Bibliography

Direct observational evidence for disturbance dynamo on the daytime low-latitude ionosphere: A case study based on the 28 June 2013 space weather event

A case of the westward disturbance dynamo (DD) electric field, influencing the daytime equatorial and low-latitude ionosphere, during a geomagnetic storm that occurred on 28\textendash29 June 2013 is presented. The GPS total electron content (TEC) observations from a network of stations in the Indian equatorial, low and middle latitude regions along with the radio beacon TEC, ionosonde, and magnetic field observations are used to study the storm time behavior of the ionosphere. Negative ionospheric storm effects were seen over the low and middle latitudes during the storm time due to the presence of a westward DD electric field. Observations show that the suppression of the equatorial ionization anomaly (EIA) from the morning hours itself on 29 June 2013 took place due to the prevailing westward DD electric field, providing evidence for the model calculations by Balan et al. (2013). Simulations using the GITM model also agree well with our results. The present study gains importance as the direct observational evidences for disturbance dynamo effects on the daytime low-latitude ionosphere and the EIA are sparse, as it has been difficult to delineate it from the compositional disturbances.

Thampi, Smitha; Shreedevi, P.; Choudhary, R.; Pant, Tarun; Chakrabarty, D.; Sunda, S.; Mukherjee, S.; Bhardwaj, Anil;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2016

YEAR: 2016     DOI: 10.1002/2016JA023037

Effects of prolonged southward interplanetary magnetic field on low-latitude ionospheric electron density

The present work describes the low-latitude ionospheric variability during an unusually prolonged (~33 h) geomagnetically disturbed condition that prevailed during 15\textendash16 July 2012. The low-latitude electron density in summer hemisphere, investigated using ground- and satellite-based observations, responded to this by generating strong negative ionospheric storm on 16 July. The maximum electron density on 16 July over Indian low latitudes was reduced by more than 50\% compared to that on a geomagnetically quiet day (14 July 2012). In contrast to the extreme reduction in total electron content (TEC) in the Northern Hemisphere, TEC from a winter hemispheric station revealed substantial (~23 total electron content unit, 1 TECU = 10¹⁶ el m^-2) enhancements on the same day. This contrasting hemispherical response in TEC is suggested to be due to the combined effects of strong interhemispheric and solar-driven day-night winds. Further, very weak equatorial electrojet (EEJ) strength on 16 July indicated that the westward electric field perturbations in the low-latitude ionosphere were possibly due to the disturbance dynamo effect associated with meridional circulation from polar to equatorial latitudes. Interestingly, despite reduction in the integrated EEJ strength on 15 July, the low-latitude electron density showed substantial enhancement, highlighting the significant effect of the positive ionospheric storm on the low-latitude ionosphere. The roles of electrodynamical/neutral-dynamical and compositional disturbances are discussed in view of these observations to understand low-latitude ionospheric response when geomagnetic disturbance persists for longer duration.

Bagiya, Mala; Hazarika, Rumajyoti; Laskar, Fazlul; Sunda, Surendra; Gurubaran, S.; Chakrabarty, D.; Bhuyan, P.; Sridharan, R.; Veenadhari, B.; Pallamraju, D.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 07/2014

YEAR: 2014     DOI: 10.1002/2014JA020156

low-latitude ionosphere; neutral winds; prolonged southward IMF Bz; thermospheric neutral composition

Storm time spatial variations in TEC during moderate geomagnetic storms in extremely low solar activity conditions (2007--2009) over Indian region

The total electron content (TEC) measurements from a network of GPS receivers were analyzed to investigate the storm time spatial response of ionosphere over the Indian longitude sector. The GPS receivers from the GPS Aided Geo Augmented Navigation (GAGAN) network which are uniquely located around the \~77\textdegreeE longitude are used in the present study so as to get the complete latitudinal coverage from the magnetic equator to low mid-latitude region. We have selected the most intense storms but of moderate intensity (-100\ nT\ \<\ Dst\ \<\ -50\ nT) which occurred during the unusually extremely low solar activity conditions in 2007\textendash2009. Though the storms are of moderate intensity, their effects on equatorial to low mid-latitude ionosphere are found to be very severe as TEC deviations are more than 100\% during all the storms studied. Interesting results in terms of spatial distribution of positive/negative effects during the main/early recovery phase of storms are noticed. The maximum effect was observed at crest region during two storms whereas another two storms had maximum effect near the low mid-latitude region. The associated mechanisms like equatorial electrodynamics and neutral dynamics are segregated and explained using the TIMED/GUVI and EEJ data during these storms. The TEC maps are generated to investigate the storm time development/inhibition of equatorial ionization anomaly (EIA).

Sunda, Surendra; Vyas, B.M.; Khekale, P.V.;

Published by: Advances in Space Research      Published on: 07/2013

YEAR: 2013     DOI: 10.1016/j.asr.2013.03.006

Electrodynamics; Equatorial and low-latitude; geomagnetic storm; Total electron content (TEC)