Journal of Atmospheric and Solar-Terrestrial Physics

Middle atmospheric planetary waves in contrasting QBO phases over the Indian low latitude region

Fri, 08/16/2019 - 19:10

Publication date: 15 October 2019

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

Author(s): Kondapalli Niranjan Kumar, Som Kumar Sharma, Vaidehi Joshi, T.K. Ramkumar

Abstract

The present study primarily focused on the characteristics of the planetary scale waves in the middle atmosphere during different phases of Quasi-Biennial Oscillation (QBO), a dominant oscillation in the low-latitude stratospheric region. The temperature profiles retrieved from the Rayleigh lidar measurements have been utilized for the 11 winter periods between 1998 and 2009 over a low-latitude station, Gadanki (13.5oN 79.2oE). The spectral analysis of temperature anomalies indicates two dominant planetary-scale modes, namely, quasi 12-day and quasi 16-day waves. The existence of these waves in the middle atmosphere is strongly controlled by the westerly and easterly phases of QBO. For instance, the 12-day wave is mainly observed in the QBO westerly phase, while the 16-day wave peaks at two heights; 30–40 km and above 60 km with large spread in the mesosphere due to Doppler shifting in presence of westerly winds. The QBO easterly phase indicates low wave activity with 16-day wave indicating appreciable amplitudes in the upper stratosphere and mesosphere and is absent in the lower altitudes. This indicates that the 16-day wave might be generated through some in-situ mechanism due to gravity breaking or instability in the mesospheric region. Moreover, the refractive index of the two dominant planetary waves are strongly negative in the easterly phase relative to the westerly phase of QBO in the lower troposphere and stratosphere. This indicates the high probability of the planetary wave vertical propagation in the westerly phase of QBO. Therefore, the presented report re-emphasizes the importance of QBO controlling the middle atmospheric dynamics through vertical propagation of planetary scale waves in low-latitudes.

Observations of middle atmospheric seasonal variations and study of atmospheric oscillations at equatorial regions

Fri, 08/16/2019 - 19:10

Publication date: 15 October 2019

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

Author(s): Nisha Patel, Som Sharma, Vaidehi Joshi, Prashant Kumar, Narendra Ojha, Kondapalli Niranjan Kumar, Harish Chandra, Gufran Beig

Abstract

The equatorial atmospheric regions are unique and one of the most important parts of the Earth's atmosphere. These regions receive the maximum energy from the Sun, and are highly turbulent and influenced by the processes of the Northern Hemisphere as well as by the Southern Hemisphere. Atmospheric temperature is one the most sensitive parameters and having imprints of dynamical, radiative and chemical processes. Thermal structure, seasonal variability and atmospheric oscillations occurring in the equatorial middle atmosphere have been studied here using temperature profiles retrieved from the Sounding of the Atmosphere using the Broadband Emission Radiometry (SABER) instrument on-board Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite during January 2002 to December 2015 (14 years). In the present work, three geographical locations over the Equatorial latitudes and ±120° longitude have been chosen, considering 5° × 15° latitude-longitude grid between the altitudes ranging from 20 to 100 km. A detailed time series and climatology analyses have been performed over these regions and significant longitudinal differences have been observed. Characteristics of Semi Annual oscillation (SAO), Annual Oscillation (AO) and Quasi Biennial Oscillation (QBO) have been investigated using Lomb Scargle Periodogram and wavelet transform analysis techniques. It has been noted the longitudinal differences in the spectral amplitudes of equatorial oscillations relative to the zonal mean spectrum. The longitudinal asymmetry might be due to the vertically propagating planetary waves. From the analysis, it is also observed that SAO is showing the highest amplitude at 45 km and 75–85 km, and QBO is showing significant amplitude in the lower stratosphere. At higher altitudes, amplitudes of different oscillations (viz. SAO, AO, and QBO) are very weak, and temperatures variations are not revealing any significant pattern. Moreover, from the climatology and time series of the temperature measurements, high temperature (∼260 K) has been noticed at 55–65 km height range. In addition to that, seasonal variations over equatorial regions have been studied and the strength of seasonal differences are found to be about 9 K (summer-winter) at higher altitudes.

Relationships between the solar wind magnetic field and ground-level longwave irradiance at high northern latitudes

Fri, 08/16/2019 - 19:10

Publication date: 15 October 2019

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

Author(s): John E. Frederick, Brian A. Tinsley, Limin Zhou

Abstract

Longwave irradiances measured from two sites at different geomagnetic latitudes show different responses to changes in the east-west component of the interplanetary magnetic field (IMF By). At Barrow, Alaska, geomagnetic latitude 69-70oN, neither downward longwave irradiance from the atmosphere nor upward longwave irradiance from the ground show a significant correlation with By. However, at Alert, Canada, geomagnetic latitude near 87oN, a negative correlation that is marginally significant at the 95% level of confidence exists between By and downward longwave irradiance measured 3 days later. On average, a +3.5 nT increase in By is followed by a daily-mean downward longwave irradiance that is smaller by −0.60 ± 0.60% than would exist for a constant By. Similarly, daily-mean upward irradiance at a lag of 4 days is −0.51 ± 0.30% smaller than would exist otherwise, where error bars denote the 95% confidence range. The difference in upward irradiance corresponds to a surface cooling at Alert of approximately 0.33 ± 0.19 K. These results are qualitatively consistent with a previously proposed mechanism in which the interplanetary magnetic field perturbs the ionosphere-to-ground potential difference and the downward atmospheric current density over limited regions near the geomagnetic poles, altering local cloud properties. We find that the atmospheric longwave emission is altered on a time scale of 3 days, with a change in surface temperature appearing one day later, attributable to the thermal inertia of the surface. When one moves from the geomagnetic latitude of Alert (3° from the north geomagnetic pole) to the latitude of Barrow (∼20° from that pole), any connection between By and longwave irradiance becomes too small to isolate from the natural background variability.

A special issue for the space science of JASTP

Fri, 08/16/2019 - 19:10

Publication date: Available online 22 June 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Wayan Suparta, Mardina Abdullah, Mahamod Ismail

Estimating the role of upper Blue Nile basin moisture budget and recycling ratio in spatiotemporal precipitation distributions

Fri, 08/16/2019 - 19:10

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

Abstract

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.

Graphical abstract

Morphological study on the ionospheric variability at Bharati, a polar cusp station in the southern hemisphere

Fri, 08/16/2019 - 19:10

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

Abstract

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.

Development of a hybrid classification technique based on deep learning applied to MSG / SEVIRI multispectral data

Fri, 08/16/2019 - 19:10

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

Abstract

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.

Predicting SuperDARN cross polar cap potential by applying regression analysis and machine learning

Fri, 08/16/2019 - 19:10

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

Abstract

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.

Surface solar radiation and its association with aerosol characteristics at an urban station in the Indo-Gangetic Basin: Implication to radiative effect

Fri, 08/16/2019 - 19:10

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

Abstract

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.

Investigating extracted total precipitable water vapor from Weather Research and Forecasting (WRF) model and MODIS measurements

Fri, 08/16/2019 - 19:10

Publication date: 15 October 2019

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

Author(s): Hossein Hassanli, Majid Rahimzadegan

Abstract

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.

Validation of the IRI 2016, IRI-Plas 2017 and NeQuick 2 models over the West Pacific regions using the SSN and F10.7 solar indices as proxy

Fri, 08/16/2019 - 19:10

Publication date: Available online 5 June 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Yekoye Asmare Tariku

Abstract

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.

White-light polar jets on rising phase of solar cycle 24

Fri, 08/16/2019 - 19:10

Publication date: 15 October 2019

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

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

Abstract

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.

Seasonal, interannual and SSW related variations of middle atmospheric N<sub>2</sub>O and NO<sub>x</sub> over low latitudes

Fri, 08/16/2019 - 19:10

Publication date: Available online 15 May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Oindrila Nath, S. Sridharan

Abstract

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.

On the prediction of geoeffectiveness of CMEs during the ascending phase of SC24 using a logistic regression method

Fri, 08/16/2019 - 19:10

Publication date: Available online 9 May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): D. Besliu-Ionescu, D.-C. Talpeanu, M. Mierla, G. Maris Muntean

Abstract

Coronal mass ejections (CMEs) are pieces of the puzzle that drive space weather. Numerous methods (theoretical, numerical and empirical) are being used to predict whether the CME will be geoeffective or not. We present here an attempt to predict the geoeffectiveness of a given CME using a modified version of logistic regression model proposed by Srivastava (2005), using only initial CME parameters. Our model attempts to forecast if the CME will be associated with geomagnetic storm defined by a minimum Dst value <−30 nT.

We applied this modified logistic regression model for CMEs detected by LASCO during the ascending phase of solar cycle 24 (April 1, 2010 to June 30, 2011). Although the hit rate and proportion correctness were not promising for the training CME set, we obtained good hit rates and proportion correctness for the validation set.

We expect to improve the model upon applying it to a dataset comprising an entire solar cycle.

Variation of chemical characteristics of precipitation with respect to altitude gradient on the northern slope of Mt. Taibai, China

Fri, 08/16/2019 - 19:10

Publication date: Available online 26 April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Yu Zhao, Qi Feng, Aigang Lu

Abstract

A systematic investigation and greater understanding of the precipitation chemistry with respect to the altitude gradient in mountainous areas is necessary to promulgate the detrimental consequences of pollution on various ecosystems. Studies on the chemical compositions of wet precipitation were performed on the northern slopes of Mt. Taibai, Qinling Mountains, one of the highest mountains in East China, from different lateral monitoring stations (i.e., with elevations between 610 and 3511 m) over the period from 2011 to 2014. All samples were analyzed for major ions (SO42−, NO3−, Cl−, F−, NH4+, Ca2+, Mg2+, Na+, and K+). The results revealed that the total ion concentration and average measured ions concentrations in precipitation decreased with the increase of altitude in the Mt. Taibai. The concentrations of precipitation ions are always higher during non–monsoon period compared to the monsoon period, except for the altitude above 3000 m a.s.l. A negative gradient of approximately −6.58 and −34.04 μeq·L−1/100 m of the total ion concentrations was obtained during the monsoon and the non–monsoon period, respectively. NH4+ was the most promising species for completely neutralize the acidity at the altitude of 500–1000 and 3000–3500 m a.s.l., while Ca2+ was the potential species for completely neutralize the acidity at the altitude of 1000–3000 m a.s.l. The crustal–derived species (Ca2+, Mg2+, Na+, K+ and Cl−) exhibit statistically significant correlations with each other at the altitude from 500 to 2500 m a.s.l. (r = 0.31–0.91). The contributions of sea salt source and terrestrial source to SO42− and NO3− are small, which is mainly contributed by human activities. For Na+, Mg2+, and K+, there was both the contribution of the terrestrial and human activities. The inorganic pollutants (major ions such as the SO42−, NO3−, Cl−, F−, NH4+, Ca2+, Mg2+, Na+, and K+) in the Mt. Taibai appear to be derived from the regional crustal dusts, anthropogenic emissions, and the long–range transported from the sea.

Correlation between ionospheric scintillation effects and GNSS positioning over Brazil during the last solar maximum (2012–2014)

Fri, 08/16/2019 - 19:10

Publication date: Available online 29 March 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Daniele Barroca Marra Alves, Eniuce Menezes de Souza, Tayná Aparecida Ferreira Gouveia

Abstract

GNSS (Global Navigation Satellite Systems) can provide high accuracy positioning at low cost. But, depending on the sources of error, e.g. the atmospheric effects, this accuracy can be degraded. The ionosphere is one of the most important error sources in GNSS positioning. Among several effects caused by the ionosphere, irregularities such as ionospheric scintillations are very relevant. They can cause cycle slips, degrade the positioning accuracy and, when severe enough, can even lead to a complete loss of signal lock. Brazil, in particular, is located in one of the regions most affected by ionospheric scintillations and these effects were intensified during the last solar maximum. The main goal of this paper is to evaluate the impact of scintillation effects on the degradation of positioning during the last solar maximum. Data from 2012 to 2014 of three reference stations located in different regions of Brazil was used. Statistically significant correlations were identified from Spearman's correlation coefficient. Using Odds Ratio, an effect-size statistic, it was possible to see that the chance of large discrepancies in 3D positioning coordinates could be three times greater under strong scintillation effects (S4 ≥ 1) than under moderate ones (0.5<S4<1).

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

Fri, 08/16/2019 - 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

Fri, 08/16/2019 - 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

Fri, 08/16/2019 - 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

Fri, 08/16/2019 - 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.

Theme by Danetsoft and Danang Probo Sayekti inspired by Maksimer