<SYSTEM_TASK:>
Given the following text description, write Python code to implement the functionality described below step by step
<END_TASK>
<USER_TASK:>
Description:
 Plot Button
Example showing how to construct a button which will execute the construction and display of a plot.
Step1:  Load cube.
Step2:  Construct button and display it.  Then define what happens when you press the button and relate the function to the button-pressing event.
<ASSISTANT_TASK:>
Python Code:
import ipywidgets
import IPython.display
import iris
import iris.plot as iplt
import matplotlib.pyplot as plt
from cube_browser import Contour, Browser, Contourf, Pcolormesh
Explanation: Plot Button
Example showing how to construct a button which will execute the construction and display of a plot.
End of explanation
cube = iris.load_cube(iris.sample_data_path('GloSea4/ensemble_001.pp'))
print cube
Explanation: Load cube.
End of explanation
go_button = ipywidgets.Button(
            description='Press Me!')
IPython.display.display(go_button)
def on_button_clicked(b):
    projection = iplt.default_projection(cube)
    
    ax = plt.subplot(111, projection=projection)
    plot = Contourf(cube, ax)
    Browser([plot]).display()
go_button.on_click(on_button_clicked)
Explanation: Construct button and display it.  Then define what happens when you press the button and relate the function to the button-pressing event.
End of explanation
<END_TASK>