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Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Megbar W. Birhan, U. Jaya Prakasha Raju, SamuelT. Kenea

Upper Blue Nile basin (UBNB) is the water tower of Ethiopia and downstream countries. It contributes significant moisture to the surrounding atmosphere. However, the contribution of the moisture from the basin to the precipitation in the UBNB is not well documented. Therefore, this paper is aimed to estimate the role of UBNB moisture budget and recycling ratio for spatiotemporal precipitation distributions. To this end, we used the European Center for Medium-range Weather Forecast (ECMWF) data from 1979 to 2017. The derived ECMWF results are correlated with in-situ observations with the correlation coefficient of 0.82. During summer season most of the UBNB moisture is converted to precipitation around the central parts of the study area, while in spring it contributes to the southern parts of the study area. Furthermore, the northwest part of the study area is affected by the basins moisture during the autumn season. The calculated recycling ratios for four seasons (summer, autumn, spring, and winter) are 9.70%, 16.33%, 19.01%, and 35.30% respectively with the annual average value of 20.11%. It is evident that the maximum amount of precipitation is captured from the local moisture during the winter season. Generally, UBNB moisture budget had a lesser contribution of precipitation over the study area. It rather contributed significant precipitation to the neighboring countries. Hence, further studies on moisture budget are required to explain this phenomenon in the context of Ethiopia.

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): P.R. Shreedevi, R.K. Choudhary, Yiqun Yu, Evan G. Thomas

Morphological features of the quiet/disturbed time variations in the Total Electron Content (TEC) at the polar cusp station Bharati (76.69°S MLAT) during a period of 5 years starting from February 2013 to December 2017 has been studied using GPS TEC measurements. The TEC at Bharati follows a diurnal pattern with its peak appearing close to local noon/magnetic noon during the summer/winter months. A nighttime enhancement in the TEC is seen around the magnetic midnight during winter. The plasma density at Bharati also exhibits semi-annual variation and a strong dependence on solar activity. A comparison of the IRI 2016 model derived TEC and the GPS TEC at Bharati shows significant differences with large underestimation of TEC especially during the nighttime period of the winter months. A two fold difference in magnitude between the GPS and modeled TEC is also observed in the summer months of the high solar activity period of 2013–2015. The response of the TEC to geomagnetic storms is found to depend on the onset time of the storm. We show that the morphological features in the temporal evolution of the plasma density at Bharati vary as the location of Bharati changes from being inside the polar cap, to the auroral region, and to the polar cusp in quick succession in a day. Our results highlight the fact that the dynamic nature of the location of Bharati with respect to the position of the polar cap plays an important role in deciding the plasma distribution at the polar cusp station.

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Salim Oukali, Mourad Lazri, Karim Labadi, Jean Michel Brucker, Soltane Ameur

The approach developed in this paper for the classification of precipitation intensities is based on deep learning of neural network. Multispectral data from the MSG satellite (Meteosat Second Generation) providing information about the cloud's physical and optical characteristics are exploited and used as inputs to a deep neural network model. The model is a combination of CNN (Convolutional Neural Network) and DMLP (Deep Multi-Layer Peceptron) which is learned and validated by comparison with the corresponding Radar data during the rainy seasons 2006/2007 and 2010/2011 respectively. The CNN extracts spatial characteristics from MSG multi-spectral images. Then, the set of spatial and multi-spectral information are used as inputs for the DMLP. The results show an improvement compared to the three other classifiers (Random Forest, Support Vector Machine and Artificial Neural Network). The CNN-DMLP method was also compared to the technique combining the three classifiers (SAR). The results indicate a percentage correct (PC) of 97% and a probability of detection (POD) of 90% for CNN-DMLP method compared to 94% and 87% for of the SAR technique, respectively. In terms of bias, the CNN-DMLP method gives 1.08 compared 1.10 for SAR technique.

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Erxiao Liu, Hongqiao Hu, Jianjun Liu, Xuyang Teng, Lei Qiao

The cross polar cap potential (CPCP) is one of the primary parameters characterizing the electrodynamic feature of the high latitude ionosphere convection. In this study, we perform a comprehensive investigation of the Super Dual Auroral Radar Network (SuperDARN) CPCP, based on a large database of measurements from 1999 to 2009, and its relationship with various parameters of the solar wind, interplanetary magnetic field (IMF) and geomagnetic indices. Specifically, the IMF clock angle, the IMF Bz, the solar wind velocity, the plasma proton density, AE index, SymH index and Dst index are under consideration. According to the results of the correlation, the input parameters are selected and two models of the CPCP based on the multivariate regression analysis and Back Propagation Artificial Neural Network (BP ANN) algorithm are proposed respectively. The regression and BP ANN models are validated and the accuracy as well as the stability of the models is tested by using independent datasets. The result shows that the root mean square error (RMSE) between the measured and the model values ranges from 3.7 to 6.7 kV and the linear correlation coefficients are close to, or above 0.7. The ANN model is shown to have a better performance than the regression model.

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Sunil Kumar, A.K. Srivastava, V. Pathak, D.S. Bisht, S. Tiwari

Short-wave incoming solar radiation and aerosol optical characteristics were examined at New Delhi, in the western Indo-Gangetic Basin (IGB) for the period from March 2010 to June 2012 to understand their possible association in different sky conditions along with their radiative implications. During the study period, solar radiation varied between 65 and 624 W m−2, with a seasonal mean of 419 ± 34, 328 ± 32, 308 ± 54 and 306 ± 56 W m−2, respectively in the summer, monsoon, post-monsoon and winter periods. Inter-annually, the magnitude of solar radiation was ∼19% and 23% higher during 2012 as compared to 2011 and 2010. Aerosol optical Depth (AOD) varied between 0.11 and 2.4 (mean: 0.69 ± 0.38) whereas Ångström Exponent (AE) was between 0.46 and 1.81 (mean: 0.8 ± 0.28) during the entire study period. The solar radiation was found to be significantly correlated with the AOD (R = −0.22) and AE (R = −0.45). The mean characteristics of solar radiation and aerosol optical parameters were found to differ significantly in different sky conditions, which were used to examine their possible implications to direct radiative effect (DRE). The DRE at the surface was as high as about −19 W m−2 during clear sky day, which was ∼16 and 48 W m−2 higher than that of haze/foggy and dusty days, respectively.

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Hossein Hassanli, Majid Rahimzadegan

Total Precipitable Water (TPW) vapor value in the earth's atmosphere and its variations are of great importance in atmospheric and climatic studies. Among the most important methods introduced for estimation of TPW are satellite products such as Moderate Resolution Imaging Spectroradiometer (MODIS) and numerical methods such as Weather Research and Forecasting (WRF). The performance of TPW estimation methods are different in various locations and require evaluations. Then, the goal of this study is investigating the performance of estimated TPW from MODIS product (MOD05) and WRF model. In this regard, two infrared (IR) and near infrared (NIR) algorithms of MOD05 were evaluated. Moreover, three nested resolutions of 27, 9, and 3 km of the WRF in 0000 and 1200 UTC were investigated. Mehrabad radiosonde station in the south of Tehran, Iran was considered as the study area. Evaluation of the two selected models was performed using radiosonde measurements of 240 days in 2013 and 2014. Among the nested domains for WRF model, the 3 km model at 0000 UTC provided the best results with determination coefficient (R2) of 0.81 and Root Mean Square Difference (RMSD) of 2.98 mm. Among the MODIS products, MODIS IR showed a better performance with R2 of 0.72 and RMSD of 3.46 mm. In general, the estimated TPW from MODIS-IR and WRF3 showed that WRF has a better performance. Then, the results proved that WRF model can be used in various meteorological conditions for estimation TPW with an acceptable accuracy.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Yingchun Yue, Tao Ye

Precipitation plays an important role in human activities, and accurate prediction of precipitation is expected to make the arrangements accordingly, especially in Antarctic area with complicated weather conditions. Since directly forecasting precipitation usually requires a lot of meteorological data, which is difficult to be collected in Antarctic area, the precipitation is usually predicted indirectly by using precipitable water vapor (PWV). The PWV can be calculated by Hopfield model using GPS zenith tropospheric delay (ZTD) data if only the temperature and pressure data is available. In this paper, we adopt the artificial neural network (ANN) with genetic algorithm (GA) to predict the PWV of the Zhongshan Station in 6 and 12 h by four different input schemes, including ZTD, ZTD with real-time meteorological data, PWV, and intrinsic mode functions (IMFs) of PWV. The predicted results show that the worst prediction is got by using ZTD sequences with the correlation coefficient of about 0.50. The results of using ZTD with real-time meteorological data and PWV have approximate correlation coefficient of about 0.80. The best prediction is obtained by using IMFs of PWV sequences to predict 6 h PWV with the correlation coefficient of 0.95.

Publication date: Available online 5 June 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Yekoye Asmare Tariku

This paper investigates the validation of the performance of the latest versions of the International Reference Ionosphere (IRI 2016), the IRI extended to the plasmasphere (IRI-Plas 2017) and NeQuick 2 models in the estimation of the variation of the Total Electron Content (TEC) over the West Pacific regions during the 2015–2017 years. This has been performed employing the GPS-derived TEC data obtained from stations located at Observation Rock, OBSR (geog 46.90°N, 238.18°W, Geom. 52.46°N), Husband, HUSB (44.12°N, 238.15°W, Geom. 49.73°N). It has been revealed that both the GPS-derived VTEC and modelled (IRI 2016, IRI-Plas 2017 and NeQuick 2 VTEC) variations attain their minima at about 13:00 UT (05:00 LT) and maxima at about 20:00 UT (12:00 LT). Moreover, because of the enhancement of photo-ionization process in the region as a result of exposure of the ionosphere for direct radiation in the summer months, large measured VTEC values are seen in the June solstice months during 2015–2017. It has also been shown that, because of the variation of the Sunspot number (SSN) and solar radio flux 10.7 cm (F10.7), the VTEC variations for both the GPS-derived and models show decrease at transition from 2015 to 2017, with some exceptions observed in the June solstice months. In addition, the root-mean-square deviations (RMSD) between the GPS-derived and modelled diurnal VTEC variations are generally less than 0.5TECU in using both the SSN and F10.7 indices. This shows that all the three models are good in TEC estimation with the IRI-Plas 2017 and NeQuick 2 perform the best on most of the hours, in comparison with the IRI 2016 model with IRI2001 option, especially in using the F10.7 index when the solar activity increases. However, when the solar activity decreases, utilizing the SSN for all the three models (especially for the IRI-Plas 2017 and NeQuick 2) shows the better performance. Moreover, during the geomagnetic storm condition, both the IRI 2016 and IRI-Plas 2017 models with the storm option “on” do not adequately reflect to the sharp increase or decrease of the GPS-derived VTEC values.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Munawar Shah, M. Arslan Tariq, Najam Abbas Naqvi

Recent advances on satellite-based measurement of different atmospheric constituents at different heights provide sufficient evidences of short and long-term earthquake (EQ) precursors. In this paper, atmospheric anomalies are investigated related to three large magnitude Mw > 6.0 EQs in Pakistan and Iran during 2010–2017 (i.e., January 18, 2011 (Mw 7.2, Southwestern Pakistan), April 16, 2013 (Mw 7.7, East of Khash Iran) and February 07, 2017 (Mw 6.3, Pasni, Pakistan)). For this purpose, satellite based Outgoing Longwave Radiation (OLR), Surface Temperature (ST), Aerosol Optical Depth (AOD) and NO2 are investigated by statistical bounds of median and standard deviation for two months before and one month after the occurrence of each event. We study the spatial OLR anomaly from National Oceanic and Atmospheric Administration/National Center for Environmental Prediction (NOAA/NCEP). Evidences suggest that abnormal atmospheric anomalies occur within one month before the main shock. For example, in case of Mw 7.2 southwestern Pakistan EQ, significant perturbations in daytime OLR are detected up to 21 days before the main shock, justifying the existence of huge amounts of energy over the tectonic lineaments. The OLR anomaly correlated with ST, AOD and NO2 during 15–21 days before the main shock, which may be attributed to the same event. Similarly, the OLR, ST, AOD and NO2 show irregularities before the 2013, Mw 7.7 East of Khash Iran EQ, where all the anomalies occur 9–10 days before the main shock. The anomalous OLR over the epicenter suggests the authenticity of all the temporal perturbations in the atmospheric parameters related to Mw 7.7 (Iran event). Furthermore, the atmospheric parameters are analyzed temporally by the statistical bounds before the Mw 6.3 (Pasni, Pakistan) EQ. All the parameters behave abnormally during 10–15 days following the Mw 6.3 Pakistan EQ and similarly subsequent spatial OLR enhancement over the epicenter may lead to the conclusion of an extensive energy emanation. The anomalies detected are consistent with the processes of stress activation of proxy defects at the Lithosphere-Atmosphere interface in the seismic breeding zone.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): M.H. Denton, R. Kivi, T. Ulich, C.J. Rodger, M.A. Clilverd, J.S. Denton, M. Lester

In this study we investigate and quantify the statistical changes that occur in the stratosphere and mesosphere during 37 sudden stratospheric warming (SSW) events from 1989 to 2016. We consider changes in the in-situ ozonesonde observations of the stratosphere from four sites in the northern hemisphere (Ny-Ålesund, Sodankylä, Lerwick, and Boulder). These data are supported by Aura/MLS satellite observations of the ozone volumetric mixing ratio above each site, and also ground-based total-column O3 and NO2, and mesospheric wind measurements, measured at the Sodankylä site. Due to the long-time periods under consideration (weeks/months) we evaluate the observations explicitly in relation to the annual mean of each data set. Following the onset of SSWs we observe an increase in temperature above the mean (for sites usually within the polar vortex) that persists for >∼40 days. During this time the stratospheric and mesospheric ozone (volume mixing ratio and partial pressure) increases by ∼20% as observed by both ozonesonde and satellite instrumentation. Ground-based observations from Sodankylä demonstrate the total column NO2 does not change significantly during SSWs, remaining close to the annual mean. The zonal wind direction in the mesosphere at Sodankylä shows a clear reversal close to SSW onset. Our results have broad implications for understanding the statistical variability of atmospheric changes occurring due to SSWs and provides quantification of such changes for comparison with modelling studies.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): I. Emmanuel

The vertical distribution of refractivity gradient is important in determining anomalous propagation condition. Thirty five years of meteorological parameters, obtained from Era-Interim archive of European Centre for Medium-Range Weather Forecasts has been used to analyze and investigated surface meteorological data linked with refractivity gradient aloft altitude across Nigeria. Spatial distribution of surface temperature, relative humidity and refractivity gradient at 0.1 km, 0.5 km, 1.0 km and 1.5 km over Nigeria were plotted. Vertical distribution of temperature, relative humidity, refractivity and refractivity gradient were obtained for some locations across Nigeria. Similarly, spatial distribution of coefficient of determination between surface temperature, relative humidity and refractivity gradient at four different height were estimated. Linear regression were developed to investigate the relationship between surface data and refractivity gradient at different altitude. The result revealed existence of sub refractive, super refractive, and ducting across the country at 0.1 km and 0.5 km however occurrence of ducting and sub refractive disappeared at 1.0 km and 1.5 km. Likewise, the existence of temperature inversion was noticed between surface and 100 m across all the locations except in Lagos. Values of refractivity across the observed locations converged around 0.5 km. Through result of correlation coefficient and statistical parameters, significant linked have been established between surface data and refractivity gradient at different height.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Priyanka Ghosh, Som Sharma

The vertical wavenumber spectra over tropical location, Gadanki (13.5° N, 79.2° E) and sub-tropical location, Mt. Abu (24.5° N, 72.7° E) is studied using the temperature measurements from ground based Rayleigh Lidar and space borne satellite observations. The slope values are lesser over Gadanki than at Mt. Abu for almost all the altitudes except for 40–50 km where it is nearly same and 60–70 km exhibiting opposite nature. Unusual spectral slope of −6.97 (Mt. Abu) and −0.09 (Gadanki) is seen at the altitude of 40–50 km in satellite temperature. Characteristics of wave oscillations perceived over both the stations are described.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): G. Zeng, C. Shen, Z.J. Rong, X. Li, T. Chen, Z.Q. Chen, Y.H. Ma

For the first time, the global structure of the geomagnetic disturbance field around the Earth as well as the magnetic storm indices have been deduced from magnetic field measurements by ground observatories in a confined range of longitude. The spatial gradient of the H component of the geomagnetic disturbance field was obtained from ground geomagnetic observatories only in the Eastern Hemisphere, provided the geomagnetic disturbance field varies approximately linearly in space. Furthermore, the storm symmetric and asymmetric indices were derived and the spatial distribution and temporal evolution of the storm ring current was investigated. It was found that the storm indices derived from observatories in the Eastern Hemisphere are consistent with the officially published Kyoto standard indices which are derived from six globally distributed observatories. We also calculated the storm indices for 1941–1956 by using data from three observatories (HER, KAK and SJG). The correlation coefficient between the symmetric index deduced from three observatories and the one from the global six observatories is 0.98, and the correlation coefficient between the two kind of asymmetric indices is 0.79. Those results suggest that our approach is reasonable and significant when global ground observatories are not readily available.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): A. Tebabal, S.M. Radicella, B. Damtie, Y. Migoya-Orue’, M. Nigussie, B. Nava

In this paper, a neural network based regional ionospheric model is developed using GPS-TEC data from 01 January 2012 to 31 December 2015. For this purpose, nine GPS station TEC data in the time intervals 2012 to 2014 were used to determine model parameters. TEC data obtained in various years and geographical locations which are excluded in the training time are used to validate the performance of the model. For the first case, TEC data from each station in the year 2015 is used to validate the performance of the model. In the second case, GPS observations at Metu, Robe, and Serb stations are used to investigate the model’s performance in the year 2012, 2014 and 2013–2014, respectively. In both cases, to validate the accuracy and quality of the model, GPS-TEC values were compared with the predicted TEC. The results indicate that the proposed model can capture most of the spatio-temporal variations of the regional TEC. The present model reproduces the observed hourly TEC with RMS values that lie around 3 to 6.05 TECU at different geographical locations for both one hour and one day ahead prediction. For one day ahead prediction, a comparison of the NN method using NeQuick 2 model outputs with GPS derived measurements have also been conducted. The results indicate that the NN TEC model proposed has a good performance in representing TEC variations compared to climate NeQuick 2 model.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): O.S. Ojo, B. Adeyemi, E.O. Ogolo

The main aim of this paper is to assess the impact of climate change on variations and trends of the net radiation flux over West Africa during night and day time. West Africa was sub-divided into six climatic zones as classified by the World Meteorological Organization such as Hyper-Arid (HAR), Arid (ARD), Semi-Arid (SAR), Semi-Humid Dry (SHD), Semi-Humid Humid (SHH) and Humid (HUM) zones. To achieve this aim, thirty-six years' surface data of shortwave and longwave radiations between 1980 and 2015 were obtained from the Archives of the Modern-Era Retrospective Analysis for Research and Application, Version 2 (MERRA-2) database. Analyses showed that the maximum values of net radiative fluxes during the nighttime and daytime have the magnitude in watt per square metres of −70.00 and 225.82 in HAR zone, −62.46 and 248.99 in ARD zone, −51.71 and 304.88 in SAR zone, −40.55 and 334.58 in SHD zone, −34.32 and 352.62 in SHH zone and −30.49 and 362.68 in HUM zone respectively. The effect of population density, emission of greenhouse gas and surface albedo on net radiation was investigated over the climatic zones using the multivariate linear regression analysis. The results of the regression analysis showed that they have significant effects on net radiation. Also, the monotonic trend analysis between 1980 and 2015 was carried out using the non-parametric Mann- Kendall statistical test. The results of the trend test revealed that net radiation showed decreasing trends mainly in the humid zones at over 95% significance level while population density, emission of greenhouse gas and surface albedo showed significant increasing trends at the 99.9% level of significance. The analyses showed that the humid zones have higher values of net radiation, radiative cloud forcing, carbon-dioxide emission, population density and lower surface albedo than arid zones. Therefore, as signatures of climate change, it can be concluded that increase in population density, cloud amount and anthropogenic activities such as land use/land cover and emission of greenhouse gas have contributed greatly to the significant decreasing trends of the radiative flux balance especially in the humid zones of West Africa.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Angelica M. Castillo, Yuri Y. Shprits, Natalia Ganushkina, Alexander Drozdov, Nikita Aseev, Dedong Wang, Stepan Dubyagin

In this study, we present initial results of the coupling between the Inner Magnetospheric Particle Transport and Acceleration Model (IMPTAM) and the Versatile Electron Radiation Belt (VERB-3D) code. IMPTAM traces electrons of 10−100 keV energies from the plasma sheet (L=9 Re) to inner L-shell regions. The flux evolution modeled by IMPTAM is used at the low energy and outer L∗ computational boundaries of the VERB code (assuming a dipole approximation) to perform radiation belt simulations of energetic electrons. The model was tested on the March 17th, 2013 storm, for a six-day period. Four different simulations were performed and their results compared to satellites observations from Van Allen probes and GOES. The coupled IMPTAM-VERB model reproduces evolution and storm-time features of electron fluxes throughout the studied storm in agreement with the satellite data (within ∼0.5 orders of magnitude). Including dynamics of the low energy population at L∗=6.6 increases fluxes closer to the heart of the belt and has a strong impact in the VERB simulations at all energies. However, inclusion of magnetopause losses leads to drastic flux decreases even below L∗=3. The dynamics of low energy electrons (max. 10s of keV) do not affect electron fluxes at energies ≥900 keV. Since the IMPTAM-VERB coupled model is only driven by solar wind parameters and the Dst and Kp indexes, it is suitable as a forecasting tool. In this study, we demonstrate that the estimation of electron dynamics with satellite-data-independent models is possible and very accurate.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Sergii V. Panasenko, Yuichi Otsuka, Max van de Kamp, Leonid F. Chernogor, Atsuki Shinbori, Takuya Tsugawa, Michi Nishioka

We present the results of a comprehensive study of traveling ionospheric disturbances (TIDs) occurring over Europe during the total solar eclipse of 20 March 2015. For detection of wave structures and estimation of TID parameters, two remote sensing techniques were combined: incoherent scatter (IS) radars and European and Finnish dense GPS receiver networks. Similar procedures were applied for processing both IS and GPS data. We developed a new method enabling to analyze TEC data separately in the temporal and spatial domain. For the first time, we produced maps of band-pass filtered TEC variations and reported both large- and medium-scale prevailing TIDs observed during this solar eclipse, both having similar periods of about 50 – 60 min. The downward phase progression indicates that TIDs were induced by atmospheric gravity waves generated at lower altitudes. The variations in IS power attained peak relative amplitudes of 0.22 (22%) at 220 km over Tromsø and of 0.17 (17%) at 200 km over Kharkiv. The vertical phase velocity was about 57 m/s over Tromsø. It increased from 25 to 170 m/s over Kharkiv with altitude increasing from 120 to 310 km. Over Western Europe, large-scale TIDs (LSTIDs) had prevailing north-east direction over the region from 45°to 50°N and 2°W to 8°E. Here, their average horizontal phase velocity Vm was 803±281m∕s and the absolute amplitudes of TEC variations usually do not exceed 0.17 TECU. For this region, we found strong differences in LSTID propagation azimuth between the solar eclipse day and the two adjacent days of 19 and 21 March 2015, used as reference. This most likely indicates that these LSTIDs were directly caused by the solar eclipse through local heating/cooling processes occurring during the passing of the Moon penumbra. Over another region, limited by 44°–50°N and 13°–19°E, the LSTIDs had south-east propagation. Over Finland, the LSTIDs also propagated southeastward having Vm=774±202m∕s and TEC amplitudes up to 0.6 TECU. A possible evidence of LSTID generation at high latitudes indirectly by this solar eclipse through an excitation of slow magnetosonic waves was experimentally detected. Medium-scale TIDs (MSTIDs) propagated southeastward over both regions having Vm values of 144±54m∕s over Western Europe and of 104±43m∕s over Finland. Over Northern Europe, the maximum MSTID amplitudes were greater by a factor of 5 compared to those over Western Europe and reached 0.4 TECU. We did not detect a clear difference in MSTID propagation between solar eclipse and reference days. The IS and GPS results are in consistency with each other. The detected TID parameters of predominant periods, relative amplitudes, altitude range and MSTID horizontal propagation direction generally correspond to the results of other studies.

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): S.K. Sangeetha, V. Sivakumar

This paper focused on the temporal and spatial variability of sulphur dioxide (SO2) from 2004 to 2013 over 36 ground-based (GB) stations located in Gauteng and Mpumalanga provinces of South Africa. The assessment was based on the in situ SO2 data, where the GB stations were sorted into different groups and in addition, kriging-based analysis and OMI SO2 data (2004–2013) were deployed to study their seasonal spatial variability. It was observed that Pretoria west, Witbank and Randwater had high SO2 levels and standard deviations. Although, winter played a major role in having peak SO2 values in most of the stations, it was surpassing that in spring the SO2 levels of Witbank and Pretoria west stations dropped and Randwater had the highest standard deviation of 11.2 ppbv in October. A prominent seasonal variation was seen in all the groups, excluding Mpumalanga power stations (MP) group. This was particularly evident in the Vaal Triangle group. Highveld group ranked topmost level with elevated SO2 values proceeded by the MP group in all the temporal time scales. The spatial based analysis further proved that the highest SO2 levels were centred around major industrial regions of Mpumalanga, regardless of all the seasons.

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): A.V. Kudriavtseva, D.V. Prosovetsky

We studied coronal white-light jets in the polar regions of solar corona in 2009–2014. Jets were tracked on data producing by coronographs COR2/STEREO with the 2.5–16 solar radii field of view. We also considered their characteristics on solar cycle progress: jet occurrence rate of jets per year above the northern and southern poles, angular distributions and measured apparent velocities. The jet mean occurrence rate per year is 234 registered events. It is defined that both occurrence rate per year and the mean apparent velocities are increased to solar cycle maximum. This changes were shown to be different for the north and south polar regions and to depend on polar magnetic fields. The mean apparent velocities are increased by 1.7 times for north pole (from 134 ± 66 km/s to 229 ± 59 km/s) and by 2.4 times for south pole (from 101 ± 37 km/s to 243 ± 79 km/s). Most of the jets with velocities > 450 km/s was registered at the solar cycle maximum.

Publication date: Available online 15 May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Oindrila Nath, S. Sridharan

The volume mixing ratios (VMRs) of Nitrous Oxide (N2O) and NOx [Nitric Oxide (NO) + Nitrogen-di-Oxide (NO2)] derived from the radiance measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) Fourier infrared spectrometer, for the period 2007–2011 have been used to study their seasonal, interannual as well as Sudden Stratospheric Warming (SSW) related variations in the equatorial (5°N-5°S) stratosphere. Both N2O and NOx VMR show a clear seasonal variation around 45 km. The N2O VMR exhibits minimum (around 200 ppbv) during July–August and remains at 250–300 ppbv during the rest of the months. The NOx VMR is found to be minimum (around 10 ppbv) during May–July, whereas it shows higher values (∼15–17 ppbv) in the other months. Higher values are found in N2O and NOx VMRs in the years 2008 and 2010 in the northern tropics (10–30°N) when the QBO is in westward phase favouring high residual meridional circulation. During the SSW of 2009, NOx VMR is found to increase by 3 ppbv. Using a primitive chemistry-transport model, the increase in NOx during the SSW is demonstrated to be due to the enhanced vertical upwelling as well as meridional circulation prior to the onset of the SSW in response to the larger planetary wave activity.