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Investigating Cold Thermosphere Effects During Solar Minimum

This workshop presentation by Stan Solomon and Liying Qian at the High Altitude Observatory delves into the peculiar behavior of the thermosphere during the extended 2007-2009 solar minimum. It examines the weak solar wind and low geomagnetic activity, questioning whether solar ultraviolet and X-ray irradiance also diminished. The analysis includes long-term thermospheric density changes due to CO2 cooling and the influence of the solar cycle on thermospheric temperature. The findings raise critical questions about solar irradiance consistency and the implications for climate.

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Investigating Cold Thermosphere Effects During Solar Minimum

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Presentation Transcript

  1. Whi is the Thermosphere Cold? Stan Solomon and Liying Qian High Altitude Observatory National Center for Atmospheric Research WHI Workshop • High Altitude Observatory • 12 November, 2008

  2. Much Speculation Concerning Solar Minimum • • The 2007-2009 solar minimum was unusually long — was it also unusually “quiet?” • —The solar wind and interplanetary magnetic field were at times very weak • —Terrestrial Geomagnetic activity was very low for extended periods • —But was solar ultraviolet and X-ray irradiance also lower than “normal?” • • Also speculation about terrestrial effects • —Anecdotal mention of unusually low ionospheric altitudes/densities • —Some evidence of unusually low thermospheric densities • ...and conjecture concerning climate • • This raises a fundamental question for solar physics: • —Are irradiance levels at solar minimum generally similar, or not? • ...meanwhile, we can take advantage of the quiet Sun to notice other important perturbations of the thermosphere-ionosphere system.

  3. Thermospheric Density during the Declining Phase of SC #23 [Qian et al., J. Geophys. Res., 2009]

  4. Long-Term Satellite Drag Data

  5. Long-term Thermospheric Density AnalysisShows the Effect of CO2 Cooling on Thermospheric Density Comparison of thermospheric densities inferred from satellite drag observations over four solar decades (1967–2007) to the NRL-MSIS empirical model [Emmert et al., Geophys. Res. Lett., 2008].

  6. Magnitude of CO2 Cooling Depends on Solar Cycle Greater thermospheric temperature and density change for perpetual solar minimum conditions than for perpetual solar maximum conditions, due to the decreased importance of nitric oxide cooling at solar minimum [Qian et al., Geophys. Res. Lett., 2006; 2008]

  7. Measurements from the TIMED Solar EUV Experiment

  8. EUV and Soft X-ray Variability in SEE v. 10

  9. TIE-GCM Comparison Using New SEE Data (initial attempt)

  10. Peak Densities of the E and F2 Ionospheric Regions at Noon Boulder, Colorado, Ionosonde data from the National Geophysical Data Center

  11. Ionospheric Climatology, 2007

  12. Ionospheric Climatology, 2008

  13. Measurement/Model Comparison during theCo-Rotating Solar Wind Streams in 2005

  14. Fourier Analysis of 2005 Density Variations

  15. Whole Heliosphere Interval, (March-April 2008) Courtesy of Jiuhou Lei

  16. So, is the Thermosphere/Ionosphere “Different” at this Solar Minimum? Yes, a little bit. But we still don’t know why.

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