The propagation of Very Low Frequency (VLF: 3–30 kHz) radio waves can be used to remotely monitor two different regions of the Earth systems. One of them is the lower ionosphere, an ionized region of the Earth’s upper atmosphere located between 60 and 90 km in altitude. The other is the magnetosphere. ORACLE uses this VLF remote sensing technique to investigate the short- and long-term variation of the lower boundary of the ionospheree which acts as a monitoring screen for phenomena originating in the Earth’s atmosphere (e.g. ozone shadowing) and in space (e.g. gamma-ray bursts from celestial objects).
The lower boundary of the ionosphere is also known as the ignorosphere because it is the least studied region of the atmosphere. At the same time, this region is where space and space weather processes couple into the Earth’s atmosphere. Thus, ORACLE’s aim is to provide new knowledge on the physical process and conditions in the lower boundary of the ionosphere.
Humankind owes its origin, evolution and present existence to the Earth and its surrounding space, from the atmosphere to the limits of the universe. Yet, this very system poses several threats to society, from galactic gamma ray bursts to solar storms, from ozone layer depletion to extreme weather changes. In fact, all these hazards are able to affect the ionosphere and the magnetosphere.
ORACLE's scientific objectives are:
1) determine whether the day-to-day variability of the VLF signal during sunrise can be explained by the stratospheric ozone variability at its upper boundary,
2) improve the detection of celestial gamma-ray bursts, known as the most energetic phenomena in the universe.
