N(h) represents the density profile (SEE Electron Density) which is a function of height.

Representation of the D line emission of the sodium atom, which is present in the airglow spectrum.

It is the opposite direction to the Zenith.

Acronym from Not a Number.

It is a prefix of units denoting a factor of 1E-9.

A unit of magnetism (1E-9 Tesla) equivalent to one Gamma (1Tesla equal to 1E-5 gamma).

Electrical discharge from cloud to ground, which transfers negative charges(electrons) from a negatively charged region within the cloud to the ground.

It is the Earth atmosphere region where just the neutral particles are considered importants.

A line along which the magnetic intensity is zero. Like a neutral point, a NL can play an central role in magnetic reconnection, but because of physical reasons, it may be a more likely setting for the actual reconnection process.

Neutral sheet is an important feature of the magnetospheric tail dividing it into two main regions with the largest flux components directed, respectively, parallel and antiparallel to the solar wind.

SEE Heliospheric Current Sheet.

Neutrinos are elementary particles that often travel close to the speed of light, lack an electric charge, are able to pass through ordinary matter almost undisturbed and are thus extremely difficult to detect. Neutrinos have a minuscule, but nonzero mass. They are usually denoted by the Greek letter ν (nu).

The neutron is a subatomic particle with no electric charge and a mass slightly larger than that of a proton.

Absorption of a radio wave as it transits the atmosphere. This mostly occurs in the D and lower E region of the ionosphere. Absorption of this kind is usually more significant than deviative absorption.

The collection of protons and neutrons in the center of an atom.