Journal of Atmospheric and Solar-Terrestrial Physics

Ionospheric anomalies preceding the low-latitude earthquake that occurred on April 16, 2016 in Ecuador

Sun, 01/13/2019 - 19:10

Publication date: January 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 182

Author(s): Carlos Sotomayor-Beltran

Abstract

A catastrophic seismic event of Mw 7.8 occurred on April 16, 2016 in Ecuador. As with some other major earthquakes, many human lives were lost. Thus in the last two decades, the search for seismo-ionospheric signatures has become an active field of research. In order to provide further insights into ionospheric precursors of earthquakes, Global Ionospheric Maps (GIMs) provided by the Center for Orbit Determination in Europe (CODE) were used to look for ionospheric anomalies prior to the earthquake in Ecuador. By producing differential Vertical Total Electron Content (VTEC) maps and using a statistical method, a negative ionospheric anomaly was observed 10 days before the incident. At different confidence levels the negative disturbance was permanently visible. This anomaly also is located within the earthquake preparation zone, defined by the Dobrovolsky equation. Additionally, due to the extreme low-latitude nature of the earthquake, the dynamics of the Equatorial Ionization Anomaly (EIA) shape were observed. A further confirmation of the ionospheric anomaly was provided by the dramatic change of the EIA 10 days before the earthquake with respect to a non-disturbed day. Due to the really quiet geomagnetic and solar conditions for April 6, 2016, the negative anomaly is considered to be a seismo-ionospheric signature.

Magnetotail boundary crossings at lunar distances: ARTEMIS observations

Sun, 01/13/2019 - 19:10

Publication date: January 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 182

Author(s): Iklim Gencturk Akay, Zerefşan Kaymaz, David G. Sibeck

Abstract

We compare results from a preliminary analysis of two years of ARTEMIS magnetopause boundary crossings at lunar distances with available empirical models. We remove the effects of variable solar wind flow directions and aberration angles to study the magnetotail cross-section as a function of solar wind conditions. The average magnetopause distance from the central axis is 26 RE, but this distance ranges from 10 RE for high solar wind dynamic pressures and strong northward IMF orientations to 39 RE for low solar wind dynamic pressures and weak southward IMF orientations compared to the nominal solar wind conditions. The time-independent Howe and Binsack (1972) model describes the average location of the crossings very well. For high solar wind dynamic pressures, the Lu et al., (2011) model performs best, while for low pressures the Petrinec and Russell (1996) model gives the closest prediction. As predicted by theory and seen in past studies, the magnetotail cross-section is suggestive of prolate during intervals of strong IMF By, but oblate during intervals of strong IMF Bz. Any asymmetric variation of the tail boundary with respect to the sign of IMF By was not observed. The decreasing size of boundary with the increasing dynamic pressure was found when dynamic pressures are smaller than 2 nPa. Although the scatter is larger, the tail size for pressures larger than 2 nPa suggests a constant radius. The tail boundary size decreases as the strength of IMF Bz increases regardless of its polarity. However, it was also observed that an even stronger southward IMF Bz can cause larger magnetopause size in the presence of large dynamic pressures.

Has global warming already arrived?

Sun, 01/13/2019 - 19:10

Publication date: January 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 182

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

Abstract

The enhancement of the atmospheric greenhouse effect due to the increase in the atmospheric greenhouse gases is often considered as responsible for global warming (known as greenhouse hypothesis of global warming). In this context, the temperature field of global troposphere and lower stratosphere over the period 12/1978–07/2018 is explored using the recent Version 6 of the UAH MSU/AMSU global satellite temperature dataset. Our analysis did not show a consistent warming with gradual increase from low to high latitudes in both hemispheres, as it should be from the global warming theory. In addition, in the lower stratosphere the temperature cooling over both poles is lower than that over tropics and extratropics. To study further the thermal field variability we investigated the long-range correlations throughout the global lower troposphere-lower stratosphere region. The results show that the temperature field displays power-law behaviour that becomes stronger by going from the lower troposphere to the tropopause.This power-law behaviour suggests that the fluctuations in global tropospheric temperature at short intervals are positively correlated with those at longer intervals in a power-law manner. The latter, however, does not apply to global temperature in the lower stratosphere. This suggests that the investigated intrinsic properties of the lower stratospheric temperature are not related to those of the troposphere, as is expected by the global warming theory.

Determining the tropopause height from 205 MHz stratosphere troposphere wind profiler radar and study the factors affecting its variability during monsoon

Sun, 01/13/2019 - 19:10

Publication date: January 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 182

Author(s): K. Nithya, Ajil Kottayil, K. Mohanakumar

Abstract

A Stratosphere-Troposphere (ST) wind profiler radar at 205 MHz is operational at Cochin (10.04 N; 76.44 E), India since January 2017 and is providing accurate three-dimensional wind profiles for an altitude range of 315 m to 20 km. In this paper, we present a method to estimate the tropopause altitude from signal to noise ratio (SNR) profiles obtained from the 205 MHz wind profiler radar. The gradient in SNR is used to estimate the cold point tropopause (CPT) height. The CPT height obtained from the ST radar is validated against co-located radiosonde tropopause height measurements and is found to be in very good agreement. The variability of CPT height during monsoon season was studied and the factors responsible for its variability were investigated. It is found that during monsoon season the Tropical Easterly Jet (TEJ) has an inverse relationship with the CPT height, i.e. CPT height increases as the strength of TEJ diminishes and vice versa. A comparison between TEJ core speed and ice cloud water path (ICWP) which represents the strength of deep convection, shows that ICWP decreases as the strength of TEJ increases. Thus, our analysis shows that TEJ affects the tropopause height through changing the concentration of ice clouds.

Dynamics of sunspot cycle ascending and descending phases asymmetry in equatorial ionospheric variability

Sun, 01/13/2019 - 19:10

Publication date: January 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 182

Author(s): S.O. Ikubanni, J.O. Adeniyi, B.O. Adebesin, S.J. Adebiyi

Abstract

Ionospheric variation from the climatological mean has been extensively studied due to its effect on ionospheric high frequency radio propagation. This work reports foF2 variation at Ouagadougou (geogr. 12oN, 1.8oW, dip ∼3°), complementing works that have been done at this station. Nighttime variability is higher than daytime and varies with season but with no consistent pattern. There is an earlier post-midnight peak variability in June solstice (around 0100LT) and occurred between 0400 and 0500LT in other seasons for all sunspot classifications except solar maxima. In this study, we have paid attention to features in the ascending/decending phase of the sunspot cycle and we observed that nighttime ionospheric variability may not always decrease with increasing sunspot number, particularly in the ascending phase. The mechanisms for the difference between observations in the ascending and descending phases could not be identified.

Physical processes in the ionosphere during the solar eclipse on March 20, 2015 over Kharkiv, Ukraine (49.6° N, 36.3° E)

Sun, 01/13/2019 - 19:10

Publication date: January 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 182

Author(s): Leonid F. Chernogor, Igor F. Domnin, Leonid Ya Emelyanov, Mykhaylo V. Lyashenko

Abstract

We present the results of observations of variations in the mid-latitude ionospheric parameters and physical processes in the geospace during March 20, 2015 partial solar eclipse over Kharkiv (49.60° N, 36.30° E) where the eclipse magnitude was about 0.54. The Kharkiv incoherent scatter (IS) radar and digital ionosonde were used for ionospheric observations and estimations of the parameters of the thermal and dynamical processes. At the time of the maximum obscuration of the Sun's area, an increase in the ionospheric F2 peak height by about 40 km was observed. At the same time, the electron density at altitudes of 190 and 210 km decreased by approximately 18.5 and 16.5%, respectively. During the eclipse, a decrease in the electron temperature and apparent changes in the vertical plasma drift velocity were observed. The observations and analysis have shown that the solar eclipse led to significant restructuring of the thermal and dynamic state of the ionospheric plasma over Kharkiv.

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 182

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.

Long-term changes in the concentration of radiocarbon and the nature of the Hallstatt cycle

Sun, 01/13/2019 - 19:10

Publication date: January 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 182

Author(s): V.A. Dergachev, S.S. Vasiliev

Abstract

Radiocarbon (C14) is formed in the atmosphere as a result of the interaction of thermal neutrons with nitrogen according to scheme n(14N,14C)p. The effectiveness of C14 formation depends on the local spectrum of cosmic rays (CR) penetrating into the atmosphere. The local CR spectrum is determined by the level of solar activity and is characterized by the solar modulation parameter (SMP). The efficiency of formation C14 also depends on the magnitude of the dipole moment (DM) of the geomagnetic field shielding the atmosphere from the CRs penetrating into it.

C14 concentration varies cyclically with time. The most famous long-term cycles are the ∼2300-year (Hallstatt cycle) and the ∼210-year (de Vries cycle).

Analysis of the radiocarbon series shows that there is an amplitude modulation of the ∼210-year cycle. The modulating signal has a main period of about 2300 years. The nature of this modulation is analysed. Is it related to changes in solar activity or to variations in the geomagnetic field?

Two models of amplitude modulation of radiocarbon variations are considered. In the first model (AM-1), there is amplitude modulation of ∼210-year variations of the SMP with a period of 2300 years. As a result of the simulation, it is shown that the amplitude of the ∼210-year oscillations in the concentration of radiocarbon does not depend on the phase of the 2300-year modulation. This contradicts the observations.

In the second case (AM-2), the modulation of ∼210-year variations of the SMP is absent. But the existence of ∼2300-year oscillations of the dipole moment is allowed. In the second case, unlike AM-1, the amplitude of the 210-year oscillations in the C14 production rate depends on the phase of the 2300-year variations in the dipole moment, which agrees with the observations.

Based on the comparison of AM-1 and AM-2 models of amplitude modulation, it can be concluded that changes in the dipole moment of the geomagnetic field are responsible for the observed ∼2300-year variations in the concentration of radiocarbon.

Editorial Board

Sun, 12/30/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part B

Author(s):

Solar cycle characteristics and their application in the prediction of cycle 25

Sun, 12/30/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part B

Author(s): F.Y. Li, D.F. Kong, J.L. Xie, N.B. Xiang, J.C. Xu

Abstract

The Solar Influences Data Analysis Center (SIDC) issued a new version (version 2) of the sunspot number data in July 2015. The 13-month smoothed monthly sunspot number from the new version is used for the first time to research the relations among the feature parameters of solar cycles under the bimodal distribution for the modern era cycles (10–23), and, their physical implications are discussed. These relations are utilized to predict the maximum amplitude of solar cycle 25. Cycle 25 is predicted to start in October 2020 and reach its maximum amplitude of 168.5±16.3 in October 2024, thus, it should be stronger than cycle 24 but weaker than cycle 23.

Discriminating cloud to ground lightning flashes based on wavelet analysis of electric field signals

Sun, 12/30/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part B

Author(s): Kamyar Mehranzamir, Mahdi Davarpanah, Zulkurnain Abdul-Malek, Hadi Nabipour Afrouzi

Abstract

Lightning discharges produce electromagnetic radiation in a wide frequency range, but its propagation in a certain frequency range are usually used by lightning detection networks. Investigation of lightning activities in time-frequency domain can be obtained by using the wavelet transform. This study proposes a new approach using the discrete wavelet transform (DWT) algorithm to classify the detected lightning strikes. The measuring station would capture lightning electric field in 500 ms time scale and then utilizes a wavelet based recognizer algorithm to duly differentiate the cloud to ground flash from other cloud activities. Wavelet transform allows the expansion of transient events into a small number of coefficients. A total of 200 lightning flashes were randomly selected among the captured lightning discharges in South of Malaysia in one year. Initially, the cloud to ground and other cloud activities were manually analysed and discriminated. Then, these lightning flashes were analysed using different mother wavelets such as Haar, symmlet, Coiflet, and Daubechies by means of MATLAB program. Haar mother wavelet gives the best result for CG decomposition analysis. A total of 24 decomposition layers were chosen and the energy level of each layer was calculated to obtain the correlation between energy fluctuation and type of signal. The investigations reveal that the CG discharges have higher energy in 17th to 20th layers compared to the rest. However, the opposite results were obtained for the case of other cloud activities. To increase the accuracy of the wavelet transform approach algorithm, another filter was added to the algorithm flowchart. The proposed CG discrimination algorithm successfully classified 92% of the randomly selected flashes.

Analysis of the dynamics of ionospheric parameters during periods of increased solar activity and magnetic storms

Sun, 12/30/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part B

Author(s): Oksana Mandrikova, Yury Polozov, Nadezhda Fetisova, Timur Zalyaev

Abstract

In this work, according to the ground observation data, we study the dynamics of the ionospheric parameters during periods of strong and moderate magnetic storm of 2015–2017. The study was carried out using new methods of modeling and data analysis proposed by the authors. Multicomponent model of ionospheric parameters presented in this work allows describing changes of the ionospheric parameters, both in the conditions of the calm ionosphere and in perturbed periods. During the study, we allocated ionospheric disturbances preceding and accompanying the periods of magnetic storms in analyzing regions. The analysis showed a high incidence of the effect of an increase in the electron concentration of the ionosphere preceding the onset of magnetic storms. Comparing the results of the study with cosmic ray data, we also noticed the correlation of effects in the ionosphere with the anomalous changes in the dynamics of cosmic rays.

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

Sun, 12/30/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part B

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.

Towards design and development of isothermal cloud chamber for seeding experiments in tropics and testing of pyrotechnic cartridge

Sun, 12/30/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part B

Author(s): P. Kumar

Abstract

Isothermal cloud chamber with capacity of 120 × 120 × 120 cm3 has been designed and developed for performing cloud seeding experiments in simulated tropical atmosphere. Purpose of the chamber is to test the efficiency of artificially generated IN (for cold region of the cloud) or CCN (for warm region of the cloud) agents, in simulated pressure, temperature or humidity condition as in natural cloud layers (levels). Level to level results can be subsequently tabulated together in sequence to view an integrated picture of the performance of the existing agent formulation in entire(simulated) natural cloud condition.

Chamber pressure is designed to achieve up to 350 hPa and lower temperature is designed to get −25 °C. Controlled higher temperature in the cloud chamber is designed to reach ≥ +10 °C (even up to +50 °C). Humidity could be controlled in the range of 30%–100%. This isothermal chamber is designed primarily to test the seeding efficiency.

Hypotheses used are;(i)If drop in luminosity is d and total concentration of particulate matters is Cp per unit volume then-dαCp(1)(ii)If the Lux meter reading at the time of release of IN is L0 and after 5 min# if it improves to L5 thenRate of Nucleation (RN)*αL5 - L0(2)(*It includes condensation and Ice nucleation both)(iii)If the Lux meter reading after 15 min# of the release of IN is L15 and after 30 min# interval if it improves to L30thenRate of Precipitation (ROP)αL30 - L15(3)(# Broad chronological classification)

The hypotheses are reasonably valid for small size of droplets (≤20 μm). For the solid phase or mixed phase of the droplets further examination is needed to apply correction factor. Loss of moisture due to deposition on wall is incessantly replenished by the humidity controller to simulate nature. Incessant growth in the luminosity-drop only indicated the active process of nucleation and subsequent growth in size of particles. The faster the process the higher is the efficiency of the seeding agent.

It was found that the optimal range of atmospheric temperature and pressure for effective cold region seeding is −3.7 °C to −19 °C. Entire process of condensation growth and precipitation takes place only ≈30 min within the chamber.

6th order polynomial successfully simulates the spontaneous nucleation process for simultaneous variation of pressure and temperature with very high coefficient of determination.

Percentage Cartridge efficiency has been defined.

Editorial Board

Fri, 11/23/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part A

Author(s):

Statistical analysis of total column ozone during three recent solar cycles over India

Fri, 11/23/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part A

Author(s): Swapnil S. Potdar, D.P. Nade, R.P. Pawar, N. Jeni Victor, S.S. Nikte, G.A. Chavan, A. Taori, Devendraa Siingh

Abstract

Total column ozone (TCO) distribution and its variation over the Indian region at different stations for the period of about 30 years from 1986 to 2015 are studied. TCO data is taken from the merged ozone data set (MOD) overpass data for 15 different stations over India. The average correlation between TCO and solar proxies such as sunspot number and F10.7 cm solar flux is more than 0.5. We further divided the time series of TCO according to solar cycle as 22nd solar cycle (September 1986 to July 1996), 23rd solar cycle (August 1996 to November 2008) and 24th solar cycle (December 2008 to December 2015) (on going cycle) for a period of 1986–2015. Herein, for the long term trend analysis of TCO, we have removed the seasonal effect by the deseasonalization process, the effects of solar activities, stratospheric waves (quasi-biennial-oscillation-QBO and El Niño–Southern Oscillation-ENSO) by the multifunction linear regression method (MLR). We have compared both the linear trends in TCO which are calculated by the simple linear regression (SLR) and deseasonalised multifunction linear regression (DMLR) analysis. It is found that the direction of the trend in 22nd and the 23rd solar cycle is similar while, it is opposite in the 24th solar cycle. We observed a more negative trend in the 22nd solar cycle and less negative trend in the 23rd solar cycle while the trend is positive in the 24th solar cycle. The results indicate that after the DMLR process, the trend values are decreased by a large factor. Therefore, it is found that the role of natural variability is more than that of the ozone depleting substances (ODS) on long term variability in TCO over India. This statistical analysis provides better analysis of trend variation in TCO series over India. The main objective of this work is to analyze the variations in trend in the TCO with respect to the recent three solar cycles.

Extreme geomagnetic and optical disturbances over Irkutsk during the 2003 November 20 superstorm

Fri, 11/23/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part A

Author(s): V.V. Mishin, S.B. Lunyushkin, A.V. Mikhalev, Yu.Yu. Klibanova, B. Tsegmed, Yu.A. Karavaev, A.V. Tashchilin, L.A. Leonovich, Yu.V. Penskikh

Abstract

We study geomagnetic disturbances and aurora observed near Irkutsk (GEO: 52.2°, 104.5°) at mid-latitude observatories of the Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS) during the 2003 November 20 superstorm. Based on the data from the world network of magnetometers and on the magnetogram inversion technique, we found the auroral oval boundaries, the westward electrojet position, and calculated the parameters for the auroral electron energy distribution. We found a relationship of precipitations of energetic electrons (≥1keV) with the bursts of the Pi1B/Pi1c pulsations and intensity in the 557.7 nm emission and in the 360–410 nm spectral channel observed in the postmidnight sector within the period, when the auroral oval southern boundary lowered below the latitude of Irkutsk. The origin of the observed emissions at the middle latitude is related to electron precipitations in the main and equatorial parts of the westward electrojet. Modeling the ionosphere parameters showed that collision of oxygen atoms with thermal electrons and deactivation of excited nitrogen atom N(2D) at collisions with oxygen molecules make the main contributions to the 630 nm total intensity. During the addressed superstorm, two types of mid-latitude auroras were probably observed: diffuse aurora and/or type « d», as well as emission irregular variations typical of normal auroras related to the auroral energy particle precipitation.

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

Fri, 11/23/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part A

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

Fri, 11/23/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part A

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.

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

Fri, 11/23/2018 - 19:10

Publication date: December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 181, Part A

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.

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