G

Gale

In popular use, an unusually strong wind. In Beaufort wind scale, it corresponds to a Force 8, with a wind speed between 34 and 40 knots.

Geomagnetic storm

It is a temporary disturbance of the Earth’s magnetosphere caused by a disturbance in the interplanetary medium. It is associated with coronal mass ejections (CME), coronal holes, or solar flares. A geomagnetic storm is caused by a solar wind shock wave and/or cloud of magnetic plasma which interacts with the Earth’s magnetic field. The sunspot cycles have a direct influence in the frequency of geomagnetic storms.

Geostationary satellite

Meteorological satellite that orbits the earth west-to-east above the equator, once every 24 hours, at an altitude of almost 22400 miles (36000 km), with the same angular velocity as the Earth. The orbital plane coincides with the Earth’s equatorial plane, describing a perfectly circular orbit.

Glacial period

Phase or period during an ice age, marked by an advance of ice toward the equator.

Global Positioning System (GPS)

Computational navigation system that has the capacity to triangulate positions near the Earth’s surface, through the data offered by 24 low earth-orbiting satellites. The system can determine positions with an accuracy of 30 to 100 meters, but if systems at two locations are used with long integration times, positions might be determined within millimeters of a known reference.

Global Warming

Observed gradual increase in the average temperature of the Earth’s atmosphere and oceans.

Glory

Ono or more sequences of faintly colored rings of light than can be seen by an observer around his own shadow cast on a water cloud (a cloud consisting mainly of small water droplets). It can also be seen on fog and exceptionally, on dew.

Gravity

Force exerted by the earth to a mass that is at rest relative to the earth. It is the resultant of the force of gravitation (mutual attraction between bodies possessing mass) and the centrifugal force arising from Earth’s rotation.

Green flash / Green ray

Flash of predominantly green light of short duration observed on or adjacent to the upper edge of a luminary (Sun or Moon, eventually a planet) when appearing above or disappearing below the horizon, caused by refraction of light.

Greenhouse Effect

Process by which certain trace gases in the atmosphere produce a heating or warming effect upon the lower atmospheric layers and therefore, upon the earth, by absorbing and reemitting infrared radiation.

Greenhouse gases

Gases, present in trace concentrations in the atmosphere, such as water vapor –the main one-, carbon dioxide, ozone, methane, nitrous oxide and chlorofluorocarbons that are very efficient absorbers of the longer wavelengths of the infrared radiation emitted by the earth and the atmosphere and relatively transparent to sunlight. By trapping heat, originally proceeding from solar radiation, these gases control the Earth’s surface temperature.

Gulf Stream

One of the western boundary currents of the North Atlantic subtropical gyre. Deep, narrow and fast current –one of the swiftest-, with one of the greatest transports. It begins continuing the Florida Current, and then penetrating into the Atlantic as a free jet; this water then rejoins the Florida current as the Gulf Stream recirculation. As a free jet, it develops meanders that may break off as eddies, or rings.

Gust

Sudden, brief increment of wind speed over its mean value. It has a transient character (usually less than 20 seconds) and it is followed by a lull.

Gyre

Large-scale oceanic circulation cell usually associated with a subtropical high pressure cell.