Air Temperature

Windographer uses the air temperature (also called ambient temperature) to calculate the air density in each time step. On the Data Columns tab of the Configure Dataset window you can identify one or more data columns as type 'air temperature' and specify heights.

You can specify the primary temperature column for your dataset in the Configure Dataset window. Windographer uses the primary temperature column to calculate air density, and to compare temperature data across datasets, for example in the Diurnal Profile, Histogram, and Long Term Patterns windows.

Tip: The Column Display settings in the Configure Dataset window control how temperature columns appear, including naming, order and whether associated SD, max, and min columns are visible.

Calculating Air Density

Windographer uses the primary temperature column to calculate air density. If the dataset does not contain air temperature data, or the primary air temperature data column does not contain data for the time step in question, Windographer estimates the air temperature at the air density elevation according to the following equation, which closely approximates the temperature of the International Standard Atmosphere up to an elevation of 11,000m:

where:
	z	is the air density elevation [m]
	T₀	is the standard sea-level temperature [288.16 K]
	B	is the standard lapse rate [0.00650 K/m]

Source: Manwell et. al (2002).

The graph below plots this equation versus elevation:

Note: Temperature varies strongly with seasonal weather patterns. The constant temperature given by the International Standard Atmosphere only roughly approximates the true temperature. If your dataset contains measured temperature data, but values are missing for some time steps, you can use the Reconstruct Single Dataset window to fill the gaps with data that is statistically similar to the measured data. That technique should produce more accurate temperature data than does the International Standard Atmosphere equation.