Journal of Atmospheric and Solar-Terrestrial Physics

Distinct thermospheric mass density variations following the September 2017 geomagnetic storm from GRACE and swarm

Tue, 01/22/2019 - 19:10

Publication date: Available online 11 January 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Liangliang Yuan, Shuanggen Jin, Andres Calabia

Abstract

Geomorphologies and mechanisms of thermospheric mass density variations caused by geomagnetic storms are still challenging due to limited observations and imprecise models. Recently, precise orbit determination (POD) of Gravity Recovery and Climate Experiment (GRACE) and Swarm satellites is able to estimate thermospheric mass density variations, which may provide data to study thermospheric mass density variations following the storm. In this paper, the thermospheric mass density is estimated from GRACE-A and Swarm-A POD and the distinct thermospheric mass density variations are investigated as function of latitude during the September 2017 geomagnetic storm. Different enhancements in mass density response to the geomagnetic storm are presented for the Northern (GRACE) and the Southern (Swarm) Hemispheres. Swarm observations show symmetric mass density variations between two hemispheres and a slightly stronger enhancement in Southern Hemisphere. GRACE POD and accelerometer observations both show a very strong enhancement in Northern Hemisphere while no corresponding enhancement in Southern Hemisphere. This anomaly may attribute to the effects of vertical winds in high latitude region and plasma drift considering the similar solar zenith angles in both hemispheres.

Fair-weather potential gradient and its coupling with ionospheric potential from three Antarctic stations: Case studies

Tue, 01/22/2019 - 19:10

Publication date: March 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 184

Author(s): N.Jeni Victor, Devendraa Siingh, C. Panneerselvam, P. Elango, V.S. Samy

Abstract

Simultaneous measurements of potential gradient (PG) from Antarctica stations, Vostok (78° 27′ S, 106° 52′ E), Dome C (75° 06′ S, 123° 20′ E) and Maitri (70° 45′ S, 11°44′ E) during magnetically disturbed days under fair-weather conditions are discussed. An attempt has been made to study the influence of solar wind-magnetosphere interaction on PG. During magnetic daytime (0600–1800 UT), linear relation between ΔPG and associated ionospheric potential from Dome C and Vostok are observed. The liner response is poor during the magnetic night time (1800-0600 UT). This trend has been addressed by the sun-aligned two-cell plasma convection flow and its differential motion over the stations. It is found that linear relation decreased when negative convection pattern moves towards, overhead and away from the stations under dawnward motion of plasma (IMF By < 0). In addition, the ionospheric potential at dusk sector modulated the PG if the plasma flow remained stable for more than 1 h. The results further showed that the scale size factor between ionospheric potential and PG may influence up to some extent in coupling efficiency. Month-wise Fair-weather PG pattern effectively accounts the ambient PG variation.

Observations of conjugated ring current auroras at subauroral latitudes

Tue, 01/22/2019 - 19:10

Publication date: March 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 184

Author(s): Yongliang Zhang, Larry J. Paxton

Abstract

We report three ring current aurora events that are conjugated in the two hemispheres observed by satellite and ground imagers on May 16, 2005, August 26, 2018 and September 5, 2005. The ring current auroras appeared as auroral spots or arcs in the day, dusk or night side. These events confirm that the particle sources are in the equatorial ring current ions and pitch angle diffusion of the ions lead to the ion precipitation in the both hemisphere on the same field lines, thus the auroras are conjugated.

A global atmospheric electricity monitoring network for climate and geophysical research

Tue, 01/22/2019 - 19:10

Publication date: March 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 184

Author(s): K.A. Nicoll, R.G. Harrison, V. Barta, J. Bor, R. Brugge, A. Chillingarian, J. Chum, A.K. Georgoulias, A. Guha, K. Kourtidis, M. Kubicki, E. Mareev, J. Matthews, H. Mkrtchyan, A. Odzimek, J.-P. Raulin, D. Robert, H.G. Silva, J. Tacza, Y. Yair

Abstract

The Global atmospheric Electric Circuit (GEC) is a fundamental coupling network of the climate system connecting electrically disturbed weather regions with fair weather regions across the planet. The GEC sustains the fair weather electric field (or potential gradient, PG) which is present globally and can be measured routinely at the surface using durable instrumentation such as modern electric field mills, which are now widely deployed internationally. In contrast to lightning or magnetic fields, fair weather PG cannot be measured remotely. Despite the existence of many PG datasets (both contemporary and historical), few attempts have been made to coordinate and integrate these fragmented surface measurements within a global framework. Such a synthesis is important in order to fully study major influences on the GEC such as climate variations and space weather effects, as well as more local atmospheric electrical processes such as cloud electrification, lightning initiation, and dust and aerosol charging.

The GloCAEM (Global Coordination of Atmospheric Electricity Measurements) project has brought together experts in atmospheric electricity to make the first steps towards an effective global network for atmospheric electricity monitoring, which will provide data in near real time. Data from all sites are available in identically-formatted files, at both 1 s and 1 min temporal resolution, along with meteorological data (wherever available) for ease of interpretation of electrical measurements. This work describes the details of the GloCAEM database and presents what is likely to be the largest single analysis of PG data performed from multiple datasets at geographically distinct locations. Analysis of the diurnal variation in PG from all 17 GloCAEM sites demonstrates that the majority of sites show two daily maxima, characteristic of local influences on the PG, such as the sunrise effect. Data analysis methods to minimise such effects are presented and recommendations provided on the most suitable GloCAEM sites for the study of various scientific phenomena. The use of the dataset for further understanding of the GEC is also demonstrated, in particular for more detailed characterization of day-to-day global circuit variability. Such coordinated effort enables deeper insight into PG phenomenology which goes beyond single-location PG measurements, providing a simple measurement of global thunderstorm variability on a day-to-day timescale. The creation of the GloCAEM database is likely to enable much more effective study of atmospheric electricity variables than has ever been possible before, which will improve our understanding of the role of atmospheric electricity in the complex processes underlying weather and climate.

Climatological analysis of the optical properties of aerosols and their direct radiative forcing in the Middle East

Tue, 01/22/2019 - 19:10

Publication date: February 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 183

Author(s): Maryam Gharibzadeh, Khan Alam, Yousefali Abedini, Abbasali Aliakbari Bidokhti, Amir Masoumi, Humera Bibi, Bahadar Zeb

Abstract

In addition to climate perturbations, various problems such as air pollution, reduction in the visibility and human health hazards were caused by atmospheric aerosols in the Middle East specifically in the last two decades. With the help of the Aerosol Robotic NETwork (AERONET), the measurement of the aerosol optical and radiative properties were carried out over seven sites in the Middle East during 2013. The analysis of the optical properties of aerosols like Single Scattering Albedo (SSA), Angstrom Exponent (AE), Aerosol Optical Depth (AOD), and Asymmetry parameter (ASY) were carried out during the study period. During spring and summer, high values of AOD and low values of AE were found in all sites except CUT-TEPAK (Limassol, Cyprus), which specified the existence of coarse mode particles and dust storms in these seasons. The AE maximum values were found in the summer and fall over CUT-TEPAK and IMS-METU-ERDEMLI(Erdemli, Turkey), whereas in other sites IASBS (Zanjan, Iran), KAUST Campus (Thuwal, Saudi Arabia), Masdar Institute (Masdar, United Arab Emirates), Mezaira (Mezaira, United Arab Emirates) and Solar Village (Riyadh, Saudi Arabia) the peak values of AE occurred in the fall and winter. The maximum values of SSA and ASY were observed in the spring and summer over all sites except over CUT-TEPAK and IMS-METU-ERDEMLI. The Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model has been used for the calculations of the Aerosol Radiative Forcing (ARF) over the selected sites. We obtained negative value of ARF at the surface, which suggesting its cooling effects because of the loss of radiation back to space due to aerosols. The averaged ARF values at the SuRFace (SRF) of the earth were −43.8 Wm-2, -31 Wm-2, -56.8 Wm-2, -61.7 Wm-2, -52.5 Wm-2, -54.9 Wm-2, and -72.2 Wm-2, over CUT-TEPAK, IASABS, IMS-METU-ERDEMLI, KAUST Campus, Masdar Institute, Mezaira and Solar Village, respectively. While the positive value of atmospheric ARF showed heating of the atmosphere.

Thunderstorm generators operating as voltage sources in global electric circuit models

Tue, 01/22/2019 - 19:10

Publication date: February 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 183

Author(s): Nikolay N. Slyunyaev, Alexey V. Kalinin, Evgeny A. Mareev

Abstract

The description of global electric circuit (GEC) generators in continuous numerical models is analysed and discussed. It is shown that voltage-source generators, sometimes employed in simple lumped-element GEC models, have a consistent generalisation in continuous GEC models: just as current-source generators generalise to source current density distributions, voltage-source generators generalise to distributions of the relative potential on cloud boundaries. The difference between non-ideal and ideal current or voltage sources is investigated for both lumped-element and continuous GEC models. As in modern three-dimensional GEC models the formal generalisation of voltage-source thunderstorms turns out to be difficult to implement, two alternative approaches involving the replacement of voltage-source generators with equivalent current-source generators are developed. One approach is based upon a rough estimation of the source current producing the same contribution to the GEC as the original voltage source; the other approach uses the fact that each voltage-source generator can be shown to be a limiting case of a certain current-source generator with increased conductivity. For the first time voltage-source generators are implemented in a numerical GEC model (using both the direct generalisation and the suggested alternative approaches).

A comparative study on the lightning sferics associated with terrestrial gamma-ray flashes observed in Americas and Asia

Tue, 01/22/2019 - 19:10

Publication date: February 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 183

Author(s): Gaopeng Lu, Hongbo Zhang, Steven A. Cummer, Yongping Wang, Fanchao Lyu, Michael Briggs, Shaolin Xiong, Alfred Chen

Abstract

We examine the broadband (<1 Hz to 400 kHz) electromagnetic lightning signals associated with Terrestrial Gamma-ray Flashes (TGFs) detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope during 2010/2011. The TGF-associated lightning sferics are mainly recorded at two stations located near National Cheng-Kung University in Taiwan and near Duke University in the United States, respectively. The general features exhibited by the TGF-associated lightning sferics are consistent with previous findings that gamma-rays in TGFs are typically produced during a slow process that creates a considerable (but not necessarily) charge moment change within several milliseconds. In some cases, this slow process can be attributed to the upward negative leader during the initial stage of normal intra-cloud (IC) lightning, and it is usually punctuated by one or several fast discharges, the major one of which (i.e. TGF-related discharge) is closely involved in the gamma-ray production. The equivalent peak current of TGF-related discharges could be as high as >+500 kA, and the associated charge transfer is also considerable (typically >+20 C km). The observed complexity of TGF-associated lightning emissions can also be interpreted in the context of the initial development of normal IC lightning flashes, where the upward negative leader drives the millisecond-scale current and may also provide the seed electrons for avalanche multiplication in the upper part of active thunderstorms. Our analyses show that the thunderstorms in the land area of South China produce TGFs that can be readily observed by Fermi/GBM, and the future ground-based coordinated observations in this area would be rather promising to gain more insights into the physical mechanism of TGFs.

Investigations of vertical wind variations at a mountain top in the Himalaya using Doppler Lidar observations and model simulations

Tue, 01/22/2019 - 19:10

Publication date: February 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 183

Author(s): K.K. Shukla, D.V. Phanikumar, Rob K. Newsom, N. Ojha, K. NiranjanKumar, Narendra Singh, Som Sharma, V.R. Kotamarthi, K.K. Kumar

Abstract

Hight-resolved observations of vertical winds remain nearly non-existing over the Himalayas, despite of anticipated crucial role of vertical motions in transporting pollution across the Himalayan hills. The present study analyze the vertical wind observations from surface to 1 km above ground level over Manora Peak (29.4° N; 79.5° E; 1958 m amsl) in the Himalaya performed using a Doppler Lidar during the Ganges Valley Aerosol Experiment (GVAX). Vertical wind exhibited a pronounced diurnal variability at Manora Peak comprising of upward motions during the daytime (05–10 UT) and downward motions during nighttime typical of a mountain-valley system. Mean vertical wind speeds are observed to be varying from −0.8 to +0.8 ms−1 during the study period with a variance of 0.1–1.5 m2s-2, which is attributed to the thermally driven turbulence. Mean vertical winds are observed to be stronger in the Doppler Lidar profiles above Manora Peak (−0.8 to 0.8 ms−1) as compared to near surface measurements at this station using an ultrasonic anemometer (−0.4 to 0.4 ms−1), and low altitude stations in India. Daytime vertical wind speeds are observed to be higher during pre-monsoon (0.81 ms−1), as compared to post-monsoon (0.24 ms−1) and winter (0.33 ms−1). Average Black Carbon (BC) concentrations are significantly higher during strong upward vertical winds, which indicates efficient transport of polluted air mass from low-altitude regions to the Himalaya. Weather Research and Forecasting (WRF) model reproduces the observed diurnal pattern in the vertical wind at the observation site however the model underestimates the variability.

Numerical simulation of the mean meridional circulation in the middle atmosphere at different phases of stratospheric warmings and mountain wave scenarios

Tue, 01/22/2019 - 19:10

Publication date: February 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 183

Author(s): Andrey V. Koval, Nikolai M. Gavrilov, Alexander I. Pogoreltsev, Ekaterina A. Drobashevskaya

Abstract

In this study, numerical simulations have been performed to estimate the transformation of the mean meridional circulation in altitude range 0–100 km at different phases of simulated stratospheric warming (SW) events in January–February including and excluding impact of mesoscale orographic gravity waves (OGWs). To obtain an ensemble of 12 pairs of model runs with and without a parameterization of OGW effects, the numerical middle and upper atmosphere model (MUAM) has been used. Obtained results demonstrate weakening of the zonal mean meridional circulation at altitudes up to 100 km during and after simulated SWs compared to the time interval before SWs. At altitudes below 50 km, southward mean meridional winds decrease (up to 15%) before and after simulated SWs. OGW effects may increase the mean northward wind at altitudes above 60 km up to 10–15%. The most significant changes of the meridional circulation in the middle atmosphere are detected at the middle and high latitudes of the Northern Hemisphere: the southward meridional circulation increases at altitudes above 40 km and decreases below 40 km. Thus, the global-scale mean meridional circulation in the middle atmosphere may significantly depend on different phases of SW events during the northern winter season. It is also quite sensitive to the dynamical and thermal OGW impacts.

Evaluating MODIS and MISR aerosol optical depth retrievals over environmentally distinct sites in Pakistan

Tue, 01/22/2019 - 19:10

Publication date: February 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 183

Author(s): Gohar Ali, Yansong Bao, Richard Boiyo, Weiyao Tang, Qifeng Lu, Jinzhong Min

Abstract

The Moderate resolution Imaging SpectroRadiometer (MODIS) and Multi-angle Imaging SpectroRadiometer (MISR) sensors provide aerosol observations suitable for a wide range of applications. The recently released MODIS Collection 6.1 (C061) includes several improvements compared to the previous products which are expected to minimize uncertainties in aerosol retrievals. Such collection needs to be validated and compared with previous collections form the same or other sensors before being applied for further scientific research on a regional scale. This study evaluates the performance of MODIS Collections 6 (C006) and 6.1 (C061) based on two algorithms: Dark Target (DT) and Deep Blue (DB) and the merged product (DTB) onboard the Terra (MOD04) and Aqua (MYD04) satellites, and the MISR AOD retrievals against ground-based Aerosol Robotic Network (AERONET) over two sites (Lahore and Karachi) in Pakistan during 2007–2014. Results elucidated that C061 MODIS AOD exhibited significant improvement as compared to C006, with the 10 km DT (DB) products generally overestimating (underestimating) AOD relative to AERONET AOD. The MOD04 and MYD04-DT and DB (3 and 10 km) showed comparable performance over the two sites, whereas The DTB was dominated by DT (DB) pixels over Lahore (Karachi). The MISR showed better performance over Karachi with high reflecting surface than over Lahore with dense vegetation cover. The annual cycle of AOD retrieved by the two sensors were consistent with AERONET AOD, with maximum AOD observed during summer months attributed to prevailing climatic conditions. On seasonal basis, the MODIS algorithms exhibited improved performance over Lahore except during summer where DT and DTB showed relatively low performance, attributed to modulations induced by local meteorology to the prevailing surface conditions. However, the sensors exhibited distinct performance over Karachi, where MODIS-DT (10 km) showed close correspondence with AERONET during autumn and winter, whereas MODIS-DT (3 km) exhibited the converse. The MISR performed relatively well during spring over the two stations. The study gives greater insights on the performance of MODIS and MISR and forms the basis for further research on the validation of satellite derived aerosol products over Pakistan.

Rapid intensification of tropical cyclones in the context of the solar wind-magnetosphere-ionosphere-atmosphere coupling

Tue, 01/22/2019 - 19:10

Publication date: February 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 183

Author(s): Paul Prikryl, Lidia Nikitina, Vojto Rušin

Abstract

Rapid intensification of tropical storms is examined in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere system. Tropical cyclone “best tracks” in the southern and northern hemispheres are used in the superposed epoch analysis of time series of solar wind parameters. The results indicate that rapid intensification of tropical storms tends to follow arrivals of high-speed streams from coronal holes or interplanetary coronal mass ejections, which can trigger geomagnetic storms. The ensuing auroral and polar cap activity including ionospheric currents and ionospheric convection generates atmospheric gravity waves that propagate from the high-latitude lower thermosphere both upward and downward. If ducted in the lower atmosphere, they can reach tropical troposphere. Despite significantly reduced wave amplitudes, but subject to amplification upon reflection in the upper troposphere, these gravity waves can trigger/release moist instabilities to initiate convective bursts, with the latent heat release leading to intensification of storms. Convective bursts have been linked to rapid intensification of tropical cyclones. Cases of tropical cyclone intensification closely correlated with the solar wind structure are found to be preceded by atmospheric gravity waves generated by the solar wind magnetosphere-ionosphere-atmosphere coupling process. The gravity waves are observed in the ionosphere as traveling ionospheric disturbances. Their propagation in the lower atmosphere is examined by ray tracing in a model atmosphere to show that they can reach tropical cyclones. It is suggested that the interaction of aurorally-generated gravity waves with the tropical cyclone vortex and the inner primary eyewall could play a role in the intensification process. Assuming that quasi-periodic convective bursts lead to vortex waves, a two-dimensional barotropic approximation is used to obtain asymptotic solutions representing propagation of vortex waves and their absorption by the mean flow in the critical layer.

High-speed video observations of branching behaviors in downward stepped leaders and upward connecting leaders in negative natural lightning

Tue, 01/22/2019 - 19:10

Publication date: February 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 183

Author(s): X. Wang, X. Zhao, Y. Hao, H. Cai, G. Liu, M. Liao, L. Qu

Abstract

Branched downward stepped leader (DSL) associated with branched upward connecting leader (UCL) were observed together in one negative natural lightning. Branching behaviors and development scenarios of DSL and UCL have been investigated and compared with high-speed video frame sequence. The optical evidence provides that most of negative leaders exhibit branching tips, with four main branching points produced during propagation. The adjacent faint segments, which are likely the newly created channel sections after two adjacent space leaders have make connection with the leader tip, are simultaneously appeared ahead of negative leader tips; most of them could contribute to the tortuosity of leader channel and only few of them lead to the concurrent branches of channel, with the common root of significantly great luminosity. However, positive leaders normally do not have branched tips, but generating one branching point at early stage of UCL initiation even though the leader channel is rather faint. The two-dimensional (2D) average speeds of five negative branches and the main branch of UCL propagating are quite similar, ranging from 3.56 × 105 m/s to 3.89 × 105 m/s.

Novel W<em>k</em>NN-based technique to improve instantaneous rainfall estimation over the north of Algeria using the multispectral MSG SEVIRI imagery

Tue, 01/22/2019 - 19:10

Publication date: Available online 21 December 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Noureddine Bensafi, Mourad Lazri, Soltane Ameur

Abstract

For the estimation of rainfall in northern Algeria, a new method is proposed in this study. It based on the k nearest weighted neighbours (WkNN) classification algorithm using the dataset from the radiometer-imager SEVIRI (Spinning Enhanced Visible and Infra-Red Imager) boarded on the satellite MSG (Meteosat Second Generation) to determine the pixel rainfall rate among the 16 predefined intensity levels observed in the Sétif meteorological radar.

The implementation of the classification consists in using the spectral characteristics of a new sample (pixel) as input variables of the WkNN classifier to predict his class of membership based on the weighted distances separating him from the samples of the set of learning. The results thus obtained are validated with respect to the rainfall intensity classes observed and co-located by ground radar. The results showed a significant improvement for instantaneous estimate of precipitation during the day, with a correlation coefficient r=0.87 and statistical parameters RMSE=2.29mm/h,Bias=0.45mm/h,MAE=0.35mm/h, and we have obtained the results similar overnight.

Geodetic contribution to predict the seismological activity of the Italian metropolis by the ionospheric variant of GPS_TEC

Tue, 01/22/2019 - 19:10

Publication date: February 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 183

Author(s): Abdennasser Tachema, Abdelmansour Nadji

Abstract

In this paper, we present a predictive approach treating the seismic hazard to detect, through to the geodetic data and the ionospheric total electron content (TEC) Anomalies, the time-origin of the seismic precursors of notable earthquakes (Mw ≥ 5). The main aim of this paper is to show the geo-spatial investigation interest to establish the ionospheric ‘TEC-Mapping’ allowing the monitoring and prediction of spontaneous vibrations of the lithospheric layer. For this purpose, we studied the seismic events that rocked the Italian peninsula (Central Italy, Mw > 6.1, late October 2016), where several IGS geodetic stations surrounding the hypocenter, were exploited to acquire raw data allowing to reconstitute in real time the GPS_TEC signal. As results, the elaborated ‘TEC’ diagram has allowed us to observe significant disturbances in the ionospheric TEC's amplitudes appear near the epicenter, a few days, before the Central Italy earthquake; which are related to the fluctuations of the electron density of the surrounding ionosphere. These anomalies represent the early percussion of seismic vibrations on earth, which truly respond the ternary coupling: Lithosphere-Atmosphere-Ionosphere. We also studied the causes that can disturb the ionosphere in order to distinguish from the pre-earthquake precursors. Finally, we confirmed the efficacy of this geodetic approach, applied in the natural hazards area, which can contribute effectively to the prediction of a significant seismic event in a given region.

Solar activities and climate change during the last millennium recorded in Korean chronicles

Tue, 01/22/2019 - 19:10

Publication date: Available online 15 November 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Hong-Jin Yang, Chan-Gyung Park, Rok-Soon Kim, Kyung-Suk Cho, Junhyeok Jeon

Abstract

Korean chronicles have a large amount of observational records of natural phenomena, including astronomical and meteorological events over two thousand years. Here we examine the correlation of solar activity and climate change from historical sunspot and frost records in the Korean chronicles. There are 42 sunspot records in Goryeo Dynasty (918–1392 CE) and 13 records in Joseon Dynasty (1392–1910 CE). The sunspot records in Goryeo Dynasty show a periodicity in good agreement with the well-known solar activity of 11 years. Korean sunspot records suggest that the solar activity in Joseon Dynasty decreased compared with that in the previous ∼500 years. In order to examine the long-period variation of solar activity, we include Chinese historical sunspot records in our analysis to supplement the lack of Korean records, and find a new ∼240-yr long-period solar activity from the power spectral analysis. Korean chronicles also have about 700 frost records during the last millennium. We investigate these frost records and find a sign of cooling down that can be interpreted as climate change during the last millennium. We also find ∼240-yr cooling period from the historical frost records, which is well in accord with that of solar activity. Therefore, we conclude that the solar activity has decreased during the last one thousand years and also has a long-term variation of ∼240 years.

Meteor head and terminal flare echoes observed with the Gadanki MST radar

Tue, 01/22/2019 - 19:10

Publication date: Available online 14 November 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): K. Chenna Reddy, B. Premkumar

Abstract

Meteor observations with Gadanki MST radar usually detect variety of meteor echoes that includes head echoes, specular and non-specular trail echoes. Sometimes, but not always head echoes are followed by a sudden increase in signal strength amounting to many decibels at terminal end point of the trail, known as terminal flare echoes - a feature mostly observed with optical and high power large aperture (HPLA) radar systems. In this study, we report some examples of terminal flare echoes observed with Gadanki MST radar. Because these echoes provide valuable insight into the role of diffusion and plasma instabilities in the formation and evolution of meteor trail. From the observations, it has been noticed that the head echoes at higher altitudes are generating non-specular trail echoes, whereas they disintegrate as terminal flares associated with meteoroid fragmentation in lower altitudes. Although meteoroid fragmentation is a common phenomenon, but terminal flaring is a rare feature observed with Gadanki radar. A small, but non-negligible fraction of meteor events (∼2.5% of all head echo events) showed flaring apparently produced by terminal destruction of a meteoroid fragmentation along with the insights into the fragmentation and terminal flaring process.

Study on the plasmaspheric Weddell Sea Anomaly based on COSMIC onboard GPS measurements

Tue, 01/22/2019 - 19:10

Publication date: Available online 28 September 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Peng Chen, Qinzheng Li, Yibin Yao, WanQiang Yao

Abstract

This study investigated the morphology of the Plasmaspheric Weddell Sea Anomaly (PWSA). Measurements by GPS receivers onboard COSMIC satellites were used to determine the slant total electron content (STEC) along signal propagation paths during 2007–2017, which were converted to the zenith direction using a specific plasmaspheric projection function to obtain vertical total electron content (VTEC). The characteristics of seasonal variation of the PWSA between the four seasons were examined under conditions of high and low solar activity that corresponded to values of the F10.7 index of >120 and ≤ 120, respectively. To investigate seasonal variation of plasmaspheric VTEC, maps of geographic latitude versus geographic longitude were constructed by binning the data into 5° latitudinal grids and 15° longitudinal grids. The median value of VTEC in each grid was calculated for each season under low and high solar activity conditions. The results showed that the WSA phenomenon could also be observed in the plasmasphere (altitude ≥ 800 km) as well as in the ionosphere. The anomaly is most prominent in winter under conditions of high solar activity, and it also can be found in spring and autumn, although its amplitude is relatively small. The equatorward neutral wind is the critical driver for PWSA formation. In addition, during the polar summer, high geographic latitudes are sunlit during the entire day, leading to prolonged photoionization. This is the most essential process for the existence of the nighttime maximum in the VTEC diurnal variation at the geographic latitudes of the PWSA.

Analysis of suborbital flight operation using PESTLE

Tue, 01/22/2019 - 19:10

Publication date: Available online 11 August 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): A.R. Zahari, F.I. Romli

Abstract

Suborbital flight has progressively emerged as the potential future transport trend, whether for space tourism or other applications. While several design concepts have been explored thus far for the suborbital flight operation, one of the main lingering concerns is actually the destination of the flight. The altitude of 100 km, which is the commonly chosen destination for suborbital flight, provides an imaginary separation between air and space. The quest for this separation sparks intense debates not only in the scientific communities but also in the political circles and legal fraternities. In conjunction with that, this research aims to analyse the suborbital flight operation by using the analytical tool of Political, Economic, Social, Technological, Legal and Environmental (PESTLE) in order to discuss its implications to a nation. From the analysis, among the advantages of suborbital flight operation include the shifting of role for space development from public agency to private enterprise, creation of new industry to generate revenue, public opportunity for access to space, new, low cost and reusable technology and material and also the enhancement of atmospheric studies. On the other hand, among established disadvantages of suborbital flight operation include the absence of international consensus on the boundary between air and space, intensive capital requirement to develop new technology and infrastructure, damage to third party liability, limited track record for flight safety, lack of regulation for new industry and also the air pollution resulting from the flight activity. All in all, it can be taken that there are many advantages that suborbital flight could bring to a nation but its subsequent disadvantages have to be carefully considered as well to ensure the sustainability of its operation and industry.

Plausible modulation of solar wind energy flux input on global tropical cyclone activity

Tue, 01/22/2019 - 19:10

Publication date: Available online 6 February 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Hui Li, Chi Wang, Shengping He, Huijun Wang, Cui Tu, Jiyao Xu, Fei Li, Xiaocheng Guo

Abstract

Studies on Sun-climate connection have been carried out for several decades, and almost all of them focused on the effects of solar total irradiation energy. As the second major terrestrial energy source from outer space, the solar wind energy flux exhibits more significant long-term variations. However, its link to the global climate change is rarely concerned and remains a mystery. As a fundamental and important aspect of the Earth's weather and climate system, tropical cyclone activity has been causing more and more attentions. Here we investigate the possible modulation of the total energy flux input from the solar wind into the Earth's magnetosphere on the global tropical cyclone activity during 1963–2012. From a global perspective, the accumulated cyclone energy increases gradually since 1963 and starts to decrease after 1994. Compare to the previously frequently used parameters, e.g., the sunspot number, the total solar irradiation, the solar F10.7 irradiation, the tropical sea surface temperature, and the south oscillation index, the total solar wind energy flux input exhibits a better correlation with the global tropical cyclone activity. Furthermore, the tropical cyclones seem to be stronger with more intense geomagnetic activities. A plausible modulation mechanism is thus proposed to link the terrestrial weather phenomenon to the seemingly-unrelated solar wind energy input.

Spectral characteristic of geomagnetically induced current during geomagnetic storms by wavelet techniques

Tue, 01/22/2019 - 19:10

Publication date: Available online 2 February 2018

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Binod Adhikari, Nirakar Sapkota, Subodh Dahal, Binod Bhattarai, Krishna Khanal, Narayan P. Chapagain

Abstract

An EMF (electromagnetic field) is induced over an incremental area when magnetized plasma from sun interacts with the Earth's magnetic field. This phenomenon delivers a Geomagnetically Induced Current (GIC) or induces geo-electric field at the Earth's surface and in the ground. GIC and horizontal component of geomagnetic field have been studied with respect to various geomagnetic events. Particularly, we have studied four events. The first one is geomagnetically quiet period (5 October 2003), the second one is weak storm (21 October 2003), the third one is moderate storm (14 October 2003) and the last one is an intense storm (30 October 2003). By comparing the development of GIC during geomagnetic storms, we found that intense geomagnetic storms show higher development on GIC magnitude. The GIC during storm events is several times greater than that during the quiet day. AE index shows more activity in the event of 30th October than other events and GIC is also more in this event. This can be accounted to the greater geomagnetic disturbance in this case. The power ranges of higher intensity are seen at various time scales on different events. We have analysed GIC signal associated with four geomagnetic storms and found distinct periodicities at the time when H component highly perturbed. The characteristic of GIC signal demonstrates high variability with time without presence of continuous periodicities. Discrete wavelet transform (DWT) analysis reveals that whenever the geomagnetic field is perturbed, there will be high possibility of detecting GIC. The singularities present in GIC signal are due to the peak value of electrical currents system in the ionosphere and magnetosphere, and corresponding high fluctuations in H component. In this work, we explore the remarkable ability of wavelets to highlight the singularities associated with discontinuities present in the GIC.

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