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Introduction

=> Japanese here.

This is a python module for calculating meteorological parameters, named wxparams, which stands for Weather Parameters. For instance, dew point temperature can be calculated given air temperature and relative humidity. At first I made this for my own use, but now I'd be happy to release it to the public.

  • Ver1.0 : 2020/04/24 Originally released
  • Ver1.1 : 2020/05/27 Added functions to convert between temperature[C] and temperature[F]
  • Ver1.2 : 2020/10/03 Modified WVP_to_T function
  • Ver1.3 : 2020/11/20 Added functions to calculate specific humidity, absolute humidity, and virtual temperature
  • Ver1.4 : 2021/01/16 Modified SSI, and added functions to calculate pressure reduced to mean sea level, and surface height
  • Ver1.5 : 2021/01/17 Modified Rd / Cp parameter value in Theta_e

Install

You can install wxparams using pip as below, or just download from the GitHub repository.

pip install git+https://github.com/Yoshiki443/weather_parameters

License

MIT license.

Main functions

  1. Wind-related functions
    • Conversion between UV components of wind and wind direction / velocity, 8 and 16 directions of wind, cross wind component, and so on
  2. Moisture-related functions
    • Conversion between relative humidity and dew point temperature, saturated water vapor pressure, mixing ratio, and so on
  3. Functions related to atmospheric thermodynamics and instability
    • Potential temperature, equivalent potential temperature, SSI, K-Index, and so on
  4. Unit conversion
    • Conversion between m/s and knot, between meter and feet, and so on

How to use

This is an example code.

import numpy as np
import wxparams as wx
temp = np.array([[0., 5.],[10., 20.]]) # air temperature[C]
rh = np.array([[90., 50.], [70., 99.5]]) # relative humidity[%]
td = wx.RH_to_Td(temp, rh) # dew point temperature[C]
print(td)
# Output
# [[-1.44330606 -4.56523582]
#  [ 4.78251527 19.91913689]]

Import wxparams with a name "wx". The name "wx" is a abbreviation of "weather". Then call a function you want to use. The example above shows the case to calculate dew point temperature given air temperature and relative humidity.

The input data is supposed to be numpy.ndarray basically. Pandas.Series may be available too. As for a single value, some functions work correctly, but some not. So numpy.ndarray is recommended.

The followings are the explanations of each function.

Wind-related functions

UV_to_SpdDir(U, V)

Calculate wind velocity[m/s, kt, etc] and wind direction[degree] given U and V components of winds[m/s, kt, etc]. U component of wind means west-east wind, and V component of wind means south-north wind. Westerly wind and southerly wind usually have plus value.

All the units of wind speed are available. As for wind direction, due north wind is 360 degree. If wind velocity is 0, then wind direction is 0.

Parameters :

  • U : array_like
    • U component of wind[m/s, kt, etc]
  • V : array_like
    • V component of wind[m/s, kt, etc]

Returns :

  • Wspd : array_like
    • Wind velocity[m/s, kt, etc]
  • Wdir : array_like
    • Wind direction[degree]

SpdDir_to_UV(Wspd, Wdir)

Calculate U and V components of winds[m/s, kt, etc] given wind velocity[m/s, kt, etc] and wind direction[degree].

Parameters :

  • Wspd : array_like
    • Wind velocity[m/s, kt, etc]
  • Wdir : array_like
    • Wind direction[degree]

Returns :

  • U : array_like
    • U component of wind[m/s, kt, etc]
  • V : array_like
    • V component of wind[m/s, kt, etc]

Deg_to_Dir8(Wdir, dir_zero=None, numeric=False)

Convert 360-degree wind direction into 8 directions of winds, like "N, NE, E, SE, S, SW, W, NW". Wind direction 0 is converted to the string which is assigned to dir_zero option. The default is None. For instance, you can assign "VRB" to dir_zero like METAR, which indicates "variable wind direction".

On the other hand, if numeric is set to True, the numbers "8, 1, 2, 3, 4, 5, 6, 7" are output. Due north is 8, not 0. Wind direction 0 is converted to 0.

Parameters :

  • Wdir : array_like
    • Wind direction[degree]
  • dir_zero : str, optional
    • String used when wind direction is 0. Default is None
  • numeric : bool, optional
    • If False, output is alphabet. It True, output is number

Returns :

  • Dir8 : array_like
    • 8 directions of winds

Deg_to_Dir16(val, dir_zero=None, numeric=False)

Convert 360-degree wind direction into 16 directions of winds, like "N, NNE, NE, ENE, E, ESE, SE, SSE, S, SSW, SW, WSW, W, WNW, NW, NNW". Wind direction 0 is converted to the string which is assigned to dir_zero option. The default is None.

On the other hand, if numeric is set to True, the numbers "16, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15" are output. Due north is 16, not 0. Wind direction 0 is converted to 0.

Parameters :

  • Wdir : array_like
    • Wind direction[degree]
  • dir_zero : str, optional
    • String used when wind direction is 0. Default is None
  • numeric : bool, optional
    • If False, output is alphabet. It True, output is number

Returns :

  • Dir16 : array_like
    • 16 directions of winds

Cross_Wind(Wspd, Wdir, RWY)

Calculate cross wind component of wind given wind velocity[m/s, kt, etc], wind direction[degree], and runway direction[degree] of a airpot. The runway direction should be assigned as 360-degree, not two digits runway number.

Parameters :

  • Wspd : array_like
    • Wind velocity[m/s, kt, ...etc]
  • Wdir : array_like
    • Wind direction[degree]
  • RWY : array_like
    • Runway direction[degree]

Returns :

  • crswind : array_like
    • Cross wind component[m/s, kt, ...etc]

Tail_Wind(Wspd, Wdir, RWY)

Calculate tail wind component of wind given wind velocity[m/s, kt, etc], wind direction[degree], and runway direction[degree] of a airpot. The runway direction should be assigned as 360-degree, not two digits runway number.

Parameters :

  • Wspd : array_like
    • Wind velocity[m/s, kt, ...etc]
  • Wdir : array_like
    • Wind direction[degree]
  • RWY : array_like
    • Runway direction[degree]

Returns :

  • tailwind : array_like
    • Tail wind component[m/s, kt, ...etc]

Head_Wind(Wspd, Wdir, RWY)

Calculate head wind component of wind given wind velocity[m/s, kt, etc], wind direction[degree], and runway direction[degree] of a airpot. The runway direction should be assigned as 360-degree, not two digits runway number.

Parameters :

  • Wspd : array_like
    • Wind velocity[m/s, kt, ...etc]
  • Wdir : array_like
    • Wind direction[degree]
  • RWY : array_like
    • Runway direction[degree]

Returns :

  • headwind : array_like
    • Head wind component[m/s, kt, ...etc]

Moisture-related functions

RH_to_Td(T, RH, formula="Bolton")

Calculate dew point temperature[C] given air temperature[C] and relative humidity[%]. Relative humidity is automatically clipped minimum 0.1% since 0% is not available.

In this function, saturated water vapor pressure[hPa] is also calculated. There are 3 formulas to calculate it. Default is "Bolton", but "Tetens" and "WMO" are also available. See T_to_WVP for the detail.

Parameters :

  • T : array_like
    • Air temperature[C]
  • RH : array_like
    • Relative humidity[%]
  • formula : str, optional (default="Bolton")
    • Select a formula to calculate saturated water vapor pressure[hPa]. "Bolton" is default, and "Tetens" and "WMO" are also available.

Returns :

  • Td : array_like
    • Dew point temperature[C]

Td_to_RH(T, Td, formula="Bolton")

Calculate relative humidity[%] given air temperature[C] and dew point temperature[C].

In this function, saturated water vapor pressure[hPa] is also calculated. There are 3 formulas to calculate it. Default is "Bolton", but "Tetens" and "WMO" are also available. See T_to_WVP for the detail.

Parameters :

  • T : array_like
    • Air temperature[C]
  • Td : array_like
    • Dew point temperature[C]
  • formula : str, optional (default="Bolton")
    • Select a formula to calculate saturated water vapor pressure[hPa]. "Bolton" is default, and "Tetens" and "WMO" are also available.

Returns :

  • RH : array_like
    • Relative humidity[%]

T_to_WVP(T, formula="Bolton")

Calculate saturated water vapor pressure[hPa] given air temperature[C]. If dew point temperature[C] is input, output water vapor pressure[hPa]. There are 3 formulas to calculate this as below. Default is "Bolton", but "Tetens" and "WMO" are also available.

Tetens equation :

WMO equation :

Bolton equation :

Parameters :

  • T : array_like
    • Air temperature[C] (or dew porint temperature[C])
  • formula : str, optional (default="Bolton")
    • Select a formula to calculate saturated water vapor pressure[hPa]. "Bolton" is default, and "Tetens" and "WMO" are also available.

Returns :

  • es : array_like
    • Saturated water vapor pressure[hPa] (or water vapor pressure[hPa]）

WVP_to_T(es, formula="Bolton")

As inverse function of T_to_WVP, calculate air temperature[C] given saturated water vapor pressure[hPa]. If water vapor pressure[hPa] is input, output dew point temperature[C].

Parameters :

  • es : array_like
    • Saturated water vapor pressure[hPa] (or water vapor pressure[hPa]）
  • formula : str, optional (default="Bolton")
    • Select a formula to calculate saturated water vapor pressure[hPa]. "Bolton" is default, and "Tetens" and "WMO" are also available.

Returns :

  • T : array_like
    • Air temperature[C] (or dew porint temperature[C])

T_Td(T, Td)

Calculate dew point depression given air temperature[C] and dew point temperature[C].

Parameters :

  • T : array_like
    • Air temperature[C]
  • Td : array_like
    • Dew point temperature[C]

Returns :

  • T-Td : array_like
    • dew point depression[C]

Mixing_Ratio(Td, P, formula="Bolton")

Calculate mixing ratio[g/g] given dew point temperature[C] and pressure[hPa].

In this function, saturated water vapor pressure[hPa] is also calculated. There are 3 formulas to calculate it. Default is "Bolton", but "Tetens" and "WMO" are also available. See T_to_WVP for the detail.

Parameters :

  • Td : array_like
    • Dew point temperature[C]
  • P : array_like
    • Pressure[hPa]
  • formula : str, optional (default="Bolton")
    • Select a formula to calculate saturated water vapor pressure[hPa]. "Bolton" is default, and "Tetens" and "WMO" are also available.

Returns :

  • w : array_like
    • Mixing ratio[g/g]

Specific_Humidity(Td, P, formula="Bolton")

Calculate specific humidity[g/g] given dew point temperature[C] and pressure[hPa].

In this function, saturated water vapor pressure[hPa] is also calculated. There are 3 formulas to calculate it. Default is "Bolton", but "Tetens" and "WMO" are also available. See T_to_WVP for the detail.

Parameters :

  • Td : array_like
    • Dew point temperature[C]
  • P : array_like
    • Pressure[hPa]
  • formula : str, optional (default="Bolton")
    • Select a formula to calculate saturated water vapor pressure[hPa]. "Bolton" is default, and "Tetens" and "WMO" are also available.

Returns :

  • q : array_like
    • Specific humidity[g/g]

Absolute_Humidity(T, Td, formula="Bolton")

Calculate absolute humidity[g/m^3] given air temperature[C] and dew point temperature[C]. Absolute humidity is equal to water vapor density.

In this function, saturated water vapor pressure[hPa] is also calculated. There are 3 formulas to calculate it. Default is "Bolton", but "Tetens" and "WMO" are also available. See T_to_WVP for the detail.

Parameters :

  • T : array_like
    • Air temperature[C]
  • Td : array_like
    • Dew point temperature[C]
  • formula : str, optional (default="Bolton")
    • Select a formula to calculate saturated water vapor pressure[hPa]. "Bolton" is default, and "Tetens" and "WMO" are also available.

Returns :

  • rho_w : array_like
    • Absolute humidity[g/m^3]

Virtual_Temperature(T, Td, P, formula="Bolton")

Calculate virtual temperature[C] given air temperature[C], dew point temperature[C], and pressure[hPa].

In this function, saturated water vapor pressure[hPa] is also calculated. There are 3 formulas to calculate it. Default is "Bolton", but "Tetens" and "WMO" are also available. See T_to_WVP for the detail.

Parameters :

  • T : array_like
    • Air temperature[C]
  • Td : array_like
    • Dew point temperature[C]
  • P : array_like
    • Pressure[hPa]
  • formula : str, optional (default="Bolton")
    • Select a formula to calculate saturated water vapor pressure[hPa]. "Bolton" is default, and "Tetens" and "WMO" are also available.

Returns :

  • Tv : array_like
    • Vertual temperature[C]

Functions related to atmospheric thermodynamics and instability

Theta(T, P)

Calculate potential temperature[K] given air temperature[C] and pressure[hPa].

Parameters :

  • T : array_like
    • Air temperature[C]
  • P : array_like
    • Pressure[hPa]

Returns :

  • Theta : array_like
    • Potential temperature[K]

Tlcl(T, Td)

Calculate air temperature at lifted condensation level[K] given air temperature[K] and dew point temperature[K]. Pay attention that the unit of air temperature and dew point temperature is required to be [K].

Parameters :

  • T : array_like
    • Air temperature[K]
  • Td : array_like
    • Dew point temperature[K]

Returns :

  • Tlcl : array_like
    • Air temperature at lifted condensation level[K]

Theta_e(T, Td, P, formula="Bolton")

Calculate equivalent potential temperature[K] given air temperature[C], dew point temperature[C], and pressure[hPa].

The implemented formula is as the same as a formula which JMA adopted. See the last page of this JMA's PDF for the detail (Japanese only).

Be aware that Rd / Cpd is 0.2854 in that PDF, but normally the value should be 0.2857. So 0.2857 is used in this module.
As original equation by Bolton (1980) uses Rd / Cpd = 0.2854, I have modified that parameter value. By this modification, calculated values may be changed on the order of 0.01 ~ 0.1[K].

Parameters :

  • T : array_like
    • Air temperature[C]
  • Td : array_like
    • Dew point temperature[C]
  • P : array_like
    • Pressure[hPa]

Returns :

  • Thetae : array_like
    • Equivalent potential temperature[K]

SSI(P0, P1, T0, T1, Td0, formula="Bolton", **kwargs)

Calculate showalter stability index (SSI). Input parameters are air temperature[C], dew point temperature[C], and pressure[hPa] at the base level of an air parcel to be lifted, and air temperature[C] and pressure[hPa] at the destination level of the lifting air parcel. Usually the base level is 850hPa and the destination level is 500hPa, but any pressure levels are available on this function.

SSI is calculated as T1 minus Tl which is temperature of air parcel lifted from P0 to P1 level. Tl is calculated as below.

  1. Calculate thickness between P0 and P1 level using hypsometric equation. If geopotential heights are input as keyword arguments named "h0" and "h1", geopotential heights are used to calculate thickness.
  2. Calculate temperature of air parcel lifted dry-adiabatically from P0 to P1 level (Tl_dry), and temperature at LCL (Tlcl).
  3. If Tl_dry > Tlcl, the lifted parcel is not saturated, and Tl_dry is used as Tl.
  4. If not, the lifted parcel is saturated, and Tl is calculated exploratory.

In this function, saturated water vapor pressure[hPa] is also calculated. There are 3 formulas to calculate it. Default is "Bolton", but "Tetens" and "WMO" are also available. See T_to_WVP for the detail.

Parameters :

  • P0 : array_like

    • Pressure at the base level[hPa]

  • P1 : array_like

    • Pressure at the destination level[hPa]

  • T0 : array_like

    • Air temperature at the base level[hPa]

  • T1 : array_like

    • Air temperature at the destination level[hPa]

  • Td : array_like

    • Dew point temperature at the base level[hPa]

  • formula : str, optional (default="Bolton")

    • Select a formula to calculate saturated water vapor pressure[hPa]. "Bolton" is default, and "Tetens" and "WMO" are also available.

  • h0 : array_like

    • Geopotential height at the base level[m]. This is an optional argument and should be input as keyword argument.

  • h1 : array_like

    • Geopotential height at the destination level[m]. This is an optional argument and should be input as keyword argument.

Returns :

  • SSI : array_like
    • SSI

K_Index(T850, Td850, T700, Td700, T500)

Calculate K-Index given air temperature[C] and dew point temperature[C] at 850hPa, air temperature[C] and dew point temperature[C] at 700hPa, and air temperature[C] at 500hPa.

Parameters :

  • T850 : array_like
    • Air temperature at 850hPa[C]
  • Td850 : array_like
    • Dew point temperature at 850hPa[C]
  • T700 : array_like
    • Air temperature at 700hPa[C]
  • Td700 : array_like
    • Dew point temperature at 700hPa[C]
  • T500 : array_like
    • Air temperature at 500hPa[C]

Returns :

  • Kindex : array_like
    • K-Index

PRES_to_PRMSL(P1, T1, Z1)

Calculate pressure reduced to mean sea level[hPa] given surface pressure[hPa], surface temperature[C], and surface height[m].

Parameters :

  • P1 : array_like
    • Surface pressure[hPa]
  • T1 : array_like
    • Surface temperature[C]
  • Z1 : array_like
    • Surface height[m]

Returns :

  • P0 : array_like
    • Pressure reduced to mean sea level[hPa]

Surface_Height(P0, P1, T1)

Calculate surface height[m] given mean sea level pressure[hPa], surface pressure[hPa], and surface temperature[C].

Parameters :

  • P0 : array_like
    • ressure reduced to mean sea level[hPa]
  • P1 : array_like
    • Surface pressure[hPa]
  • T1 : array_like
    • Surface temperature[C]

Returns :

  • Z1 : array_like
    • Surface height[m]

Unit conversion

MPS_to_KT(x)

Convert the unit of speed [m/s] to [knot].

Parameters :

  • x : array_like
    • speed[m/s]

Returns :

  • y : array_like
    • speed[kt]

KT_to_MPS(x)

Convert the unit of speed [knot] to [m/s].

Parameters :

  • x : array_like
    • speed[kt]

Returns :

  • y : array_like
    • speed[m/s]

M_to_FT(x)

Convert the unit of length [meter] to [feet].

Parameters :

  • x : array_like
    • length[m]

Returns :

  • y : array_like
    • length[ft]

FT_to_M(x)

Convert the unit of length [feet] to [meter].

Parameters :

  • x : array_like
    • length[ft]

Returns :

  • y : array_like
    • length[m]

degF_to_degC(x)

Convert the unit of temperature [F:degrees Fahrenheit] to [C:degrees Celsius].

Parameters :

  • x : array_like
    • temperature[F]

Returns :

  • y : array_like
    • temperature[C]

degC_to_degF(x)

Convert the unit of temperature [C:degrees Celsius] to [F:degrees Fahrenheit].

Parameters :

  • x : array_like
    • temperature[C]

Returns :

  • y : array_like
    • temperature[F]

Plan of update

This module will be updated some time to add the following parameters.

  1. LFC, CAPE, CIN, Lifted Index, and so on
  2. Advection, vorticity, vertical wind shear, stability, and so on
  3. Wet-bulb temperature, wet-bulb potential temperature
  4. Severe weather parameters for supercell, tornado, and so on

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