Characteristics of the equatorial plasma drifts as obtained by using Canadian Doppler ionosonde over southern tip of India

Abstract

We present here characteristics of the Doppler drift measurements over Tirunelveli (8.73°N, 77.70°E; dip 0.5°N), an equatorial site over Southern India using Doppler interferometry technique of Canadian ionosonde. Three‐dimensional bulk motions of the scatterers as reflected from the ionosphere are derived by using Doppler interferometry technique at selected frequencies using spaced receivers arranged in magnetic E‐W and N‐S directions. After having compared with Lowell's digisonde drifts at Trivandrum, we studied the temporal and seasonal variabilities of quiet time drifts for the year 2012. The observations showed higher vertical drifts during post sunset in the equinox followed by winter and summer seasons. The comparison of Doppler vertical drifts with the drifts obtained from (a) virtual height and (b) Fejer drift model suggests that Doppler vertical drifts are relatively higher as compared to the drifts obtained from model and virtual height methods. Further, it is seen that vertical drifts exhibited equinoctial asymmetry in prereversal enhancement quite similar to such asymmetry observed in the spread F in the ionograms and GPS L band scintillations. The zonal drifts, on the other hand, showed westward during daytime with mean drifts of ~150–200 m/s and correlated well with equatorial electrojet strength indicating the role of E region dynamo during daytime, while they are eastward during nighttime with mean drifts of ~100 m/s resembling F region dynamo process. Also, zonal drifts showed large westward prior to the spread F onset during autumn equinox than vernal equinox, suggesting strong zonal shears which might cause equinoctial asymmetry in spread F.

On the Co‐Seismic Ionospheric Disturbances (CIDs) in the Rapid Run Ionosonde Observations Over Allahabad Following Mw 7.8 Nepal Earthquake on April 25, 2015

“…It may be mentioned here that the satellite and receiver bias corrections have been applied to the TEC data using least squares technique to obtain absolute TEC values (See Ma & Maruyama, 2003). Advantage of this system is that it can operate at both single frequency mode as well as ionogram mode (see e.g., Sripathi et al, 2016). The ionosonde is typical radar used to sound the ionosphere wherein it sweeps several radio frequencies in the range of 1-20 MHz into the ionosphere and it receives the reflected signals from the different regions of the ionosphere where plasma frequency equals to that of the radar frequency.…”

“…The ionosonde is typical radar used to sound the ionosphere wherein it sweeps several radio frequencies in the range of 1-20 MHz into the ionosphere and it receives the reflected signals from the different regions of the ionosphere where plasma frequency equals to that of the radar frequency. Advantage of this system is that it can operate at both single frequency mode as well as ionogram mode (see e.g., Sripathi et al, 2016). The single frequency mode of operation provides line of sight as well as skymap to identify the location of the reflected signal.…”

Unusual Generation of Localized EPB in the Dawn Sector Triggered by a Moderate Geomagnetic Storm

“…Ionosonde observations were made at Tirunelveli (8.73°N, 77.7°E, magnetic latitude: 0.23°N), an equatorial station in the southern part of India. The ionosonde, which is a CADI (Canadian Advanced Digital Ionosonde; e.g., Grant et al, ) setup in the year 2006 (see Sripathi et al, ), can operate both in ionogram and drift modes. In the ionogram mode, it sweeps through the sounding frequencies usually from 2 to 16 MHz with resolution of a few kilohertz to produce one ionogram at every 10‐min interval.…”

On the Nocturnal Downward and Westward Equatorial Ionospheric Plasma Drifts During the 17 March 2015 Geomagnetic Storm

“…The CADI is operational at Tirunelveli since 2006 and provides (a) the echo delay (virtual height) as a function of frequency, (b) the amplitude and phase of the reflected signal, and (c) the Doppler shift due to motion of the reflector at selected frequencies. It is an established diagnostic tool to study the climatological behavior of vertical and zonal plasma drifts over the equatorial region (e.g., Sripathi et al, ). The Doppler drift (both vertical and zonal) observations reported in the present study are recorded at 7 MHz frequency with 1 min time resolution in between two consecutive ionograms.…”

“…The Doppler drift (both vertical and zonal) observations reported in the present study are recorded at 7 MHz frequency with 1 min time resolution in between two consecutive ionograms. More details on the functioning of CADI at Tirunelveli can be found in Sripathi et al ().…”