At the Top of the Troposphere: Starting up START08
The region of the atmosphere near the tropopause where the upper troposphere meets the lower stratosphere, known as the UTLS, can have a significant impact on climate and climate change. It is in the troposphere where clouds form and most of Earth’s weather happens. The stratosphere is where Earth’s protective ozone layer resides, shielding the planet from much of the Sun’s incoming ultraviolet radiation. The boundary between these parts of the atmosphere is characterized by large variations in chemical concentrations and atmospheric dynamics. Because the UTLS boundary region is at very high altitudes⎯approximately eleven miles at lower latitudes, six miles at the poles⎯few instruments are capable of capturing first-hand views of the UTLS. Limited observational data hampers the ability of computer models to accurately portray the dynamics of the Upper Troposphere/Lower Stratosphere region. With the debut of the NSF/NCAR Gulfstream-V (GV) research aircraft, scientists have exciting opportunities to pursue photochemistry, cloud, aerosol, radiation, and transport research in the UTLS.Limited observational data hampers the ability of computer models to accurately portray the chemical and physical dynamics of the UTLS, or to capture the influence of this region’s dynamics on the broader atmosphere.
With the 2007 debut of the NSF/NCAR Gulfstream-V (GV) research aircraft, with its high altitude and long-range capabilities, scientists have new and exciting opportunities to pursue photochemistry, cloud, aerosol, radiation, and transport research in the UTLS.
With improved new technology and more detailed observations directly focused on the UTLS region, scientists will gain increased insight into the processes that regulate the composition of the UTLS. Their enhanced observations provide key diagnostics to test the next generation of climate computer models and their ability to accurately predict the feedbacks among climate, chemistry and dynamics in the UTLS region.
With the GV in mind, the scientific community has developed a UTLS Initiative that is investigating the coupled dynamic, chemical, and microphysical processes in the UTLS. The initiative will take advantage of in situ observations collected by instruments mounted on the aircraft. Used in combination with an array of available satellite measurements and computer models of varying scale and complexity, the resulting data set is expected to greatly enhance current scientific understanding of the UTLS. As part of the initiative, scientists will study the interactions between atmospheric chemicals and clouds and look at perturbations and feedbacks of radiative processes that can affect compounds (such as ozone) that are sensitive to changes in short- and long-wave radiation.
Transport processes dominate the chemical distributions and microphysical conditions in the UTLS. As a result, one of the early UTLS field programs, the Stratosphere-Troposphere Analyses of Regional Transport (START08) experiment, studied the chemical and transport characteristics of the UTLS region, looking at specific major transport pathways over the Northern Hemisphere’s mid-latitudes. Led by Elliot Atlas of the University of Miami, NCAR’s Laura Pan, and Kenneth Bowman of Texas A&M, a total of 18 START08 missions flew between April and June 2008. Flights extended in range from the Gulf of Mexico to Northern Canada, and in altitude from sea level to 47,000 feet. During flight, GV instruments measured meteorological parameters, atmospheric structure, trace gas species, and microphysical properties that will be used in combination with model simulations of regional dynamics to trace the history of the air found in this region and to better understand the transport boundary between the UT and LS. START08 will improve understanding of the chemistry and microphysics of this region by developing effective observational and modeling tools for characterizing major transport influences.
