calculate_cwt: calculate_cwt
In jcext: Extended Classification of Weather Types

Description Usage Arguments Details Value See Also

Applies the rules to obtain the weather types. (more details, see Jones et al. 1997)

1	calculate_cwt(Z, TF, directionflow, G, thr = 6, Gth = 30)

`Z`	Data frame with the total shear vorticity and dates.
`TF`	Data frame with resultant flow and dates.
`directionflow`	Data frame with the direction of the flow and dates.
`G`	Data frame with Gale days and dates.
`thr`	Numeric threshold used for Unclassified days.
`Gth`	Numeric threshold used for Gale days.

As defined in the original scheme, the threshold to determine unclassified days is 6. Gale days are estimated by using a threshold of 30. If Gale days with a greater intensity (e.g. 40 or 50) is wanted, Gth must be changed. The airflow indices are used within the following rules to define the appropriate Lamb weather types.

The appropriate direction is calculated on an eight-point compass allowing 45° per sector.
If abs(Z) is less than TF, flow is essentially pure directional type.
If |Z| is greater than 2TF, then the pattern is strongly cyclonic (Z > 0) or anticyclonic (Z < 0).
If |Z| lies between TF and 2TF then the flow is partly (anti-) cyclonic and this corresponds to one of Lamb’s synoptic/direction hybrid types, e.g. AE.
If TF is less than 6 and |Z| is less than 6, there is light indeterminate flow corresponding to Lamb’s unclassified type U.

A list with two objects:

Total_CWT with five groups of weather types: LWT_D, LWT_C, LWT_CH, LWT_U and LWT_G The main four groups contain the total of 27 weather types and the five list LWT_G refers to the gale days.
- LWT_D: 8 directional types.
- LWT_C: 1 anticyclonic and 1 cyclonic.
- LWT_CH: 16 hybrid types.
- LWT_U: 1 unclassified type.
Logical values of daily occurrence of each type. The user might want to use these values to get composites with specific atmospheric fields (e.g. pressure, temperature).