sweat_index#

metpy.calc.sweat_index(pressure, temperature, dewpoint, speed, direction, vertical_dim=0)#

Calculate SWEAT Index.

SWEAT Index derived from [Miller1972]:

\[SWEAT = 12Td_{850} + 20(TT - 49) + 2f_{850} + f_{500} + 125(S + 0.2)\]

where:

  • \(Td_{850}\) is the dewpoint at 850 hPa; the first term is set to zero if \(Td_{850}\) is negative.

  • \(TT\) is the total totals index; the second term is set to zero if \(TT\) is less than 49

  • \(f_{850}\) is the wind speed at 850 hPa

  • \(f_{500}\) is the wind speed at 500 hPa

  • \(S\) is the shear term: \(sin{(dd_{850} - dd_{500})}\), where \(dd_{850}\) and \(dd_{500}\) are the wind directions at 850 hPa and 500 hPa, respectively. It is set to zero if any of the following conditions are not met:

  1. \(dd_{850}\) is between 130 - 250 degrees

  2. \(dd_{500}\) is between 210 - 310 degrees

  3. \(dd_{500} - dd_{850} > 0\)

  4. both the wind speeds are greater than or equal to 15 kts

Calculation of the SWEAT Index consists of a low-level moisture, instability, and the vertical wind shear (both speed and direction). This index aim to determine the likeliness of severe weather and tornadoes.

Parameters:

  • pressure (pint.Quantity) – Pressure level(s), in order from highest to lowest pressure

  • temperature (pint.Quantity) – Temperature corresponding to pressure

  • dewpoint (pint.Quantity) – Dewpoint temperature corresponding to pressure

  • speed (pint.Quantity) – Wind speed corresponding to pressure

  • direction (pint.Quantity) – Wind direction corresponding to pressure

  • vertical_dim (int, optional) – The axis corresponding to vertical, defaults to 0. Automatically determined from xarray DataArray arguments.

Returns:

pint.Quantity – SWEAT Index