Calm Threshold

The calm threshold is a wind speed value below which Windographer considers the wind to be 'calm'. You specify the calm threshold on the Dataset tab of the Configure Dataset window.

The value of the calm threshold affects two wind rose graphs and tables: frequency versus all direction sensors and occurrences versus all direction sensors. When drawing wind frequency roses, which show the frequency with which the wind blows from each direction sector, Windographer includes only those direction observations that occur in time steps in which the associated wind speed sensor exceeds the calm threshold. The associated wind speed sensor is the one that you have associated with the wind direction sensor in the Configure Dataset window. If you choose to have no speed sensor associated with a given direction sensor (by setting the associated speed sensor to <none>) Windographer will not take the calm threshold into account.

The percentage of time that the wind speed is at or below the calm threshold does not appear on wind rose graphs, but you can see this value in the tabular representation of the same data, for example in the 'frequency versus all direction sensors' table (found on the Wind Rose window) below. You can see from this table that the calm frequency, combined with the frequency in each direction sensor, must sum to 100% (i.e. when the wind is 'calm' Windographer does not treat it as having any direction at all).

The calm threshold also affects the 'frequency of calms' variable that appears in the Wind Speed Sensor Summary table.