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[PEM12-P12] Modulation sources of the semidiurnal tide on solar activity in the polar lower thermosphere
Keywords:EISCAT radar, Semidiurnal tide, Lower thermosphere
We have studied variabilities of the semidiurnal tide in the polar lower thermosphere with respect to season, solar activity, and geomagnetic activity. Their causes are not yet well understood. Since the ozone heating in the stratosphere is a major source of the semidiurnal tide, we have investigated whether the ozone heating varies with the solar activity.
Major components of the ozone heating are total ozone, solar energy density, and sunlit hours. We investigated the correlation between solar activity (F10.7) and total ozone using data from TOMS and Aura OMI satellite during 1987-2019. We showed the correlation coefficient was 0.17, indicating the ozone does not change much with the solar activity. We, thus, focus on solar energy density; the peak absorption coefficient of ozone occurs at 255 nm [Lindzen and Will, 1973]. We have investigated the energy flux variation at a wavelength of 255 nm with respect to the F10.7 index using UV data from SORCE satellite during 2003-2020. The F10.7 index varied by a factor of about 3 from the low solar activity to the high solar activity, while the energy flux at 255 nm varied by only about 3.5%. These results indicate that the ozone heating does not change much with the solar activity, thus it is not a cause for the solar activity dependence of the semidiurnal tide.
The ion drag is another possible source. The strength of the ion drag varies with the electron density, ion-neutral collision frequency, and the velocity difference between the neutral gas and the ion motions. Since it is well known that the F10.7 index is a good proxy of the EUV flux from the Sun, the electron density may be a key parameter; changes in the electron density would be a significant source of the solar activity dependence of the semidiurnal tide. To prove this idea, we have investigated statistically the dependence of the electron density on the solar activity in the polar lower thermosphere for the first time using the EISCAT radar data.
Acknowledgments
Earth Probe TOMS and Aura OMI daily total ozone data were provided by NASA Goddard Space Flight Center, USA, from their website at https://ozonewatch.gsfc.nasa.gov/. The SORCE data were downloaded from the SORCE website at https://lasp.colorado.edu/home/sorce/data/.
References
Lindzen, R. S., and D. I. Will. (1973), An analytic formula for heating rate due to ozone absorption, J. Atmos. Sci., 30, 513-515.
Major components of the ozone heating are total ozone, solar energy density, and sunlit hours. We investigated the correlation between solar activity (F10.7) and total ozone using data from TOMS and Aura OMI satellite during 1987-2019. We showed the correlation coefficient was 0.17, indicating the ozone does not change much with the solar activity. We, thus, focus on solar energy density; the peak absorption coefficient of ozone occurs at 255 nm [Lindzen and Will, 1973]. We have investigated the energy flux variation at a wavelength of 255 nm with respect to the F10.7 index using UV data from SORCE satellite during 2003-2020. The F10.7 index varied by a factor of about 3 from the low solar activity to the high solar activity, while the energy flux at 255 nm varied by only about 3.5%. These results indicate that the ozone heating does not change much with the solar activity, thus it is not a cause for the solar activity dependence of the semidiurnal tide.
The ion drag is another possible source. The strength of the ion drag varies with the electron density, ion-neutral collision frequency, and the velocity difference between the neutral gas and the ion motions. Since it is well known that the F10.7 index is a good proxy of the EUV flux from the Sun, the electron density may be a key parameter; changes in the electron density would be a significant source of the solar activity dependence of the semidiurnal tide. To prove this idea, we have investigated statistically the dependence of the electron density on the solar activity in the polar lower thermosphere for the first time using the EISCAT radar data.
Acknowledgments
Earth Probe TOMS and Aura OMI daily total ozone data were provided by NASA Goddard Space Flight Center, USA, from their website at https://ozonewatch.gsfc.nasa.gov/. The SORCE data were downloaded from the SORCE website at https://lasp.colorado.edu/home/sorce/data/.
References
Lindzen, R. S., and D. I. Will. (1973), An analytic formula for heating rate due to ozone absorption, J. Atmos. Sci., 30, 513-515.