Sounding Calculation Examples

Use functions from metpy.calc to perform a number of calculations using sounding data.

The code below uses example data to perform many sounding calculations for a severe weather event on May 22, 2011 from the Norman, OK sounding.

Imports

import numpy as np
import pandas as pd

import metpy.calc as mpcalc
from metpy.cbook import get_test_data
from metpy.units import units

Effective Shear Algorithm for use in Supercell Composite Calculation

def effective_layer(pressure, temperature, dewpoint, height, height_layer=False):
    """A function that determines the effective inflow layer for a convective sounding.

    Uses the default values of Thompason et al. (2004) for CAPE (100 J/kg) and CIN (-250 J/kg).

    Input:
      - pressure: sounding pressure with units
      - temperature: sounding temperature with units
      - dewpoint: sounding dewpoint temperature with units
      - height: sounding heights with units

    Returns:
      - pbot/hbot, ptop/htop: pressure/height of the bottom level,
                              pressure/height of the top level
    """
    from metpy.calc import cape_cin, parcel_profile
    from metpy.units import units

    pbot = None

    for i in range(pressure.shape[0]):
        prof = parcel_profile(pressure[i:], temperature[i], dewpoint[i])
        sbcape, sbcin = cape_cin(pressure[i:], temperature[i:], dewpoint[i:], prof)
        if sbcape >= 100 * units('J/kg') and sbcin > -250 * units('J/kg'):
            pbot = pressure[i]
            hbot = height[i]
            bot_idx = i
            break
    if not pbot:
        return None, None

    for i in range(bot_idx + 1, pressure.shape[0]):
        prof = parcel_profile(pressure[i:], temperature[i], dewpoint[i])
        sbcape, sbcin = cape_cin(pressure[i:], temperature[i:], dewpoint[i:], prof)
        if sbcape < 100 * units('J/kg') or sbcin < -250 * units('J/kg'):
            ptop = pressure[i]
            htop = height[i]
            break

    if height_layer:
        return hbot, htop
    else:
        return pbot, ptop

Obtain Data and Format

Upper air data can be obtained using the siphon package, but for this example we will use some of MetPy’s sample data. as_file_obj=False), skiprows=5, usecols=[0, 1, 2, 3, 6, 7], names=col_names) is necessary due to the formatting of the MetPy sample data. This formatting is not needed when using upper air data obtained via Siphon. Obtaining data with Siphon will be covered in a later notebook.

col_names = ['pressure', 'height', 'temperature', 'dewpoint', 'direction', 'speed']

sounding_data = pd.read_fwf(get_test_data('20110522_OUN_12Z.txt', as_file_obj=False),
                 skiprows=7, usecols=[0, 1, 2, 3, 6, 7], names=col_names)

# Drop any rows with all not a number (NaN) values for temperature, dewpoint, and winds
sounding_data = sounding_data.dropna(subset=('temperature', 'dewpoint', 'direction', 'speed'),
               how='all').reset_index(drop=True)

Downloading file '20110522_OUN_12Z.txt' from 'https://github.com/Unidata/MetPy/raw/v1.6.2/staticdata/20110522_OUN_12Z.txt' to '/home/runner/.cache/metpy/v1.6.2'.

Assign Units

We will pull the data out of the example dataset into individual variables and assign units. This is explained in further detain in the Simple Sounding notebook and in the Metpy documentation.

pres = sounding_data['pressure'].values * units.hPa
temp = sounding_data['temperature'].values * units.degC
dewpoint = sounding_data['dewpoint'].values * units.degC
wind_speed = sounding_data['speed'].values * units.knots
wind_dir = sounding_data['direction'].values * units.degrees
u, v = mpcalc.wind_components(wind_speed, wind_dir)
height = sounding_data['height'].values * units.meter

Compute the wind components

u, v = mpcalc.wind_components(wind_speed, wind_dir)

Compute common sounding index parameters

ctotals = mpcalc.cross_totals(pres, temp, dewpoint)
kindex = mpcalc.k_index(pres, temp, dewpoint)
showalter = mpcalc.showalter_index(pres, temp, dewpoint)
total_totals = mpcalc.total_totals_index(pres, temp, dewpoint)
vert_totals = mpcalc.vertical_totals(pres, temp)

Compture the parcel profile for a surface-based parcel

prof = mpcalc.parcel_profile(pres, temp[0], dewpoint[0])

Compute the corresponding Lifted Index (LI), Convective Available Potential Energy (CAPE), Convective Inhibition (CIN) values for a surface parcel

lift_index = mpcalc.lifted_index(pres, temp, prof)
cape, cin = mpcalc.cape_cin(pres, temp, dewpoint, prof)

Determine the Lifted Condensation Level (LCL), Level of Free Convection (LFC), and Equilibrium Level (EL) for our surface parcel

lclp, lclt = mpcalc.lcl(pres[0], temp[0], dewpoint[0])
lfcp, _ = mpcalc.lfc(pres, temp, dewpoint)
el_pressure, _ = mpcalc.el(pres, temp, dewpoint, prof)

Compute the characteristics of a mean layer parcel (50-hPa depth)

ml_t, ml_td = mpcalc.mixed_layer(pres, temp, dewpoint, depth=50 * units.hPa)
ml_p, _, _ = mpcalc.mixed_parcel(pres, temp, dewpoint, depth=50 * units.hPa)
mlcape, mlcin = mpcalc.mixed_layer_cape_cin(pres, temp, prof, depth=50 * units.hPa)

Compute the characteristics of the most unstable parcel (50-hPa depth)

mu_p, mu_t, mu_td, _ = mpcalc.most_unstable_parcel(pres, temp, dewpoint, depth=50 * units.hPa)
mucape, mucin = mpcalc.most_unstable_cape_cin(pres, temp, dewpoint, depth=50 * units.hPa)

Compute the Bunkers Storm Motion vector and use to calculate the critical angle

(u_storm, v_storm), *_ = mpcalc.bunkers_storm_motion(pres, u, v, height)
critical_angle = mpcalc.critical_angle(pres, u, v, height, u_storm, v_storm)

Work on the calculations needed to compute the significant tornado parameter

# Estimate height of LCL in meters from hydrostatic thickness
new_p = np.append(pres[pres > lclp], lclp)
new_t = np.append(temp[pres > lclp], lclt)
lcl_height = mpcalc.thickness_hydrostatic(new_p, new_t)

# Compute Surface-based CAPE
sbcape, _ = mpcalc.surface_based_cape_cin(pres, temp, dewpoint)

# Compute SRH, given a motion vector toward the NE at 9.9 m/s
*_, total_helicity = mpcalc.storm_relative_helicity(height, u, v, depth=1 * units.km,
                                                    storm_u=u_storm, storm_v=v_storm)

# Copmute Bulk Shear components and then magnitude
ubshr, vbshr = mpcalc.bulk_shear(pres, u, v, height=height, depth=6 * units.km)
bshear = mpcalc.wind_speed(ubshr, vbshr)

# Use all computed pieces to calculate the Significant Tornado parameter
sig_tor = mpcalc.significant_tornado(sbcape, lcl_height,
                                     total_helicity, bshear).to_base_units()

Compute the supercell composite parameter, if possible

# Determine the top and bottom of the effective layer using our own function
hbot, htop = effective_layer(pres, temp, dewpoint, height, height_layer=True)

# Perform the calculation of supercell composite if an effective layer exists
if hbot:
    esrh = mpcalc.storm_relative_helicity(height, u, v, depth=htop - hbot, bottom=hbot)
    eubshr, evbshr = mpcalc.bulk_shear(pres, u, v, height=height, depth=htop - hbot, bottom=hbot)
    ebshear = mpcalc.wind_speed(eubshr, evbshr)

    super_comp = mpcalc.supercell_composite(mucape, esrh[0], ebshear)
else:
    super_comp = np.nan

Print Important Sounding Parameters

print('Important Sounding Parameters for KOUN on 22 Mary 2011 12 UTC')
print()
print(f'        CAPE: {cape:.2f}')
print(f'         CIN: {cin:.2f}')
print(f'LCL Pressure: {lclp:.2f}')
print(f'LFC Pressure: {lfcp:.2f}')
print(f' EL Pressure: {el_pressure:.2f}')
print()
print(f'   Lifted Index: {lift_index:.2f}')
print(f'        K-Index: {kindex:.2f}')
print(f'Showalter Index: {showalter:.2f}')
print(f'   Cross Totals: {ctotals:.2f}')
print(f'   Total Totals: {total_totals:.2f}')
print(f'Vertical Totals: {vert_totals:.2f}')
print()
print('Mixed Layer - Lowest 50-hPa')
print(f'     ML Temp: {ml_t:.2f}')
print(f'     ML Dewp: {ml_td:.2f}')
print(f'     ML CAPE: {mlcape:.2f}')
print(f'      ML CIN: {mlcin:.2f}')
print()
print('Most Unstable - Lowest 50-hPa')
print(f'     MU Temp: {mu_t:.2f}')
print(f'     MU Dewp: {mu_td:.2f}')
print(f' MU Pressure: {mu_p:.2f}')
print(f'     MU CAPE: {mucape:.2f}')
print(f'      MU CIN: {mucin:.2f}')
print()
print('Bunkers Storm Motion Vector')
print(f'  u_storm: {u_storm:.2f}')
print(f'  v_storm: {v_storm:.2f}')
print(f'Critical Angle: {critical_angle:.2f}')
print()
print(f'Storm Relative Helicity: {total_helicity:.2f}')
print(f'Significant Tornado Parameter: {sig_tor:.2f}')
print(f'Supercell Composite Parameter: {super_comp:.2f}')

Important Sounding Parameters for KOUN on 22 Mary 2011 12 UTC

        CAPE: 3223.89 joule / kilogram
         CIN: -96.26 joule / kilogram
LCL Pressure: 949.09 hectopascal
LFC Pressure: 735.99 hectopascal
 EL Pressure: 194.72 hectopascal

   Lifted Index: [-6.96] delta_degree_Celsius
        K-Index: 22.10 degree_Celsius
Showalter Index: [-0.08] delta_degree_Celsius
   Cross Totals: 17.10 delta_degree_Celsius
   Total Totals: 50.20 delta_degree_Celsius
Vertical Totals: 33.10 delta_degree_Celsius

Mixed Layer - Lowest 50-hPa
     ML Temp: 20.99 degree_Celsius
     ML Dewp: 20.55 degree_Celsius
     ML CAPE: 3254.17 joule / kilogram
      ML CIN: -138.20 joule / kilogram

Most Unstable - Lowest 50-hPa
     MU Temp: 20.40 degree_Celsius
     MU Dewp: 20.40 degree_Celsius
 MU Pressure: 925.00 hectopascal
     MU CAPE: 3693.64 joule / kilogram
      MU CIN: -60.50 joule / kilogram

Bunkers Storm Motion Vector
  u_storm: 21.85 knot
  v_storm: 4.55 knot
Critical Angle: 67.33 degree

Storm Relative Helicity: 279.49 meter ** 2 / second ** 2
Significant Tornado Parameter: [4.60] 
Supercell Composite Parameter: [9.07]
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