MODERN, broad-beamed merchant vessels are well able to withstand the rough and tumble of the waves, but sailors still prefer to avoid storms at sea if they can. Containers may come loose in heavy weather and there is always a chance of lightning knocking out communications. It is therefore ironic that some storms may be caused by ships themselves. That, at least, is the conclusion reached by Joel Thornton of the University of Washington, in Seattle, and his colleagues in a paper just published in Geophysical Research Letters. They demonstrate that lightning strikes the Indian Ocean and the South China Sea almost twice as often along shipping lanes as it does other areas of these waters.