Journal of Atmospheric and Solar-Terrestrial Physics

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

Fri, 05/17/2019 - 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.

Local temperature changes in the mesosphere due to a “horizontally propagating” turbulent patch

Fri, 05/17/2019 - 19:10

Publication date: Available online 11 May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Alexey N. Belyaev

Abstract

In this study, we model thermal changes in the background atmosphere due to a horizontally” moving” turbulent patch. We divide the process of mutual adjustment of the turbulent patch and the background atmosphere into the two stages: (i) Fast high-to-low transition of the atmospheric stability within the turbulent patch induced by strong adiabatic mixing within the “moving” turbulent patch. (ii) Slow adjustment of the ambient background atmosphere to a quasi-stabilized, near-adiabatic thermal stratification within the turbulent patch. Within the framework of the first stage, assuming the existence of a background downward heat flux, we developed a boundary value problem for a non-homogeneous heat equation that accounts for turbulent dissipative heating and mixing. This two-point boundary value problem was solved analytically by applying the Fourier method (separation of variables) to the thickness of the turbulent patch. The solution obtained tends towards equilibrium as the distance from the front border of the “moving” turbulent patch increases. Within the scope of the second stage, we solved the problem of thermal coupling of the two heat-transfer domains, one of which is characterized by a high coefficient of heat transfer. Solving this problem is the basis of our proposing that the thermal structure of a turbulent patch does not change under the influence of an ambient atmosphere, while the ambient atmosphere is cooled slowly above the turbulent patch and warmed slowly below it. Consequently, it is shown that the model temperature profiles demonstrate the same features as those observed in mesospheric inversion layers (MILs): temperature inversions and a near-adiabatic lapse rate between them.

On the seasonal and solar cycle variation of the ULF fluctuations at low latitudes: A comparison with the ionospheric parameters

Fri, 05/17/2019 - 19:10

Publication date: Available online 10 May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): U. Villante, P. Tiberi, M. Pezzopane

Abstract

A long term analysis (1996–2015) of the occurrence and characteristics of the wave events (Pc3; f = 20–100 mHz; H and D component), detected at a low latitude ground-based station (L'Aquila, Italy), and the comparison with the ionospheric parameters reveal some interesting aspects of their seasonal and solar cycle variation. In general, the daytime wave activity, which basically consists of penetrating upstream waves and, at higher frequencies, of resonances of local field lines, appears more intense (with a more relevant percentage of D events) in winter than in summer, suggesting a seasonal dependence of the attenuation and rotation of the downgoing signal through the ionosphere and, during winter, less efficient ionospheric conditions for the onset of resonance processes (typically occurring along the H component). This situation persists during solar minima, while, during solar maxima, the summer occurrence rate of events exceeds the winter one: this aspect might be related to the more frequent impact on the magnetosphere of energetic solar wind structures during solar maxima; in summer, given the favourable ionospheric conditions, they might determine a much more frequent manifestation of relevant resonance events. Rapidly increasing after midnight, the wave activity reveals a pre-sunrise peak followed by a minimum, on average coincident with the foF2 minimum, and the winter pattern appears to be delayed ≈1 h compared to the summer one.

Cloud fraction retrieval and its variability during daytime from ground-based sky imagery over a tropical station in India

Fri, 05/17/2019 - 19:10

Publication date: Available online 9 May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Akshaya Nikumbh, B. Padmakumari, Sneha Sunil

Abstract

Total Sky Imager (TSI) is operated at a high altitude station in the Western Ghats of the Indian sub-continent from June 2012 to June 2013. The TSI image content is classified as clear, thin and thick clouds using red-blue ratio (RBR) threshold technique and then cloud fraction (CF) is retrieved. An algorithm is proposed to improve the accuracy of CF retrieval, by adapting the methodologies used in earlier studies and new developments are suggested in sections of the validation of clear sky image and the aerosol correction factor. Time series of thin, thick and total CF are constructed for each day at 5 min interval. These measurements at high temporal resolution are first of their kind over a tropical station in India. Both thick and thin CFs showed high temporal variability. The transition from one season to another season also showed distinct CF variability. Monthly mean CF showed a mono model distribution in the winter months (December and January) and a bimodal distribution in the pre-monsoon months (March, April, May) including February. During the monsoon season (JJAS) about 90% CF is observed throughout the day. The post-monsoon months (October, November) show a bimodal distribution with one peak in the morning hours and another peak in the afternoon hours. Unlike thin CF, total and thick CFs showed almost similar variability. The comparison of CF retrieved from MODIS (Terra and Aqua) and TSI showed a good correlation for overcast sky conditions, while partial cloudy skies showed less correlation due to the effect of satellite viewing angles. Such continuous measurements of CF at high temporal resolution are essential for cloud radiative forcing studies.

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

Fri, 05/17/2019 - 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 a=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.

Simultaneous dimming and brightening under all and clear sky at Camagüey, Cuba (1981–2010)

Fri, 05/17/2019 - 19:10

Publication date: 1 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 190

Author(s): Juan Carlos Antuña-Marrero, Frank García, René Estevan, Boris Barja, Arturo Sánchez-Lorenzo

Abstract

The annual trends of the all sky (Eg↓ASky) and clear sky global horizontal irradiances (Eg↓CSky) for the climatologically standard period 1981–2010 at Camagüey, Cuba, are negative and positive respectively, showing the simultaneous occurrence of dimming and brightening phenomena. Positive cloud cover (CC) annual trend, is among the plausible causes of the Eg↓ASky dimming. The Eg↓CSky annual mean increasing trend could be explained in part by the decreasing broadband aerosol optical depth trend. For the 1981–2016 a period non-standard climatologically the absolute magnitudes of the trends decrease for both Eg↓ASky and Eg↓CSky annual means, with no change in their signs but becoming non-significant statistically. That feature resembles an attenuation process for both dimming and brightening. The series of Eg↓ and CC observations were subject of test for determining in homogeneities identifying change points. For each one of the Eg↓ASky and Eg↓CSky and CC series show no change point statistically significant. The consistency and stability of the Eg↓ASky annual means series were tested using measured and calculated Eg↓ annual means for conditions where the solar disk is empty of clouds. The magnitudes and signs of trends for the measured and calculated Eg↓ annual means are very similar and both are statistically significant at the same level, confirming the series of Eg↓ASky annual means are consistent and stable.

The cause of the strengthening of the Antarctic polar vortex during October–November periods

Fri, 05/17/2019 - 19:10

Publication date: 1 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 190

Author(s): Vladimir V. Zuev, Ekaterina Savelieva

The stratospheric polar vortex strength in spring determines to a great extent the duration and intensity of ozone depletion in the polar regions. The size of the Antarctic ozone hole usually reaches its maximum in September, and then drops off during October and November. However, in 1987, 1998, 1999, 2001, 2006, 2011 and especially in 2015, a significant increase in the ozone hole area relative to climatological mean values was observed in October and November under strong polar vortex conditions. Furthermore, in these years it occurred simultaneously with a temperature increase in the subtropical lower stratosphere in the Southern Hemisphere. Based on the ERA-Interim reanalysis temperature and zonal wind data, we reveal a high correlation between interannual variations of the subtropical temperature and the zonal wind at 60° S in October and November (the Pearson correlation coefficients r equal 0.71 and 0.82, respectively). Thus, a temperature increase in the subtropical lower stratosphere from October to November can strengthen the Antarctic polar vortex in this period.

Possible process of ball lightning training in nature

Fri, 05/17/2019 - 19:10

Publication date: 1 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 190

Author(s): Anatoly I. Nikitin

Abstract

An electrodynamic model of ball lightning is proposed, according to which it is considered as a collection of plasmoids, consisting of electrons and protons, which rotate in closed orbits. Protons are retained in the orbit due to Coulomb attraction to the electron ring, while electrons are drifting in the crossed electric and the magnetic field, generated by the protons’ motion. This system has a non-compensated positive electric charge. These plasmoids placed inside a water shell serve to isolate a vacuum cavity from the atmosphere and to create a force, preventing expansion of proton rings. A mechanism of ball lightning creating near a loop of linear lightning channel is discussed. Ultraviolet radiation of the lightning discharge ionizes air, and due to the action of radio-frequency radiation with a non-uniform spatial distribution of intensity, a vacuum cavity is formed. The action on the plasma exerted by the crossed magnetic and eddy electric fields leads to separation and acceleration of charges. Losing a part of electrons, the system acquires a positive charge. Due to motion of water drops in the non-uniform field of this charge a dielectric shell around the ensemble of plasmoids is formed. A scheme of setup for ball lightning creation in laboratory is proposed.

Analysis of the first positive polarity gigantic jet recorded near the Yellow Sea in mainland China

Fri, 05/17/2019 - 19:10

Publication date: 1 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 190

Author(s): Qijia He, Jing Yang, Gaopeng Lu, Zhixiong Chen, Yu Wang, Mitsuteru Sato, Xiushu Qie

Abstract

At 12:16:22 UTC on 12 August 2010, a gigantic jet (GJ) was recorded over a thunderstorm near the Yellow Sea in China. The extremely low-frequency (ELF) magnetic field recorded at the Onagawa Observatory indicates that this GJ transferred positive charge from the thundercloud to the ionosphere (namely a +GJ event), which is the first observation of a +GJ reported in mainland China. The top altitude of this GJ was estimated to be about 89 km. The parent thunderstorm formed in a very moist environment (precipitable water of 75.4 mm) with moderate convective available potential energy (1294 J/kg) and lifted index (−3.19), and strong 0–6 km wind speed shear (16.3 m/s). The meteorological parameters are not much different from typical summer thunderstorms. The area of cloud top brightness temperature colder than −60 °C (altitudes above 14 km) increased significantly after 10:00 UTC and reached the maximum at 12:00 UTC (16 min before the GJ), suggesting the occurrence of the GJ was related to the strong vertical development of the thunderstorm. Around the time of the GJ, the south cell of the storm featured overshooting top as indicated by radar data. Additionally, the storm was dominated by negative cloud-to-ground (-CG) flashes with an increase in -CG flash rate around the time of the GJ occurrence, indicating the storm appeared to be of normal polarity (the main positive charge region located above the main negative charge region). The + GJ was probably produced by a normally electrified thunderstorm, and a possible explanation for this unexpected behavior and different lightning activity of GJ-producing storms were discussed.

Relationship between time series cosmic ray data and aerosol optical properties: 1999–2015

Fri, 05/17/2019 - 19:10

Publication date: 1 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 190

Author(s): A. Maghrabi, K. Kudela

Abstract

High energy cosmic ray (CR) particles are capable of ionizing the Earth's atmosphere, which lead to changes in the atmospheric properties that affect its physical and chemical characteristics. One of the most important results of the interactions between the CR particles and the atmospheric molecules is the formation of aerosol and its subsequent condensation processes. In this study, the relationship between the time series of the aerosol optical properties; namely the aerosol optical depth (AOD) and Angstrom exponent (α), and the CR muons and neutrons was investigated and established. AOD and α monthly mean data were obtained from the AERONET site located in central Saudi Arabia (24.91° N, 46.41° E, 760 m), for the period of 1999–2015 and the corresponding CR data from Oulu neutron monitor were used for these investigations. Cosmic ray data for the period of 2002–2012 obtained from KACST muon detector were also used in this study. Correlation analyses between the time series of CR data (measured by NM and muon detector) and the aerosol optical properties were carried out and showed significant correlations between these variables. While AOD was positively correlated with the CR data, α showed the opposite.

Power spectral analyses using Fast Fourier transform (FFT) were applied on the monthly mean time series of the considered variables to search for possible common periodicities between them. The results showed that there is similarity in position of at least one local peak in PSD (near 1.6–1.7 years) in α and in CR. The correlation and power spectral analyses indicate possible mutual relation between variations of aerosols observed at a particular site and CR intensity observed on the ground.

Assessment of heavy precipitation events associated with floods due to strong moisture transport during summer monsoon over India

Fri, 05/17/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): D. Dhana Lakshmi, A.N.V. Satyanarayana, Arun Chakraborty

Abstract

Integrated water vapor transport (IVT) detection algorithm is implemented over the Arabian Sea basin for the identification of strong moisture transport events (SMTs) over Indian subcontinent during 1979–2013. Attempt has been made through the spatiotemporal characteristics whether SMTs are responsible for the occurrence of heavy precipitation events (HPEs) and floods. The results demonstrated that the persistent SMTs are related to HPEs towards flooding over parts of Indian subcontinent during summer monsoon. In the study a total of 364 SMTs have been identified. It is seen that the SMT axes is reaching from eastward direction crosses over land mass of west coast of India and moves in north-westerly direction through Assam, Bihar and Uttarakhand. The results reveal a better correlation of occurrence of HPEs with the presence of SMTs and a large portion of SMTs lead to HPEs, as well as large fraction of HPEs occurs after SMTs. The characteristics of specific flood and rainfall events associated with the occurrence of SMTs show that existence of strong relation between presence of SMTs and extreme precipitation events for the western region where SMTs make landfalls (over Mumbai in 2005), for the north western region where SMTs penetrate inland (over Uttarakhand in 2013), whereas the relations is weakened in the north eastern region (e.g., over Bihar in 2008). The results emphasize that the existence of large amount of atmospheric moisture over the study regions 2–3 days before extreme precipitation events is due to SMTs. Given the narrowness of SMTs, the location of SMTs over each region is related to the occurrence or lack of extreme precipitation events. In addition, rainfall intensity enhanced with the duration of persistent SMTs of the majority of identified events. A significant negative (positive) dependence was found between SMT totals and the Southern Oscillation Index (SOI) (Indian Ocean Dipole (IOD)), with a greater frequency of SMTs associated with lower SOI (higher IOD) values. This study is helpful in inspiring more detailed analysis of the relationship between SMTs and extreme precipitation events over India.

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

Fri, 05/17/2019 - 19:10

Publication date: Available online 26 April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Y. Zhao, Q. Feng, A.g. Lu, R. Deo

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 = 0.44–0.99). 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.

On the link between atmospheric cloud parameters and cosmic rays

Fri, 05/17/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): J. Christodoulakis, C.A. Varotsos, H. Mavromichalaki, M.N. Efstathiou, M. Gerontidou

Abstract

We investigate the cosmic rays behavior with respect to the scaling features of their temporal evolution. Our analysis is based on cosmic rays measurements by three neutron monitor stations in Athens (Greece), Jungfraujoch (Switzerland) and Oulu (Finland), for the period 2000 to early 2017. Each of these datasets was analyzed by using the Detrended Fluctuation Analysis (DFA) and Multifractal Detrended Fluctuation Analysis (MF-DFA) in order to investigate intrinsic properties, like self-similarity and the spectrum of singularities. The main result obtained is that the cosmic rays time series as recorded by the aforementioned neutron monitor stations exhibit positive long-range correlations of 1/f type with multifractal behavior meaning that this behavior is characteristic for cosmic rays at North Hemisphere. In addition, we investigate the possible similar scaling features in the temporal evolution of meteorological parameters that are closely associated with the cosmic rays, such as physical properties of clouds. The main conclusions drawn from the latter investigation are that positive long-range correlations are observed in cloud optical thickness liquid mean and cirrus reflectance mean, while both of them do not present statistically significant correlation with cosmic rays, which is in agreement with earlier studies.

Problems in calculating long-term trends in the upper atmosphere

Fri, 05/17/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): J. Laštovička, Š. Jelínek

Abstract

Anthropogenic polluting substances, mainly CO2, affect the lower atmosphere where they excite the well-known greenhouse warming. However, they also affect the upper atmosphere (mesosphere, thermosphere and embedded ionosphere), where they cause long-term trends stronger than those in the troposphere. Calculations of long-term trends in the upper atmosphere suffer from various problems, which may be divided into three groups: (1) natural variability, (2) data problems, and (3) methodology. These problems have often been underestimated in trend calculations, which lead to controversial trend results. Here we briefly treat various problems of long-term trend calculations in the upper atmosphere and some ways how to deal with these problems are suggested.

A global assessment of ray-traced and blind tropospheric models in the retrieval of tropospheric parameters from ground-based GPS observations

Fri, 05/17/2019 - 19:10

Publication date: 1 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 190

Author(s): Qiuying Guo, Xuxiang Wu

Abstract

The number of ground-based GNSS reference stations has increased significantly in recent years, which provides very favorable conditions for ZTD/ZWD retrieval. The methods of estimating ZTD/ZWD based on three a-priori troposphere values are discussed using GNSS reference stations without meteorological equipments. GPS observation data for two weeks in different seasons from 22 global IGS stations were processed using online GAPS software with static and kinematic PPP mode based on ECMWF grid product and GPT2.1w/UNB3m blind tropospheric models. Vienna Mapping Function 1 (VMF1) is used for all the a-priori models. The numerical results show that: compared with the IGS ZTD products, mm-level and about 2 cm-level ZTD products can be obtained based on the three a-priori troposphere values using static PPP and kinematic PPP respectively. About 1 cm-level and 2 cm-level ZWD products can be obtained based on ECMWF grid product/GPT2.1w model using static PPP and kinematic PPP respectively. The discrepancy between the ZTD estimates based on the three a-priori troposphere values is no more than 3 mm, and the differences of the averaged ZTD Mbias, RMSE and Std of the 22 IGS stations based on the three a-priori troposphere values are no more than 0.3 mm. While there is obvious differences in ZWD estimates based on the three a-priori troposphere values. The differences of the averaged ZWD Mbias/RMSE between ECMWF grid product and GPT2.1w model is about 0.2 cm, and the differences of the averaged ZWD Mbias/RMSE between ECMWF grid product and UNB3m model are about 0.5–1 cm. There is a systematic bias of about ±1 cm between the ZWD estimates based on GPT2.1w and UNB3m. This study shows that GNSS PPP technology based on ECMWF grid product and blind tropospheric model has great potential for ZTD/ZWD retrieval using ground-based GNSS reference stations.

Examining the influence of current waveform on the lightning electromagnetic field at the altitude of halo formation

Fri, 05/17/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): Huan Ren, Ye Tian, Gaopeng Lu, Yunfeng Zhang, Yanfeng Fan, Rubin Jiang, Mingyuan Liu, Dongshuai Li, Xiao Li, Xiushu Qie

Abstract

In this paper, we extend the analysis of Lu (2006) to calculate the electric field (E-field) of lightning return stroke in the region of sprite initiation and halos using a transmission line model that uses various lightning stroke current measured during the triggered lightning experiment as the driving source to examine the individual components (i.e., electrostatic, induction, and radiation) of E-field perturbation. As the altitude increases, the maximum strength of electrostatic and induction field gradually decreases, and the induction field decays slower than electrostatic field above 80 km. The electrostatic and induction field in the region of halo formation have a much larger contribution to the total E-field than the radiation field. Therefore, it is proposed that in addition to the electrostatic field, the induction field (with amplitude more than half of total E-field) is the main component of the total E-field within the first half millisecond directly above the stroke. Our analysis indicates that the induction field might play a significant role in the halo formation and probably also the sprite initiation. The M-component, the longer rising edge, the wavy long tail, and the relatively long time scale of stroke current can increase the amplitude of electrostatic and induction field at the height of halos, and drive the occurrence of halos and the subsequent development of streamers, therefore forming sprites. Our results enrich the understanding on the mechanism of halo production and the lightning electromagnetic field in the middle and high-altitude atmosphere, and also pave the way for future accurate modeling of halo formation.

The structure of equidistant-frequency groups in the oscillation spectra of the dayside magnetosphere

Fri, 05/17/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): A.R. Polyakov

Abstract

The structure of natural signals (geomagnetic field disturbances in the ULF range registered at Mondy and Borok observatories) is studied for the first time by means of the APCF (amplitude and phase correlation function) method, unrelated to spectral analysis but based on analysing a specially constructed correlation function of the amplitude and phase fluctuations in the recorded signal. This method can detect the presence of a group of equidistant frequencies in the spectrum of the original signal as well as measuring the difference, Δf, of two adjacent frequencies in the group. The end product of the APCF method is a histogram of multiple Δf values. In the traditional spectral method of signal analysis, the presence in the spectrum of a peak at a certain frequency means that, in the original signal, the oscillation amplitude has a local maximum at this frequency. In the APCF “spectrum” (histogram), each peak corresponds, not to one, but to a whole group of equidistant frequencies in the original signal. The position of the peak on the horizontal axis defines, not a specific frequency, but the difference of two adjacent frequencies which is typical of the entire group.

Comparison of one of the histograms for ULF disturbance records with the traditional spectrum shows that the chaotic spectrum, which is generally assumed to be noise, in reality possesses a strictly ordered structure. Most spectral peaks have been found to belong to one of many (more than 10) equidistant frequency groups. In the full spectrum, the peaks of these groups overlap forming a complex chaotic sequence.

The analysis of the peaks in all the hist ograms makes it possible to conclude that the equidistant frequency groups corresponding to peaks in each histogram, are eigenfrequencies of a 2D Alfvén resonator. The existence of such a resonator in the magnetosphere, in the vicinity of the plasmapause outer edge, was earlier predicted in theoretical studies [Guglielmi, Polyakov, 1983; Leonovich, Mazur, 1987]. The APCF processing method allows this prediction to be confirmed experimentally.

Optical properties of intracloud and cloud-to-ground discharges derived from JEM-GLIMS lightning observations

Fri, 05/17/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): K. Bandholnopparat, M. Sato, T. Adachi, T. Ushio, Y. Takahashi

Abstract

We developed a new method to distinguish the lightning discharge type using lightning data obtained by JEM-GLIMS spaced-based mission and ground-based lightning network that are JLDN, NLDN, WWLLN, and GEON. As a first step, we selected 1057 lightning events detected by the JEM-GLIMS cameras (LSI) and spectrophotometers (PH) in 2014. Then, we compared the JEM-GLIMS optical data to the ground-based lightning data in order to check the simultaneous detection of JEM-GLIMS lightning events by the ground-based lightning networks, and finally we identified the discharge type of the JEM-GLIMS lightning events. We succeed in identifying 941 simultaneous lightning events and found that 582, 93, and 266 lightning events were IC, +CG, and -CG discharges, respectively. As a next step, we calculated intensity ratios between blue and red PH channels, i.e., 337nm/762 nm, 316nm/762 nm, 392nm/762 nm, 337nm/(599–900 nm), 316nm/(599–900 nm), and 392nm/(599–900 nm) for the 941 lightning events in order to specify the optical characteristics of IC, +CG, and -CG discharges. It is found that the PH intensity ratio of +CG discharges is the highest and that the PH intensity ratio of IC and -CG discharges is smaller than that of +CG discharge. We also found that the characteristics of the LSI intensity ratio are almost comparable to those of the PH intensity ratio. As the differences of the 337nm/762 nm, 337nm/(599–900 nm), and 392nm/(599–900 nm) ratio of IC, +CG, and -CG discharges are relatively large, these three ratios are a useful proxy for classifying the discharge types for additional 7349 lightning events detected by JEM-GLIMS in order to estimate the global ratio between IC and CG discharges (Z ratio).

Multi-instrument investigation of troposphere-ionosphere coupling and the role of gravity waves in the formation of equatorial plasma bubble

Fri, 05/17/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): M. Sivakandan, I. Paulino, T.K. Ramkumar, A. Taori, A.K. Patra, S. Sripathi, K. Niranjan, A.V. Bilibio

Abstract

Present study investigates the role of gravity waves in the generation of equatorial plasma bubbles (EPBs) during geomagnetic quiet conditions using co-located observations from Gadanki (13.5oN, 79.2° E) an all sky airglow imager, Gadanki Ionospheric Radar Interferometer (GIRI) and Ionosonde observations from Tirunelveli (8.7° N, 77.8° E). To avoid any changes occurring in the background ionosphere, four consecutive nights of observation during 03–06 February 2014 is used. Out of these four nights, three nights (i.e., 03, 05 and 06 February 2014) exhibit occurrence of EPBs in the OI 630 nm airglow emission and radar plumes and there is no bubble occurrence during one night, though the ionospheric peak altitude (h′F) value is more than 350 km in all these nights. During these four nights the structures observed in the E-region drifts and gravity waves noted in the mesospheric OH emissions are analyzed. It is found that there are common periodic oscillations in the OH peak emission altitude and E-region in three nights (03, 04 and 05 February 2014). The mesospheric gravity wave structures are ray traced to their potential sources in the lower atmosphere and also for the possibility of their propagation to the E-region. Our results suggest that apart from horizontal wavelength and amplitudes, the propagation angle of gravity wave may also be important for seeding of the Rayleigh-Taylor (R-T) instability. Thus, it gives an insight about the role of lower – middle and upper atmospheric coupling on the occurrence of the noted EPBs.

On the role of F3 layers as well as solar flux in modulating the topside ionization over Indian region: An analysis

Fri, 05/17/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): N. Mridula, Tarun Kumar Pant, G. Manju, K.V. Subrahmanyam, K. Kishore Kumar

Abstract

The behavior of ionization in the topside ionosphere above F region peak is quite different from the lower ionosphere owing to the diverse processes operational there. This paper presents a comprehensive study on the topside ionosphere and brings out the role of F3 layers as well as increase in solar flux in modulating the topside ionization. Data used comprises of the electron density obtained from COSMIC satellite for the period 2007 to 2012 as well as RaBIT tomograms for the period May to December 2011. This study clearly shows that the ionization in the height region of 300 km–400 km is affected by the presence of F3 layer while above 450 km ionization is not significantly altered by the formation of F3 layer during the solar minimum period. The important factor which affects topside ionization above this altitude is the solar flux. The present study has generated an empirical relationship between the topside electron density and F10.7 cm solar flux during the rising phase of solar cycle 24. This empirical relationship is compared using tomographic observations obtained from RaBIT (Radio Beacon for Ionospheric Tomography) data over Indian region.

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