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I S Batista - One of the best experts on this subject based on the ideXlab platform.
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incoherent scatter radar ionosonde and satellite measurements of equatorial f region vertical plasma drifts in the evening sector
1996Co-Authors: Bela G Fejer, Eurico De Paula, L Scherliess, I S BatistaAbstract:Studies of equatorial F region evening vertical plasma drifts using different measurement techniques have produced conflicting results. We examine the relationship of incoherent scatter radar and ionosonde drift observations over the Peruvian equatorial region, and AE-E satellite drifts for different geophysical conditions. Our data show that there is large day-to-day variability on the ratios of radar and ionosonde drifts, but on the average the measurements from these two techniques are in fair agreement during low and moderate solar flux conditions. For high solar activity, however, the Jicamarca evening drifts during equinox and December solstice are significantly larger than the ionosonde drifts. These results can be explained by the different height ranges of the radar and ionosonde measurements, and the increase of the upward drift velocity with height below the F region peak. This altitudinal variation is related to the longitudinal gradient of the zonal plasma drifts as a result of the curl-free electric field condition. Our results also indicate that during equinox the increase of the vertical prereversal velocity enhancement with solar activity is largely longitude independent.
Gang Chen - One of the best experts on this subject based on the ideXlab platform.
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nighttime ionospheric enhancements induced by the occurrence of an evening solar eclipse
2013Co-Authors: Gang Chen, Zhengyu Zhao, Baiqi Ning, Ming Yao, Zhongxing Deng, Shuo Huang, Wenchao FengAbstract:[1] The solar eclipse on 15 January 2010 traversed Asia and completed its travel on the Shandong Peninsula in China at sunset. Two vertical incidence Ionosondes at Wuhan and Beijing and the oblique incidence ionosonde network in North China were implemented to record the ionospheric response to the solar eclipse. Following the initial electron density decrease caused by the eclipse, the ionosphere was characterized by a strong premidnight enhancement, and a subsequent ionospheric decay, and a ~10 h later postmidnight enhancement. Neither geomagnetic disturbance occurred during the eclipse day nor did obvious nighttime peak appear for the 10 day mean of the F2-layer critical frequency (foF2). The electron density profilogram of the Beijing ionosonde indicates that the two enhancements were the result of the plasma flux downward from the top ionosphere, possibly due to the steep decrease of the ionospheric electron density and plasma temperature during the solar eclipse. The two-dimensional differential foF2 maps present the regional variations of the nighttime electron density peaks and decay. Both the pre- and postmidnight enhancements initially appeared in a belt almost in parallel with the eclipse track and then drifted southward. The different magnitudes of greatest eclipse in the umbra and outside tend to account for the different occurrence times of the plasma flux. The ionospheric decay following the premidnight enhancement is also considered as a consequence of the eclipse shade.
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latitudinal dependence of the ionospheric response to solar eclipse of 15 january 2010
2011Co-Authors: Gang Chen, Zhengyu Zhao, Baiqi Ning, Zhongxin Deng, Guobin Yang, Chen Zhou, Ming YaoAbstract:[1] The ionospheric responses to the solar eclipse of 15 January 2010 in the equatorial anomaly region have been investigated by three vertical-incidence and seven oblique-incidence Ionosondes arranged along the meridian from geomagnetic latitudes 18°N to 30°N in eastern China. Though the solar eclipse occurred later in the evening, the eclipse effect on electron density and reflection height of ionospheric F2 layer was clearly observed. The study of the eclipse lag (the time lag between the occurrence of the eclipse maximum obscuration and the occurrence of the maximum depletion of foF2) with latitude indicates it increased with F2 layer altitude. Results suggest also that this eclipse enhanced the prereversal enhancement. An unusual peak occurred after the maximum reduction in foF2 and this was observed by all our Ionosondes. The following F2 layer plasma density increase was considered to be caused by the increased westward electric field.
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A Novel Radar Waveform for Monostatic Ionosonde
2011Co-Authors: Zhengyu Zhao, Fanfan Su, Zuowei He, Shipeng Li, Ting Li, Shuo Huang, Guobin Yang, Gang Chen, Ning Li, Tianyao PuAbstract:Monostatic radar, whether using interpulse or intrapulse coded pulse trains, will suffer from the blind zones caused by eclipsing. This letter proposes a novel biphase interpulse coded radar waveform using diverse Pulse Repetition Intervals (PRIs) instead of a consistent PRI within each coherent processing interval (CPI). This waveform can achieve long unambiguous range, high-range resolution and high Doppler resolution without blind zones, and is specially suitable for a monostatic ionosonde.
Zhengyu Zhao - One of the best experts on this subject based on the ideXlab platform.
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nighttime ionospheric enhancements induced by the occurrence of an evening solar eclipse
2013Co-Authors: Gang Chen, Zhengyu Zhao, Baiqi Ning, Ming Yao, Zhongxing Deng, Shuo Huang, Wenchao FengAbstract:[1] The solar eclipse on 15 January 2010 traversed Asia and completed its travel on the Shandong Peninsula in China at sunset. Two vertical incidence Ionosondes at Wuhan and Beijing and the oblique incidence ionosonde network in North China were implemented to record the ionospheric response to the solar eclipse. Following the initial electron density decrease caused by the eclipse, the ionosphere was characterized by a strong premidnight enhancement, and a subsequent ionospheric decay, and a ~10 h later postmidnight enhancement. Neither geomagnetic disturbance occurred during the eclipse day nor did obvious nighttime peak appear for the 10 day mean of the F2-layer critical frequency (foF2). The electron density profilogram of the Beijing ionosonde indicates that the two enhancements were the result of the plasma flux downward from the top ionosphere, possibly due to the steep decrease of the ionospheric electron density and plasma temperature during the solar eclipse. The two-dimensional differential foF2 maps present the regional variations of the nighttime electron density peaks and decay. Both the pre- and postmidnight enhancements initially appeared in a belt almost in parallel with the eclipse track and then drifted southward. The different magnitudes of greatest eclipse in the umbra and outside tend to account for the different occurrence times of the plasma flux. The ionospheric decay following the premidnight enhancement is also considered as a consequence of the eclipse shade.
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latitudinal dependence of the ionospheric response to solar eclipse of 15 january 2010
2011Co-Authors: Gang Chen, Zhengyu Zhao, Baiqi Ning, Zhongxin Deng, Guobin Yang, Chen Zhou, Ming YaoAbstract:[1] The ionospheric responses to the solar eclipse of 15 January 2010 in the equatorial anomaly region have been investigated by three vertical-incidence and seven oblique-incidence Ionosondes arranged along the meridian from geomagnetic latitudes 18°N to 30°N in eastern China. Though the solar eclipse occurred later in the evening, the eclipse effect on electron density and reflection height of ionospheric F2 layer was clearly observed. The study of the eclipse lag (the time lag between the occurrence of the eclipse maximum obscuration and the occurrence of the maximum depletion of foF2) with latitude indicates it increased with F2 layer altitude. Results suggest also that this eclipse enhanced the prereversal enhancement. An unusual peak occurred after the maximum reduction in foF2 and this was observed by all our Ionosondes. The following F2 layer plasma density increase was considered to be caused by the increased westward electric field.
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A Novel Radar Waveform for Monostatic Ionosonde
2011Co-Authors: Zhengyu Zhao, Fanfan Su, Zuowei He, Shipeng Li, Ting Li, Shuo Huang, Guobin Yang, Gang Chen, Ning Li, Tianyao PuAbstract:Monostatic radar, whether using interpulse or intrapulse coded pulse trains, will suffer from the blind zones caused by eclipsing. This letter proposes a novel biphase interpulse coded radar waveform using diverse Pulse Repetition Intervals (PRIs) instead of a consistent PRI within each coherent processing interval (CPI). This waveform can achieve long unambiguous range, high-range resolution and high Doppler resolution without blind zones, and is specially suitable for a monostatic ionosonde.
Gérard Jean-claude - One of the best experts on this subject based on the ideXlab platform.
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Comparison of ICON O+ density profiles with electron density profiles provided by COSMIC-2 and ground-based Ionosondes
2020Co-Authors: Wautelet Gilles, Hubert Benoît, Gérard Jean-claude, Immel Tom, Frey Harald, Mende Stephen, Kamalabadi Farzad, Kamaci Ulas, Stephan AndrewAbstract:In October 2019, NASA-ICON was launched to observe the low-latitude ionosphere using in-situ and remote sensing instruments, from a LEO circular orbit at about 575 km altitude. The six satellites of the radio-occultation program COSMIC-2 were also successfully launched and currently provide up to 3000 electron density profiles on a daily basis since October 1, 2019. Besides, the network of ground-based Ionosondes is constantly growing and allows retrieving very accurate measurements of the electron density profile up to the peak altitude. These three sources of scientific observation of the Earth ionosphere therefore provide a very complementary set of data. We compare O+ density profiles provided during nighttime by the ICON-FUV instrument and during daytime by the ICON-EUV instrument against electron density profiles measured by COSMIC-2 and Ionosondes. Co-located and simultaneous observations are compared on statistical grounds, and the differences between the several methods are investigated. Particular attention is given to the most important variables, such as the altitude and the density of the F-peak, hmF2 and NmF2. The time interval considered in this study covers the whole ICON data availability period, which started on November 16, 2019. Manual screening and scaling of ionograms is performed to ensure reliable ionosonde data, while COSMIC-2 data are carefully selected using an automatic quality control algorithm. A particular attention has been brought to the geometry of the observation, because the line-of-sight integration of both airglow and radio-occultation measurements assimilates horizontal and vertical gradients. As a consequence, the local density profiles obtained by inversion of the ICON and COSMIC-2 observation cannot be exactly assimilated to vertical measurements, such as vertical incidence soundings from Ionosondes. This slightly limits the reach of the interpretation of the comparison between data of different origin. However, using similar observing geometries, the comparison of ICON and COSMIC-2 data does nevertheless provide very reliable and valuable comparisons.Peer reviewe
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Detection of medium scale traveling ionospheric disturbances with TIMED/GUVI limb observations at mid and low latitude regions
2019Co-Authors: Wautelet Gilles, Hubert Benoît, Gérard Jean-claudeAbstract:peer reviewedaudience: researcher, professional, studentMedium-scale traveling ionospheric disturbances (MSTIDs) are the most recurrent type of ionospheric irregularities at mid-latitudes but also occur in low-latitude regions. Whether they are due to the propagation of atmospheric gravity waves originating from the lower atmosphere or related to sporadic E layers, their harmonic signature is a common feature that allows them to be easily identified. MSTIDs have been extensively studied and characterized during the last two decades, mainly using GNSS measurements, ground-based all-sky imagers, radars or Ionosondes. However, only few studies aimed to describe their vertical structure using remote sensing observations from space, which is helpful to understand their propagation and their dissipation processes. NASA’s TIMED mission was launched in December 2001 on a 74° inclination orbit at an altitude of 625 km, which allowed covering both low and high-latitude regions. The Global Ultraviolet Imager (GUVI) instrument aimed at remotely sense, among others, the ionospheric ion and electron densities. GUVI performed disk observations and limb scans in five FUV wavelength channels, making it an ideal tool to characterize the vertical structure of the ionosphere as well as to contextualize the study. The purpose of this work is to use GUVI limb scans to characterize MSTIDs preliminary detected by GNSS before December 2007, until the limb scanning mode failed. We first select a few MSTID cases during maximum background conditions of the Total Electron Content (TEC) computed by GNSS ground stations. Then, coincidental GUVI limb scans of the OI-135.6 nm emission are analyzed to characterize the vertical structure of the MSTIDs. The comparison is completed by the analysis of ionosonde profiles collected in the vicinity of the region where the MSTIDs have been previously detected by GNSS and GUVI.Combining airglow, GNSS and ionosonde data to study ionospheric irregularities over low latitude
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Detection of medium scale traveling ionospheric disturbances with TIMED/GUVI limb observations at mid and low latitude regions
2019Co-Authors: Wautelet Gilles, Hubert Benoît, Gérard Jean-claudeAbstract:Medium-scale traveling ionospheric disturbances (MSTIDs) are the most recurrent type of ionospheric irregularities at mid-latitudes but also occur in low-latitude regions. Whether they are due to the propagation of atmospheric gravity waves originating from the lower atmosphere or related to sporadic E layers, their harmonic signature is a common feature that allows them to be easily identified. MSTIDs have been extensively studied and characterized during the last two decades, mainly using GNSS measurements, ground-based all-sky imagers, radars or Ionosondes. However, only few studies aimed to describe their vertical structure using remote sensing observations from space, which is helpful to understand their propagation and their dissipation processes. NASA’s TIMED mission was launched in December 2001 on a 74° inclination orbit at an altitude of 625 km, which allowed covering both low and high-latitude regions. The Global Ultraviolet Imager (GUVI) instrument aimed at remotely sense, among others, the ionospheric ion and electron densities. GUVI performed disk observations and limb scans in five FUV wavelength channels, making it an ideal tool to characterize the vertical structure of the ionosphere as well as to contextualize the study. The purpose of this work is to use GUVI limb scans to characterize MSTIDs preliminary detected by GNSS before December 2007, until the limb scanning mode failed. We first select a few MSTID cases during maximum background conditions of the Total Electron Content (TEC) computed by GNSS ground stations. Then, coincidental GUVI limb scans of the OI-135.6 nm emission are analyzed to characterize the vertical structure of the MSTIDs. The comparison is completed by the analysis of ionosonde profiles collected in the vicinity of the region where the MSTIDs have been previously detected by GNSS and GUVI.Peer reviewe
M A Abdu - One of the best experts on this subject based on the ideXlab platform.
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On the production of traveling ionospheric disturbances by atmospheric gravity waves
2009Co-Authors: John Macdougall, M A Abdu, Inez S Batista, Paulo Roberto Fagundes, Yogeshwar Sahai, P T JayachandranAbstract:This paper deals with how atmospheric gravity waves produce the traveling ionospheric disturbances (TIDs) that are observed by Ionosondes. It is shown that, rather than directly producing variations of ionospheric height, a likely mechanism involves changes in ionization density by gradients in the horizontal atmospheric gravity wave air motion. These density changes can be observed as variations of the height of an ionospheric isodensity surface (the usual way of measuring TIDs). This mechanism involving enhancement/depletion of ionospheric density requires quite moderate atmospheric gravity wave air motion speeds, and works well at almost all latitudes.
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magnetospheric disturbance induced equatorial plasma bubble development and dynamics a case study in brazilian sector
2003Co-Authors: M A Abdu, J W Macdougall, Inez S Batista, H Takahashi, J H A Sobral, A F Medeiros, N B TrivediAbstract:[1] Equatorial ionospheric plasma bubble irregularity development and dynamics during the major magnetospheric storm of 26 August 1998 are investigated using the data collected by a multistation and multi-instrument diagnostic network operated at equatorial and low latitude sites in Brazil, and auroral electrojet activity (AU/AL), IMF, and Dst indices. A magnetospheric disturbance onset in the morning of 26 August 1998 was initiated by a solar wind shock and associated IMF Bz polarity reversals and ssc that were soon followed by a succession of substorm-like auroral electrojet (AE) intensifications and Dst development. An IMF Bz southward turning and associated AE intensifications in the Brazilian dusk sector produced intense prompt penetration eastward electric field that caused large F region vertical drift and consequently the developments of intense postsunset equatorial anomaly and a series of intense plasma bubbles, the latter event lasting the entire night, as observed by digital Ionosondes at Sao Luis (2.33°S, 315.8°E, dip angle: −.5°) and Fortaleza (3.9°S, 321.55°W, dip angle: −9°) and an all-sky imager, two scanning photometers, and a Digisonde at the low-latitude site Cachoeira Paulista (22.6°S, 315°E; dip angle: −28°). A notable aspect of the dynamics of the bubbles was their initially very low eastward drift velocity which turned into steadily increasing westward velocity that lasted till early morning hours. The results show for the first time a relationship between the zonal drift velocities of optically observed large-scale bubbles (tens to hundreds of kilometers) and that of the smaller scale (kilometer sizes) structures as observed by a digital ionosonde. The results point to the dominant role of a disturbance dynamo associated westward thermospheric wind to maintain the plasma irregularity drift increasingly westward going into postmidnight hours. As an important finding, the results further show that significant contribution to the westward plasma bubble irregularity drift, normally attributed to disturbance dynamo effect, could arise from prompt penetration disturbance zonal electric field, in the course of a disturbance sequence lasting several hours. Such effect is attributed to Hall electric field arising from the primary disturbance zonal electric field, under enhanced nighttime ionospheric conductivities produced possibly by storm associated particle precipitation, in the Brazilian longitude sector in agreement with recent evidences [Abdu et al., 1998b].
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equatorial density depletions observed at 840 km during the great magnetic storm of march 1989
1991Co-Authors: M E Greenspan, C E Rasmussen, W J Burke, M A AbduAbstract:Early on March 14, 1989, a thermal plasma probe on the Defense Meteorological Satellite Program (DMSP) F9 spacecraft detected extensive and dramatic decreases in the ion density at 840 km, near 2130 LT, during two consecutive transequatorial passes over South America. The order of magnitude decreases in the ion density extended more than 4000 km along the satellite track. The depletions were accompanied by upward and westward plasma drifts, both in excess of 100 m/s. Their onsets and terminations were marked by extremely sharp density gradients. DMSP F9 observed no similar depletions over the Atlantic during preceding orbits. A partial depletion was detected over the eastern Pacific during the following orbit. The DMSP F9 ground track passed slightly west of a Brazilian total electron content (TEC) station and two Brazilian Ionosondes during the first depletion encounter. The TEC fell far below normal during the night of March 13–14. The ionosonde measurements indicate that, in the hour after sunset, before DMSP passed through the depletions, the F2 layer rose rapidly and disappeared, but at the time of the first depletion encounter, hmF2 was decreasing over one of the stations. The DMSP F8 satellite, which orbits in the dawn-dusk meridian, made related measurements on March 13 and 14. Crossing the equator at dust on March 13, at the same longitude where DMSP F9 encountered the first depletion, DMSP F8 detected upward and westward drifts, but it measured extremely large rather then depleted ion densities. During two dawn passes over the eastern Pacific on March 14, DMSP F8 observed depletions somewhat similar to those detected by DMSP F9. Large westward drifts accompanied the depletions detected by DMSP F8. It is quite probable that the morningside depletions detected on March 14 are remnants of those detected earlier by DMSP F9 in the evening sector. We develop a phenomenological model reconciling DMSP F8, F9, and ground-based measurements. Our calculations show that rapid upward drifts sustained for several hours can produce depletions in the equatorial ion density with sharp gradients at their high-latitude boundaries, consistent with the data. We discuss possible contributing mechanisms for generating these upward drifts. These include direct penetration of the magnetospheric electric field to low latitudes, the electric fields generated by the disturbance dynamo, and the effects of conductivity gradients near the dusk terminator and the South Atlantic anomaly.