Bright polar mesospheric clouds formed by main engine exhaust from the space shuttle's final launch

摘要

The space shuttle launched for the last time on 8 July 2011. As with most shuttle launches, the three main engines injected about 350t of water vapor between 100 and 115km off the east coast of the United States during its ascent to orbit. We follow the motion of this exhaust with a variety of satellite and ground-based data sets and find that(1)the shuttle water vapor plume spread out horizontally in all directions over a distance of 3000 to 4000km in 18h, (2) a portion of the plume reached northern Europe in 21h to form polar mesospheric clouds(PMCs)that are brighter than over 99% of all PMCs observed in that region, and(3)the observed altitude dependence of the particle size is reversed with larger particles above smaller particles. We use a one-dimensional cloud formation model initialized with predictions of a plume diffusion model to simulate the unusually bright PMCs. We find that eddy mixing can move the plume water vapor down to the mesopause near 90km where ice particles can form. If the eddy diffusion coefficient is 400 to 1000m ~2/s, the predicted integrated cloud brightness is in agreement with both satellite and ground-based observations of the shuttle PMCs. The propellant mass of the shuttle is about 20% of that from all vehicles launched during the northern 2011 PMC season. We suggest that the brightest PMC population near 70N is formed by space traffic exhaust.