Daytime Ionospheric TEC Weather Study Over Latin America Romero‐Hernandez, E.; Denardini, C. M.; Takahashi, H. ...
Journal of geophysical research. Space physics,
December 2018, 2018-12-00, 20181201, Letnik:
123, Številka:
12
Journal Article
Recenzirano
Odprti dostop
The present work is the first of a two‐part weather study of the ionospheric Total Electron Content (TEC), based on data collected by four ground‐based Global Navigation Satellite System networks ...that cover the whole Latin America from the Patagonia to the north of Mexico. From the best of our knowledge, the maps presented here are the first TEC maps obtained using ground‐based data that covers the entire Latin America region, which represent an advance to the space weather monitoring and forecasting of the ionosphere. This work provides a qualitative and quantitative daytime analysis of the ionospheric TEC variation, which encompasses: (a) the response of TEC to the solar flux at midday; (b) the seasonal variation of TEC in different latitudinal ranges; and (c) the North‐South asymmetry of TEC over Latin America. The response to the solar flux is based on day‐to‐day TEC variations during two periods of different solar activity conditions: 2011 (ascending phase) and 2014 (maximum). The approximations of meridional wind component derived from Horizontal Wind Model‐14 model and hmF2 obtained from International Reference Ionosphere model were used. Equinoctial asymmetries with an opposite configuration in high and moderate solar activity were identified in the TEC variation. For 2011, it was related to the solar flux change. However, in 2014, according to the hmF2 variation, the influence of neutral wind becomes dominant. Among the results, we highlight an absence of winter anomaly in the Northern Hemisphere in 2014 and a stronger annual anomaly for latitudes under −20∘.
Key Points
The response of TEC to solar flux over Latin America is investigated
The seasonal variation of TEC over Latin America during daytime is analyzed
North‐South asymmetries of TEC over Latin America during daytime are identified
Main phase flux dropouts often promote depletion of the outer electron radiation belt. The quantification of the contributions of various loss mechanisms to MeV electron dropouts has not yet been ...elucidated in detailed case studies for moderate geomagnetic storms. This work focuses on quantifying radial diffusion to study relativistic electron flux losses observed by Van Allen Probes during two moderate storms in 2017. The events are identified as Case 1 (27 March), with losses deep in L, and Case 2 (21 November), with less deep losses. Event‐specific radial diffusion coefficients (DLL) were calculated from global magnetohydrodynamic (MHD) fields simulated by the SWMF/BATS‐R‐US. The MHD‐DLL was used as an input to radial diffusion simulations of both events for relativistic electrons. For the outer boundary conditions defined at L* = 6, electron fluxes measured by GOES‐15 at geosynchronous orbit were converted to phase space densities (PSDs) and then calibrated against the Van Allen Probe A measurements. Using these calibrated PSD of GOES‐15 at the outer boundary and event‐specific MHD‐DLL, the main phase dropout is well captured with radial diffusion simulation for Case 2, but not for the deep dropout in Case 1 down to L* < 4.5. Scaling MHD‐DLL based on validations of the MHD waves against in situ wave observations improves the simulation results of Case 1, but still does not fully resolve its deep dropout. However, analyzing the uncertainty of simulated PSD imposed by the uncertainty in the scaled MHD‐DLL, it was found that outward radial diffusion could still account for the losses at L* < 4.5.
Key Points
Two moderate geomagnetic storms with similar solar wind conditions produced MeV electron dropouts of different flux levels in the outer belt
Radial diffusion simulations performed for the case studies using event‐specific DLL capture the main phase dropouts above L* = 4.5
Stronger outward radial diffusion loss or additional mechanism is needed to explain losses down to L* < 4.5 in the strong dropout case
The rate of change of the geomagnetic field (dB/dt) observed at Earth’s surface has been used as a proxy of geomagnetically induced currents, which are known to be hazardous for grounded ...technological systems such as high-voltage power grid systems. The dB/dt rates have been well characterized in the high latitude region (≳60°), but much less information is available for the low latitudes to date. To overcome this limitation, we have examined dB/dt rates on the H component of the geomagnetic field as measured by an array of stations operated by the EMBRACE Magnetometer Network in Brazil. The main focus is to characterize dB/dt occurrence at very low latitudes (≲22°) of the Brazilian peculiar territory, whose magnetic measurements are influenced by the equatorial electrojet and the presence of the South Atlantic Magnetic Anomaly (SAMA). The period investigated is from 2021 to 2022, over the ascending phase of the solar cycle 25. The statistical analysis demonstrates that dB/dt peak magnitudes are generally below 0.5 nT/s during magnetic storms, and exhibit a dependence on the solar cycle for the station near the center of the SAMA. However, we obtain for a particular case in 2021 that dB/dt reached 1.35 nT/s in magnitude at the magnetic equator during daytime, which is a significant value even for higher latitudes. A case study of the induced geoelectric fields during this event shows that the conductivity structure beneath two compared sites plays a major role in the amplitude of such fields than dB/dt amplitude. Also, the MLT distributions of dB/dt indicate that ultra-low frequency waves can be a major source of these signals in lower latitudes.
•This study shows that significant values of dB/dt can be observed in low latitudes of Brazil.•There is an indication of solar cycle dependence on dB/dt obtained over the SAMA region.•We find that Earth’s ground conductance account to a great extent for GIC modeling.
Using global magnetohydrodynamic (MHD) simulations, we investigate the role played by a complex solar structure composed of a corotating interaction region (CIR) followed by solar wind Alfvénic ...fluctuations on the magnetosphere's nightside, equatorial electric field oscillations in the ultra-low-frequency range. A series of numerical experiments are performed employing synthetic solar wind inputs resembling those of a real CIR+Alfvénic fluctuation event that reached Earth's magnetosphere on 2003 April 20. The following is found: (i) Radial electric field component fluctuations are excited via magnetopause boundary motions driven either by solar wind density variations characteristic of CIRs or by solar wind Alfvénic fluctuations with a given oscillation period. (ii) Azimuthal electric field component fluctuations nearer to Earth, that is, at radial distances R less than about 5RE ( Earth radius), are apparently not related to either of the two types of sinusoidal solar wind Alfvénic fluctuations used in this study featuring monochromatic frequencies of 0.833 mHz (20-minute period) and 1.666 mHz (10-minute period). Instead, these innermost azimuthal component fluctuations show enhanced activity when inner magnetosphere convection increases as a result of a southward turning of the interplanetary magnetic field component Bz. (iii) Lastly, outermost (R 7 RE) azimuthal electric field oscillations weakly respond to monochromatic solar wind Alfvénic fluctuations by showing power spectral density peaks at both driving frequencies, but only near the flanks of the magnetopause, thus suggesting that such oscillations are being excited also owing to magnetopause boundary motions driven by solar wind Alfvénic fluctuations.
An economical and efficient approach to reduce the impact of P discharge by aquaculture industry is to adjust the P level in fish feeds to the precise nutrient requirement at different growth stages ...in a digestible nutrient basis. However, P requirement seems to be species specific and affected by several physiological, dietary and environmental factors. Based on the importance of tambaqui (Colossoma macropomum) to Latin American aquaculture, we designed a 63‐day trial to evaluate the effect of available P (AP) levels on growth, nutrient digestibility, haematology and blood biochemical parameters, carcass proximate composition and bone mineralization. Quadruplicate groups of tambaqui juveniles (144 ± 2.0 g) were fed five isonitrogenous (278 g kg−1 digestible protein) and isocaloric (13.5 Mj DE kg−1) diets containing graded AP levels (3.0, 5.6, 7.5, 9.1 and 11.0 g kg−1) following a completely randomized design. Dicalcium phosphate (DCP) was used as the main P source. No mortalities and signs of P deficiency were observed among the dietary treatments. A remarkably high P digestibility was observed in all plant‐based diets with a tendency of decreasing P digestibility with the increase in total P levels. Tambaqui seems to be able to grow well without inorganic P supplementation during the trials; however, this species required 7.0 g AP kg−1 diet for proper bone mineralization. P supplementation had a limited effect on haematology and blood biochemistry of tambaqui. Ecological implications of natural feeding habit and evolutionary position of this species are further discussed, and new hypothesis are drawn based on our results.
Ionospheric weather maps using the total electron content (TEC) monitored by ground‐based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been ...operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Contínuo) RBMC/Brazilian Institute for Geography and Statistics, Low‐latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total ~140 sites, have been used. TECMAPs with a time resolution of 10 min are produced in 12 h time delay. Spatial resolution of the map is rather low, varying between 50 and 500 km depending on the density of the observation points. Large day‐to‐day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1 TECU = 1016 el m−2 (TECU) <10) to the crest region (TECU > 80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS‐based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high‐technology positioning system and telecommunication.
Plain Language Summary
Ionospheric weather conditions over South American Continent are presented in term of the ionospheric total electron content (TEC), in other words, ionospheric plasma clouds. Large temporal and spatial variations of plasma clouds were observed. It is well known that the ionospheric variability affects GNSS signal propagation and results in satellite based positioning error. We present the plasma cloud variations by using 2‐dimensional TEC maps, and to estimate ionospheric range delay.
Key Points
Ionospheric weather monitored by total electron content (TEC)
Dynamical development of ionospheric plasma bubbles (IPB)
Influence of plasma bubbles on the GNSS‐based positioning system
On January 15, 2022, we observed various unusual atmospheric wave events over South America: Atmospheric pressure waves (Lamb mode) around 12:30 to 17:30 UT, tsunamis along the Chilean coast at ...around 17:00 to 19:00 UT, and ionospheric disturbances between 11:30 and 20:00 UT. We understand that these events were generated by the Tonga volcanic eruption that occurred at (20.55°S, 175.39°W) in South Pacific Ocean at 04:15 UT. Several traveling ionospheric disturbances (TIDs), the horizontal wavelengths of 330 to 1174 km and the phase speed of 275–544 m/s were observed before and after the Lamb wave passed over the continent and the arrival of the tsunami on the Chile coast. The observed TID characteristics suggest us that these waves might be generated by the two atmospheric events, Lamb wave and gravity waves induced by the tsunamis. This is the first time to report the signature of ionospheric disturbances over the South American continent generated by the huge volcanic eruption.
Graphical Abstract
Plain Language Summary
A huge volcanic eruption occurred at the volcano Hunga Tonga Hunga Ha’apai (20.55°S, 175.39°W), one of the islands of the Tonga archipelago in the South Pacific Ocean, on 15 January 2022, at 04:15 UT (Universal Time). The eruption released a huge amount of thermal energy into the atmosphere that reached up to ~ 50 km altitude. Such an explosive release of thermal energy produced atmospheric pressure waves, acoustic waves, and internal gravity waves in the lower atmosphere propagating horizontally and vertically up to the ionosphere (above 200 km altitude). The present work, as the first time, reports signatures of the ionospheric disturbances caused by the tsunami and atmospheric pressure waves over the South American continent.
Energy coupling between the solar wind and the Earth's magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external ...mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how ultralow frequency (ULF) wave activity during the passage of Alfvenic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on 22 September 2014, which coincides with the corotating interaction region preceding a high‐speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground‐ and space‐based observational data and global magnetohydrodynamic simulations and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L‐shells. Magnetohydrodynamic simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfven modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by phase space density calculations for this global recovery period.
We discovered and mapped a 1200 km‐long zone of enhanced electrical conductivity through a large array of magnetometers, over a narrow corridor parallel to the Paraguay and Araguaia belts which ...surround the Amazon craton. The anomaly has been further studied using magnetotelluric measurements made along a 300 km profile crossing the Paraguay belt; modeling shows the anomaly at this location as a very strong 100 km‐wide upper‐crust to mid‐crust conductor, located under a region where surficial rocks show an increase in deformation and metamorphism within the belt. From the high conductivity of the anomalous structure, its observed geometry and surface rock exposures, the most likely interpretation of its source is graphitized biogenic material in metasediments, now deeply underthrust in a Neoproterozoic or Early Cambrian suture zone. This result strongly supports the hypothesis that the collision between the Amazon plate and the western Paraná block has probably closed an ocean in the Paraguay belt region, contrary to former propositions of an ensialic evolution for this belt. Although the precise age of this ocean closure have been a matter of debate, our finding significantly constrains the tectonic setting of West Gondwana amalgamation involving the Amazon plate and its surrounding blocks.
Key Points
Mapping of geoelectric anomalies using a large array of magnetometers
Strong conductivity anomalies in the lithosphere marginal to the Amazon craton
Integration of GDS and MT data constrains the West Gondwana amalgamation
Mast cell tumours (MCTs) are one of the most frequent neoplasms in dogs. Glucocorticoids (GCs) are widely used in the management of this disease, although no guidelines for their use have been ...established. The aim of this study was to evaluate the correlation of MCT prognostic factors with measurable response to GCs. This retrospective study included 60 dogs treated with prednisone or prednisolone prior to surgical biopsy of MCT. Incisional or excisional biopsy was performed 7–14 days after initiation of GC therapy. Histopathology, immunohistochemical labelling for Ki67 and KITr, and polymerase chain reaction for the c-KIT gene were performed. Partial response occurred in 63.3% of cases (38/60), while 36.7% (22/60) did not respond. A response to GCs was correlated with lower stage of the disease, low histological grade, lower pattern of KITr expression and Ki67 score. Response to GCs was positively correlated with well-established favourable prognostic factors.
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