Ask A Scientist© Weather Archive

 >    name         Donald
 >    status       other
 >    age          50s

 >    Question -   what is the temperature of a lightening bolt and how does that temperature compare to that of the sun?


>Dear Donald-
>
>The following is from the Encyclopaedia Britannica...
>(http://www.britannica.com/bcom/eb/article/0/0,5716,49370+1+48228,00.html)
>
>LIGHTNING -the visible discharge of atmospheric  electricity occurs when a
>region of the atmosphere acquires an electrical charge, or potential
>difference, sufficient to overcome the resistance of the air.
>Lightning is usually associated with cumulonimbus clouds (thunderclouds) but
>also occurs in nimbostratus in snowstorms and dust storms, and sometimes in
>the dust and gases emitted from erupting volcanoes. During a thunderstorm, a
>lightning flash can occur within a cloud, between clouds, between a cloud
>and air, or from cloud to ground.
>
>Lightning occurs because regions of net charge are generated by
>charge-separation processes that produce an electric dipole structure in a
>cloud. The charges within a thundercloud are distributed between a large
>net-positive charge in the upper region of the cloud, a large net-negative
>charge in the lower region, and a small net-positive charge in the lowest
>part of the cloud. Charges reside on water drops, ice particles, or both. If
>the surrounding air has a net charge, an air discharge from the cloud may
>occur.
>
>The flash of cloud-to-ground lightning is initiated by the neutralization of
>the small net-positive charge in the lowest region of the cloud. A
>cloud-to-ground flash comprises at least two strokes: a   stroke and a
>return stroke. A leader stroke carrying a negative charge passes from cloud
>to ground. (Occasionally, however, the leader stroke is from ground to
>cloud--especially with very high structures such as church steeples,
>multistory buildings, or tall trees.) The leader stroke is not very bright
>and is often stepped and has many branches extending out from the main
>channel. As it nears the ground, it induces an opposite charge, concentrated
>at the point to be struck, and a return stroke carrying a positive charge
>from ground to cloud is generated through the channel. The two strokes
>generally meet about 50 m (164 feet) above the ground. At this juncture, the
>cloud is short-circuited to the ground and a highly luminous return stroke
>of high current passes through the channel to the cloud.
>
>A typical lightning flash involves a potential difference between cloud and
>ground of several hundred million volts, with peak currents on the order of
>20,000 amperes. Temperatures in the channel are on the order of 30,000 K
>(50,000º F). The entire process is very rapid; the leader stroke reaches the
>juncture point or the ground in about 20 milliseconds, and the return stroke
>reaches the cloud in about 70 microseconds.
>
>The thunder associated with lightning is caused by the rapid heating of air
>to high temperatures along the whole length of the lightning channel. The
>air thus heated expands at supersonic speeds, but within a metre or two the
>shock wave decays into a sound wave, which is then modified by the
>intervening medium of air and topography. The result is a series of claps
>and rumbles.
>Although lightning strikes are dangerous because of their high-voltage
>discharges, the tendency of strikes to occur at high points enables
>lightning rods  of conductive metal to draw the strikes and conduct them
>harmlessly into the ground. By moving indoors or by sheltering in a low,
>depressed area, such as a ditch, exposed persons can avoid being struck.
>
>
>...and here is some information on the temperature of the sun...also from
>the Encyclopaedia Britannica...
>
>The High Temperature of the Corona
>The most remarkable aspect of the corona is its high temperature, deduced by
>the Swedish astronomer Bengt Edlen in 1942 after a study of the corona's
>light. Much of that is sunlight scattered by coronal dust, but some light is
>also produced by the corona itself, in narrowly defined colors ("spectral
>lines") characteristic of its emitting atoms. In the 19th century, some of
>the spectral lines of sunlight did not match the lines of any substance on
>Earth, and it was proposed that they came from a new unknown chemical
>element, named helium (from the Greek helios--Sun). Later, in 1895, Norman
>Ramsey actually discovered helium on Earth.
>Unknown spectral lines emitted by the corona were similarly credited to a
>new element "coronium" until Edlen showed that they came from the familiar
>atoms of iron, nickel and calcium, after they had lost an appreciable number
>of electrons (e.g. 13 or 14 for iron). Such high levels of ionization
>require the atoms to be buffeted around by extremely high temperatures,
>around 1,000,000 C (1,800,000 F).
>The source of the corona's heat remains a puzzle. It is almost certain that
>its energy comes from the Sun's internal furnace, which also supplies the
>rest of the Sun's heat. However, as a rule, temperatures are expected to
>drop the further one gets from the furnace, whereas the million-degree
>corona lies outside the surface layer where sunlight originates, whose
>temperature is less that 6000 C.
>
>Wendell Bechtold, meteorologist
>Forecaster, National Weather Service
>Weather Forecast Office, St. Louis, MO

=========================================================
>Donald,
>
>A typical lightning stroke heats the air to
>about 50,000 degrees F, whereas the surface
>temperature of the Sun is only about 10,000
>degrees F.
>
>David Cook
>Argonne National Laboratory
=========================================================