Journal of Atmospheric and Solar-Terrestrial Physics

Ionosonde observations of daytime spread F at middle latitudes during a geomagnetic storm

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): Guobin Yang, Chunhua Jiang, Ting Lan, Wengeng Huang, Zhengyu Zhao

Abstract

Recently, Jiang et al., (2016) reported daytime spread F at Puer station (22.7oN, 101.05oE, Dip Lat 12.9oN). As a continual work, daytime spread F at middle latitudes was investigated in this study through ionograms recorded by an ionosonde installed at Zhangye (ZHY, 39.4oN, 100.0oE, Dip Lat 29.6oN) in the Northwest of China. The ionosonde at ZHY station recorded daytime spread F three times on 6 January, 2017. The first case occurred at approximately 06:45 LT and disappeared at about 08:35 LT. The second and third cases lasted from 09:50 LT to 10:30 LT and from 11:10 LT to 11:30 LT, respectively. In addition, Swarm satellite observations were used to reveal the possible mechanism in this study. Results show that daytime spread F observed in this study might be attributed to Traveling Ionospheric Disturbances (TIDs)/atmospheric gravity waves induced by a geomagnetic storm. However, the physical processes might be different for these cases. Ionospheric instabilities produced by local F region electric field might be contributed to the first case. The second and third cases might be attributed to off-vertical reflections from wave-like ionospheric structure generated by TIDs/atmospheric gravity waves.

Characteristics of surface boundary layer during active and weak phases of southwest monsoon over Kochi: A tropical station

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): B.L. Sudeepkumar, C.A. Babu, Hamza Varikoden

Abstract

This study explores the features of atmospheric surface layer over Kochi during active and weak phases of the southwest monsoon season. The classification of active and weak phases of monsoon is made on the basis of monsoon organized convection over the region. When the monsoon organized convection is over (away from) Kochi, considered it as an active (weak) phase. The study primarily utilizes sonic anemometer data. The diurnal variation of surface fluxes and turbulent kinetic energy (TKE) during active and weak conditions are examined in addition to surface wind and temperatures. It is found that monsoon clouds spread extensively over large area stabilizes the surface layer and a drastic decrease in sensible heat flux is observed during the active monsoon conditions. The average value of momentum flux and TKE decreases, surface layer becomes stable, and Atmospheric Boundary Layer (ABL) height lowers during active monsoon phase. A significant oscillation of 3.5 h periodicity is found to be embedded in the momentum flux and in the wind speed which is attributed to the penetration of the low level monsoon circulation. Weak monsoon phase is characterized by higher value of fluxes and TKE with higher amplitude of diurnal variation due to local heating and sea breeze circulation. Unstable condition between 00:00 IST and 01:00 IST and stable conditions in the early morning is observed during both active and weak phases. It is observed that there are two different relations for the growth and dissipation of fluxes and TKE. The dissipation is faster than growth in the case of surface fluxes with temperature. The sensible heat flux, momentum flux and TKE are logarithmically related with wind speed. Sensible heat flux has logarithmic relation with temperature, whereas momentum flux and TKE have exponential relation.

Fair weather criteria for atmospheric electricity measurements

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): R.G. Harrison, K.A. Nicoll

Abstract

The global atmospheric electric circuit, which links the space environment with terrestrial weather, has mostly been investigated using fair-weather surface atmospheric electricity measurements. Retrieving global circuit information, however, requires the selection of “fair weather” data, to avoid local meteorological disturbances. The research results presented here challenge the applicability of long-standing definitions of electrically fair weather atmospheric conditions. From detailed new measurements and theory, three improved requirements (FW1 to FW3) for fair weather atmospheric electricity conditions are described. These are: (FW1) absence of hydrometeors, aerosol and haze, as apparent through the visual range exceeding 2 km, (FW2) negligible cumuliform cloud and no extensive stratus cloud with cloud base below 1500 m, and (FW3) surface wind speed between 1 m s−1 and 8 m s−1. Automatic and manual measurement approaches to identifying these requirements are given. Through applying these criteria at the many measurements sites now operating, the noise from meteorological variability will be reduced, leading to data more representative of the global electric circuit.

Coherent changes of solar and ionospheric activity during long-lived coronal mega-hole from Carrington rotation CR2165 to CR2188

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): T.L. Gulyaeva, R.A. Gulyaev

Abstract

Correlations of solar and ionospheric activity are investigated during the long-lived coronal mega-hole (CMH) for 24 solar rotations at the decline phase of SC24 from June, 2015, to March, 2017. Pch index (Luo et al., 2008) which is a function of the intensity in the central area developed for forecasting of daily solar wind speed (Vsw) is used as characteristic of efficiency of CMH. The solar activity indices Pch, SSN2, F10.7, Lyman-α, MgII, Vsw, and the ionospheric indices – global electron content GEC and global noon TECgn index averaged from data of 288 IGS observatories are analyzed. Sporadic disturbances in solar and ionospheric data are smoothed by the time-weighted exponential accumulation of their history with the persistence factor τ (0 ≤τ < 1) for the preceding 27 days. Growing coronal hole power Pch(τ) during the CMH life is observed while all other solar and ionospheric indices are decreasing at the decreasing phase of SC24. The solar wind speed near the Earth is diminishing from CR2165 to CR2174 but growing afterwards. Delayed correlation of solar wind speed Vsw(τ) with Pch(τ) shows lag (delay) of Vsw(τ) by 4 days relative Pch(τ) index while the ionospheric data don't show any delay. Examination of relations of the ionosphere activity with the solar and ionospheric global indices is made with noon measurements of the foF2 critical frequency and total electron content TEC at eight observatories (4 from the northern hemisphere and 4 from the southern hemisphere). The best linear correlation of foF2(τ) and TEC(τ) at selected sites is obtained with GEC(τ) and TECgn(τ) indices (the correlation coefficient ρ from 0.7 to 0.9 in the most cases) so that TECgn(τ) and GEC(τ) global indices could serve as potential candidates for driving the ionospheric model in the real time regime.

Detecting the solar new magnetic flux regions on the base of vector magnetograms

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): A.A. Golovko, I.I. Salakhutdinova

Abstract

To understand better the origin of CME and other non-stationary processes, the detailed information about emerging flux regions must be known. The advanced method of mapping emerging magnetic flux regions through the multifractal segmentation of vector photospheric magnetograms, is created. It is free from influence of effects of projection. Maps of the vertical component of the field Hz and of the two transversal components Hx, Hy are processed separately and the computed segmented images are summarized. As a result, the detailed picture of distribution of new magnetic fluxes at the current time, is obtained. The SOT Hinode magnetograms for 2006–2015 were used. Observations of the flare-productive active regions NOAA 11158 and 11520 were processed. Hills of a new field in case of their birth have the considerable elongation which is possibly related to their rope-like geometry. In the centers of flare activity, in the vicinity of polarity inversion lines, exits of new magnetic flux alternate with processes of “magnetic cancellation”.

On the QBO modulation in the frequency of occurrence of pre noon F3 layers over the dip equatorial location of Thiruvananthapuram

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): N. Mridula, Tarun Kumar Pant, A. Ajesh

Abstract

Using the ionosonde observations, over Thiruvananthapuram (8.5° N, 77oE, 0.5oN dip lat.), India, for a period of 20 years (1990–2009), the present study reveals the presence of quasi biennial oscillation (QBO) in the pre noon F3 layer occurrence percentage. The presence of a strong QBO modulation in the occurrence of pre noon F3 layers is observed during the period from 1992 to 2000 beyond which it is rather weak/nonexistent. The wavelet periodogram analysis indicates the fact that F3 occurrences are more during the eastward phase of MQBO and less during the westward phase of MQBO.

The pattern of ionospheric disturbances caused by complex interplanetary structure on 19–22 December 2015

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): V.I. Kurkin, N.M. Polekh, N.A. Zolotukhina

Abstract

The pattern of the ionospheric storm that was observed during the severe two-step geomagnetic storm on 19–22 December 2015 in East Asia is investigated. The study is performed using a combination of vertical and oblique-incidence sounding, total electron content, riometer and magnetometer data obtained near 120° E meridian in 19–66° N latitude zone. The revealed ionospheric disturbances are compared with the features of ionospheric storm, developed over the same region during the severe one step magnetic storm on 14–16 December 2006. Compared magnetic storms are almost identical in the season and the onset time. They have approximately equal peak intensities (Dst = −155 nT and −162 nT), but differ noticeably in the duration of the main phases (19 h and 2.5 h) and the rate of the ring current field amplification. Through the comparison the ionospheric disturbances which are similar and dissimilar for both storms are revealed. Our study suggests that the main differences between ionospheric storms were observed during the initial and early recovery phases. They could be due to the differences between pre-storm states of the magnetosphere-ionosphere system as well as between interplanetary drivers.

On the ionospheric propagation of VLF waves generated by currents in the lower ionosphere

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): I.V. Kuzichev, I. Yu. Vasko, A. Yu. Malykhin, A.R. Soto-Chavez

Abstract

The consistent description of ELF/VLF wave propagation in the ionosphere is essential for understanding the properties of the wave phenomena observed both at the ground and satellites. Due to strong inhomogeneity of the lower ionosphere coupled with collisional damping of a wave, the geometrical optics approach is not valid, while the full-wave approach suffers from the problem of numerical instability. In this paper, we implement a rather general and powerful method avoiding the numerical instability to study propagation of the wave generated in the lower ionosphere. Our calculations demonstrate the quasi-periodic behaviour of the field in the upper ionosphere, which is associated with the Earth-ionosphere waveguide. The field distribution varies significantly with frequency, from being nearly sign-definite to oscillating with comparable positive and negative values, producing the ring structure in wave-vector space. The field distribution at the ground is studied and shown to have resonant structure defined by two parameters: number of the resonance, which depends on wave frequency, and spatial scale of the Earth-ionosphere waveguide.

Southwest monsoon onset dates over Malaysia and associated climatological characteristics

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): Sheeba Nettukandy Chenoli, P.R. Jayakrishnan, Azizan Abu Samah, Ooi See Hai, Muhammad Yunus Ahmad Mazuki, Chai Heng Lim

Abstract

In Malaysia precipitation prevails throughout the year. However, the southwest monsoon (late May to September) is characterised with low precipitation, less cloud, high outgoing long-wave radiation (OLR) and often featured by dry epochs. Therefore, onset of the monsoon here is best determined by considering multiple onset parameters such as wind, OLR, rainfall and relative humidity. We used modified Malaysian Meteorological Department wind shear index based on major convection centres during the monsoon onset. The 850 hPa winds were chosen to investigate the onsets of the monsoon in view of the marked orographic and mesoscale processes. The next criterion was the presence of sustained westerlies averaged between 850 hPa and 600 hPa from all the available radiosonde stations data over Malaysia for at least 5 days. As the strongest convective activity in the tropics is represented by OLR of less than 220 W m-2, the third criterion was to check whether the value of OLR was greater than 220 W m-2 over the region. The mean date of the summer monsoon onset over Malaysia is found to be 19 May, with a standard deviation of 8 days. Further, climatological composites show that there is a gradual change from easterlies to westerlies from the surface up to 500 hPa in Malaysian stations both in Peninsular Malaysia and East Malaysia during May. OLR and rainfall analysis reveal that, the southwest monsoon daily rainfall over Malaysia is less than 10 mm and OLR is greater than 220 W m-2. Additionally, monsoon onset tends to be late during the El Niño years and earlier during the La Niña years.

Near-global GPS-derived PWV and its analysis in the El Niño event of 2014–2016

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): Qingzhi Zhao, Yibin Yao, Wan Qiang Yao, Zufeng Li

Abstract

Precipitable water vapour (PWV) is a key factor in activities related to climate monitoring and the global hydrologic cycle. In this paper, the PWV time series with an accuracy of about 1.3 mm is obtained on a global scale using the zenith total delay (ZTD) derived from International GNSS Service (IGS). A theoretical error formula from ZTD to PWV reveals that the PWV error induced by errors in ZTD, surface pressure (Ps) and weighted mean temperature (Tm) is about 1–1.5 mm. Ps and Tm are two key factors during the conversion of ZTD to PWV, which can be derived from the Global Geodetic Observing System (GGOS) Atmosphere. The GPS-derived and radiosonde-derived PWV time series are compared at 97 collocated stations on a global scale, which shows the maximum/minimum/mean root mean square (RMS) errors and Bias of 1.8/0.6/1.3 mm and 2.6/2.9/4.0/5.2 mm, respectively with a data utilisation rate of 96.8%. By analysing the periodograms of GPS-derived PWV time series using the Lomb-Scargle method, preliminary result shows the various oscillations characteristics of PWV time series at different stations. Finally, the diurnal variations of PWV time series during the El Niño event of 2014–2016 are analysed and revealed an interesting climate signal.

A 13-year climatological study on the variations of aerosol and cloud properties over Kazakhstan from remotely sensed satellite observations

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): K. Raghavendra Kumar, Richard Boiyo, Altayeva Madina, Na Kang

Abstract

The Republic of Kazakhstan, by geographical and climatological conditions, is a key location for the characterization of atmospheric aerosols due to an unprecedented increase of aerosol's concentrations in the recent years. This study presents a 13-year (2003-2015) analysis of the spatiotemporal distributions and trends of aerosol and cloud properties derived from the Moderate Resolution Imaging Spectroradiometer (MODIS)–Aqua (Dark Target–DT) and Ozone Monitoring Instrument (OMI) over Kazakhstan. The spatial patterns of annual mean AOD were generally characterized with low (<0.1), moderate (0.1–0.5) and high (>035) AOD centers over Kazakhstan. The respective maximum and minimum values of AOD550 were observed in July (0.22 ± 0.07) and November (0.12 ± 0.03), with an annual mean of 0.18 ± 0.03. The seasonal mean values of AOD was noticed to be maximum (0.21 ± 0.02) during summer and minimum (0.14 ± 0.01) during autumn seasons. The inter-annual variations in AOD showed enhanced AOD values during 2012 (0.23) followed by 2014 (0.21) and low during 2003 (0.15) and 2004 (0.14). The spatial trend analysis revealed an increase in AOD over most parts of the study domain. Also, the most important cloud parameters such as cloud fraction (CF) and cloud effective radius (CER) were investigated to assess their relationship with the AOD over Kazakhstan. It was found that the CF and CER were negatively and positively correlated with AOD over most parts of the study domain attributed to the strong influence of dust and continental background aerosols, respectively. The backward trajectories obtained from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model showed air parcels originating from the Barents Sea, Russia, Europe, China, and the mainland of Kazakhstan. The results derived from the present study gives a sense of aerosol and cloud properties, and form a basis for further research over this unique and unexplored landmass of the Asian Continent.

Graphical abstract

Time-Frequency Analysis of vertical and horizontal electric field changes of lightning negative return strokes observed in Sri Lanka

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): T.A.L.N. Gunasekara, S.N. Jayalal, M. Fernando, U. Sonnadara, V. Cooray

Abstract

Simultaneously captured vertical and horizontal (total) electric field signatures of lightning negative Return Strokes (RS) were analyzed to obtain Time-Frequency (TF) variation using Stockwell Transformation (ST). In the study, ST was utilized since it is known to possess comparatively better time resolution at high frequency regions compared to other available TF methods. The data were obtained during the monsoon season of April–May 2014. The vertical and horizontal component of fifty negative RSs was utilized in the study. The resultant ST spectrum was analyzed and the regions of interest were demarcated based on the color which represented their relative power output intensities for different frequency components of the signal. The spread area was identified as the region of frequencies which consisted of power intensity equal or above 90th percentile when compared to the maximum possible value. The spectral area was identified as the area of frequencies in the borderline to the natural background noise. The spread region for the vertical E field had a range between 10 kHz and 650 kHz. Its average values were in between 126 kHz and 331 kHz. The spectral region of the vertical electric field change spanned from 1 kHz to 1020 kHz. Its average distribution was 44 kHz–660 kHz. Horizontal electric fields had a range of 20 kHz–1940 kHz in the spectral region. The same for the spread region was 80 kHz–910 kHz. The averages of the horizontal E field's spectral region were 46–1112 kHz and its spread region varied between 227 and 599 kHz. The results display a higher frequency range for all aspects of the horizontal E field changes which implies that its influence on the high frequency radiation is much higher than its vertical counterpart.

Possibility of simultaneous [O<sub>3</sub>] and [CO<sub>2</sub>] altitude distribution retrievals from the daytime emissions of electronically-vibrationally excited molecular oxygen in the mesosphere

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): Valentine Yankovsky, Rada Manuilova

Abstract

In this study we have formulated the multi-channel method for retrieval of the O(3P), O3 and CO2 volume mixing ratios, Cv,O(3P),Cv,O3 and Cv,CO2, altitude profiles in the daytime mesosphere and lower thermosphere from the simultaneous measurements of intensities of three emissions formed by transitions from three electronically-vibrationally excited states, O2(b1Σg+, v = 2), O2(b1Σg+, v = 1) and O2(b1Σg+, v = 0). Only using the YM2011 model of kinetics of O3 and O2 photolysis (Yankovsky et al., 2016. J. Molec. Spectr., 327, 209–232) allowed us to consider in detail the complex groups of the processes of excitation and quenching of the states O2(b1Σg+, v = 0, 1, 2), the transitions from which form the system of the O2 Atmospheric bands observed in the dayglow of the Earth. For the altitude range 50–85 km we developed in details the two-channel method of simultaneously retrieval of the volume mixing ratios of O3 and CO2. For this method, we succeeded in obtaining formulas that can be used for remote sensing of the Earth atmosphere from satellites.

Diurnal variation of the tropospheric water vapour over a coastal and an inland station in Southern Indian Peninsula

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): Maria Emmanuel, S.V. Sunilkumar, M. Venkat Ratnam, M. Muhsin, K. Parameswaran, B.V. Krishna Murthy

Abstract

Diurnal variation of atmospheric water vapour in the troposphere over two tropical stations Trivandrum (8.5°N, 76.9°E) and Gadanki (13.5°N, 79.2°E) are studied using radiosonde observations for three years (December 2010–March 2014) carried out as part of Tropical Tropopause dynamics (TTD) campaigns under CAWSES (Climate And Weather of the Sun-Earth System) India Phase II program. Trivandrum is a coastal station and Gadanki an inland station in the Indian Peninsula. Even though the absolute value of columnar integrated water vapour content (IWV) is higher over Trivandrum in all the seasons, the amplitude of its diurnal variation is almost the same (∼± 5–8 kg m−2) at both the stations with lower values during the day and higher values during night. Though the absolute humidity decreases exponentially with altitude, the amplitude of normalized diurnal anomaly is more-or-less the same (15–20%) from the surface up to 10 km in all the seasons. There exists a time difference in the peaking hours of water vapour density between the two stations with Gadanki always leading Trivandrum. While the water vapour density maximizes around midnight over Trivandrum, it peaks in the late evening over Gadanki. Harmonic analysis shows that the diurnal and semi-diurnal components together account for almost all the sub-daily variations in IWV and absolute humidity. The contribution of semi-diurnal component is only 25% of that of the diurnal component. Diurnal variation of surface wind speed and direction together with the vertical motion associated with convection regulated by the diurnal variation in temperature seems to play the lead role in causing the diurnal variation in water vapour. While the diurnal variation over Gadanki is mainly controlled by the convectively induced vertical motion, the diurnal variation in the rate of evaporation due to surface wind and local circulation also plays a significant role over Trivandrum.

On the relationship between filaments and solar energetic particles

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): Ts Tsvetkov, R. Miteva, N. Petrov

Abstract

In the current study the association rate between solar energetic particles (protons) and filaments and/or filament eruptions (FEs) is investigated using the largest reported event sample. Proton events observed in the period 2010–2016 are accompanied by filaments in 92% (143/156) of the cases. Due to the lack of comprehensive catalog of all filaments, a catalog of FEs is used for the reversed association. Only 5% of FEs have in situ proton signatures with larger peak intensity, compared to the median of the entire proton sample. Other solar activity phenomena (flares and coronal mass ejections) related to the proton events show differences in their distributions compared to the respective FE-samples. The indication for a shock wave formation using the type II radio signatures is also considered and discussed.

Decadal variability in the Northern Hemisphere winter circulation: Effects of different solar and terrestrial drivers

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): Ville Maliniemi, Timo Asikainen, Kalevi Mursula

Abstract

Northern Hemisphere winter circulation is affected by both solar and terrestrial forcings. El-Niño events and volcanic eruptions have been shown to produce a negative and a positive North Atlantic Oscillation (NAO) signature, respectively. Recent studies show a positive NAO signature related to both geomagnetic activity (proxy for solar wind driven particle precipitation) and sunspot activity (proxy for solar irradiance). Here the relative role of these four different drivers on the Northern Hemisphere wintertime circulation is studied using a statistical analysis of observational and reanalysis data during 1868–2014. The phase of the Quasi-Biennial Oscillation (QBO) is used to study driver signals in different stratospheric conditions. Moreover, the effects are separated for early/mid- and late winter. Our findings suggest a stratospheric mediation of the ENSO signal to the Atlantic side, which is delayed and modulated by the QBO unlike the signal in the Pacific side. The positive NAO by volcanic activity is preferentially obtained in the westerly QBO. We also find a substantial QBO modulation for geomagnetic activity and late winter sunspot activity, which favours a stratospheric pathway and the top-down mechanisms. However, signal in the North Pacific produced by early/mid-winter sunspot activity remain rather similar in different QBO phases and supports a direct forcing from the troposphere by the bottom-up sunspot mechanism.

The expected fluxes observed by STIX during low solar activity

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): M. Gryciuk, P. Podgórski, S. Gburek, T. Mrozek, M. Siarkowski, M. Steslicki, J. Barylak, A. Barylak

Abstract

The Spectrometer Telescope for Imaging X-rays (STIX) is one of the instruments installed onboard Solar Orbiter mission which will be launched in February 2020. After 1.5 years of cruise phase it will start to gather scientific data from the orbit with perihelion distance about 0.28 au. It means that STIX will operate also during the next solar minimum. In the paper we estimate flux measured by the instrument during periods of low solar activity. For this purpose we used solar observations which were recorded by the Solar Photometer in X-rays (SphinX) during the last minimum of solar activity. The estimation was obtained for instruments overlapping energy range from 4 to 15 keV. Presented results indicate that STIX instrument will provide efficient imaging the solar emission even during low level of solar activity (B1 GOES class).

Analysis of the unique case of ball lightning observation in Mitino, the northwest district of Moscow

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): Anatoly I. Nikitin, Alexander M. Velichko, Tamara F. Nikitina, Ilya G. Stepanov

Abstract

Observations of eyewitnesses are the main source of data on ball lightning (BL) properties, but often their descriptions turn out to be incomplete, contradictory and lacking in details. Recently due to the wide use of digital camcorders, still cameras and smart-phones the appearance of a large number of video films enable to study the properties of these objects in more detail. However, even the film caught by the lone observer doesn't allow measuring such the important properties as the dimension of the object and the distance to it. On 27 July 2015 the unique event occurred: BL was simultaneously recorded by three observers located at different points. This allowed us to determine a distance to BL, its diameter (0.75 m) and velocity of its motion at various moments of time. BL movement could be broken into three stages. At first it was approaching to the observers with a velocity of the wind. Then for about 80 s it was moving at a height 40–50 m inside a restricted region with a width 12 m and a length 100 m. At the last stage it rose with a velocity 5.7 m/s to the approaching cloud and flew away with a velocity of the wind 15 m/s. The analysis has shown that such a character of BL motion can be explained if to assume that BL has a positive electric charge (Qbl = 10−3 C) and its attraction to the storm cloud (Qc = 5 C) compensates the wind pressure on BL. Stabilization of BL position at a height 40 m can be explained by variations of electric field intensity above the treetops, by instabilities of wind direction or by BL rotation around a horizontal axis with a linear velocity 0.84 m/s. Evaluations showed that the nearby electricity line did not affect BL motion. The details of BL behavior may serve as an evidence for its material nature.

Dust and dust storms over Kuwait: Ground-based and satellite observations

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): Ismail Sabbah, Jean-François Léon, Mar Sorribas, Benjamin Guinot, Carmen Córdoba-Jabonero, Amaury de Souza, Faisal Al Sharifi

Abstract

We investigate the consistency between Aerosol Optical Depth (AOD) retrieved by MODerate resolution Imaging Spectroradiometer (MODIS) sensor aboard NASA's Aqua satellite and measurements collected by ground-based AErosol RObotic NETwork (AERONET) site in Kuwait for 2007–2012. A good correlation (r = 0.7) is obtained between the two data sets. The volume size distributions (VSDs) of particles with geometric mean radius ranges of 0.05–15 μm has been studied as well. Seasonal variations are clearly found in the shape and magnitude of the VSDs for fine and coarse particles. The VSD of aerosol coarse particles was the highest during spring and summer. It increases substantially during dust storms, reaching the highest value during the dust storm of 24 May 2012. Satellite lidar observations from CALIPSO reveals a moderate vertical extent of the dust storms with the highest extinction coefficients below 500 m height. The method of superposed epoch analysis is used to test the behavior of meteorological parameters during the dusty days of 2012. Increase in wind speed together with significant reductions in visibility and diurnal temperature range (DTR) during dusty days are observed. Additionally, air temperature decreases one day after dust events. This effect can be due to scattering of sunlight back to space by the suspended dust particles.

Prominence activation by increase in electric current

Fri, 11/09/2018 - 19:10

Publication date: November 2018

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

Author(s): V.V. Zaitsev, A.V. Stepanov

Abstract

We consider activation of a solar prominence by sharp increase in electric current in the frame of the Kuperus-Raadu model. The dynamics of the prominence is described in terms of the Ampère force, gravity, and the drag force. We suggest that the drag force is determined by the ion viscosity of ambient plasma. The upward Ampère force acting on the filament increases with the electric current in the filament, which results in the increase in the height of the filament. As a result of the dynamical process, a new equilibrium state corresponding to the new value of the electric current is reached. The maximum height and velocity of the prominence are estimated using the nonlinear equation for prominence dynamics. A sharp increase in the electric current can be due to the magnetic Rayleigh-Taylor instability in the chromospheric footpoints of the filament. Two examples of solar active filaments are analyzed in the context of the proposed model. Failed or two-stage eruption of the prominences is also discussed.

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