Obliquity
of the Ecliptic - the orbital element that determines the amplitude
of the seasonal variation of incident solar
radiation. The present value is 23°2' to 24°27'.
Obscuration
- the term used when the sky is completely hidden by surface-based
obscuring phenomena
Obscuring
Phenomena - any atmospheric phenomenon, except clouds, that
restricts vertical visibility (e.g., dust,
rain, snow, etc.).
Occluded
Front - the front formed by a cold
front overtaking a warm or stationary
front and lifting the warm air above the earth's surface
Occluded
Mesocyclone - A mesocyclone
in which air from the rear-flank downdraft has
completely surrounded the circulation at low levels, cutting off the inflow
of warm unstable low-level air
Orographic
Lift - the lifting of air caused by its passage up and over
mountains or other sloping terrain
Outflow
Boundary - a storm-scale or
mesoscale boundary separating thunderstorm-cooled
air (outflow) from the surrounding air
Overcast
- sky cover classification describing a sky with 95% or more
cloud cover
Overhang
- a radar term indicating a region
of high reflectivity at middle and upper
levels above an area of weak reflectivity at low levels. The overhang
is found on the inflow side of a thunderstorm
(normally the south or southeast side).
Overshooting
Top (or Penetrating Top) - a dome-like protrusion above
a thunderstorm anvil; it represents a very
strong updraft and, hence, a higher potential
for severe weather with that storm. A persistent and/or large overshooting
top often is present on a supercell.
Oxygen
- in its free form, a colorless, tasteless, and odorless gas
in the atmosphere of which it forms about 21% by volume
Ozone
- a triatomic form of oxygen that is
nearly colorless gas of pungent odor; it is formed
naturally in the upper atmosphere, generally
between the heights of about 10 and 50 km and it results in the absorption
of a large part of the sun's most intense incoming radiation
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