Equatorial Location Research Articles

On ultraviolet emission observed on the flanks of Io

Two very bright ultraviolet (UV) radiation sources (equatorial spots) which are located on the limb of Io near its equator have been detected in a series of observations with the Hubble space telescope. In this paper, we propose the mechanism that provides the sufficient energy of the equatorial spots to explain their high brightness in the UV wavelength range. According to the proposed model, this UV radiation is generated due to electrons which are formed as a result of additional ionization of the atmosphere in the front part of the satellite. These secondary electrons in crossed electric and magnetic fields are shifted downstream into Io's flanks. The optical depth of the source increases on the flanks of Io's atmosphere (from the vantage point of the observer), and we therefore observe the brightest UV radiation in this region, the value of which is in good agreement with the measured values. Also, a reasonable explanation is given for the main observed properties of the UV equatorial spots, such as (1) a correlation between the brightness of the emission and the magnetic longitude of Io and as a result, Io's distance from the plasma torus centrifugal equator; (2) a correlation between the equatorial spot location and the planetary magnetic field orientation; and (3) the excess of the brightness of anti‐Jovian UV source over the brightness of sub‐Jovian source.

First observational evidence of the modulation of the threshold height h'Fc for the occurrence of equatorial spread F by neutral composition changes

In the present study, the seasonal and solar activity variations of the threshold height for equatorial spread F occurrence irrespective of the polarity of the meridional winds during magnetically disturbed period are presented for the first time. The modulation of the seasonal pattern of the threshold height by the seasonal mean O/N2 values is also examined. The Ionosonde data of magnetic equatorial location Trivandrum (8.5°N, 76.5°E) and low latitude station SHAR (13.7°N, 80.2°E) in the Indian longitude sector during equinoxes, winter, and summer seasons of 2002 to 2006 and the corresponding Thermosphere Ionosphere Mesosphere Energetics and Dynamics/GUVI (Global Ultra Violet Imager) O/N2 data are used for the study. The important findings that have emerged from this study are (i) the substantial increase of threshold height with magnetic activity for all the seasons and (ii) the modulation of h'Fc by neutral density changes, irrespective of season, solar, or magnetic activity.

On the storm‐time evolution of relativistic electron phase space density in Earth's outer radiation belt

We report on internal, magnetospheric processes related to markedly different storm‐time responses of phase space density (PSD) in invariant coordinates corresponding to equatorially mirroring, relativistic electrons in Earth's outer radiation belt. Two storms are studied in detail, selected from a database of 53 events (Dstmin < −40 nT) during the THEMIS era thus far (December 2007–August 2012). These storms are well covered by a number of in situ THEMIS spacecraft and complemented by additional ground‐based and in situ observatories, and they epitomize the divergent behaviors that the outer radiation belt electrons can exhibit during active periods, even during otherwise similar Dst and auroral electrojet (AE) profiles. From our statistical results with the full database, the changes in the radial profile peak in PSD reveal notably consistent behavior with prior studies: 58% of geomagnetic storms resulted in PSD peak enhancements, 17% resulted in PSD peak depletions, and 25% resulted in no significant change in the PSD peak after the storm. For the two case studies, we examined the PSD at multiple equatorial locations (using THEMIS), trapped and precipitating fluxes from low‐Earth orbit (using POES), and chorus, hiss, EMIC, and ULF waves (using THEMIS spacecraft, ground observatories, and the GOES spacecraft). We show that (1) peaks in PSD were collocated with observed chorus waves outside of the plasmapause during the most active periods of the PSD‐enhancing storm but not during the PSD‐depleting storm, providing evidence for the importance of local acceleration by wave‐particle interactions with chorus; (2) outer belt dropouts occurred following solar wind pressure enhancements during both storms and were consistent with losses from magnetopause shadowing and subsequent outward radial transport; during the PSD‐enhancing storm, this revealed how the outer belt can replenish itself seemingly independently of the remnant of the pre‐existing belt leftover after a dropout, which in this case resulted in a double‐peaked outer belt distribution; (3) slow decay in PSD was associated with corresponding locations in L* and enhanced wave amplitudes of plasmaspheric hiss; (4) precipitation loss associated with wave‐particle interactions with hiss and EMIC waves appeared to be significantly more important during the PSD‐depleting storm than the PSD‐enhancing storm; and (5) PSD transport during the recovery phase of both storms and throughout the PSD‐enhancing storm was consistent with ULF‐wave‐driven radial diffusion away from maxima in PSD; this indicates the importance of ULF waves in redistributing outer belt PSD after local acceleration occurs. We conclude that these source, transport, and loss processes, individually well characterized by previous studies, do indeed appear to act in concert, leading to predominance of local acceleration in one case and loss in another. These processes can therefore conspire toward optimal source or loss of outer belt electrons under suitable external drivers, and the conditions resulting in wave growth for these acceleration and loss mechanisms are therefore an important area of future research.

Activity of Comet 29P/Schwassmann–Wachmann 1

Comet 29P/Schwassmann–Wachmann 1 is a continually active object moving along nearly circular orbit at a large heliocentric distance ∼6AU. The comet is famous for its repeated outbursts. We look for structure and composition of the nucleus that leads to the observed frequent outbursts. We performed series of numerical simulations dealing with evolution of the nucleus, including changes of the structure and of the CO gas pressure. In our model the porous nucleus has layered structure. Outermost layer is composed of grains with nonvolatile cores mantled by crystalline water ice. Deeper the grains have three components: non-volatile cores, amorphous water ice and, the carbon monoxide ice. The simulations include crystallization of amorphous ice in the nucleus, sublimation of the CO ice and local explosions. We have found, that for an equatorial location the explosions can be expected only in special case, when the nucleus is fine grained, fluffy and rich in CO. In polar regions explosions are possible for almost any composition and structure of the nucleus. Explosions can be either single, or multiple.

Precisely locating the Ordovician equator in Laurentia

Research Article| February 01, 2013 Precisely locating the Ordovician equator in Laurentia Jisuo Jin; Jisuo Jin 1Department of Earth Sciences, Western University, London, Ontario N6A 5B7, Canada Search for other works by this author on: GSW Google Scholar David A.T. Harper; David A.T. Harper 2Department of Earth Sciences, Durham University, Durham DH1 3LH, UK Search for other works by this author on: GSW Google Scholar L. Robin M. Cocks; L. Robin M. Cocks 3Department of Earth Sciences, Natural History Museum, London SW7 5BD, UK Search for other works by this author on: GSW Google Scholar Phil J.A. McCausland; Phil J.A. McCausland 1Department of Earth Sciences, Western University, London, Ontario N6A 5B7, Canada Search for other works by this author on: GSW Google Scholar Christian M.Ø. Rasmussen; Christian M.Ø. Rasmussen 4Natural History Museum of Denmark, University of Copenhagen, 1350 Copenhagen K, Denmark Search for other works by this author on: GSW Google Scholar Peter M. Sheehan Peter M. Sheehan 5Department of Geology, Milwaukee Public Museum, Milwaukee, Wisconsin 53233, USA Search for other works by this author on: GSW Google Scholar Geology (2013) 41 (2): 107–110. https://doi.org/10.1130/G33688.1 Article history received: 29 May 2012 rev-recd: 05 Jul 2012 accepted: 06 Jul 2012 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jisuo Jin, David A.T. Harper, L. Robin M. Cocks, Phil J.A. McCausland, Christian M.Ø. Rasmussen, Peter M. Sheehan; Precisely locating the Ordovician equator in Laurentia. Geology 2013;; 41 (2): 107–110. doi: https://doi.org/10.1130/G33688.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Late Ordovician equatorial zone, like the zone today, had few hurricane-grade storms within 10° of the equator, as emphasized by the preservation of massive-bedded Thalassinoides ichnofacies in a trans-Laurentian belt more than 6000 km long, from the southwestern United States to North Greenland. That belt also includes nonamalgamated shell beds dominated by the brachiopod Proconchidium, which would not have been preserved after hurricane-grade storms. The belt lacks such storm-related sedimentary features as rip-up clasts, hummocky cross-stratification, or large channels. In contrast, other contemporaneous Laurentian Thalassinoides facies and shell beds on either side of the belt have been disturbed by severe storms below fair-weather wave base. The position of the biofacies-defined equatorial belt coincides with the Late Ordovician equator deduced from paleomagnetic data from Laurentia, thus providing both a high-precision equatorial location and an independent test of the geocentric axial dipole hypothesis for that time. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

In situ water vapor and ozone measurements in Lhasa and Kunming during the Asian summer monsoon

The Asian summer monsoon (ASM) anticyclone circulation system is recognized to be a significant transport pathway for water vapor and pollutants to enter the stratosphere. The observational evidence, however, is largely based on satellite retrievals. We report the first coincident in situ measurements of water vapor and ozone within the ASM anticyclone. The combined water vapor and ozonesondes were launched from Kunming, China in August 2009 and Lhasa, China in August 2010. In total, 11 and 12 sondes were launched in Kunming and Lhasa, respectively. We present the key characteristics of these measurements, and provide a comparison to similar measurements from an equatorial tropical location, during the Tropical Composition, Cloud and Climate Coupling (TC4) campaign in July and August of 2007. Results show that the ASM anticyclone region has higher water vapor and lower ozone concentrations in the upper troposphere and lower stratosphere than the TC4 observations. The results also show that the cold point tropopause in the ASM region has a higher average height and potential temperature. The in situ observations therefore support the satellite‐based conclusion that the ASM is an effective transport pathway for water vapor to enter stratosphere.

Seasonal variability of GPS-VTEC and model during low solar activity period (2006–2007) near the equatorial ionization anomaly crest location in Chinese zone

Variability of vertical TEC recorded at Fuzhou (26.1°N, 119.3°E, geomagnetic latitude 14.4°N), Xiamen (24.5°N, 118.1°E, geomagnetic latitude 13.2°N), Nanning (22.8°N, 108.3°E, geomagnetic latitude 11.4°N), China, during the low solar activity in 2006–2007 have been analyzed and discussed. Remarkable seasonal anomaly was found over three stations with the highest value during spring and the lowest value during summer. The relative standard deviation of VTEC is over 20% all the time, with steady and smooth variation during daytime while it has a large fluctuation during nighttime. The biggest correlation coefficient was found in the VTEC-sunspot pair with a value of over 0.5. It seems that solar activity has a better correlation ship than geomagnetic activity with the variation of VTEC and better correlations are found with more long-term data when comparing our previous study. The results of comparing observation with model prediction in three sites reveal again that the SPIM model overestimates the measured VTEC in the low latitude area.

In situ observations of the “preexisting auroral arc” by THEMIS all sky imagers and the FAST spacecraft

Auroral substorms were first described more than 40 years ago, and their atmospheric and magnetospheric signatures have been investigated extensively. However, because magnetic mapping from the ionosphere to the equator is uncertain especially during active times, the magnetospheric source regions of the substorm‐associated features in the upper atmosphere remain poorly understood. In optical images, auroral substorms always involve brightening followed by poleward expansion of a discrete auroral arc. The arc that brightens is usually the most equatorward of several auroral arcs that remain quiescent for ∼30 min or more before the break‐up commences. In order to identify the magnetospheric region that is magnetically conjugate to this preexisting arc, we combine auroral images from ground‐based imagers, magnetic field and particle data from low‐altitude spacecraft, and maps of field‐aligned currents based on ground magnetometer arrays. We surveyed data from the THEMIS all sky imager (ASI) array and the FAST spacecraft from 2007 to April 2009 and obtained 5 events in which the low altitude FAST spacecraft crossed magnetic flux tubes linked to a preexisting auroral arc imaged by THEMIS ASI prior to substorm onset. The observations show that, in each of the five cases: 1) the precipitating electrons associated with the preexisting arc are accelerated by a field‐aligned potential drop, with characteristic energy ranging from a few hundred eV to a few keV. 2) The preexisting arc is located 1°∼2° poleward of the equatorward edge of the 1 keV electron plasma sheet in the ionosphere, and it maps to equatorial locations within the electron plasma sheet and tailward of its inner edge. 3) The preexisting arc is located at or very near the boundary between the Region 1 and Region 2 field‐aligned currents. The localization relative to the Region 1/Region 2 current is confirmed by comparison with maps of field‐aligned currents inferred from ground magnetometer data.

Modeling the daytime, equatorial ionospheric ion densities associated with the observed, four‐cell longitude patterns in E × B drift velocities

Previous studies have quantified the longitude gradients in E × Bdrift associated with the four‐cell tidal structures and have confirmed that these sharp gradients exist on a day‐to‐day basis. For this paper, we incorporate the Ion Velocity Meter (IVM) sensor on the Communications/Navigation Outage Forecasting System satellite to obtain the daytime, verticalE × B drift velocities at the magnetic equator as a function of longitude, local time, and season and to theoretically calculate the F region ion densities as a function of altitude, latitude, longitude, and local time using the Global Ionosphere Plasmasphere model. We compare calculated ion densities assuming no longitude gradients in E × Bdrift velocities with calculated ion densities incorporating the IVM‐observedE × Bdrift at the boundaries of the four‐cell tidal structures in the Peruvian and the Atlantic longitude sectors. Incorporating the IVM‐observedE × B drift velocities, the ion density crests rapidly converge to the magnetic equator between 285 and 300°E geographic longitude, are absent between 300° and 305°, and move away from the magnetic equator between 305° and 340°. In essence, the steeper the longitude gradient in E × B drifts, the steeper the longitude gradient in the equatorial anomaly crest location.

Magnetospheric location of the equatorward prebreakup arc

We address the long‐standing problem of the location and origin of the equatorwardmost Pre‐Breakup auroral Arc (PBA) by combining energetic particle observations from NOAA Polar Operational Environmental Satellites (POES) overpasses of prebreakup arcs with auroral imaging and magnetospheric observations from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. The prebreakup arc was observed within a few minutes of auroral breakup and ∼1–2 hours in MLT from the breakup meridian. For three ideal conjunctions out of 16 PBA crossings, we also construct a dynamically‐adapted magnetospheric model after adding concurrent magnetic observations by the GOES spacecraft. Model‐predicted isotropy boundaries of energetic particles are compared with observations, informing us about model uncertainties. Direct mapping with adapted models as well as particle flux comparisons between the ionosphere and the magnetosphere confirm that the PBA source lies within the region of the steep equatorial magnetic field gradient, where the equatorial field is also small (5–20 nT). That equatorial location, at roughly 8–10 Re, is likely the earthwardmost edge of the thin cross‐tail current sheet. From observations we find that the prebreakup arc nearly coincides in latitude with the energy‐dispersed, 30–300 keV electron isotropy boundary. Here the non‐adiabatic electron precipitation from the high flux region of the outer radiation belt near its outer edge produces a narrow, intense energetic electron precipitation region, called the energetic electron arc (EEA). Two fortuitous conjunctions with DMSP also confirm that energetic (>20 keV) EEA electrons and lower energy, inverted‐V electrons associated with the PBA are collocated. We suggest that EEA formation is an inherent part of the PBA formation process. By creating an enhanced conductance strip, the EEA (a seed arc) produces ionospheric polarization that leads to field‐aligned current generation and associated field‐aligned electron precipitation. We also discuss implications of our findings for the substorm onset mechanism.

Response of spherical diffusion flames subjected to rotation: Microgravity experimentation and computational simulation

Microgravity experiments were conducted in the 2.2-s drop tower and zero-gravity facility at NASA-GRC to gain fundamental understanding of the effects of spinning on an otherwise spherical diffusion flame. The flames were generated by injecting either a fuel or an oxidizer mixture from a porous burner to a controlled ambient of either an oxidizer or fuel mixture, respectively. Results show that the polar flame location scales with the angular velocity monotonically as ω a , where a is greater and smaller than unity for small and large spinning velocities, respectively. On the contrary, the equatorial flame location responds nonmonotonically to increasing spinning velocity: first increasing and then decreasing. The experimental observations agree well with the computational simulation where the simulated results demonstrate that the nonmonotonic response of the equatorial flame location is caused by dilution of the reactant concentration in the outwardly-directed radial flow by the product and inert that are carried by the inwardly-directed polar flow upon traversing the flame segment in the polar region.

Cluster analysis of inorganic elements in particulate matter in the air environment of an equatorial urban coastal location

Concentrations of nine inorganic elements (Na, Zn, Ca, Fe, Ni, Mn, Cu, Cd and Al) in particulate matter (PM10) in the air of an equatorial urban coastal location during 2009 were studied during summer and winter monsoon seasons using high-volume sampling techniques. Atomic absorption spectrophotometry was used to analyse the samples. The concentrations of most inorganic elements were higher during summer than winter, except for Cu and Zn. The main inorganic elements in PM10 are Na, Zn and Ca. High concentrations of Na and Ca are due to marine aerosols. Analysis of enrichment factors showed that inorganic elements are from non-crustal sources. Cluster analysis identified five clusters in the summer and six in the winter: (1) PM10–Ni, (2) Zn–Na, (3) Fe–Cu–Ca–Cd, (4) Mn and (5) Al for summer; and (1) PM10, (2) Zn, (3) Fe–Ni, (4) Cu–Ca–Na–Cd, (5) Mn and (6) Al for winter. Combining both correlation and cluster analysis, it was found that Fe–Cu–Cd was from industry/vehicle emissions, Zn was from resuspended soil, Mn was from metallurgical processes, Ni was from a nearby power plant and Al was from crustal sources. Inorganic element concentrations could be a good indicator of local sources of PM10.

Variation of ionospheric slab thickness observations at Chumphon equatorial magnetic location

This study presents the diurnal and seasonal variations of slab thickness at the equatorial magnetic latitudes in Thailand during 2004–2006, corresponding to the declining part of low solar activity. The GPS-derived total electron content (TEC) and the maximum electron density of the F-region (NmF2) are used to compute the slab thickness (τ) at the Chumphon station (10.72°N, 99.37°E), located near the magnetic equator. The results show that large peaks of slab thickness exist during the pre-sunrise hours in all three seasons at Chumphon when compared with other latitudes. The maximum value of slab thickness occurs when the peak electron density in the F2 region is at the lowest level. During daytime, the slab thickness ranges from 200 kilometers to 580 kilometers for all seasons. During nighttime, the maximum value of slab thickness is 1250 kilometers in the summer of 2004. Moreover, the diurnal variation shows two minima that appear around 0900 LT and 1900 LT, during the post-sunrise and sunset hours. The seasonal variations show that the average slab thickness daily value is greater during summer and winter than those during equinox. Our study finds that the slab thickness at Chumphon located near the equatorial latitude is much larger than those found at low, mid, and high latitudes. The difference in slab thickness between the equatorial latitude and other zones is explained by the lack of plasma flow from the plasmasphere to the F2 region at the magnetic equator.

Westward electric field penetration to the dayside equatorial ionosphere during the main phase of the geomagnetic storm on 22 July 2009

[1] The moderate geomagnetic storm (minimum SYM-H = −89 nT) that occurred during the period from 21 to 25 July 2009 is anomalous because the storm main phase developed during northward interplanetary magnetic field (IMF). A reduction (for ∼4 h) in the daytime E region westward drift (eastward electric field) over the magnetic equatorial location of Trivandrum (8.5°N, 77°E; dip latitude ∼0.5°N) in India is observed during the storm main phase. This reduction in the drift is also indicated by the disappearance of the equatorial sporadic E region (Esq) echoes on the ionograms. It is suggested that an additional westward prompt penetration electric field characterized by the northward IMF Bz is superposed on the ionosphere during the storm main phase which contributed to the observed reduction in the drift. These are the first observations which indicate the effects of the dusk-to-dawn penetration electric fields on the east-west drifts during northward IMF.

The atmospheric lead record preserved in lagoon sediments at a remote equatorial Pacific location: Palmyra Atoll, northern Line Islands

Anthropogenic lead (Pb) inputs to the atmosphere increased greatly over the past century and now dominate Pb supply to the oceans. However, the Pb content of sediments across the equatorial Pacific region is relatively unknown, and data exist only for deep sea sites where Pb deposition lags surface water inputs by up to a century. Here we present ICP-MS analyses of Pb of a core from a lagoon at Palmyra Atoll, northern Line Islands, that spans approximately the past 160years. The non-bioturbated sediments of the euxinic lagoon, coupled with rapid rates of deposition, provide a unique fine-scale record of atmospheric Pb supply at a remote Pacific location. These first observations of historic Pb sedimentation in an atoll lagoon reveal a 63-fold increase in Pb flux to sediments during the past century and correlate directly with the North American consumption of leaded gasoline that began in 1926.

Features of the F3 layer occurrence over the equatorial location of Trivandrum

Abstract. The general features of the F3 layer occurrence over the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip lat ~0.5° N) in India during the period from 1996–2005 are presented using the ionosonde observations. The study brings out that the F3 layer occurrence over Trivandrum is weak and rare compared to the other equatorial locations. The F3 layer occurrence is relatively more pronounced during the magnetically active conditions, thus indicating the dependence of the layer formation over Trivandrum on magnetic activity. It is also observed that the percentage occurrence of the F3 layer decreases with increasing solar activity.

Inverted fluvial features in the Aeolis/Zephyria Plana region, Mars: Formation mechanism and initial paleodischarge estimates

A subset of the sinuous ridges (SRs) in the Aeolis/Zephyria Plana (AZP) region of Mars has been previously hypothesized to be inverted fluvial features, although the precise induration and erosion mechanisms were not specified. Morphological observations and thermal inertia data presented here support this hypothesis. A variety of mechanisms can cause inversion, and identification of the specific events that lead to fluvial SR formation can provide insights into the sedimentological, geochemical, and climatic processes of the region. Reconnaissance of two terrestrial lava‐capped ridges suggests some criteria that may be used to identify inverted fluvial features formed by lava infill on Mars, but these criteria are not satisfied by the majority of the AZP fluvial SRs. Armoring also appears inconsistent with terrestrial analogs. Layering and surface textures of fluvial SRs indicate that the most likely induration mechanism was geochemical cementation of fluvial sediments, and that the primary erosional mechanism that exposed the fluvial SRs was aeolian abrasion. This analysis of formation mechanism provides a foundation for estimating paleodischarge using an empirical form‐discharge approach, to which we have applied scaling, for Martian gravity. For those fluvial SRs meeting a set of criteria for accurate paleodischarge estimates, paleodischarge values generally range between 101 and 103 m3 s−1. The largest of these initial estimates are comparable to paleodischarge estimates for some late‐stage Noachian fluvial channels on Mars, and provide a constraint on the atmospheric conditions at this equatorial location during the late Hesperian to early Amazonian time frame.

Pyrite framboid study of marine Permian–Triassic boundary sections: A complex anoxic event and its relationship to contemporaneous mass extinction

Size analysis of pyrite framboids has been undertaken on epicontinental Permian- Triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia. Mid-paleolatitude sections from the margins of the Boreal (Spitsbergen, Greenland) and Neotethyan oceans (Western Australia) reveal intense anoxia throughout the Permian-Triassic boundary interval with euxinic conditions frequently developing, and dysoxia encountered even in relatively shallow-water settings above storm wave base. At equatorial paleolatitudes, weakly oxygenated (dysoxic) conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition, although euxinia was rare. Western and eastern Tethyan locations re- veal a complex and unstable redox history: anoxia in the Hindeodus praeparvus Zone was replaced by oxygenated facies in the Permian- Triassic boundary interval (H. changxingensis to H. parvus zones). Oxygen-poor deposition returned during the succeeding Isarcicella isarcica Zone. The more persistent and intense development of oxygen restriction in cooler water, mid-paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of Permian-Triassic bound- ary anoxia. In higher paleolatitudes the ben- thic invertebrate extinctions occurred during a prolonged phase of oxygen-poor deposition, while in equatorial Tethyan locations benthic losses occurred at the end of the fi rst anoxic phase (in the late H. praeparvus Zone).

Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 "Halloween Storms"

Abstract. The response of the ionospheric F-region in the South American sector during the super geomagnetic storms on 29 and 30 October 2003 is studied in the present investigation. In this paper, we present ionospheric sounding observations during the period 29–31 October 2003 obtained at Palmas (a near equatorial location) and Sao Jose dos Campos (a location under the southern crest of the equatorial ionospheric anomaly), Brazil, along with observations during the period 27–31 October 2003 from a chain of GPS stations covering the South American sector from Imperatriz, Brazil, to Rio Grande, Argentina. Also, complementary observations that include sequences of all-sky images of the OI 777.4 and 630.0 nm emissions observed at El Leoncito, Argentina, on the nights of 28–29 (geomagnetically quiet night) and 29–30 (geomagnetically disturbed night) October 2003, and ion densities observed in the South American sector by the DMSP F13, F14 and F15 satellites orbiting at about 800 km on 29 and 30 October 2003 are presented. In addition, global TEC maps derived from GPS observations collected from the global GPS network of International GPS Service (IGS) are presented, showing widespread and drastic TEC changes during the different phases of the geomagnetic disturbances. The observations indicate that the equatorial ionospheric irregularities or plasma bubbles extend to the Argentinean station Rawson (geom. Lat. 33.1° S) and map at the magnetic equator at an altitude of about 2500 km.

Gadanki radar observations of F region field‐aligned irregularities during June solstice of solar minimum: First results and preliminary analysis

In this paper we present the first results of F region field‐aligned irregularities (FAI) made during the summer of low solar condition using the Gadanki mesosphere‐stratosphere‐troposphere radar. FAI echoes were observed on all 20 nights of radar observations and were mostly confined to the postmidnight hours. Echo morphology is found to be very different from the equinoctial postsunset features reported earlier from Gadanki. Echo SNRs are lower by 25 dB than their equinoctial postsunset counterparts but are quite comparable to those of the equinoctial decaying FAI during the postmidnight hours. The Doppler velocities, which lie in the range of ±100 m s−1, are predominantly upward‐northward during 0000–0300 LT and downward‐southward afterward, in contrast to those observed as predominantly downward‐southward associated with the decaying equinoctial postmidnight F region FAI. Spectral widths of the summer echoes, which are well below 50 m s−1 and are very similar to those of the decaying equinoctial irregularities, represent the presence of weak plasma turbulence. Simultaneous observations made using a collocated ionosonde show no ionogram trace during 2200–0530 LT except for a few cases of weak spread F events. Concurrent ionosonde observations made from magnetic equatorial location Trivandrum also show very similar results. The observations are discussed in the light of current understanding on the postmidnight occurrence of F region irregularities in the summer of low solar condition.