scholarly journals Analysis of a long-lived, two-cell lightning storm on Saturn

2019 ◽  
Vol 621 ◽  
pp. A113 ◽  
Author(s):  
G. Fischer ◽  
J. A. Pagaran ◽  
P. Zarka ◽  
M. Delcroix ◽  
U. A. Dyudina ◽  
...  
Keyword(s):  
Optical Observations ◽  
Local Times ◽  
Convective System ◽  
Radio Waves ◽  
Convective Storm ◽  
Electrostatic Discharges ◽  
First Occurrence ◽  
Limited Frequency ◽  
Storm Cells ◽  
Horizon Effect

Lightning storms in Saturn’s atmosphere can last for a few days up to several months. In this paper we analyze a lightning storm that raged for seven and a half months at a planetocentric latitude of 35° south from the end of November 2007 until mid-July 2008. Thunderstorms observed by the Cassini spacecraft before this time were characterized by a single convective storm region of ~2000 km in size, but this storm developed two distinct convective storm cells at the same latitude separated by ~25° in longitude. The second storm cell developed in March 2008, and the entire two-cell convective system was moving with a westward drift velocity of about 0.35 deg per day, which differs from the zonal wind speed. An exhaustive data analysis shows that the storm system produced ~277000 lightning events termed Saturn electrostatic discharges (SEDs) that were detected by Cassini’s Radio and Plasma Wave Science (RPWS) instrument, and they occurred in 439 storm episodes. We analyzed the SED intensity distributions, the SED polarization, the burst rates, and the burst and episode durations. During this storm Cassini made several orbits around Saturn and observed the SEDs from all local times. A comparison with optical observations shows that SEDs can be detected when the storm is still beyond the visible horizon. We qualitatively describe this so-called over-the-horizon effect which is thought to be due to a temporary trapping of SED radio waves below Saturn’s ionosphere. We also describe the first occurrence of so-called SED pre- and post-episodes, which occur in a limited frequency range around 4 MHz separated from the main episode. Pre- and post-episodes were mostly observed by Cassini located at local noon, and should be a manifestation of an extreme over-the-horizon effect. Combined radio and imaging observations suggest that some decreases in SED activity are caused by splitting of the thunderstorm into a bright cloud and a dark oval.

scholarly journals Survey of electron density changes in the daytime ionosphere over the Arecibo observatory due to lightning and solar flares

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Caitano L. da Silva ◽  
Sophia D. Salazar ◽  
Christiano G. M. Brum ◽  
Pedrina Terra
Keyword(s):  
Electron Density ◽  
Solar Flares ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Weather Conditions ◽  
Optical Observations ◽  
Radio Waves ◽  
D Region ◽  
E Region ◽  
Arecibo Observatory

AbstractOptical observations of transient luminous events and remote-sensing of the lower ionosphere with low-frequency radio waves have demonstrated that thunderstorms and lightning can have substantial impacts in the nighttime ionospheric D region. However, it remains a challenge to quantify such effects in the daytime lower ionosphere. The wealth of electron density data acquired over the years by the Arecibo Observatory incoherent scatter radar (ISR) with high vertical spatial resolution (300-m in the present study), combined with its tropical location in a region of high lightning activity, indicate a potentially transformative pathway to address this issue. Through a systematic survey, we show that daytime sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). These changes typically correspond to electron density depletions in the D and E region. The survey also shows that these disturbances are different than the ones associated with solar flares, which tend to have longer duration and most often correspond to an increase in the local electron density content.

scholarly journals A fast radio burst source at a complex magnetised site in a barred galaxy

2021 ◽  
Author(s):  
K.J. Lee ◽  
Heng Xu ◽  
J.R. Niu ◽  
P. Chen ◽  
Weiwei Zhu ◽  
...  
Keyword(s):  
Optical Observations ◽  
Host Galaxy ◽  
Radio Bursts ◽  
Radio Waves ◽  
Galactocentric Distance ◽  
Burst Source ◽  
Radiation Mechanism ◽  
Circular Polarisation ◽  
Rotation Measure ◽  
Fast Radio Burst

Abstract Fast radio bursts (FRBs) are highly dispersed radio bursts prevailing in the universe. The recent detection of FRB~200428 from a Galactic magnetar suggested that at least some FRBs originate from magnetars, but it is unclear whether the majority of cosmological FRBs, especially the actively repeating ones, are produced from the magnetar channel. Here we report the detection of 1863 polarised bursts from the repeating source FRB~20201124A during a dedicated radio observational campaign of Five-hundred-meter Aperture Spherical radio Telescope (FAST). The large sample of radio bursts detected in 88 hr over 54 days indicate a significant, irregular, short-time variation of the Faraday rotation measure (RM) of the source during the first 36 days, followed by a constant RM during the later 18 days. Significant circular polarisation up to 75\% was observed in a good fraction of bursts. Evidence suggests that some low-level circular polarisation originates from the conversion from linear polarisation during the propagation of the radio waves, but an intrinsic radiation mechanism is required to produce the higher degree of circular polarisation. All of these features provide evidence for a more complicated, dynamically evolving, magnetised immediate environment around this FRB source. Its host galaxy was previously known. Our optical observations reveal that it is a Milky-Way-sized, metal-rich, barred-spiral galaxy at redshift z=0.09795+-0.00003, with the FRB residing in a low stellar density, interarm region at an intermediate galactocentric distance, an environment not directly expected for a young magnetar formed during an extreme explosion of a massive star.

scholarly journals A mesoscale convective system trapped along the Spanish Mediterranean Coast

2006 ◽  
Vol 7 ◽  
pp. 153-156 ◽  
Author(s):  
J. M. Sánchez-Laulhé
Keyword(s):  
Convective Instability ◽  
Heavy Rainfall ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Precipitable Water ◽  
Mediterranean Coast ◽  
Convective System ◽  
Convective Storm ◽  
Low Level ◽  
Mesoscale Convective

Abstract. This paper describes the evolution of a mesoscale convective system (MCS) developed over the Alboran Sea on 7 February 2005, using surface, upper-air stations, radar and satellite observations, and also data from an operational numerical model. The system developed during the night as a small convective storm line in an environment with slight convective instability, low precipitable water and strong low-level vertical wind shear near coast. The linear MCS moved northwards reaching the Spanish coast. Then it remained trapped along the coast for more than twelve hours, following the coast more than five hundred kilometres. The MCS here described had a fundamental orographic character due to: (1) the generation of a low-level storm inflow parallel to the coast, formed by blocking of the onshore flow by coastal mountains and (2) the orientation of both the mesoscale ascent from the sea towards the coastal mountains and the midlevel rear inflow from the coastal mountains to the sea. The main motivation of this work was to obtain a better understanding of the mechanisms relevant to the formation of heavy rainfall episodes occurring at Spanish Mediterranean coast associated with this kind of stationary or slowly moving MCSs.

A modern digital High Frequency Receiver to explore Uranus and Neptune radio emitters

2020 ◽  
Author(s):  
Laurent Lamy ◽  
Baptiste Cecconi ◽  
Mustapha Dekkali ◽  
Keyword(s):  
Plasma Wave ◽  
High Frequency ◽  
Plasma Waves ◽  
Modern Concept ◽  
Radio Waves ◽  
Electrostatic Discharges ◽  
Planetary Magnetospheres ◽  
The Earth ◽  
General Radio ◽  
Atmospheric Radio

<div class="">Among the known planetary magnetospheres, those of Uranus and Neptune display very similar radio environments so that they have early been referred to as ‘radio twins’. They produce a variety of electromagnetic radio waves ranging from ~0 to a few tens of MHz similar to - although more complex than - those of Saturn or the Earth (Desch et al., 1991, Zarka et al., 1995). These include the well known Uranian/Neptunian Kilometric Radiations (UKR/NKR) below 1MHz or the Uranian/Neptunian Electrostatic Discharges (UED/NED) beyond, which remain only known from Voyager 2 radio observations. Here, we present a modern concept of digital High Frequency Receiver (HFR) within the frame of a general Radio and Plasma Wave (RPW) experiment retained in various mission concepts toward Uranus and Neptune (e.g. Hess et al., 2010 ; Arridge et al., 2011, 2013, 2014 Christophe et al., 2011; Masters et al., 2013; Hofstadter at al., 2019). The presented HFR concept, based on the heritage of Cassini/RPWS/HFR, Bepi-Clompobo/PWI/Sorbet, Solar Orbiter/RPW and JUICE/RPWI/JENRAGE is aimed at providing a light, robust, low-consumption versatile instrument capable of goniopolarimetric and waveform measurements from a few kHz to ~20MHz, devoted to the study of auroral and atmospheric radio and plasma waves or dust impacts.</div>

scholarly journals Radar-derived convective storms' climatology for the Prut River basin: 2003–2017

2019 ◽  
Vol 19 (7) ◽  
pp. 1305-1318 ◽  
Author(s):  
Sorin Burcea ◽  
Roxana Cică ◽  
Roxana Bojariu
Keyword(s):  
River Basin ◽  
Selection Criterion ◽  
Movement Speed ◽  
Movement Direction ◽  
The Black Sea ◽  
Peak Time ◽  
Convective Storm ◽  
Convective Storms ◽  
Storm Cells ◽  
Prut River

Abstract. Weather radar measurements are used to study the climatology of convective storms and their characteristics in the transboundary Prut River basin. The Storm Cell Identification and Tracking (SCIT) algorithm was used to process the volumetric reflectivity measurements, in order to identify, characterize, and track the convective storm cells. The storm attribute table output of the algorithm was used to separate the convective from the stratiform storm cells, by applying a simple selection criterion based on the average vertically integrated liquid (VIL) values. The radar-derived characteristics of convective storms were used to document the spatial and temporal distributions and storm properties in terms of duration, distance travelled, movement direction, and intensity. The results show that 94.3 % of all convective storm cells were detected during May–August, with the peak in July. The peak time for convective storm cells' occurrence was in the afternoon and evening hours between 10:00 and 18:00 UTC. The median duration of a convective storm was 42 min, the median distance travelled was 23 km, and the median movement speed was 7.7 m s−1. The average movement of storms varied with months, but overall most convective storms move from the south-west and south–south-east. Also, the analysis shows that the longer-lasting convective storms were the most intense. The spatial distribution of the convective cells reveals yearly variation patterns and hotspots but also highlights the limitations of radar measurement at longer distances. Reanalysis data suggest that low values of sea level pressure over the Black Sea can act as a dynamical driver of convective storms in the analysed area.

scholarly journals Balanço de Vorticidade Associado a um Sistema Convectivo Intenso (Vorticity Budget Associated to an Intense Convective Storm )

2011 ◽  
Vol 4 (1) ◽  
pp. 189
Author(s):  
Rafaela Lisboa Costa ◽  
Enio Pereira de Souza
Keyword(s):  
Vorticity Equation ◽  
Convective System ◽  
Convective Storm ◽  
Advection Term ◽  
Cyclonic Vortex ◽  
Vorticity Budget ◽  
Order Of Magnitude ◽  
Low Levels ◽  
Upper Level ◽  
Developing System

O presente trabalho teve como objetivo analisar um sistema convectivo intenso ocorrido sobre o estado de Alagoas nos dias 17 e 18 de março de 2008. Para tanto, simulou-se o referido evento em questão com o modelo BRAMS e analisou-se sua dinâmica fazendo uso da equação da vorticidade. Os resultados obtidos mostraram que se pode reproduzir o evento com a utilização do BRAMS, que mostrou a presença de um Vórtice Ciclônico de Altos Níveis (VCAN) atuando sobre o Nordeste Brasileiro. Em relação a analise da equação da vorticidade, esta mostrou que o termo de maior influencia sobre a dinâmica deste sistema é o da advecção de vorticidade relativa, pois possui uma maior magnitude e atua como um “freio” no desenvolvimento do sistema. O termo da advecção de vorticidade planetária atuou como um favorecedor ao desenvolvimento deste sistema, induzindo convergência em baixos níveis e divergência em altos níveis. O termo da divergência também contribuiu pouco em relação aos altos níveis atmosféricos. Não obstante, esse termo foi de grande importância em baixos níveis, onde mostrou a geração de forte vorticidade ciclônica próximo à superfície, favorecendo a intensificação do sistema.Palavras – Chave: VCAN, sistema convectivo, BRAMS.  Vorticity Budget Associated to an Intense Convective Storm  ABSTRACTThe objective of the present work is to analyze a storm that occurred over Alagoas State-Brazil at 17 and 18 March 2008. The storm was simulated with the BRAMS model and its dynamics was analyzed through the vorticity equation. Results show that the BRAMS model can reproduce the storm that is associated to an Upper Level Cyclonic Vortex (ULCV) that was over Northeast Brazil. The analysis using the vorticity equation showed that the vorticity advection term is an order of magnitude greater that the others and acts as a “brake” to the developing system. The planetary advection term acts to intensifying the storm causing mass convergence at lower levels and divergence at the upper levels. The divergence term was small at the upper levels. Nevertheless, this term was very important in producing mass convergence in the low levels, thus contributing to intensifying the storm.   Keywords: ULCV, convective system, BRAMS.

scholarly journals Radar-derived convective storms climatology for Prut River Basin: 2003−2017

2018 ◽  
Author(s):  
Sorin Burcea ◽  
Roxana Cică ◽  
Roxana Bojariu
Keyword(s):  
River Basin ◽  
Selection Criterion ◽  
Movement Speed ◽  
Movement Direction ◽  
Peak Time ◽  
Convective Storm ◽  
Convective Storms ◽  
Basin Scale ◽  
Storm Cells ◽  
Prut River

Abstract. Weather radar measurements are used to study the climatology of convective storms and their characteristics in the transboundary Prut river basin. The Storm Cell Identification and Tracking (SCIT) algorithm was used to processes the volumetric reflectivity measurements, in order to identify, characterize, and track the convective storm cells. The storm attributes table output of the algorithm was used to separate the convective from the stratiform storm cells, by applying a simple selection criterion based on the average Vertically Integrated Liquid (VIL) values. The radar-derived characteristics of convective storms were used to document the spatial and temporal distributions, and storm properties in terms of duration, traveled distance, movement direction, and intensity. The results show that 94.3 % of all convective storm cells were detected during May–August, with the peak in July. The peak time for convective storm cells occurrence was in the afternoon and evening hours between 10:00 and 18:00 UTC. The average duration of a convective storm was 48.7 min, the average traveled distance was 28 km, and the average movement speed was 8.5 m s−1. The average movement of storms varied with months, but overall most convective storms move from southwest and south-southeast. Also, the analysis shows that the longer-lasting convective storms were the most intense. The spatial distribution of the convective cells reveals yearly variation patterns and hotspots, but also highlights the limitations of radar measurement at longer distances. At the basin scale, the total monthly number of storm cells positively correlates with the precipitation amounts at confidence levels statistically significant.

scholarly journals 3D Convective Storm Identification, Tracking, and Forecasting—An Enhanced TITAN Algorithm

2009 ◽  
Vol 26 (4) ◽  
pp. 719-732 ◽  
Author(s):  
Lei Han ◽  
Shengxue Fu ◽  
Lifeng Zhao ◽  
Yongguang Zheng ◽  
Hongqing Wang ◽  
...  
Keyword(s):  
Cross Correlation ◽  
Motion Vector ◽  
Correlation Method ◽  
Optimization Method ◽  
Radar Data ◽  
Convective Storm ◽  
Performance Improvements ◽  
Motion Vector Field ◽  
Storm Cells ◽  
The Individual

Abstract Storm identification, tracking, and forecasting make up an essential part of weather radar and severe weather surveillance operations. Existing nowcasting algorithms using radar data can be generally classified into two categories: centroid and cross-correlation tracking. Thunderstorm Identification, Tracking, and Nowcasting (TITAN) is a widely used centroid-type nowcasting algorithm based on this paradigm. The TITAN algorithm can effectively identify, track, and forecast individual convective storm cells, but TITAN tends to provide incorrect identification, tracking, and forecasting in cases where there are dense cells whose shape changes rapidly or where clusters of storm cells occur frequently. Aiming to improve the performance of TITAN in such scenarios, an enhanced TITAN (ETITAN) algorithm is presented. The ETITAN algorithm provides enhancements to the original TITAN algorithm in three aspects. First, in order to handle the false merger problem when two storm cells are adjacent, and to isolate individual storm cells from a cluster of storms, ETITAN uses a multithreshold identification method based on mathematical morphology. Second, in the tracking phase, ETITAN proposes a dynamic constraint-based combinatorial optimization method to track storms. Finally, ETITAN uses the motion vector field calculated by the cross-correlation method to forecast the position of the individual isolated storm cells. Thus, ETITAN combines aspects of the two general classes of nowcasting algorithms, that is, cross-correlation and centroid-type methods, to improve nowcasting performance. Results of experiments presented in this paper show the performance improvements of the ETITAN algorithm.

Initiation of Convective Storms at Low-Level Mesoscale Boundaries in Southwestern Ontario

2018 ◽  
Vol 33 (2) ◽  
pp. 583-598 ◽  
Author(s):  
Lisa S. Alexander ◽  
David M. L. Sills ◽  
Peter A. Taylor
Keyword(s):  
Radar Data ◽  
Moving Boundaries ◽  
Lake Breeze ◽  
Convective Storm ◽  
Convective Storms ◽  
Low Level ◽  
New Findings ◽  
Gust Fronts ◽  
Storm Cells ◽  
The Relationship

Abstract The relationship between low-level mesoscale boundaries and convective storm initiation was investigated in southwestern Ontario, Canada. The influence of lake-breeze fronts, a type of boundary that frequently affects this region of the Great Lakes watershed in summer, presented a particular interest. Radar data were processed using thunderstorm cell identification and tracking algorithms. The distances between the locations of storm cells reaching an intensity of 40 dBZ and the closest low-level mesoscale boundary were measured. Considering only days not influenced by a warm front, more than 75% of cells developed within 30 km of a low-level mesoscale boundary. Further examination by boundary type showed that cell initiations associated with moving boundaries and storm gust fronts occurred most often 0–5 km behind the boundaries. However, cell initiations associated with lake-breeze fronts most often occurred 0–5 km ahead of the boundaries. The analysis also suggested that lake-breeze fronts would often initiate the first storms of the day, which in turn generated gust fronts that could initiate subsequent storms. Overall, the results were similar to a previous study investigating storm initiation in the vicinity of low-level mesoscale boundaries in eastern Colorado and include some new findings in relation to lake-breeze fronts. The findings can be used by forecasters as well as automated nowcasting algorithms in order to improve predictions of storm initiation.

scholarly journals Anti-interference technology of communication system

2018 ◽  
Vol 1 (1) ◽  
Author(s):  
Lv Chunhai
Keyword(s):  
Communication System ◽  
Information Age ◽  
Wireless Transmission ◽  
System Capacity ◽  
Radio Waves ◽  
Electromagnetic Environment ◽  
Radio Communications ◽  
Limited Frequency ◽  
Network Communications

Communication modernization is an important symbol of human societies as we enter into the information age. An importantproblem encountered in modern communication is interference. With the development of communication, the establishment of variouscommunication networks, making the limited frequency of resources more crowded, intertwined to the serious. How to ensure that thecommunication is effective, accurate and rapid in the harsh environment conditions in front of today's communications researchers is adifficult problem. As the mobile communication system must use wireless transmission technology in order to achieve the exchange ofinformation in the mobile, wireless transmission is vulnerable to a variety of other radio waves interference, a large number of interferencewill greatly affect the quality of network communications and system capacity. Anti-jamming technology with strong resistance, strongtechnical, difficult, practical and reliable high characteristics, in today's increasingly harsh electromagnetic environment, anti-jammingtechnology is particularly compelling. It can greatly improve the effectiveness and reliability of the communication system in thecommunication system. Today, anti-jamming technology has become the mainstream of radio communications technology, it is the mostclosely linked with the field of communications. This paper mainly discusses the interference problem of GSM system in mobilecommunication anti-jamming technology, including the interference type in GSM, the anti-interference ability of GSM itself and how tooptimize the network to achieve the purpose of anti-jamming, so as to meet the requirements of users System capacity while maintaininggood call quality.

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