Journal of Atmospheric and Solar-Terrestrial Physics

South-Atlantic Anomaly magnetic storms effects as observed outside the International Space Station in 2008–2016

Thu, 08/16/2018 - 19:10

Publication date: Available online 16 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Tsvetan P. Dachev

Abstract

Two Liulin type spectrometers performed measurements of the energetic particles flux outside the International Space Station (ISS) in 3 long-term periods between 2008 and 2016. The linear regression analysis is performed of 1053 averaged per day South-Atlantic anomaly (SAA) proton flux measurements from the daily Dst index. The data reveal that the SAA flux dependence from the Joule heating in the high latitudes and respectively from the neutral atmosphere density, isn't observed only in the time of the magnetic storms. This is a permanent, continues process influencing the SAA fluxes all the time. The data, obtained during the two magnetic storms in 2010 and to powerful storms of March and June 2015, were used to find and classify the following short-term magnetic storm effects: 1) The SAA proton flux maximum and area show strong decrease during the main phase of the magnetic storms. The protons losses can be caused by the collisions with the storm-enhanced neutral oxygen atoms. This hypothesis is proved by a comparison with the prediction by the NRLMSISE-00 model global neutral Oxygen density; 2) Increase of the proton flux, in the presence of solar energetic protons, is observed during the storm sudden commencements (SSC); 3) An enhanced flux of relativistic electrons is recorded in SAA during the recovery phase of the magnetic storms at L-values higher than 1.7. They migrate from the outer radiation belt. Their presence was proved by the analysis of the energy deposition spectra.

Investigation on slab-thickness and B0 over an equatorial station in Africa and comparison with IRI model

Thu, 08/16/2018 - 19:10

Publication date: Available online 16 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): O.O. Odeyemi, J.O. Adeniyi, O.A. Oladipo, A.O. Olawepo, I.A. Adimula, E.O. Oyeyemi

Abstract

The present study investigates the simultaneous morphologies of slab-thickness (τ) and thickness parameter (Bo) over Ilorin (8.500 N, 4.680 E; dip lat. 2.95), an equatorial station, during a year of low solar activity (2010). The τ is deduced from global positioning system total electron content (GPS-TEC) while the F2 peak electron density (NmF2), from digisonde portable sounder (DPS). The use of measured TEC for this type of investigation takes care of the inclusion of plasmaspheric electron content (PEC). The PEC distributions on the topside and bottomside electron density (Ne) profile add considerably to the genuine signatures of τ and Bo. Therefore, the dynamic contributions of the PEC need to be emphasized for the accurate prediction of the ionospheric models. Apart from daytime signatures of the τ and Bo which are not primarily influenced by PEC, we found that between two and 3 h of pre-sunrise and dusk periods are mainly controlled by PEC which manifests as huge peaks in the τ and Bo. Also, our investigation reveals that the Bo profile is thicker than the τ profile during the pre-sunrise periods in June indicating partial flow or halt in PEC. The result revealed approximately the same values of τ and Bo around the sunrise period suggesting the absence or negligible PEC contributions. Our investigation also shows that there are maximum and minimum of the thickness in Bo and τ during the December solstice and June solstice, respectively. We also observed a moderate sunrise enhancement in τ that is not conspicuous in the Bo signature. On the relationship between the τ and Bo, we found a significant association between τ and Bo with the highest coefficient value observed during the June seasons indicating the possibility of predicting τ in the absence of Bo and vice-versa, especially during the June season. The validation of International Reference Ionosphere (IRI) model with observed τ and Bo revealed appreciable discrepancies between the model and observed values, particularly between the IRI-τ and observed τ values. Our result revealed the underestimation of IRI-τ with respect to observed τ value in November and December.

New estimation of non-thermal electron energetics in the giant solar flare on 28 October 2003 based on Mars Odyssey observations

Thu, 08/16/2018 - 19:10

Publication date: Available online 15 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): B.A. Nizamov, I.V. Zimovets, D.V. Golovin, A.B. Sanin, M.L. Litvak, V.I. Tretyakov, I.G. Mitrofanov, A.S. Kozyrev

Abstract

A new estimation of the total number and energy of the non-thermal electrons produced in the giant (>X17) solar flare on 2003 October 28 is presented based on the analysis of the observations of the hard X-ray (HXR) emission by the High Energy Neutron Detector (HEND) onboard the Mars Odyssey spacecraft orbiting Mars. Previous estimations of the non-thermal electron energy based on the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) data were incomplete since RHESSI missed the peak of the flare impulsive phase. In contrast, HEND observed the whole flare. We used two models to estimate the energy of the non-thermal electrons: the cold thick target model and the warm thick target model. More specifically, in the second case we employed an approximation which relates the pitch-angle averaged injection spectrum with the electron spectrum integrated over the emitting source. We found that, depending on the model used and the low-energy cutoff (Ec) of the non-thermal electrons, the estimate of their total energy in the entire flare can vary from 2.3×1032 to 6.2×1033 ergs. The lowest estimate, 2.3×1032 ergs, obtained within the cold thick target model and fixed Ec=43 keV, is consistent with the previous estimate. In this case, non-thermal electrons accelerated in the peak of the flare impulsive phase missed by RHESSI contained approximately 40% of the total energy of non-thermal electrons of the entire flare. The highest value, 6.2×1033 ergs, obtained with the cold thick target model and fixed Ec=10 keV, looks abnormally high, since it exceeds the total non-potential magnetic energy of the parent active region and the total bolometric energy radiated in the flare. Our estimates also show that the total number and energetics of the HXR-producing electrons in the flare region is a few orders of magnitude higher than of the population of energetic electrons injected into interplanetary space.

The performance of the IRI-Plas model as compared with Alouette II and GIM-TEC data over the midlatitude

Thu, 08/16/2018 - 19:10

Publication date: Available online 14 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): G.I. Gordiyenko, O.A. Maltseva, F. Arikan, A.F. Yakovets

Abstract

Climatic ionospheric models present an important medium for both investigation of physical structure and correction of detrimental effects of ionospheric variability on space based communication, navigation and positioning systems. International Reference Ionosphere Extended to Plasmasphere (IRI-Plas) is one of the empirical models that can provide ionospheric layer parameters and electron density profiles up to GPS satellite orbital height of 20,200 km. IRI-Plas can input not only F2 layer critical parameters, foF2 and hmF2, but also the Total Electron Content (TEC) values. In this study, Ne(h)-profiles and TEC values obtained from the IRI-Plas model are compared with topside Alouette II satellite profiles and Global Ionospheric Map (GIM) TEC values, respectively. The satellite Ne(h) profiles are averaged over a midlatitude region for various seasons of 1966 and 1969. It is observed that IRI-Plas is in good agreement with Alouette profiles between 300 km and 500 km. After 500 km up to 2000 km, the profiles seem to differ where IRI-Plas Ne(h) usually overestimates the Alouette profile. When IRI-Plas TEC is compared with GIM-TEC, it is observed that model TEC generally overestimates the GIM-TEC values during daytime hours. The lowest ΔTEC values (10–20%) are observed in March and September, and the highest values are observed in the months of January (around 30%) and July (up to 67%). During nighttime, the IRI-Plas model results mainly underestimate the observational ones, up to 30% in equinoctial months, and with ±10% discrepancies in January and July. Since the IRI-Plas model can scale foF2 and hmF2 values using an external TEC input by equating instantaneous and median slab thickness (TEC/NmF2 ratio), the correlation between GIM-TEC and ionosonde NmF2 values measured at the midlatitude station Alma-Ata located at [43.25°N, 76.92°E] is obtained for various seasons during 1999, 2000, 2008, 2009 and 2012. The study showed a positive correlation for all seasons and levels of solar activity. The correlation coefficients between the data sets were very high (greater than or equal to 0.79) for hourly data and (greater than or equal to 0.91) for monthly-medians at a significance level of 5%. Thus, for the practical applications, the correlation results can be used to update slab thickness model of IRI-Plas which will lead to better scaling of foF2 and hmF2 values and plasmaspheric Ne(h)-profile with external instantaneous TEC input.

Thunderstorm induced changes in near-surface O<sub>3</sub>, NO<sub>x</sub> and CH<sub>4</sub> and associated boundary layer meteorology over a tropical coastal station

Thu, 08/16/2018 - 19:10

Publication date: Available online 14 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): M. Kavitha, Prabha R. Nair, R. Renju

Abstract

The paper presents four cases of the response of near-surface O3, NOx and CH4 to thunderstorm activity at a tropical coastal site in India, occurred during pre-monsoon and post-monsoon seasons. The associated changes in boundary layer meteorology in terms of temperature, relative humidity (RH), wind and boundary layer height (BLH) are also examined. The meteorological parameters like temperature and RH respond very fast depicting changes during the initial phase of the thunderstorm activity, whereas a delayed response is observed in the wind direction (changing from the sea breeze to land breeze) and collapse of the BLH (1–1:30 h delay) at the mature phase of the activity. Associated with the thunderstorm activity, significant changes were observed in the mixing ratios of the near-surface O3, NOx and CH4. An increase in NOx (5.2–8.7 ppbv) and CH4 (36.7–134.6 ppbv) and reduction in O3 (9.9–18.8 ppbv) were recorded at the mature phase of the thunderstorm. The rise in NOx is attributed to combined effect of thunderstorm activity and wind reversal whereas that in CH4 is attributed to the wind reversal and associated change in air mass. A post activity increase is observed in mixing ratio of O3 in all the four cases. This is attributed to the downdrafts characteristic of the dissipation phase of thunderstorm activity which brings in O3 rich upper air down.

Analysis of suborbital flight operation using PESTLE

Thu, 08/16/2018 - 19:10

Publication date: Available online 11 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): A.R. Zahari, F.I. Romli

Abstract

Suborbital flight has progressively emerged as the potential future transport trend, whether for space tourism or other applications. While several design concepts have been explored thus far for the suborbital flight operation, one of the main lingering concerns is actually the destination of the flight. The altitude of 100 km, which is the commonly chosen destination for suborbital flight, provides an imaginary separation between air and space. The quest for this separation sparks intense debates not only in the scientific communities but also in the political circles and legal fraternities. In conjunction with that, this research aims to analyse the suborbital flight operation by using the analytical tool of Political, Economic, Social, Technological, Legal and Environmental (PESTLE) in order to discuss its implications to a nation. From the analysis, among the advantages of suborbital flight operation include the shifting of role for space development from public agency to private enterprise, creation of new industry to generate revenue, public opportunity for access to space, new, low cost and reusable technology and material and also the enhancement of atmospheric studies. On the other hand, among established disadvantages of suborbital flight operation include the absence of international consensus on the boundary between air and space, intensive capital requirement to develop new technology and infrastructure, damage to third party liability, limited track record for flight safety, lack of regulation for new industry and also the air pollution resulting from the flight activity. All in all, it can be taken that there are many advantages that suborbital flight could bring to a nation but its subsequent disadvantages have to be carefully considered as well to ensure the sustainability of its operation and industry.

Solar activity in the following decades

Thu, 08/16/2018 - 19:10

Publication date: September 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 176

Author(s): V. Obridko, K. Georgieva

Editorial Board

Thu, 08/16/2018 - 19:10

Publication date: September 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 176

Author(s):

Temporal and spatial variations of the equatorial electrojet during storm times from CHAMP observations

Thu, 08/16/2018 - 19:10

Publication date: Available online 10 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Zhichao Zheng, Hui Wang, Lei Yu, Yangfan He, Keling Li

Abstract

In this study, we examined the characteristics of temporal and spatial variations of the equatorial electrojet (EEJ) as extracted from the scalar magnetic field data from the CHAMP satellite during magnetic storms on 15 May and 24 August 2005. The main physical mechanisms of EEJ disturbances were analyzed using CHAMP data for the field-aligned currents (FACs), atmospheric mass density, thermospheric zonal winds, and ionospheric electron density. We found that the EEJ had eastward and westward enhancements in the main phase and recovery phase, respectively. The region 1 FACs were significantly strengthened after the storm onset and were much stronger than those in region 2, and they also moved to middle and low latitudes, which indicates that the dawn-to-dusk convection electric field in the auroral zone can penetrate from high latitudes to middle and low latitudes. Therefore, we believed that the prompt penetration electric field was mainly responsible for the eastward enhancement of the EEJ during the main phase. Interestingly, the westward peak of the EEJ coincided in time and space with the propagation of the atmospheric mass density disturbance from high latitudes to middle and low latitudes, whereas the zonal wind weakened and even turned eastward during the recovery phase. In this study, the enhanced equatorward wind at middle and low latitudes can be the main reason for the westward enhancement in the EEJ, whereas previous studies suggested that the enhanced westward zonal wind was responsible for the westward enhancement in the EEJ.

Formation of red arc in the polarization jet band

Thu, 08/16/2018 - 19:10

Publication date: Available online 9 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): V.L. Khalipov, A.E. Stepanov, I.B. Ievenko, G.A. Kotova, V.A. Panchenko

Abstract

Complex optical and ionospheric measurements in the region of the formation of red arcs accompanying the polarization jet development are analyzed. Optical measurements were done at subauroral station Maimaga, and ionospheric measurements were fulfilled at subauroral stations Yakutsk and Zhigansk. Spatial location and intensity of red-arcs were detected by the meridional scanning photometer. The temperature of the neutral atmosphere was recorded by Fabry-Perot interferometer. It is shown that the temperature of the neutral atmosphere increases in the red arc region and changes in accordance with variations in the emission. On 02 December 1989 the neutral temperature increased by 500 K in the red arc relative to the undisturbed level determined for quiet days during the month. This evidences on the strong heating process in the red arc region. According to ionospheric and satellite data on 18 February 1999 the red arc was observed simultaneously with polarization jet development – fast westward plasma drift in the poleward electric field. The magnitude of this electric field was 50–80 mV/m. Due to frictional interaction of ions and neutrals, ions were heated up to 5000–6000 K and neutrals gain energy of some hundreds degrees.

The response of longwave radiation at the South Pole to electrical and magnetic variations: Links to meteorological generators and the solar wind

Thu, 08/16/2018 - 19:10

Publication date: November 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 179

Author(s): John E. Frederick, Brian A. Tinsley

Abstract

An increasing body of evidence supports the conclusion that electrical variations in the Polar Regions influence atmospheric radiative properties. These influences can be transmitted (1) by the global electric circuit from remote thunderstorms and electrified shower clouds; (2) from local electric fields associated with ionospheric currents that generate magnetic activity, and (3) from local penetration of the solar wind electric field. A regression-based analysis reveals a positive relationship between downwelling longwave radiation observed during the dark portion of the year at the South Pole and the vertical electric field measured at the Antarctic stations Vostok and Concordia from 1998 to 2011, component (1). An increase in the electric field of 22.4 Vm-1, equal to one standard deviation of the nighttime mean, is followed one day later by a longwave irradiance 2.78 ± 1.90% larger than would exist otherwise. In addition, a significant negative correlation with a lag of two days exists between longwave irradiance recorded from late 1993 to mid-2017 and the Ap index, which measures temporal variations in the surface magnetic field associated with electric fields of ionospheric origin, component (2). There is a weaker, less-definitive, positive correlation of longwave irradiance with the interplanetary magnetic field index By which is associated with the solar wind electric field, component (3). These results are consistent with previous work using visible radiation, and with the hypothesis that the ionosphere-earth current density influences the microphysics of polar clouds, with consequences for radiative processes and meteorological variables such as surface pressure.

The role of Boundary Layer Height (BLH) variations on pollution dispersion over a coastal station in the Southwest Peninsular India

Thu, 08/16/2018 - 19:10

Publication date: Available online 7 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Sandhya K. Nair, M.S. Madhusoodanan, R.K. Mehajan

Abstract

We report the variability of Boundary Layer Height (BLH) and Ventilation Coefficient (VC) over a coastal station in southwest Peninsular India from vertical soundings. Altitude profile of Virtual Potential Temperature (θv) (derived from balloon-borne GPS radiosonde observations) was used to study the seasonal changes of BLH over Thumba (8.5°N, 77°E), a coastal station in southwest Peninsular India. Variability in the BLH is maximum during the pre-monsoon season and minimum during the winter, whereas the VC was found to be highest in the summer and lowest during winter. It is revealing the excellent efficiency in the dispersion of pollutants during the summer monsoon season. Conversely, low VC during winter and post-monsoon seasons showed great potential for pollution at this site. Role of VC on the dispersion of pollution was also examined using surface mass concentration of Black and Organic Carbon (BC and OC), sulphate and columnar Aerosol Optical Depth (AOD). High value of VC lowers the surface mass concentrations of BC, OC and sulphate during winter and maximises during summer monsoon and decreases the pollution potential.

Investigation on the occurrence of positive cloud to ground (+CG) lightning in UMP Pekan

Thu, 08/16/2018 - 19:10

Publication date: November 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 179

Author(s): Hwee Geem Chan, Amir Izzani Bin Mohamed

Abstract

This paper is going to find the direction of +CG lightning and its relationship with monsoon season in Malaysia by using data obtained from Malaysia Meteorological Department (MMD) for 2015. Analysis from this study found that a high numbers of lightning occur during dry season compares to rainy season. This is contradicted with general perception in Malaysia where lightning only occurs during rainy day. It is also understood that +CG lightning makes up approximately 20% of total lightning and the rest is −CG lightning events. The occurrence of +CG lightning during day and night will be discussed. From this, the direction where most +CG lightning occurs will be determined and used as a guide in order to observe TLEs afterward.

Study on carbon dioxide atmospheric distribution over the Southwest Indian Ocean islands using satellite data: Part 2 –the influence of meteorology and air transportation

Thu, 08/16/2018 - 19:10

Publication date: Available online 2 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): X.G. Ncipha, V. Sivakumar

Abstract

This investigation is a follow-up to the 3-dimensional distribution analysis of atmospheric CO2 and its surface temporal variation over the Southwest Indian Ocean (SWIO) islands (part 1). Here, we demonstrate the influence of meteorology and the associated air transport on CO2 spatial and vertical distribution determined in part 1. The Hybrid Single-Particle Lagrangian Integrated Trajectories (HYSPLIT) atmospheric model backward trajectories were used to determine the long-range air transport impacting on SWIO islands CO2 atmospheric loading, and to trace the origin of the air masses impacting on the atmosphere of SWIO islands. This study shows that meteorology and long-range air transport results in accumulation or dilution of atmospheric CO2 at various sites on the SWIO islands and this depends on the source region and type of air flow. Long-range air transport from different source regions at the upper atmospheric levels between the 700 and 500 hPa stable layers and the layer above 500 hPa is found to strengthen the inhomogeneity in the vertical distribution of CO2, caused by the decoupling effect of the upper atmosphere stable layers. This long-range air transport is also found to involve intercontinental air transport.

Graphical abstract

Study on carbon dioxide atmospheric distribution over the Southwest Indian Ocean islands using satellite data: Part 1 – Climatology and seasonal results

Thu, 08/16/2018 - 19:10

Publication date: Available online 2 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): X.G. Ncipha, V. Sivakumar, S. Rakotondraompiana, H. Bencherif

Abstract

The forests of the Southwest Indian Ocean (SWIO) islands States are large carbon sinks. Rapid population growth in these islands is responsible for deforestation, which in turn is the main source of carbon dioxide (CO2) emissions. This study is divided into two parts: The present study (Part 1) describes the seasonal vertical and surface spatial distribution of CO2 over the SWIO islands and the temporal variation of surface CO2 concentrations using data measured by the Tropospheric Emission Spectrometer (TES) on board the Aura Satellite. The CO2 hotspots over these islands were identified and assessed to determine if they were associated with deforestation and forest degradation anthropogenic activities. Areas of minimum or low CO2 atmospheric loading were also identified, and investigated to determine if they coincided with strong sink areas. Atmospheric CO2 concentration was building-up from summer to spring. The spatial extent of CO2 hotspots was found to increase from summer to spring. Over the study region, semi-permanent stable layers at 700 hPa and 500 hPa were shown to separate the troposphere into three layers of CO2. Furthermore, surface CO2 levels over all the study areas were found to be increasing during the period of the investigation. Part 2 of this study demonstrates the influence of meteorology and associated air transport on atmospheric CO2 distribution over the study region.

Graphical abstract

Conjugate gradient descent learned ANN for Indian summer monsoon rainfall and efficiency assessment through Shannon-Fano coding

Thu, 08/16/2018 - 19:10

Publication date: November 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 179

Author(s): Surajit Chattopadhyay, Goutami Chattopadhyay

Abstract

Work reported in the present paper demonstrates a neurocomputing based predictive model for the average rainfall in India during the season of summer monsoon. Backpropagation method with Conjugate Gradient Descent algorithm has been implemented to develop the neurocomputing model. After three runs of the model, it is found that a high prediction yield is available. Finally, Shannon-Fano coding has been implemented and the coding efficiency has been measured by dividing the error percentage of prediction into various classes. The efficiency of Conjugate Gradient Descent algorithm for multilayer ANN has been finally established through Shannon-Fano coding.

Anomalous mesospheric ozone variability is not a precursor to earthquakes: A case study in Greece

Thu, 08/16/2018 - 19:10

Publication date: November 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 179

Author(s): P.K. Varotsos, M.N. Efstathiou, C.A. Varotsos

Abstract

Very recently, it has been found that intense anomalies of the mesospheric ozone occur a few days before major earthquakes. This paper explores the credibility of this finding in the case of the last two major earthquakes in Greece. Indeed, the study of the mesospheric ozone vertical distribution showed that unusual anomalies occurred a few days before these two earthquakes. However, at time periods with no significant seismicity the same unusual changes in the mesospheric ozone vertical distribution were observed. Consequently, significant temporal changes of the mesospheric ozone can not be considered as precursors for upcoming significant seismic activity.

Sun-to-earth propagation of the 2015 June 21 coronal mass ejection revealed by optical, EUV, and radio observations

Thu, 08/16/2018 - 19:10

Publication date: November 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 179

Author(s): N. Gopalswamy, P. Mӓkelӓ, S. Akiyama, S. Yashiro, H. Xie, N. Thakur

Abstract

We investigate the propagation of the 2015 June 21 CME-driven shock as revealed by the type II bursts at metric and longer wavelengths and coronagraph observations. The CME was associated with the second largest geomagnetic storm of solar cycle 24 and a large solar energetic particle (SEP) event. The eruption consisted of two M-class flares, with the first one being confined, with no metric or interplanetary radio bursts. However, there was intense microwave burst, indicating accelerated particles injected toward the Sun. The second flare was eruptive that resulted in a halo CME. The CME was deflected primarily by an equatorial coronal hole that resulted in the modification of the intensity profile of the associated SEP event and the duration of the CME at Earth. The interplanetary type II burst was particularly intense and was visible from the corona all the way to the vicinity of the Wind spacecraft with fundamental-harmonic structure. We computed the shock speed using the type II drift rates at various heliocentric distances and obtained information on the evolution of the shock that matched coronagraph observations near the Sun and in-situ observations near Earth. The depth of the geomagnetic storm is consistent with the 1-AU speed of the CME and the magnitude of the southward component.

Nonkinematic solar dynamo models with double-cell meridional circulation

Thu, 08/16/2018 - 19:10

Publication date: November 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 179

Author(s): V.V. Pipin

Abstract

Employing the standard solar interior model as input we construct a dynamically-consistent nonlinear dynamo model that takes into account the detailed description of the Λ- effect, turbulent pumping, magnetic helicity balance, and magnetic feedback on the differential rotation and meridional circulation. The background mean-field hydrodynamic model of the solar convection zone accounts the solar-like angular velocity profile and the double-cell meridional circulation. We investigate an impact of the nonlinear magnetic field generation effects on the long-term variability and properties of the magnetic cycle. The nonlinear dynamo solutions are studied in the wide interval of the α effect parameter from a slightly subcritical to supercritical values. It is found that the magnetic cycle period decreases with the increasing cycle's magnitude. The periodic long-term variations of the magnetic cycle are excited in case of the overcritical α effect. These variations result from the hemispheric magnetic helicity exchange. It depends on the magnetic diffusivity parameter and the magnetic helicity production rate. The large-scale magnetic activity modifies the distribution of the differential rotation and meridional circulation inside convection zone. It is found that the magnetic feedback on the global flow affects the properties of the long-term magnetic cycles. We confront our findings with solar and stellar magnetic activity observations.

Ionosonde observations of daytime spread F at middle latitudes during a geomagnetic storm

Thu, 08/16/2018 - 19:10

Publication date: November 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 179

Author(s): Guobin Yang, Chunhua Jiang, Ting Lan, Wengeng Huang, Zhengyu Zhao

Abstract

Recently, Jiang et al., (2016) reported daytime spread F at Puer station (22.7oN, 101.05oE, Dip Lat 12.9oN). As a continual work, daytime spread F at middle latitudes was investigated in this study through ionograms recorded by an ionosonde installed at Zhangye (ZHY, 39.4oN, 100.0oE, Dip Lat 29.6oN) in the Northwest of China. The ionosonde at ZHY station recorded daytime spread F three times on 6 January, 2017. The first case occurred at approximately 06:45 LT and disappeared at about 08:35 LT. The second and third cases lasted from 09:50 LT to 10:30 LT and from 11:10 LT to 11:30 LT, respectively. In addition, Swarm satellite observations were used to reveal the possible mechanism in this study. Results show that daytime spread F observed in this study might be attributed to Traveling Ionospheric Disturbances (TIDs)/atmospheric gravity waves induced by a geomagnetic storm. However, the physical processes might be different for these cases. Ionospheric instabilities produced by local F region electric field might be contributed to the first case. The second and third cases might be attributed to off-vertical reflections from wave-like ionospheric structure generated by TIDs/atmospheric gravity waves.

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