Statistics of pulsating auroras on the basis of all-sky TV data from five stations. I. Occurrence frequency

1981 ◽  
Vol 59 (8) ◽  
pp. 1150-1157 ◽  
Author(s):  
T. Oguti ◽  
S. Kokubun ◽  
K. Hayashi ◽  
K. Tsuruda ◽  
S. Machida ◽  
...  
Keyword(s):  
Local Time ◽  
Cold Plasma ◽  
Geomagnetic Latitude ◽  
Auroral Oval ◽  
Magnetic Activity ◽  
Occurrence Frequency ◽  
Frequency Of Occurrence ◽  
Occurrence Probability ◽  
Energetic Electrons ◽  
Plasma Irregularities

The frequency of occurrence of pulsating auroras is statistically examined on the basis of all-sky TV data for 34 nights from five stations, in a range from 61.5 to 74.3° in geomagnetic latitude. The results are that: (1) occurrence probability of a pulsating aurora is 100% after 4 h in geomagnetic local time, (2) pulsating auroras occur in the morning hours along the auroral oval even when magnetic activity is as small as 0o ≤ Kp ≤ 1, (3) pulsating auroras occur even in the evening when Kp increases to greater than 3−, (4) drift of pulsating auroras is westward in the evening while it is eastward in the morning hours, (5) the region of pulsating auroras splits into two zones, 64 to 68° and 61 to 63° in geomagnetic latitude, after 4 h geomagnetic local time for Kp from 2o to 3−, and the splitting also appears to exist for greater Kp as evidenced by observation other than our auroral data. These results are discussed in relation to distributions of cold plasma irregularities and energetic electrons in the magnetosphere.

scholarly journals Magnetic local time dependence of geomagnetic disturbances contributing to the AU and AL indices

2011 ◽  
Vol 29 (4) ◽  
pp. 673-678 ◽  
Author(s):  
S. Tomita ◽  
M. Nosé ◽  
T. Iyemori ◽  
H. Toh ◽  
M. Takeda ◽  
...  
Keyword(s):  
Local Time ◽  
Geomagnetic Field ◽  
Field Data ◽  
Geomagnetic Latitude ◽  
Magnetic Activity ◽  
Auroral Zone ◽  
Magnetic Local Time ◽  
Geomagnetic Disturbances ◽  
Current Systems ◽  
Local Time Dependence

Abstract. The Auroral Electrojet (AE) indices, which are composed of four indices (AU, AL, AE, and AO), are calculated from the geomagnetic field data obtained at 12 geomagnetic observatories that are located in geomagnetic latitude (GMLAT) of 61.7°–70°. The indices have been widely used to study magnetic activity in the auroral zone. In the present study, we examine magnetic local time (MLT) dependence of geomagnetic field variations contributing to the AU and AL indices. We use 1-min geomagnetic field data obtained in 2003. It is found that both AU and AL indices have two ranges of MLT (AU: 15:00–22:00 MLT, ~06:00 MLT; and AL: ~02:00 MLT, 09:00–12:00 MLT) contributing to the index during quiet periods and one MLT range (AU: 15:00–20:00 MLT, and AL: 00:00–06:00 MLT) during disturbed periods. These results are interpreted in terms of various ionospheric current systems, such as, Sqp, Sq, and DP2.

scholarly journals Surveying pulsating auroras

2020 ◽  
Vol 38 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Eric Grono ◽  
Eric Donovan
Keyword(s):  
Local Time ◽  
Equatorial Plane ◽  
Early Morning ◽  
Auroral Oval ◽  
Magnetic Local Time ◽  
Occurrence Probability ◽  
Inner Magnetosphere ◽  
Magnetic Latitude ◽  
Source Regions ◽  
Proton Aurora

Abstract. The early-morning auroral oval is dominated by pulsating auroras. These auroras have often been discussed as if they are one phenomenon, but they are not. Pulsating auroras are separable based on the extent of their pulsation and structuring into at least three subcategories. This study surveyed 10 years of all-sky camera data to determine the occurrence probability for each type of pulsating aurora in magnetic local time and magnetic latitude. Amorphous pulsating aurora (APAs) are a pervasive, nearly daily feature in the early-morning auroral oval which have an 86 % chance of occurrence at their peak. Patchy pulsating auroras (PPAs) and patchy auroras (PAs) are less common, peaking at 21 % and 29 %, respectively. Before local midnight, pulsating auroras are almost exclusively APAs. Occurrence distributions of APAs, PPAs, and PAs are mapped into the equatorial plane to approximately locate their source regions. The PA and PPA distributions primarily map to locations approximately between 4 and 9 RE, while some APAs map to farther distances, suggesting that the mechanism which structures PPAs and PAs is constrained to the inner magnetosphere. This is in agreement with Grono and Donovan (2019), which located these auroras relative to the proton aurora.

scholarly journals Surveying pulsating auroras

2019 ◽  
Author(s):  
Eric Grono ◽  
Eric Donovan
Keyword(s):  
Local Time ◽  
Early Morning ◽  
Auroral Oval ◽  
Magnetic Local Time ◽  
Occurrence Probability ◽  
Magnetic Latitude ◽  
Source Regions ◽  
As If

Abstract. The early morning auroral oval is dominated by pulsating auroras. This category of aurora has often been discussed as if it is just one phenomenon, but it is not. Pulsating auroras are separable based on the extent of their pulsation and structuring into at least three subcategories. This study surveyed 10 years of all-sky camera data to determine the occurrence probability for each type of pulsating aurora in magnetic local time and magnetic latitude. Amorphous pulsating aurora is found to be a nearly ubiquitous early morning aurora, and pulsating aurora is almost exclusively amorphous pre-midnight. Occurrence distributions for each type of pulsating aurora are mapped into the magnetosphere to approximately determine the location of their source regions. The patchy and patchy pulsating aurora distributions primarily map to locations approximately between 4 and 9 RE, while some amorphous pulsating aurora maps to farther distances.

scholarly journals Remote sensing of a NTC radio source from a Cluster tilted spacecraft pair

2013 ◽  
Vol 31 (11) ◽  
pp. 2097-2121 ◽  
Author(s):  
P. M. E. Décréau ◽  
S. Kougblénou ◽  
G. Lointier ◽  
J.-L. Rauch ◽  
J.-G. Trotignon ◽  
...  
Keyword(s):  
Electric Field ◽  
Circular Polarization ◽  
Source Region ◽  
Plane Waves ◽  
Geomagnetic Latitude ◽  
Magnetic Activity ◽  
Spectral Signature ◽  
Time Interval ◽  
Field Polarization ◽  
Electric Field Polarization

Abstract. The Cluster mission operated a "tilt campaign" during the month of May 2008. Two of the four identical Cluster spacecraft were placed at a close distance (~50 km) from each other and the spin axis of one of the spacecraft pair was tilted by an angle of ~46°. This gave the opportunity, for the first time in space, to measure global characteristics of AC electric field, at the sensitivity available with long boom (88 m) antennas, simultaneously from the specific configuration of the tilted pair of satellites and from the available base of three satellites placed at a large characteristic separation (~1 RE). This paper describes how global characteristics of radio waves, in this case the configuration of the electric field polarization ellipse in 3-D-space, are identified from in situ measurements of spin modulation features by the tilted pair, validating a novel experimental concept. In the event selected for analysis, non-thermal continuum (NTC) waves in the 15–25 kHz frequency range are observed from the Cluster constellation placed above the polar cap. The observed intensity variations with spin angle are those of plane waves, with an electric field polarization close to circular, at an ellipticity ratio e = 0.87. We derive the source position in 3-D by two different methods. The first one uses ray path orientation (measured by the tilted pair) combined with spectral signature of magnetic field magnitude at source. The second one is obtained via triangulation from the three spacecraft baseline, using estimation of directivity angles under assumption of circular polarization. The two results are not compatible, placing sources widely apart. We present a general study of the level of systematic errors due to the assumption of circular polarization, linked to the second approach, and show how this approach can lead to poor triangulation and wrong source positioning. The estimation derived from the first method places the NTC source region in the dawn sector, at a large L value (L ~ 10) and a medium geomagnetic latitude (35° S). We discuss these untypical results within the frame of the geophysical conditions prevailing that day, i.e. a particularly quiet long time interval, followed by a short increase of magnetic activity.

scholarly journals Influence of high-latitude geomagnetic pulsations on recordings of broadband force-balanced seismic sensors

2012 ◽  
Vol 1 (2) ◽  
pp. 85-101 ◽  
Author(s):  
E. Kozlovskaya ◽  
A. Kozlovsky
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Geomagnetic Latitude ◽  
Low Frequency ◽  
Auroral Oval ◽  
Polar Regions ◽  
Geomagnetic Pulsations ◽  
Seismic Sensors ◽  
Magnetic Poles ◽  
Magnetic Disturbances

Abstract. Seismic broadband sensors with electromagnetic feedback are sensitive to variations of surrounding magnetic field, including variations of geomagnetic field. Usually, the influence of the geomagnetic field on recordings of such seismometers is ignored. It might be justified for seismic observations at middle and low latitudes. The problem is of high importance, however, for observations in Polar Regions (above 60° geomagnetic latitude), where magnitudes of natural magnetic disturbances may be two or even three orders larger. In our study we investigate the effect of ultra-low frequency (ULF) magnetic disturbances, known as geomagnetic pulsations, on the STS-2 seismic broadband sensors. The pulsations have their sources and, respectively, maximal amplitudes in the region of the auroral ovals, which surround the magnetic poles in both hemispheres at geomagnetic latitude (GMLAT) between 60° and 80°. To investigate sensitivity of the STS-2 seismometer to geomagnetic pulsations, we compared the recordings of permanent seismic stations in northern Finland to the data of the magnetometers of the IMAGE network located in the same area. Our results show that temporary variations of magnetic field with periods of 40–150 s corresponding to regular Pc4 and irregular Pi2 pulsations are seen very well in recordings of the STS-2 seismometers. Therefore, these pulsations may create a serious problem for interpretation of seismic observations in the vicinity of the auroral oval. Moreover, the shape of Pi2 magnetic disturbances and their periods resemble the waveforms of glacial seismic events reported originally by Ekström (2003). The problem may be treated, however, if combined analysis of recordings of co-located seismic and magnetic instruments is used.

scholarly journals KOMUNITAS MAKRO ALGA DI PERAIRAN PANTAI ERI TELUK AMBON

2019 ◽  
Vol 15 (1) ◽  
pp. 40-45
Author(s):  
Frijona F Lokollo
Keyword(s):  
Community Structure ◽  
Species Composition ◽  
Relative Frequency ◽  
Occurrence Frequency ◽  
Frequency Of Occurrence ◽  
Gracilaria Salicornia ◽  
Turbinaria Ornata ◽  
Belt Transect ◽  
Macro Algae

This research was conducted in Eri Beach, Ambon Bay on November 2016 to study community structure which consist of species composition, density and occurrence frequency of macro algae.  Sample of macro algae was collected by using belt transect method.  The results showed that there were 11 species of macro algae in the area which were belonged to 11 genera, 9 families, 8 orders, 3 classes and 3 divisions. Those species were Halimeda opuntia and Caulerpa serrulata (Chlorophyta), Padina minor and Turbinaria ornata (Phaeophya), Amphiroa rigida, Galaxaura rugosa, Ceratodictyon spongiosum, Gracilaria Salicornia, Laurencia papillosa, Acanthophora muscoides and Halymenia durvillaei (Rhodophyta). The highest density was represented by Amphiroa rigida (2.02 ind/m2) while the highest relative frequency of occurrence belonged to Padina minor (27%). Keywords : Community, macro algae, density, Eri, Ambon Bay   ABSTRAK Penelitian ini bertujuan untuk mengetahui struktur komunitas makro alga meliputi komposisi jenis, frekuensi kehadiran serta kepadatan di Pantai Eri. Penelitian dilakukan pada bulan November 2016. Stasiun pengamatan makro alga yaitu di perairan pantai Eri. Metode sampling menggunakan Belt Transect. Hasil penelitian ditemukan 11 spesies, 11 genus, 9 famili, 8 ordo, 3 kelas dan 3 devisi. Chlorophyta terdiri dari Halimeda opuntia dan Caulerpa serrulata. Phaeophya terdiri dari Padina minor dan Turbinaria ornata. Rhodophyta terdiri dari Amphiroa rigida, Galaxaura rugosa, Ceratodictyon spongiosum, Gracilaria Salicornia, Laurencia papillosa, Acanthophora muscoides dan Halymenia durvillaei. Kepadatan jenis tertinggi spesies A. rigida (2.02 ind/m2) dan frekuensi kehadiran relatif tertinggi spesies Padina minor (27%).

Research Progresses of Ionospheric Plasma Irregularities from the Ground–Based Airglow Network in China

2021 ◽  
Author(s):  
Jiyao Xu ◽  
Wei Yuan ◽  
Kun Wu ◽  
Longchang Sun
Keyword(s):  
Ionospheric Plasma ◽  
Ionospheric Disturbance ◽  
Geomagnetic Latitude ◽  
Extreme Weather Events ◽  
Plasma Bubble ◽  
Low Latitude ◽  
Plasma Irregularities ◽  
Middle Latitudes ◽  
Weather Events ◽  
New Phenomena

<p>China, from north to south, spans from the middle latitudes to the low latitude both in geographic latitude and geomagnetic latitude. And China has a variety of topography environment, which including high lands, plains, seas, and long coasts. To better understand topographic and latitudinal effects on the mesosphere and thermosphere and features of ionospheric plasma irregularities at various latitudes in China, we have established a ground-based airglow network in China gradually since 2010, which consists of 16 stations. This network almost cover China, which focuses on two airglow layers: the OI (~250 km) and OH (~87 km) airglow layers. The observations from OI airglow layers provide convenience to systematically investigate the morphologic feature and evolution of ionospheric plasma irregularities over China. Based on the airglow network observations, we mainly report some important research results of ionospheric plasma irregularities in recent years. These findings include (1) statistical characteristic of equatorial plasma bubble (EPB) over China, (2) the influences of severe extreme weather events on the ionosphere, (3) interaction between medium-scale traveling ionospheric disturbance (MSTIDs) and ionospheric irregularity, and (4) some new phenomena of ionospheric irregularities.</p>

scholarly journals Comparison of the magnetic equivalent convection direction and ionospheric convection observed by the SuperDARN radars

2006 ◽  
Vol 24 (11) ◽  
pp. 2981-2990 ◽  
Author(s):  
L. V. Benkevitch ◽  
A. V. Koustov ◽  
J. Liang ◽  
J. F. Watermann
Keyword(s):  
Local Time ◽  
High Latitude ◽  
Early Morning ◽  
Auroral Oval ◽  
Magnetic Local Time ◽  
Ionospheric Convection ◽  
Morning Sector ◽  
Magnetometer Data ◽  
Different Seasons

Abstract. SuperDARN radar and high-latitude magnetometer observations are used to statistically investigate quality of the convection direction estimates from magnetometer data if assumption is made that the magnetic equivalent convection vector (MEC) corresponds to the convection direction. The statistics includes five full days, ~75 000 of joint individual measurements for different seasons. It is demonstrated that the best (worst) agreement between the MEC and ionospheric convection occurs for the sunlit, summer (dark, winter) ionosphere. Overall, the MEC direction is reasonable (deviates less than 45° from the SuperDARN direction) in at least ~55% of points and it is better for the latitudes of the auroral oval. In terms of the magnetic local time, the agreement is the best (worst) in the dusk (early morning) sector. Possible reasons for differences between the MEC and ionospheric convection directions are discussed.

The peak frequency source of Saturn’s Kilometric Radiation

2020 ◽  
Author(s):  
Laurent Lamy
Keyword(s):  
Local Time ◽  
Outer Part ◽  
Low Frequency ◽  
Peak Frequency ◽  
Auroral Oval ◽  
Relativistic Electrons ◽  
Survey Analysis ◽  
Nonthermal Radio Emission ◽  
F Ring ◽  
Electron Gyrofrequency

<p>Before to ultimately plunge into Saturn’s atmosphere, the Cassini spacecraft explored between 2016 and 2017 the auroral regions of Saturn’s magnetosphere, where rises the Saturn’s Kilometric Radiation (SKR). This powerful, nonthermal, radio emission analog to Earth’s Auroral Kilometric Radiation, is radiated through the Cyclotron Maser Instability (CMI) by mildly relativistic electrons at frequencies close to the local electron gyrofrequency. The typical SKR spectrum, which ranges from a few kHz to ~1MHz, thus corresponds to auroral magnetic flux tubes populated by radiosources at altitudes ranging from ~4 kronian radii (Rs) down to the planetary ionosphere.<span class="Apple-converted-space">  </span>During the F-ring orbital sequence, Cassini probed the outer part of both northern and southern auroral regions, ranging from ~2.5 to ~4 Rs altitudes, and crossed several SKR low frequency sources (~10-30 kHz). Their analysis showed that the radiosources strongly vary with time and local time, with the lowest frequencies reached on the dawn sector. They were additionally colocated with the UV auroral oval and controlled by local time-variable magnetospheric electron densities, with importants consequences for the use SKR low frequency extensions as a proxy of magnetospheric dynamics. Along the proximal orbits, Cassini then explored auroral altitudes below ~2.5 Rs and crossed numerous, deeper, SKR sources at frequencies close to, or within the emission peak frequency (~80-200 kHz). Here, we present preliminary results of their survey analysis. Understanding how the CMI operates in the widely different environments of solar system magnetized planets has direct implications for the ongoing search of radio emissions from exoplanets, ultracool dwarves or stars.</p>

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