Journal of Atmospheric and Solar-Terrestrial Physics

Characterizing black carbon aerosols in relation to atmospheric boundary layer height during wet removal processes over a semi urban location

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): M. Ashok Williams, T.V. Lakshmi Kumar, D. Narayana Rao

Abstract

Black Carbon (BC) mass concentration has been analysed during rainy and non-rainy days of Northeast (NE) Monsoon months of the years 2015 and 2017 over a semi-urban environment near Chennai (12.81 N, 80.03 E), located on the east coast of India. BC, measured using an Aethalometer (AE-31) has been related to the atmospheric Boundary Layer Height (BLH) obtained from the ERA Interim Reanalysis data during rainy and non-rainy days on monthly mean basis to understand the wet removal of BC over the study location. The study reveals that BLH has a profound effect on the BC concentration on rainy days and non rainy days. It is found that the BC concentration in the night time is lower on rainy days compared to non rainy days owing to wash out on rainy days and the BLH remaining nearly the same on rainy and non rainy days. On the other hand, in the daytime it is found that the BC concentration remains nearly the same on rainy and non rainy days whereas the BLH is lower on rainy days compared to non rainy days. This reveals that in daytime lower boundary layer heights compensate for the wet removal effect on BC concentration on rainy days. A quantitative relation is found between the product of BC and BLH during rainy and non-rainy days which indicates the extent of redistribution of BC during non-rainy days when compared to the rainy days. In the process of analysing BC during the wet removal processes, the basic features of BC such as its mean diurnal variations, transport pathways, local sources and its relation with relative humidity were also reported.

Modeling solar energetic particle transport in 3D background solar wind: Influences of the compression regions

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Wenwen Wei, Fang Shen, Zicai Yang, Lulu Zhao, Yang Wang, Pingbing Zuo, Jie Zhang

Abstract

In modeling the transport process of solar energetic particles (SEPs) in the heliosphere, previous simulation works often simplify the solar wind velocity as radial and constant, and treat the magnetic field as Parker spiral. In order to fully understand the effect of solar wind velocity and interplanetary magnetic field on the particles’ transport process, a realistic background solar wind and magnetic field is required. In this work, we use the focused transport model to investigate the transport of SEPs in the solar wind velocity and magnetic field generated by the 3D high-resolution MHD model with a six-component grid. We find that in the uncompressed solar wind, the time intensity profiles of energetic particles show similar trend in both the MHD background and the Parker magnetic field assumption. However, the simulated SEP flux displays an enhancement in the decay phase when a compression region sweeps past the local observer. Through investigating various effects, we find that the magnetic focusing effect is primarily responsible for the intensity enhancement, suggesting that the magnetic focusing effect has an important influence on the transport of SEPs. Further, we show that the magnetic focusing could also be effective in large heliocentric distances.

Responses of the D region ionosphere to solar flares revealed by MF radar measurements

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Na Li, Jiuhou Lei, Xiaoli Luan, Jinsong Chen, Jiahao Zhong, Qian Wu, Zhengwen Xu, Leke Lin

Abstract

Electron density (Ne) and effective reflection height (H', where the electron density reaches its peak value) in the D region observed by medium frequency (MF) radar at Kunming (25.6°N, 103.8°E) were utilized to quantitatively study the ionospheric response to solar flares. It was found that the H' and Ne had profound responses to solar flares. The results showed a sharp decrease in the H' from 76 to 80 km during the non-flare period to nearly 58 km with flares, and a sudden increase in the Ne from below 4×108 m3 in non-flare period to 1.8×109 m3 during 13 M-level flares. The behavior of Ne was strongly and positively correlated with the variation of the X-ray flux, with the largest coefficient being 0.93, while the changes of H' exhibited a strongly negative correlation of −0.96 with that of the X-ray flux. Moreover, variations of H' and ΔNe depended on not only the flare level, but also upon the onset time and duration of flare.

Impact of nitric oxide, solar EUV and particle precipitation on thermospheric density decrease

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Yongliang Zhang, Larry J. Paxton, Gang Lu, Sam Yee

Abstract

Recent studies have revealed that the post-storm thermospheric mass density at a fixed altitude could be lower than the pre-storm mass density. This phenomenon has been attributed to an overcooling effect caused by enhanced infrared emissions from nitric oxide (NO). Here we report that thermospheric density decrease can take place under both storm and non-storm conditions. Relevant observations are presented during two superstormes, one intense storm, and one non-storm case. Thermospheric neutral density variations observed by GOCE and CHAMP satellites are investigated along with simultaneous measurements of thermospheric nitric oxide density and emissions from TIMED/GUVI and TIMED/SABER, respectively, together with auroral hemispheric power from DMSP, Joule heating rate from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) algorithm, and solar extreme ultraviolet (EUV) flux from SOHO/SEM and TIMED/SEE. It was found that the apparent storm-time density decrease or “overcooling” is a result of combined effects: an increase in NO cooling and a decrease in both the solar EUV flux and the auroral energy input. It was also found that whether or not a density decrease exists depends on whether there are auroral activities prior to the pre-storm reference day and how the reference day is chosen. The relative contributions of the different drivers (namely, enhanced NO cooling and variations in auroral hemispheric power, Joule heating, and solar EUV at the pre-storm and post-storm days) to thermospheric density decrease remain to be determined.

The study of in situ wind and gravity wave determination by the first passive falling-sphere experiment in China's northwest region

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Wei Ge, Zheng Sheng, Yiyao Zhang, Zhiqiang Fan, Yu Cao, Weilai Shi

Abstract

This paper reports on the study of China's first falling-sphere experiment, which was conducted in the northwest of China. The process of deriving wind profiles using the sphere's position data and NRLMSISE-00 model data as inputs is shown. The results show that inaccuracies in the NRLMSISE-00 density have hardly any influence on the calculated winds, while the uncertainties in the vertical acceleration of the sphere can create large wind errors at high altitudes. The second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) data matches closely with the experimentally determined zonal wind, with a correlation coefficient of 0.98 and a root mean square error of 7.53 m/s. However, the experimentally determined meridional wind is much less consistent with the MERRA-2 data. This may be due to the reanalysis data not being able to capture the full features of the meridional wind. The wind shear reaches its maximum at approximately 40 km, and the main wavelengths of gravity wave extracted from the horizontal wind are concentrated at 8.5 km, 5 km and 3 km.

Electromagnetic internal gravity waves in an ideally conducting incompressible medium

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): T.D. Kaladze, L.V. Tsamalashvili, D.T. Kaladze

Abstract

Properties and peculiarities of linear 3D - propagation of electromagnetic internal gravity waves in an ideally conducting incompressible medium embedded in a uniform magnetic field are studied. Local and non-local (plane waves) approaches are applied. It is shown that ordinary internal gravity waves couple with Alfven waves. Associated partial differential equations and dispersion relations are obtained. New branches of oscillations are revealed. The results obtained may be applicable to the Earth's ionosphere and solar atmosphere.

Medium frequency gravity wave characteristics obtained using Weather Research and Forecasting (WRF) model simulations

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): H. Hima Bindu, M. Venkat Ratnam, Viswanadhapalli Yesubabu, D. Hari Prasad

Abstract

Many studies have reported the characteristics of wide spectrum of Gravity Wave (GW) using radiosonde, MST Radar, Lidar and other observations. In this study, we made an attempt to obtain the characteristics of medium frequency GWs over a tropical station Gadanki (13.5°N and 79.2°E) using the Weather Research and Forecasting (WRF) model simulations for the period 2006–2017. Prior to GWs analysis, we have validated the model outputs with radiosonde measurements over Gadanki to check the performance of the model in capturing the realistic features as seen in the observations. Profiles of horizontal winds and temperature are validated and the results of statistical analysis indicate that there is a good correspondence between the WRF model simulations and the radiosonde measurements. The FFT and wavelet analysis on the winds revealed the spectrum of waves. The band pass filtered wind perturbations showed clear downward phase propagation with the dominant periods 2–5 h. The observed vertical and horizontal wave lengths are in the range of 6–8 km (3–8 km) and 100–200 km (100–500 km) in the troposphere (stratosphere), respectively. These characteristics match well with those reported from the same location using MST radar and radiosonde observations. Further, the long-term features like semi-annual oscillation, annual oscillation and quasi-biannual oscillations are also simulated very well in the WRF outputs. These results show the model's ability to simulate near realistic features as seen the observations and can also be used to supplement the missing observations with errors limits as its uncertainty.

Significant ELF perturbations in the Schumann Resonance band before and during a shallow mid-magnitude seismic activity in the Greek area (Kalpaki)

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Vasilis Christofilakis, Giorgos Tatsis, Constantinos Votis, Ioannis Contopoulos, Christos Repapis, Vasilis Tritakis

Abstract

Strong ELF perturbations in the Schumann Resonance band (0–50 Hz) were detected in the North of Greece close to the village of Kalpaki during a shallow (17 km) mid-magnitude earthquake (5,3R) and the post-seismic sequence that followed it. The observation site was serendipitously located almost above the main quake epicenter (3,65 km away). It is probably the first time that such a detailed recording of ELF electromagnetic emission of lithospheric and/or ionospheric origin was obtained so close to a seismic epicenter. This event is very significant in the study of the interaction between seismic waves and ELF electromagnetic radiation. It will certainly contribute to the understanding of that interaction, and may even lead to more accurate earthquake predictions.

Reconstructing nonlinear force-free fields by a constrained optimization

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): S. Nasiri, T. Wiegelmann

Abstract

It seems that the potential and linear force-free magnetic fields are inadequate to represent the observed magnetic events occurring in different regions of the solar corona. To reconstruct the nonlinear force-free fields from the solar surface magnetograms, various analytical and numerical methods have already been examined by different authors. Here, using the Lagrange multiplier technique, a constrained optimization approach for reconstructing force-free magnetic fields is proposed. In the optimization procedure the solenoidal property is considered as a constraint on the initial non-force-free field. In the Wheatland et al. (2000) method as an unconstrained optimization, both solenoidal and force-free conditions are fulfilled approximately. In contrast, the constrained optimization method, up to numerical precision, leads us to a nearly force-free magnetic field with exactly zero divergence. The solutions are obtained and tested by the Low and Lou (1990) semi-analytic solution.

A complete solar cycle (2006–2016) studies of scale heights derived using COSMIC radio occultation retrieved electron density profiles

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): G. Uma, P.S. Brahmanandam, S. Tulasi Ram, K.-H. Wu, Y.H. Chu

Abstract

Various ionospheric vertical scale heights (VSH) including, the Chapman (Hm), VSH at upper ionosphere (VSHUP) and 500 km (VSH500) derived using COSMIC radio occultation (RO) retrieved electron density profiles during a complete solar cycle (2006–2016) are presented in this research. VSH show distinct latitudinal variations and solar-activity dependencies. VSH follow the geomagnetic equator with a longitudinal structure irrespective of the season and year, although mid and high latitudes show higher values and irregular variations in low (2006–2010) and moderate-to-high (2011–2016) sunspot years during the daytime hours (1300 LT-1500 LT). The longitudinal structure of VSH500 appears only in moderate-to-high sunspot years, which is an important observation reported for the first time in this communication. Diurnal variations of Hm at equatorial latitudes show higher values starting from ∼0400 LT to ∼2300 LT with a post-sunset peak. However, an absence of the post-sunset peak is seen in VSHUP and VSH500 which is probably due to the altitudinal gradients of vertical drifts that increase (decrease) below (above) the F-layer peak during evening pre-reversal enhancements. The reduced drifts above the F-layer peak thereby, suppresses the post-sunset peak in VSH. Concurrent and large-scale structures in VSH500 and VSHUP at mid and high latitudes in summer hemispheres during June and December solstice seasons are reported for the first time, which occurred possibly due to the long-duration exposure to the Sun's strong radiation during summer seasons. A one-to-one correlation exists between the Chapman scale heights and peak height of the F2 layer (hmF2) at equatorial latitudes in different seasons, while moderate correlation is seen between them away from the equatorial latitudes. These presented scale heights at a global scale are very significant, particularly, for future empirical modeling studies and the long-term availability of COSMIC RO retrieved electron density profiles allowed us to present these scale heights.

Characterization of ionospheric irregularities at different longitudes during quiet and disturbed geomagnetic conditions

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): O.S. Bolaji, S.J. Adebiyi, J.B. Fashae

Abstract

This paper investigates the plasma irregularities at different longitudes in the month of March 2015; a period that consists of both quiet and disturbed geomagnetic conditions. The average rate of change of TEC index (ROTIave), derived from Global Positioning System (GPS) measurements obtained at South America, Africa, Asia and Oceania equatorial regions, was used as indicator. The observations revealed significant longitudinal differences for both quiet and disturbed conditions. The quiet-time observations indicate that irregularities were most frequent in the American and African sectors, it is rarely observed in the Asian sector and mostly absent in the Oceania longitudes. The strength is however observed to decrease eastward i.e. it is most prominent in the American sector (up to ∼1.6 TECU/min.) and absent in the Oceania longitudes. The results of the investigation of the 17 March, 2015 storm event revealed that the storm appeared not to hinder the development of irregularities in all the stations in the America sector during the night following the main phase. However, significant longitudinal variation is observed within the sector on the first night following the storm's recovery. In the African sector, the storm inhibits the development of irregularities in all the stations during the storm days considered: a development that is fundamentally different from the America sector. Generally, no significant storm effect is observed in the Asian and Oceania stations considered. The storm-time longitudinal variations of irregularities have been partly attributed to the storm timing and significant longitudinal difference in the action of storm-induced related drivers.

GNSS-derived PWV and comparison with radiosonde and ECMWF ERA-Interim data over mainland China

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Qingzhi Zhao, Yibin Yao, Wanqiang Yao, Shubi Zhang

Abstract

Precipitable water vapour (PWV) is a key factor for monitoring climate and the hydrological cycle. Here, PWV is calculated using 249 ground-based GNSS stations derived from the Crustal Movement Observation Network of China (CMONOC). Zenith total delay (ZTD) is estimated using the GAMIT/GLOBK (Ver. 10.4) and the zenith hydrostatic delay (ZHD) is calculated using the layered European Centre for Medium-Range Weather Forecasting (ECMWF) ERA-Interim data. The GNSS-derived ZTD is validated using the radiosonde and ECMWF data with the root mean square errors (RMSE) of 19.1 mm and 12.5 mm, respectively. The ECMWF-derived surface pressure (Ps) used to calculate the ZHD and the weighted mean temperature (Tm) calculated based on the layered ECMWF data are also evaluated using radiosonde data with RMSE values of 1.14 hPa and 1.24 K, respectively. Consequently, the final CMONOC-derived PWV at 249 stations is obtained and compared with radiosonde-derived and ECMWF-derived PWV while the RMSE values are 1.38 mm and 1.30 mm, respectively. The two-dimensional (2-d) PWV image derived from CMONOC is also compared with that from ECMWF, which shows good consistency across different seasons.

Study of the Ångström turbidity over Romanian Black Sea coast

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Sanda Voinea, Sabina Stefan

Abstract

The atmospheric turbidity has an important role in the climate changes studies and solar radiation modelling. A three years AERONET data set (2010–2012) was used to study the variation of the aerosol optical properties and Ångström turbidity at Eforie Nord (Romania), on the Black Sea coast. The study emphasizes a similar seasonal variation for aerosol optical depth (AOD) and turbidity (β), consisting of maximum averaged value in spring and summer and minimum averaged value in winter. The Ångström exponent (AE) reached the maximum average in summer and the minimum in autumn. The results indicate the main contribution of the fine particles to the local load of atmosphere and low turbidity. The dependence of turbidity on the Ångström exponent highlights that turbidity can be computed based on a constant value of AE = 1.3, even in the climatological conditions of the Black Sea coast. Statistical analysis shows a moderate correlation between daily values of turbidity and precipitable water (r = 0.51). The days with the highest turbidity values from the perspective of meteorological parameters and air mass trajectories were analyzed. This study shows that a significant transport of aerosol from the western and southwestern part of Europe influenced the air turbidity.

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.

Theme by Danetsoft and Danang Probo Sayekti inspired by Maksimer