1 / 14

Stan Solomon and Liying Qian High Altitude Observatory National Center for Atmospheric Research

Annual/Semiannual Seasonal Variations in Thermospheric Density: Evidence for Lower Atmosphere Effects. Stan Solomon and Liying Qian High Altitude Observatory National Center for Atmospheric Research with thanks to Bruce Bowman Air Force Space Command.

Download Presentation

Stan Solomon and Liying Qian High Altitude Observatory National Center for Atmospheric Research

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Annual/Semiannual Seasonal Variations in Thermospheric Density: Evidence for Lower Atmosphere Effects Stan Solomon and Liying Qian High Altitude Observatory National Center for Atmospheric Research with thanks to Bruce Bowman Air Force Space Command NADIR MURI Meeting • CU/LASP • 21 October 2008

  2. Model & Measurement of Thermosphere Solar Cycle Variation Qian, L., S. C. Solomon, and T. J. Kane, J. Geophys. Res., submitted, 2008.

  3. Model-Data Comparison for 2003

  4. Model-Data Comparison for 2003 07337 08744 12138 12388 14483

  5. Issues with the Annual/Semiannual Seasonal Variation In order to obtain this good agreement between model and measurement of thermospheric neutral density, we apply an ad-hoc correction to the seasonal variation.

  6. Observed Seasonal Variation is Larger than Standard Model

  7. Multi-Satellite, Multi-Year Comparison with Standard Model

  8. Issues with the Annual/Semiannual Seasonal Variation • In order to obtain this good agreement between model and measurement of thermospheric neutral density, we apply an ad-hoc correction to the seasonal variation. • What could be the physical mechanism behind such variation? • Inadequate model description of thermospheric general circulation? • Effect of Sun-Earth distance? • Russell-McPherron effect? • Magnetic field asymmetry? • Variation in momentum deposition at mesopause? • Variation in eddy mixing at mesopause?

  9. Effect of Thermospheric Circulation and Sun-Earth Distance z=400km ln(p0/p)=2 Global mean, solar maximum, geomagnetic quiet, constant eddy diffusivity.

  10. Issues with the Annual/Semiannual Seasonal Variation • In order to obtain this good agreement between model and measurement of thermospheric neutral density, we apply an ad-hoc correction to the seasonal variation. • What could be the physical mechanism behind such variation? • Inadequate model description of thermospheric general circulation? • Effect of Sun-Earth distance? • Russell-McPherron effect? • Magnetic field asymmetry? • Variation in momentum deposition at mesopause? • Variation in eddy mixing at mesopause? • The way to change the density of the upper thermosphere is to change its scale height (kT/Mg) • This could take the form of a temperature correction or a composition correction. • Increase in temperature leads to increase in density • Decrease in mean molecular mass leads to increase in density • (We are pretty much stuck with k and g) • We have chosen to change M through the mechanism of changing the eddy diffusion coefficient at the lower boundary, which changes the O/N2 ratio. • (Increase in Kzz reduces O by increasing downward transport.)

  11. Imposed Variation of Eddy Diffusion Coefficient at ~97 km This solves the seasonal density problem through imposing compositional variation But, is there evidence for this effect in actual composition measurements?

  12. Comparison with Density and Composition Data TIEGCM with/without seasonal variation of eddy diffusivity at lower boundary

  13. What are the Implications of this Hypothesis? • It is entirely reasonable that there should be systematic seasonal changes in turbulent mixing in the mesopause region. Breaking gravity waves are a likely source of turbulence. Wave generation, stratospheric and mesospheric jets, and atmospheric tides, are all known to have significant seasonal variation. • But what could cause the “hemispherical asymmetry?” • I.e., higher eddy diffusivity during northern hemisphere summer than southern hemisphere summer • We have ruled out Earth-orbit and geomagnetic asymmetry, i.e., the external drivers. • That leaves the lower-middle atmospheric system, which is known to be significantly hemispherically asymmetric. • The ultimate cause of this is the land-mass distribution. • So, thermospheric variation is fundamentally a product of planetary geology.

  14. A Local Result on Eddy Diffusion Coefficient Starfire results from Alan Liu and Chet Gardner, COSPAR 2008

More Related