Journal of Atmospheric and Solar-Terrestrial Physics

Spectral characteristic of geomagnetically induced current during geomagnetic storms by wavelet techniques

Fri, 08/16/2019 - 19:10

Publication date: Available online 2 February 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Binod Adhikari, Nirakar Sapkota, Subodh Dahal, Binod Bhattarai, Krishna Khanal, Narayan P. Chapagain

Abstract

An EMF (electromagnetic field) is induced over an incremental area when magnetized plasma from sun interacts with the Earth's magnetic field. This phenomenon delivers a Geomagnetically Induced Current (GIC) or induces geo-electric field at the Earth's surface and in the ground. GIC and horizontal component of geomagnetic field have been studied with respect to various geomagnetic events. Particularly, we have studied four events. The first one is geomagnetically quiet period (5 October 2003), the second one is weak storm (21 October 2003), the third one is moderate storm (14 October 2003) and the last one is an intense storm (30 October 2003). By comparing the development of GIC during geomagnetic storms, we found that intense geomagnetic storms show higher development on GIC magnitude. The GIC during storm events is several times greater than that during the quiet day. AE index shows more activity in the event of 30th October than other events and GIC is also more in this event. This can be accounted to the greater geomagnetic disturbance in this case. The power ranges of higher intensity are seen at various time scales on different events. We have analysed GIC signal associated with four geomagnetic storms and found distinct periodicities at the time when H component highly perturbed. The characteristic of GIC signal demonstrates high variability with time without presence of continuous periodicities. Discrete wavelet transform (DWT) analysis reveals that whenever the geomagnetic field is perturbed, there will be high possibility of detecting GIC. The singularities present in GIC signal are due to the peak value of electrical currents system in the ionosphere and magnetosphere, and corresponding high fluctuations in H component. In this work, we explore the remarkable ability of wavelets to highlight the singularities associated with discontinuities present in the GIC.

Modeling the global ionospheric variations based on complex network

Fri, 08/16/2019 - 19:10

Publication date: Available online 1 February 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Shikun Lu, Hao Zhang, Xihai Li, Yihong Li, Chao Niu, Xiaoyun Yang, Daizhi Liu

Abstract

The modern science of networks has brought significant advances to our understanding of complex systems. We employ the probabilistic graphical model to build complex networks to model the global ionospheric variations. The global ionospheric maps (GIMs) of vertical total electron content (VTEC) for the 12 months in 2012 have been selected analyze the ionospheric variations from the perspective of complex network. The information flow in the networks represents the causal interactions between the ionospheric variations at different locations. The distributions of the edges' geospatial distances in the ionospheric networks show that the information flow in the ionosphere is mainly transmitted locally, almost obeying the geospatial proximity principle. The asymmetric distribution of the edges' distances probably elucidates the more efficient transmission of ionospheric variations in the westward and southward directions. The community topologies within the ionospheric networks indicate the effect of the geomagnetic field and geographical distance on the information flow in the ionosphere. The geomagnetic field has shown an enhanced effect on the meridional interaction in the ionosphere, causing the vertical community topologies within the ionospheric networks at middle and low latitudes. For the ionospheric cells located at high latitudes in GIM, the geographical distances result in the horizontal community topologies. The fractal analysis reveals the existence of self-similar structure in the ionospheric networks on the global scale. The fractality in the ionospheric information flow may indicate the reasonability of the VTEC's prediction at a certain location by spatial prediction based on the data obtained in known regions.

Features of the inter-hemispheric field-aligned current system over Malaysia ionosphere

Fri, 08/16/2019 - 19:10

Publication date: Available online 31 January 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Zamri Zainal Abidin, M.H. Jusoh, M. Abbas, O.S. Bolaji, A. Yoshikawa

Abstract

Magnetic records of the declination (D) component for the solar quiet year 2011–2013 obtained from Magnetic Data Acquisition System (MAGDAS) at Langkawi (Geog. Lon. 99.68∘ E, Geog. Lat. 6.30∘N), Malaysia were utilized in this study. The minutes averages were used to delineate the diurnal (Sq(D)) variation. The monthly mean (MSq(D)) and their seasonal variabilities (SVq(D)) were also analysed. The Sq(D) and their MSq(D) exhibit smooth regular occurring pattern in the month of April–September and became highly perturbed in October–March across the years. The highest positive (∼3.5 arc-min) and the negative (∼−3.0 arc-min) values were observed in August 2011 during the dawn and noon sectors. These maxima shifted to July and September in 2012 with peaks ∼3.2 and −3.0 arc-min. In 2013, the positive maximum (∼3.0 arc-min) and its negative (∼−2.5 arc-min) were again seen in August. This implies that the dawn and noon sectors of August 2011 and 2013 are strongly influenced by IHFACs and this effect shifted to July and September in 2012. IHFACs through the years flow from the winter to summer hemisphere during the noon and dusk sectors and flow in opposite direction during the dawn sector. The day-to-day magnitudes of Sq(D) and MSq(D) seems to suggest the inter-hemispheric imbalance of the ionospheric Sq current earlier established by Van Sabben as the cause of IHFACs is not strongly affected by the changes in annual solar variation. Dusk-side IHFACs were observed to be northbound in all the seasons with the exception of June solstice. The direction of IHFACs does not change except in April and November. The current intensity is not large in solstices except in August 2011 and 2013 but it shifted to July in 2012. The result further showed that the magnitude of the duskside IHFACS is determined to some extent by the strength of the noontime IHFACs. IHFACs were generally observed to be greater during the daytime than night-time hours.

Application of solar quiet (Sq) current in determining mantle conductivity-depth structure in Malaysia

Fri, 08/16/2019 - 19:10

Publication date: Available online 31 January 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Zamri Zainal Abidin, M.H. Jusoh, M. Abbas, A. Yoshikawa

Abstract

The mantle electrical conductivity-depth structure of Malaysia was determined for the first time using solar quiet day ionospheric current (Sq) variations. Spherical harmonic analysis (SHA) was employed to separate the external and internal field contribution to the Sq variations. A transfer function was applied in estimating the conductivity-depth profile for the paired of external and internal coefficients of the SHA. We observed a downward increase in electrical conductivity with initial magnitude of 0.0065 S/m at a depth of ∼ 56 km which gradually rose to 0.0106 and 0.0140 S/m at 118 and 180 km. Subsequently, the conductivity profile rose to about 0.0228 S/m at 380 km (near the base of the upper mantle) and reached 0.0260 S/m at 435 km, after which a sharp steep increase was observed at 450 km with conductivity profile of 0.0278 S/m. Consequently, the conductivity profile increases significantly to about 0.1367 S/m at a depth of 973 km and reached its peak value 0.1975 S/m at the depth of 1097 km in the lower mantle with no indication of leveling off. An evidence of discontinuity was observed near 390–460 km and 675–746 km. A slight increase in conductivity values at depth between 150 and 300 km corresponds to the region of unusual global low velocity zone with high electrical conductivity. The conductivity profile showed a less steep increase above 450 km below which a steep increase was observed. The present profile showed the deepest penetration depth which may be attributed to the influence of equatorial electrojet current (EEJ) that is actively supported by the conductive properties of the Earth's interior within the study region.

Polar cap patches observed by the EISCAT Svalbard Radar: A statistical study of its dependence on the solar wind and IMF conditions

Fri, 08/16/2019 - 19:10

Publication date: Available online 16 January 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Yuyan Jin, Zanyang Xing, Qinghe Zhang, Yong Wang, Yuzhang Ma

Abstract

Polar cap patches are common irregularities in the polar ionosphere, where their formation and evolution can directly affect satellite navigations and communications as well as over-the-horizon radar observations, etc. However, affected by the various dynamic processes during the solar wind-magnetosphere-ionosphere coupling, there is no fully accepted formation mechanism of polar cap patches. In this paper, a statistical analysis of 345 patches at the dayside sectors during 09:00–15:00 magnetic local time (MLT), observed by EISCAT Svalbard Radar (ESR) 42 m antenna from 2010 to 2013, has been performed. The dependence of their occurrence on solar wind and interplanetary magnetic field (IMF) conditions as well as their MLT distribution has been statistically investigated. The results show that the polar cap patches are preferentially formed during southward IMF conditions. In particular, the MLT dependence of the patches presents a clear IMF By-related prenoon-postnoon asymmetry, suggesting the patch formation is clearly modulated by the IMF By polarity. Moreover, our statistical results indicate that the patches should not be caused by the variations of the solar wind dynamic pressure or the solar wind velocity. All the results indicate that the pulsed dayside magnetic reconnection is possibly a significant formation mechanism of polar cap patches.

Understanding the global dynamics of the equatorial ionosphere in Africa for space weather capabilities: A science case for AfrequaMARN

Fri, 08/16/2019 - 19:10

Publication date: Available online 6 January 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Hammed A. Lawal, Mark Lester, Stanley W.H. Cowley, S.E. Milan, T.K. Yeoman, Gabby Provan, Suzie Imber, A.Babatunde Rabiu

Abstract

The equatorial region of the Earth's ionosphere is one of the most complex ionospheric regions due to its interactions, instabilities, and several unresolved questions regarding its dynamics, electrodynamics, and physical processes. The equatorial ionosphere overall spans three continents with the longest region being that over the African continent. Satellite observations have demonstrated that very large differences exist in the formation of ionospheric irregularities over the African sector compared with other longitudinal sectors. This may be a consequence of the symmetric shape of the magnetic equator over the continent and the lack of variability in latitude. In this paper, we propose a science campaign to equip the African sector of the magnetic equator with ground-based instruments, specifically magnetometers and radars. The network of radars proposed is similar in style and technique to the high-latitude SuperDARN radar network, while the magnetometers will form an array along the equatorial belt. These two proposed space physics instruments will be used to study this region of the equatorial ionosphere over a long interval of time, at least one solar cycle. The deployment of an array of magnetometers (AfrequaMA) and a radar network (AfrequaRN) in the African sector of the magnetic equator is jointly called the Africa Equatorial Magnetometer Array and Radar Network (AfrequaMARN), which will provide simultaneous observations of both electric and magnetic variations over the African sector. We also examine the possible science questions such a magnetometer array and radar network would be able to address, both individually and in conjunction with other space-based and ground-based instrumentation. The proposed projects will clearly improve our understanding of the dynamics of the equatorial ionosphere and our understanding of its role in balancing the large-scale ionospheric current system, and will contribute to our ability to adequately model ionospheric and plasmaspheric densities. It will also enhance our understanding of global ionospheric processes, which will improve the space weather capabilities of the African and international space science communities.

Editorial Board

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s):

Predicting precipitable water vapor by using ANN from GPS ZTD data at Antarctic Zhongshan Station

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Yingchun Yue, Tao Ye

Abstract

Precipitation plays an important role in human activities, and accurate prediction of precipitation is expected to make the arrangements accordingly, especially in Antarctic area with complicated weather conditions. Since directly forecasting precipitation usually requires a lot of meteorological data, which is difficult to be collected in Antarctic area, the precipitation is usually predicted indirectly by using precipitable water vapor (PWV). The PWV can be calculated by Hopfield model using GPS zenith tropospheric delay (ZTD) data if only the temperature and pressure data is available. In this paper, we adopt the artificial neural network (ANN) with genetic algorithm (GA) to predict the PWV of the Zhongshan Station in 6 and 12 h by four different input schemes, including ZTD, ZTD with real-time meteorological data, PWV, and intrinsic mode functions (IMFs) of PWV. The predicted results show that the worst prediction is got by using ZTD sequences with the correlation coefficient of about 0.50. The results of using ZTD with real-time meteorological data and PWV have approximate correlation coefficient of about 0.80. The best prediction is obtained by using IMFs of PWV sequences to predict 6 h PWV with the correlation coefficient of 0.95.

Atmospheric anomalies associated with M<sub>w</sub>>6.0 earthquakes in Pakistan and Iran during 2010–2017

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Munawar Shah, M. Arslan Tariq, Najam Abbas Naqvi

Abstract

Recent advances on satellite-based measurement of different atmospheric constituents at different heights provide sufficient evidences of short and long-term earthquake (EQ) precursors. In this paper, atmospheric anomalies are investigated related to three large magnitude Mw > 6.0 EQs in Pakistan and Iran during 2010–2017 (i.e., January 18, 2011 (Mw 7.2, Southwestern Pakistan), April 16, 2013 (Mw 7.7, East of Khash Iran) and February 07, 2017 (Mw 6.3, Pasni, Pakistan)). For this purpose, satellite based Outgoing Longwave Radiation (OLR), Surface Temperature (ST), Aerosol Optical Depth (AOD) and NO2 are investigated by statistical bounds of median and standard deviation for two months before and one month after the occurrence of each event. We study the spatial OLR anomaly from National Oceanic and Atmospheric Administration/National Center for Environmental Prediction (NOAA/NCEP). Evidences suggest that abnormal atmospheric anomalies occur within one month before the main shock. For example, in case of Mw 7.2 southwestern Pakistan EQ, significant perturbations in daytime OLR are detected up to 21 days before the main shock, justifying the existence of huge amounts of energy over the tectonic lineaments. The OLR anomaly correlated with ST, AOD and NO2 during 15–21 days before the main shock, which may be attributed to the same event. Similarly, the OLR, ST, AOD and NO2 show irregularities before the 2013, Mw 7.7 East of Khash Iran EQ, where all the anomalies occur 9–10 days before the main shock. The anomalous OLR over the epicenter suggests the authenticity of all the temporal perturbations in the atmospheric parameters related to Mw 7.7 (Iran event). Furthermore, the atmospheric parameters are analyzed temporally by the statistical bounds before the Mw 6.3 (Pasni, Pakistan) EQ. All the parameters behave abnormally during 10–15 days following the Mw 6.3 Pakistan EQ and similarly subsequent spatial OLR enhancement over the epicenter may lead to the conclusion of an extensive energy emanation. The anomalies detected are consistent with the processes of stress activation of proxy defects at the Lithosphere-Atmosphere interface in the seismic breeding zone.

Observed response of stratospheric and mesospheric composition to sudden stratospheric warmings

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): M.H. Denton, R. Kivi, T. Ulich, C.J. Rodger, M.A. Clilverd, J.S. Denton, M. Lester

Abstract

In this study we investigate and quantify the statistical changes that occur in the stratosphere and mesosphere during 37 sudden stratospheric warming (SSW) events from 1989 to 2016. We consider changes in the in-situ ozonesonde observations of the stratosphere from four sites in the northern hemisphere (Ny-Ålesund, Sodankylä, Lerwick, and Boulder). These data are supported by Aura/MLS satellite observations of the ozone volumetric mixing ratio above each site, and also ground-based total-column O3 and NO2, and mesospheric wind measurements, measured at the Sodankylä site. Due to the long-time periods under consideration (weeks/months) we evaluate the observations explicitly in relation to the annual mean of each data set. Following the onset of SSWs we observe an increase in temperature above the mean (for sites usually within the polar vortex) that persists for >∼40 days. During this time the stratospheric and mesospheric ozone (volume mixing ratio and partial pressure) increases by ∼20% as observed by both ozonesonde and satellite instrumentation. Ground-based observations from Sodankylä demonstrate the total column NO2 does not change significantly during SSWs, remaining close to the annual mean. The zonal wind direction in the mesosphere at Sodankylä shows a clear reversal close to SSW onset. Our results have broad implications for understanding the statistical variability of atmospheric changes occurring due to SSWs and provides quantification of such changes for comparison with modelling studies.

Linkage of meteorological parameters and anomalous radio propagation profile over Nigeria

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): I. Emmanuel

Abstract

The vertical distribution of refractivity gradient is important in determining anomalous propagation condition. Thirty five years of meteorological parameters, obtained from Era-Interim archive of European Centre for Medium-Range Weather Forecasts has been used to analyze and investigated surface meteorological data linked with refractivity gradient aloft altitude across Nigeria. Spatial distribution of surface temperature, relative humidity and refractivity gradient at 0.1 km, 0.5 km, 1.0 km and 1.5 km over Nigeria were plotted. Vertical distribution of temperature, relative humidity, refractivity and refractivity gradient were obtained for some locations across Nigeria. Similarly, spatial distribution of coefficient of determination between surface temperature, relative humidity and refractivity gradient at four different height were estimated. Linear regression were developed to investigate the relationship between surface data and refractivity gradient at different altitude. The result revealed existence of sub refractive, super refractive, and ducting across the country at 0.1 km and 0.5 km however occurrence of ducting and sub refractive disappeared at 1.0 km and 1.5 km. Likewise, the existence of temperature inversion was noticed between surface and 100 m across all the locations except in Lagos. Values of refractivity across the observed locations converged around 0.5 km. Through result of correlation coefficient and statistical parameters, significant linked have been established between surface data and refractivity gradient at different height.

Vertical wavenumber spectral characteristics of temperature in the stratosphere-mesosphere over tropical and subtropical regions

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Priyanka Ghosh, Som Sharma

Abstract

The vertical wavenumber spectra over tropical location, Gadanki (13.5° N, 79.2° E) and sub-tropical location, Mt. Abu (24.5° N, 72.7° E) is studied using the temperature measurements from ground based Rayleigh Lidar and space borne satellite observations. The slope values are lesser over Gadanki than at Mt. Abu for almost all the altitudes except for 40–50 km where it is nearly same and 60–70 km exhibiting opposite nature. Unusual spectral slope of −6.97 (Mt. Abu) and −0.09 (Gadanki) is seen at the altitude of 40–50 km in satellite temperature. Characteristics of wave oscillations perceived over both the stations are described.

Monitoring the global evolution of the storm ring current and storm indices from confined ground geomagnetic observatories

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): G. Zeng, C. Shen, Z.J. Rong, X. Li, T. Chen, Z.Q. Chen, Y.H. Ma

Abstract

For the first time, the global structure of the geomagnetic disturbance field around the Earth as well as the magnetic storm indices have been deduced from magnetic field measurements by ground observatories in a confined range of longitude. The spatial gradient of the H component of the geomagnetic disturbance field was obtained from ground geomagnetic observatories only in the Eastern Hemisphere, provided the geomagnetic disturbance field varies approximately linearly in space. Furthermore, the storm symmetric and asymmetric indices were derived and the spatial distribution and temporal evolution of the storm ring current was investigated. It was found that the storm indices derived from observatories in the Eastern Hemisphere are consistent with the officially published Kyoto standard indices which are derived from six globally distributed observatories. We also calculated the storm indices for 1941–1956 by using data from three observatories (HER, KAK and SJG). The correlation coefficient between the symmetric index deduced from three observatories and the one from the global six observatories is 0.98, and the correlation coefficient between the two kind of asymmetric indices is 0.79. Those results suggest that our approach is reasonable and significant when global ground observatories are not readily available.

Feed forward neural network based ionospheric model for the East African region

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): A. Tebabal, S.M. Radicella, B. Damtie, Y. Migoya-Orue’, M. Nigussie, B. Nava

Abstract

In this paper, a neural network based regional ionospheric model is developed using GPS-TEC data from 01 January 2012 to 31 December 2015. For this purpose, nine GPS station TEC data in the time intervals 2012 to 2014 were used to determine model parameters. TEC data obtained in various years and geographical locations which are excluded in the training time are used to validate the performance of the model. For the first case, TEC data from each station in the year 2015 is used to validate the performance of the model. In the second case, GPS observations at Metu, Robe, and Serb stations are used to investigate the model’s performance in the year 2012, 2014 and 2013–2014, respectively. In both cases, to validate the accuracy and quality of the model, GPS-TEC values were compared with the predicted TEC. The results indicate that the proposed model can capture most of the spatio-temporal variations of the regional TEC. The present model reproduces the observed hourly TEC with RMS values that lie around 3 to 6.05 TECU at different geographical locations for both one hour and one day ahead prediction. For one day ahead prediction, a comparison of the NN method using NeQuick 2 model outputs with GPS derived measurements have also been conducted. The results indicate that the NN TEC model proposed has a good performance in representing TEC variations compared to climate NeQuick 2 model.

Assessments of the night-time and daytime radiative fluxes balance on seasonal timescale over West Africa

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): O.S. Ojo, B. Adeyemi, E.O. Ogolo

Abstract

The main aim of this paper is to assess the impact of climate change on variations and trends of the net radiation flux over West Africa during night and day time. West Africa was sub-divided into six climatic zones as classified by the World Meteorological Organization such as Hyper-Arid (HAR), Arid (ARD), Semi-Arid (SAR), Semi-Humid Dry (SHD), Semi-Humid Humid (SHH) and Humid (HUM) zones. To achieve this aim, thirty-six years' surface data of shortwave and longwave radiations between 1980 and 2015 were obtained from the Archives of the Modern-Era Retrospective Analysis for Research and Application, Version 2 (MERRA-2) database. Analyses showed that the maximum values of net radiative fluxes during the nighttime and daytime have the magnitude in watt per square metres of −70.00 and 225.82 in HAR zone, −62.46 and 248.99 in ARD zone, −51.71 and 304.88 in SAR zone, −40.55 and 334.58 in SHD zone, −34.32 and 352.62 in SHH zone and −30.49 and 362.68 in HUM zone respectively. The effect of population density, emission of greenhouse gas and surface albedo on net radiation was investigated over the climatic zones using the multivariate linear regression analysis. The results of the regression analysis showed that they have significant effects on net radiation. Also, the monotonic trend analysis between 1980 and 2015 was carried out using the non-parametric Mann- Kendall statistical test. The results of the trend test revealed that net radiation showed decreasing trends mainly in the humid zones at over 95% significance level while population density, emission of greenhouse gas and surface albedo showed significant increasing trends at the 99.9% level of significance. The analyses showed that the humid zones have higher values of net radiation, radiative cloud forcing, carbon-dioxide emission, population density and lower surface albedo than arid zones. Therefore, as signatures of climate change, it can be concluded that increase in population density, cloud amount and anthropogenic activities such as land use/land cover and emission of greenhouse gas have contributed greatly to the significant decreasing trends of the radiative flux balance especially in the humid zones of West Africa.

Simulations of the inner magnetospheric energetic electrons using the IMPTAM-VERB coupled model

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Angelica M. Castillo, Yuri Y. Shprits, Natalia Ganushkina, Alexander Drozdov, Nikita Aseev, Dedong Wang, Stepan Dubyagin

Abstract

In this study, we present initial results of the coupling between the Inner Magnetospheric Particle Transport and Acceleration Model (IMPTAM) and the Versatile Electron Radiation Belt (VERB-3D) code. IMPTAM traces electrons of 10−100 keV energies from the plasma sheet (L=9 Re) to inner L-shell regions. The flux evolution modeled by IMPTAM is used at the low energy and outer L∗ computational boundaries of the VERB code (assuming a dipole approximation) to perform radiation belt simulations of energetic electrons. The model was tested on the March 17th, 2013 storm, for a six-day period. Four different simulations were performed and their results compared to satellites observations from Van Allen probes and GOES. The coupled IMPTAM-VERB model reproduces evolution and storm-time features of electron fluxes throughout the studied storm in agreement with the satellite data (within ∼0.5 orders of magnitude). Including dynamics of the low energy population at L∗=6.6 increases fluxes closer to the heart of the belt and has a strong impact in the VERB simulations at all energies. However, inclusion of magnetopause losses leads to drastic flux decreases even below L∗=3. The dynamics of low energy electrons (max. 10s of keV) do not affect electron fluxes at energies ≥900 keV. Since the IMPTAM-VERB coupled model is only driven by solar wind parameters and the Dst and Kp indexes, it is suitable as a forecasting tool. In this study, we demonstrate that the estimation of electron dynamics with satellite-data-independent models is possible and very accurate.

Observation and characterization of traveling ionospheric disturbances induced by solar eclipse of 20 March 2015 using incoherent scatter radars and GPS networks

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Sergii V. Panasenko, Yuichi Otsuka, Max van de Kamp, Leonid F. Chernogor, Atsuki Shinbori, Takuya Tsugawa, Michi Nishioka

Abstract

We present the results of a comprehensive study of traveling ionospheric disturbances (TIDs) occurring over Europe during the total solar eclipse of 20 March 2015. For detection of wave structures and estimation of TID parameters, two remote sensing techniques were combined: incoherent scatter (IS) radars and European and Finnish dense GPS receiver networks. Similar procedures were applied for processing both IS and GPS data. We developed a new method enabling to analyze TEC data separately in the temporal and spatial domain. For the first time, we produced maps of band-pass filtered TEC variations and reported both large- and medium-scale prevailing TIDs observed during this solar eclipse, both having similar periods of about 50 – 60 min. The downward phase progression indicates that TIDs were induced by atmospheric gravity waves generated at lower altitudes. The variations in IS power attained peak relative amplitudes of 0.22 (22%) at 220 km over Tromsø and of 0.17 (17%) at 200 km over Kharkiv. The vertical phase velocity was about 57 m/s over Tromsø. It increased from 25 to 170 m/s over Kharkiv with altitude increasing from 120 to 310 km. Over Western Europe, large-scale TIDs (LSTIDs) had prevailing north-east direction over the region from 45°to 50°N and 2°W to 8°E. Here, their average horizontal phase velocity Vm was 803±281m∕s and the absolute amplitudes of TEC variations usually do not exceed 0.17 TECU. For this region, we found strong differences in LSTID propagation azimuth between the solar eclipse day and the two adjacent days of 19 and 21 March 2015, used as reference. This most likely indicates that these LSTIDs were directly caused by the solar eclipse through local heating/cooling processes occurring during the passing of the Moon penumbra. Over another region, limited by 44°–50°N and 13°–19°E, the LSTIDs had south-east propagation. Over Finland, the LSTIDs also propagated southeastward having Vm=774±202m∕s and TEC amplitudes up to 0.6 TECU. A possible evidence of LSTID generation at high latitudes indirectly by this solar eclipse through an excitation of slow magnetosonic waves was experimentally detected. Medium-scale TIDs (MSTIDs) propagated southeastward over both regions having Vm values of 144±54m∕s over Western Europe and of 104±43m∕s over Finland. Over Northern Europe, the maximum MSTID amplitudes were greater by a factor of 5 compared to those over Western Europe and reached 0.4 TECU. We did not detect a clear difference in MSTID propagation between solar eclipse and reference days. The IS and GPS results are in consistency with each other. The detected TID parameters of predominant periods, relative amplitudes, altitude range and MSTID horizontal propagation direction generally correspond to the results of other studies.

Long-term temporal and spatial analysis of SO<sub>2</sub> over Gauteng and Mpumalanga monitoring sites of South Africa

Sun, 08/04/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): S.K. Sangeetha, V. Sivakumar

Abstract

This paper focused on the temporal and spatial variability of sulphur dioxide (SO2) from 2004 to 2013 over 36 ground-based (GB) stations located in Gauteng and Mpumalanga provinces of South Africa. The assessment was based on the in situ SO2 data, where the GB stations were sorted into different groups and in addition, kriging-based analysis and OMI SO2 data (2004–2013) were deployed to study their seasonal spatial variability. It was observed that Pretoria west, Witbank and Randwater had high SO2 levels and standard deviations. Although, winter played a major role in having peak SO2 values in most of the stations, it was surpassing that in spring the SO2 levels of Witbank and Pretoria west stations dropped and Randwater had the highest standard deviation of 11.2 ppbv in October. A prominent seasonal variation was seen in all the groups, excluding Mpumalanga power stations (MP) group. This was particularly evident in the Vaal Triangle group. Highveld group ranked topmost level with elevated SO2 values proceeded by the MP group in all the temporal time scales. The spatial based analysis further proved that the highest SO2 levels were centred around major industrial regions of Mpumalanga, regardless of all the seasons.

Graphical abstract

Spatio-temporal variations of absorbing aerosols and their relationship with meteorology over four high altitude sites in glaciated region of Pakistan

Fri, 06/21/2019 - 19:10

Publication date: 1 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 190

Author(s): Jawad Nasir, Bahadar Zeb, Armin Sorooshian, Muhammad Mansha, Khan Alam, Ifthikhar Ahmad, Hussain Haider Rizvi, Muhammad Shafiq

Abstract

In high Asia, absorbing aerosols, particularly black carbon (BC) and dust, reportedly have strong effects on glaciers and the hydrological cycle. Knowledge about influence of BC over Hindukush-Karakoram-Himalaya (HKH) region in northern Pakistan is limited and therefore, required in-depth investigation. This study reports on the ground based BC and satellite based aerosol variations during the period 2016–2017, over four high altitude stations, including Astore, Gilgit, Sost, and Skardu, representing HKH range in northern Pakistan. Hourly, daily, and monthly variations of BC aerosol were examined in relation to meteorology. BC aerosols exhibited diurnal variations with sharp morning and evening peaks. During the study period BC concentrations were in the range of 0.9–6.1 μg/m3 over the study locations. During the study period, the average BC concentration over Astore, Gilgit, Sost and Skardue were 2.6 ± 0.7, 3.7 ± 0.6, 2.1 ± 1.1 and 3.0 ± 1.0 μg/m3, respectively. AOD varies from 0.01 to 0.16 and AI ranges from 0.2 to 5.5 during the study period. BC aerosols exhibited positive correlations with temperature and wind speed, in addition to a negative correlation with relative humidity. BC also has a positive correlation with AOD and AI. The long range transport of aerosols to the receptor sites were from central Asia, Eastern Europe, Middle East and India as well.

Is the Madden–Julian Oscillation reliably detectable in Schumann Resonances?

Fri, 06/21/2019 - 19:10

Publication date: 1 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 190

Author(s): Ciarán D. Beggan, Malgorzata A. Musur

Abstract

The Madden–Julian Oscillation (MJO) is a quasi-periodic (∼30–90 days) eastward-moving atmospheric mode which primarily modifies rainfall patterns in the equatorial regions from Africa to the Pacific Ocean. It has been proposed that its signature is detectable within the intensity variations of the Schumann Resonances (SR) due to changes in the location and magnitude of the major lightning centres. Using six years of induction coil data recorded at the Eskdalemuir Observatory in the UK, we investigate whether the MJO is detectable in the first three Schumann Resonances. We extract the frequency and intensity values from each resonance every 10 min, averaged to a daily value and compare them to the Realtime Multivariate MJO (RMM) index. We use Empirical Mode Decomposition (EMD) to determine if certain modes correlate between the SR and RMM curves. We find that the EMD 30–70 day modes of the SR and RMM index occasionally beat in-phase during the La Niña periods of the El Niño Southern Oscillation (ENSO) but not El Niño periods. However, the relationship is not wholly consistent, implying that robust and reliable detection of the MJO in SR data remains challenging.

Graphical abstract

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