The March 11, 2001 earthquake and tsunami disturbed the upper atmosphere in a way that was detectable by our GPS receivers. In this map showing the region around Japan, we see color dots representing the point at which a radio signal sent by a GPS satellite in space passes through the atmosphere on its way to GPS receivers on the ground. Each clump of color dots represents one satellite in communication with all 1200 receivers on the ground in Japan. The clumps move across the sky just as the GPS satellites move overhead. And when they get too far away from Japan, they disappear as the GPS satellite goes over the horizon. The color of these dots, represent the disturbance in the upper atmosphere caused by the earthquake and tsunami below. Now that we’ve explained the map, let’s take a look at the actual signals. Immediately after the earthquake, you can see two waves moving out toward the left, west on this map; A Rayleigh wave and an acoustic wave moving away from the epicenter. You can also see slower moving gravity waves also caused by the earthquake and the tsunami. Notice that these gravity waves align quite well with a model of the ocean tsunami itself represented in blue and white on the right of the screen. The fact that these upper atmospheric disturbances are aligned well with the ocean tsunami, imply that they are causally related. This may provide a way to improve our future tsunami warning systems by tracking tsunamis as they move across the ocean in regions where we might not have other means to detect them.