Journal of Atmospheric and Solar-Terrestrial Physics

Editorial Board

4 hours 13 min ago

Publication date: November 2018

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

Author(s):

Real “guests” from the Solar System or just earth rocks, slag or scrap

4 hours 13 min ago

Publication date: Available online 17 October 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): V. Rusanov, V. Gushterov, N. Velinov, I. Mitov

Abstract

The Mössbauer spectroscopy investigation of mineralogical objects is used in combination with other analytical methods for identification of meteorites as well as for their further classification into groups of iron, stone, and stony-iron meteorites. Only one object found in а small private mineralogical collection was identified as a meteorite most probably a polished section from the Pavel meteorite. A dozen other findings were unambiguously rejected as meteorwrongs. They are no more than earth rocks, steel fragments or man-made cast iron, wrought iron containing slag and residual products from modern or ancient metallurgical processes. According to our estimates, perhaps only one of 100–150 findings can be proved to be an interesting object of extraterrestrial origin. The same set of experimental analytical methods can be used successfully for identification of air- or spacecraft fragments.

Graphical abstract

Meteorites from the Solar System are rare “guests” on the surface of Earth. Large metal pieces with a high iron content tested with strong permanent magnet very often show ferromagnetic behaviors and are declared wrongly as meteorites without any analytical investigations. In this contribution we present some examples of Mössbauer spectroscopic research combined with other analytical methods for mineralogical objects. Our main goal is to unambiguously identify original meteorites and to reject meteorwrongs.

An introduction to equatorial electrodynamics and a review of an additional layer at low latitudes

4 hours 13 min ago

Publication date: Available online 16 October 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): N. Balan, Qiaoling Li, Libo Liu, Huijun Le

Abstract

This paper presents a review of the progress in the understanding of an additional layer in the low latitude ionosphere, the F3 layer. A brief introduction to the daytime equatorial electrodynamics required for understanding the formation of F3 layer and formation of the usual ionospheric regions and layers are also included for continuity. Numerous papers on various aspects of F3 layer and topside ledge (F3 layer in the topside ionosphere) were published by different research groups using observations and modelling. The first time observations and important new aspects are highlighted and areas for further studies are suggested in this review. The important new aspects include an automated procedure for identifying F3 layer, global map of F3 layer and its longitudinal wave structure, solar activity variation of F3 layer and its long term trend, F3 layer in TEC, F3 layer at sunrise and sunset hours, simultaneous observations of F3 layer and upward ExB drift velocity, simultaneous observations of F3 layer in conjugate summer and winter locations, rapid ascend of F3 layer during geomagnetic storms as an indicator of eastward prompt penetration electric field and mechanism of F4 layer. Main points are summarized at the end.

ULF waves observed during substorms in the solar wind and on the ground

4 hours 13 min ago

Publication date: Available online 15 October 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): M. Alimaganbetov, A.V. Streltsov

Abstract

We present results of analysis of ultra-low-frequency (ULF) waves observed by the Advanced Composite Explorer (ACE) satellite at the Earth's L1 Lagrangian point (in the solar wind) and the fluxgate magnetometer at the Poker Flat ground station in Alaska, USA. We considered 75 high-intensity substorm events occurring between October 2015 and April 2017. Our goal is to investigate possible correlation between spectral characteristics of the waves observed in the solar wind and on the ground. Our findings show that: 1) ULF waves with the same frequencies are frequently observed at both locations, in particular, about 30% of the cases yield very good correlation between power spectral density of corresponding signals; 2) the waves with frequencies of 0.60 mHz, 0.70–0.75 mHz are most often seen at both locations; 3) the trend of repeating dominant frequencies is consistent throughout the whole period of observation of about a year and a half. There are also some cases of either mismatch of expectation and occurrence of substorm or a poor correlation between the frequencies of ULF waves detected in space and on the ground. Our findings suggest that the variations of plasma density or the magnetic field in the solar wind indeed serves as a driver for the ULF waves in the Earth's magnetosphere-ionosphere system. This system works like a resonator, and when the frequency of the driver matches one of the eigenfrequencies of the resonator, the large amplitude waves are observed on the ground. When the frequency of the driver mismatch the eigenfrequency, the amplitude of the ground oscillations are much smaller.

Solar wind diamagnetic structures as a source of substorm-like disturbances

4 hours 13 min ago

Publication date: Available online 15 October 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): V.А. Parkhomov, N.L. Borodkova, V.G. Eselevich, M.V. Eselevich, A.V. Dmitriev, V.E. Chilikin

Abstract

The purpose of this study is to generalize the results of investigation of the magnetosphere response to two types of diamagnetic structures. Type 1 is related to sporadic SW, type 2 - to the quasi-stationary “slow” solar wind (SW). First, we consider the Type 1 of diamagnetic structures that are connected with sporadic SW, whose source on the Sun is coronal mass ejections (СМЕs). Near the rear side of a magnetic cloud, one often observes a thin magnetic rope with a high-density plasma. This rope is ejected by a filament (or an eruptive prominence) from the solar surface. The rope is a diamagnetic structure with the same properties, as those of a magnetic tube. Such tubes are diamagnetic, i.e., a diamagnetic current flows on their surface. This current decreases the magnetic field inside the pipe and increases the latter outside. The total pressure (magnetic plus gas-kinetic) is approximately constant inside and outside the tube. Tubes keep their angular size during propagation from the Sun to the Earth, i.e., they are quasi-static. Type 2 represents magnetic tubes (in general case, magnetic ropes) whose sources on the Sun are the streamer belt and the streamer chains or pseudo-streamers. In the Earth orbit, the SW diamagnetic structures are detected by the presence of anti-correlation between the SW proton density and the magnitude of interplanetary magnetic field (IMF). The analysis showed that an interaction of diamagnetic structures (DSs) with the Earth magnetosphere generates substorm-like (sawtooth) magnetic disturbances in the nightside magnetosphere. The disturbances are different from classical substorms because of the absence of the growth phase and of the breakup. The diamagnetic structures related to the quasi-stationary slow SW cause a global modulation of the magnetic activity and of the ionospheric currents with a period close to the period of the variations in the SW plasma density and in the IMF strength inside the diamagnetic structure.

Seismoionospheric anomalies associated with earthquakes from the analysis of the ionosonde data

4 hours 13 min ago

Publication date: November 2018

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

Author(s): Junaid Ahmed, Munawar Shah, Waqar Ali Zafar, Muhammad Ayaz Amin, Talat Iqbal

Abstract

Previous researchers have reported the earthquakes (EQs) induced ionospheric abnormalities, such as electron density depletion and/or enhancement, which they claimed were related to the impending EQs. In this paper, the peak plasma frequency of the ionosonde data from the Islamabad station was studied related to the July 24, 2015 (M5.1), October 26, 2015 (M7.5) and April 25, 2015 (M7.8) EQs in Pakistan and Nepal, respectively. The baseline of the running 30-day median (commonly used in other studies) was deployed on the foF2 data to detect the abnormality in the long term data before the EQs. A detailed analysis of the foF2 variability in a month before all the EQs of this study is then undertaken, where two out of three EQs showed simultaneous deviation in peak plasma frequency relative to the confidence intervals. There is no percentage deviation in foF2 data for the days associated with M7.8, proved no ionospheric signatures in the peak plasma frequency. We believe that the reason is the distance between the epicenter of M7.8 and the ionosonde station, which was approximately 12° longitudinal extension. On the other hand, the negative deviation beyond the lower confidence interval in critical frequency was detected for the mega thrust of M5.1. Similarly, positive foF2 anomalies were recorded within 10 days before the main shock of M7.5, where there was no high intensity geomagnetic storm. These results suggested that in order to detect reliable seismoionospheric precursor, the ionosonde station must operate within the range of seismic breeding zone.

The quasi-6-day waves in NOGAPS-ALPHA forecast model and their climatology in MLS/Aura measurements (2005–2014)

4 hours 13 min ago

Publication date: Available online 11 October 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Dora Pancheva, Plamen Mukhtarov, David E. Siskind

Abstract

This study has examined both: (i) the global structure and seasonal variability of the eastward- and westward-travelling quasi 6-day waves (Q6DWs) observed in the geopotential height (GPH) NOGAPS-ALPHA hourly forecast data during the time interval of 14 months (January 2009–February 2010), and (ii) the climatology and interannual variability of the Q6DWs observed in the satellite MLS/Aura GPH data for an extended period of 10 years (January 2005–December 2014). Both data sets are analyzed by using the same approach. The detailed analysis revealed that the westward-travelling Q6DWs have been identified mainly at mid-high latitudes with zonal wave numbers 1 and 2. Two different types of eastward-travelling waves have been found: (i) waves at middle and high latitudes with zonal wave numbers 1 and 2, which are observed in the local winters, and (ii) waves observed over the equator with zonal wave number 1, which maximize mainly between June and September with a secondary enhancement between January–March belonging to the fast Kelvin waves. Some signatures of the solar cycle and SSW impact on the interannual variability as well as ∼2–3-year variability have been distinguished in the different ∼6-day waves. This study draws attention to both the rarely studied winter-time eastward-travelling PWs and the impact of the SSW events, particularly the major ones, on the short- and long-term variability of the PW populations.

Spatial interpolation of meteorological fields using a multilevel parametric dynamic stochastic low-order model

4 hours 13 min ago

Publication date: Available online 11 October 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): A.V. Lavrinenko, E.A. Moldovanova, D.F. Mymrina, A.I. Popova, K.Y. Popova, Y.B. Popov

Abstract

The paper focuses on a new method of spatial interpolation of air temperature and wind velocity fields in the troposphere. The method is based on Kalman filtering and a multilevel parametric dynamic stochastic low-order model. The key feature of the proposed model is that it has parameters, which are responsible for the altitude levels. Generally, models use so-called “shallow water” (shallow water approximation), and altitude correlation is not taken into account, or they may rely only on mandatory isobaric levels data, thus ignoring the data obtained for significant levels. Standard levels are located at considerable distances in altitude from each other and the altitude correlation there is not usually significant. By using parameters that are responsible for the altitude levels, this model allows us to estimate the effect that information coming from neighbouring altitude levels may have on the final estimate. The paper presents the results of a statistical estimation of the proposed spatial interpolation algorithm. A comparison of the results statistical estimation spatial interpolation of the proposed algorithm with a four-dimensional dynamic-stochastic model is given.

The mean zonal wind effect on the long-term variation of ultra-fast Kelvin waves in the mesosphere and lower thermosphere and in the upper stratosphere

4 hours 13 min ago

Publication date: November 2018

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

Author(s): Wei-Sheng Chen, C.J. Pan, Uma Das

Abstract

This study investigates 14-year ultra-fast Kelvin wave (UFKW) activity in the mesosphere and lower thermosphere (MLT) and in the upper stratosphere where the mesopause semiannual oscillation (MSAO) and the stratopause semiannual oscillation (SSAO) dominate the two altitude regions, respectively. The wave properties are derived from SABER temperature data for the period from 2003 to 2016 by two-dimensional fast Fourier transform. The investigations focus on the UFKW with zonal wavenumber 1 and periods of 2.5–4.5 days. The spectra, daily variations, and seasonal variations of UFKW are investigated. The wave activity is also compared with the background zonal wind derived from the horizontal wind model 2014 (HWM14) for the MLT region and from European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis for the upper stratosphere. The results are that periods of UFKW are mainly in the range of 2.5–4.5 days, but the dominated periods change from year to year. The UFKW amplitudes increase with altitude, and the largest amplitudes occur at altitudes above 90 km. Above 95 km, the mean zonal wind is westward at all times and the amplitude of UFKW is large most of the time. In the MLT region and the upper stratosphere, the large-amplitude UFKW tend to occur in the westward phase of the MSAO and the SSAO. The seasonal variation of UFKW in the MLT region and the upper stratosphere both show a semiannual variation in which the maximum and the secondary maximum are in August and February, respectively. The correlation analysis shows that the time lags between the 90-km wave variation and lower altitude wave variations do not match the theoretical expectation of the wave upward velocity. Finally, the MSAO and the SSAO act like two filters, which modify the wave amplitude and result in different daily variations in the MLT region and in the upper stratosphere.

Energetic cosmic-ray secondary electron distribution at thunderstorm altitudes

4 hours 13 min ago

Publication date: November 2018

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

Author(s): N.C. Lindy, E.R. Benton, W.H. Beasley, D.A. Petersen

Abstract

At present, there is no complete theory describing how lightning discharges are initiated in thunderstorms. The greatest deficiency in existing lightning initiation model is the lack of an explanation for how lightning discharges occur in thunderstorm electric fields that are much weaker than the electric fields required for dielectric breakdown (Bazelyan & Raizer, 1998; McGorman and Rust 1998). Recently it has been suggested energetic cosmic ray secondary electrons propagating in strong thunderstorm electric fields could initiate lightning discharges (Gurevich, A. V. et al., 1992; Carlson et al. 2008). However, the distribution and energy spectrum of secondary electrons at thunderstorm altitudes in the atmosphere have been heretofore not well known. In this paper we report on use of the Monte Carlo code CORSIKA 6.790 to simulate the distribution and determine the energy spectrum of secondary electrons at thunderstorm altitudes. Results from these simulations show that the average secondary electron energy is > 10 MeV with ∼10% of secondary electrons having energy >100 MeV in energy at thunderstorm altitudes. This result is consistent with previous studies.

Relative role of the azimuthal Pedersen current component in the substorm global electric circuit

4 hours 13 min ago

Publication date: November 2018

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

Author(s): M.A. Kurikalova, V.V. Mishin, V.V. Mishin, S.B. Lunyushkin, Yu V. Penskikh

Abstract

In the early, well-known model of the substorm current wedge (SCW) circuit, the azimuthal Pedersen current in the ionosphere closes a pair of the down- and up-ward field-aligned currents connecting the magnetosphere's generator with the ionosphere. In an alternative SCW model, the Pedersen currents flow through the ionosphere in the meridional direction. In this paper, we describe the dynamics of electric currents during the expansion phase of two selected, winter and summer substorms to compare the relative role of the meridional and azimuthal Pedersen currents at the expansion phase peak.

Spatial characteristics of recurrent ionospheric storms at low latitudes during solar minimum

4 hours 13 min ago

Publication date: November 2018

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

Author(s): A. Dmitriev

Abstract

Low-latitude ionospheric disturbances with amplitudes of 20 TECU occurred during moderate recurrent magnetic storms were analyzed in time period from 2007 to 2008. The analysis of these so-called recurrent ionospheric storms (RISs) was based on global ionospheric maps of vertical total electron content derived from the ground based GPS network. It was found that positive RISs were developed predominantly in the noon and postnoon sector and they have very large latitudinal and longitudinal extensions of up to 70 and 160°, respectively. Negative RISs occur mainly in the evening sector and they have ∼1.5 time smaller latitudinal and longitudinal extensions. The different location and spatial scales can be explained by different origins of the ionospheric storms. The large-scale positive ionospheric storms are generated by the mechanism of prompt penetration electric field, operating on the dayside, and by equatorward neutral wind disturbance. The negative storms can be related to the mechanism of disturbance dynamo electric field, operating in the evening sector, and to the changing of the thermospheric neutral composition, operating on sunlight side.

First seasonal and annual variations of atmospheric electric field at a subtropical station in Islamabad, Pakistan

4 hours 13 min ago

Publication date: November 2018

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

Author(s): S.F. Gurmani, N. Ahmad, J. Tacza, T. Iqbal

Abstract

The variation of the atmospheric electric field from the ground is analyzed by using an electric field mill sensor for Islamabad, Pakistan. The first early results of atmospheric electric field are presented in this paper. These results are based on fair-weather days for the diurnal, seasonal, and annual variations in Islamabad from 2015 to 2017. The variation in the values of the atmospheric electric field is studied extensively during the monsoon, the pre-monsoon and the winter season. Minimum values are observed during the monsoon season, and maximum values are observed during winter and spring. The measured values of the atmospheric electric field are also compared with the universal standard values of the Carnegie curve. The trend of the diurnal variation shows a sharp single oscillation in fair-weather with a maximum at ∼ 4:00 UT (universal time), which could be due to the influence of local effects such as aerosol.

Variation of the TEC at a dip equatorial station, Trivandrum and a mid latitude station, Hanle during the descending phase of the solar cycle 24 (2014–2016)

4 hours 13 min ago

Publication date: November 2018

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

Author(s): P.R. Shreedevi, R.K. Choudhary, Sneha Yadav, SmithaV. Thampi, A. Ajesh

Abstract

Morphological variations in the Total Electron Content (TEC) of the ionosphere at a dip equatorial station, Trivandrum (8.47°N, 76.91° E) and a mid latitude station, Hanle (32.78° N, 78.95° E) during the period 2014–2016 is studied using the GPS TEC measurements from the InSWIM (Indian Network for Space Weather Impact Monitoring) network of stations. The variation of the TEC at Hanle, which is located in the same longitude sector as that of Trivandrum, is presented here for the first time. At Hanle, the TEC peaks at local noontime while its peak appears with a delay (1600 LT) at Trivandrum. The minima in the TEC at both stations appear during the early morning hours. Nighttime enhancements in the TEC are seen at Trivandrum during the equinoctial months while at Hanle they appear in the summer months. The TEC at both the stations exhibit semi-annual anomaly and equinoctial asymmetry. However, the winter anomaly is seen only at Trivandrum. The TEC at both Trivandrum and Hanle is seen to display strong solar activity dependence with the average TEC decreasing as solar activity decreases. We surmise that the observed diurnal/seasonal/annual variations in the TEC at the dip equatorial station, Trivandrum is controlled by the processes induced by electrodynamics while the TEC variations at the mid latitude station, Hanle is mostly affected by the neutral dynamical processes. The morphological comparison between the TEC at Trivandrum derived from the IRI 2012 model and GPS TEC measurements shows only a qualitative agreement. The IRI 2012 model is found to overly underestimate the daytime as well as nighttime TEC at the dip equatorial station, Trivandrum while it is well in agreement with the TEC measurements at the mid latitude station, Hanle.

A mathematical model of quasistationary electric field penetration from ground to the ionosphere with inclined magnetic field

4 hours 13 min ago

Publication date: November 2018

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

Author(s): V.V. Denisenko, S.A. Nesterov, M.Y. Boudjada, H. Lammer

Abstract

A quasi stationary model of the electric fields and currents in the conductor that includes the Earth's atmosphere and ionosphere is developed. The role of the inclination of the magnetic field is considered. A mathematical simulation has shown that the resulting electric field in the ionosphere decreases. The penetration of the electric field and current from the ground to the ionosphere can be a physical process which creates observed ionospheric precursors of earthquakes only if the electric field strength and conductivity of the air near ground as well as the size of the pre-earthquake perturbations zone can simultaneously reach extreme possible values. Additional experiments are necessary to verify such a possibility. Other models are analyzed and compared to the main outcomes of our investigations.

Analysis of the differential emission measure distributions for solar flares observed by RESIK

4 hours 13 min ago

Publication date: November 2018

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

Author(s): A. Kepa, B. Sylwester, J. Sylwester, M. Gryciuk, M. Siarkowski

Abstract

The Polish X-ray spectrometer RESIK observed the spectra in four wavelength bands from 3.3 Å to 6.1 Å. This spectral range contains many emission lines of H- and He-like ions for Si, S, Ar and K formed in the high temperature of solar coronal plasma. Analysis of measured spectra gives a possibility to study the differential emission measure distributions (DEM) in the temperature range between 1 MK and 30 MK. We present the analysis of DEM distributions of the multi-peaked C9.8 flare observed by RESIK on 9 January 2003 adopting the model of elementary flare profile (EFP). The model allows to distinguish the individual flare components based on the observed light curves in selected spectral bands.

Spatial, temporal and source study of black carbon in the atmospheric aerosols over different altitude regions in Southern India

4 hours 13 min ago

Publication date: November 2018

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

Author(s): B. Vijay Bhaskar, R.M. Rajeshkumar, K. Muthuchelian, S. Ramachandran

Abstract

Ambient equivalent black carbon (EBC) aerosol mass concentration is regularly observed over a period of 2 years (June 2014 to May 2016) at Kodaikanal, a high-altitude and Madurai, a semi-arid location to study its spatial and temporal characteristics and its sources. The diurnal variation of EBC had two peaks, early morning sharp peak that occurred between 06:00 and 09:00 h (LT) almost an hour after the local sunrise and the evening broad peak that occurred between 19:00 to 22:00 h (LT), while in Kodaikanal late afternoon peaks showed maximum contribution. The difference in the sunshine hours with respect to seasons also caused an effect on the EBC concentration. The mean seasonal values of EBC over Kodaikanal are 2.58 ± 0.15 μg m−3, 1.98 ± 0.19 μg m−3, 1.01 ± 0.19 μg m−3 and 2.48 ± 0.15 μg m−3 and over Madurai 8.97 ± 2.34 μg m−3, 4.69 ± 2.14 μg m−3, 6.70 ± 3.83 μg m−3 and 3.34 ± 2.53 μg m−3 during winter, summer, monsoon and post-monsoon seasons, respectively. The effects of meteorological parameters on EBC at the two stations are investigated and it is found that wind speed and rainfall plays a major role. Source identification is done by calculating absorption Angstrom exponent (α). The absorption Angstrom exponent values ranged from 0.99 to 1.15 with the average value of 1.05 for Madurai and a range from 0.54 to 1.92 with an average value of 1.43 for Kodaikanal, indicating that the major sources of EBC on the study site are from biomass burning and fossil fuel burning sources.

Circulation characteristics of EP and CP ENSO and their impacts on precipitation in South China

4 hours 13 min ago

Publication date: November 2018

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

Author(s): Jiangnan Li, Dazhen Huang, Fangzhou Li, Zhiping Wen

Abstract

EP and CP events have different effects on precipitation in South China (SC). In EP El Niño years, the winter precipitation increases and the summer precipitation is distributed in the form of a tri-pole; specifically, it increases in the northeastern and southwestern parts of SC and decreases in the central and northwestern parts. In EP La Niña years, the winter precipitation decreases in the most part of SC and the summer precipitation increases in the central part of SC and decreases in the eastern and southwestern parts. In CP El Niño years, the summer precipitation increases and the winter precipitation increases in the northeastern part of SC and decreases in the southwestern part. In CP La Niña years, the winter precipitation generally decreases and the summer precipitation decreases in the western and southeastern parts of SC but increases in the central and northeastern parts.

The results of both numerical simulations and diagnostic analyses show that in EP El Niño winters, there is a northerly wind on the lower troposphere of SC conducive to the southward movement of cold air to SC, converging in the south and diverging in the north, in agreement with the distribution of the precipitation anomalies. In the lower troposphere of SC in summer, an abnormal southwester is dominant, facilitating the movement of warm and moist air in the southwest toward SC, which is conducive to an increase in precipitation there. In EP La Niña winter, there is a southwester anomaly in the lower troposphere of SC, which is adverse to the southward movement of cold air from the north to SC, with the divergence field diverging in the south and converging in the north, in agreement with the distribution of precipitation anomalies in this region. In EP La Niña summer, there is a northeaster anomaly in SC that is in the water vapor convergence area, which is conducive to precipitation in SC. In CP El Niño summer. There are northerly winds over SC and an anomalous cyclone over the western Pacific and South China Sea, which was beneficial to precipitation.

Automatic identification of Spread F using decision trees

4 hours 13 min ago

Publication date: November 2018

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

Author(s): Ting Lan, Yuannong Zhang, Chunhua Jiang, Guobin Yang, Zhengyu Zhao

Abstract

Spread F is a commonly observed phenomenon on ionograms caused by plasma irregularities or wave-like structures in the ionosphere. In general, Spread F could induce fluctuations of amplitude and phase of radio waves which travel through the ionosphere. Therefore, investigation of Spread F could be used to not only reveal ionospheric electrodynamics process, but also have a significant engineering application. Due to a large amount of ionograms recorded by ionosondes, it is a challenge work to manually identify ionograms with Spread F to study characteristics of Spread F. Thus, much work has been devoted to automatic identification of Spread F. In the present study, a machine learning method related to decision tree was adopted to automatically identify Spread F from ionograms. First, ionograms were processed by image method and projection techniques to provide input parameters for decision tree. The output of the proposed decision tree is whether Spread F is present or not on ionograms. Then, a set of ionograms was used to construct a decision tree. At last, a set of ionograms was adopted to validate the performance of this decision tree. In this study, ionograms recorded at Puer station (Geographic latitude and longitude: 22.7°N, 101.5°E; Geomagnetic latitude: 12.8°N) in the Yunnan province were used. Results indicate that the decision tree performed well in automatic identification of Spread F on ionograms. The accuracy of automatic identification in a set of ionograms with Spread F was reached up to 89%. It inspires us to continually improve the performance of automatic identification of Spread F in the future work.

Kinematics of CMEs and related shocks from LASCO data: Comparative analysis

4 hours 13 min ago

Publication date: November 2018

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

Author(s): V.G. Fainshtein, Ya.I. Egorov, Yu.S. Zagainova

Abstract

We estimated the positions and velocities of the 10 fast limb CMEs with sources within the 30-degree from the limb and 10 fast halo CMEs with sources within the 30-degree from the solar disk center (central CMEs) using the LASCO-C2 and C3 images. The considered velocities, on which the results are based, include projection effects. We compared kinematic characteristics of the CME body with CME-related shocks whose linear projection velocities greater than 1500 km/s. For all the considered events: (1) the distance between the CME body and the related shock ΔR=(Rsh−Rb) increases with time; (2) the shock velocity Vsh is greater than the CME body velocity Vb; (3) the CME body acceleration modulus |ab| and the related shock acceleration modulus |ash| differ. Herewith, in some cases, |ash|>|ab|, and in other cases, on the contrary, |ash|<|ab|; (4) the difference in the velocities ΔV=(Vsh−Vb) grows with time for limb CMEs and decreases for central CMEs; (5) the variations of velocity-time profiles for the CME and shock are established to be equal: the velocities of both coronal structures either increase or decrease simultaneously. The following averaged values characterize the differences in the kinematics of the CME and shock: 〈ΔR〉  = 1.7 R⊙ (R⊙ is the solar radius), 〈ΔV〉  = 250 km/s, 〈Vsh/Vb〉  = 1.2, 〈ab〉  = 65 m/s2, 〈ash〉  = 70 m/s2.

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