Diaxiom Technologies

Lightning

The ionosphere/ thermosphere is a multi-layered plasma filled with ions and electrons that are constantly in motion.  These ions and electrons move and change places acoss the ionosphere depending on the time of day.   See diagram below.

The lowest part of the Earth's atmosphere is called the troposphere and it extends from the surface up to about 10 km (6 miles). The atmosphere above 10 km is called the stratosphere, followed by the mesosphere.  It is in the stratosphere that incoming solar radiation creates the ozone layer.  At heights of above 80 km (50 miles), in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion.  The number of these free electrons is sufficient to affect radio propagation. This portion of the atmosphere is ionized and contains a plasma which is referred to as the ionosphere.  In a plasma, the negative free electrons and the positive ions are attracted to each other by the electromagnetic force, but they are too energetic to stay fixed together in an electrically neutral molecule.

Solar radiation at ultraviolet (UV) and shorter X-Ray wavelengths is considered to be ionizing since photons at these frequencies are capable of dislodging an electron from a neutral gas atom or molecule during a collision.  At the same time, however, an opposing process called recombination begins to take place in which a free electron is "captured" by a positive ion if it moves close enough to it. As the gas density increases at lower altitudes, the recombination process accelerates since the gas molecules and ions are closer together. The point of balance between these two processes determines the degree of ionization present at any given time.

The ionization depends primarily on the Sun and its activity. The amount of ionization in the ionosphere varies greatly with the amount of radiation received from the sun.  Thus, there is a diurnal (time of day) effect and a seasonal effect. The local winter hemisphere is tipped away from the Sun, thus there is less received solar radiation. The activity of the sun is associated with the sunspot cycle, with more radiation occurring with more sunspots. Radiation received also varies with geographical location (polar, auroral zones, mid-latitudes, and equatorial regions).  There are also mechanisms that disturb the ionosphere and decrease the ionization.  There are disturbances such as solar flares and the associated release of charged particles into the solar wind which reaches the Earth and interacts with its geomagnetic field.

Thermal escape mechanisms

One classical thermal escape mechanism is Jeans escape. It is the escape of individual molecules from the high tail of the Maxwell distribution, at a level in the atmosphere where the mean free path is comparable to the scale height. Maxwell's distribution prescribes the kinetic energy distribution of the molecules, which depends on the mass and the velocity according to

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From this dependence, we see that the more massive a gas molecule is, the lower its average speed at a given temperature, meaning it is less likely to escape. This is why hydrogen escapes from a given atmosphere more easily than carbon dioxide. Also, if the planet has a higher mass, the escape velocity is greater, and fewer particles will escape. This is why the gas giant planets are able to have significant amounts of hydrogen and helium, while they escape on Earth. The distance to the Sun also plays a part; a close planet has a hotter atmosphere, which generally leads to a faster range of velocities, and more chance of escape. This helps Titan, which is small compared to Earth but further from the Sun, keep its atmosphere.

However, while it has not been observed, it is theorized that an atmosphere with a high enough pressure and temperature can undergo a 'blow-off'. In this situation molecules basically just flow off into space. Here it is possible to lose heavier molecules than would not normally be lost.