lightning bolts are formed by discharges between oppositely charged regions of a cloud — or a cloud and the ground — many kilometres apart. But turbulent mixing high in a cloud may bring oppositely charged regions within about a kilometre of each other, creating very short but powerful bursts of electric current.”