HAO 2011 Profiles In Science: Dr. Stan Solomon
Contact
303-497-2179
stans@ucar.edu
Area of expertise: Sun and Upper Atmosphere
Specialties: physics and chemistry of Earth's upper atmosphere and ionosphere, theoretical modeling and data analysis of impacts of solar output on Earth's atmosphere, solar terrestrial physics, satellite system design
Dr. Stan Solomon is a Senior Scientist at NCAR's High Altitude Observatory. The physics and chemistry of the Earth's upper atmosphere and ionosphere are Stan Solomon's specialty. He works on theoretical modeling and data analysis to investigate the impacts of solar output on Earth's atmosphere. He is Co-Director for the ionosphere-thermosphere of the CISM (Center for Integrated Space Weather Modeling). He is an Interdisciplinary Scientist on the TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) mission. Instruments on this NASA satellite are gathering data to help understand how the Sun controls weather at the edge of space. In addition to his research, Solomon has served as a lecturer at the University of Colorado, teaching topics that range from solar-terrestrial physics to satellite system design.
Publications
(1) Causes of Low Thermospheric Density During the 2007-2009 Solar Minimum
Solomon, S. C., L. Qian, L. V. Didkovsky, R. A. Viereck, and T. N. Woods. 2011: Causes of low thermospheric density during the 2007–2009 solar minimum. J. Geophys. Res., 116, A00H07, doi:10.1029/2011JA016508.
Abstract: Satellite drag data indicate that the thermosphere was lower in density, and therefore cooler, during the protracted solar minimum period of 2007–2009, than at any other time in the past 47 years. Measurements indicate that solar extreme-ultraviolet (EUV) irradiance was also lower than during the previous solar minimum. However, secular change due to increasing levels of CO2 and other greenhouse gases, which cool the upper atmosphere, also plays a role in thermospheric climate, and changes in geomagnetic activity could also contribute to the lower density. Solar EUV measurements from the Solar EUV Monitor (SEM) on the Solar and Heliospheric Observatory have previously been used as input to the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model, and good agreement was obtained between the density changes from 1996 to 2008 and the changes in solar EUV. Since there is some uncertainty in the long-term calibration of SEM measurements, model calculations were performed using the MgII core-to-wing ratio as a solar EUV proxy index. The contributions of increased CO2 and decreased geomagnetic activity to the changes were also quantified. According to these simulations, CO2 and geomagnetic activity play small but significant roles, and the primary cause of the low temperatures and densities remains the unusually low levels of solar EUV irradiance.
Figure 1 caption: Time series of model simulations, using the scaled MgII core-to-wing ratio as input, compared to global mean thermospheric density measurements at 400 km. (a) TIE-GCM and density for 1996. (b) TIE-GCM and density for 2008. (c) NRLMSISE-00 and density for 1996. (d) NRLMSISE-00 and density for 2008. Black lines: global mean thermospheric density measurements. Red lines: daily mean model simulations. Blue lines: model simulations, excluding the effects of geomagnetic activity by setting the driving input parameters to constant, very low values. Green lines: daily Ap geomagnetic index, divided by 100, for comparison.