scholarly journals Seasonal dependence of the "forecast parameter" based on the EIA characteristics for the prediction of Equatorial Spread F (ESF)

2008 ◽  
Vol 26 (7) ◽  
pp. 1751-1757 ◽  
Author(s):  
S. V. Thampi ◽  
S. Ravindran ◽  
T. K. Pant ◽  
C. V. Devasia ◽  
R. Sridharan
Keyword(s):  
Seasonal Variability ◽  
Seasonal Pattern ◽  
Onset Time ◽  
Critical Value ◽  
Latitudinal Gradients ◽  
Electron Content ◽  
Total Electron ◽  
Equatorial Spread F ◽  
Spread F ◽  
Definite Role

Abstract. In an earlier study, Thampi et al. (2006) have shown that the strength and asymmetry of Equatorial Ionization Anomaly (EIA), obtained well ahead of the onset time of Equatorial Spread F (ESF) have a definite role on the subsequent ESF activity, and a new "forecast parameter" has been identified for the prediction of ESF. This paper presents the observations of EIA strength and asymmetry from the Indian longitudes during the period from August 2005–March 2007. These observations are made using the line of sight Total Electron Content (TEC) measured by a ground-based beacon receiver located at Trivandrum (8.5° N, 77° E, 0.5° N dip lat) in India. It is seen that the seasonal variability of EIA strength and asymmetry are manifested in the latitudinal gradients obtained using the relative TEC measurements. As a consequence, the "forecast parameter" also displays a definite seasonal pattern. The seasonal variability of the EIA strength and asymmetry, and the "forecast parameter" are discussed in the present paper and a critical value for has been identified for each month/season. The likely "skill factor" of the new parameter is assessed using the data for a total of 122 days, and it is seen that when the estimated value of the "forecast parameter" exceeds the critical value, the ESF is seen to occur on more than 95% of cases.

scholarly journals LONGITUDINAL AND DAY-TO-DAY VARIATIONS OF EQUATORIAL SPREAD F OCCURRENCE FROM OBSERVATIONS OVER SOUTH AMERICA

2017 ◽  
Vol 35 (1) ◽  
Author(s):  
Ricardo Yvan de La Cruz Cueva ◽  
Cesar E. Valladares ◽  
Eurico Rodrigues de Paula ◽  
Mangalathayil Ali Abdu ◽  
Igo Paulino ◽  
...  
Keyword(s):  
South America ◽  
Periodic Structures ◽  
Detection Algorithm ◽  
Electron Content ◽  
Total Electron ◽  
Equatorial Spread F ◽  
Bubble Detection ◽  
December Solstice ◽  
Spread F ◽  
Occurrence Pattern

ABSTRACT. In this work we studied the longitudinal and day-to-day variability of equatorial spread F occurrence over South America. Digisonde from the equatorial stations of São Luís and Jicamarca, and Total Electron Content (TEC) data from several GPS receivers were used to analyse the ionospheric conditions conductive to ionospheric plasma irregularity generation during the solar minimum months of September 2009 to January 2010. To support this analysis an Automatic-Bubble- Detection-Algorithm was used to detect abrupt decreases that plasma bubbles introduce in the TEC values. The bubble occurrence pattern over SA observed in this work maximizes on September-October (equinox) in the west and November-January (December solstice) in the east-longitudes. However, on a day-to-day basis bubble signatures are also detected all over SA during this period. Besides being observed during days with pronounced prereversal enhancement (PRE), as expected, the TEC depletions were also observed during days without PRE, during equinox at Jicamarca and December solstice at São Luís. This unexpected occurrence of TEC depletions (TECds) suggests that seeding mechanisms, like periodic structures are present and modify the onset conditions of bubble-events. In this report are shown evidences of wave-like structures previous to bubble development. Keywords: day-to-day variation, equatorial spread F, aeronomy. RESUMO. Neste trabalho estuda-se a variabilidade longitudinal e dia-a-dia da ocorrência do spread F equatorial sobre América do Sul. Digissondas das estações equatoriais de São Luís e Jicamarca, e dados de Conteúdo Eletrônico Total (TEC) de vários receptores GPS foram usados para analisar as condições ionosféricas para a geração de irregularidades de plasma ionosférico durante os meses de mínimo solar de Setembro 2009 a Janeiro 2010. Para dar suporte a esta análise um Algoritmo de Detecção Automática de Bolhas foi usado para detectar decréscimos abruptos nos valores de TEC. O padrão de ocorrência de bolhas sobre SA observado neste trabalho são Setembro-Outubro (equinócio) no leste e Novembro-Janeiro (solstício de Dezembro) nas longitudes leste. Entretanto, na observação dia-a-dia as assinaturas de bolhas são também detectadas sobre toda SA neste período. Além de ter sido observado durante dias com pronunciado pré-reversal enhancement (PRE), como esperado, as depleções TEC foram também observadas durante dias sem PRE, durante equinócio em Jicamarca e solstício de Dezembro em São Luís. Esta ocorrência inesperada de depleções TEC (TECds) sugere que mecanismos geradores, como estruturas períodicas estão presentes e modificam as condições de início de eventos-bolhas. Neste trabalho são apresentados resultados mostrando evidências de estruturas tipo onda prévio ao desenvolvimento de uma bolha. Palavras-chave: variabilidade dia a dia, spread F equatorial, aeronomia.

scholarly journals Investigation of Low Latitude Spread-F Triggered by Nighttime Medium-Scale Traveling Ionospheric Disturbance

2021 ◽  
Vol 13 (5) ◽  
pp. 945
Author(s):  
Zhongxin Deng ◽  
Rui Wang ◽  
Yi Liu ◽  
Tong Xu ◽  
Zhuangkai Wang ◽  
...  
Keyword(s):  
Ionospheric Disturbance ◽  
Phase Speed ◽  
Morphological Processing ◽  
Wave Number ◽  
Occurrence Rate ◽  
Electron Content ◽  
Low Latitude ◽  
Total Electron ◽  
Medium Scale ◽  
Spread F

In the current study, we investigated the mechanism of medium-scale traveling ionospheric disturbance (MSTID) triggering spread-F in the low latitude ionosphere using ionosonde observation and Global Navigation Satellite System-Total Electron Content (GNSS-TEC) measurement. We use a series of morphological processing techniques applied to ionograms to retrieve the O-wave traces automatically. The maximum entropy method (MEM) was also utilized to obtain the propagation parameters of MSTID. Although it is widely acknowledged that MSTID is normally accompanied by polarization electric fields which can trigger Rayleigh–Taylor (RT) instability and consequently excite spread-F, our statistical analysis of 13 months of MSTID and spread-F occurrence showed that there is an inverse seasonal occurrence rate between MSTID and spread-F. Thus, we assert that only MSTID with certain properties can trigger spread-F occurrence. We also note that the MSTID at night has a high possibility to trigger spread-F. We assume that this tendency is consistent with the fact that the polarization electric field caused by MSTID is generally the main source of post-midnight F-layer instability. Moreover, after thorough investigation over the azimuth, phase speed, main frequency, and wave number over the South America region, we found that the spread-F has a tendency to be triggered by nighttime MSTID, which is generally characterized by larger ΔTEC amplitudes.

scholarly journals The role of the F-region vertical drift on the onset time of the equatorial spread F over Ilorin, Nigeria

2019 ◽  
Vol 128 (5) ◽  
Author(s):  
O A Oladipo ◽  
J O Adeniyi ◽  
I A Adimula ◽  
A O Olawepo ◽  
A Olowookere ◽  
...  
Keyword(s):  
Onset Time ◽  
Equatorial Spread F ◽  
F Region ◽  
Vertical Drift ◽  
Spread F

scholarly journals Evaluation of Seasonal Variability of First-order Ionospheric Delay Correction at L5 and S1 Frequencies Using Dual-frequency Navic System

2021 ◽  
Author(s):  
Sharat chandra Bhardwaj ◽  
Anurag Vidyarthi ◽  
Bhajan Singh Jassal ◽  
Ashish kumar Shukla
Keyword(s):  
Seasonal Variability ◽  
Ionospheric Delay ◽  
Electron Content ◽  
Dual Frequency ◽  
Satellite Constellations ◽  
Total Electron ◽  
First Order ◽  
Seasonal Characteristics ◽  
Geosynchronous Satellites ◽  
Delay Correction

Abstract For the precise positioning application it is important to determine and eliminate the positioning error introduced by various sources such as the ionosphere. To develop a standalone precise navigation system, India has launched the seven satellite constellations of NavIC (Navigation with Indian Constellation) system to provide precision positioning over India and surrounded landmass. Since the ionospheric delay depends on the frequency of the satellite signal and NavIC systems work at different frequencies (L5 and S1) than GPS systems (L1 and L2), it is not possible to use the GPS data-driven study for NavIC based location calculations directly. Thus there is a need for a specialized ionospheric study for NavIC systems. In addition, the ionospheric delay is directly proportional to Slant Total Electron Content (STEC) which is dependent upon diurnal and seasonal solar activity. To achieve accurate positioning facilities, there is also a need for evaluation for seasonal variability of ionospheric delay correction for NavIC receivers. This paper deals with the STEC estimation; its smoothing, and removal of instrumental biases from STEC. The determined true STEC has been used to determine first-order ionospheric delay at L5 and S1 frequencies. The delay at S1 has been found less (2 to 7m) as compared to L5 (10 to 30m). Furthermore, the seasonal variability of ionospheric delay has been analyzed using about 19 months of data (from June 2017 to December 2018) and found that the ionospheric delay follows unique seasonal characteristics which can be utilized for delay modeling. It has been also observed that the geostationary satellites of the NavIC system are more appropriate than geosynchronous satellites for ionospheric related studies.

scholarly journals Status of CAS global ionospheric maps after the maximum of solar cycle 24

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Zishen Li ◽  
Ningbo Wang ◽  
Ang Liu ◽  
Yunbin Yuan ◽  
Liang Wang ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Single Layer ◽  
Latitudinal Gradients ◽  
Electron Content ◽  
International Gnss Service ◽  
Total Electron ◽  
Solar Cycle 24 ◽  
Cycle 24 ◽  
Global Ionospheric Maps

AbstractAs a new Ionosphere Associate Analysis Center (IAAC) of the International GNSS Service (IGS), Chinese Academy of Sciences (CAS) started the routine computation of the real-time, rapid, and final Global Ionospheric Maps (GIMs) in 2015. The method for the generation of CAS rapid and final GIMs and recent updates are presented in the paper. The quality of CAS post-processed GIMs is assessed during 2015–2018 after the maximum of solar cycle 24. To perform an independent and fair assessment, Jason-2/3 Vertical Total Electron Contents (VTEC) are first used as the references over the ocean. GPS differential Slant TECs (dSTEC) generated from 55 Multi-GNSS Experimental (MGEX) stations of the IGS are also employed, which provides a complementing way to evaluate the ability of electron content models to reproduce the spatial and temporal gradients in the ionosphere. During the test period, Jet Propulsion Laboratory (JPL) GIMs present significantly positive deviations compared to the Jason VTEC and GPS dSTEC. Technical University of Catalonia (UPC) rapid GIM UQRG exhibits the best performance in both Jason VTEC and GPS dSTEC analysis. The CAS GIMs show comparable performance with the results of the first four IAACs of the IGS. As expected, the poor performance of all GIMs is in equatorial regions and the high latitudes of the southern hemisphere. The consideration of generating multi-layer or three-dimensional ionospheric maps is emphasized to mitigate the inadequacy of ionospheric single-layer assumption in the presence of pronounced latitudinal gradients. The use of ionospheric observations from the new GNSS constellations and other space- or ground-based observation techniques is also suggested in the generation of future GIMs, given the sparse GPS/GLONASS stations in the southern hemisphere.

scholarly journals A comparative study of GPS ionospheric scintillations and ionogram spread F over Sanya

2015 ◽  
Vol 33 (11) ◽  
pp. 1421-1430 ◽  
Author(s):  
Y. Zhang ◽  
W. Wan ◽  
G. Li ◽  
L. Liu ◽  
L. Hu ◽  
...  
Keyword(s):  
Comparative Study ◽  
Temporal Variations ◽  
Electron Content ◽  
Total Electron ◽  
Gps Scintillation ◽  
June Solstice ◽  
Spread F ◽  
Ionospheric Scintillations ◽  
The Difference ◽  
Sporadic E

Abstract. We analyze the data recorded during December 2011–November 2012 by a digital ionosonde and a GPS (Global Positioning System) scintillation and (total electron content) TEC receiver collocated at Sanya (109.6° E, 18.3° N; dip lat. 12.8° N), a low-latitude station in the Chinese longitude sector, to carry out a comparative study of ionospheric scintillations and spread F. A good consistency between the temporal variations of GPS scintillation (represented by the S4 index) and of ionogram spread F (represented by the QF index) is found in the pre-midnight period during equinox. However in the post-midnight period during equinox and in the period from post-sunset to pre-sunrise during June solstice, moderate spread F is seen without concurrent GPS scintillation. The possible cause responsible for the difference between post-midnight GPS scintillation and spread F during equinox could be due to the decaying of 400 m scale irregularities associated with equatorial spread F. Regarding the irregularities producing moderate QF and low S4 indices during June solstice, we suggest that the frequently observed sporadic E (Es) layer and the medium-scale traveling ionospheric disturbances (MSTIDs) over Sanya could play important roles in triggering the June solstitial spread-F events.

scholarly journals Observations in equatorial anomaly region of total electron content enhancements and depletions

2005 ◽  
Vol 23 (7) ◽  
pp. 2449-2456 ◽  
Author(s):  
N. Dashora ◽  
R. Pandey
Keyword(s):  
Total Electron Content ◽  
Scintillation Index ◽  
Electron Content ◽  
Equatorial Anomaly ◽  
Low Latitude ◽  
Total Electron ◽  
First Results ◽  
Spread F ◽  
New Feature ◽  
Low Latitude Ionosphere

Abstract. A GSV 4004A GPS receiver has been operational near the crest of the equatorial anomaly at Udaipur, India for some time now. The receiver provides the line-of-sight total electron content (TEC), the phase and amplitude scintillation index, σφ and S4, respectively. This paper presents the first results on the nighttime TEC depletions associated with the equatorial spread F in the Indian zone. The TEC depletions are found to be very well correlated with the increased S4 index. A new feature of low-latitude TEC is also reported, concerning the observation of isolated and localized TEC enhancements in the nighttime low-latitude ionosphere. The TEC enhancements are not correlated with the S4 index. The TEC enhancements have also been observed along with the TEC depletions. The TEC enhancements have been interpreted as the manifestation of the plasma density enhancements reported by Le et al. (2003). Keywords. Ionosphere (Equatorial ionosphere; Ionospheric irregularities)

scholarly journals Small-Scale Ionospheric Irregularities of Auroral Origin at Mid-latitudes during the 22 June 2015 Magnetic Storm and Their Effect on GPS Positioning

2020 ◽  
Vol 12 (10) ◽  
pp. 1579 ◽  
Author(s):  
Yury Yasyukevich ◽  
Roman Vasilyev ◽  
Konstantin Ratovsky ◽  
Artem Setov ◽  
Maria Globa ◽  
...  
Keyword(s):  
Signal Amplitude ◽  
Auroral Oval ◽  
Ionospheric Irregularities ◽  
Small Scale ◽  
Electron Content ◽  
Quiet Time ◽  
Data Set ◽  
Total Electron ◽  
Cygnus A ◽  
Spread F

Small-scale ionospheric irregularities affect navigation and radio telecommunications. We studied small-scale irregularities observed during the 22 June 2015 geomagnetic storm and used experimental facilities at the Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS) located near Irkutsk, Russia (~52°N, 104°E). The facilities used were the DPS-4 ionosonde (spread-F width), receivers of the Irkutsk Incoherent Scatter Radar (Cygnus A signal amplitude scintillations), and GPS/GLONASS receivers (amplitude and phase scintillations), while 150 MHz Cygnus A signal recording provides a unique data set on ionosphere small-scale structure. We observed increased spread-F, Cygnus A signal amplitude scintillations, and GPS phase scintillations near 20 UT on 22 June 2015 at mid-latitudes. GPS/GLONASS amplitude scintillations were at a quiet time level. By using global total electron content (TEC) maps, we conclude that small-scale irregularities are most likely caused by the auroral oval expansion. In the small-scale irregularity region, we recorded an increase in the precise point positioning (PPP) error. Even at mid-latitudes, the mean PPP error is at least five times that of the quiet level and reaches 0.5 m.

scholarly journals Characteristics of equatorial plasma bubbles observed by TEC map based on ground-based GNSS receivers over South America

2018 ◽  
Vol 36 (1) ◽  
pp. 91-100 ◽  
Author(s):  
Diego Barros ◽  
Hisao Takahashi ◽  
Cristiano M. Wrasse ◽  
Cosme Alexandre O. B. Figueiredo
Keyword(s):  
Drift Velocity ◽  
Latitudinal Gradient ◽  
Onset Time ◽  
Electron Content ◽  
Total Electron ◽  
Plasma Bubbles ◽  
Equatorial Plasma Bubbles ◽  
Gnss Receivers ◽  
The Difference ◽  
Field Lines

Abstract. A ground-based network of GNSS receivers has been used to monitor equatorial plasma bubbles (EPBs) by mapping the total electron content (TEC map). The large coverage of the TEC map allowed us to monitor several EPBs simultaneously and get characteristics of the dynamics, extension and longitudinal distributions of the EPBs from the onset time until their disappearance. These characteristics were obtained by using TEC map analysis and the keogram technique. TEC map databases analyzed were for the period between November 2012 and January 2016. The zonal drift velocities of the EPBs showed a clear latitudinal gradient varying from 123 m s−1 at the Equator to 65 m s−1 for 35∘ S latitude. Consequently, observed EPBs are inclined against the geomagnetic field lines. Both zonal drift velocity and the inclination of the EPBs were compared to the thermospheric neutral wind, which showed good agreement. Moreover, the large two-dimensional coverage of TEC maps allowed us to study periodic EPBs with a wide longitudinal distance. The averaged values observed for the inter-bubble distances also presented a clear latitudinal gradient varying from 920 km at the Equator to 640 km at 30∘ S. The latitudinal gradient in the inter-bubble distances seems to be related to the difference in the zonal drift velocity of the EPB from the Equator to middle latitudes and to the difference in the westward movement of the terminator. On several occasions, the distances reached more than 2000 km. Inter-bubble distances greater than 1000 km have not been reported in the literature. Keywords. Ionosphere (equatorial ionosphere; ionospheric irregularities) – meteorology and atmospheric dynamics (thermospheric dynamics)

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