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Sporadic E (Es) layers could be composed of metallic ions and formed, modified, or transported by the action of convective electric fields in the high latitude ionosphere. In this paper, by utilizing simultaneous observations from Digisonde and Super Dual Auroral Radar Network (SuperDARN) HF radars at Zhongshan Station (ZHS, 69.4°S, 76.4°E), Antarctica, a thin Es layer, which initially formed in the lower F region and descended into the lower E region, with wavelike structures, was recorded by Digisonde on 14 November 2019. The Es layer‐related concurrent ionospheric irregularities were also detected by the SuperDARN ZHS HF radar. By using a global‐scale 2‐D convection map, combined with images from the Special Sensor Ultraviolet Spectrographic Imager instruments onboard Defense Meteorological Satellite Program (DMSP) spacecraft, it is proposed that the flow shears associated with the duskside convective circulation are responsible for the evolution of the Es layer. Moreover, using the HF radar elevation angle data to measure the scatter height, it is strongly suggested that the Es layer was elongated with convection circulation. The electrodynamic processes responsible for the formation and evolution of the Es layer are discussed. Key Points: An Es layer formed in the lower F region and descended to the E region, observed simultaneously by Digisonde and Super Dual Auroral Radar Network (SuperDARN) HF radarsThe formation and evolution of the Es layer related to the afternoon convection reversalSuperDARN HF radar measurements suggest the Es layer is elongated with convection circulation [ABSTRACT FROM AUTHOR]

A longitudinal chain and a latitudinal chain of ionosondes, located at Yakutsk (129.60°E, 62.00°N), Mohe (122.37°E, 53.50°N), Beijing (116.25°E, 40.25°N), Wuhan (114.61°E, 30.53°N), Sanya (109.42°E, 18.34°N), I‐Cheon (127.54°E, 37.14°N), San Vito (17.80°E, 40.60°N), Roquest (0.50°E, 40.80°N), Millstone Hill (71.50°W, 42.60°N), and Alpena (83.56°W, 45.07°N) ionosondes, are utilized to statistically investigate the sporadic E layer (Es) occurrence rate and variation. The Es occurrence rates at all stations show a similar dependence on local time and season. However, the seasonal dependence of Es occurrence is more distinct at middle latitudes than that at low latitudes along the 120°E longitude. Results at different stations along ∼40°N latitude show much lower Es occurrence at the American sector than that at European and East Asian sectors, which is most likely because the horizontal geomagnetic field in north America is smaller than in other regions. The statistical results demonstrate that the seasonal variations of Es occurrence and strength are related to the annual variation of meteor counts. Simulation results show that the summer maximum of the ion vertical drift velocity driven by the variations of neutral densities and winds could also contribute to the seasonal variations of Es occurrence and intensity. The seasonal variations of the quasi‐6‐day and quasi‐16‐day oscillations in Es are also investigated. The seasonal variations of periodic disturbances of the Es differ between each station. Planetary waves in the MLT region cannot fully explain the seasonal variations of the periodic disturbance of Es. Solar and geomagnetic activities can also result in periodic variations of the Es. Plain Language Summary: Sporadic E layer is an ionized cloud composed of metallic ions. Meteor flux and atmospheric waves, such as planetary waves and tides, play an important role in the formation of Es. In this work, we investigate the latitudinal and longitudinal distribution of Es occurrence and variations based on ionosonde data of 10 stations around the world. The Es occurrence rates at all stations show a similar dependence on season, which are mostly related to the variation of meteor input. In addition, simulation results show that the summer maximum of the ion vertical drift velocity driven by the variations of neutral densities and winds could also contribute to the seasonal variation of Es occurrence and intensity. The seasonal variations of quasi‐6‐day and quasi‐16‐day oscillation in sporadic E layer are also studied. The results demonstrate that the seasonal variations of periodic disturbances in Es differ between each station and enhanced quasi periodic oscillation can be observed in all seasons. Besides, in addition to the PWs in the MLT region, geomagnetic and solar activities can also lead to the periodic disturbance in Es layers. Key Points: The occurrence rate of Es in north America is lower than that at 120{degree sign}E sector due to horizontal geomagnetic field differenceEffects of meteor counts, neutral density, and winds contribute to the seasonal dependence of Es layer occurrenceSolar and geomagnetic activities can also contribute to the periodic oscillations in the Es layer variations [ABSTRACT FROM AUTHOR]

In this paper, we examine the mechanism of middle‐ and low‐latitude sporadic‐E (Es) layer formation. Observations of ionosondes and meteor radars at stations of different latitudes show that Es layer also formed at low‐altitude nonwindshear points, which is distinct from prototypical windshear theory. The theoretical modeling results show that metallic ions can effectively accumulate by the combined effect of the zonal and meridional winds in the mesosphere and the lower thermosphere region. Numerical simulation results also demonstrate that metallic ions can accumulate without wind shear at lower height (90–105 km) as a consequence of the MLT winds leading to the ion drifting downward. We suggest that the turbopause at 90–105 km plays an important role in forming low‐altitude Es layer in the middle‐ and low‐latitude regions. Plain Language Summary: Sporadic‐E layer is an enhanced ionization patch, which can reflect radio wave signals, and plays a significant role in the telecommunication and navigation system. The occurrence of Es layer is inconsecutive and influenced by many factors, such as wind, electric field, and meteor input, which makes the prediction of Es layer very difficult. In this study, we try to investigate the process of the formation of Es layer from electrodynamic theory of ionosphere. Our simulation results demonstrate that the wind shear, a classical theory for the Es layer formation at midlatitude, is not the only mechanism leading to the generation of Es layer, and turbopause at 90–105 km height can provide the concentration location for metallic ions. Key Points: Windshear Theory of sporadic‐E (Es) formation is reexaminedMeteor radar and ionosonde observations show that Es can form at nonwindshear pointsSimulation results show that Es formation can be affected by the turbopause [ABSTRACT FROM AUTHOR]

A sodium Doppler lidar system with three‐directional measurements of sodium density, atmospheric wind field, and temperature was established at Zhongshan (69.4°S, 76.4°E), Antarctica. On November 14, 2019, a sporadic sodium layer (SSL) was observed at an altitude range of 93–103 km. The temporal/spatial sodium density variations of this SSL are associated with a strong sporadic E (Es) layer at nearly the same height, which is modulated by the convective electric field. By considering the structures and the time lags of the SSL's growth at three positions, the SSL appears to have a horizontal advection in an approximately westward direction with a velocity of the order of 80 m/s. This is consistent with the zonal wind velocity derived from the lidar system itself. The temporal/spatial sodium density variations strongly indicate that the formation and perturbation of SSLs are related to the evolution of ES layers due to varied electric fields and atmospheric gravity waves, while it is advected by the horizontal wind. Plain Language Summary: A sporadic E layer (Es) could be formed by metallic ions and then modified or transported by the action of magnetospheric electric fields in the high latitude ionosphere. It has been widely proposed that Es layers play an important role in the formation of sporadic sodium layers (SSL), but detailed studies of their dynamic process and evolution are still lacking. A three‐frequency Sodium (Na) resonance fluorescence Doppler lidar has been recently deployed by the Polar Research Institute of China, which could measure the sodium density, temperature, and wind profiles simultaneously in three directions. To clarify the dynamic properties of Es/SSL, we have performed observations of an event at Zhongshan Station (69.4°S, 76.4°E), Antarctica, which includes sodium density profiles and wind velocity measured by the multidirectional lidar system, detection of the Es layer by a collocated Digisonde radar, F region ion velocity, that is, electric field, derived by the SuperDARN HF radar network, as well as gravity wave perturbations determined from the Davis medium frequency radar. Key Points: Separation of temporal/spatial variations in sporadic sodium layer (SSLs) is observed by a three‐directional lidar system at Zhongshan, AntarcticaThe formation and perturbance of SSLs are associated with a sporadic E layer at the same heightThe SSLs are advected by the background wind [ABSTRACT FROM AUTHOR]

Sporadic E (Es) layers are known for their layered structures with enhanced electron density. Recently, some scientists have studied the relationship between the occurrence rate and intensity of the Es layer in the global distribution. However, the relationship between the Es layer parameters (Es layer occurrence rate, Es layer intensity, Es layer thickness) in the vertical direction seems to be ignored to date. This paper highlights the vertical profiles of the occurrence rate, intensity, and thickness of the Es layers by using scintillation index (S4) from FORMOSAT‐3/COSMIC satellites from July 2007 to March 2015. The results show that there are some persistent differences between the occurrence rate, intensity, and thickness of the Es layers in the vertical profiles, which is different from their general similarity in the latitude distribution. It is found that the Es layer occurrence rate has a maximum value at ∼102 km altitude, but the Es layer intensity and Es layer thickness reach their maximum at an altitude of ∼110 km. Besides, the intensity and thickness of the Es layer exhibit a high linear relationship, which suggests that the larger electron density of the Es layer, the thicker its thickness. The Horizontal Wind Model (HWM14) indicates that the latitudinal variations in Es layers parameters are highly coincident with the zonal wind shear. However, the altitudinal variations in Es layers parameters do not agree well with the zonal wind shear. Key Points: The vertical variations of the occurrence rate, intensity, and thickness of the Sporadic E (Es) layers are presented in detailTheir vertical variations exist obvious discrepancies, which is different from their high similarity in latitudeCompared with the Es layer occurrence rate, the Es layer intensity can better reflect the evolution of the Es layer in vertical direction [ABSTRACT FROM AUTHOR]

The COSMIC radio occultation observations are used to investigate the wavenumber‐4 (WN4) structure of the Sporadic E (Es) layer during 2007–2018. The WN4 pattern is observed in the Es occurrence rate over the middle‐ and low‐latitudes. This pattern is stronger at the low‐latitudes than at the middle‐latitudes. It shows the peak intensity in latitude bands between 5° and 15° dip latitudes in both hemispheres. The WN4 structure occurs predominantly during daytime. It appears above 110 km in the morning, then descends slowly down to about 105 km, and finally disappears after sunset. The WN4 structure moves eastward with a speed of approximately 90°/day. It is prominent in boreal autumn and summer, and disappears in boreal winter. The dominant role of the DE3 tide for the formation of the WN4 structure is supported by similar features between the Es occurrence rate and the DE3 tide of the zonal wind shear, such as the phase, eastward speed, seasonal variation, symmetrical distribution, and strong activity at the low‐latitudes. Key Points: The wavenumber‐4 (WN4) structure is observed in the sporadic E layer over the middle‐ and low‐latitudesThe diurnal, seasonal, and altitudinal variations of the WN4 pattern are analyzedThe diurnal eastward non‐migrating tide with zonal wavenumber‐3 plays the dominant role in the formation of the WN4 structure [ABSTRACT FROM AUTHOR]

Ionospheric sporadic E layers are irregularities with enhanced plasma density which occur in the ionosphere E region. In the present work, we have focused on an interesting wavenumber 4(WN4) pattern of sporadic E layer based on the Constellation Observing System for Meteorology, Ionosphere and Climate radio occultation S4 indices observation. It is found that amplitude of WN4 pattern has a significant seasonal dependency with the maximum appearing in summer/autumn and minimum in winter. The seasonal variation of the WN4 pattern is basically consistent with the eastward propagating diurnal tide with zonal wavenumber 3 (DE3) tide features. Inconsistencies, mainly an anomalous weak amplitude during the summer in southern hemisphere and propagation direction (speed), are also found. By removing the zonal ion drift factor effect, WN4 pattern of sporadic E layers exhibits a closer relation with the DE3 tide with larger amplitude in the northern hemisphere and ~90° shift in longitude on average during autumn in the southern hemisphere. In general, it is reasonable to conclude that DE3 tide greatly contributes to this WN4 pattern of sporadic E layers. [ABSTRACT FROM AUTHOR]

We investigate the correlation of sporadic E (Es) with the occurrence of medium‐scale traveling ionospheric disturbances (MSTIDs) at night in middle latitudes (25°–40°N and 25°–40°S magnetic latitudes) by examining their occurrence climatology. The occurrence climatology of Es and MSTIDs is derived using the Challenging Minisatellite Payload satellite data acquired in 2001–2008 and 2001–2009, respectively. Electron density irregularities and radio scintillations are used as the detection proxies of MSTIDs and Es, respectively. The occurrence rate of MSTIDs shows a semi‐annual variation with the primary peak during June solstices and the secondary peak during December solstices in both hemispheres. However, the occurrence rate of Es shows a seasonal variation with a pronounced peak in summer in both hemispheres. The occurrence of MSTIDs during local summer and equinoxes is correlated with the occurrence of local Es, but the high occurrence rate of MSTIDs in local winter is not correlated with local winter hemisphere Es. MSTIDs in the winter hemisphere are correlated with magnetically conjugate MSTIDs in the summer hemisphere; these summer hemisphere MSTIDs are correlated with the occurrence of Es in the summer hemisphere. The occurrence rate of MSTIDs clearly shows an increase with decreasing solar activity, but the solar cycle dependence of Es is not obvious from the data. This observation suggests that the generation of MSTIDs is significantly affected by factors other than Es such as the growth rate of the Perkins instability, atmospheric gravity waves, and the F region conductance. Key Points: Nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) in summer and equinoxes are correlated with sporadic E in the local hemisphereWinter hemisphere MSTIDs can be explained by summer hemisphere sporadic EThe role of sporadic E in winter is contingent upon the conjugacy of MSTIDs [ABSTRACT FROM AUTHOR]

Observations of backscatter from field‐aligned plasma density irregularities in sporadic E (Es) layers made with a 30‐MHz coherent scatter radar imager in Ithaca, New York are presented and analyzed. The volume probed by the radar lies at approximately 54° geomagnetic latitude, under the midlatitude trough and at the extreme northern edge of the zone where Es layers are prevalent. Nonetheless, the irregularities exhibit many of the characteristics of quasiperiodic echoes observed commonly at lower middle latitudes. These include a tendency to occur in elongated bands stretching from the northwest to southeast in the Northern hemisphere separated by tens of kilometers and propagating to the southwest. In addition, the irregularities were found to exhibit finer‐scale structures with secondary bands oriented nearly normally to the primary bands. We investigate the proposition that the primary bands are telltale of Es‐layer structuring caused by neutral Kelvin Helmholtz (KH) instability in the lower thermosphere and that the secondary bands signify secondary KH instability. Results from a 3D numerical simulation of KH support this proposition. Key Points: Quasiperiodic (QP) sporadic E layers observed under the midlatitude trough using coherent scatter radarRadar imagery shows secondary bands of irregularities normal to the primary QP bandsThe secondary bands are attributed to secondary Kelvin Helmholtz instability in the lower thermosphere [ABSTRACT FROM AUTHOR]

Sporadic potassium (Ks) and sodium (Nas) layers were investigated using more than 1,500 h of simultaneous Na/K LIDAR data at São José dos Campos, Brazil (23.1°S, 45.9°W). These events were observed on more than 88% of the analyzed nights. Although Na and K are both alkali metals, their sporadic layers show different behaviors. The Nas layers were in general 0.7 km wider and occurred ∼2 km higher than Ks layers. Moreover, the Nas layers progression is faster than that of Ks layers not only in the process of reaching their maximum amplitude but also in terms of dissipation. Our study showed that most Ns events (80% of Ks layers and 90% of Nas layers) have a strength factor of upto 5. Moreover, on average, Ks presented a strength factor ∼1.3 times stronger than that of Nas. The relative frequency of occurrence for both Ks and Nas layers exhibits an almost semiannual variation, with maxima in January/October and February/September, respectively. On the other hand, no similar variation was observed in the peak density or in the peak height. The peak density shows an annual variation, with a maximum occurring during winter for Ks events and a semiannual variation with a maxima occurring at the equinoxes for Nas. Different seasonal behaviors were also seen in the peak height of the identified layers, with Ks presenting a semiannual variation with maxima around January/October, while an annual variation occurred in Nas with lower layers occurring around winter. Key Points: This study presents the first simultaneous analysis of averaged K and Na sporadic layer parameters in the Southern HemisphereSeasonal and nocturnal variations in sporadic events were observed in K and Na layersThe differing behaviors of neutral sporadic layers were described as seen in K and Na mesospheric layers [ABSTRACT FROM AUTHOR]

The great solar eclipse traveled eastward through the American Continent from coast to coast on August 21, 2017 and provided a rare opportunity to investigate the ionospheric responses to the rapid solar radiation variations. We have analyzed the peak electron density and density gradient variations in Sporadic E (Es) and applied the data of four Digisondes close to the eclipse path. All the four Digisondes have recorded the same interesting phenomena. One is the depletion on the fbEs (blanketing frequency of Es layer) curve during the solar eclipse and the other is the enhancements on the semi‐transparency parameter of Es layer Δf after the solar eclipse, where Δf = ftEs−fbEs, and ftEs is the top frequency of Es layer. The wind disturbances on the tidal wind and the photoionization decrease during the eclipse are put forward as a possible reason for the peak plasma density reduce. The periodic gravity waves have been observed in both ionospheric E and F region. However, the Δf enhancements occurred after the gravity waves had passed through the Es layer. Thus, we suggest that the solar induced waves did not raise the plasma density gradient directly. Gravity waves breaking may occur in the Mesosphere/Lower Thermosphere region to deposit momentum and produce turbulence, and so the accompanying instabilities may be generated to enhance the electron density gradient in E‐region. Key Points: Four Digisondes have recorded the same interesting phenomena in Sporadic E during and after the solar eclipse of August 21, 2017Depletion on fbEs curves were recorded during the solar eclipse and the minimum fbEs appeared around the eclipse maximumEnhancement on ftEs‐fbEs curves were recorded after the solar eclipse and may be related to the gravity wave breaking [ABSTRACT FROM AUTHOR]

In this study, the difference in the sporadic E layer occurrence ratio between two low‐magnetic‐latitude (±5° to ±15°) regions is analyzed by using COSMIC scintillation observations covering the period from 2007.001 to 2017.365. Obvious longitudinal, seasonal, and LT dependencies of this phenomenon are found. Most features of the differences between two hemispheres could be explained by the difference in zonal vertical wind shear between the two hemispheres induced by the difference between the magnetic and geographic latitudes of the studied regions. This result also indicates that the wind shear mechanism still dominates sporadic E layer formation in low‐magnetic‐latitude regions. Key Points: The difference in the sporadic E layer occurrence ratio between two low‐magnetic‐latitude regions is analyzedThe difference in the sporadic E layer occurrence ratio between two hemispheres shows obvious longitudinal, seasonal, and LT dependenciesThe longitudinal, seasonal, and LT dependencies of this difference could be partly explained by the difference in vertical zonal wind shear [ABSTRACT FROM AUTHOR]

We present passive observations of midlatitude sporadic E (Es) structures in the 30–50 MHz range using the long wavelength array telescopes in New Mexico. Spectral and temporal analysis of the structures reveals that some of the emissions can be characterized by broadband, spark‐like radiation occurring at a repetition frequency of 60 Hz. The azimuthal distribution indicates that the brightest emissions come from the directions of several large metropolitan centers with distances ranging from 700 to 1,250 km from the telescopes. This implies that the source is unintended human‐made noise, originating from devices connected to 60 Hz alternating current power. The geometry of our observations rule out coherent scatter from field‐aligned irregularities, and indicate that the unintended noise must undergo a specular reflection off of over‐dense plasma distributed approximately parallel to Earth's surface. On certain occasions the reflections are seen at such high frequencies and high elevation angles that the local plasma frequency must be above 30 MHz. During both day and night Es conditions, the dense structures are observed to be arranged in propagating fronts, and travel at speeds of 70–100 m/s. We also present observations that reveal quasi‐periodic amplitude oscillations with frequencies consistent with atmospheric gravity waves and acoustic waves. Plain Language Summary: Dense, patchy layers of plasma that form in the E layer of the ionosphere (sporadic E) often reflect high frequency radio waves from distant, over‐the‐horizon sources. While detectable with current radar techniques, sporadic E is difficult to image over large regions due to the limited field of view of a typical radar. We show that unintentional, human‐made radio emissions, originating from the electrical grid, act as a widespread set of radio sources, with hotspots centered on large metropolitan areas. The radio emissions reflect off of sporadic E plasma and are readily detectable and imaged by radio telescopes such as the Long Wavelength Array (LWA) in New Mexico. We present LWA observations that prove this capability, which enables the tracking and mapping of sporadic E over large regions. Key Points: Radio emissions from the electrical grid act as a widespread illumination source for imaging sporadic EThe technique described in this paper enables tracking and mapping of sporadic E structuresSince the source of RF is broadband, this method may also enable tracking of sporadic E electron density [ABSTRACT FROM AUTHOR]

An unseasonal equatorial plasma bubble (EPB) event over South-East Asia was observed on July 22, 2014 that has not been studied before. An investigation into this event is presented with the 26th July, 2014 as a comparison, non-bubble day. The 22nd July EPB event occurred in the late post-sunset sector and was associated with a small upward plasma drift. This event was highlighted using a new filter on the SCINDA S4 data. Ionosonde data show that sporadic E was present during the growth period for the EPB event. Modeling results from Thermosphere-Ionosphere Electrodynamics (TEC) Global Circulation Model were used to conduct a numerical experiment investigating the direct effect of sporadic E on the linear R-T growth rate. It was shown that sporadic E located in the correct latitude and local time can increase the linear growth rate. The seeding conditions were investigated using TEC data from Patumwan, Thailand. Wave-like structures were observed for both days of interest, with larger amplitudes on 22nd July compared with the 26th July. Finally, simulations using the high-resolution model PBMOD showed that for forcing from above conditions similar to the days of interest, EPBs would form in the presence of large seed perturbations. Therefore, it is likely that this unseasonal event was caused by large seed perturbations in TEC. [ABSTRACT FROM AUTHOR]

Sporadic E (Es) structures have been observed occasionally covering a large horizontal scale of more than 1,000 km over China. Their onset locations and propagation features, and related generation mechanisms still remain unknown. In this study, a statistical analysis of large-scale Es structures is performed based on the ionospheric total electron content obtained from ground-based receiver networks, in combination with data from multiple ionosondes in China. The large-scale strong Es structures mainly occur during summer months, with dominant horizontal azimuth in the east-west and northwestsoutheast directions and dimensions of 1,000--3,000 km along the elongation. They predominantly drift southwestward at the speed of 30--210 m/s. The main onset region for the large-scale Es structures over China is identified for the first time, which is around 20°--45°N and 100°--125°E. Based on the morphological features of large-scale Es structures, and the observation of concurrent cases of traveling ionospheric disturbances, we surmise that gravity waves could play an important role in the generation of large-scale Es structures. [ABSTRACT FROM AUTHOR]

During disturbed periods, E region electric fields can cause anomalous Es layer behavior, which is observed in the digital ionosonde data. To investigate the influence of these electric fields in the Es layer development, we analyzed a set of 20 magnetic storms from 2015 to 2018 over Boa Vista (BV, 2.8°N, 60.7°W, dip ~18°), São Luís (SLZ, 2.3°S, 44.2°W, dip ~8°), and Cachoeira Paulista (CXP, 22.41°S, 45°W, dip ~35°). The electric field zonal components during the main and recovery phases of each magnetic storm are computed to study the corresponding characteristics of these Es seen in ionograms. Additionally, a numerical model (MIRE, Portuguese acronym for E Region Ionospheric Model) is used to analyze the Es layer dynamics modification around disturbed times. Using observation data and simulations, we were able to establish a threshold value for the electric field intensity for each region that can affect the Es layer formation. The results sustain that the strong Es layer in BV can be an indicator of the disturbed dynamo event. At SLZ, on the other hand, the Es layers are affected by the competition mechanisms of their formation, as equatorial electrojet irregularities and winds, during the main phase of the magnetic storm. Over CXP, the Es layer dynamics are dominated by the wind shear mechanism. Finally, this study provides new insights into the real impact of the electric field in the Es layer development over the Brazilian sector. Thus, our results lead to a better understanding of the underlying mechanisms related to the Es layer formation and dynamics. [ABSTRACT FROM AUTHOR]

Nearly 200 hr of observing with the Murchison Widefield Array (MWA) radio telescope during the Galactic and Extragalactic All‐sky MWA (GLEAM) survey was used to assemble images of ionospheric structure. These images cover a nearly 50° wide area on the sky at a cadence of 10 min over many 5–7 hr long observing runs. They are generated by tracking the apparent motions of ∼200–800 cosmic radio sources caused by changes in the transverse gradient of the ionospheric total electron content. Spectral analysis of these images revealed that the data set was dominated by three distinct signatures. The first is consistent with field‐aligned structures within the topside ionosphere/lower plasmasphere previously imaged with the MWA. The second are structures that are relatively large and aligned nearly east/west. Regional weather data imply that these are preferentially detected when there is a noticeable shear within the subtropical jet stream, which passes near the MWA. This suggests that this signature may be related to gravity waves launched by jet stream shear. The final signature is consistent with the properties of so‐called electrobuoyancy waves that are known to occur at midlatitudes at night. Detections of these were more common when regional sporadic E (ES) was present, supporting a proposed connection between these waves and polarization electric fields that may arise within ES. We discuss the implications for future observations with the Square Kilometer Array. Key Points: One hundred eighty hours of data from the GLEAM survey at frequencies below 100 MHz were used to image ionospheric structures over a ∼50° field of viewMost wavefronts were found to have one of three orientations: (1) field aligned, (2) nearly east‐west, and (3) northeast to southwestCategory (2) wavefronts appear associated with shear within the jet stream; category (3) waves appear associated with sporadic E [ABSTRACT FROM AUTHOR]

A complex daytime sporadic E (Es) case with extremely high critical frequency (foEs) was observed over the low latitude of China on 19 May 2018. Simultaneous observational results from two very high frequency (VHF) radars, two ionosondes, and multiple Global Navigation Satellite System total electron content and scintillation receivers are analyzed to investigate the evolution of the complex Es occurrence, which consisted of a relatively weak ambient Es layer (foEs < 8 MHz) and band‐like strong Es structures (foEs > 17 MHz) drifting from higher latitude. The strong Es structures elongated more than 500 km in the northwest‐southeast direction, drifted southwestward at a speed of ~65 m/s. VHF radar backscatter echoes were generated when the strong Es structures passed the radar field of view, with different echo patterns due to different radar and antenna configurations. No VHF radar backscatter echo was associated with the ambient Es layer. The mechanisms responsible for the formations of the ambient Es layer and band‐like strong Es structures are addressed and discussed. Key Points: Daytime complex Es composed of a relatively weak ambient Es layer and drifting strong Es was observed over low‐latitude ChinaThe strong Es structures showed band‐like elongation aligned NW‐SE, drifting southwestward with velocity of ~65 m/sVHF radar backscatter echoes were generated with different echo patterns due to different radar and antenna configurations [ABSTRACT FROM AUTHOR]

This study analyzes strong sporadic E layer (Es) formation in Boa Vista (BV, 2.8°N, 60.7°W, dip: 18°), a low‐latitude region in the Brazilian sector, which occurred far after the onset of a magnetic storm recovery phase. Such occurrences were observed during seven magnetic storms with available data for BV. Thus, the ionospheric behavior on days around the magnetic storm that occurred on 20 January 2016 was investigated to search for possible explanations. This analysis indicated that the probable mechanism acting during the Es layer strengthening is the zonal westward electric field caused by a disturbance dynamo. The same evidence was also observed in two other magnetic storms at the same location. Hence, a numerical model of the E region dynamics, called MIRE (Portuguese acronym for E Region Ionospheric Model), was used to confirm whether the disturbance dynamo could cause the Es layer intensification. The inputs for the model were the electric field deduced from the vertical drift and the wind components provided by GSWM‐00 model. The simulations indicate that the Es layer density is significantly enhanced when the zonal electric field is present compared to the reference scenario with only the winds. Therefore, it is concluded that the disturbance dynamo electric field is the likely cause of the strong Es layers in the analyzed cases. Finally, the combined results from the model and observational data seem to contribute significantly to advance our understanding of the role of the electric fields in the Es layer formation at low latitudes. Key Points: Data analysis and modeling taking into account wind and E field are employed to study anomalous Es layers in Boa VistaThe results show that the most probable mechanism responsible for the Es layer strengthening in Boa Vista is the zonal westward electric field caused by the disturbance dynamoSimulations support our assumption that the disturbance dynamo electric field leads the observed Es layer intensification in Boa Vista [ABSTRACT FROM AUTHOR]

Ionospheric anomalies before earthquakes termed as seismo‐ionospheric precursors have been extensively discussed due to the importance of earthquake prediction. Electric field driven mechanism is commonly used to explain seismo‐ionospheric precursors. Kim et al. (1993) first theoretically demonstrated that seismogenic electric fields could form intensified sporadic E layers in higher altitudes, which is so influential that motivates considerable statistical work on variations of foEs and h'Es before earthquakes. We attempt to establish a physical model of sporadic E layers at middle latitudes based on wind shear theory with the objective to reexamine the influence of seismogenic electric fields on sporadic E layers. The results show that zonal electric fields of several mV/m can influence the formation of higher sporadic E layers: For existing higher sporadic E layers, eastward/westward electric fields are capable of inhibiting/facilitating the existing layers accompanied by ascent/descent in altitude. For normal E region without sporadic E layers, the effect of eastward electric fields is not notable, while westward electric fields are able to form wider sporadic E layers. Taking into account their complicated response and inherently high variability, a suggestion is made about the necessity to be cautious when attributing variations of sporadic E layers to forthcoming earthquakes. Key Points: A sporadic E layer model considering ionospheric and metallic ions at middle latitudes is established based on shear wind theoryResponse of higher sporadic E layers depends on the directions of presumably seismogenic electric fieldsComplicated response and inherently variability of sporadic E layers make it hard to attribute sporadic E layer variations to earthquakes [ABSTRACT FROM AUTHOR]

This paper describes insights into the nature of corotating plasmaspheric irregularities (CPIs) enabled by a newly developed method for range‐ and time‐resolved tomographic images of these structures. The method is based on high‐precision measurements of total electron content gradients measure toward cosmic radio sources using an interferometric radio telescope, the Very Large Array (VLA). Exploiting hundreds of hours of data from the VLA Low‐band Ionosphere and Transient Experiment, we confirm that CPIs are predominantly detected at night and at L shells ∼2–4. Combining this large data set with other ionospheric, atmospheric, and space weather databases, we have established that CPI detection rates are much higher when levels of solar and geomagnetic activity are low. We also demonstrate that higher detection rates coincide with drivers of perturbations in the ionospheric electric field, including sporadic E and gravity waves. The gravity wave sources most commonly associated with CPIs are jet stream bend/shear and substorm‐triggered atmospheric disturbances. We also show that simulations of the plasmaspheric impact of both gravity wave‐driven electric field perturbations and polarization electric fields associated with electrobuoyancy waves/sporadic E produce results that are very similar to what is observed with the VLA. Key Points: A new method has been developed to generate range‐ and time‐resolved images of corotating plasmaspheric irregularities (CPIs)More than 300 hr of range/time imaging data have been generated with the Very Large Array (VLA) radio telescope using this methodThese data imply that CPIs are generally caused by perturbations in the ionospheric electric field due to gravity/electrobuoyancy waves [ABSTRACT FROM AUTHOR]

This paper investigates the variations of middle‐ and low‐latitude sporadic E (Es) layers during 2011–2012 and 2012–2013 sudden stratospheric warming (SSW) events by using observations from six ionosondes in East Asia over China and Japan region. Observations of Es critical frequency (foEs) at all these ionosondes present obvious enhancements around the days of new and full moon during SSW periods. Wavelet spectra of foEs during two SSW events exhibit noticeable enhanced 14.5‐day modulation, which resembles the lunar semimonthly period. In addition, simultaneous wind measurements by meteor radar also show enhancement of 14.5‐day periodic oscillation after SSW onset. Tidal components extracted from meteor radar wind measurements in mesosphere and lower thermosphere region and from ionospheric F region critical frequency (foF2) are noticeably modulated by the lunar phase. These observational evidences reveal that the semimonthly lunar period of 14.5 days can be a contributing factor to variations of Es layer during SSW event. Key Points: The foEs observed at middle‐ and low‐latitude show evident enhancement around the day of new and full moon during 2011–2012 and 2012–2013 SSWfoEs presents enhancement of 14.5‐day wave‐type oscillationsThe variations of sporadic E layers in middle and low latitudes during SSW periods can be closely linked to the lunar cycle [ABSTRACT FROM AUTHOR]

Ionospheric sporadic E layer is thin irregularity with much higher plasma density in the ionospheric E region (~90‐120 km). Morphology of sporadic E intensity is investigated by using the COSMIC radio occultation data during 2007‐2012. Maximum gradient value of total electron content fluctuation is defined as Smax index, and it shows good linear relationship with the sporadic E intensity parameter (ordinary critical frequency, foEs) in the low‐latitude and midlatitude regions. By using this Smax index as the sporadic E layer intensity, distribution of sporadic E intensity is obtained. Some known features are confirmed such as the hemisphere summer enhancement, diurnal and semidiurnal behavior, and intensity depression anomaly regions. New findings are also obtained, especially the different behavior pattern in the low‐latitude region. (1) Both positive and negative correlations exist between sporadic E intensity and solar activity, and this correlation also shows complex magnetic latitude dependency. (2) Weaker seasonal variation is found in the low‐latitude region. Besides, hemisphere asymmetries of sporadic E intensity/location are also found during the equinox. (3) Longitudinal wave number‐4 feature of sporadic E intensity is prominent in the lower latitude region, which may be related to the diurnal eastward wave number‐3 tide. In a word, it is feasible to investigate the sporadic E layer intensity distribution based on radio occultation data, which also allows for a global morphology analysis. Key Points: Correlation between sporadic E intensity and solar activity shows complex magnetic latitude dependencyWeaker seasonal variation is identified in low‐latitude region, as well as hemisphere asymmetries of sporadic E intensity during equinoxLongitudinal WN4 feature is prominent in the lower latitude region, which may be related to the diurnal eastward WN3 tide [ABSTRACT FROM AUTHOR]

In the long era of sporadic E layer (Es) ionosonde research, the ordinary wave critical frequency foEs is used as a measure of Es layer occurrence and intensity. This practice, however, undermines that sporadic E layers are in fact metal ion layers, whereas foEs relates inherently to the sum of both the layer metal and the regular E region plasma densities. This means that foEs acts as an overestimate of Es intensity, a fact that somehow has been overlooked and escaped attention. To deal with this deficiency, an algorithm is introduced which combines the ionosonde‐measured foEs and virtual height h'Es parameters with International Reference Ionosphere model predictions of E region electron densities, to arrive at a new critical frequency which depends on sporadic E metal plasma density only; therefore, it represents an unbiased estimate of Es layer intensity. The extensive use of foEs in numerous sporadic E studies must have introduced errors in various results in relation with the Es variability in the time, frequency, and space domains. It is therefore important that this new parameter, notated as foμEs, is now adopted and used instead of foEs in the evaluation of sporadic E. The same methodology applies also for the sporadic E blanketing critical frequency fbEs, which at times is taken as an alternative estimate of Es intensity; similarly, a new parameter, notated as fbμEs, should be used instead of fbEs. Key Points: The ionosonde foEs critical frequency is used as a measure of sporadic E layer intensity; this undermines that Es are metal ion layersfoEs overestimates sporadic E intensity because it relates to the sum of the layer metal atomic ion and E region molecular ion densitiesA method is developed combining ionosonde Es parameters and IRI model electron densities to derive an unbiased estimate of Es intensity [ABSTRACT FROM AUTHOR]

We analyze tidal (diurnal, semidiurnal, terdiurnal, quarterdiurnal) phases and related wind shear in the mesosphere/lower thermosphere as observed by meteor radar over Collm (51.3 ∘ N, 13.0 ∘ E). The wind shear phases are compared with those of sporadic E (Es) occurrence rates, which were derived from GPS radio occultation signal-to-noise ratio (SNR) profiles measured by the COSMIC/FORMOSAT-3 satellites. At middle latitudes Es are mainly produced by wind shear, which, in the presence of a horizontal component of the Earth's magnetic field, leads to ion convergence in the region where the wind shear is negative. Consequently, we find good correspondence between radar derived wind shear and Es phases for the semidiurnal, terdiurnal, and quarterdiurnal tidal components. The diurnal tidal wind shear, however, does not correspond to the Es diurnal signal. [ABSTRACT FROM AUTHOR]

Abstract Imaging observations of faint meteors were carried out on April 11 and 14, 2016 with a wide-field CMOS mosaic camera, Tomo-e PM, mounted on the 105-cm Schmidt telescope at Kiso Observatory, the University of Tokyo. Tomo-e PM, which is a prototype model of Tomo-e Gozen, can monitor a sky of ∼ 1.98 deg 2 at 2 Hz. The numbers of detected meteors are 1514 and 706 on April 11 and 14, respectively. The detected meteors are attributed to sporadic meteors. Their absolute magnitudes range from + 4 to + 10 mag in the V -band, corresponding to about 8.3 × 10 − 2 to 3.3 × 10 − 4 g in mass. The present magnitude distributions we obtained are well explained by a single power-law luminosity function with a slope parameter r = 3.1 ± 0.4 and a meteor rate log 10 N 0 = − 5.5 ± 0.5. The results demonstrate a high performance of telescopic observations with a wide-field video camera to constrain the luminosity function of faint meteors. The performance of Tomo-e Gozenis about two times higher than that of Tomo-e PM. A survey with Tomo-e Gozenwill provide a more robust measurement of the luminosity function. Highlights • More than 2000 faint meteors were recorded in two days with a newly-developed wide-field CMOS mosaic camera, Tomo-e PM. • The visual magnitudes of the detected meteors range from +4 to +10 mag. • The present magnitude distribution is consistent with a power-law function with a slope parameter r = 3.1 ± 0.4 and a meteor rate log 10 N 0 = −5.5 ± 0.5. • Tomo-e Gozen, a successor to Tomo-e PM, will provide a practical tool to investigate the luminosity function of faint meteors. [ABSTRACT FROM AUTHOR]

Abstract: Ionospheric anomaly crest regions are most challenging for scientific community to understand its mechanism and investigation, for this purpose we are investigating some inospheric result for this region. The study is based on the ionogram data recorded by IPS-71 Digital Ionosonde installed over anomaly crust region Bhopal (Geo. Lat. 23.2° N, Geo. Long 77.4° E, Dip latitude 18.4°) over a one year period from January 2010 to December 2010. The studies were examined in four different variations such as: Hourly variation, diurnal variation, seasonal variation and hourly-seasonal variation. The occurrence probability of this layer is highest in summer solstice, moderate during equinox and low during winter solstice. Remarkable occurrence peaks appear from June to July in summer and from December to January in winter. The layer occurrence showed a double peak variation with distinct layer groups, in the morning between 0000-0400 UT and the other during evening between 1100-1600 UT. The morning layer descent was associated with layer density increase indicating the strengthening of the layer while it decreased during the evening layer descent. The result indicates the presence of semi-diurnal tide over the location while the higher descent velocities could be due to the modulation of the ionization by gravity waves along with the tides. The irregularities associated with the gradient-drift instability disappear during the counter electrojet and the current flow is reversed in westward. [ABSTRACT FROM AUTHOR]

By using the 2015–2016 data set of newly built Wuhan very high-frequency (VHF) radar, we investigate the occurrence of E-region field-aligned irregularities (FAIs) in mid-latitude China region for the first time. Wuhan E-region FAIs present the strongest occurrence of quasi-periodic (QP) echoes at postsunset period in the height range of 100–120 km and moderate occurrence of continuous echoes at postsunrise period in the height range of 90–100 km. Characteristics including temporal and altitudinal distribution, Doppler spectra and period of QP echoes are presented from a statistical point of view. We find that E-region FAIs observed by Wuhan VHF radar show strong linkage with the concurrent sporadic E layer observed by ionosonde. In general, Doppler spectra present type 2 feature with velocity in the range of ±50 m/s and width less than 50 m/s. Our results also indicate that mid-latitude E-region FAIs are closely associated with Es layer. Several mechanisms were proposed to interpret the mid-latitude E-region FAIs; however, further investigation is required to understand the generation with different ionospheric background and irregularity types. [ABSTRACT FROM AUTHOR]

This paper presents a case study exploring the variability of daytime ionospheric sporadic E (Es) during Counter Equatorial Electrojet (CEJ) events over Trivandrum (8.5°N, 77°E, 0.5°N dip lat.), a dip equatorial station in India. It makes use of collocated measurements of (a) daytime mesopause temperature estimated using a Multiwavelength Dayglow Photometer, (b) base height of sporadic E-layer i.e. E sq obtained from a Digital Ionosonde, (c) Equatorial Electrojet (EEJ) induced magnetic field at the surface measured using a Proton Precession Magnetometer and (d) neutral meridional and zonal winds measured using meteor wind radar. The study addresses why, only on certain CEJ days, the Es layer turns into a blanketing Es layer, also referred to as E sb layer, appearing for a brief period and almost simultaneously as the CEJ induced magnetic field on the surface is either zero or very small, and not on all the CEJ days despite the reversal of the zonal winds in the dynamo region (∼98 km). Further, a simulation using the simultaneously measured zonal wind and temperature shows that during CEJ, especially when the zonal wind reverses and the mesopause temperature lowers, the conditions are in fact less favourable for the ionization to converge resulting in E sb . On the other hand, on such occasions, the meridional wind exhibits a tendency to turn equatorward with time with the changeover gradually happening as the altitude decreases. These observations have been discussed to allude to the possible role of the overall wind system and its spatio-temporal changes in the ionospheric altitudes which could influence the gradual transition of E sq to E sb over the dip equator. [ABSTRACT FROM AUTHOR]

The results of many-year photometric observations of the weak-line T Tauri star V715 Per in the optical (V RI) and infrared (JHK) photometric bands are presented. The period of the star’s lowamplitude brightness variations in the V RI bands detected earlier, 5.23d, is confirmed. This period persists during the entire 14-year time interval of the observations, but its amplitude varies with time. The same period was found in the variations of JHK infrared fluxes, with the brightness variations in the two ranges being almost synchronous. The most probable origin of these variations is periodic eclipses of the star by its own disk, perturbed by its interaction with the magnetosphere (AA Tau-type variations). In addition to the periodic brightness variations, the star also displayed sporadic Algol-like minima characteristic of UX Ori stars during several years (2005-2011). The amplitude of these variations increasedmonotonically, reaching approximately 1m in the V band by the end of 2010, after which the deep fadings ended. During this entire time interval, the amplitude of the periodic variations was observed to decrease. After 2011, the periodic component began to become stronger again. These changes of the photometric activity of V715 Per can be explained by an increasing rate of gas accretion onto the star, decreasing the radius of warped regions of the disk and leading to accompanying Algol-like fadings. This model assumes a low inclination of the circumstellar disk in V715 Per to the line of sight. [ABSTRACT FROM AUTHOR]

This paper summarizes the years of studies devoted to the self-similarity of anomalies originating in the ionosphere above the regions of the preparation of strong earthquakes. Using statistical processing of data on electron density variations obtained by methods of vertical sounding and measurements of the total electronic content, we have formed a pattern of similar variations observed at midlatitudes before strong earthquakes; we call it a precursor mask for earthquakes. It was found that the positive anomaly in the ionosphere formed at nighttime after sunset and ended at sunrise. In the case of strong earthquakes, the anomaly can last 12 h and emerge within a few days at the same local time. We propose a physical mechanism of anomaly formation in the ionosphere bound with the diurnal dynamics of the atmospheric boundary layer, which regulates the height distribution of cluster ions. [ABSTRACT FROM AUTHOR]

This work analysis the blanketing sporadic layers (Es b ) behavior over São Luís, Brazil (2° 31′ S, 44° 16′ W, dip: −4.80) which is classified as a transition region between equatorial and low-latitude. Hence, some peculiarities can appear as Es b occurrence instead of the common Es q , which is a non-blanketing irregularity layer. The analysis presented here was obtained using a modified version of a theoretical model for the E region (MIRE), which computes the densities of the metallic ions (Fe + and Mg + ) and the densities of the main molecular ions (NO + , O 2 + , N 2 + ) by solving the continuity and momentum equations for each one of them. In that model, the Es layer physics driven by both diurnal and semidiurnal tidal winds are taken into account and it was extended in height coverage by adding a novel neutral wind model derived from the all-sky meteor radar measurements. Thus, we provide more trustworthy results related to the Es layer formation in the equatorial region. We verified the contribution of each tidal wind component to the Es b layer formation in this equatorial region. Additionally, we compared the Es layer electron density computed by MIRE with the data obtained by using the blanketing frequency parameter ( fb Es) deduced from ionograms. The results show that the diurnal component of the tidal wind is more important in the Es b layer formation whereas the semidiurnal component has a little contribution in our simulations. Finally, it was verified that the modified MIRE presented here can be used to study the Es b layers occurrence over the equatorial region in the Brazilian sector. [ABSTRACT FROM AUTHOR]

The radio occultation experiment aboard the FORMOSAT-3/COSMIC satellites enables the observation of phenomena in Earth's ionosphere on a global scale. Numerous radio occultation profiles are used to analyse the occurrence of sporadic E layers as well as its properties. We will present a new method to approach additionally to the presence of sporadic E also its intensity which is closely related to the blanketing frequency ( f b E s ) provided by ionosondes. We observed that the sporadic E occurrence and its intensity show a highly developed annual cycle with high occurrence rates and intensities in the actual summer hemisphere. The global latitude/longitude distribution of both parameters is strongly related to Earth's magnetic field which is reflected by the missing of sporadic E observations along the magnetic equator. [ABSTRACT FROM AUTHOR]

We present the first simultaneous observation of mesopause sodium (Na) and potassium (K) layer by a lidar which has Na and K channel simultaneously at the South Hemisphere site, São José dos Campos (23.1°S, 45.9°W). Measurements reported here were conducted on two nights with 3.5 and 8 h of observations in November 2016. On 20 November 2016, sporadic layers in both Na and K layer occurred above 100 km, and the higher layers corresponded well with sporadic E (Es) layer. And the density of Na at 100–105 km is higher than that at main layer around 90 km, but K density around 100 km is at least 3 times smaller compared with the K density around 90 km for the similar period. On 21 November 2016, both sporadic layers occurred in main layer height with obvious descending variations with time, which seems like tidal induced. Notably, the peak K/Na ratio slowly increased with time. And Na layer and K layer showed different processes along with time with K density reaching its maximum 1 h later than that of Na. Correlations of Na/K density, Es, and winds were also discussed. [ABSTRACT FROM AUTHOR]

This work presents new results about sporadic E-layers (Es layers) using GPS (global positioning system) radio occultation (RO) measurements obtained from the FORMOSAT-3/COSMIC satellites and digisonde data. The RO profiles are used to study the Es layer occurrence as well as its intensity of the signal-to-noise ratio (SNR) of the 50 Hz GPS L1 signal. The methodology was applied to identify the Es layer on RO measurements over Cachoeira Paulista, a low-latitude station in the Brazilian region, in which the Es layer development is not driven tidal winds only as it is at middle latitudes. The coincident events were analyzed using the RO technique and ionosonde observations during the year 2014 to 2016. We used the electron density obtained using the blanketing frequency parameter (fbEs) and the Es layer height (h'Es) acquired from the ionograms to validate the satellite measurements. The comparative results show that the Es layer characteristics extracted from the RO measurements are in good agreement with the Es layer parameters from the digisonde. [ABSTRACT FROM AUTHOR]

Ionosonde data and crustal earthquakes with magnitude M ≤ 6:0 observed in Greece during the 2003-2015 period were examined to check if the relationships obtained earlier between precursory ionospheric anomalies and earthquakes in Japan and central Italy are also valid for Greek earthquakes. The ionospheric anomalies are identified on the observed variations of the sporadic E-layer parameters (h0Es, foEs) and foF2 at the ionospheric station of Athens. The corresponding empirical relationships between the seismoionospheric disturbances and the earthquake magnitude and the epicentral distance are obtained and found to be similar to those previously published for other case studies. The large lead times found for the ionospheric anomalies occurrence may confirm a rather long earthquake preparation period. The possibility of using the relationships obtained for earthquake prediction is finally discussed. [ABSTRACT FROM AUTHOR]

We systematically compared the impacts of four Cr salts (chromic chloride, chromic nitrate, potassium chromate and potassium bichromate) on physiological parameters and chlorophyll fluorescence in indigenous moss Taxiphyllum taxirameum . Among the four Cr salts, K 2 Cr 2 O 7 treatment resulted in the most significant decrease in photosynthetic efficiency and antioxidant enzymes, increase in reactive oxygen species (ROS), and obvious cell death. Different form the higher plants, although hexavalent Cr(VI) salt treatments resulted in higher accumulation levels of Cr and were more toxic than Cr(III) salts, Cr(III) also induced significant changes in moss physiological parameters and chlorophyll fluorescence. Our results showed that Cr(III) and Cr(VI) could be monitored distinguishably according to the non-photochemical quenching (NPQ) fluorescence of sporadic purple and sporadic lavender images respectively. Then, the valence states and concentrations of Cr contaminations could be evaluated according to the image of maximum efficiency of PSII photochemistry (Fv/Fm) and the quantum yield of PSII electron transport (ΦPSII). Therefore, this study provides new ideas of moss's sensibility to Cr(III) and a new method to monitor Chromium contaminations rapidly and non-invasively in water. [ABSTRACT FROM AUTHOR]

Possible thunderstorm – sporadic E (Es) layer coupling effects are investigated during two measurement periods, one in 2013 and one in 2014. The analysis was based on ionospheric observations obtained from a Digisonde at Pruhonice, the Czech Republic, an ionosonde at Nagycenk, Hungary, and a 3.59 MHz five-point continuous HF Doppler system located in the western part of the Czech Republic. The latter is capable of detecting ionospheric wave-like variations caused by neutral atmospheric waves generated by thunderstorms. The present study searches for possible impacts on Es layers caused by the presence of two active thunderstorms: one passing across the Czech Republic on June 20, 2013 (19:00–01:00 LT), and one through Hungary on July 30, 2014 (11:00-01:00 LT). During these two time periods, presence and parameters of Es layer were inferred from ionograms, recorded every minute at Pruhonice and every two minutes at Nagycenk, whereas concurrent lightning activity was monitored by the LINET detection network. In addition, transient luminous events (TLEs) were also observed during both nights from Sopron, Hungary and from Nýdek, the Czech Republic. A noticeable fact was the reduction and disappearance of the ongoing Es layer activity during part of the time in both of the traversing thunderstorms. The analysis indicated that the critical frequency foEs dropped below ionosonde detection levels in both cases, possibly because of thunderstorm activity effects. This option, however, needs more case studies in order to be further substantiated. [ABSTRACT FROM AUTHOR]

We study the causes of sporadic and long-term variations in the polarization spectrum of the ultralow-frequency (ULF) magnetic background noise at midlatitudes. Data records of low-frequency horizontal magnetic components at the Novaya Zhizn midlatitude observatory of the Radiophysical Research Institute (56N, 45.74E) and the Japanese station Moshiri (44.37N, 142.27E) were used. Ionosonde data from the sites located in Russia (Vasilsursk station) and in Japan (Wakkanai station) were also analyzed. The effect of the sporadic E layers on the frequency spectrum of noise polarization was detected. It is shown that the appearance of quite intense sporadic Es layers with the cutoff frequencies f0E > 3-5 MHz can significantly alter the polarization spectrum parameters, which is due to variations in the optical depth and Q factor of the sub-ionospheric Alfvén resonator (sub-IAR) formed by the valley between the E and F regions. Numerical simulation of the polarization parameters of the background noise using the IRI-2012 model corrected by the ionosonde data confirmed that the Es layer about 5 km thick, with the cutoff frequencies f0E > 3-5 MHz, may lead to a sharp decrease in the boundary frequency f between the frequency ranges of the left- and right-hand polarized noise, or even to a complete disappearance of the sub-IAR manifestation in the polarization parameter spectrum. Numerical calculations have also revealed the impact of the altitude position of the E layer on the Q factor of the sub-IAR. The effect of variations in the altitude and cutoff frequency of the F-layer maximum, as well as the electron density at the altitudes of the E layer and the valley, on the features of the diurnal dynamics of the ULF noise polarization spectra is discussed. [ABSTRACT FROM AUTHOR]

Three experiments assessed how appetitive conditioning in rats changes over the duration of a trace conditioned stimulus (CS) when unsignaled unconditioned stimuli (USs) are introduced into the intertrial interval. In Experiment 1, a target US occurred at a fixed time either shortly before (embedded), shortly after (trace), or at the same time (delay) as the offset of a 120-s CS. During the CS, responding was most suppressed by intertrial USs in the trace group, less so in the delay group, and least in the embedded group. Unreinforced probe trials revealed a bell-shaped curve centered on the normal US arrival time during the trace interval, suggesting that temporally specific learning occurred both with and without intertrial USs. Experiments 2a and 2b confirmed that the bulk of the trace CS became inhibitory when intertrial USs were scheduled, as measured by summation and retardation tests, even though CS offset evoked a temporally precise conditioned response. Thus, an inhibitory CS may give rise to new stimuli specifically linked to its termination, which are excitatory. A modification to the microstimulus temporal difference model is offered to account for the data. [ABSTRACT FROM AUTHOR]

The fall armyworm, Spodoptera frugiperda (J. E. Smith)(Lepidoptera: Noctuidae), is an important agricultural pest of the Western Hemisphere noted for its broad host range, long distance flight capabilities, and a propensity to develop resistance to pesticides that includes a subset of those used in genetically modified corn varieties. These characteristics exacerbate the threat fall armyworm poses to agriculture, with the potential that a resistance trait arising in one geographical location could rapidly disseminate throughout the hemisphere. A region of particular concern is the Caribbean, where a line of islands that extends from Florida to Venezuela provides a potential migratory pathway between populations from North and South America that could allow for consistent and substantial genetic interactions. In this study, surveys of populations from Peru, Bolivia, Paraguay, and Trinidad & Tobago expand on previous work in South America that indicates a generally homogeneous population with respect to haplotype markers. This population differs from that found in most of the Lesser Antilles where a combination of genetic and meteorological observations is described that indicate fall armyworm migration from Puerto Rico to as far south as Barbados, but does not support significant incursion into Trinidad & Tobago and South America. Air transport projections demonstrate that the wind patterns in the Caribbean region are not conducive to consistent flight along the north-south orientation of the Lesser Antilles, supporting the conclusion that such migration is minor and sporadic, providing few opportunities for genetic exchanges. The implications of these findings on the dissemination of deleterious traits between the two Western Hemisphere continents are discussed. [ABSTRACT FROM AUTHOR]

Topography exerts a key role in controlling permafrost distribution in areas where mean annual temperatures are slightly negative. One such case is the low-altitude environments of Maritime Antarctica, where permafrost is sporadic to discontinuous below 20–40 m asl and continuous at higher areas and active layer dynamics are thus strongly conditioned by geomorphological setting. In January 2014 we installed three sites for monitoring active layer temperatures across Byers Peninsula (Livingston Island, South Shetland Islands) at elevations between 45 and 100 m. The sites are situated in lake catchments (lakes Escondido, Cerro Negro, and Domo) that have different geomorphological and topographical conditions. Our objective was to examine the role of topography and microclimatic conditions in determining the active layer thermal regime in order to identify the factors that control geomorphic processes in these lake catchments. At each site a set of loggers was installed to monitor air temperature (AT), snow thickness (SwT) and soil temperature (ST) down to 80 cm depth. Mean annual air temperatures (MAAT) showed similar values in the three sites (− 2.7 to − 2.6 °C) whereas soil temperatures showed varying active layer thicknesses at the three catchments. The ground thermal regime was strongly controlled by soil properties and snow cover thickness and duration, which is influenced by local topography. Geomorphological processes operating at the lake catchment scale control lacustrine sedimentation processes, and both are dependent on the combination of topographical and climatic conditions. Therefore, the interpretation of lake sediment records from these three lakes requires that soil thermal regime and snow conditions at each site be taken into account in order to properly isolate the geomorphological, environmental and climatic signals preserved in these lake records. [ABSTRACT FROM AUTHOR]

Following general explanations of the working principles of different existing retardation systems to restrain an advancing powerless ship the principles of a new overhead retardation system are presented. A two dimensional simplified model of the activated overhead system is formulated based on Huston’s interpretation of the Kane methodology. Reduced Kane equations are used in the actual simulation, once initial conditions and mechanical analysis of constituent elements have been formulated. Having presented the computational process the various velocity, motion and joint constraint force characteristics of the anchor, the ship and the other elements are monitored in the time domain for the duration of the retardation process. Validation of the Kane based method is established utilising the conservation law and the Lagrangian based formulation of the retardation system within the ADAMS software. The results indicate that a peak value of constraint will occur because of the sudden movement of anchor and this peak is affected significantly by initial ship speed. Variation in anchor chain, overall cable length and its horizontal projected length has little influence upon retardation system performance, whilst the changes of sea bed friction, anchor mass, water depth, initial ship velocity and ship mass will make retardation behaviour different. [ABSTRACT FROM AUTHOR]

This work presents new results about simulations of blanketing sporadic E-layers, Es b , using a modified version of a theoretical model for the E region (MIRE) for a Brazilian region: Cachoeira Paulista, a low latitude station. MIRE computes the densities of the metallic ions (Fe + and Mg + ) and of the main molecular ions (NO + , O 2 + , N 2 + ) by solving the continuity and momentum equations for each one of them. Additionally, this model includes the physics of Es layer development driven by tidal winds. In this study, we extend MIRE adding a novel neutral wind model derived from the all-sky meteor radar measurements, which provides more trustworthy results related to the Es layer formation in the Brazilian sector. Afterwards, this new model is validated comparing the computed electron density for the Es layer with the electron density obtained using the blanketing frequency parameter ( fb Es) deduced from ionograms in the analyzed region. The results show that the values computed by the extended MIRE are in good agreement with the observational data for the Es layers formed by the wind shear mechanism. Therefore, the extended MIRE presented in this work is the only available model that allows simulating Es b layers with a much higher confidence level for the low-latitude in the Brazilian sector. [ABSTRACT FROM AUTHOR]

Background: Avian influenza virus (AIV) causes both severe outbreaks and endemic disease among poultry and has caused sporadic human infections in Asia, furthermore the routes of transmission in avian species between geographic regions can be numerous and complex. Using nucleotide sequences from the internal protein coding segments of AIV, we performed a Bayesian phylogeographic study to uncover regional routes of transmission and factors predictive of the rate of viral diffusion within China. Results: We found that the Central area and Pan-Pearl River Delta were the two main sources of AIV diffusion, while the East Coast areas especially the Yangtze River delta, were the major targets of viral invasion. Next we investigated the extent to which economic, agricultural, environmental and climatic regional data was predictive of viral diffusion by fitting phylogeographic discrete trait models using generalised linear models. Conclusions: Our results highlighted that the economic-agricultural predictors, especially the poultry population density and the number of farm product markets, are the key determinants of spatial diffusion of AIV in China; high human density and freight transportation are also important predictors of high rates of viral transmission; Climate features (e.g. temperature) were correlated to the viral invasion in the destination to some degree; while little or no impacts were found from natural environment factors (such as surface water coverage). This study uncovers the risk factors and enhances our understanding of the spatial dynamics of AIV in bird populations [ABSTRACT FROM AUTHOR]

It has long been recognized that composting yields a large quantity of thermal energy, which is normally lost to the surrounding environment as heat. Efforts to recover this heat using compost heat recovery systems (CHRSs) have been sporadic. Literature on the subject is also disjointed. To summarize the research that has been conducted, the authors performed an extensive literature review, covering publications in scientific journals, trade magazines, books, theses, and published reports. A focus on CHRS design and heat recovery rates is presented. The review covers 45 CHRSs in 16 different countries, ranging from simple hotbeds used in China 2000 years ago, to advanced super-thermal conductor heat pipe systems in 2016. Heat recovery rates varied significantly, with no predictable trend among the 45 systems. Recovery rates averaged 1895 kJ/hr (1159 kJ/kg DM) for lab-scale systems, 20,035 kJ/hr (4302 kJ/kg DM) for pilot-scale systems, and 204,907 kJ/hr (7084 kJ/kg DM) for commercial systems. [ABSTRACT FROM AUTHOR]

The paper presents a comparative study of the ionospheric sporadic E layer parameters (fbEs, foEs, and h'Es) retrieved from ground based ionosonde at mid latitude station Yamagawa, Japan (31.20 N, 130.370 E) during the ascending phase of 24th solar cycle i.e. during January 2012 to December 2014. The comparison between the E-region parameters has been carried out on a diurnal, seasonal, annual and day night basis. The diurnal maxima of foEs, fbEs, and h'Es are generally higher during high solar activity. From the present study it is found that the highest values of fbEs are observed during the summer while the lowest values are observed during autumn at mid latitude. Similarly, the highest values of foEs are observed during the summer season while the lowest values are recorded in autumn season. However, the highest values of h'Es are recorded during the spring and the lowest values are recorded in autumn. The variability of Es during the day and night time is also studied. The sporadic E can form and disappear in a short time during either the day or night. We have also studied the percentage occurrence of sporadic E. The occurrence of Es changes from year to year. [ABSTRACT FROM AUTHOR]

In the present work, we analyze the competition between tidal winds and electric fields in the formation of blanketing sporadic E layers (Es) over São Luís, Brazil (2° 31′ S, 44° 16′ W), a quasi-equatorial station. To investigate this competition, we have used an ionospheric E region model (MIRE) that is able to model the Es layers taking into account the E region winds and electric fields. The model calculates the densities for the main molecular and metallic ions by solving the continuity and momentum equations for each of the species. Thus, the main purpose of this analysis is to verify the electric fields role in the occurrence or disruption of Es layers through simulations. The first results of the simulations show that the Es layer is usually present when only the tidal winds were considered. In addition, when the zonal component of the electric field is introduced in the simulation, the Es layers do not show significant changes. However, the simulations show the disruption of the Es layers when the vertical electric field is included. In this study, we present two specific cases in which Es layers appear during some hours over São Luís. We can see that these layers appear when the vertical electric field was weak, which means that the tidal components were more effective during these hours. Therefore, the vertical component of the electric field is the main agent responsible for the Es layer disruption. [ABSTRACT FROM AUTHOR]

A comprehensive study of the ionospheric processes encountered during the superstorm which started on March 17th 2015 has been carried out using magnetometer, ionosonde, riometer, ionospheric tomography and an all-sky camera installed in the observatory of Sodankylä, Finland. The storm manifested a number of interesting features. From 12:00 on March 17 there was a significant decrease of critical frequencies foF2 and intensive sporadic Es layers were observed. During the disturbance, there was a lack of variation of the X-component of the magnetic field at times, but the absorption level measured by the riometer was high. A comparison of the electron density distributions for the quiet and disturbed days as shown in the tomography data were very different. Where results were available at the same times, the tomographic foF2 values coincided with the “real” foF2 values from the ionosonde. Where the ionosonde data was missing due to absorption, the tomographic foF2 values were used instead. The keograms from the all-sky camera showed that during disturbed days the aurorae manifested themselves as bright discrete forms. It was shown that the peaks of absorption due to particle precipitation seen by the riometer coincided in time with the brightenings of aurorae seen on the keograms. [ABSTRACT FROM AUTHOR]