INTERPLANETARY MAGNETIC FIELD   :   

The magnetic field carried with the solar wind.

INVASIVE SPECIES   :   

Refers to a subset of introduced species or non-indigenous species that are rapidly expanding outside of their native range.

ION   :   

An atom or molecular fragment that has a positive electrical charge due to the loss of one or more electrons; the simplest ion is the hydrogen nucleus, a single proton.

IONOSPHERE   :   

A region of charged particles in a planet's upper atmosphere; the part of the earth's atmosphere beginning at an altitude of about 400 kilometers (25 miles) and extending outward 400 kilometers (250 miles) or more.

ISOBARS   :   

Lines on a map connecting points having the same barometric pressure.