idx = mpl.dates.date2num(df.index)
ax.xaxis.set_major_formatter(mpl.dates.DateFormatter('%d-%m-%Y'))
ax.plot(idx, df.V * 0.1 + 4, 'o-', color='k')
ax.quiver(idx, np.ones(size) * 3.5, df.U.values, df.V.values, pivot='mid')
ax.barbs(idx, np.ones(size) * 6.5, df.U.values, df.V.values, length=8,
    pivot='middle')
Quiver or Barb with a date axis