Night sky radiation. This term is usually used to refer to the loss of long-
wave radiant energy from relatively warm building surfaces to the cooler sky.
The loss is greatest on clear nights when there is little water vapor in the
atmosphere to intercept the outgoing radiation.
Normal. When referring to direction (as of wind), this term means
"perpendicular" or "at right angles."
Operative temperature. The uniform temperature of an imaginary enclosure with
which man will exchange the same dry heat by radiation and convection as with
the actual environment.
A system that uses non-mechanical means to satisfy space
pressure of wind brought to a halt on the windward face of a flat plate. This
latter pressure is the maximum pressure to be extracted from the force of the
wind, and is also known as the 'stagnation pressure'.
Psychrometric Chart. A graphic representation of air temperature and humidity
relationships on a chart.
R-value. A measure of building insulation, or resistance to heat flow driven
by temperature differences. The higher the R- value, the better the
resistance to heat flow. R-values for building materials, air spaces, air
films, etc. are established and used to calculate the overall thermal
resistance of building envelope components such as walls and roofs.
Reflectivity (albedo). The ratio of reflected radiation to received
radiation. Reflectivities differ for shortwave (solar) and longwave
to vapor pressure at saturation (the dew point temperature). RH is plotted on
the psychrometric chart as curved lines from lower left to upper right.
Revised Uniform Summary of Surface Weather Observations (RUSSWO). A weather
summary distributed by the National Climatic Center containing detailed
summaries of different weather variable for numerous weather station
worldwide. A revision of the SMOS summary.
Second-order weather station. Minor weather stations at which a limited
number of climatic variables are collected daily. Climatic data from such
stations are presented primarily as monthly means and extremes.
Shelter effect. A phenomenon in which the air speeds on the leeward side of
an obstruction are lower than those of the free stream due to the influence of
the obstruction on the airflow.
Solar altitude. The vertical angle between the sun's position in the sky and
a horizontal plane. The angle is lowest at winter solstice and highest at