Initial Examination of the Long Term Thermosphere Changes As Seen in the Whole Atmosphere Community Climate Model - eXtended (WACCM-X) J. M. McInerney, L. Qian, and H.-L Liu

It has been over two decades since the projection that, not only will the human induced increase in atmospheric CO2 produce a warming in the troposphere, it will also produce a cooling in the middle to upper atmosphere into the 21st century with significant consequences. The thermospheric density decrease associated with this projected upper atmosphere cooling due to greenhouse gases has been confirmed by observations, in particular satellite drag measurements, and by various modeling studies. Recent studies also suggest potential impacts from the lower atmosphere on thermosphere dynamics such as atmospheric thermal tides and gravity waves. With the current advance of whole atmosphere climate models which extend from the ground through the thermosphere, it is now possible to include effects of these and other lower atmosphere processes in modeling studies of long term thermospheric changes. One such whole atmosphere model under development at the National Center for Atmospheric Research (NCAR) is the Whole Atmosphere Community Climate Model - eXtended (WACCM-X). WACCM-X is a self consistent climate model extending from the ground to approximately 500 kilometers and is based on the Whole Atmosphere Community Climate Model (WACCM) / Community Atmosphere Model (CAM) component of the Community Earth System Model (CESM). Although an interactive ionosphere module is not complete, the globally averaged structure of thermosphere temperature and neutral species from WACCM-X are reasonable compared with the NCAR global mean model. In this study, we will examine a transient WACCM-X simulation from 1955 to 2005 with realistic tropospheric CO2 input and solar and geomagnetic forcing. The preliminary study will focus on the long term changes in the thermosphere from this simulation, in particular the secular changes of thermosphere neutral density and temperature due to anthropogenic forcing.