Below are 5-day forecasts of meteorological (1o
x 1o) fields (geopotential height at 500 hPa, surface pressure reduced to msl,
surface temperature) including total atmospheric ozone. The fields are
extracted from Global Forecast System (GFS) data of the National Centers for Environmental Prediction
(NCEP). The animated fields are normally updated once a day.
Special Notes
Geopotential Height represnts
the height above sea level of a pressure level. For example, if a station
reports that the 500 mb height at its location is
5600 m, it means that the level of the atmosphere over that station at which
the atmospheric pressure is 500 mb is 5600 meters
above sea level.
Mean Sea Level Pressure (MSLP) is the pressure at sea level or (when measured
at a given elevation on land) the station pressure reduced to sea level
assuming an isothermal layer at the station temperature. Standardizing pressure
to sea level is important because the surface pressure isn't the same over the
entire surface of the Earth (mountains and valleys). Denver's surface is
about a 'Mile High' above sea level, giving an average surface pressure of 840 millibars. Cape Hatteras is
at sea level giving it an average surface pressure of 1013 millibars.
We account for this pressure disparity by standardizing pressure to sea level.
Otherwise, we might be fooled into thinking that a massive storm system shown
by extremely low pressure is always over the Denver area, when in fact the
pressure is naturally low because of its elevation.
Ozone is a minor but important constituent of the earth's atmosphere. While
it is essential for life as we know it today, it is also a toxic gas that can
result in significant physiological and ecological damage if exposures exceed
critical limits. In both the stratosphere and troposphere, ozone concentration
levels depend on many linked chemical and meteorological mechanisms, which vary
significantly with space and time. If all the ozone in a column of an area were
to be compressed to stp (0
deg C and 1 atmosphere pressure) and spread out evenly over the area, it would
form a slab of Xmm thick. 1 Dobson Unit (DU) is
defined to be 0.01 mm thickness at stp,
or One Dobson unit is the equivalent of 2.69 x 10~16 molecules of ozone/cm~2.