Artykuły w czasopismach: „Low latitude station”

1

Kumar, Edwin A., i Sushil Kumar. "Geomagnetic Storm Effect on F2-Region Ionosphere during 2012 at Low- and Mid-Latitude-Latitude Stations in the Southern Hemisphere". Atmosphere 13, nr 3 (15.03.2022): 480. http://dx.doi.org/10.3390/atmos13030480.

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The ionospheric effects of six intense geomagnetic storms with Dst index ≤ −100 nT that occurred in 2012 were studied at a low-latitude station, Darwin (Geomagnetic coordinates, 21.96° S, 202.84° E), a low-mid-latitude station, Townsville (28.95° S, 220.72° E), and a mid-latitude station, Canberra (45.65° S, 226.30° E), in the Australian Region, by analyzing the storm–time variations in the critical frequency of the F2-region (foF2). Out of six storms, a storm of 23–24 April did not produce any ionospheric effect. The storms of 30 September–3 October (minimum Dst = −122 nT) and 7–10 October (minimum Dst = −109 nT) are presented as case studies and the same analysis was done for the other four storms. The storm of 30 September–3 October, during its main phase, produced a positive ionospheric storm at all three stations with a maximum percentage increase in foF2 (∆foF2%) of 45.3% at Canberra whereas during the recovery phase it produced a negative ionospheric storm at all three stations with a maximum ∆foF2% of −63.5% at Canberra associated with a decrease in virtual height of the F-layer (h’F). The storm of 7–10 October produced a strong long-duration negative ionospheric storm associated with an increase in h’F during its recovery phase at all three stations with a maximum ∆foF2% of −65.1% at Townsville. The negative ionospheric storms with comparatively longer duration were more pronounced in comparison to positive storms and occurred only during the recovery phase of storms. The storm main phase showed positive ionospheric storms for two storms (14–15 July and 30 September–3 October) and other three storms did not produce any ionospheric storm at the low-latitude station indicating prompt penetrating electric fields (PPEFs) associated with these storms did not propagate to the low latitude. The positive ionospheric storms during the main phase are accounted to PPEFs affecting ionospheric equatorial E × B drifts and traveling ionospheric disturbances due to joule heating at the high latitudes. The ionospheric effects during the recovery phase are accounted to the disturbance dynamo electric fields and overshielding electric field affecting E × B drifts and the storm-induced circulation from high latitudes toward low latitudes leading to changes in the natural gas composition [O/N2] ratio.

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Wang, Ren, Jingxiang Gao, Yifei Yao, Peng Sun i Moufeng Wan. "Assessment of the Algorithm for Single Frequency Precise Point Positioning at Different Latitudes and with Distinct Magnetic Storm Conditions". Applied Sciences 10, nr 7 (26.03.2020): 2268. http://dx.doi.org/10.3390/app10072268.

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This paper analyzes the convergence time and the root mean square (RMS) error of single frequency (SF) precise point positioning (PPP) in the ionospheric-constrained (TIC1) and troposphere- and ionospheric-constrained (TIC2) conditions, when the stations are at a low latitude, mid-latitude, and high latitude area during the period of a magnetic storm (MS) and a non-magnetic storm (NMS). In this paper, 375 IGS (international global navigation satellite system (GNSS) service) stations were selected from all over the world for 30 days in September 2017. The 24 hour daily observations were split for each station into 8 data sets of 3 hours each, so that a total of 90,000 tests were carried out. After statistical analysis, it was concluded that: during the MS period, the percentage of TIC2 shortened compared to the TIC1 convergence time, and it was by at least 3.9%, 3.0%, and 9.3% when the station was at global, low latitude, and high latitude areas, respectively. According to the statistical analysis, during the NMS period the convergence time was shortened about at least 12.8%, 11.0%, and 30.0% with respect to the stations in the MS period at global, low, and high latitude areas, respectively. If the station was located in the mid-latitude region, the convergence time was not shortened in some modes. The ionospheric activity in the mid-latitude region was less than that in the low-latitude region, while there were more stations in the mid-latitude region, and the precision of the global ionospheric maps (GIMs) and zenith tropospheric delay (ZTD) products were also slightly higher. Overall, TIC1 and TIC2 have a greater impact on convergence time, but have less impact on positioning accuracy, and only have a greater impact in different environments during the MS and NMS periods.

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Owolabi, Temitope Pascal, Emmanuel Ariyibi, Olatunbosun Lilian i Ayomide O. Olabode. "Diurnal and Seasonal Variations of Equivalent Slab thickness over Low and Mid Latitude Regions". JOURNAL OF ADVANCES IN PHYSICS 16, nr 1 (5.05.2019): 64–78. http://dx.doi.org/10.24297/jap.v16i1.8229.

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The equivalent slab-thickness is very important in the study of the complex dynamics of the ionosphere as a result of its ability to determine the skewness of the ionospheric electron density profile. This study involves the day to day and monthly variations of . Ionosonde (FoF2) and Total electron content (TEC) data at the low latitude station of Sao Luis (Glat 2.60° S, Glong 315.80° E and Mlat 6.05° N and Mlong 28.40° E), Brazil and mid latitude station of Chilton (Glat 51.50° N, Glong 359.40° E and Mlat 53.35° N and Mlong 84.34° E), United Kingdom from January 2013 to December 2015 were used in the study of . For Sao Luis station, the diurnal pattern for the different days are characterized by day time (08:00 – 16:00 UT) high values and nighttime (20:00 – 04:00 UT) low values; however, Chilton shows signatures, such as day time low values and nighttime high values. Also, the daytime values (~600 km) of for the low latitude station (Sao Luis) is more than double the mid latitude station (Chilton) maximum value (~235 km) over the years considered. The monthly variation of also indicate a seasonal variation with highest daytime values (400 km) during winter months and lowest (below 300 km) during summer months for the low latitude station (Sao Luis). However, the nighttime values are of the same order (about 200 km) for the low latitude station (Sao Luis). Also, highest daytime values (above 250 km) are observed during summer months and the nighttime values are below 200 km over the years for the mid latitude station (Chilton).

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Zhang, M. L., J. K. Shi, X. Wang i S. M. Radicella. "Ionospheric variability at low latitude station: Hainan, China". Advances in Space Research 34, nr 9 (2004): 1860–68. http://dx.doi.org/10.1016/j.asr.2004.04.005.

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Singh, Ashutosh K., K. K. Singh, S. B. Singh i A. K. Singh. "Multiflash whistlers in ELF-band observed at low latitude". Annales Geophysicae 29, nr 1 (10.01.2011): 91–96. http://dx.doi.org/10.5194/angeo-29-91-2011.

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Abstract. Multiflash whistler-like event in the ELF-band, observed during March 1998 at low latitude station Jammu, is reported. The most prominent feature of these events is the multiflash nature along with the decrease in frequency within a very short span of time resembling similar to terrestrial whistlers. The events have a significantly smaller time duration (0.5–3.5 s) than those reported earlier from high, mid and low latitudes and also display a diurnal maximum occurring around 09:30 h (IST). There have been similar reportings from other latitudes, but whistlers in the ELF-band with a multiflash nature along with a precursor emission have never been reported. Lightning seems to be the dominant source for the ELF whistlers reported here.

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6

Bertoni, F., Y. Sahai, W. L. C. Lima, P. R. Fagundes, V. G. Pillat, F. Becker-Guedes i J. R. Abalde. "IRI-2001 model predictions compared with ionospheric data observed at Brazilian low latitude stations". Annales Geophysicae 24, nr 8 (13.09.2006): 2191–200. http://dx.doi.org/10.5194/angeo-24-2191-2006.

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Abstract. In this work, the F-region critical frequency (foF2) and peak height (hmF2) measured by digital ionosondes at two Brazilian low-latitude stations, namely Palmas (10.17° S, 48.20° W, dip –10.80°) and São José dos Campos (23.20° S, 45.86° W, dip –38.41°), are compared with the IRI-2001 model predictions. The comparison at the latter station shows quite a reasonable agreement for both parameters. The former station exhibits a better agreement for hmF2 than for foF2. In general, the model generates good results, although some improvements are still necessary to implement in order to obtain better simulations for equatorial ionospheric regions.

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Lepidi, Stefania, Patrizia Francia, Lili Cafarella, Domenico Di Mauro i Martina Marzocchetti. "Determining the Polar Cusp Longitudinal Location from Pc5 Geomagnetic Field Measurements at a Pair of High Latitude Stations". Proceedings of the International Astronomical Union 13, S335 (lipiec 2017): 139–41. http://dx.doi.org/10.1017/s174392131701002x.

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AbstractWe use low frequency geomagnetic field measurements at two Antarctic stations to statistically investigate the longitudinal location of the polar cusp. The two stations are both located in the polar cap at a geomagnetic latitude close to the cusp latitude; they are separated by one hour in magnetic local time. At each station the Pc5 power maximizes when the station approaches the cusp, i.e. around magnetic local noon. The comparison between the Pc5 power at the two stations allows to determine the longitudinal location of the cusp. Our analysis is conducted considering separately different orientation of the interplanetary magnetic field. The results, which indicate longitudinal shifts of the polar cusp depending on the selected conditions, are discussed in relation to previous studies of the polar cusp location based on polar magnetospheric satellite data.

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Farah, Ashraf. "Single-Frequency Ionospheric-Delay Correction from BeiDou & GPS Systems for Northern Hemisphere". Artificial Satellites 54, nr 1 (1.03.2019): 1–15. http://dx.doi.org/10.2478/arsa-2019-0002.

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Abstract The range delay caused by the ionosphere layer is the major current source of error for GNSS users with single-frequency receivers. GNSS advice users to correct this type of error using ionospheric models whose coefficients are sent in their navigation messages. GPS-users use the Klobuchar model to correct this type of error. GPS navigation message contains the model’s eight coefficients which vary on the basis of seasonal ionospheric variations and average solar flux. The correction accuracy of Klobuchar model is about 50% (rms) of the ionospheric range delay. Beidou system calculates and broadcast 8 parameters of Klobuchar model based on continuous monitoring stations. BeiDou system updates the ionospheric coefficients every two hours. GPS-Klobuchar model uses completely different coefficients than BeiDou-Klobuchar model. This research demonstrates a comparison study between the Klobuchar model using the GPS broadcast coefficients and the same model using BeiDou-coefficients. The correction accuracy offered by the two models has been judged using the most accurate International GNSS Service-Global Ionospheric Maps (IGS-GIMs) for three different-latitude stations along northern hemisphere, one station in low-latitude region, the second station is in mid-latitude region and the third station is in high-latiude region to reflect models’ behaviour in different geographic regions. The study was applied over three different months of the year 2017 that each of them reflects a different activity state for the ionosphere layer. The study proves that BeiDou model is able to show the ionosphere’s day-to-day fluctuations while GPS model can’t. It can be concluded that GPS model offers better behaviour than BeiDou model in correcting range delay in low-latitude and high-latitude geographic regions under any activity state for the ionosphere. BeiDou model offers better correction accuracy than GPS model in mid-latitude under any activity state for the ionosphere.

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Villante, U., P. Francia i S. Lepidi. "Pc5 geomagnetic field fluctuations at discrete frequencies at a low latitude station". Annales Geophysicae 19, nr 3 (31.03.2001): 321–25. http://dx.doi.org/10.5194/angeo-19-321-2001.

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Abstract. A statistical analysis of the geomagnetic field fluctuations in the Pc5 frequency range (1–5 mHz) at a low latitude station (L = 1.6) provides further evidence for daytime power peaks at discrete frequencies. The power enhancements, which become more pronounced during high solar wind pressure conditions, may be interpreted in terms of ground signatures of magnetospheric cavity/waveguide compressional modes driven by solar wind pressure pulses. In this sense, the much clearer statistical evidence for afternoon events can be related to corotating structures mainly impinging the postnoon magnetopause. A comparison with results obtained for the same time intervals from previous investigations at higher latitudes and in the Earth’s magnetosphere confirms the global character of the observed modes.Key words. Magnetospheric physics (MHD waves and instabilities; solar wind-magnetospheric interactions)

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10

Olatunbosun, LG, A. O. Olabode i EA Ariyibi. "Variability of Equatorial Electrojet (EEJ) at EIA regions". Physics & Astronomy International Journal 6, nr 1 (25.01.2022): 1–4. http://dx.doi.org/10.15406/paij.2022.06.00241.

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The EEJ is a worldwide solar-driven wind that results in the solar quiet (Sq) current system in the E region of the earth’s ionosphere. The variability of some features such as EEJ, are very important in understanding the complex nature of the ionosphere, especially the low-latitude ionosphere. The magnetometer data from stations located near the equator and outside the edge of the electrojet strip for Africa and India stations were used to estimate and investigate the variability of EEJ in African and Indian Low-Latitudes. The stations are Addis Ababa, Ethiopia (geographic lat/long: 9.03oN/38.76oE) and at Mbour, Senegal for African region (geographic lat/long 14.392oN/343.042oE) and Hyderabad, India (geographic lat/long: 17.413oN/78.555oE) and Beijing Ming Tombs, China for Indian region (geographic lat/long: 40.3oN/116.2oE). The data in XYZ orientation was used to estimate the EEJ strength. The result shows that EEJ exhibits diurnal and seasonal variations and that its variability is stronger in African station than in Indian station, so also is the occurrence of counter electrojet (CEJ).

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11

Singh, Birbal. "Middle and High Latitude Whistlers Observed Simultaneously in a Low Latitude Station at Agra." Journal of geomagnetism and geoelectricity 49, nr 8 (1997): 995–1000. http://dx.doi.org/10.5636/jgg.49.995.

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Singh, R. P., U. P. Singh, Ashok Kumar Singh i D. P. Singh. "Daytime observations of chorus emissions at low latitude". Canadian Journal of Physics 72, nr 1-2 (1.01.1994): 73–79. http://dx.doi.org/10.1139/p94-012.

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Discrete very-low-frequency chorus emissions observed during the daytime at ground station Gulmarg (geomag. lat. 24°10′N) are reported. The generation of these emissions is explained in terms of transverse resonance interaction between whistler waves and counter-streaming energetic electrons. The theory is tested by evaluating different parameters.

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Singh, Krishna Kumar, Ravindra Pratap Patel, Balraj Kumar, Mohamad Altaf, Prince Ahmad Ganai, Abhay Kumar Singh, Ram Pal Singh i Lalmani. "Hisslers observed during daytime in a low latitude ground station". Acta Geophysica 57, nr 2 (4.02.2009): 536–47. http://dx.doi.org/10.2478/s11600-008-0078-y.

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Patel, R. P., A. K. Singh, S. Singh, R. Singh, K. Singh i R. P. Singh. "VLF Emissions observed at the low latitude Indian station Varanasi". Advances in Space Research 41, nr 10 (styczeń 2008): 1699–703. http://dx.doi.org/10.1016/j.asr.2007.05.014.

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Scidá, L. A., R. G. Ezquer, M. A. Cabrera i M. Mosert. "IRI 2001/90 TEC predictions over a low latitude station". Advances in Space Research 44, nr 6 (wrzesień 2009): 736–41. http://dx.doi.org/10.1016/j.asr.2009.04.028.

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Olatunbosun, LG, AO Olabode, AB Babinisi i EA Ariyibi. "HF Propagation during geomagnetic storms at a low latitude station". Physics & Astronomy International Journal 4, nr 1 (16.01.2020): 11–16. http://dx.doi.org/10.15406/paij.2020.04.00197.

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The variations in the ionosphere affect the radio wave propagation. These variations become more pronounced as a result of geomagnetic storms. The data from a Digitonide installed at Guam station (Lat. 13.62oN and Long. 144.86oE) during geomagnetic events was scaled for an ionogram, which shows the heights of different layers in the ionosphere at different frequencies. The ionogram was then analysed and interpreted. Results showed that virtual heights steadily increased as frequency increased. The splitting of waves into ordinary and extraordinary waves as they enter the ionosphere was an indication that waves divide on entering the ionosphere. The extraordinary was consistently higher than the ordinary wave. The highest frequency the ionosphere above the station could refract signal at 180o was 12.625 MHz. This is the frequency at which communication was to be made from one location to another location within the location of the station. Comparative results between the iongrams of disturbed and undisturbed ionosphere showed that geomagnetic storms lead to increased foF2, MUF values and NmF2. The results also revealed that the strength of the refracted signals were particularly good, strong enough to rebound from the earth and refract again.

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Nosé, M., M. Uyeshima, J. Kawai i H. Hase. "Ionospheric Alfvén resonator observed at low‐latitude ground station, Muroto". Journal of Geophysical Research: Space Physics 122, nr 7 (lipiec 2017): 7240–55. http://dx.doi.org/10.1002/2017ja024204.

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Barkhatov, N. A., S. E. Revunov, O. T. Cherney, Zh V. Smirnova i M. V. Mukhina. "Low-frequency oscillations while magnetic storms as a tool to determine the types of solar plasma flows". E3S Web of Conferences 220 (2020): 01090. http://dx.doi.org/10.1051/e3sconf/202022001090.

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Comparison of wavelet spectrum (skeletons) local maxima for disturbed components of solar plasma flow parameters and geomagnetic field disturbances recorded along the meridional station chain during geomagnetic storm intervals is performed in the range of magnetohydrodynamic (MHD) waves. An algorithm for quantitative evaluation of analyzed skeletons consistency has been developed. It has been used to demonstrate the possibility of the type of solar wind plasma flow elaboration on unique spectral signs of Solar wind speed disturbances, density and interplanetary magnetic field. It is shown that the energy spectrum of oscillations for these parameters reflects the internal structure of the corresponding plasma formation. The skeletons application to the analysis of the interplanetary space main parameters made it possible to estimate the magnetosphere reaction time in geomagnetic field horizontal component oscillations at different latitudes on the disturbance. As a result, the distributed magnetosphere reaction over latitude was determined in the form of geomagnetic field oscillations on the disturbed solar flow parameters. It is shown that the dynamics of the components of the solar wind parameters disturbance spectra corresponding to plasma flows manifest themselves in the MHD spectra of high-latitude stations magnetograms and can be used as a diagnostic tool.

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Pant, T. K., i R. Sridharan. "A case-study of the low-latitude thermosphere during geomagnetic storms and its new representation by improved MSIS model". Annales Geophysicae 16, nr 11 (30.11.1998): 1513–18. http://dx.doi.org/10.1007/s00585-998-1513-8.

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Abstract. The thermospheric temperatures from low and equatorial latitudes during geomagnetically disturbed periods are known to exhibit significant deviations from atmospheric model predictions. Also, the oscillatory features seen in the observations are not accounted for by the models. A simple relation has been established between the difference in the observed and model-predicted temperatures and the rate of change of Dst, the magnetic index representing the ring current variabilities. Using this relation, a correction term has been added to the latest MSIS-90 model algorithm and almost all the observed variations in neutral temperatures spectroscopically determined from Mt.Abu, a low-latitude station in India, are successfully reproduced for two moderate geomagnetic storms.Key words. Low-latitude thermosphere · MSIS model · Stormtime model predictions · FP spectroscopic temperatures

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Iluore, Kenneth, Jianyong Lu, Francisca Okeke i Kesyton Oyamenda Ozegin. "Performance of NeQuick-2 and IRI-Plas 2017 Models during Solar Maximum Years in 2013–2014 over Equatorial and Low Latitude Regions". Universe 8, nr 2 (13.02.2022): 125. http://dx.doi.org/10.3390/universe8020125.

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This paper carries out a comparative investigation of the Total Electron Content (TEC) values calculated by using the NeQuick-2 and IRI-Plas 2017 models. The investigation was carried out for the solar maximum year of 2013–2014 with data from eight GPS stations within the equatorial and low latitude regions. The results show that both models agree quite well with the observed TEC values obtained from GPS measurements in all the stations, although with some overestimations and underestimations observed during the daytime and nighttime hours. The NeQuick-2 model, in general, performed better in months, seasons, and in most of the stations when the IRI-Plas overestimates the GPS-TEC. However, it is interesting to know that with an increase in solar activity in some seasons, the quality of forecasting IRI-Plas can improve, whereas for the NeQuick-2 model, it decreases, but this is not true for all the seasons and all the stations. Factors causing the discrepancies in the IRI-Plas data model might be caused by the plasmaspheric part included in the IRI, and it is found to be maximum at the MBAR (34%) station, whereas that of the NeQuick-2 data model is found to be maximum at the ADIS (47.7%) station. There is a latitudinal dependence for both models in which the prediction error decreases with the increasing latitudes.

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Praveena, Kaitha, Prof Perumalla Naveen Kumar i Prof D. Krishna Reddy. "Analysis of Ionospheric Scintillations Measurement on NavIC Signals". International Journal of Engineering and Advanced Technology 12, nr 2 (30.12.2022): 132–35. http://dx.doi.org/10.35940/ijeat.b3950.1212222.

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Ionospheric scintillation is a rapid change in amplitude and phase of an electromagnetic signal in the ionospheric environment. Amplitude scintillations indicated by S4 index and phase scintillations by. Low latitude regions are prone to ionosphere scintillation. Since India is a low latitude region, ionospheric scintillations must be analysed. Indian NavIC or IRNSS planned and implemented by the Indian Space Research Organization (ISRO). In this paper S4 index is investigated for NavIC L5 (1.17645 GHz) and S1 (2.492028 GHz) signals (1B,1C,1D,1E,1F,1G). For the analysis Guntur station (Lat:16.44N, Lon:80.62E) and Hyderabad station (Lat:17°24’28.10″N, Lon: 78°31′4.22″E) IGS receiver data is considered. The S4 index is calculated using carrier to noise ratio of IRNSS L5 and S band signals. From the results it is observed that S4 index is more for L5 band signals compared to S band signals, as ionospheric scintillations are frequency dependent. Guntur station S4 average value is low for all (L5 and S) band satellite signals compared to Hyderabad station satellite signals. Over Indian region, it shows latitude-dependent scintillations.

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Pasricha, P. K., S. Aggarwal i B. M. Reddy. "Estimation of the hourly variability of f0F2at a low-latitude station". Radio Science 22, nr 1 (styczeń 1987): 125–32. http://dx.doi.org/10.1029/rs022i001p00125.

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Ahmad, Altaf, Lalmani i M. M. Ahmad. "Observations of discrete emissions at the low latitude ground station Gulmarg". Earth, Moon, and Planets 60, nr 3 (marzec 1993): 265–69. http://dx.doi.org/10.1007/bf00572523.

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Batista, I. S., M. A. Abdu, R. T. de Medeiros i E. R. de Paula. "Comparison between IRI predictions and digisonde measurements at low latitude station". Advances in Space Research 18, nr 6 (styczeń 1996): 49–52. http://dx.doi.org/10.1016/0273-1177(95)00899-3.

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Collaud Coen, Martine, Elisabeth Andrews, Diego Aliaga, Marcos Andrade, Hristo Angelov, Nicolas Bukowiecki, Marina Ealo i in. "Identification of topographic features influencing aerosol observations at high altitude stations". Atmospheric Chemistry and Physics 18, nr 16 (24.08.2018): 12289–313. http://dx.doi.org/10.5194/acp-18-12289-2018.

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Abstract. High altitude stations are often emphasized as free tropospheric measuring sites but they remain influenced by atmospheric boundary layer (ABL) air masses due to convective transport processes. The local and meso-scale topographical features around the station are involved in the convective boundary layer development and in the formation of thermally induced winds leading to ABL air lifting. The station altitude alone is not a sufficient parameter to characterize the ABL influence. In this study, a topography analysis is performed allowing calculation of a newly defined index called ABL-TopoIndex. The ABL-TopoIndex is constructed in order to correlate with the ABL influence at the high altitude stations and long-term aerosol time series are used to assess its validity. Topography data from the global digital elevation model GTopo30 were used to calculate five parameters for 43 high and 3 middle altitude stations situated on five continents. The geometric mean of these five parameters determines a topography based index called ABL-TopoIndex, which can be used to rank the high altitude stations as a function of the ABL influence. To construct the ABL-TopoIndex, we rely on the criteria that the ABL influence will be low if the station is one of the highest points in the mountainous massif, if there is a large altitude difference between the station and the valleys or high plains, if the slopes around the station are steep, and finally if the inverse drainage basin potentially reflecting the source area for thermally lifted pollutants to reach the site is small. All stations on volcanic islands exhibit a low ABL-TopoIndex, whereas stations in the Himalayas and the Tibetan Plateau have high ABL-TopoIndex values. Spearman's rank correlation between aerosol optical properties and number concentration from 28 stations and the ABL-TopoIndex, the altitude and the latitude are used to validate this topographical approach. Statistically significant (SS) correlations are found between the 5th and 50th percentiles of all aerosol parameters and the ABL-TopoIndex, whereas no SS correlation is found with the station altitude. The diurnal cycles of aerosol parameters seem to be best explained by the station latitude although a SS correlation is found between the amplitude of the diurnal cycles of the absorption coefficient and the ABL-TopoIndex.

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Idosa, C., B. Adhikari i K. Shogile. "Responses of Total Electron Content to Solar Flares over Low and Mid-Latitude Regions during Sun Halo Day". Journal of Nepal Physical Society 9, nr 1 (25.08.2023): 11–22. http://dx.doi.org/10.3126/jnphyssoc.v9i1.57543.

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The responses of total electron content (TEC) to solar flares over low- and mid-latitude regions during the sun halo days were investigated. The research is based on GPS data obtained from Bangalore (13.02117°N, 77.57038°E) on May 24, 2021; Cape Town (-33.918861°N, 18.423300°E) on October 26, 2020; and North Dakota (46.55756°N, -96.472300°E) on December 27, 2021, during the solar halo days. The results of this study demonstrate that the values of TEC increased at Bangalore and Cape Town stations during solar halo days as compared to other days. However, over the North Dakota station, TEC during the sun halo day was greater than that on the days before and after the halo day from around 19:00 UT to 23:59 UT hours. During the sun halo over Bangalore and Cape Town stations, positive relative changes in TEC prevail, suggesting that the action of the interplanetary electric field, the prompt penetration electric field, and the disturbance dynamo electric field lead to higher TEC values. However, during the sun halo over North Dakota station, negative relative changes in TEC prevail, which might be related to the consequence that low solar activity with no earth’s field disturbances (a positive Dst) leads to lower ionospheric TEC values. Stations that have greater relative changes in TEC have shown greater power spectrum and global wave spectrum energy. Cape Town has a greater relative change in TEC, a greater power spectrum, and a larger global wave spectrum than Bangalore and North Dakota stations. The values of TEC over three stations are different due to the latitudinal and longitudinal differences in addition to the universal time effects. Finally, solar flares have a major influence on ionosphere electrodynamics, and the upward drift velocity of ionospheres at the low latitude station is more strongly influenced by solar flares due to the effects of the ExB drifts, which induce TEC disturbances during the halo days over the suggested stations.

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Jain, S., S. K. Vijay, A. K. Gwal i Y. N. Huang. "Nighttime enhancements in ionospheric electron content: seasonal and solar cycle variation". Annales Geophysicae 13, nr 3 (31.03.1995): 256–61. http://dx.doi.org/10.1007/s00585-995-0256-z.

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Abstract. Various characteristics of anomalous nighttime enhancement in ionospheric electron content (IEC) at Lunping (14.08°N geomagnetic), a station near the crest of the equatorial anomaly, have been presented by considering the IEC data for the 21st solar cycle. Out of a total of 1053 enhancements, 354 occur in pre-midnight and 699 occur in post-midnight hours, which indicates an overall dominance of post-midnight events at Lunping. The occurrence is more frequent during summer, less during the equinox and least during winter months. All the characteristics of the enhancements have seasonal dependencies and they reach their maximum values during summer months. The occurrence of the pre-midnight events show positive and post-midnight events show negative correlation with solar activity. The results have been discussed and compared with those at low-latitude stations in India and Hawaii and at the mid-latitude station, Tokyo.

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Singh, D. K., Ashok K. Singh, R. P. Patel, R. P. Singh i A. K. Singh. "Two types of ELF hiss observed at Varanasi, India". Annales Geophysicae 17, nr 10 (31.10.1999): 1260–67. http://dx.doi.org/10.1007/s00585-999-1260-5.

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Abstract. The morphology of ELF hiss events observed at low-latitude ground station Varanasi (L = 1.07, geomagnetic latitude 14°55'N) are reported, which consist of two types: (1) events which propagated in ducted mode along the geomagnetic field line corresponding to observing station Varanasi and (2) events which propagated in ducted mode along higher L-values (L = 4–6), after reaching the lower edge of ionosphere excite the Earth-ionosphere wave guide and propagate towards equator to be received at Varanasi. To understand the generation mechanism of ELF hiss, incoherent Cerenkov radiated power from the low latitude and middle latitude plasmasphere are evaluated. Considering this estimated power as an input for wave amplification through wave-particle interaction, the growth rate and amplification factor is evaluated which is too small to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of ELF hiss.Key words. Ionosphere (equatorial ionosphere; ionosphere · magnetosphere interactions; wave · particle interactions)

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29

Feng, Jian, Yuqiang Zhang, Na Xu, Bo Chen, Tong Xu, Zhensen Wu, Zhongxin Deng i in. "Statistical Study of the Ionospheric Slab Thickness at Yakutsk High-Latitude Station". Remote Sensing 14, nr 21 (24.10.2022): 5309. http://dx.doi.org/10.3390/rs14215309.

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The ionospheric equivalent slab thickness (EST, also named τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. This paper presents a comprehensive statistical study of the ionospheric slab thickness at Yakutsk, located at the high latitude of East Asia, using the GPS-TEC and ionosonde NmF2 data for the years 2010–2017. The results show that the τ has different diurnal and seasonal variations in high- and low-solar-activity years, and the τ is greatest in the winter, followed by the equinox, and it is smallest in the summer in both high- and low-solar-activity years, except during the noontime of low-solar-activity years. Specifically, the τ in inter of high-solar-activity year shows an approximate single peak pattern with the peak around noon, while it displays a double-peak pattern with the pre-sunrise and sunset peaks in winter of the low-solar-activity years. Moreover, the τ in the summer and equinox have smaller diurnal variations, and there are peaks with different magnitudes during the sunrise and post-sunset periods. The mainly diurnal variation of τ in different seasons of high- and low-solar-activity years can be explained within the framework of relative variation of TEC and NmF2 during the corresponding period. By defining the disturbance index (DI), which can visually assess the relationship between instantaneous values and the median, we found that the geomagnetic storm would enhance the τ at Yakutsk. An example on 7 June 2013 is also presented to analyze the physical mechanism. It should be due to the intense particle precipitation and expanded plasma convection electric field during the storm at high-latitude Yakutsk station. The results would improve the current understanding of climatological and storm-time behavior of τ at high latitudes in East Asia.

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Sarma, M. S. S. R. K. N., C. Raghava Reddy i K. Niranjan. "HF Doppler radar observations of sporadic E at an Indian low latitude station, Visakhapatnam". Annales Geophysicae 27, nr 2 (2.02.2009): 537–45. http://dx.doi.org/10.5194/angeo-27-537-2009.

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Abstract. 5.5 MHz HF Doppler radar observations of Sporadic E over an Indian low latitude station, Visakhapatnam (17.7° N, 83.3° E and Dip 20°) with 10 s resolution showed quasi-periodic variations of the echo strength and Doppler velocity variations with periods of a few minutes to a few tens of minutes. The echo strength and Doppler velocity variations with time in different range bins of the ES echo showed variations which are some times similar and some times significantly different in successive range bins at intervals of 7.5 km. The ES echo occurs with the height of maximum echo strength in the range of 100 km to 120 km and some times at 130 km. The altitude variation of the average Doppler velocity is highly variable and the height of maximum echo strength is not the same as the height of maximum Doppler velocity. Observations of ES echoes at different times of the day are presented to bring out the differences between the day and night time ES echoes. The relationship between Radar and ES parameters derived from Ionograms is poorer than that of mid latitudes which is quite consistent with the expectations based on gradient drift instability.

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31

Villante, U., M. Vellante, P. Francia, M. De Lauretis, A. Meloni, P. Palangio, B. Zolesi i in. "ULF fluctuations of the geomagnetic field and ionospheric sounding measurements at low latitudes during the first CAWSES campaign". Annales Geophysicae 24, nr 5 (3.07.2006): 1455–68. http://dx.doi.org/10.5194/angeo-24-1455-2006.

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Abstract. We present an analysis of ULF geomagnetic field fluctuations at low latitudes during the first CAWSES campaign (29 March-3 April 2004). During the whole campaign, mainly in the prenoon sector, a moderate Pc3-4 pulsation activity is observed, clearly related to interplanetary upstream waves. On 3 April, in correspondence to the Earth's arrival of a coronal mass ejection, two SIs are observed whose waveforms are indicative of a contribution of the high-latitude ionospheric currents to the low-latitude ground field. During the following geomagnetic storm, low frequency (Pc5) waves are observed at discrete frequencies. Their correspondence with the same frequencies detected in the radial components of the interplanetary magnetic field and solar wind speed suggests that Alfvénic solar wind fluctuations may act as direct drivers of magnetospheric fluctuations. A cross-phase analysis, using different pairs of stations, is also presented for identifying field line resonant frequencies and monitoring changes in plasmaspheric mass density. Lastly, an analysis of ionospheric vertical soundings, measured at the Rome ionosonde station (41.8° N, 12.5° E), and vertical TEC measurements deduced from GPS signals within an European network shows the relation between the ULF resonances in the inner magnetosphere and thermal plasma density variations during geomagnetically quiet conditions, in contrast to various storm phases at the end of the CAWSES campaign.

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32

Dashora, N., S. Sharma, R. S. Dabas, S. Alex i R. Pandey. "Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone". Annales Geophysicae 27, nr 5 (4.05.2009): 1803–20. http://dx.doi.org/10.5194/angeo-27-1803-2009.

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Abstract. Results pertaining to the response of the equatorial and low latitude ionosphere to a major geomagnetic storm that occurred on 15 May 2005 are presented. These results are also the first from the Indian zone in terms of (i) GPS derived total electron content (TEC) variations following the storm (ii) Local low latitude electrodynamics response to penetration of high latitude convection electric field (iii) effect of storm induced traveling atmospheric disturbances (TAD's) on GPS-TEC in equatorial ionization anomaly (EIA) zone. Data set comprising of ionospheric TEC obtained from GPS measurements, ionograms from an EIA zone station, New Delhi (Geog. Lat. 28.42° N, Geog. Long. 77.21° E), ground based magnetometers in equatorial and low latitude stations and solar wind data obtained from Advanced Composition Explorer (ACE) has been used in the present study. GPS receivers located at Udaipur (Geog. Lat. 24.73° N, Geog. Long. 73.73° E) and Hyderabad (Geog. Lat. 17.33° N, Geog. Long. 78.47° E) have been used for wider spatial coverage in the Indian zone. Storm induced features in vertical TEC (VTEC) have been obtained comparing them with the mean VTEC of quiet days. Variations in solar wind parameters, as obtained from ACE and in the SYM-H index, indicate that the storm commenced on 15 May 2005 at 02:39 UT. The main phase of the storm commenced at 06:00 UT on 15 May with a sudden southward turning of the Z-component of interplanetary magnetic field (IMF-Bz) and subsequent decrease in SYM-H index. The dawn-to-dusk convection electric field of high latitude origin penetrated to low and equatorial latitudes simultaneously as corroborated by the magnetometer data from the Indian zone. Subsequent northward turning of the IMF-Bz, and the penetration of the dusk-to-dawn electric field over the dip equator is also discernible. Response of the low latitude ionosphere to this storm may be characterized in terms of (i) enhanced background level of VTEC as compared to the mean VTEC, (ii) peaks in VTEC and foF2 within two hours of prompt penetration of electric field and (iii) wave-like modulations in VTEC and sudden enhancement in hmF2 within 4–5 h in to the storm. These features have been explained in terms of the modified fountain effect, local low latitude electrodynamic response to penetration electric field and the TIDs, respectively. The study reveals a strong positive ionospheric storm in the Indian zone on 15 May 2005. Consequences of such major ionospheric storms on the systems that use satellite based navigation solutions in low latitude, are also discussed.

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33

Lepidi, S., L. Cafarella, P. Francia, A. Meloni, P. Palangio i J. J. Schott. "Low frequency geomagnetic field variations at Dome C (Antarctica)". Annales Geophysicae 21, nr 4 (30.04.2003): 923–32. http://dx.doi.org/10.5194/angeo-21-923-2003.

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Abstract. We conduct an analysis of the geomagnetic field variations recorded at the new Antarctic station Dome C, located very close to the geomagnetic pole, which has been operating for approximately one month during the 1999–2000 campaign. We also perform a comparison with simultaneous measurements at the Italian Antarctic station Terra Nova Bay, in order to investigate the spatial extension of the phenomena observed at very high latitude. Our results show that between the two stations the daily variation is similar and the fluctuations with f ~ 1 mHz are coherent, provided that in both cases the comparison is made between geographically oriented components, suggesting that ionospheric currents related to the geographic position, more than field-aligned currents, are responsible for the lowest frequency variations; conversely, higher frequency (Pc5) fluctuations are substantially decoupled between the two stations. We also found that at Dome C the fluctuation power in the 0.55–6.7 mHz frequency band is well related with the solar wind speed during the whole day and that at Terra Nova Bay the correlation is also high, except around local geomagnetic noon, when the station approaches the polar cusp. These results indicate that the solar wind speed control of the geomagnetic field fluctuation power is very strict in the polar cap and less important close to the polar cusp.Key words. Magnetospheric physics (MHD waves and instabilities; Polar cap phenomena; Solar wind-magnetosphere interactions)

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34

Rahim, Nurliyana Abdul. "L-Band Amplitude Scintillations During Solar Maximum at a Low Latitude Station". International Journal of Advanced Trends in Computer Science and Engineering 9, nr 1.4 (15.09.2020): 465–70. http://dx.doi.org/10.30534/ijatcse/2020/6691.42020.

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35

Singh, R. P., Lalmani i U. P. Singh. "Discrete emissions and whistler precursors recorded at low latitude ground station Gulmarg". Earth, Moon, and Planets 60, nr 3 (marzec 1993): 225–32. http://dx.doi.org/10.1007/bf00572520.

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36

Singh, Shubha, R. P. Patel, Krishna K. Singh, A. K. Singh i R. P. Singh. "Role of geomagnetic disturbance on whistler occurrence at a low latitude station". Planetary and Space Science 55, nr 10 (lipiec 2007): 1218–24. http://dx.doi.org/10.1016/j.pss.2007.02.001.

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37

Vellante, M., U. Villante, M. de Lauretis i P. Cerulli-Irelli. "An analysis of micropulsation events at a low-latitude station during 1985". Planetary and Space Science 37, nr 7 (lipiec 1989): 767–73. http://dx.doi.org/10.1016/0032-0633(89)90128-1.

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38

Singh, Ashutosh K., A. K. Singh, R. Singh, R. P. Singh, K. Adams i R. L. Dowden. "Subionospheric VLF perturbations observed at a low latitude station Varanasi (L=1.07)". Advances in Space Research 55, nr 2 (styczeń 2015): 576–85. http://dx.doi.org/10.1016/j.asr.2014.10.032.

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39

Wang, Guojun, Jiankui Shi i Xiao Wang. "Tidelike Periodicities of Ionospheric Sporadic E Observed at Low Latitude Hainan Station". Chinese Journal of Space Science 33, nr 5 (2013): 501. http://dx.doi.org/10.11728/cjss2013.05.501.

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40

Liu, Guoqi, Wengeng Huang, Hua Shen i Jiancun Gong. "Vertical TEC variations and model during low solar activity at a low latitude station, Xiamen". Advances in Space Research 49, nr 3 (luty 2012): 530–38. http://dx.doi.org/10.1016/j.asr.2011.10.024.

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41

Gu, Sheng-hong, Andrew Collier Cameron i Kang Min Kim. "Doppler imaging of the active star PW And". Proceedings of the International Astronomical Union 5, S264 (sierpień 2009): 90–92. http://dx.doi.org/10.1017/s1743921309992456.

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AbstractWe present spot activity of the K2V pre-main-sequence star PW And based on the high-resolution spectroscopic data obtained at Xinglong station and BOAO in 2005 November and December. Using the Least-Squares Deconvolution method, we have derived time series of composite profiles of PW And with high signal to noise ratio. These have been used to reconstruct its starspot pattern via the Doppler imaging method. The result shows that intermediate to high-latitude spots are the dominant features and weak low-latitude spots also appear. Comparing Doppler images from two data subsets, it can be found that almost no difference between two images exists except the small position evolution of weak low-latitude spots, which suggests that the intermediate to high-latitude spots have longer lifetimes than one month, and the low-latitude spots have shorter lifetimes.

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42

Patra, A. K., S. Sripathi, P. B. Rao i K. S. V. Subbarao. "Simultaneous VHF radar backscatter and ionosonde observations of low-latitude E region". Annales Geophysicae 23, nr 3 (30.03.2005): 773–79. http://dx.doi.org/10.5194/angeo-23-773-2005.

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Abstract. The first results of simultaneous observations made on the low-latitude field-aligned irregularities (FAI) using the MST radar located at Gadanki (13.5° N, 79.2° E, dip 12.5°) and the Es parameters using an ionosonde at a nearby station Sriharikota (13.7° N, 80.1° E, dip 12.6°) are presented. The observations show that while the height of the most intense radar echoes is below the virtual height of Es (h'Es) during daytime, it is found to be either below or above during nighttime. The strength of the FAI is better correlated with the top penetration frequency (ftEs) and the blanketing frequency (fbEs) during the night (r=0.4 in both cases) as compared to the day (r=0.35 and -0.04, respectively). Furthermore, the signal strength of FAI is reasonably correlated with (ftEs-fbEs) during daytime (r=0.59) while very poorly correlated during nighttime (r=0.18). While the radar observations in general appear to have characteristics close to that of mid-latitudes, the relationship of these with the Es parameters are poorer than that of mid-latitudes. The observations reported here, nevertheless, are quite consistent with the expectations based on the gradient drift instability mechanism.

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43

Wei, Lehui, Chunhua Jiang, Yaogai Hu, Ercha Aa, Wengeng Huang, Jing Liu, Guobin Yang i Zhengyu Zhao. "Ionosonde Observations of Spread F and Spread Es at Low and Middle Latitudes during the Recovery Phase of the 7–9 September 2017 Geomagnetic Storm". Remote Sensing 13, nr 5 (7.03.2021): 1010. http://dx.doi.org/10.3390/rs13051010.

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This study presents observations of nighttime spread F/ionospheric irregularities and spread Es at low and middle latitudes in the South East Asia longitude of China sectors during the recovery phase of the 7–9 September 2017 geomagnetic storm. In this study, multiple observations, including a chain of three ionosondes located about the longitude of 100°E, Swarm satellites, and Global Navigation Satellite System (GNSS) ROTI maps, were used to study the development process and evolution characteristics of the nighttime spread F/ionospheric irregularities at low and middle latitudes. Interestingly, spread F and intense spread Es were simultaneously observed by three ionosondes during the recovery phase. Moreover, associated ionospheric irregularities could be observed by Swarm satellites and ground-based GNSS ionospheric TEC. Nighttime spread F and spread Es at low and middle latitudes might be due to multiple off-vertical reflection echoes from the large-scale tilts in the bottom ionosphere. In addition, we found that the periods of the disturbance ionosphere are ~1 h at ZHY station, ~1.5 h at LSH station and ~1 h at PUR station, respectively. It suggested that the large-scale tilts in the bottom ionosphere might be produced by LSTIDs (Large scale Traveling Ionospheric Disturbances), which might be induced by the high-latitude energy inputs during the recovery phase of this storm. Furthermore, the associated ionospheric irregularities observed by satellites and ground-based GNSS receivers might be caused by the local electric field induced by LSTIDs.

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44

Dabas, R. S., R. M. Das, V. K. Vohra i C. V. Devasia. "Space weather impact on the equatorial and low latitude F-region ionosphere over India". Annales Geophysicae 24, nr 1 (7.03.2006): 97–105. http://dx.doi.org/10.5194/angeo-24-97-2006.

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Abstract. For a detailed study of the space weather impact on the equatorial and low latitude F-region, the ionospheric response features are analysed during the periods of three recent and most severe magnetic storm events of the present solar cycle which occurred in October and November 2003, and November 2004. The F-layer base height (h'F), peak height (hmF2) and critical frequency (foF2) data, from Trivandrum, an equatorial station and Delhi, a low latitude location, are examined during the three magnetic storm periods. The results of the analysis clearly shows that the height of the F-region (both h'F and hmF2), at the equator and low latitude, simultaneously increases by 200 to 300 km, in association with maximum negative excursion of Dst values around the midnight hours with a large depletion of ionization over the equator, which is followed by an ionization enhancement at low latitude during the recovery phase of the storm. At Delhi, fast variations up to 200 m/s are also observed in the F-layer vertical upward/downward velocity, calculated using Doppler shifts, associated with the maximum negative excursion of Dst. This shows that during magnetic disturbances, the equatorial ionization anomaly (EIA) expands to a much wider latitude than the normal fountain driven by the E/F-layer dynamo electric fields. It is also observed that during the main phase of the storm, at low latitude there is generally an enhancement of F-region ionization with an increase in h'F/hmF2 but in the equatorial region, the ionization collapses with a decrease in h'F/hmF2, especially after sunset hours. In addition, at the equator the normal pre-sunset hours' enhancement in h'F is considerably suppressed during storm periods. This might be due to changes in magnitude and direction of the zonal electric field affecting the upward E×B drift and hence the plasma distribution in the form of a decrease in electron density in the equatorial region and an increase in the low latitude region. In association with disturbance electric fields, the enhanced storm-induced equatorward meridional winds in the thermosphere can also further amplify the F-layer height rise at low latitudes during the post-midnight hours, as observed in two of the storm periods.

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45

Yi, Wen, Xianghui Xue, Iain M. Reid, Damian J. Murphy, Chris M. Hall, Masaki Tsutsumi, Baiqi Ning i in. "Climatology of the mesopause relative density using a global distribution of meteor radars". Atmospheric Chemistry and Physics 19, nr 11 (6.06.2019): 7567–81. http://dx.doi.org/10.5194/acp-19-7567-2019.

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Abstract. The existing distribution of meteor radars located from high- to low-latitude regions provides a favorable temporal and spatial coverage for investigating the climatology of the global mesopause density. In this study, we report the climatology of the mesopause relative density estimated using multiyear observations from nine meteor radars, namely, the Davis Station (68.6∘ S, 77.9∘ E), Svalbard (78.3∘ N, 16∘ E) and Tromsø (69.6∘ N, 19.2∘ E) meteor radars located at high latitudes; the Mohe (53.5∘ N, 122.3∘ E), Beijing (40.3∘ N, 116.2∘ E), Mengcheng (33.4∘ N, 116.6∘ E) and Wuhan (30.5∘ N, 114.6∘ E) meteor radars located in the midlatitudes; and the Kunming (25.6∘ N, 103.8∘ E) and Darwin (12.3∘ S, 130.8∘ E) meteor radars located at low latitudes. The daily mean relative density was estimated using ambipolar diffusion coefficients derived from the meteor radars and temperatures from the Microwave Limb Sounder (MLS) on board the Aura satellite. The seasonal variations in the Davis Station meteor radar relative densities in the southern polar mesopause are mainly dominated by an annual oscillation (AO). The mesopause relative densities observed by the Svalbard and Tromsø meteor radars at high latitudes and the Mohe and Beijing meteor radars at high midlatitudes in the Northern Hemisphere show mainly an AO and a relatively weak semiannual oscillation (SAO). The mesopause relative densities observed by the Mengcheng and Wuhan meteor radars at lower midlatitudes and the Kunming and Darwin meteor radars at low latitudes show mainly an AO. The SAO is evident in the Northern Hemisphere, especially at high latitudes, and its largest amplitude, which is detected at the Tromsø meteor radar, is comparable to the AO amplitudes. These observations indicate that the mesopause relative densities over the southern and northern high latitudes exhibit a clear seasonal asymmetry. The maxima of the yearly variations in the mesopause relative densities display a clear latitudinal variation across the spring equinox as the latitude decreases; these latitudinal variation characteristics may be related to latitudinal changes influenced by gravity wave forcing. In addition to an AO, the mesopause relative densities over low latitudes also clearly show an intraseasonal variation with a periodicity of 30–60 d.

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46

Jun, Chae-Woo, Khan-Huk Kim, Hyuck-Jin Kwon, Dong-Hun Lee, Ensang Lee, Young-Deuk Park i Junga Hwang. "Statistical Analysis of Low-latitude Pi2 Pulsations Observed at Bohyun Station in Korea". Journal of Astronomy and Space Sciences 30, nr 1 (15.03.2013): 25–32. http://dx.doi.org/10.5140/jass.2013.30.1.025.

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47

Bhardwaj, Shivangi, Parvaiz A. Khan, Azad A. Manssori, Rafi Ahmad i P. K. Purohit. "Variability of ionospheric TEC at low latitude station, Hyderabad during medium solar activity". Russian Journal of Earth Sciences 21, nr 2 (17.05.2021): 1–12. http://dx.doi.org/10.2205/2020es000749.

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48

Singh, Birbal, Raghuraj Singh i Rajvir Singh. "Whistler triplets, bands, and fine structures observed in a low latitude ground station". Geophysical Research Letters 24, nr 20 (15.10.1997): 2507–10. http://dx.doi.org/10.1029/97gl02574.

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49

Agrawal, Anita. "Analytical Study of Storm Effect on Nighttime Enhancement at Low Latitude Station Jicamarca". American Journal of Mechanics and Applications 7, nr 2 (2019): 15. http://dx.doi.org/10.11648/j.ajma.20190702.11.

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50

Singh, A. K., i K. Rönnmark. "Generation mechanism for VLF chorus emissions observed at a low-latitude ground station". Annales Geophysicae 22, nr 6 (14.06.2004): 2067–72. http://dx.doi.org/10.5194/angeo-22-2067-2004.

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Abstract. A detailed spectral analysis of VLF chorus emissions observed at the low-latitude ground station Gulmarg (geomag. lat., 24° 26' N, geomag. long., 147° 9' E, L=1.28) during the strong magnetic activity on 7-8 March 1986 have been carried out, which shows that each chorus element originates from the upper edge of the underlying hiss band. To explain various temporal and spectral features of these emissions, a possible generation mechanism has been presented based on the backward wave oscillator regime of the magnetospheric cyclotron maser. On the basis of this model, we have computed various chorus parameters as well as some magnetospheric parameters affecting the generation process. A comparison of the observed chorus characteristics with the proposed generation mechanism shows a good agreement.

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