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GGOS tropospheric delay forecast product performance evaluation and its application in real-time PPP

Thu, 05/24/2018 - 17:16
Publication date: October 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175

Author(s): Yibin Yao, Xingyu Xu, Chaoqian Xu, Wenjie Peng, Yangyang Wan

Tropospheric delay is one of the main error sources in Global Navigation Satellite System (GNSS) precise positioning, as the GNSS signal is influenced by refraction when travelling through the troposphere. Generally, tropospheric delay is estimated as a parameter in GNSS data processing. With the increasing demand for GNSS real-time applications, high-precision tropospheric delay augmentation information is essential to enhance convergence speed and precision of positioning. The Global Geodetic Observing System (GGOS) Atmosphere provides total zenith tropospheric delay (ZTD) forecast grid data, globally, one day in advance, where the time resolution is 6 h and spatial resolution is 2.5° × 2°. Here, the GGOS ZTD forecast product is assessed compared with ZTD information from global IGS sites, including an analysis of the spatial and temporal distribution of its error and the weather influence on its precision. Ultimately, the application effect of the GGOS Atmosphere ZTD forecast product in real-time precise point positioning (PPP) is examined. The results show that the positioning precision and the speed of convergence are obviously advanced, especially in the U direction, which informs the potential for real-time application of GGOS forecast products.





A deterministic model for forecasting long-term solar activity

Thu, 05/24/2018 - 17:16
Publication date: October 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175

Author(s): Eleni Petrakou

A phenomenological model is presented for the quantitative description of individual solar cycles' features, such as onset, intensity, evolution, in terms of the number of M and X-class solar flares. The main elements of the model are the relative ecliptic motion of the planets Jupiter and Saturn, and its synergy with a quasi-periodic component of solar activity. Using as input the temporal distribution of flares during cycle 21, the general evolution of cycles 22–24 is reproduced in notable agreement with the observations, including the resurgence of activity in the last months of 2017, and further predictions are provided for cycle 25. This deterministic description could contribute to elucidating the responsible physical mechanisms and forecasting space weather.





First results on the retrieval of noctilucent cloud albedo and occurrence rate from SCIAMACHY/Envisat satellite nadir measurements

Thu, 05/24/2018 - 17:16
Publication date: October 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175

Author(s): M.P. Langowski, C. von Savigny, T. Bachmann, M.T. DeLand

We present the first results on the retrieval of noctilucent cloud (NLC) albedos and occurrence rates from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartography) nadir data. The applicability of already available algorithms is discussed and necessary changes are reasoned. The occurrence rates for different latitude ranges are presented. During the summer period, when NLCs occur, the NLC occurrence rates show a maximum which is strongest at the highest latitudes. This is consistent with other observation methods. For the spring and autumn period, however, false NLC detections are observed at latitudes between 45°N and 65°N, where no NLCs are expected. The reason for this, and why it does not affect the retrieval during the NLC season is discussed. We also compared the SCIAMACHY nadir NLC occurrence rates with the ones retrieved from the SCIAMACHY limb measurements and the ones of SBUV and found qualitative agreement of these data sets.





Reflection from and transmission through the ionosphere of VLF electromagnetic waves incident from the mid-latitude magnetosphere

Thu, 05/24/2018 - 17:16
Publication date: October 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 175

Author(s): P.A. Bespalov, V.G. Mizonova, O.N. Savina

Trans-ionospheric propagation of the VLF electromagnetic wave from an altitude of 800 km to the Earth's surface is considered using the model of stratified media. The numerical solution of the wave equations for the mid-latitude ionosphere model conditions is found. The wave field in the lower ionosphere is calculated using the full-wave approach. The wave field in the upper ionosphere is calculated using the matrix method of perturbations for a slightly inhomogeneous plasma. Energy reflection coefficient and the horizontal magnetic field amplitude of the wave on the ground surface are calculated. Peculiarities of the wave reflection and transmission at different times of the day are analyzed. The obtained results are important for studying the ELF/VLF emission phenomena observed both onboard the satellites and in ground-based observatories.





Editorial Board

Thu, 05/24/2018 - 17:16
Publication date: September 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 174









Observations by incoherent scatter radar of related D- and F-region structuring at very high latitude

Thu, 05/24/2018 - 17:16
Publication date: September 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 174

Author(s): J.K. Hargreaves, M.J. Birch

Properties and associations of F- and D-region ionospheric structures during weak electron precipitation at very high latitude are investigated using the Longyearbyen incoherent scatter radar. The radio absorption deduced from the electron density observations revealed evidence of a persistent low-altitude absorption layer peaking at 80-85 km. Inversion of the electron density profile to give an estimate of the incoming energetic electron spectrum suggests that its source may be the solar wind. Strong similarities are seen between variations in the F and D regions which suggest that the electron flux reaching the D-region is being modulated in energy by the variations of electron density in the F-region.





Multi-scale ionospheric irregularities occurrence over South America during the St. Patrick's day storm on March 17, 2015

Thu, 05/24/2018 - 17:16
Publication date: September 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 174

Author(s): F.R.E. Barbosa, P.R. Fagundes, K. Venkatesh, B.G. Fejer, V.G. Pillat, C.M. Denardini, M.T.A.H. Muella

During the solar cycle 24 there was a very intense geomagnetic storm due to the St. Patrick's day storm and the effects of this storm on ionosphere has become a topic of extensive space weather investigation. Up to now several aspects of the St. Patrick's ionospheric storm have been study such as the prompt penetration electric fields (PPEFs), TEC changes, electron density disturbances, plasma drift, O+ concentration modification, hemispherical asymmetry developments, equatorial ionization anomaly (EIA) modification, and ionospheric irregularities. Besides all these important studies, there are some essential aspects, which have not been addressed yet, related to the occurrence of multi-scale ionospheric irregularities. In this paper, we present and discuss the generation and suppression of multi-scale ionospheric irregularities, using the observations conducted in the Latin American Sector from 4 ionosondes, 20 dual frequency GPS stations, and JULIA radar observations during the month of March 2015, which includes the St. Patrick's day geomagnetic storm period. Suppression of large-small scales ionospheric irregularities has occurred during the main and second night of the recovery phases. However, during the first night of recovery phase there was post-midnight ionospheric irregularities.





A new and quantitative prediction scheme for solar flares

Thu, 05/24/2018 - 17:16
Publication date: September 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 174

Author(s): Syun-Ichi Akasofu

At the present time, there is no quantitative way to predict not only the onset time of solar flares, but also their intensity. In the past, most solar flare prediction studies have searched for various precursors of the onset of flares. In this paper, we consider a new and quantitative approach to predict the onset of the explosive process of solar flares and their intensity, based on the principle that solar flares are basically various manifestations of electromagnetic energy dissipation, so that a dynamo process in the photosphere as its power supply is essential. The power is a basic physical quantity (erg/s), so that it can, at least in principle, be universally applicable for all flares. The power of the photospheric dynamo is given by the Poynting flux P= V(B 2 /8π)S erg/s, where V and B are the plasma speed and magnetic field intensity, and S is the dimension of the plasma flow; these quantities are in principle observable simultaneously all together, in addition to the dissipation rate δ (for example, the Hα emission rate). In fact, if one can follow the development of the power P(t) and [∫ P(t)dt − ∫ δ(t)dt], it may be possible, together with various precursors, to predict in principle the onset time and the intensity of flares at least semi-quantitatively, although this task will require much experience on the basis of a large number of flares. Unfortunately, however, all the needed simultaneous data set (V, B, S, δ) is not available in the present literature, so that one incomplete case is examined. This concept has been examined for auroral substorms, which are also manifestations of electromagnetic energy dissipation and have the explosive feature. This was possible, because the simultaneous data sets (V, B, S, δ) are available.





Using smartphones for monitoring atmospheric tides

Thu, 05/24/2018 - 17:16
Publication date: September 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 174

Author(s): Colin Price, Ron Maor, Hofit Shachaf

By 2020 there will be more than 6 billion smartphones around the globe, carried by the public. These smartphones are equipped with sensitive sensors that can be used to monitor our environment (temperature, pressure, humidity, magnetic field, etc.) In this paper we use the pressure sensor (barometer) within smartphones to study atmospheric tides. These tides are produced by the absorption of solar radiation by water vapor in the troposphere, and by ozone in the stratosphere. The strongest tides are the semi-diurnal tides (period of 12 h) with maximum pressure at 9am/9pm and minimum pressure at 3am/3pm. Given the proliferation of smartphones around the globe, this source of environmental data may become extremely useful for scientific research in the near future.





Magnetic structure of solar flare regions producing hard X-ray pulsations

Thu, 05/24/2018 - 17:16
Publication date: September 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 174

Author(s): I.V. Zimovets, R. Wang, Y.D. Liu, C. Wang, S.A. Kuznetsov, I.N. Sharykin, A.B. Struminsky, V.M. Nakariakov

We present analysis of the magnetic field in seven solar flare regions accompanied by the pulsations of hard X-ray (HXR) emission. These flares were studied by Kuznetsov et al. (2016) (Paper I), and chosen here because of the availability of the vector magnetograms for their parent active regions (ARs) obtained with the SDO/HMI data. In Paper I, based on the observations only, it was suggested that a magnetic flux rope (MFR) might play an important role in the process of generation of the HXR pulsations. The goal of the present paper is to test this hypothesis by using the extrapolation of magnetic field with the non-linear force-free field (NLFFF) method. Having done this, we found that before each flare indeed there was an MFR elongated along and above a magnetic polarity inversion line (MPIL) on the photosphere. In two flare regions the sources of the HXR pulsations were located at the footpoints of different magnetic field lines wrapping around the central axis, and constituting an MFR by themselves. In five other flares the parent field lines of the HXR pulsations were not a part of an MFR, but surrounded it in the form of an arcade of magnetic loops. These results show that, at least in the analyzed cases, the “single flare loop” models do not satisfy the observations and magnetic field modeling, while are consistent with the concept that the HXR pulsations are a consequence of successive episodes of energy release and electron acceleration in different magnetic flux tubes (loops) of a complex AR. An MFR could generate HXR pulsations by triggering episodes of magnetic reconnection in different loops in the course of its non-uniform evolution along an MPIL. However, since three events studied here were confined flares, actual eruptions may not be required to trigger sequential particle acceleration episodes in the magnetic systems containing an MFR.





Thermosphere climate indexes: Percentile ranges and adjectival descriptors

Thu, 05/24/2018 - 17:16
Publication date: September 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 174

Author(s): Martin G. Mlynczak, Linda A. Hunt, James M. Russell, B. Thomas Marshall

Thermosphere Climate Indexes (TCI) represent the 60-day running average of the global infrared cooling power radiated from the thermosphere by nitric oxide and by carbon dioxide. The TCI are accurately expressed as linear combinations of the 60-day running averages of the F10.7, Ap, and Dst indexes, thus providing terrestrial context to the long record of solar and geomagnetic indexes. We examine the percentile distribution in quintiles of the TCI generated using solar and geomagnetic indexes covering five complete solar cycles. We further assign adjectival descriptors (Cold, Cool, Neutral, Warm, or Hot) to these quintiles as the TCI largely indicate the global thermal state of the thermosphere. We suggest that the TCI are valuable new solar-terrestrial indexes due to the information they contain about the global thermosphere and due to their ease of calculation from standard indexes. Specifically, given dynamic range of the TCI associated with NO cooling, and its significant dependence on both solar irradiance and geomagnetic processes, we recommend that it be included henceforth as a new, standard solar-terrestrial Index. The NO TCI data show that the thermosphere was “Warm” only for a brief period of time at the maximum of solar cycle 24 and thus experienced the coolest solar maximum of the past seven solar cycles. As of February, 2018, the thermosphere power is in the lowest quintile of values, to which we assign the level of ‘Cold.’





Multi-instrument view on solar eruptive events observed with the Siberian Radioheliograph: From detection of small jets up to development of a shock wave and CME

Thu, 05/24/2018 - 17:16
Publication date: September 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 174

Author(s): V.V. Grechnev, S.V. Lesovoi, A.A. Kochanov, A.M. Uralov, A.T. Altyntsev, A.V. Gubin, D.A. Zhdanov, E.F. Ivanov, G.Ya. Smolkov, L.K. Kashapova

The first 48-antenna stage of the Siberian Radioheliograph (SRH) started single-frequency test observations early in 2016, and since August 2016 it routinely observes the Sun at several frequencies in the 4–8 GHz range with an angular resolution of 1–2 arc minutes and an imaging interval of about 12 s. With limited opportunities of the incomplete antenna configuration, a high sensitivity of about 100 Jy allows the SRH to contribute to the studies of eruptive phenomena along three lines. First, some eruptions are directly visible in SRH images. Second, some small eruptions are detectable even without a detailed imaging information from microwave depressions caused by screening the background emission by cool erupted plasma. Third, SRH observations reveal new aspects of some events to be studied with different instruments. We focus on an eruptive C2.2 flare on 16 March 2016 around 06:40, one of the first flares observed by the SRH. Proceeding from SRH observations, we analyze this event using extreme-ultraviolet, hard X-ray, white-light, and metric radio data. An eruptive prominence expanded, brightened, and twisted, which indicates a time-extended process of the flux-rope formation together with the development of a large coronal mass ejection (CME). The observations rule out a passive role of the prominence in the CME formation. The abrupt prominence eruption impulsively excited a blast-wave-like shock, which appeared during the microwave burst and was manifested in an “EUV wave” and Type II radio burst. The shock wave decayed and did not transform into a bow shock because of the low speed of the CME. Nevertheless, this event produced a clear proton enhancement near Earth. Comparison with our previous studies of several events confirms that the impulsive-piston shock-excitation scenario is typical of various events.





Editorial Board

Thu, 05/24/2018 - 17:16
Publication date: August 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 173









Attenuation of decameter wavelength sky noise during x-ray solar flares in 2013–2017 based on the observations of midlatitude HF radars

Thu, 05/24/2018 - 17:16
Publication date: August 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 173

Author(s): O.I. Berngardt, J.M. Ruohoniemi, N. Nishitani, S.G. Shepherd, W.A. Bristow, E.S. Miller

Based on a joint analysis of data from 10 midlatitude decameter wavelength radars effects are investigated during 80 x-ray flares that occurred in the period 2013–2017. For the investigation nine mid-latitude SuperDARN radars of the northern hemisphere (Adak Island West and East radars, Blackstone radar, Christmas Valley East and West radars, Fort Hays East and West radars, Hokkaido East radar and Wallops radar) and Ekaterinburg coherent decameter radar of ISTP SB RAS are used. All the radars work in the same 8–20 MHz frequency band and have similar hardware and software. During the analysis the temporal dynamics of noise from each of the radar direction and for each flare is investigated separately. As a result, on the basis of about 13000 daily measurements we found a strong anticorrelation between noise power and x-ray flare intensity, indicating that short-wave sky noise can be used to diagnose the ionospheric effects of x-ray solar flares. It is shown that in 88.3% of cases an attenuation of daytime decameter radio noise is observed during solar flares, and the attenuation correlates with the temporal dynamics of the solar flare. The intensity of decameter noise anticorrelates well (the Pearson correlation coefficient better than −0.5) with the shape of the X-ray flare in the daytime (for solar elevation angle > 0 ) in 33% of cases, the average Pearson correlation over the daytime is about −0.34. Median regression coefficient between GOES 0.1–0.8 nm x-ray intensity and daytime sky-noise attenuation is about − 4.4 ⋅ 10 4 [ d B ⋅ m 2 / W t ] . Thus, it is shown that measurements of the sky noise level at midlatitude decameter radars can be used to study the ionospheric absorption of high-frequency waves in the lower ionosphere during x-ray solar flares. This can be explained by the assumption that the larger part of the decameter sky noise detected by the radars is produced by ground sources at distances of the first propagation hop (∼3000 km).





Asymmetric DE3 causes WN3 in the ionosphere

Thu, 05/24/2018 - 17:16
Publication date: August 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 173

Author(s): Jinzhe Jiang, Weixing Wan, Zhipeng Ren, Xinan Yue

This study investigates a mechanism to generate the wavenumber-3 longitude variation in the ionosphere, using the simulations with the Global Coupled Ionosphere Thermosphere Electrodynamics Model, developed by the Institute of Geology and Geophysics, Chinese Academy of Sciences (GCITEM-IGGCAS). Due to the asymmetry of geomagnetic field, the asymmetric Hough mode of diurnal eastward wavenumber-3 (DE3) also produces the WN3 structure in the ionosphere by coupling with the magnetic line. The densities of the neutral mass and the plasmas in the ionosphere are studied in detail. The results show a clear WN3 pattern driven by tide's electro-dynamical coupling. We then conclude that the asymmetric component of the DE3 can also cause the WN3 structure in the ionosphere, which confirms the assumption that more than one source could generate WN3 structure in previous studies.





Wolf ratios and the ionospheric L and S dynamo region

Thu, 05/24/2018 - 17:16
Publication date: August 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 173

Author(s): Cengiz Çelik

One of the long-standing unresolved issues in geomagnetism is the location of the two dynamos that produce the S and L variations in the geomagnetic field on quiet days. To shed some light on this problem, Wolf ratios of properties of the ionosphere from 90 to 300 km, which includes the dynamo region, were analyzed using the data produced from the IRI2012 model. The Wolf ratio (104 M) for the E layer is found to be 28 ± 0.7 rather than 33, as assumed earlier. The ionosphere between 90 and 300 km was found to show significant seasonal dependence. The Wolf ratio of L agrees with that of the plasma density in the E-region ionosphere, while the Wolf ratio of S is greater, which indicates contributions from other altitudes.





Large-scale magnetic fields and anomalies of chemical composition of stellar coronae

Thu, 05/24/2018 - 17:16
Publication date: August 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 173

Author(s): V.V. Pipin, V.M. Tomozov

We present evidence that anomalies in abundance of the chemical admixtures with the low first ionization potential (FIP) in the low corona of the late-type stars can be related to a topology of the large-scale magnetic field. Observational data from Ulysses and the Stanford Solar Observatory reveal the high correlations between the FIP effect of the solar wind and amount of the open magnetic flux. To analyze the stellar activity data we relate the amount of the open magnetic flux with the ratio between poloidal and toroidal magnetic field of a star. The solar-type stars show the increase abundance of the low FIP elements relative to elements with the high FIP with the decrease of the large-scale poloidal magnetic field (and increase the toroidal component of the magnetic field). The branch of the fully convective stars demonstrates inversion of the FIP-effect. This inversion can result from strong coronal activity, which is followed by the strong poloidal magnetic on these stars.





Assessment of aerosol optical properties using remote sensing over highly urbanised twin cities of Pakistan

Thu, 05/24/2018 - 17:16
Publication date: August 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 173

Author(s): Muhammad Awais, Muhammad I. Shahzad, Majid Nazeer, Irfan Mahmood, Shahid Mehmood, Muhammad Farooq Iqbal, Nighat Yasmin, Imran Shahid

Ability of aerosols to attenuate solar radiation can be measured in terms of Aerosol Optical Depth (AOD) or Aerosol Optical Thickness (AOT), which can be accurately monitored from ground-based stations using ambient air samplers. However, such methods are very expensive and spatially incomplete whereas, satellite-based remote sensing of AOD can be used effectively to quantify the effects of atmospheric aerosols. Developing countries like Pakistan need to enhance usage of such techniques (i.e. ambient air samplers). Currently, Lahore and Karachi are the only two cities in Pakistan where ground-based stations i.e. Aerosol Robotic Network (AERONET) are available for air quality measurements. Therefore, this is the first ever study to monitor AOD of Pakistan for cities other than Lahore and Karachi. This study uses AOD simultaneously from Moderate Resolution Imaging Spectroradiometer (MODIS) and a handheld sun photometer in densely populated twin (adjoining) cities of Rawalpindi and Islamabad. It is found that MODIS (Terra and Aqua) can reveal the distribution of aerosols over these cities with 80% of agreement to handheld sun photometer. Mean AOD calculated from green (508 nm) and red (625 nm) channels of handheld sun photometer is 0.49 and 0.37 respectively, with MODIS retrieved AOD found to be 0.40 in green channel. A standard deviation of 0.29 was observed in MODIS 0.26 in green and 0.20 in red channel of the sun photometer in monthly average measurements. There was good agreement between AOD from MODIS and handheld sun photometer with a Slope of 0.87, MAE of 0.15 and RMSE of 0.19 for green channel. However, there was a slightly more than unity slope of 1.14, MAE of 0.12, RMSE of 0.17 for red channel. The area is abundant in medium sized aerosols. Results of the study will be helpful in establishing a baseline for the accuracy assessment of AOD retrieved from satellite over Rawalpindi/Islamabad. Further, it will also help policy makers to measure the impacts of spatiotemporal variations of size and nature of aerosols on air quality and health of the region.





Negative flare in the He i 10830 Å line in facula

Thu, 05/24/2018 - 17:16
Publication date: August 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 173

Author(s): Nikolai Kobanov, Andrei Chelpanov, Vasiliy Pulyaev

A small-scale flare SOL2012-09-21T02:19 (B2) occurred in a spotless active region that we observed the Horizontal Solar Telescope which is equipped with a spectrograph. During the flare, we registered an increase in absorption in the He i 10830 Å line by 25%, while other chromospheric and coronal spectral lines demonstrated increases in brightness at the same location. This phenomenon, called a negative flare, has rarely been observed on the Sun before. In this paper, we describe the morphology of this flare and investigate its dynamics based on our spectral observations and space imaging data. The brightening first occurred in the 171 Å Solar Dynamics Observatory (SDO) channel followed by the 94 Å and 304 Å signals ∼2 min after (for the maximum phases). The Hα and He i 10830 Å lines reach their extreme intensities 5 and 6 min after the 171 Å line. However, the abrupt changes in line-of-sight (LOS) velocities in the chromospheric lines occur simultaneously with the intensity changes in the 304 Å and 1600 Å lines: we observed a downward motion that was followed by two upward motions. The measured apparent horizontal speed of the perturbation propagation was close to 70 km s−1 both in the chromospheric and coronal lines. We suggest that we observed the photoionization-recombination process caused by UV radiation from the transition region and corona during the coronal flare. With this, we point out the difficulties in interpreting the time lag between the emission maximum in the SDO UV channels and the second absorption maximum in the He i 10830 Å line.





Horizontal electric fields of lightning return strokes and narrow bipolar pulses observed in Sri Lanka

Thu, 05/24/2018 - 17:16
Publication date: August 2018
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 173

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

Simultaneous measurement of both vertical and horizontal electric field signatures of lightning was carried out in an elevated location in Colombo, Sri Lanka. The experimental setup used in this work was similar to an earlier study carried out by a different group in the late 1980s. To our knowledge, this is the first instance that such a study is conducted in this region. Data were acquired during the active months (April–May) of the southwest monsoon period in 2014. Lightning flashes from the most active thunderstorm was analyzed by selecting 65 Return Strokes (RS), 50 Negative Narrow Bipolar Pulses (NNBP) and 40 Positive Narrow Bipolar Pulses (PNBP). The wave shapes were initially validated against results of a previous study and subsequently via a theoretical method as well. Since the direction and the distance information was not available, rather than the amplitudes, ratios of the peak amplitudes of vertical electric field (Ev) and corresponding horizontal electric field (Eh) were compared. The average ratio for the return stroke was 0.024 ± 0.008. The same for the NNBP was 0.041 ± 0.004. The PNBP had a ratio of 0.031 ± 0.006. The average 10%–90% rise times (Tr) for Ev for RS, NNBP and PNBP was 2.124 ± 1.088 μs, 0.734 ± 0.077 μs and 1.141 ± 0.311 μs respectively. The Tr values for Eh for RS, NNBP and PNBP were 1.865 ± 1.200 μs, 0.538 ± 0.061 μs and 1.086 ± 0.423 μs.





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