What can be done to continue HF communications during a sudden ionospheric disturbance (SID)?

A Sudden Ionospheric Disturbance (SID) is usually caused by a solar flare that emits extreme ultraviolet and X-ray radiation. This radiation penetrates deep into the Earth's atmosphere, rapidly increasing the ionization density in the D region (the lowest layer of the ionosphere). The D layer is highly absorptive of radio waves, especially at lower frequencies. When a SID occurs, it quickly absorbs signals on the lower HF bands (such as 80 and 40 meters), causing those bands to completely 'black out' or go dead. Because radio waves at higher frequencies are less susceptible to D-layer absorption, they can often pass through the disturbance and still reflect off the higher F layers. Therefore, switching to a higher frequency band is the best strategy to maintain communications during a SID.