stabilityClass() computes stability class according to IAEA method based
on net radiation, total cloud cover tcc and wind speed.
Net radiation and wind are used by day; tcc and wind are used by night.
Three different algorithms are implemented, selected by the option
argument.
iaea option implements the *radiation-wind method recommended by the
International Atomic Energy Agency (IAEA) and it is based on the net
radiation during the day and cloud cover by night.
pasquill option is based on the original Pasquill formulation and
lacks the "very weak" solar insolation present in the modified iaea
version.
Eventually, the custom options is similar to iaea,
with slightly different set of parameters for net radiation, wind speed
and cloud cover.
Previously used option impact is the same as iaea and it is now
deprecated.