APL Colloquium

January 4, 2008

Colloquium Topic: Upper Atmosphere: Gateway Region for Solar-Terrestrial Interaction

Humans and our immediate environment are shielded from the continuous stream of energetic particles and radiation emitted from the Sun by the Earth's upper atmosphere and magnetosphere. The upper atmosphere absorbs much of the solar extreme ultraviolet and x-ray radiation (creating the ionosphere we use for radio communication) and the energetic particles from the magnetosphere (causing the auroral light displays at high latitudes). At the same time, energy from the lower atmosphere is being re-distributed upwards in the form of atmospheric waves. Just as in the ocean, these waves reach a surf zone at ~90 km where they break and deposit their energy. In addition, our humans are slowly changing the composition of the atmosphere, especially the amounts of minor greenhouse gases. These changes are modifying the energy balance of the upper atmosphere, resulting in a "potentially" detectable change in its basic structure. It is this complex region, the ionosphere, thermosphere and mesosphere (ITM), the gateway between Earth's environment and space, where the Sun's energy is first deposited and ultimately re-distributed via the lower atmosphere and magnetosphere. It is this region that the NASA Thermosphere . Ionosphere . Mesosphere . Energetics and Dynamics (TIMED) mission was launched on December 2001 to investigate. TIMED is in the middle of a comprehensive study of the interconnection between the ITM system and its drivers from above and below. Its measurements have spanned half a solar cycle so far, allowing us to look at the temporal evolution of the ITM system in a 3D sense - a tremendous leap beyond past capabilities. TIMED has documented for the first time the dynamical impacts on the ITM structure resulting from varying levels of solar activity including solar flares, geomagnetic storms powered by solar coronal mass ejections and powerful high-speed solar wind streams, and the inter-annual and long term variability caused by the atmosphere below.

Colloquium Speaker: Sam Yee

Jeng-Hwa (Sam) Yee received a B.S. degree in space physics from National Central University in Taiwan and M.S. and Ph.D. degrees in atmospheric physics from the University of Michigan. He joined the APL Space Department in 1992. He is a Principal Professional Staff member and is currently the supervisor of the Atmospheric Sensing Techniques Section and the Project Scientist for the TIMED mission. Dr. Yee is an atmospheric physicist with expertise in the areas of optical remote sensing instrumentation and techniques, inversion algorithm and theoretical modeling of atmospheric processes. His experience also includes atomic and molecular spectroscopy, and collision theory in atomic and molecular processes.