Variations of the standard atmosphere are defined. Among the variants are the hot day, the cold day, the polar day and the tropical day. In addition an atmosphere may be defined that is a fixed increment in temperature from a standard day.
The standards group COESA has not defined the characteristics of a typical hot day or cold day, but there is a definition that has been released as MIL-STD-210A and MIL-STD-210C by the US Department of Defense. This MIL-STD defines a hot day, a cold day, a polar day and a tropical day. The definition extends from sea level to 30.5 km (100000 ft). In addition, it is common practice among some aerospace designers to define a non-standard day by an increment in temperature that is applied at all altituded to the standard day temperature. I have coded all of these atmospheres and the full source code is included with the CD-ROM (new in version 10, Jan 2005).
The computational algorithm for all non-standard atmospheres is as follows:
The new subroutines in the package are:
The arguments are:
Some of you may be alarmed at this point, because you may have programs
that use Atmosphere or SimpleAtmosphere that are coded with only
Not to worry!
The new routines are coded with deltaT as an OPTIONAL variable.
If you have
CALL Atmosphere(altKm, sigma,delta,theta)
you will get the same effect as if you had
CALL Atmosphere(altKm, sigma,delta,theta,0.0)
and you will not be flagged as being in error.
For additional information, I have a page that describes the MIL-STD-210 atmospheres and the extension to altitudes greater than 30.5 kilometers. A hot day is similar to a +15 K increment day and a cold day is somewhat similar to a -20 K day. However, the temperature profile for a cold day actually has temperature increasing from 0 to 1 km, then levelling off up to 4km, before beginning a decline as in the standard atmosphere.