• Electron precipitation in Jupiter's northern auroral oval can increase microwave opacity at frequencies observed by the Juno MicroWave Radiometer, appearing as cold spots in brightness temperature. • Precipitation of 32 keV-10 MeV electrons results in ionization of the lower stratosphere below the methane homopause, producing short-lived hydrocarbon ions. • Rapid changes in MWR antenna temperatures over consecutive spacecraft spins highlight short-time scale temporal variations in the ionospheric medium. They imply downward electron fluxes whose fluxes vary within 10 s.