- Open Access
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, Planets and Space volume 61, pages1339–1343(2009)
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.
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.
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.
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.
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.
Fejer, B. G. and M. C. Kelley, Ionospheric irregularities, Rev. Geophys Space Phys., 18, 401–454, 1980.
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.
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.
Haerendel, G., Theory of equatorial Spread F, Report, Max-Plank inst. fur Phys. and Astrophys., Munich, 1973.
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.
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.
Kelley, M. C. and J. P. McClure, Equatorial Spread-F: a review of recent experimental results, J. Atmos. Terr. Phys., 43, 427–435, 1981.
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.
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.
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.
Maruyama, T. and N. Matuura, Longitudinal variability of annual changes in activity of ESF and plasma depletions, J. Geophys. Res., 89, 10903–109012, 1984.
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.
Subbarao, K. S. V. and B. V. Krishna Murthy, Seasonal variations of equatorial Spread F., Ann. Geophys., 12, 33–39, 1994.
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.
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.
Woodman, R. F. and C. LaHoz, Radar observations of F region equatorial irregularities, J. Geophys. Res., 81, 5447–5466, 1976.
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
- Equatorial ionosphere
- ionospheric irregularities
- plasma instability
- equatorial Spread F