Ionospheric vertical drifts over an Indian low latitude station and its comparison with IRI-2007 vertical drift model

The vertical plasma drift velocity (V-z = dh'F/dt) of the Ionospheric F-Region is calculated using the Ionosonde data over an Indian low latitude station, Waltair (17.7 degrees N, 83.3 degrees E, dip 20 degrees N). The vertical drift velocities thus computed are compared with those of the IRI-2007 vertical drift model during the post sunset hours of the high sunspot period of 2001-2002. The vertical drift values are entirely downward between 2000 and 0700 h LT for the IRI-2007 vertical drift model compared to those derived using Ionosonde. The root mean square errors (RMSE) in the vertical drifts during the post sun-set hours computed between the IRI vertical drift model and Ionosonde measured values are found to be 13.54, 21.68 and 22.39 m/s for summer, equinox and winter seasons respectively. The average vertical drifts derived using Ionosonde showing pre-reversal enhancements during evening hours (1700-1900 h LT) over Waltair are found to be 8, 16 and 12 m/s, whereas the IRI-2007 model derived values show 15, 35 and 36 m/s during summer, equinox and winter seasons respectively. The correlation analysis of peak drift velocities derived using Ionosonde and those from IRI model with Rz and F10.7 shows more or less similar variation while they are differed in their variation with Ap index. A good correlation is observed between the vertical plasma drift obtained using Ionosonde and Equatorial Electrojet Strength (EEJ) except during winter, while the correlation coefficients computed using IRI model are little higher than those obtained using Ionosonde with maximum values during summer season. The percentage of deviation for IRI-model correlation coefficient and that of Ionosonde-inferred drift for equinoctial and summer months is around 50% and 25% respectively where as it is more than 100% for winter. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.