Geomagnetic a-index vs K-index

Plot of the geomagnetic a-index vs K-index. The data is obtained from NOAA "Geomagnetic kp and ap Indices", www.ngdc.noaa.gov/stp/GEOMAG/kp_ap.html. The plot is produced by the following script in python.



import numpy as np
import matplotlib.pyplot as plt
from scipy.interpolate import UnivariateSpline

plt.rcParams['font.family'] = 'serif'
plt.rcParams['font.size'] = 14

data = np.array([
[ 0., 0.],
[ 1., 4.],
[ 2., 7.],
[ 3., 15.],
[ 4., 27.],
[ 5., 48.],
[ 6., 80.],
[ 7., 132.],
[ 8., 207.],
[ 9., 400.]])

k_index = data[:, 0]
a_index = data[:, 1]

spl = UnivariateSpline(k_index, a_index)
k_fit = np.linspace(0,9)

plt.plot(k_index, a_index, 'o')
plt.plot(k_fit, spl(k_fit), 'k')
plt.axis([0, 10, 0, 500])
plt.grid(True)
plt.xlabel(r"K index")
plt.ylabel(r"a index")
plt.show()