- Open Access
The seasonal and solar cycle variations of electron density gradient scale length during magnetically disturbed days: implications for Spread F
Earth, Planets and Space volume 61, pages913–917(2009)
The behaviour of electron density gradient scale length, L, around post-sunset hours during the magnetically disturbed days of the summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995) has been studied, 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 L. Seasonal variations of the maximum vertical drift of the F layer were also examined on these days. In particular, the seasonal variation of the Equatorial Spread F (ESF) during this period is examined in terms of the relative roles of L and the vertical drift of the F layer in the triggering of the collisional Rayleigh-Taylor instability. Our results on the clear-cut seasonal and solar cycle variation in L for disturbed days and its control of ESF occurrence 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.
Abdu, M. A., Outstanding problems in equatorial ionospherethermosphere electrodynamics relevant to Spread F, J. Atmos. Sol.-Terr. Phys., 63, 869–884, 2001.
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.
Costa, E. and M. C. Kelley, On the role of steepened structures and drift waves in equatorial Spread F, J. Geophys. Res., 83, 4359–4364, 1978.
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. Moett, 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. Phys. Astrophys., Munich, 1973.
Huang, Y. N., K. Cheng, and W. T. Huang, Seasonal and solar cycle variations of Spread F at equatorial anomaly crest zone, J. Geomag. Geoelectr., 39, 639–657, 1987.
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.
Lee, C. C., J. Y. Liu, B. W. Reinisch, W. S. Chen, and F. D. Chiu, The effects of the pre-reversal drift, EIA asymmetry and magnetic activity on ESF during solar minimum, Ann. Geophys., 23, 745–751, 2005.
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.
Maruyama, T., A diagnostic model for equatorial Spread F 1. Model description and applications to the electric field and neutral wind effects, J. Geophys. Res., 93, 14611–14622, 1988.
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 M. C. Kelley, On the combined effects of vertical shear and zonal electric field patterns on nonlinear equatorial Spread F evolution, J. Geophys. Res., 103, 735–755, 1998.
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.
Sridharan, R., D. Pallam Raju, and R. Raghavarao, Precursor to equatorial Spread-F in OI 630.0 nm dayglow, Geophys. Res. Lett., 21, 2797–2800, 1994.
Subbarao, K. S. V. and B. V. Krishna Murthy, Seasonal variations of equatorial Spread F, Ann. Geophys., 12, 33–39, 1994.
Tsunoda, R. T., Control of the seasonal and longitudinal occurrence of equatorial scintillation by longitudinal gradients in integrated Pedersen conductivity, J. Geophys. Res., 90, 447–456, 1985.
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.
Zalesak, S. T., S. L. Ossakow, and P. K. Chaturvedi, Nonlinear equatorial Spread F: The effects of neutral winds and background Pedersen conductivity, J. Geophys. Res., 87, 151–166, 1982.
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 during magnetically disturbed days: implications for Spread F. Earth Planet Sp 61, 913–917 (2009). https://doi.org/10.1186/BF03353202
- Equatorial ionosphere
- ionospheric irregularities
- plasma instability
- Equatorial Spread F