Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) is a NASA Earth Venture Suborbital research project to investigate the impacts of intense thunderstorms over the U.S. on the summertime stratosphere.
DCOTSS will use the NASA ER-2 high-altitude research aircraft to measure the composition of these convective plumes and determine their effects on the chemistry and composition of the stratosphere. ER-2 flights for DCOTSS will be based in Salina, KS, which offers an ideal location for sampling convective plumes in the stratosphere. The ER-2 will carry an extensive suite of instruments to measure trace gases and aerosol properties and can operate at altitudes as high as 70,000 feet. Commercial airliners, by comparison, typically fly at around 35,000 feet.
During the summer, strong convective storms over North America overshoot the tropopause into the lower stratosphere. These storms carry water and pollutants from the troposphere into the normally very dry stratosphere, where they can have a significant impact on radiative and chemical processes, potentially including stratospheric ozone. The photo below, taken from the International Space Station, shows one of these storms with an anvil, which is typically near the tropopause level; an overshooting top; and a plume of cirrus (ice) clouds injected into the stratosphere by the overshooting top. Overshooting tops can reach many kilometers above the tropopause into the stratosphere.
Material transported from the troposphere to the stratosphere by these storms may be trapped by the atmospheric circulation in the lower stratosphere. During the summer, the circulation over North America is dominated by a large high pressure system known as the North American Monsoon Anticyclone (NAMA). As the map below illustrates, air within the NAMA can circulate in a clockwise manner for a considerable period before it escapes.
In tandem with DCOTSS field research, modeling efforts are attempting to understand how much material is irreversibly injected into the stratosphere using Lagrangian back trajectory analysis and remote soundings from the Microwave Limb Sounder Instrument (MLS). Trajectories are initialized at MLS footprints that observe above background levels of stratospheric water vapor. The air parcels are then advected backwards in time through a numerical model. By quantifying the number of tropopause overshooting convective storms that a parcel has encountered, we look to define a relationship between deep convection events and water vapor enhancements observed be remote sensing instruments and identify convective source regions that substantially contribute to lower stratospheric water vapor.