Bibliography

High and mid latitude and near subsolar point ionospheric and thermospheric responses to the solar flares and geomagnetic storms during low solar activity periods of 2017 and 2020

The paper observes the super-imposed effects of intense and moderate solar flares and Coronal Mass Ejection (CME) and High Speed Solar Wind (HSSW) driven geomagnetic storm events on the ionosphere and thermosphere at mid and high latitudes during low solar activity periods. The observations are conducted over a fixed longitude (∼117°W geographic) during May 27–31, 2017 (duration with intense geomagnetic storm without any significant solar flare event), September 3–6, 2017 (duration with solar flare events), September 7–16, 2017 (duration with intense to moderate solar flares as well as geomagnetic storms) and November 28–30, 2020 (duration with a moderate solar flare event with no geomagnetic storm in association). It is found that the effects were the highest during May 27–31, 2017 among all of these events. From the observations of super-imposed effects of the geophysical events, it was found that the effects of an X-class solar flare on September 10–12, 2017 on mid-latitude ionization were suppressed by the Disturbed Dynamo Electric Field (DDEF) from high latitudes during the recovery phase of an intense CME driven geomagnetic storm. The weak effects were also explained by the position of origination of the flare at the Sun. Correlations were observed between the variations in O/N2, neutral wind velocities and the mid and high latitude Total Electron Content (TEC) during these periods. Possible explanation is given for those few cases (for example, September 14, 2017) when the variations in O/N2 mismatched with the local TEC especially in the mid-latitudes. The effects of the solar flare event on November 28–30, 2020 which were short-lived have also been also observed at locations near the subsolar point from low latitudes in the southern hemisphere.

Sur, Dibyendu; Ray, Sarbani; Paul, Ashik;

Published by: Advances in Space Research      Published on: jul

YEAR: 2022     DOI: 10.1016/j.asr.2022.04.024

CME driven storms; HSSW driven storms; Joule heating; O/N ratio; Plasmaspheric contributions; Solar flare

Investigation of the negative ionospheric response of the 8 September 2017 geomagnetic storm over the European sector

In this study, we investigate the negative ionospheric response over the European sector during two storms that took place on 8 September 2017, primarily, by exploiting observations over ten European locations. The spatial and temporal variations of TEC, foF2 and hmF2 ionospheric characteristics are examined with the aim to explain the physical mechanisms underlying the strong negative ionospheric response. We detected very sharp electron density (in terms of foF2 and TEC) decrease during the main phases of the two storms and we attributed this phenomenon to the large displacement of the Midlatitude Ionospheric Trough (MIT). Our study also revealed that the two storms show different features caused by different processes. In addition, Large Scale Traveling Ionospheric Disturbances (LSTIDs) were observed during both storms, followed by enhanced Spread F conditions over Digisonde stations. The regional dependence of ionospheric storm effects was demonstrated, as the behavior of ionospheric effects over the northern part of Europe differed from that over the southern part.

Oikonomou, Christina; Haralambous, Haris; Paul, Ashik; Ray, Sarbany; Alfonsi, Lucilla; Cesaroni, Claudio; Sur, Dibyendu;

Published by: Advances in Space Research      Published on: aug

YEAR: 2022     DOI: 10.1016/j.asr.2022.05.035

Large-scale traveling ionospheric disturbances; Mid-latitude ionospheric trough; September 2017 geomagnetic storm; Swarm satellite

Statistics of GPS TEC at the northern EIA crest region of the Indian subcontinent during the solar cycle 24 (2013-2018): comparison with IRI-2016 and IRI-2012 models

In this study the statistics of ionospheric total electron content (TEC), derived from a GSV4004B dual-frequency Global Positioning System (GPS) receiver at Agartala station (23.450°N, 91.150°E) located in northern equatorial ionization anomaly (EIA) crest region of the Indian subcontinent, is reported with a performance analysis of IRI-2016 and IRI-2012 models during the ascending, maxima, declining and minima phases (2013-2018) of the solar cycle 24. Variations of model total electron content, as obtained from the IRI-2016 and IRI-2012 for the three options of topside electron density namely NeQuick, IRI 2001 and IRI 01-corr, are compared with the observed total electron content during different periods of interest viz. monthly, seasonal, annual and the correlations with solar activity parameters viz. sunspot number (SSN), 10.7 cm solar radio flux (F10.7), solar EUV flux, are also investigated. All the three options of IRI-2016 and IRI-2012 models show an earlier occurrence of diurnal maximum total electron content, as compared to the observed diurnal maximum GPS total electron content, throughout all the months during the complete period of observation. As the solar activity decreases (from 2015 to 2018), the model starts underestimating GPS total electron content, which becomes significantly high during the very low solar activity period of 2017-18 for all the months. IRI-2016 model underestimates the GPS total electron content before the hours of diurnal maximum and overestimates after the hours of diurnal maximum in the years from 2013-2018. IRI-2012 model underestimates the GPS total electron content before the hours of diurnal maximum and overestimates after the hours of diurnal maximum in the years from 2013-17 but overestimate during the whole day in the year of 2018. Overestimation by IRI-2012 is much more than that by IRI-2016 in the year of 2018. Predictions given by IRI-2016 are better than that given by IRI-2012 for our region. The seasonal mean maximum total electron content values are highest during the spring equinox months and lowest during the winter months except the year of 2014 and 2013. The correlation analysis, between the GPS total electron content and solar indices, show that the correlation coefficient is higher for the solar EUV flux, as compared to the sunspot number (SSN) and 10.7 cm solar radio flux (F10.7).

Patari, Arup; Paul, Bapan; Guha, Anirban;

Published by: Astrophysics and Space Science      Published on: may

YEAR: 2021     DOI: 10.1007/s10509-021-03950-6

EIA; EUV flux; F10.7; GPS TEC; IRI-2012 TEC; IRI-2016 TEC; SSN

Impact of CME and HSSW driven geomagnetic storms on thermosphere and ionosphere as observed from mid-latitudes

The present paper reports magnetospheric-thermospheric-ionospheric interactions, observed during geomagnetically disturbed periods in 2015–2016 from mid-latitude stations located in the US-Pacific longitudes (\textasciitilde120°W geographic). These interactions have been analyzed for a series of Coronal Mass Ejection (CME) and High Speed Solar Wind (HSSW) driven geomagnetic storms during the moderate solar activity periods. The geomagnetically disturbed periods under consideration in this paper have an interesting feature of the occurrences of one or more HSSW events following an intense CME driven intense geomagnetic storm. Correlations were observed between the solar and geomagnetic parameters, hemispherically integrated Joule heating, changes in O/N2 ratio, corresponding changes in neutral wind velocities and mid-latitude Vertical Total Electron Content (VTEC) in most of the cases. Prolonged effects of neutral wind driven equatorward plasma transport process were noticed during the period of the summer solstice (June 23–26, 2015) which was correlated with the hemispherically integrated Joule heating and ionospheric conductivities. The effects of storm onset were observed during March 17–18, 2015. The influences of the ‘super-fountain effect’ in terms of Prompt Penetration Electric Field (PPEF) were seen during the main phases of the geomagnetic storms from these mid-latitude stations. This is correlated with the strength of Equatorial Electrojet (EEJ).

Sur, Dibyendu; Ray, Sarbani; Paul, Ashik;

Published by: Advances in Space Research      Published on: aug

YEAR: 2021     DOI: 10.1016/j.asr.2021.03.027

CME and HSSW storms; Joule heating; Meridional and zonal wind; O/N ratio; Plasma transport; VTEC

Multi-wavelength coordinated observations of ionospheric irregularity structures from an anomaly crest location during unusual solar minimum of the 24th cycle

The present paper reports coordinated ionospheric irregularity measurements at optical as well as GPS wavelengths. Optical measurements were obtained from Tiny Ionospheric Photometer (TIP) sensors installed onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. GPS radio signals were obtained from a dual frequency GPS receiver operational at Calcutta (22.58\textdegreeN, 88.38\textdegreeE geographic; geomagnetic dip: 32.96\textdegree; 13.00\textdegreeN, 161.63\textdegreeE geomagnetic) under the SCIntillation Network Decision Aid (SCINDA) program. Calcutta is located near the northern crest of Equatorial Ionization Anomaly (EIA) in the Indian longitude sector. The observations were conducted during the unusually low and prolonged solar minima period of 2008\textendash2010. During this period, four cases of post-sunset GPS scintillation were observed from Calcutta. Among those cases, simultaneous fluctuations in GPS Carrier-to-Noise ratios (C/N_o) and measured radiances from TIP over a common ionospheric volume were observed only on February 2, 2008 and September 25, 2008. Fluctuations observed in measured radiances (maximum 0.95 Rayleigh) from TIP due to ionospheric irregularities were found to correspond well with C/N₀ fluctuations on the GPS links observed from Calcutta, such effects being noted even during late evening hours of 21:00\textendash22:00 LT from locations around 40\textdegree magnetic dip. These measurements indicate the existence of electron density irregularities of scale sizes varying over several decades from 135.6\ nm to 300\textendash400\ m well beyond the northern crest of the EIA in the Indian longitude sector during late evening hours even in the unusually low solar activity conditions.

Paul, Ashik; Sur, Dibyendu; Haralambous, Haris;

Published by: Advances in Space Research      Published on: 03/2020

YEAR: 2020     DOI: 10.1016/j.asr.2019.11.035

GPS radio measurements; ionospheric irregularities; Northern crest of EIA; Optical measurements; solar minimum; TIP

Effects of CME and CIR induced geomagnetic storms on low-latitude ionization over Indian longitudes in terms of neutral dynamics

Chakraborty, Sumanjit; Ray, Sarbani; Sur, Dibyendu; Datta, Abhirup; Paul, Ashik;

Published by: Advances in Space Research      Published on:

YEAR: 2020     DOI:

I. Ionospheric Response to the Second Strongest Geomagnetic Storm of the Solar Cycle 24: First Results from the Arabian Peninsula

Dayanandan, Baiju; Paul, Bapan; Galav, Praveen;

Published by:       Published on:

YEAR: 2020     DOI:

Study of the low and mid-latitude ionospheric response to the geomagnetic storm of 20th December 2015

Paul, Bapan; Gordiyenko, Galina; Galav, Praveen;

Published by: Astrophysics and Space Science      Published on:

YEAR: 2020     DOI:

Response of Equatorial Ionization in Indian Longitudes to HSSW Driven Geomagnetic Storm

Sur, Dibyendu; Firdaus, Jasmine; Paul, Trisha; Dutta, Raktima; Bhattacharyya, Chaitali;

Published by:       Published on:

YEAR: 2020     DOI:

Conjugate hemispheric response of earth\textquoterights ionosphere due to geomagnetic storms occurred during two equinox periods

The ionospheric response of two geomagnetic storms of 2016 occurred during spring equinox (5-8 March, 2016) and autumn equinox (12-15 October, 2016) is investigated using the total electron content (TEC) data derived from Global Positioning System (GPS) receivers located in the equatorial ionization anomaly (EIA) crest regions at northern hemisphere (Tripura University, Agartala, India) and southern hemisphere (Karratha, Australia). While in southern EIA station ionospheric responses for the two storms are found to be symmetric but in northern EIA station the responses are completely asymmetric. The observations are explained by the contribution of storm-time prompt penetration electric fields (PPEFs), disturb dynamo electric fields (DDEFs), disturbed meridional (equatorward) winds as well as the neutral compositional changes over low latitudes.

Patari, Arup; De, Barin; Guha, Anirban; Paul, Bapan;

Published by: Journal of Physics: Conference Series      Published on: 10/2019

YEAR: 2019     DOI: 10.1088/1742-6596/1330/1/012004

Effects of CME and CIR induced geomagnetic storms on low-latitude ionization over Indian longitudes in terms of neutral dynamics

This paper presents the response of the ionosphere during the intense geomagnetic storms of October 12\textendash20, 2016 and May 26\textendash31, 2017 which occurred during the declining phase of the solar cycle 24. Total Electron Content (TEC) from GPS measured at Indore, Calcutta and Siliguri having geomagnetic dips varying from 32.23\textdegreeN, 32\textdegreeN and 39.49\textdegreeN respectively and at the International GNSS Service (IGS) stations at Lucknow (beyond anomaly crest), Hyderabad (between geomagnetic equator and northern crest of EIA) and Bangalore (near magnetic equator) in the Indian longitude zone have been used for the storms. Prominent peaks in diurnal maximum in excess of 20\textendash45 TECU over the quiet time values were observed during the October 2016 storm at Lucknow, Indore, Hyderabad, Bangalore and 10\textendash20 TECU for the May 2017 storm at Siliguri, Indore, Calcutta and Hyderabad. The GUVI images onboard TIMED spacecraft that measures the thermospheric O/N₂ ratio, showed high values (O/N₂ ratio of about 0.7) on October 16 when positive storm effects were observed compared to the other days during the storm period. The observed features have been explained in terms of the O/N₂ ratio increase in the equatorial thermosphere, CIR-induced High Speed Solar Wind (HSSW) event for the October 2016 storm. The TEC enhancement has also been explained in terms of the Auroral Electrojet (AE), neutral wind values obtained from the Horizontal Wind Model (HWM14) and equatorial electrojet strength from magnetometer data for both October 2016 and May 2017 storms. These results are one of the first to be reported from the Indian longitude sector on influence of CME- and CIR-driven geomagnetic storms on TEC during the declining phase of solar cycle 24.

Chakraborty, S.; Ray, S.; Sur, D.; Datta, A.; Paul, A.;

Published by: Advances in Space Research      Published on: 10/2019

YEAR: 2019     DOI: 10.1016/j.asr.2019.09.047

Response of the Earth\textquoterights equatorial ionosphere during the severe G4-class geomagnetic storm of 8 ^th September 2017

Equatorial and low latitude ionospheric response of the 8^th September 2017 severe G4-class geomagnetic storm is investigated using the total electron content (TEC) data from a longitudinal chain of global positioning system (GPS) receivers over Asian, African and American sectors. During the main phase, a positive storm effect is observed over Asian sector, a complete negative storm effect over African sector and both are observed over American sector. A sharp increase in peak TEC is observed over the complete longitudinal chain during the recovery phase. The results show the decisive contribution of prompt penetration electric fields (PPEFs) and disturbance dynamo electric fields (DDEFs), storm time disturbed meridional (equatorward) wind as well as the neutral compositional changes over equatorial and low latitudes in the observed ionospheric storm effects.

Paul, Bapan; Patari, Arup; De, Barin; Guha, Anirban;

Published by: Journal of Physics: Conference Series      Published on: 10/2019

YEAR: 2019     DOI: 10.1088/1742-6596/1330/1/012005

Response of the Earth’s equatorial ionosphere during the severe G4-class geomagnetic storm of 8th September 2017

Paul, Bapan; Patari, Arup; De, Barin; Guha, Anirban;

Published by:       Published on:

YEAR: 2019     DOI:

Conjugate hemispheric response of earth’s ionosphere due to geomagnetic storms occurred during two equinox periods

Patari, Arup; De, Barin; Guha, Anirban; Paul, Bapan;

Published by:       Published on:

YEAR: 2019     DOI:

Observations of storm-time thermospheric O/N2 ratio and TEC in the northern hemisphere during intense geomagnetic storms of 2015-2017

It has already been established that during the main phase and recovery phase of any geomagnetic storm, thermospheric O/N2 column density ratio decreases in the high latitudes

Sur, Dibyendu; Ray, Sarbani; Paul, Ashik;

Published by:       Published on:

YEAR: 2019     DOI:

Latitudinal variation of F-region ionospheric response during three strongest geomagnetic storms of 2015

The latitudinal ionospheric response of the three strongest geomagnetic storms of 2015 of the current solar cycle 24 during 16\textendash19 March 2015, 21\textendash24 June 2015 and 19\textendash22 December 2015 is investigated using the total electron content data derived from a latitudinal chain of Global Positioning System (GPS) receivers extending from 70\textdegreeN to 70\textdegreeS. The storm time perturbations of the ionosphere during main and recovery phase is presented by the GPS derived vertical total electron content (VTEC) data which is further supported by ionospheric F region critical frequency (foF2) and F region peak height (hmF2) data. We observed symmetrical hemispheric response of the ionosphere during the strongest 17th March (St. Patrick\textquoterights Day) storm whereas asymmetrical hemispheric response of the ionosphere during 22nd June and 20th December storm over the Asian-Australian sector. The observations are explained by the combined transport of background inter-hemispheric seasonal wind and storm time disturbed meridional wind and by the global thermospheric compositional variation [O/N₂] data.

Paul, Bapan; De, Barin; Guha, Anirban;

Published by: Acta Geodaetica et Geophysica      Published on: 12/2018

YEAR: 2018     DOI: 10.1007/s40328-018-0221-4

Latitudinal features of Total Electron Content over the African and European longitude sector following the St. Patrick’s day storm of 2015

Paul, A; Kascheyev, A; Rodriguez-Bouza, M; PATHAK, K; Ferreira, AA; Shetti, D; Yao, JN;

Published by: Advances in Space Research      Published on:

YEAR: 2018     DOI:

Total electron content responses to HILDCAAs and geomagnetic storms over South America

Total electron content (TEC) is extensively used to monitor the ionospheric behavior under geomagnetically quiet and disturbed conditions. This subject is of greatest importance for space weather applications. Under disturbed conditions the two main sources of electric fields, which are responsible for changes in the plasma drifts and for current perturbations, are the short-lived prompt penetration electric fields (PPEFs) and the longer-lasting ionospheric disturbance dynamo (DD) electric fields. Both mechanisms modulate the TEC around the globe and the equatorial ionization anomaly (EIA) at low latitudes. In this work we computed vertical absolute TEC over the low latitude of South America. The analysis was performed considering HILDCAA (high-intensity, long-duration, continuous auroral electrojet (AE) activity) events and geomagnetic storms. The characteristics of storm-time TEC and HILDCAA-associated TEC will be presented and discussed. For both case studies presented in this work (March and August\ 2013) the HILDCAA event follows a geomagnetic storm, and then a global scenario of geomagnetic disturbances will be discussed. Solar wind parameters, geomagnetic indices, O / N₂ ratios retrieved by GUVI instrument onboard the TIMED satellite and TEC observations will be analyzed and discussed. Data from the RBMC/IBGE (Brazil) and IGS GNSS networks were used to calculate TEC over South America. We show that a HILDCAA event may generate larger TEC differences compared to the TEC observed during the main phase of the precedent geomagnetic storm; thus, a HILDCAA event may be more effective for ionospheric response in comparison to moderate geomagnetic storms, considering the seasonal conditions. During the August HILDCAA event, TEC enhancements from \~ 25 to 80 \% (compared to quiet time) were observed. These enhancements are much higher than the quiet-time variability observed in the ionosphere. We show that ionosphere is quite sensitive to solar wind forcing and considering the events studied here, this was the most important source of ionospheric responses. Furthermore, the most important source of TEC changes were the long-lasting PPEFs observed on August\ 2013, during the HILDCAA event. The importance of this study relies on the peculiarity of the region analyzed characterized by high declination angle and ionospheric gradients which are responsible for creating a complex response during disturbed periods.

Negreti, Patricia; de Paula, Eurico; Candido, Claudia;

Published by: Annales Geophysicae      Published on: 06/2017

YEAR: 2017     DOI: 10.5194/angeo-35-1309-2017

Analysis of High-Latitude Ionospheric Processes During the Nov 2015 HSS and CME-Induced Geomagnetic Storm: A Multi-Instrument Observational Approach

Durgonics, Tibor; Komjathy, Attila; Verkhoglyadova, Olga; Hoeg, Per; Paul, Ashik;

Published by:       Published on:

YEAR: 2016     DOI:

Characteristics of post-midnight L-band scintillation in the transition region from the equatorial to mid-latitudes over the Indian longitude sector using COSMIC, C/NOFS and GPS measurements

Occurrence of L band scintillations around midnight and postmidnight hours have not been well studied and reported from the higher equatorial latitudes in the transition region from the equatorial to midlatitudes over the Indian longitude sector. The present paper reports cases of postmidnight L band scintillation observations by COSMIC during March 2014 over the Indian longitude sector. GPS\ S₄measurements from the International Global Navigation Satellite Systems Service station at Lucknow (26.91\textdegreeN, 80.96\textdegreeE geographic; magnetic dip: 39.75\textdegreeN) corroborate occurrence of postmidnight scintillations. The\ F\ region vertical upward velocities around the magnetic equator during evening hours have been used to understand the possibility of impact of irregularities generated over the magnetic equator at latitudes north of 30\textdegreeN. Postmidnight L band scintillations at latitudes greater than 30\textdegreeN without corresponding premidnight scintillations present interesting scientific scenario and give rise to suggestions of (1) any coupling mechanism between the equatorial and midlatitudes through which irregularities seeded in the midlatitudes may affect transionospheric satellite links at low latitudes or (2) irregularity generation at midlatitudes not connected with equatorial instabilities. Long-term analysis of\ S₄\ at L band measured by COSMIC over the Indian longitudes during March 2007\textendash2014 exhibits a well-defined longitude swath around 75\textendash83\textdegreeE of reduced (0.2 \< S₄ \< 0.4) or no scintillations which may be attributed to the longitudinal variability of scintillation occurrence following the global four-cell pattern of ionospheric activity.

Paul, A.; Haralambous, H.; Oikonomou, C.;

Published by: Radio Science      Published on: 12/2015

YEAR: 2015     DOI: 10.1002/2015RS005807

postmidnight L band scintillation over Indian longitude sector

Characteristics of postmidnight L band scintillation in the transition region from the equatorial to midlatitudes over the Indian longitude sector using COSMIC, C/NOFS, and GPS measurements

Paul, A; Haralambous, H; Oikonomou, C;

Published by: Radio Science      Published on:

YEAR: 2015     DOI:

Effects of transionospheric signal decorrelation on Global Navigation Satellite Systems (GNSS) performance studied from irregularity dynamics around the northern crest of the EIA

Transionospheric satellite navigation links operate primarily at L band and are frequently subject to severe degradation of performances arising out of ionospheric irregularities. Various characteristic features of equatorial ionospheric irregularity bubbles like the drift velocity, characteristic velocity, decorrelation time, and decorrelation distance can be determined using spaced aerial measurements at VHF. These parameters measured at VHF from a station Calcutta situated near the northern crest of the Equatorial Ionization Anomaly (EIA) in the geophysically sensitive Indian longitude sector have been correlated with L band scintillation indices and GPS position accuracy parameters for identifying possible proxies to L band scintillations. Good correspondences have been observed between decorrelation times and distances at VHF with GPS S₄ and Position Dilution of Precision during periods of GPS scintillations (S₄ \> 0.3) for February\textendashApril 2011, August\textendashOctober 2011, and February\textendashApril 2012. A functional relation has been developed between irregularity drift velocity measured at VHF and S₄ at L band during February\textendashApril 2011, and validation of measured S₄ and predicted values performed during August\textendashOctober 2011 and February\textendashApril 2012. Significant improvement in L band scintillation prediction and consequent navigational accuracy will result using such relations derived from VHF irregularity measurements which are much simpler and inexpensive.

Das, T.; Roy, B.; Paul, A.;

Published by: Radio Science      Published on: 10/2014

YEAR: 2014     DOI: 10.1002/rds.v49.1010.1002/2014RS005406

GNSS position determination accuracy under adverse ionospheric conditions; GUVI; irregularity dynamics at VHF

GPS L1-Frequency Observations of Equatorial Scintillations and Irregularity Zonal Velocities

In this work, the climatology of ionospheric scintillations at global positioning system (GPS) L-band frequency and the zonal drift velocities of scintillation-producing irregularities were depicted for the equatorial observatory of S\~ao Luis (2.33\textdegreeS; 44.21\textdegreeW; dip latitude 1.3\textdegreeS), Brazil. This is the first time that the hourly, monthly, and seasonal variations of scintillations and irregularity zonal drifts at S\~ao Luis were characterized during periods of different solar activity levels (from December 1998 to February 2007). The percentage occurrence of scintillations at different sectors of the sky was also investigated, and the results revealed that the scintillations are more probable to be observed in the west sector of the sky above S\~ao Luis, whereas the north\textendashsouth asymmetries are possibly related to asymmetries in the plasma density distribution at off-equatorial latitudes. The scintillations on GPS signals occurred more frequently around solar maximum years, but it is also clear from the results of a strong variability in the scintillation activity in the years with moderate solar flux during the descending phase of the solar cycle. The equatorial scintillations occur predominantly during pre-midnight hours with a broad maximum near the December solstice months. In general, weak level of scintillations (S ₄ index between 0.2 and 0.4) dominated at all seasons; however, during the winter months around solar maximum years (although the scintillation occurrence is extremely low), stronger levels of scintillations (S ₄\ \>\ 0.6) may occur at comparable rate with the weak scintillations. The irregularity zonal velocities, as estimated from the GPS spaced-receiver technique, presented a different scenario for the two seasons analyzed; during the equinoxes, the magnitude of the zonal velocities appeared not to change with the solar activity, whereas during the December solstice months, the larger magnitudes were observed around solar maximum years. Other relevant aspects of the observations are highlighted and discussed.

Muella, Marcio; de Paula, Eurico; Jonah, Olusegun;

Published by: Surveys in Geophysics      Published on: 08/2014

YEAR: 2014     DOI: 10.1007/s10712-013-9252-0

GPS; Ionospheric drifts; ionospheric irregularities; Ionospheric scintillation

Scintillation-producing Fresnel-scale irregularities associated with the regions of steepest TEC gradients adjacent to the equatorial ionization anomaly

Muella, M.; Kherani, E.; de Paula, E.; Cerruti, A.; Kintner, P.; Kantor, I.; Mitchell, C.; Batista, I.; Abdu, M.;

Published by: Journal of Geophysical Research      Published on: Jan-01-2010

YEAR: 2010     DOI: 10.1029/2009JA014788

Gravity wave initiation of equatorial spread F/plasma bubble irregularities based on observational data from the SpreadFEx campaign

The data from ground based experiments conducted during the 2005 SpreadFEx campaign in Brazil are used, with the help of theoretical model calculations, to investigate the precursor conditions, and especially, the role of gravity waves, in the instability initiation leading to equatorial spread F development. Data from a digisonde and a 30 MHz coherent back-scatter radar operated at an equatorial site, Sao Luis (dip angle: 2.7\textdegree) and from a digisonde operated at another equatorial site (dip angle: -11.5\textdegree) are analyzed during selected days representative of differing precursor conditions of the evening prereversal vertical drift, F layer bottom-side density gradients and density perturbations due to gravity waves. It is found that radar irregularity plumes indicative of topside bubbles, can be generated for precursor vertical drift velocities exceeding 30 m/s even when the precursor GW induced density oscillations are marginally detectable by the digisonde. For drift velocities <=20 m/s the presence of precursor gravity waves of detectable intensity is found to be a necessary condition for spread F instability initiation. Theoretical model calculations show that the zonal polarization electric field in an instability development, even as judged from its linear growth phase, can be significantly enhanced under the action of perturbation winds from gravity waves. Comparison of the observational results with the theoretical model calculations provides evidence for gravity wave seeding of equatorial spread F.

Abdu, M.; Kherani, Alam; Batista, I.; de Paula, E.; Fritts, D.; Sobral, J.;

Published by: Annales Geophysicae      Published on: Jan-01-2009

YEAR: 2009     DOI: 10.5194/angeo-27-2607-2009

Overview and summary of the Spread F Experiment (SpreadFEx)

We provide here an overview of, and a summary of results arising from, an extensive experimental campaign (the Spread F Experiment, or SpreadFEx) performed from September to November 2005, with primary measurements in Brazil. The motivation was to define the potential role of neutral atmosphere dynamics, specifically gravity wave motions propagating upward from the lower atmosphere, in seeding Rayleigh-Taylor instability (RTI) and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12, and the GUVI instrument aboard the TIMED satellite.\ 

Initial results of our SpreadFEx analyses are described separately by Fritts et al. (2009). Further analyses of these data provide additional evidence of 1) gravity wave (GW) activity near the mesopause apparently linked to deep convection predominantly to the west of our measurement sites, 2) small-scale GWs largely confined to lower altitudes, 3) larger-scale GWs apparently penetrating to much higher altitudes, 4) substantial GW amplitudes implied by digisonde electron densities, and 5) apparent influences of these perturbations in the lower F-region on the formation of equatorial spread F, RTI, and plasma bubbles extending to much higher altitudes. Other efforts with SpreadFEx data have also yielded 6) the occurrence, locations, and scales of deep convection, 7) the spatial and temporal evolutions of plasma bubbles, 8) 2-D (height-resolved) structures in electron density fluctuations and equatorial spread F at lower altitudes and plasma bubbles above, and 9) the occurrence of substantial tidal perturbations to the large-scale wind and temperature fields extending to bottomside F-layer and higher altitudes. Collectively, our various SpreadFEx analyses suggest direct links between deep tropical convection and large GW perturbations at large spatial scales at the bottomside F-layer and their likely contributions to the excitation of RTI and plasma bubbles extending to much higher altitudes.

Fritts, D.; Abdu, M.; Batista, B.; Batista, I.; Batista, P.; Buriti, R.; Clemesha, B.; Dautermann, T.; de Paula, E.; Fechine, B.; Fejer, B.; Gobbi, D.; Haase, J.; Kamalabadi, F.; Kherani, E.; Laughman, B.; Lima, P.; Liu, H.-L.; Medeiros, A.; Pautet, P.-D.; Riggin, D.; Rodrigues, F.; Sabbas, F.; Sobral, J.; Stamus, P.; Takahashi, H.; Taylor, M.; Vadas, S.; Vargas, F.; Wrasse, C.;

Published by: Annales Geophysicae      Published on: Jan-01-2009

YEAR: 2009     DOI: 10.5194/angeo-27-2141-2009

Simultaneous observation of ionospheric plasma bubbles and mesospheric gravity waves during the SpreadFEx Campaign

Takahashi, H.; Taylor, M.; Pautet, P.-D.; Medeiros, A.; Gobbi, D.; Wrasse, C.; Fechine, J.; Abdu, M.; Batista, I.; Paula, E.; Sobral, J.; Arruda, D.; Vadas, S.; Sabbas, F.; Fritts, D.;

Published by: Annales Geophysicae      Published on: Jan-01-2009

YEAR: 2009     DOI: 10.5194/angeo-27-1477-2009

The Spread F Experiment (SpreadFEx): Program overview and first results

Fritts, D.; Abdu, M.; Batista, B.; Batista, I.; Batista, P.; Buriti, R.; Clemesha, B.; Dautermann, T.; de Paula, E.; Fechine, B.; Fejer, B.; Gobbi, D.; Haase, J.; Kamalabadi, F.; Kherani, E.; Laughman, B.; Lima, J.; Liu, H.-L.; Medeiros, A.; Pautet, P.-D.; Riggin, D.; Rodrigues, F.; Sabbas, Sao; Sobral, J.; Stamus, P.; Takahasi, H.; Taylor, M.; Vadas, S.; Vargas, F.; Wrasse, C.;

Published by: Earth Planets Space      Published on:

YEAR: 2009     DOI:

Disturbed time observations of the temporal dependence and dynamics of TEC, scintillation, and ionospheric irregularity zonal drifts

Muella, Marcio; de Paula, Eurico; Kintner, Paul; Kantor, Ivan; Cerruti, Alessandro; Mitchell, Cathryn; Crowley, Geoff; Smorigo, Paulo; Batista, Inez;

Published by: 37th COSPAR Scientific Assembly      Published on:

YEAR: 2008     DOI:

Coherent backscatter radar imaging in Brazil: large-scale waves in the bottomside F-region at the onset of equatorial spread F

Rodrigues, FS; Hysell, DL; de Paula, ER;

Published by:       Published on:

YEAR: 2008     DOI:

Simultaneous observation of ionospheric plasma bubble and mesospheric gravity wave activities during CAWSES 2005 SpreadFEx Campaign

During the SpreadFEx campaign from September 22 to November 8, 2005, two airglow CCD imagers, located at near Brasilia (14.8S, 47.6W, Mag. 10S) and at Cariri (7.4S, 36.5W, Mag. 9S) were operated simultaneously and measured the equatorial ionospheric bubble structures and their time evolution by monitoring the OI 6300 emission. From the 10 nights of coincident data, we observed that on some nights the bubbles was formed at the west of Cariri, but not seen from the Brasilia site. This suggests that the bubble formation and development started near the Cariri observation site. Identification of a longitudinal zone where the SpF is seeding is very important in order to find the mechanism of formation. The present paper will discuss SpF seeding mechanisms and possible contribution of the mesospheric gravity wave activity.

Takahashi*, H.; Pautet, P.-D.; Fechine, J.; Abdu, M.; Batista, I.; Paula, E.; Sobral, J.H.A.; Gobbi, D.; Arruda, D.; Batista, P.; Sabba, F.; Taylor, M.; Medeiros, A.; Buriti, R.; Wrasse, C.; Fritts, D.;

Published by:       Published on:

YEAR: 2007     DOI: 10.1190/sbgf2007-404