http://nopr.niscair.res.in/handle/123456789/14008 <b>Special issue: Low-latitude upper atmosphere-ionosphere-plasmasphere system in a record low solar minimum in Asian sector</b> http://nopr.niscair.res.in/retrieve/60490 http://nopr.niscair.res.in/handle/123456789/14008 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/14051 Title: Corotating interaction region (CIR) induced magnetic storms during solar minimum and their effects on low-latitude geomagnetic field and ionosphere <br/> <br/>Authors: Veenadhari, B; Kumar, Sandeep; Ram, S Tulasi; Singh, Rajesh; Alex, S <br/> <br/>Abstract: The corotating interaction region (CIR) induced magnetic storms which occurred during solar minimum are investigated to study their effects on equatorial and low-latitude ionosphere and geomagnetic field at Indian sector. This work was a part of Indian CAWSES campaign for the period of March – April 2006. The penetration electric fields play a crucial role in modifying equatorial electric fields during severe magnetic storms and these effects are not studied in detail for moderate magnetic storm originated by CIRs. The present paper investigates the effects of CIR related moderate storms and found that during the moderate magnetic storms, the short lived (duration of 2 - 3 h) penetration of high latitude electric fields to equatorial ionosphere exists during local morning and noon hours during main phase as inferred from changes in EEJ with the response to interplanetary electric field. The variations of EEJ are linearly correlated with the sudden changes in interplanetary electric field (IEF_Y) around morning to noon hours, which confirms existence of the penetration of electric fields. <br/> <br/>Page(s): 306-315 http://nopr.niscair.res.in/handle/123456789/14050 Title: Sporadic E over Allahabad during the extremely prolonged low solar activity period of 2007-2009 <br/> <br/>Authors: Tiwari, P; Tiwari, D; Surve, G; Nayak, C <br/> <br/>Abstract: In this paper, the characteristics of sporadic E (Es) layer echoes, observed using a Canadian Advanced Digital Ionosonde (CADI) from equatorial ionization anomaly crest region of Allahabad (25.3ºN, 81.5ºE, and dip latitude 16.3ºN) during extremely prolonged low solar activity period of 2007-2009, have been investigated. Quarter hourly ionograms have been used to study the Es characteristics, viz. the top frequency reflected by the Es layer (ftEs), the blanketing frequency (fbEs), virtual height of Es (h’Es) and their local time and seasonal variations. Also, the occurrence statistics of Es and total blanketing type Es are presented. The most notable feature of the sporadic Es layer at Allahabad is the high percentage occurrence during daytime in the summer months. Interestingly, observation shows that the occurrence of total blanketing type Es layer is more during the nighttime of summer months than in other times and other months. Height migration of h’Es shows descending pattern indicating the role of tidal winds. These results are finally compared with those reported earlier and discussed in the light of current understanding of the solar cycle and seasonal variability of the temperate latitude Es. <br/> <br/>Page(s): 285-293 http://nopr.niscair.res.in/handle/123456789/14049 Title: Corotating interaction regions (CIRs) at sub-harmonic solar rotational periods and their impact on ionosphere-thermosphere system during the extreme low solar activity year 2008 <br/> <br/>Authors: Ram, S Tulasi; Yamamoto, M; Veenadhari, B; Kumar, Sandeep; Gurubaran, S <br/> <br/>Abstract: The past solar minimum year 2008 has been exceptionally quiet with more than 70% spotless days and the solar EUV irradiance and F10.7 solar flux levels steadily at low values for a prolonged period. During this unique solar minimum epoch, however, the geospace environment is recurrently intercepted by solar wind high speed streams from the low-latitude coronal holes, which are the primary contributors for recurrent geomagnetic activity at solar rotational (27-day) and its sub-harmonic (13.5 and 9-day) periodicities. In response, both the neutral and ionized upper atmospheric properties continued to ring with same periodicities. The results indicate that both the neutral and electron density response at 400 km (topside ionosphere) is dominated by the changes in temperature and/or scale height and exhibits coherent enhancements concurrently with the periodicities in geomagnetic activity. However, the equatorial electrojet (EEJ) strength does not exhibit any recurrent signatures at these periodicities. <br/> <br/>Page(s): 294-305 http://nopr.niscair.res.in/handle/123456789/14048 Title: On the linkage between mesospheric gravity waves and occurrence of equatorial plasma bubble observed during the low solar activity <br/> <br/>Authors: Taori, A; Kamalakar, V; Joshi, L M; Sripathi, S; Patra, A K <br/> <br/>Abstract: In this paper, the linkage between the low-latitude mesospheric gravity waves and the equatorial plasma bubble (EPB) have been investigated using simultaneously Rayleigh lidar and VHF radar observations from Gadanki (13.5^oN, 79.2^oE) and ionosonde observations from Tirunelveli (8.7^oN, 77.8^oE) made between 2007 and 2009 when solar activity was undergoing a deep minima. The two sets of observations have been analysed, each comprising of one case having EPB and another without EPB observed on two nearby nights. Observations show that the occurrences of plume structures in the radar observations are found to have a close link with the amplitudes of the short period gravity waves in the mesospheric temperature. It is argued that such waves have an important role in seeding the Rayleigh-Taylor (RT) instability manifesting EPB. <br/> <br/>Page(s): 264-270