improver.generate_ancillaries.generate_svp_derivative_table module

A module for creating a table of the first derivative of saturated vapour pressure

class SaturatedVapourPressureDerivativeTable(t_min=183.15, t_max=338.25, t_increment=0.1, water_only=False, ice_only=False)

Bases: SaturatedVapourPressureTable

Plugin to create a first derivative saturated vapour pressure lookup table, which is only valid for temperatures between 173 K and 373 K.

First derivative of the saturated vapour pressure (SVP)

Output is a table of values for the first derivative of the SVP with respect to temperature.

The first derivative SVP is provided for the input temperature values, for which default values are provided, ranging from 183.15 K to 338.15 K (inclusive) in 0.1 K increments. This results in a table of 1550 rows (data points).

The resulting table of SVP derivative values has been plotted against the input temperature values in the figure below. Here we can see a positive rate of change of the SVP with respect to temperature, which is expected, as the SVP increases with increasing temperature. We can also see a kink in the line around 273.16 K, which is the triple point of water where the three phases (solid, liquid, and gas) coexist. This kink is caused by different equations being used for the SVP below and above this temperature.

_abc_impl = <_abc._abc_data object>

cube_name = 'saturated_vapour_pressure_derivative'

derivative_saturation_vapour_pressure_goff_gratch(temperature)

Saturation vapour pressure first derivative in a water vapour system calculated using the Goff-Gratch Equation (WMO standard method).

Parameters:

temperature (ndarray) – Temperature values in Kelvin. Valid from 173 K to 373 K (173 K < T < 273.15 K for ice, 223 K < T < 373 K for water).

Return type:

ndarray

Returns:

Corresponding values of saturation vapour pressure first derivative for a pure water vapour system, in hPa.

References

Numerical data and functional relationships in science and technology. New series. Group V. Volume 4. Meteorology. Subvolume b. Physical and chemical properties of the air, P35.

process()

Create a lookup table of saturation vapour pressure first derivative in a pure water vapour system for the range of required temperatures.

Parameters:

• self.t_min (float) – The minimum temperature (in Kelvin or Celsius, as appropriate) for the lookup table.

• self.t_max (float) – The maximum temperature (in Kelvin or Celsius, as appropriate) for the lookup table.

• self.t_increment (float) – The increment between temperature points in the lookup table.

• self.derivative_saturation_vapour_pressure_goff_gratch (callable) – Method to calculate saturation vapour pressure first derivative for given temperatures.

• self.as_cube (callable) – Method to convert data and temperatures into a Cube object.

Returns:

A cube of saturated vapour pressure derivative values at temperature points defined by t_min, t_max, and t_increment (defined above).

Return type:

Cube

svp_si_units = 'Pa/K'

svp_units = 'hPa/K'