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Journal of Atmospheric and Solar-Terrestrial Physics
Journal Prestige (SJR): 0.696
Citation Impact (citeScore): 2
Number of Followers: 139  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1364-6826
Published by Elsevier Homepage  [3162 journals]
  • The expected fluxes observed by STIX during low solar activity
    • Abstract: Publication date: November 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 179Author(s): M. Gryciuk, P. Podgórski, S. Gburek, T. Mrozek, M. Siarkowski, M. Steslicki, J. Barylak, A. Barylak The Spectrometer Telescope for Imaging X-rays (STIX) is one of the instruments installed onboard Solar Orbiter mission which will be launched in February 2020. After 1.5 years of cruise phase it will start to gather scientific data from the orbit with perihelion distance about 0.28 au. It means that STIX will operate also during the next solar minimum. In the paper we estimate flux measured by the instrument during periods of low solar activity. For this purpose we used solar observations which were recorded by the Solar Photometer in X-rays (SphinX) during the last minimum of solar activity. The estimation was obtained for instruments overlapping energy range from 4 to 15 keV. Presented results indicate that STIX instrument will provide efficient imaging the solar emission even during low level of solar activity (B1 GOES class).
  • Southwest monsoon onset dates over Malaysia and associated climatological
    • Abstract: Publication date: November 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 179Author(s): Sheeba Nettukandy Chenoli, P.R. Jayakrishnan, Azizan Abu Samah, Ooi See Hai, Muhammad Yunus Ahmad Mazuki, Chai Heng Lim In Malaysia precipitation prevails throughout the year. However, the southwest monsoon (late May to September) is characterised with low precipitation, less cloud, high outgoing long-wave radiation (OLR) and often featured by dry epochs. Therefore, onset of the monsoon here is best determined by considering multiple onset parameters such as wind, OLR, rainfall and relative humidity. We used modified Malaysian Meteorological Department wind shear index based on major convection centres during the monsoon onset. The 850 hPa winds were chosen to investigate the onsets of the monsoon in view of the marked orographic and mesoscale processes. The next criterion was the presence of sustained westerlies averaged between 850 hPa and 600 hPa from all the available radiosonde stations data over Malaysia for at least 5 days. As the strongest convective activity in the tropics is represented by OLR of less than 220 W m-2, the third criterion was to check whether the value of OLR was greater than 220 W m-2 over the region. The mean date of the summer monsoon onset over Malaysia is found to be 19 May, with a standard deviation of 8 days. Further, climatological composites show that there is a gradual change from easterlies to westerlies from the surface up to 500 hPa in Malaysian stations both in Peninsular Malaysia and East Malaysia during May. OLR and rainfall analysis reveal that, the southwest monsoon daily rainfall over Malaysia is less than 10 mm and OLR is greater than 220 W m-2. Additionally, monsoon onset tends to be late during the El Niño years and earlier during the La Niña years.
  • GGOS tropospheric delay forecast product performance evaluation and its
           application in real-time PPP
    • Abstract: Publication date: October 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175Author(s): Yibin Yao, Xingyu Xu, Chaoqian Xu, Wenjie Peng, Yangyang Wan Tropospheric delay is one of the main error sources in Global Navigation Satellite System (GNSS) precise positioning, as the GNSS signal is influenced by refraction when travelling through the troposphere. Generally, tropospheric delay is estimated as a parameter in GNSS data processing. With the increasing demand for GNSS real-time applications, high-precision tropospheric delay augmentation information is essential to enhance convergence speed and precision of positioning. The Global Geodetic Observing System (GGOS) Atmosphere provides total zenith tropospheric delay (ZTD) forecast grid data, globally, one day in advance, where the time resolution is 6 h and spatial resolution is 2.5° × 2°. Here, the GGOS ZTD forecast product is assessed compared with ZTD information from global IGS sites, including an analysis of the spatial and temporal distribution of its error and the weather influence on its precision. Ultimately, the application effect of the GGOS Atmosphere ZTD forecast product in real-time precise point positioning (PPP) is examined. The results show that the positioning precision and the speed of convergence are obviously advanced, especially in the U direction, which informs the potential for real-time application of GGOS forecast products.
  • Sausage oscillations in a plasma cylinder with a surface current
    • Abstract: Publication date: October 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175Author(s): Daye Lim, Valery M. Nakariakov, Yong-Jae Moon Linear sausage oscillations of a cylinder embedded in a plasma with an azimuthal magnetic field, created by a current on the surface of the cylinder, are studied. Such a plasma configuration could be applied to modelling flaring loops, and magnetic ropes in coronal mass ejections. The plasma is assumed to be cold everywhere. Dispersion relations demonstrate that the lowest radial harmonic of the sausage mode is in the trapped regime for all values of the parallel wave number. In the long-wavelength limit, phase and group speeds of this mode are equal to the Alfvén speed in the external medium. It makes the oscillation period to be determined by the ratio of the parallel wavelength, e.g. double the length of an oscillating loop, to the external Alfvén speed, allowing for its seismological estimations. The application of the results obtained to the interpretation of long-period (longer than a minute) oscillations of emission intensity detected in solar coronal structures, gives reasonable estimations of the external Alfvén speed. Cutoff values of the parallel wavenumber for higher radial harmonics are determined analytically. Implications of this finding to the observational signatures of fast magnetoacoustic wave trains guided by cylindrical plasma non-uniformities are discussed.
  • Measurement of continuing charge transfer in rocket-triggered lightning
           with low-frequency magnetic sensor at close range
    • Abstract: Publication date: October 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175Author(s): Gaopeng Lu, Yanfeng Fan, Hongbo Zhang, Rubin Jiang, Mingyuan Liu, Xiushu Qie, Steven A. Cummer, Congzheng Han, Kun Liu Based on the magnetic fields recorded with a compact low-frequency (LF) magnetic sensor deployed at 78 m distance from the channel base, we reconstruct the time-resolved current waveform for the continuously discharging processes in classical rocket-and-wire triggered lightning flashes, including the initial continuous current (ICC) and long continuing current. Both the overall feature and the millisecond-scale slow variations (e.g., initial current variation, ICC pulses and M-components) embedded in the channel-base current as measured with the conventional methods (such as the shunt or Pearson coil) can be retrieved through the numerical integral of close LF magnetic signals. Despite the artifact caused by the magnetic fields radiated by the fast in-cloud processes, the new approach has the advantage of significantly reduced noise in comparison with the measurements of conventional methods, and it is likely applicable to remotely measure the initial continuous current in upward lightning from high objects and altitude-triggered lightning, as well as long continuing current in natural cloud-to-ground (CG) lightning strokes that occur at sufficiently close range (e.g., within 100 m).
  • Signature of gravity waves and ionospheric perturbations over European and
           North African region during the solar eclipse of 1 August 2008
    • Abstract: Publication date: October 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175Author(s): Ayman Mahrous, Mohammed Mainul Hoque, Eman M. El-Desoky Solar eclipses provide unique chances to study the ionospheric/thermospheric response to solar radiation changes. The solar eclipse of 1 August 2008 was an outstanding event since it has occurred during the deep minimum of the solar cycle 23. The ionospheric behavior during that event has been investigated using global GPS-Total Electron Content (TEC) maps, COSMIC satellite measurements and Coherent Ionospheric Doppler Radar (CIDR). We analyzed the behavior of total ionospheric ionization over European and North African region by reconstructing TEC maps and differential TEC maps. TEC estimation showed that the total ionization reduces up to 30% at high latitude region during the eclipse as a function of obscuration. COSMIC observations showed a height profile of percentage reduction in electron density with a maximum reduction at the F2 layer of about 30%. The CIDR system allowed us to study the spatial changes of the ionospheric F2 layer during the passage of the solar eclipse which revealed many interesting features of horizontally-propagating gravity waves with wavelength (λ) about 752.39 km and velocity ∼ 151.28 km/min associated with the solar eclipse. The wavelet analysis displays the existence of Wave-like Structures (WLS) of ∼5 min period at F-region altitude.
  • Reflection from and transmission through the ionosphere of VLF
           electromagnetic waves incident from the mid-latitude magnetosphere
    • Abstract: Publication date: October 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175Author(s): P.A. Bespalov, V.G. Mizonova, O.N. Savina Trans-ionospheric propagation of the VLF electromagnetic wave from an altitude of 800 km to the Earth's surface is considered using the model of stratified media. The numerical solution of the wave equations for the mid-latitude ionosphere model conditions is found. The wave field in the lower ionosphere is calculated using the full-wave approach. The wave field in the upper ionosphere is calculated using the matrix method of perturbations for a slightly inhomogeneous plasma. Energy reflection coefficient and the horizontal magnetic field amplitude of the wave on the ground surface are calculated. Peculiarities of the wave reflection and transmission at different times of the day are analyzed. The obtained results are important for studying the ELF/VLF emission phenomena observed both onboard the satellites and in ground-based observatories.
  • First results on the retrieval of noctilucent cloud albedo and occurrence
           rate from SCIAMACHY/Envisat satellite nadir measurements
    • Abstract: Publication date: October 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175Author(s): M.P. Langowski, C. von Savigny, T. Bachmann, M.T. DeLand We present the first results on the retrieval of noctilucent cloud (NLC) albedos and occurrence rates from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartography) nadir data. The applicability of already available algorithms is discussed and necessary changes are reasoned. The occurrence rates for different latitude ranges are presented. During the summer period, when NLCs occur, the NLC occurrence rates show a maximum which is strongest at the highest latitudes. This is consistent with other observation methods. For the spring and autumn period, however, false NLC detections are observed at latitudes between 45°N and 65°N, where no NLCs are expected. The reason for this, and why it does not affect the retrieval during the NLC season is discussed. We also compared the SCIAMACHY nadir NLC occurrence rates with the ones retrieved from the SCIAMACHY limb measurements and the ones of SBUV and found qualitative agreement of these data sets.
  • Dust modification of the plasma conductivity in the Earth's mesosphere
    • Abstract: Publication date: October 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175Author(s): B.P. Pandey, S.V. Vladimirov Relative transverse drift (with respect to the ambient magnetic field) between the weakly magnetized electrons and the unmagnetized ions at the lower altitude (
  • Mechanisms for varying non-LTE contributions to OH rotational temperatures
           from measurements and modelling. I. Climatology
    • Abstract: Publication date: October 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175Author(s): Stefan Noll, Bastian Proxauf, Wolfgang Kausch, Stefan Kimeswenger Rotational temperatures Trot from OH line intensities are an important approach to study the Earth's mesopause region. However, the interpretation can be complicated as the resulting Trot are effective values weighted for the varying OH emission layer. Moreover, the measured Trot only equal kinetic temperatures Tkin if the rotational level population distribution for the considered OH lines is fully thermalised. In many cases, this basic condition of a local thermodynamic equilibrium (LTE) does not seem to be fulfilled. In order to better understand the non-LTE temperature excesses ΔTNLTE and their variations, we used Trot measurements based on 1526 high-resolution spectra of the UVES spectrograph at the Very Large Telescope at Cerro Paranal in Chile in combination with Tkin weighted for the OH emission layer based on 4496 nighttime temperature and OH emission profiles from the SABER radiometer onboard TIMED taken at a similar location. Both data sets were linked via climatologies consisting of the nighttime and seasonal temperature variations. The study focusses on the non-LTE effects at the vibrational level v=9, which is directly populated by the OH-producing hydrogen–ozone reaction and therefore especially prone to incomplete thermalisation of the rotational level population. In comparison to the less critical v=3, the ΔTNLTE climatology showed clear and strongly variable temperature excesses of several kelvins with minima in the evening around the equinoxes and a reliable maximum in the second half of the night around the turn of the year. The Trot non-LTE contributions are positively correlated with the effective OH emission height and volume mixing ratio of atomic oxygen. A significant anti-correlation is found for the air density. Thus, especially variations in the OH emission layer altitude and shape, which are related to changes in the layer-weighted chemical composition and density, are important for the amount of ΔTNLTE.
  • Mechanisms for varying non-LTE contributions to OH rotational temperatures
           from measurements and modelling. II. Kinetic model
    • Abstract: Publication date: October 2018Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175Author(s): Stefan Noll, Bastian Proxauf, Wolfgang Kausch, Stefan Kimeswenger OH rotational temperatures Trot deviate from kinetic temperatures Tkin if the rotational level populations derived from the measured OH lines are not in local thermodynamic equilibrium (LTE). In particular,. from OH bands wi Trot th high upper vibrational level appear to be affected by incomplete rotational relaxation and corresponding non-LTE temperature excesses ΔTNLTE. The processes that lead to these non-LTE effects and their variations have not been investigated in detail so far since this requires thorough modelling of the rotational relaxation based on suitable observing data. We performed such an effort for the vibrational level v=9. As it is the highest v that can be populated by the OH-producing hydrogen–ozone reaction, the relaxation processes are the least complex ones. Nevertheless, there are many systematic uncertainties. Therefore, we studied the ΔTNLTE depending on the Einstein A-coefficients used, the very uncertain rate coefficient for the v=9 deactivating collisions of OH with atomic oxygen, and the input profiles for Tkin, air density, and the volume mixing ratios of N2, O2, O, and O3. For the profiles, we used SABER products, where we adapted the O retrieval for a better agreement with the model, and the empirical NRLMSISE-00 model. The profiles were selected or calculated for the Cerro Paranal region in Chile since this allowed us to combine OH Trot measurements based on high-resolution spectra of the UVES spectrograph at the Very Large Telescope with the SABER Tkin and OH emission profiles for an alternative, fully observation-based ΔTNLTE derivation. Moreover, we measured OH(v=9) rotational level populations up to the rotational state N=10 based on UVES OH(9-3) and OH(9-4) line measurements. With these data in comparison with a grid of models, we derived the best-fitting crucial rate coefficients for the rotational relaxation at v=9, which have not been studied before. With the final models, we calculated ΔTNLTE climatologies and compared them with those from the UVES-based data. Significant ΔTNLTE and similar variability structures could be identified. Moreover, we analysed the model in order to find the mechanisms that cause the variations. Here, the steep increase of ΔTNLTE with altitude combined with the height variations of the OH layer appears to be the most important process.
  • On the ionospheric propagation of VLF waves generated by currents in the
           lower ionosphere
    • Abstract: Publication date: Available online 11 July 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): I.V. Kuzichev, I. Yu Vasko, A. Yu Malykhin, A.R. Soto-Chavez The consistent description of ELF/VLF wave propagation in the ionosphere is essential for understanding the properties of the wave phenomena observed both at the ground and satellites. Due to strong inhomogeneity of the lower ionosphere coupled with collisional damping of a wave, the geometrical optics approach is not valid, while the full-wave approach suffers from the problem of numerical instability. In this paper, we implement a rather general and powerful method avoiding the numerical instability to study propagation of the wave generated in the lower ionosphere. Our calculations demonstrate the quasi-periodic behaviour of the field in the upper ionosphere, which is associated with the Earth-ionosphere waveguide. The field distribution varies significantly with frequency, from being nearly sign-definite to oscillating with comparable positive and negative values, producing the ring structure in wave-vector space. The field distribution at the ground is studied and shown to have resonant structure defined by two parameters: number of the resonance, which depends on wave frequency, and spatial scale of the Earth-ionosphere waveguide.
  • A GNSS-based weather forecasting approach using Nonlinear Auto Regressive
           Approach with Exogenous Input (NARX)
    • Abstract: Publication date: Available online 30 June 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Zhoobin Rahimi, Helmi Zulhaidi Mohd Shafri, Masayu Norman The rapid variation of precipitation that occurs in the troposphere potentially affects weather conditions. Using GNSS-derived precipitable water vapour (PWV) and external input of rainfall data is useful and beneficial for the prediction of rapid changes of PWV which eventually leads to rainfall prediction in near real time. A nonlinear autoregressive approach with exogenous input (NARX) is an effective approach to statistical forecasting which is used in weather forecasting studies. Furthermore, choosing the most effective algorithm between the Levenberg Marquardt regularization and Bayesian Regularization may be ideal for predicting rainfall. Ten GNSS stations from the Malaysia real-time kinematic network (MyRTKnet) were selected. The selected GNSS stations cover Perak states in Malaysia from 1 January to 31 December 2013. While Obtained results from linear regression model show only 1% correlation between rainfall data and GNSS-derived PWV, comparing the predicted values by NARX networks and actual data show a significant improvement. Addition of GNSS-derived PWV along with daily rainfall data collected from meteorological stations significantly improves the prediction results between 30% and 59% correlation for Bayesian and Levenberg Marquardt regularization, respectively. Furthermore, the Levenberg Marquardt training algorithm may be the most accurate model among the forms of ANN used. Such a significant improvement is favourable to use NARX networks for near real time prediction.
  • Dust and dust storms over Kuwait: GROUND-BASED and satellite observations
    • Abstract: Publication date: Available online 19 June 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Ismail Sabbah, Jean-François Léon, Mar Sorribas, Benjamin Guinot, Carmen Córdoba-Jabonero, Amaury de Souza, Faisal Al Sharifi We investigate the consistency between Aerosol Optical Depth (AOD) retrieved by MODerate resolution Imaging Spectroradiometer (MODIS) sensor aboard NASA's Aqua satellite and measurements collected by ground-based AErosol RObotic NETwork (AERONET) site in Kuwait for 2007–2012. A good correlation (r = 0.7) is obtained between the two data sets. The volume size distributions (VSDs) of particles with geometric mean radius ranges of 0.05–15 μm has been studied as well. Seasonal variations are clearly found in the shape and magnitude of the VSDs for fine and coarse particles. The VSD of aerosol coarse particles was the highest during spring and summer. It increases substantially during dust storms, reaching the highest value during the dust storm of 24 May 2012. Satellite lidar observations from CALIPSO reveals a moderate vertical extent of the dust storms with the highest extinction coefficients below 500 m height. The method of superposed epoch analysis is used to test the behavior of meteorological parameters during the dusty days of 2012. Increase in wind speed together with significant reductions in visibility and diurnal temperature range (DTR) during dusty days are observed. Additionally, air temperature decreases one day after dust events. This effect can be due to scattering of sunlight back to space by the suspended dust particles.
  • Prominence activation by increase in electric current
    • Abstract: Publication date: Available online 18 June 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): V.V. Zaitsev, A.V. Stepanov We consider activation of a solar prominence by sharp increase in electric current in the frame of the Kuperus-Raadu model. The dynamics of the prominence is described in terms of the Ampère force, gravity, and the drag force. We suggest that the drag force is determined by the ion viscosity of ambient plasma. The upward Ampère force acting on the filament increases with the electric current in the filament, which results in the increase in the height of the filament. As a result of the dynamical process, a new equilibrium state corresponding to the new value of the electric current is reached. The maximum height and velocity of the prominence are estimated using the nonlinear equation for prominence dynamics. A sharp increase in the electric current can be due to the magnetic Rayleigh-Taylor instability in the chromospheric footpoints of the filament. Two examples of solar active filaments are analyzed in the context of the proposed model. Failed or two-stage eruption of the prominences is also discussed.
  • Variations of the main nighttime ionospheric density anomalies observed by
           DEMETER during the descending phase of solar cycle 23
    • Abstract: Publication date: Available online 5 June 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Rui Yan, Michel Parrot, Jean-Louis Pinçon This paper is related to analysis of the Weddell Sea Anomaly (WSA) and the Mid-latitude Summer Nighttime Anomaly (MSNA) observed by the low altitude satellite DEMETER during nighttime between 2004 and 2010. This time interval corresponds to the decrease of the solar cycle 23 which was unusually long. It appears that, if these two anomalies have a peak in local summer (December in the Southern hemisphere for the WSA, June in the Northern hemisphere for the MSNA), the anomalies are also observed during the months around December and June with a decreased intensity. But at the end of the solar cycle 23 the summer peaks dramatically decrease and even relatively more quickly than the solar index F10.7. This phenomenon is much more significant for the WSA. It is shown that the mechanism producing the two anomalies (thermospheric neutral winds and magnetic declination effects) is strengthened by the solar ionization which is active during the night above the WSA and the MSNA areas. But at solar minimum, this mechanism is weakened. These results are valid at the satellite altitude (660 km) and may vary at lower altitudes.
  • Analyses on the altitude variation of radiation contributions for
           submillimeter channel sets
    • Abstract: Publication date: Available online 4 June 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Hai-Ying Li, Zhen-Sen Wu, Le-Ke Lin, Chang-Sheng Lu, Zhen-wei Zhao, Tan Qu, Cheng Wang This study investigated variation in the upwelling radiation contribution to typical remote sensing channels of temperature (50–60 GHz, 118 GHz, and 424 GHz) and water vapor (22 GHz, 183 GHz, and 380 GHz) with altitude to evaluate their sounding abilities and obtain channel sets for sounding of lower atmosphere with high resolution. The gaseous attenuation described in Recommendation ITU-R P.676–11 and atmosphere profiles illustrated in Recommendation ITU-R P.835–6 were applied to calculate the upwelling radiation based on radiative transfer theory. The variation of brightness temperature contribution (Tb contribution vs. altitude) with both channels and profiles was analyzed in detail. The Tb contribution altitude at microwave channels was lower than that at submillimeter channels, making higher frequency channels suitable for remote sensing of the middle and upper atmosphere. Offset frequencies were selected to extend the sounding range: offsets of up to 1 GHz for the 118 GHz channel and up to 10 GHz for the 183 GHz channel enable sounding of the Earth's atmosphere. Differences in the Tb contribution altitudes to different profiles were more significant for water vapor than temperature channels because of the variable distribution of water vapor in the atmosphere. Therefore, the sounding ability of one channel varies for different profiles. An offset frequency of 10 GHz for the 380 GHz channel is sufficient for sounding the Earth's atmosphere in high latitude winter. Sea surface radiation calculations indicated that it can be neglected for the 380 GHz and 424 GHz channels even for the high latitude winter.
  • Solar activity variations inducing effects of light scattering and
           refraction in the Earth's atmosphere
    • Abstract: Publication date: Available online 2 June 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Pavel Kovadlo, Artem Shikhovtsev, Vladimir Lukin, Elena Kochugova Possible mechanism of solar activity effect on scattering radiation as well as the intensity of exchange processes in the different layers of the troposphere is discussed in this paper. In particular the response of the earth's atmosphere scattering and refraction characteristics to the 11 year variations of the sunspots' formation activity is considered. Analysis of the radiation data show that one may observe significant growth of the mean annual values of diffuse radiation while a total solar activity decreasing in certain years. The effect of solar activity on the diffuse radiation fluctuations is most pronounced over a long time periods, the duration of which is more than 11 years. The effect of any connection becomes invisible at the shortest time intervals when high-frequency perturbations are imposed.
  • Three case studies of height-time profiles of prominence eruptions
           observed by AIA and LASCO
    • Abstract: Publication date: Available online 2 June 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Ts Tsvetkov, N. Petrov The motions of three solar eruptive prominences are studied. The behaviour of the rising prominence body during the eruption is tracked. Height-time profiles of the eruption up to 6 R⊙ (based on observations by Solar Dynamics Observatory/Atmospheric Imaging Assembly (HeII 304 Å) and Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2/Solar and Heliospheric Observatory (SOHO)) and possible changes of the velocity of the prominence material are presented. The mechanisms that generate the variations in the material movement are discussed.
  • Peculiarities of acoustic-gravity waves in inhomogeneous flows of the
           polar thermosphere
    • Abstract: Publication date: Available online 31 May 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): A.K. Fedorenko, E.I. Kryuchkov, O.K. Cheremnykh, Yu.O. Klymenko, Yu.M. Yampolski The peculiarities of acoustic-gravity waves propagating in inhomogeneous polar thermosphere flows have been investigated. It is shown that a spectrum filtration and a change in amplitudes of acoustic-gravity waves occur in the region of polar thermosphere circulation. As a result, the waves with horizontal lengths of 500–700 km and periods of ∼ 10 min are predominated in satellite observations. We have shown that such spectral properties correspond to the waves which are blocked in the counter flow. The amplitudes of the blocked waves are greatly enhanced due to their interaction with the non-uniform flow. A ground-based observer registers these waves with periods from 30 min to more than 1 h, depending on the flow velocity. Taking in to account the interaction of the waves with the flows we can explain the discrepancy between the results of satellite and ground-based observations of acoustic-gravity wave in the polar regions.
  • Comparison of planetary and local geomagnetic disturbance indices:
           Operational implications
    • Abstract: Publication date: Available online 30 April 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Wonhyeong Yi, Jiyoung Kim Geomagnetic storms can disrupt social infrastructure on Earth; thus, accurate and timely monitoring is required to reduce their future socioeconomic impact. This study compares the planetary geomagnetic disturbance index (KP) with local indices at Fredericksburg (FRD) and Kakioka (KAK) stations. Local K indices at KAK and Cheongyang (CYG) are estimated and validated using indices observed at both stations. We found generally similar correlations between the KP index and the local K indices at FRD and KAK; however, their details differ. The results show that, even when planetary geomagnetic storms are observed, the local K can be smaller than the observed KP. This implies that both KP and local K should be simultaneously monitored. Real-time estimation of local K shows that the estimated K at KAK and CYG correlates well with the observed K. The estimation probability at KAK and CYG, with an error range of ±1, is greater than 98% when the local K is greater than 3. This suggests that the estimation approach used in this study can be operationally applied for timely monitoring of local geomagnetic disturbances.
  • Long-term solar activity studies using microwave imaging observations and
           prediction for cycle 25
    • Abstract: Publication date: Available online 23 April 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): N. Gopalswamy, P. Mӓkelӓ, S. Yashiro, S. Akiyama We use microwave imaging observations from the Nobeyama Radioheliograph at 17 GHz for long-term studies of solar activity. In particular, we use the polar and low-latitude brightness temperatures as proxies to the polar and active-region magnetic fields, respectively. We also use the locations of prominence eruptions as a proxy to the filament locations to study their time variation. We show that the polar microwave brightness temperature is highly correlated with the polar magnetic field strength and the fast solar wind speed. We also show that the polar microwave brightness in one solar cycle is correlated with the low latitude brightness with a lag of about half a solar cycle. We use this correlation to predict the strength of the solar cycle 25: the smoothed sunspot numbers in the southern and northern hemispheres can be predicted as 89 and 59, respectively. These values indicate that cycle 25 will not be too different from cycle 24 in its strength. We also combined the rush-to-the-pole data from Nobeyama prominences with historical data going back to 1860 to study the north-south asymmetry of sign reversal at solar poles. We find that the reversal asymmetry has a quasi-periodicity of 3–5 cycles.
  • Current sheets in corona and X-ray sources for flares above the active
           region 10365
    • Abstract: Publication date: Available online 27 February 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): A.I. Podgorny, I.M. Podgorny, N.S. Meshalkina The coincidence of current sheets positions obtained from results of numerical MHD simulation for flares May 27, 2003 at 02:53 UT and May 29, 2003 at 00:51 UT with positions of observed X-ray sources confirm the mechanism of solar flare according to which the magnetic energy of the current sheet is released in corona above an active region. To study the magnetic field configuration obtained from 3D MHD simulation, the system of graphic presentation is developed. Magnetic field lines in 3D space have a complex configuration near a current sheet above the active region which can be investigated using the developed system of visualization. The physical meaning of the processes in the current sheet is best demonstrated by the lines in the plane of the current sheet configuration which are tangential to the projections of the magnetic field vectors on this plane. Position of such lines defines the magnetic forces, which create the current sheet and then destroy it, when the system turns into an unstable state. Analysis of magnetic lines in large area above the active region allows make a preliminary conclusion about existence of the magnetic lines that connect the hard X-ray sources and the current sheet.
  • Magnetospheric Multiscale Observations of Turbulent Magnetic and Electron
           Velocity Fluctuations in Earth's Magnetosheath Downstream of a
           quasi-parallel bow shock
    • Abstract: Publication date: Available online 13 February 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): C.J. Pollock, J.L. Burch, A. Chasapis, B.L. Giles, D.A. Mackler, W.H. Matthaeus, C.T. Russell We present statistical single-spacecraft observations of magnetic and electron velocity fluctuations in Earth's magnetosheath, likely in the vicinity of the magnetopause, downstream of a bow shock immersed in quasi-parallel interplanetary magnetic field conditions, a situation conducive to plasma turbulence in the downstream flow. These fluctuations exhibit scale-dependent behavior, wherein histograms of their Partial Variance of Increments (PVIB or PVIVe) demonstrate highly non-Gaussian forms at small scales and are reasonably well-described by kappa distributions, albeit with fitted values of the kappa parameter only slightly larger than 1.5, exemplifying their power law nature at large values of PVI. At larger scales, the PVI histograms lose their non-Gaussian nature and are well described by both Gaussian and kappa distributions with large values of the kappa parameter. The PVI histograms furthermore exhibit kurtosis that increases with decreasing scale, a characteristic that is much more prominent in the magnetic fluctuations than in the electron velocity fluctuations. This feature that is not yet explained. In both cases, the results are characteristic of turbulent intermittency.
  • Integration of RAM-SCB into the Space Weather Modeling Framework
    • Abstract: Publication date: Available online 7 February 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Daniel T. Welling, Gabor Toth, Vania K. Jordanova, Yiqun Yu Numerical simulations of the ring current are a challenging endeavor. They require a large set of inputs, including electric and magnetic fields and plasma sheet fluxes. Because the ring current broadly affects the magnetosphere-ionosphere system, the input set is dependent on the ring current region itself. This makes obtaining a set of inputs that are self-consistent with the ring current difficult. To overcome this challenge, researchers have begun coupling ring current models to global models of the magnetosphere-ionosphere system. This paper describes the coupling between the Ring current Atmosphere interaction Model with Self-Consistent Magnetic field (RAM-SCB) to the models within the Space Weather Modeling Framework. Full details on both previously introduced and new coupling mechanisms are defined. The impact of self-consistently including the ring current on the magnetosphere-ionosphere system is illustrated via a set of example simulations.
  • Plausible modulation of solar wind energy flux input on global tropical
           cyclone activity
    • Abstract: Publication date: Available online 6 February 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Hui Li, Chi Wang, Shengping He, Huijun Wang, Cui Tu, Jiyao Xu, Fei Li, Xiaocheng Guo Studies on Sun-climate connection have been carried out for several decades, and almost all of them focused on the effects of solar total irradiation energy. As the second major terrestrial energy source from outer space, the solar wind energy flux exhibits more significant long-term variations. However, its link to the global climate change is rarely concerned and remains a mystery. As a fundamental and important aspect of the Earth's weather and climate system, tropical cyclone activity has been causing more and more attentions. Here we investigate the possible modulation of the total energy flux input from the solar wind into the Earth's magnetosphere on the global tropical cyclone activity during 1963–2012. From a global perspective, the accumulated cyclone energy increases gradually since 1963 and starts to decrease after 1994. Compare to the previously frequently used parameters, e.g., the sunspot number, the total solar irradiation, the solar F10.7 irradiation, the tropical sea surface temperature, and the south oscillation index, the total solar wind energy flux input exhibits a better correlation with the global tropical cyclone activity. Furthermore, the tropical cyclones seem to be stronger with more intense geomagnetic activities. A plausible modulation mechanism is thus proposed to link the terrestrial weather phenomenon to the seemingly-unrelated solar wind energy input.
  • Spectral characteristic of geomagnetically induced current during
           geomagnetic storms by wavelet techniques
    • Abstract: Publication date: Available online 2 February 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Binod Adhikari, Nirakar Sapkota, Subodh Dahal, Binod Bhattarai, Krishna Khanal, Narayan P. Chapagain 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
    • Abstract: Publication date: Available online 1 February 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Shikun Lu, Hao Zhang, Xihai Li, Yihong Li, Chao Niu, Xiaoyun Yang, Daizhi Liu 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
    • Abstract: Publication date: Available online 31 January 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Zamri Zainal Abidin, M.H. Jusoh, M. Abbas, O.S. Bolaji, A. Yoshikawa 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
    • Abstract: Publication date: Available online 31 January 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Zamri Zainal Abidin, M.H. Jusoh, M. Abbas, A. Yoshikawa 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.
  • Statistic study of the geoeffectiveness of compression regions CIRs and
    • Abstract: Publication date: Available online 31 January 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Yu I. Yermolaev, I.G. Lodkina, N.S. Nikolaeva, M.Yu Yermolaev, M.O. Riazantseva, L.S. Rakhmanova We statistically study the geoeffectiveness of two types of compression regions: corotating interaction regions (CIRs) before the solar wind high-speed streams (HSSs) from the coronal holes and Sheaths before the fast interplanetary CMEs (ICMEs) including flux-rope magnetic clouds (MCs) and non-MC Ejecta using the OMNI dataset ( (King and Papitashvili, 2004)) and our Catalog of large-scale solar wind phenomena for 1976–2000 ( et al., 2009)). Our analysis shows that the magnitude of the interplanetary magnetic field B in CIRs and Sheaths increases with increasing speed of both types of pistons: HSS and ICME; the increase of the piston speed results in the increase of geoeffectiveness of both compression regions. The value B in Sheaths before Ejecta is higher than B in Ejecta. The value B in Sheaths before MCs in the beginning of phenomena interval is lower than in MCs but in the end of interval it is close to B in MCs. The contribution of Sheath in storm generation can be significant for so-called "CME-induced" storms and Sheath-induced storms should be identified and analyzed separately.
  • Polar cap patches observed by the EISCAT Svalbard Radar: A statistical
           study of its dependence on the solar wind and IMF conditions
    • Abstract: Publication date: Available online 16 January 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Yuyan Jin, Zanyang Xing, Qinghe Zhang, Yong Wang, Yuzhang Ma 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.
  • Extension of ITU-R method for 1-hour to 1-minute conversion of rain rate
           statistics for satellite propagation in Malaysia
    • Abstract: Publication date: Available online 8 January 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Yun Yann Ng, Mandeep Singh Jit Singh, Vinesh Thiruchelvam 1-min rain rate is the key element to precisely predicting rain attenuation at a given location. However, there is a limitation in 1-min rain rate availability in Malaysia for long-term local measurement, because rain rate statistics are commonly derived on the rain gauge recordings base with actual integration times of 10 min or longer. Therefore, conversion of available rain rate distributions with longer integration times to 1-min rain rate distributions is necessary. This study proposes a novel set of coefficients to current ITU-R for Malaysia in order to improve the accuracy of the 1-h to 1-min rain rate conversion process. According to the results, the test indicates that the proposed set of coefficients outperformed previous work in terms of accuracy. This study is crucial to provide more accurate regression coefficients to system designers when designing link margins.
  • Understanding the global dynamics of the equatorial ionosphere in Africa
           for space weather capabilities: A science case for AfrequaMARN
    • Abstract: Publication date: Available online 6 January 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Hammed A. Lawal, Mark Lester, Stanley W.H. Cowley, S.E. Milan, T.K. Yeoman, Gabby Provan, Suzie Imber, A.Babatunde Rabiu 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.
  • Data-adaptive harmonic analysis and modeling of solar wind-magnetosphere
    • Abstract: Publication date: Available online 4 January 2018Source: Journal of Atmospheric and Solar-Terrestrial PhysicsAuthor(s): Dmitri Kondrashov, Mickaël D. Chekroun The solar wind-magnetosphere coupling is studied by new data-adaptive harmonic decomposition (DAHD) approach for the spectral analysis and inverse modeling of multivariate time observations of complex nonlinear dynamical systems. DAHD identifies frequency-based modes of interactions in the combined dataset of Auroral Electrojet (AE) index and solar wind forcing. The time evolution of these modes can be very efficiently simulated by using systems of stochastic differential equations (SDEs) that are stacked per frequency and formed by coupled Stuart-Landau oscillators. These systems of SDEs capture the modes' frequencies as well as their amplitude modulations, and yield, in turn, an accurate modeling of the AE index' statistical properties.
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Heriot-Watt University
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