The ionospheric effect of Total solar eclipse of 22 July 2009 in the equatorial anomaly region

Response of the D and E and F-region of the ionosphere to the total solar eclipse of 22 July 2009 at low latitude, Varanasi (geomagnetic lat = 140 55'N, longitude = 1540 E, dip. angle = 37.30) was investigated using multi-instrument. The solar eclipse started at 05:30:04.4 hrs IST and lasted up to 07:27 hrs IST with totally from 6.25 IST to 6.27 IST in the morning hours at Varanasi. Here we have analyzed narrowband (Amplitude and phase of transmitted signal) as well as broadband (entire VLF signal spectrum) VLF data to find any significant changes in amplitude and/or phase of the signals from various transmitters across the world and any variation from the normal diurnal behavior in ionospheric parameters such as electron density, VLF reflection height. The changes in D-region ionospheric VLF reflection heights and electron density during eclipse have been estimated from tweek analysis. The reflection height increased from ~90 km from the first occurrence of tweek to about 93-94 km at the totality and then decreased to ~89 km at the end of the eclipse. Observations suggest that about 30-40% obscuration of solar disc can lead to the tweeks occurrence which otherwise occur only in the nighttime. A significant increase of 3 dB in the strength of the amplitude of VLF signal of 22.2 kHz transmitted from JJI-Japan is observed around the time of the total solar eclipse (TSE) as compared to a normal day. The modeled electron density height profile of the lower ionosphere depicts linear variation in the electron density with respect to solar radiation as observed by tweek analysis also. We have also used GPS based TEC measurement along with the VHF scintillation to study effect of total solar eclipse. To observe the variability of TEC at Varanasi we have used the VTEC of some selected PRNs and quiet mean VTEC of the same PRN. The percentage change in VTEC (DTEC) compared to quiet mean for each PRN is also plotted to observe the effect. There is considerable reduction in VTEC compared to quiet mean VTEC from all the PRN (Maximum up to 58 % for PRN 24) during the total solar eclipse. Signature of gravity waves in the VTEC variation is also discussed. Scintillations bubbles are also observed during and after the eclipse period indicating irregularities in plasma density. These low latitude ionospheric perturbations on the eclipse day are discussed and compared with other normal days.