Models of auroral processes have been advanced in which the ionosphere plays an active role in stimulating auroral particle precipitation. The validity of these suggestions can be investigated by releasing an artificial plasma cloud into the ionosphere and studying the effects. To this end, the sounding rocket experiment Trigger, comprising a diagnostic and a chemical release payload, was conducted. As a consequence of the release, a drastic increase of the field-aligned charged particle flux was observed over the approximate energy range 10 eV to more than 300 keV, starting about 150 ms after the release and lasting about 1 s. There is also evidence of a second particle burst, starting 1 s after the release and lasting for tens of seconds. In addition, there is evidence for a periodic train of particle bursts occurring with a 7.7-s period from 40 to 130 s after the release. A transient electric field pulse of 200 mV/m appeared just before the particle flux increase started. Electrostatic wave emission around 2 kHz, as well as a delayed perturbation of the E region below the plasma cloud were also observed. Some of the particle observations are interpreted in terms of field-aligned electrostatic acceleration a few hundred kilometers above the injected plasma cloud. It is suggested that the accelerating electric field was created by an instability driven by field-aligned currents caused by the plasma cloud release. This paper gives an overview of the experiment design and the general result. Particular observations and their interpretation are discussed in more detail in companion papers.