MadSci Network: Earth Science

Re: Auroras

Area: Earth Science
Posted By: Keith Little, Systems Analyst/Programmer
Date: Sat Nov 23 15:14:38 1996
Message ID: 845999030.Es


I'll take your questions one at a time (in a slightly different order).


* What is an isochasm?

  An "Isochasm" is a Meteorological "Isopleth".  The word Isopleth
  is derived from the Greek "Iso" meaning equal, and "Plethes" meaning
  quantity.  Specific Isopleth names have been derived with the prefix
  "Iso", and a suffix referring to the particular measurement quantity.
  Whenever possible, the suffixes have a Greek derivation.

  Isopleths are used for analyzing meteorological maps and charts for
  various atmospheric properties.  Two dimensional fields can be
  analyzed by drawing field lines of equal value. In a continuous
  field, these lines never cross or end abruptly.

  An example of this can be seen in the weather maps during your local
  evening news.  The black lines with numbers around 1000 are called
  "Isobars", which follow paths of equal ("Iso") barometric pressure
  ("Bars", where 1 "Bar" equals 1000 "millibars").  These are used to
  indicate pressure gradients, which can correspond to different weather
  systems boundries (areas of high and low pressure).

  Therefore, an "Isochasm" is a path of equal ("Iso") auroral frequency
  ("Chasm").  Another term for this is "Isaurore".

* Are kiloralies and intensity the same thing?

  Sorry, but I'm not sure what "Kiloralies" are.  However, you might
  mean "Kilocalories".  A "Calorie" is the amount of heat required to
  raise the temperature of 1 gram of water by 1 degree Celsius, and a
  Kilocalorie (or "kcal") is 1000 calories. Unfortunately, I don't
  know how this relates to auroras.

* Has an aurora ever been seen from anywhere in the US?

  Auroras can be seen in Alaska and the northern continental states
  (actually in the higher latitudes of both northern and southern

* Are auroras more likely to occur in summer or winter?

  Auroras occur all year round, but the seasons determine where they
  can be seen.  This is due to the tilt of the earth's pole, which
  changes the angle of the solar radiation striking the earth, and
  hence, the latitude.

* Which shapes/forms do auroras occur in most?  Are auroras always a
  mix of colors or can it be only one color?  How is the color violet
  made in auroras?

  Auroras have no definite shape or color, and are determined by the
  random nature of solar radiation.  The colors in an aurora are
  produced by the quantum mechanics of atomic ionization.  Higher
  solar radiation energies cause to light with shorter wavelengths
  (more blue, violet or ultraviolet) to be emitted by the aurora.

* How do solar flares cause auroras to become more intense?  How does
  electrical discharge make up the light of auroras?

  Auroras are caused when gasses in the earths upper atmosphere are
  struck by solar radiation (infrared, visible and ultraviolet light,
  X-rays, Gamma rays and charged particals from the solar wind).
  When this happens, they become a "Plasma", which is the fourth state
  of matter (the other three are solid, liquid and gas).

  A Plasma is a low-density gas in which the individual atoms are
  charged, even though the total number of positive and negative 
  charges is equal, maintaining an overall electrical neutrality.

  When an atom in the atmospheric gas absorbs a packet of energy
  (or "Photon") from the sun, or interacts with a high-energy
  partical, an electron orbiting the atom is ejected.  The atom
  is then said to be "Ionized".  Some time later, an electron will
  rejoin the atom in an attempt to rebalance its charge.  When this
  happens, a photon is emitted, and can be seen if its wavelength
  falls within the visible spectrum.

  In addition, solar flares can intensify auroras, as they release
  large amounts of charged particals into the solar wind.

* Can airplanes disturb auroras by flying through them?  Or can they
  fly through them at all?

  Auroras occur at altitudes generally too high for airplanes,
  except for highly specialized vehicles like the SR-71 Blackbird,
  the Space Shuttle or other rocket boosters.  If an aircraft or
  spacecraft flew through an aurora, it would definitely disturb it,
  due to the gasses expended by the engines.

  By the way, there is reportedly an experimental air/space craft
  dubbed the "Aurora", which might be able to fly that high, and
  with speeds approaching Mach 9!  Not to really hard to believe,
  as the Space Shuttle re-enters the atmosphere at around Mach 25.


Hope this helps!

Keith Little

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