Spatial distribution of ionization in the equatorial and low-latitude ionosphere of the Indian sector and its effect on the pierce point altitude for GPS applications during low solar activity periods (original) (raw)

Abstract

1] The equatorial and low-latitude ionosphere is characterized by dynamic changes in the spatial distribution of F region electron density. The in situ density data from Indian SROSS C2 satellite was used in conjunction with the international reference ionosphere (IRI) to demonstrate how the median models have limitations to represent the spatial gradients in the equatorial and subtropical latitudes in the Indian sector. The ground-based ionosonde data was used to derive the bottomside electron density profiles which were matched with IRI to derive the complete F region electron density profile for different times to show the variability in the centroid of ionization mass distribution due to the equatorial plasma dynamics associated with Appleton ionization anomaly. The study brings out that a uniform ionospheric pierce point altitude cannot be assumed for GPS applications in this sector. However, during low sunspot activity periods, the GPS-derived total electron content (TEC) using 2 Â 2 grid point data indicates that spatial gradients in TEC are not too significant in meridian transects and that the assumption of homogeneous distribution is valid for the conversion of slant to vertical TEC even in the equatorial latitudes during solar minimum. Keeping this in view, a qualitative study has been carried out on the possible variability in ionospheric pierce point altitude at representative subtropical latitude in the Indian sector and the results are discussed in light of diurnal and seasonal features of the equatorial ionosphere.

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References (19)

  1. Balan, N., and G. J. Bailey (1995), Equatorial plasma fountain and its effects: Possibility of an additional layer, J. Geophys. Res., 100, 21,421.
  2. Balan, N., G. J. Bailey, R. J. Moffett, Y. Z. Su, and J. E. Titheridge (1995), Modeling studies of the conjugate-hemisphere differences in ionospheric ionization at equatorial anomaly latitudes, J. Atmos. Terr. Phys., 57, 279.
  3. Balan, N., G. J. Bailey, M. A. Abdu, K. I. Oyama, P. G. Richards, J. MacDougall, and I. S. Batista (1997), Equatorial plasma fountain and its effects over three locations: Evidence for an additional layer, the F 3 layer, J. Geophys. Res., 102, 2047.
  4. Balan, N., I. S. Batista, M. A. Abdu, G. J. Bailey, S. Watanabe, J. MacDougall, and J. H. A. Sobral (2000), Variability of an additional layer in the equatorial ionosphere over Fortleza, J. Geophys. Res., 105, 10,603.
  5. Bencze, P., F. Marcz, and J. Szendroi (1997), Difference between the length of the true propagation path and the geometrical path of radio waves transmitted by GPS satellite, Acta Geod. Geophys. Hung., 32, 417.
  6. Birch, M. J., J. K. Hargreaves, and G. J. Bailey (2002), On the use of an effective ionospheric height in electron content measurement by GPS reception, Radio Sci., 37(1), 1015, doi:10.1029/2000RS002601.
  7. Davies, K. (1980), Recent progress in satellite radio beacon studies with particular emphasis on the ATS-6 Radio Beacon Experiment, Space Sci. Rev., 25, 357.
  8. Greenspan, M. E., W. J. Burke, F. J. Rich, W. J. Hughes, and R. A. Heelis (1994), DMSP F8 observations of the mid-latitude and low-latitude top- side ionosphere near solar minimum, J. Geophys. Res., 99, 3817.
  9. Haragreaves, J. K. (1998), Comments on protonopsheric content: ATS-6 revisited, Acta Geod. Geophys. Hung., 33, 129.
  10. Klobuchar, J. A., J. Stalker, and P. H. Doherty (1990), Converting slant to equivalent vertical TEC, paper presented at URSI International Beacon Satellite Symposium, Natl. Univ. of Tucuman, Tucuman, Argentina.
  11. Klobuchar, J. A., P. H. Doherty, A. Das Gupta, M. R. Sivaraman, and A. D. Sarma (2001), Equatorial anomaly gradient effects on a space based augmentation system, paper presented at International Beacon Satellite Symposium, Inst. for Sci. Res., Boston Coll., Boston, Mass.
  12. Lu ¨hr, H., M. Rother, S. Maus, W. Mai, and D. Cooke (2003), The diamag- netic effect of the equatorial Appleton anomaly: Its characteristics and impact on geomagnetic field modeling, Geophys. Res. Lett., 30(17), 1906, doi:10.1029/2003GL017407.
  13. Leitinger, R., and G. Kirchengast (1997), Easy to use global and regional ionospheric models -A report on approaches used in GRAZ, Acta Geod. Geophys. Hung., 32, 329.
  14. Leitinger, R., P. Spalla, and L. Ciraolo (1998), Latitude dependent mean ionospheric height-A new approach to the TEC evaluation from NNSS data, Acta Geod. Geophys. Hung., 33, 61.
  15. Lunt, N., L. Kersley, G. Bishop, and A. Mazzella (1998), Protonospheric electron contents from GPS/NNSS observations, Acta Geod. Geophys. Hung., 33, 137.
  16. Niranjan, K., P. S. Brahmanandam, and B. Srivani (2006), Signatures of equatorial midnight temperature maximum as observed from in-situ and ground based ionospheric measurements in the Indian sector, J. Geophys. Res., 111, A07309, doi:10.1029/2005JA011386.
  17. Rama Rao, P. V. S B. V. Ramana Rao, D. Nru, B. V. P. Subramanyeswara Rao, and M. Srirama Rao (1979), Total electron content measurements at Waltair using ETS II Geo-stationary satellite, in Low Latitude Aeronomi- cal Processes, COSPAR Symp. Ser., vol. 8, pp. 153 -156, Elsevier, New York.
  18. Rama Rao, P. V. S., K. Niranjan, D. S. V. V. D. Prasad, P. S. Brahmanandam, and S. Gopikrishna (2005), Features of additional stratification in iono- spheric F 2 layer observed for half a solar cycle over Indian low latitudes, J. Geophys. Res., 110, A04307, doi:10.1029/2004JA010646.
  19. ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À S. Gopikrishna, K. Niranjan, P. V. S. Rama Rao, and B. Srivani, Department of Physics, Andhra University, Visakhapatnam 530 003, India. (gopikrishna@yahoo.com; niranjankandula@hotmail.com; palurirao@ yahoo.com; srivani_30@yahoo.com)