**McIDAS Programmer's Manual
Version 2006**

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The McIDAS-X library provides a set of scientific utilities for computing meteorological parameters such as potential temperature, equivalent potential temperature, and mixing ratio.

The table below provides an alphabetical listing of the scientific utilities provided in McIDAS-X.

For more information about these scientific functions, see the online man pages provided with the McIDAS-X software. |

Given
the temperature, dew point and pressure, the **lab** function
computes the following:

To compute
these meteorological parameters using the pressure at the station instead of
the reported pressure, which has been corrected to sea level, the **lab** function
will automatically adjust for the pressure differences due to elevation.

The following example computes potential and equivalent potential temperatures, and mixing ratio with adjustments made to the pressure based on the height.

Given the temperature
and dew point, the functions **McHeatIndex** and **mcheatindex** will
compute the heat index. The value returned will be given in the same units
as the input temperature. Below is an example of the function **mcheatindex**.

Given the temperature
and dew point, the functions **McRelativeHumidity** and **mcrelativehumidity** will
compute the relative humidity. The value returned will be given in the dimensionless
units of percentage. Below is an example of the function **mcrelativehumidity**.

Given the temperature
and wind speed, the functions **McWindChill** and **mcwindchill** will
compute the wind chill. The value returned will be given in the same units
as the input temperature. Below is an example of the **mcwindchill** function.

Given a temperature,
in Kelvin, and the pressure, in mb, the **rmix** function
will return the mixing ratio. The returned value, ws, is defined as the mass
of water vapor per mass of dry air. It is dimensionless, with units of g/kg.
The sample code below computes the saturation mixing ratio at 0° Celsius
for all pressures 100, 150, 200, 250, ... 950, 1000 mb, resulting in 40.44,
26.39, 19.59, 15.57, ... 4.02, 3.82 g/kg.

integer i real temperature real pressure real mix temperature=273.15 do 100 i=1000,100,-50 pressure=float(i) |

Given
vertical profiles of pressure, temperature, dew point, wind speed and direction,
the **sndanl** function computes these stability
indices:

- Parcel dew point, potential temperature, equivalent potential temperature and mixing ratio
- Precipitable water
- Convective temperature and forecast maximum temperature (for data from 1200 UTC only)
- Lifted index, total-totals index, K-index and sweat index
- Equilibrium pressure level

Below is an
example of the **sndanl** function.

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