[Python] Rotating the y-axis label

I am trying to rotate the title of the Y axis so it is horizontal. I do not want the tick labels horizontal just the title of the Y axis. I have to use subplots as I am making multiple plots at once. Here is the below script in which I have tried to rotate the Y axis title.

import matplotlib.pyplot as plt
import sys

fig, ax = plt.subplots()

ax.set_title(r'$\alpha$ > \beta_i$', fontsize=20)
ax.set(xlabel='meters $10^1$', ylabel=r'Hertz $(\frac{1}{s})$')
ax.set(xlabel=r's(t) = \mathcal(A)\/\sin(2 \omega t)', ylabel=r'Hertz $(\frac{1}{s})$')
ax.set(ylabel="North $\uparrow$",fontsize=9,rotate=90)
plt.show()


When I run it I get an error:

TypeError: There is no AxesSubplot property "rotate"
​

How can I tweak this program so that the Y axis is rotating horizontally?

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