The weather history files contain a time history of meteorological conditions at the scene site. The file must contain at least 48-hours of weather data so that can simulate any time of the day and have 24-hours of previous weather history available to it.
The weather history file is organized as column data, where each row includes the observed parameters for the given time. The columns can be separated by either space or tab characters. Table 34-7 describes the values and units for each column in a file.
Table 34-7. Values and units for a weather history () file.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
| Relative Time | Air Temp | Pressure | Relative Humidity | Dew Point | Wind Speed | Direct Insltn | Diffuse Insltn | Sky Exposure | Cloud Type | Precip Type | Precip Rate | Precip Temp |
| [hours] | [C] | [mbars] | [fraction] | [C] | [m/s] | [L/hr] | [L/hr] | [fraction] | (below) | (below) | [cm/hr] | [C] |
The ``Sky Exposure'' column describes the amount of visible sky and should be set to 0 for a completely overcast observation and 1 for severe clear. The type of clouds making up the cloud fraction is described by the ``Cloud Type'' column (see below).
Table 34-8 defines the numeric values corresponding to the possible cloud types. This cloud type will be assigned to the cloud fraction of the sky defined by the ``Sky Exposure'' parameter.
Direct insolation (``Direct Insltn'') is the energy that comes from the sun and does not interact with the atmosphere; diffuse insolation (``Diffuse Insltn'') does interact with the atmosphere. Both parameters feed the thermal model. Note that the units for are Langleys per hour. These values can be generated using the integrated irradiance from MODTRAN. The conversion factor from integrated irradiance to L/hr is 0.0858.
Table 34-8. Possible values and descriptions for ``Cloud Type'' in weather history.
| 0 | None |
| 1 | Cirrus |
| 2 | Cirrostratus |
| 3 | Altocumulus |
| 4 | Altostratus |
| 5 | Stratocumulus |
| 6 | Stratus |
| 7 | Nimbostratus |
| 8 | Fog |
The ``Precipitation Type'' column controls the appearance of precipitation for the observation time. If this value is set to 0 , then no rain was observed. If this value is set to 1 then the ``Precipitation Rate'' and ``Precipitation Temperature'' values are used.
Below is a condensed weather history file. The first line contains the number of entries in the file and the time interval (hours) for the observations.
193 0.25
0.00 10.17 1000.00 0.70 5.00 3.00 0.00 0.00 1.00 0 0 0.00 0.00
0.25 10.15 1000.00 0.70 5.00 3.00 0.00 0.00 1.00 0 0 0.00 0.00
0.50 10.13 1000.00 0.70 5.00 3.00 0.00 0.00 1.00 0 0 0.00 0.00
[values deleted for documentation purposes]
5.25 10.00 1000.00 0.70 5.00 3.00 0.00 0.00 1.00 0 0 0.00 0.00
5.50 10.02 1000.00 0.70 5.00 3.00 48.29 0.20 1.00 0 0 0.00 0.00
5.75 10.14 1000.00 0.70 5.00 3.00 61.19 0.70 1.00 0 0 0.00 0.00
[values deleted for documentation purposes]
23.75 10.17 1000.00 0.70 5.00 3.00 0.00 0.00 1.00 0 0 0.00 0.00
24.00 10.17 1000.00 0.70 5.00 3.00 0.00 0.00 1.00 0 0 0.00 0.00
24.25 10.17 1000.00 0.70 5.00 3.00 0.00 0.00 1.00 0 0 0.00 0.00
24.50 10.17 1000.00 0.70 5.00 3.00 0.00 0.00 1.00 0 0 0.00 0.00
[values deleted for documentation purposes]
48.00 10.17 1000.00 0.70 5.00 3.00 0.00 0.00 1.00 0 0 0.00 0.00