strm = ax0.streamplot(X, Y, Vx, Vy, color=speed, linewidth=lw, density=
    density, cmap=plt.cm.jet, start_points=stpts_right)
ax0.streamplot(-X, Y, -Vx, Vy, color=speed, linewidth=lw, density=density,
    cmap=plt.cm.jet, start_points=stpts_left)
Matplotlib: How to increase colormap/linewidth quality in streamplot?