Skip to main content

The seasonal and solar cycle variations of electron density gradient scale length, vertical drift and layer height during magnetically quiet days: Implications for Spread F over Trivandrum, India

Abstract

A study has been carried out on the behaviour of electron density gradient scale length, L, vertical drift and layer height, around post sunset hours, during the magnetically quiet days of summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995), using ionosonde data of Trivandrum (8.5°N, 76.5°E, dip = 0.5°N) in the Indian longitude sector. The results indicate a clear seasonal and solar cycle variation in all the three parameters. Further, the seasonal variation of equatorial Spread F (ESF) during the above period is examined in terms of the relative roles of L, the vertical drift and layer height (of the F layer) in the triggering of the collisional Rayleigh-Taylor instability. The results, show for the first time, that L also plays an important role, in controlling the quiet time seasonal and solar cycle variability of ESF; whereas in earlier studies this parameter had been taken to be constant. The detailed results are presented and discussed.

References

  1. Abdu, M. A., I. S. Batista, and J. A. Bittencourt, Some characteristics of Spread F at the magnetic equatorial station Fortaleza, J. Geophys. Res., 86(A8), 6836–6842, 1981.

    Article  Google Scholar 

  2. Chandra, H. and R. G. Rastogi, Solar cycle and seasonal variation of Spread F near the magnetic equator, J. Atmos. Sol. Terr. Phys., 32, 439–444, 1970.

    Article  Google Scholar 

  3. Devasia, C. V., N. Jyoti, K. S. Viswanathan, K. S. V. Subbarao, D. Tiwari, and R. Sridharan, On the plausible linkage of thermospheric meridional winds with equatorial Spread F, J. Atmos. Sol. Terr. Phys., 64, 1–12, 2002.

    Article  Google Scholar 

  4. Farley, D. T., B. B. Balsley, R. F. Woodman, and J. P. McClure, Equatorial Spread F: Implications of VHF radar observations, J. Geophys. Res., 75, 7199–7216, 1970.

    Article  Google Scholar 

  5. Fejer, B. G. and M. C. Kelley, Ionospheric irregularities, Rev. Geophys Space Phys., 18, 401–454, 1980.

    Article  Google Scholar 

  6. Fejer, B. G., L. Scheerliess, and E. R. de Paula, Effects of the vertical plasma drift velocity on the generation and evolution of equatorial Spread F, J. Geophys. Res., 104, 19859–19869, 1999.

    Article  Google Scholar 

  7. Fuller-Rowell, T. J., M. V. Codrescu, R. J. Moffett, and S. Quegan, On the seasonal response of the thermosphere and ionosphere to geomagnetic storms, J. Geophys. Res., 101, 2343–2353, 1996.

    Article  Google Scholar 

  8. Haerendel, G., Theory of equatorial Spread F, Report, Max-Plank inst. fur Phys. and Astrophys., Munich, 1973.

    Google Scholar 

  9. Hysell, D. L. and J. Burcham, Long term studies of equatorial spread F using the JULIA radar at Jicamarca, J. Atmos. Terr. Phys., 64, 1531–1543, 2002.

    Article  Google Scholar 

  10. Jyoti, N., C. V. Devasia, R. Sridharan, and D. Tiwari, Threshold height (h’Fc) for the meridional wind to play a deterministic role in the bottom side equatorial Spread F and its dependence on solar activity, Geophys. Res. Lett., 31, L12809, doi:10.1029/2004GL019455, 2004.

  11. Kelley, M. C. and J. P. McClure, Equatorial Spread-F: a review of recent experimental results, J. Atmos. Terr. Phys., 43, 427–435, 1981.

    Article  Google Scholar 

  12. Krishna Murthy, B. V., S. S. Hari, and V. V. Somayajulu, Nighttime equatorial thermospheric meridional winds from h’F data, J. Geophys. Res., 95, 4307–4310, 1990.

    Article  Google Scholar 

  13. Manju, G., C. V. Devasia, and R. Sridharan, On the seasonal varations of the threshold height for the occurrence of equatorial Spread F during solar minimum and maximum years, Ann. Geophys., 25, 1, 2007.

    Article  Google Scholar 

  14. Manju, G., C. V. Devasia, and S. Ravindran, The seasonal and solar cycle variations of electron density gradient scale length during magnetically disturbed days: implications for Spread F, Earth Planets Space, 61, 913–917, 2009.

    Article  Google Scholar 

  15. Maruyama, T. and N. Matuura, Longitudinal variability of annual changes in activity of ESF and plasma depletions, J. Geophys. Res., 89, 10903–109012, 1984.

    Article  Google Scholar 

  16. Sekar, R. and R. Raghavarao, Role of vertical winds on the Rayleigh- Taylor instabilities of the nighttime equatorial ionosphere, J. Atmos. Terr. Phys., 49, 981–985, 1987.

    Article  Google Scholar 

  17. Subbarao, K. S. V. and B. V. Krishna Murthy, Seasonal variations of equatorial Spread F., Ann. Geophys., 12, 33–39, 1994.

    Google Scholar 

  18. Tulasi Ram, S., P. V. S. Rama Rao, K. Niranjan, D. S. V. V. D. Prasad, R. Sridharan, C. V. Devasia, and Sudha Ravindran, The role of post-sunset vertical drifts in predicting the onset of VHF scintillations during high and low sunspot activity, Ann. Geophys., 24, 1609–1616, 2006.

    Article  Google Scholar 

  19. Whitehead, J., Ionization disturbances caused by gravity waves in the presence of an electrostatic field and background wind, J. Geophys. Res., 76, 238–241, 1971.

    Article  Google Scholar 

  20. Woodman, R. F. and C. LaHoz, Radar observations of F region equatorial irregularities, J. Geophys. Res., 81, 5447–5466, 1976.

    Article  Google Scholar 

Download references

Author information

Affiliations

Authors

Corresponding author

Correspondence to G. Manju.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Manju, G., Devasia, C.V. & Ravindran, S. The seasonal and solar cycle variations of electron density gradient scale length, vertical drift and layer height during magnetically quiet days: Implications for Spread F over Trivandrum, India. Earth Planet Sp 61, 1339–1343 (2009). https://doi.org/10.1186/BF03352986

Download citation

Key words

  • Equatorial ionosphere
  • ionospheric irregularities
  • plasma instability
  • equatorial Spread F