Journal of Atmospheric and Solar-Terrestrial Physics

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

Wed, 02/06/2019 - 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.

ULF electromagnetic noise from regional lightning activity: Model and observations

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Nadezda V. Yagova, Ashwini K. Sinha, Vyacheslav A. Pilipenko, Evgeny N. Fedorov, Robert Holzworth, Geeta Vichare

Abstract

Contribution of lightning to geomagnetic field variations in ULF (f<1 Hz) frequency range is estimated within the framework of a simple model of ULF response to lightning strokes. ULF lightning index is introduced to quantify a contribution of lightning to ULF power at observational site. The computed pulse series are compared with the pulse-like interference recorded at the low latitude observatory (KNY). Lightning stroke is modeled as a vertical dipole with the perfectly conducting model ionosphere. A program of automatic detection of pulse-like interference in recorded signal is developed. The analysis of the time series of hourly ULF lightning index at KNY during several weeks in summer of 2012 has shown that the contribution of thunderstorms to ULF power may be significant, especially at frequencies f>80 mHz. This effect should be taken into account in any application utilizing estimates of local ULF power including seismo-electromagnetics.

Analysis of a dense haze event over North-eastern Pakistan using WRF-Chem model and remote sensing

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Muhammad Zeeshaan Shahid, Imran Shahid, Farrukh Chishtie, Muhammad Imran Shahzad, Gufran Bulbul

Abstract

Urban areas in Pakistan are experiencing escalation in haze episodes. Due to increase in economy, emissions of gaseous and aerosol components from automobiles, road constructions and industry is growing in Pakistan which has resulted in worsening air quality during winter and post-monsoon season. North Eastern (NE) Pakistan (71–74.5°E, 28–34°N) is experiencing haze and fog episodes because of the increase in aerosol pollution levels. In addition to anthropogenic emissions, winter pollution over NE Pakistan is associated with unfavourable meteorological conditions. Lahore, a metropolitan city in NE Pakistan experienced a dense haze event during the first week of November 2016. In this article, we examine the pollution levels before, during and after this heavily polluted episode in NE Pakistan based on model simulations and remote sensing data. In particular, the Weather Research Forecasting model coupled with chemistry (WRF-Chem) and pertinent satellite data from MODIS are utilized towards validation. Another goal of this study is to characterize sources and causes of this haze event especially over Lahore. Particulate matter concentrations, AOD, and concentration of gaseous components increased many folds than the usual levels. Additionally, Vertical Feature Mask (VFM) results are presented from measurements by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite revealing vertical layers of aerosol of thickness ranging from 2 to 5 km in the study region and period.

Solar variability manifestations in weather and climate characteristics

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): G.A. Zherebtsov, V.A. Kovalenko, S.I. Molodykh, K.E. Kirichenko

Abstract

We discuss the issues of primary importance to understand the nature of climate changes in the 20th century and main physical processes responsible for these changes and present a physical model for the solar activity (SA) effect on climate characteristics. A key concept of this model is the heliogeophysical disturbance effect on the Earth climate system parameters driving the long-wave radiation flux moving away from the Earth out into space in high-latitude regions. We address the solar activity effect on the changes in the temperature of the atmosphere and of the World Ocean. The aa–index of the geomagnetic activity (GA) was used as an SA proxy index. We discuss the results of analyzing the regularities and peculiarities of the tropospheric and sea surface temperature (SST) responses to both separate heliogeophysical disturbances and long-term changes in solar and geomagnetic activity. The structure of the tropospheric and SST temperature responses was shown to feature a spatial time irregularity. We revealed the regions, where long-term SST changes are determined mainly by SA variations.

<em>PC</em> index as a proxy of the solar wind energy that entered into the magnetosphere: 4. Relationship between the solar wind dynamic pressure (P<sub>SW</sub>) impulses and <em>PC, AL</em> indices

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): O.A. Troshichev, D.A. Sormakov

Abstract

The solar wind dynamic pressure (PSW) impulses impacting on the magnetosphere were separated on the basis of solar wind parameters measured in the point of libration L1 in 1998–2017. Comparison of the “estimated” PSW impulses reduced to the Earth's magnetopause with the appropriate sudden impulses (SI), revealed in the ground-based 1-min SymH index, showed that features of the really observed sudden impulses (moment of beginning, time evolution, intensity) can be significantly different from characteristics of the estimated PSW impulses. Because of this the preference was given to the real SI events over the estimated PSW impulses. Only the events with sudden impulses starting against the background of steady quiet pressure levels were taken for the analysis (N = 143). Relationship between the positive (leaps) and negative (drops) SI events, on the one hand, and PC and AL indices, on the other hand, were examined under the various solar wind conditions, such as: growing and steady solar wind speed at negative and positive values of the IMF BZ component, fluctuating BZ and solar wind speed, steady solar wind speed and BZ = 0. Analysis of SI events showed that the solar wind dynamic pressure impulses themselves are not promote (or insignificantly promote) the solar wind energy input into the magnetosphere, which is controlled by the interplanetary electric field EKL = Vsw*(BY2+BZ2)1/2 and is displayed by the polar cap magnetic activity PC index. When the PSW impulses (leaps or drops) are accompanied by the corresponding changes in EKL field, the PC index correlates (increases or decreases) with the PSW changes. Inconsistency between the PSW and PC behavior becomes evident as soon as the EKL and PSW courses start to diverge. Development of magnetic disturbances (AL index) is governed only by the EKL field and PC index increase irrespective of the PSW impulses magnitude and time evolution.

Generalized Schumann and variation moment methods used for the determination of the equatorward boundary of the ultra-energetic relativistic electron precipitations into the auroral middle atmosphere

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): George F. Remenets, Aleksandr M. Astafiev

Abstract

In this paper, we present (i) the comparison of a solution accuracy of an inverse VLF problem for very low frequency (VLF) wave propagation (10–16 kHz) in the “Earth – sporadic Ds layer of atmosphere ionization” as estimated by three different methods of eiganvalue calculation and (ii) an estimation of latitude uncertainty for the equatorward (southern) boundary of Ultra-energetic Relativistic Electron (URE) precipitations into the middle polar atmosphere. The uncertainty for 1982–1987 years was caused by the different years, seasons, months, hours of daytime and electric conductivities of ground surface.

Sporadic Ds layer was caused by the URE precipitations with the electron energies about 100 MeV into the polar region of atmosphere with a geographical latitude range 63–67 N degrees. The results of application of new accurate generalized Schumann (GS) method and of the approximate variation moment (VM) method used for an eigenvalue problem were compared with the results of another accurate method in which the Ricatti nonlinear equation (RNLE) was used. Comparison has been performed for the values of one (main) eigenvalue of a transversal operator for the corresponding model waveguide and for the determined positions of the URE precipitation equatorward boundary, the eigenvalue was being a function of the disturbance time. This comparison provides an estimation which method is preferable during simultaneous observations and analysis of a geophysical disturbance.

In the second part of the study, the influence of the electrical conductivity in the waveguide model on the accuracy of equatorward boundary determination for the 16 kHz radio path “England – Kola peninsula” was analyzed, based on the data from the fixed location of two sources (in North Norway and in England) and a receiver (on Kola Peninsula) of the radio signal. It was shown that the uncertainty introduced by different values of the ground conductivity was 2–3 times less than the differences in the boundary position between different events under study.

Proton-electron model of ball lightning structure

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Alexander G. Oreshko, Anna A. Oreshko, Timur B. Mavlyudov

Abstract

Experiments were performed in which the decay of the ion nuclei as a result of the nuclear photoeffect has been detected during generating of a ball lightning. The decay of the ion nuclei was accompanied by a neutrons burst, with the magnitude exceeding the level of the natural neutrons background in absence of the ball lightning. The measured value of the potential of the ball lightning after its formation was within 15–20 MV. High values of potential lead to the conclusion that nuclear photoeffect is the single possible cause of neutron emission in the stage of ball lightning generation. Due to presence of the charge, the protons remain in the external spherical shell of the ball lightning under the influence of its electric and magnetic fields. Neutrons leave the region of the ball lightning generation due to diffusion. Proton-electron model of ball lightning is created. Ball lightning is an electrical domain of spherical shape, which external spherical shell mainly consists of high-energy protons whereas the kernel consists of electrons.

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

Electromagnetic internal gravity waves in an ideally conducting incompressible medium

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

Reconstructing nonlinear force-free fields by a constrained optimization

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

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

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

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

Abstract

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

Study of the Ångström turbidity over Romanian Black Sea coast

Sun, 01/13/2019 - 19:10

Publication date: January 2019

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

Author(s): Sanda Voinea, Sabina Stefan

Abstract

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

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