ABSTRACT

The two major research objectives of this EIS award are to study through the application of comprehensive analysis approaches a merged satellite data base of temperatures within the mesosphere and lower thermosphere (MLT)region extending over 27 years to detect possible long-term cooling trends and also to assess possible solar cycle dependence. Two potential processes driving the long-term variability: (1) dynamical forcing and (2) direct solar forcing, would be examined by comparisons with results obtained using a state-of-the-art general global circulation model - the Whole Atmosphere Community Climate Model(WACCM. The satellite data to be used for this study includes MLT temperature observations from HALOE, SABER, MLS and SOFIE that would be merged to generate the extended database. The award would also include support of research aimed at achieving a theoretical understanding of long-term trends and solar cycle variations in the MLT region by using WACCM to compare with and to help diagnose the observed trends and solar cycle variations in the satellite data. Because of the possible anthropogenic and solar origin of the decadal changes in the MLT temperatures, the funded research would include a comprehensive modeling analysis of sources from which trends and solar cycle variations might originate, e.g., ozone chemistry, radiative cooling and lower atmosphere wave forcing and related MLT dynamics. This research would help enhance the assessment of changes in the upper atmosphere relative to the WACCM model predictions. The findings obtained in this research are expected to help inform policy decisions on orbital lifetimes and potential debris mitigation strategies. In addition to these benefits to society, this award would also support the research of a graduate student at a HBCU institution as well as introducing six undergraduates (over three years) to research activities.

This award would support the first comprehensive study of long-term MLT temperature trends using a 27-year global scale data record constructed from the combined measurements made by four satellite instruments on different platforms. This merger would be accompanied with a validation analysis that would test the success of the merger of these separate databases. The achievements of the award research objectives would significantly advance knowledge of mesosphere decadal changes driven by possible anthropogenic greenhouse gas increases as well as solar irradiance variability and lower atmosphere dynamical forcing. These results would form a base supporting the development of a much better understanding of the variability and structure of the MLT region and a better capability to predict the future mesosphere state. The outcome of funding this award research would provide clarity as to whether the increasing concentration of carbon dioxide (CO2) within the Earth's atmosphere would eventually lead to a substantial global cooling of the ionosphere-thermosphere-mesosphere (ITM) region by 10 to 50 K for doubled CO2 concentrations from pre-industrial times. The implications of this cooling go far beyond the substantial modification of the Earth's upper atmosphere. A significant MLT cooling trend is known to indicate corresponding thermosphere density decrease at orbital altitudes, reducing aerodynamic drag on all orbiting assets, from the International Space Station to orbital debris, and thus leads to higher probabilities of collisions over time, given the proliferation of orbital assets and especially orbital debris.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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