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total_totals_index#

metpy.calc.total_totals_index(pressure, temperature, dewpoint, vertical_dim=0)[source]#

Calculate Total Totals Index from the pressure temperature and dewpoint.

Total Totals Index formula derived from [Miller1972]:

\[TT = (T850 + Td850) - (2 * T500)\]

where:

  • \(T850\) is the temperature at 850 hPa

  • \(T500\) is the temperature at 500 hPa

  • \(Td850\) is the dewpoint at 850 hPa

Calculation of the Total Totals Index is defined as the temperature at 850 hPa plus the dewpoint at 850 hPa, minus twice the temperature at 500 hPa. This index consists of two components, the Vertical Totals (VT) and the Cross Totals (CT).

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

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

Returns:

pint.Quantity – Total Totals Index

Examples

>>> from metpy.calc import dewpoint_from_relative_humidity, total_totals_index
>>> from metpy.units import units
>>> # pressure
>>> p = [1008., 1000., 950., 900., 850., 800., 750., 700., 650., 600.,
...      550., 500., 450., 400., 350., 300., 250., 200.,
...      175., 150., 125., 100., 80., 70., 60., 50.,
...      40., 30., 25., 20.] * units.hPa
>>> # temperature
>>> T = [29.3, 28.1, 23.5, 20.9, 18.4, 15.9, 13.1, 10.1, 6.7, 3.1,
...      -0.5, -4.5, -9.0, -14.8, -21.5, -29.7, -40.0, -52.4,
...      -59.2, -66.5, -74.1, -78.5, -76.0, -71.6, -66.7, -61.3,
...      -56.3, -51.7, -50.7, -47.5] * units.degC
>>> # relative humidity
>>> rh = [.85, .65, .36, .39, .82, .72, .75, .86, .65, .22, .52,
...       .66, .64, .20, .05, .75, .76, .45, .25, .48, .76, .88,
...       .56, .88, .39, .67, .15, .04, .94, .35] * units.dimensionless
>>> # calculate dewpoint
>>> Td = dewpoint_from_relative_humidity(T, rh)
>>> # compute the TT index
>>> total_totals_index(p, T, Td)
<Quantity(42.6741081, 'delta_degree_Celsius')>

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