Space shuttle exhaust plumes in the lower thermosphere: Advective transport and diffusive spreading

The space shuttle main engine plume deposited between 100 and 115\ km altitude is a valuable tracer for global-scale dynamical processes. Several studies have shown that this plume can reach the Arctic or Antarctic to form bursts of polar mesospheric clouds (PMCs) within a few days. The rapid transport of the shuttle plume is currently not reproduced by general circulation models and is not well understood. To help delineate the issues, we present the complete satellite datasets of shuttle plume observations by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument and the Sub-Millimeter Radiometer instrument. From 2002 to 2011 these two instruments observed 27 shuttle plumes in over 600 limb scans of water vapor emission, from which we derive both advective meridional transport and diffusive spreading. Each plume is deposited at virtually the same place off the United States east coast so our results are relevant to northern mid-latitudes. We find that the advective transport for the first 6\textendash18\ h following deposition depends on the local time (LT) of launch: shuttle plumes deposited later in the day (~13\textendash22 LT) typically move south whereas they otherwise typically move north. For these younger plumes rapid transport is most favorable for launches at 6 and 18 LT, when the displacement is 10\textdegree in latitude corresponding to an average wind speed of 30\ m/s. For plumes between 18 and 30\ h old some show average sustained meridional speeds of 30\ m/s. For plumes between 30 and 54\ h old the observations suggest a seasonal dependence to the meridional transport, peaking near the beginning of year at 24\ m/s. The diffusive spreading of the plume superimposed on the transport is on average 23\ m/s in 24\ h. The plume observations show large variations in both meridional transport and diffusive spreading so that accurate modeling requires knowledge of the winds specific to each case. The combination of transport and spreading from the STS-118 plume in August 2007 formed bright PMCs between 75 and 85\textdegreeN a day after launch. These are the highest latitude Arctic PMCs formed by shuttle exhaust reported to date.