scholarly journals Source mechanism of Saturn narrowband emission

2010 ◽  
Vol 28 (4) ◽  
pp. 1013-1021 ◽  
Author(s):  
J. D. Menietti ◽  
P. H. Yoon ◽  
B. Cecconi ◽  
A. M. Rymer ◽  
Keyword(s):  
Cyclotron Frequency ◽  
Mode Conversion ◽  
Source Region ◽  
Source Mechanism ◽  
Inner Magnetosphere ◽  
Rate Analysis ◽  
Source Regions ◽  
Cyclotron Maser ◽  
Hybrid Frequency

Abstract. Narrowband emission (NB) is observed at Saturn centered near 5 kHz and 20 kHz and harmonics. This emission appears similar in many ways to Jovian kilometric narrowband emission observed at higher frequencies, and therefore may have a similar source mechanism. Source regions of NB near 20 kHz are believed to be located near density gradients in the inner magnetosphere and the emission appears to be correlated with the occurrence of large neutral plasma clouds observed in the Saturn magnetotail. In this work we present the results of a growth rate analysis of NB emission (~20 kHz) near or within a probable source region. This is made possible by the sampling of in-situ wave and particle data. The results indicate waves are likely to be generated by the mode-conversion of directly generated Z-mode emission to O-mode near a density gradient. When the local hybrid frequency is close n fce (n is an integer and fce is the electron cyclotron frequency) with n=4, 5 or 6 in our case, electromagnetic Z-mode and weak ordinary (O-mode) emission can be directly generated by the cyclotron maser instability.

scholarly journals The low-frequency source of Saturn’s kilometric radiation

Science ◽  
2018 ◽  
Vol 362 (6410) ◽  
pp. eaat2027 ◽  
Author(s):  
L. Lamy ◽  
P. Zarka ◽  
B. Cecconi ◽  
R. Prangé ◽  
W. S. Kurth ◽  
...  
Keyword(s):  
Source Region ◽  
Low Frequency ◽  
Auroral Oval ◽  
Emission Region ◽  
Radio Emissions ◽  
Cyclotron Maser ◽  
Frequency Source ◽  
Field Lines ◽  
Plasma Measurements

Understanding how auroral radio emissions are produced by magnetized bodies requires in situ measurements within their source region. Saturn’s kilometric radiation (SKR) has been widely used as a remote proxy of Saturn’s magnetosphere. We present wave and plasma measurements from the Cassini spacecraft during its ring-grazing high-inclination orbits, which passed three times through the high-altitude SKR emission region. Northern dawn-side, narrow-banded radio sources were encountered at frequencies of 10 to 20 kilohertz, within regions of upward currents mapping to the ultraviolet auroral oval. The kilometric waves were produced on the extraordinary mode by the cyclotron maser instability from 6– to 12–kilo–electron volt electron beams and radiated quasi-perpendicularly to the auroral magnetic field lines. The SKR low-frequency sources appear to be strongly controlled by time-variable magnetospheric electron densities.

scholarly journals Directly comparing coronal and solar wind elemental fractionation

2020 ◽  
Vol 640 ◽  
pp. A28
Author(s):  
D. Stansby ◽  
D. Baker ◽  
D. H. Brooks ◽  
C. J. Owen
Keyword(s):  
Solar Wind ◽  
Extreme Ultraviolet ◽  
Source Region ◽  
Imaging Spectrometer ◽  
Elemental Fractionation ◽  
Source Regions ◽  
Individual Source ◽  
Wind Source ◽  
Solar Wind Composition

Context. As the solar wind propagates through the heliosphere, dynamical processes irreversibly erase the signatures of the near–Sun heating and acceleration processes. The elemental fractionation of the solar wind should not change during transit, however, making it an ideal tracer of these processes. Aims. We aim to verify directly if the solar wind elemental fractionation is reflective of the coronal source region fractionation, both within and across different solar wind source regions. Methods. A backmapping scheme was used to predict where solar wind measured by the Advanced Composition Explorer (ACE) originated in the corona. The coronal composition measured by the Hinode Extreme ultraviolet Imaging Spectrometer (EIS) at the source regions was then compared with the in situ solar wind composition. Results. On hourly timescales, there is no apparent correlation between coronal and solar wind composition. In contrast, the distribution of fractionation values within individual source regions is similar in both the corona and solar wind, but distributions between different sources have a significant overlap. Conclusions. The matching distributions directly verify that elemental composition is conserved as the plasma travels from the corona to the solar wind, further validating it as a tracer of heating and acceleration processes. The overlap of fractionation values between sources means it is not possible to identify solar wind source regions solely by comparing solar wind and coronal composition measurements, but a comparison can be used to verify consistency with predicted spacecraft-corona connections.

scholarly journals Inferring the source regions of pulsating auroras

2020 ◽  
Author(s):  
Eric Grono ◽  
Eric Donovan
Keyword(s):  
Remote Sensing ◽  
Large Scale ◽  
Source Region ◽  
In Situ Measurements ◽  
Source Regions ◽  
Morning Sector ◽  
Essential Tool

Abstract. The aurora is an essential tool for remote sensing the large-scale dynamics of the magnetosphere which are to difficult to observe in situ and impossible to recreate in a lab. Despite pulsating aurora being a common and widespread morning-sector phenomenon, the processes responsible for its differentiation are not understood. In situ measurements of the pulsating aurora source regions are difficult to associate with specific auroral features, yet such observations will be necessary for identifying the unique causes of pulsating auroras. This study reports a method of inferring when a spacecraft is passing through the source region of patchy aurora (PA) based on the structuring of chorus. The locations of longer-lived chorus packets are found to correspond to the region of PA occurrence reported by Grono et al. (2019b). This result constrains the region where the structuring mechanisms and conditions responsible for PA and patchy pulsating aurora (PPA) can exist.

Compositional in situ analysis of dusty material stemming from Saturn’s main rings

2021 ◽  
Author(s):  
Simon Linti ◽  
Jon Hillier ◽  
Christian Fischer ◽  
Hsiang-Wen Hsu ◽  
Mario Trieloff ◽  
...  
Keyword(s):  
Interstellar Dust ◽  
Impact Ionization ◽  
Source Region ◽  
Relative Sensitivity ◽  
Cosmic Dust ◽  
Dust Grains ◽  
Element Ratios ◽  
Sensitivity Factors ◽  
Compositional Diversity

<p>During the final mission phase, the Cassini spacecraft travelled through the gap between Saturn and its innermost D ring. One goal of these highly inclined orbits was sampling the dust population, mostly made of impact ejecta from the main rings, in the vicinity of the planet. These in situ measurements were primarily carried out by the Cosmic Dust Analyzer (CDA) onboard the spacecraft, which provided time-of-flight mass spectra of individual ice and dust grains, mostly between about 10 and 50 nm in size. Here we present an update on the composition of the silicate dust fraction stemming from Saturn’s main rings, which makes up about 30 % of the observed particles with water ice being the remaining fraction [1].</p> <p>Elemental analysis of the silicate spectra was performed using an updated deconvolution method, based on a technique originally applied to the interpretation of CDA interstellar dust measurements [2]. Neighboring spectral peaks due to mineral-forming ions such as Mg<sup>+</sup>, Al<sup>+</sup> and Si<sup>+</sup> are often unresolvable, because of CDA’s relatively low (m/dm = 20–50) mass resolution [3]. Therefore, application of a deconvolution technique is required to disentangle the peak interferences and derive valuable compositional information. The robustness of the applied method has been tested and optimized through comparison with an independent automated fit algorithm. In order to calculate elemental abundances within the particles, the derived ion abundances were combined with experimentally-determined relative sensitivity factors (RSFs) [4]. To provide context to the measured element ratios, we compared them with a variety of space-relevant materials. We find an overlap with chondritic material for Mg/Si and Fe/Mg ratios. The observed range within the element ratios, however, indicates the contribution of a variety of minerals such as olivine, plagioclase or pyroxenes. Although our results agree with realistic mineral compositions, the calculated abundances of Al<sup>+</sup> ions are still relatively uncertain and can be seen as an upper limit.</p> <p>Additionally, we present the results of a dynamical model, which allow us to derive the likely source region within the main rings of individually detected silicate grains. We find the C and B rings to be the most likely sources of the vast majority of grains with the D ring being only a minor source. Currently an analysis of compositional diversity between the different ring segments is under way.</p> <p> </p> <p><strong>References</strong></p> <p>[1] H.-W. Hsu et al. (2018) In situ collection of dust grains falling from Saturn’s rings into its atmosphere. Science 362.</p> <p>[2] N. Altobelli et al. (2016) Flux and composition of interstellar dust at Saturn from Cassini’s Cosmic Dust Analyzer. Science 352, 312–318.</p> <p>[3] R. Srama et al. (2004) The Cassini Cosmic Dust Analyzer. Space Science Reviews 114, 465–518.</p> <p>[4] K. Fiege et al. (2014) Calibration of relative sensitivity factors for impact ionization detectors with high-velocity silicate microparticles. Icarus 241, 336–345.</p>

scholarly journals Melt segregation from partially molten source regions: The importance of melt density and source region size

1981 ◽  
Vol 86 (B7) ◽  
pp. 6261-6271 ◽  
Author(s):  
Edward Stolper ◽  
David Walker ◽  
Bradford H. Hager ◽  
James F. Hays
Keyword(s):  
Source Region ◽  
Source Regions ◽  
Melt Density ◽  
Melt Segregation ◽  
Region Size

scholarly journals Progress on Coronal, Interplanetary, Foreshock, and Outer Heliospheric Radio Emissions

2000 ◽  
Vol 17 (1) ◽  
pp. 22-34 ◽  
Author(s):  
Iver H. Cairns ◽  
P. A. Robinson ◽  
G. P. Zank
Keyword(s):  
Solar Wind ◽  
Plasma Waves ◽  
Recent Theory ◽  
Type Ii ◽  
Solar Radio Bursts ◽  
Radio Emissions ◽  
Source Regions ◽  
Earth’S Bow Shock ◽  
Made In

AbstractType II and III solar radio bursts are associated with shock waves and streams of energetic electrons, respectively, which drive plasma waves and radio emission at multiples of the electron plasma frequency as they move out from the corona into the interplanetary medium. Analogous plasma waves and radiation are observed from the foreshock region upstream of Earth's bow shock. In situ spacecraft observations in the solar wind have enabled major progress to be made in developing quantitative theories for these phenomena that are consistent with available data. Similar processes are believed responsible for radio emissions at 2–3 kHz that originate in the distant heliosphere, from where the solar wind interacts with the local interstellar medium. The primary goal of this paper is to review the observations and theories for these four classes of emissions, focusing on recent progress in developing detailed theories for the plasma waves and radiation in the source regions. The secondary goal is to introduce and review stochastic growth theory, a recent theory which appears quantitatively able to explain the wave observations in type III bursts and Earth's foreshock and is a natural theory to apply to type II bursts, the outer heliospheric emissions, and perhaps astrophysicalemissions.

scholarly journals Annual variation in event-scale precipitation <i>δ</i><sup>2</sup>H at Barrow, AK, reflects vapor source region

2017 ◽  
Vol 17 (7) ◽  
pp. 4627-4639 ◽  
Author(s):  
Annie L. Putman ◽  
Xiahong Feng ◽  
Leslie J. Sonder ◽  
Eric S. Posmentier
Keyword(s):  
Source Region ◽  
Arctic Sea Ice ◽  
Dew Point ◽  
Precipitation Event ◽  
Boolean Variable ◽  
Deuterium Excess ◽  
Vapor Source ◽  
Source Regions ◽  
Circulation Cell ◽  
Transport Path

Abstract. In this study, precipitation isotopic variations at Barrow, AK, USA, are linked to conditions at the moisture source region, along the transport path, and at the precipitation site. Seventy precipitation events between January 2009 and March 2013 were analyzed for δ2H and deuterium excess. For each precipitation event, vapor source regions were identified with the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) air parcel tracking program in back-cast mode. The results show that the vapor source region migrated annually, with the most distal (proximal) and southerly (northerly) vapor source regions occurring during the winter (summer). This may be related to equatorial expansion and poleward contraction of the polar circulation cell and the extent of Arctic sea ice cover. Annual cycles of vapor source region latitude and δ2H in precipitation were in phase; depleted (enriched) δ2H values were associated with winter (summer) and distal (proximal) vapor source regions. Precipitation δ2H responded to variation in vapor source region as reflected by significant correlations between δ2H with the following three parameters: (1) total cooling between lifted condensation level (LCL) and precipitating cloud at Barrow, ΔTcool, (2) meteorological conditions at the evaporation site quantified by 2 m dew point, Td, and (3) whether the vapor transport path crossed the Brooks and/or Alaskan ranges, expressed as a Boolean variable, mtn. These three variables explained 54 % of the variance (p<0. 001) in precipitation δ2H with a sensitivity of −3.51 ± 0.55 ‰ °C−1 (p<0. 001) to ΔTcool, 3.23 ± 0.83 ‰ °C−1 (p<0. 001) to Td, and −32.11 ± 11.04 ‰ (p = 0. 0049) depletion when mtn is true. The magnitude of each effect on isotopic composition also varied with vapor source region proximity. For storms with proximal vapor source regions (where ΔTcool <7 °C), ΔTcool explained 3 % of the variance in δ2H, Td alone accounted for 43 %, while mtn explained 2 %. For storms with distal vapor sources (ΔTcool > 7°C), ΔTcool explained 22 %, Td explained only 1 %, and mtn explained 18 %. The deuterium excess annual cycle lagged by 2–3 months during the δ2H cycle, so the direct correlation between the two variables is weak. Vapor source region relative humidity with respect to the sea surface temperature, hss, explained 34 % of variance in deuterium excess, (−0.395 ± 0.067 ‰ %−1, p<0. 001). The patterns in our data suggest that on an annual scale, isotopic ratios of precipitation at Barrow may respond to changes in the southerly extent of the polar circulation cell, a relationship that may be applicable to interpretation of long-term climate change records like ice cores.

Azimuth estimation capabilities of the ARCESS regional seismic array

1993 ◽  
Vol 83 (4) ◽  
pp. 1213-1231
Author(s):  
Dorthe B. Carr
Keyword(s):  
Time Window ◽  
Source Region ◽  
Event Data ◽  
Small Aperture ◽  
Data Set ◽  
Low Frequencies ◽  
Source Regions ◽  
The Mean ◽  
Local Geology ◽  
Regional Arrays

Abstract The effect of local geology and noise conditions on the performance of a small regional array is investigated by comparing the regional Pn backazimuth estimation capabilities of the ARCESS array in northern Norway to the NORESS array. A broadband frequency-wavenumber estimator was used to calculate backazimuths from the Pn arrival for each of 203 regional events recorded at ARCESS while varying element spacing, frequency band, and time window. Most of the errors in backazimuth are less than 20° when appropriate parameter combinations are used, and mean backazimuth errors are close to zero. The best results are obtained using a 13-element configuration that has a 1.4 km aperture and a maximum station spacing of about 600 m. With the 13-element configuration and the data filtered to include frequencies between 3 and 10 Hz, the mean errors for the 203 event data set are less than 0.9°, and S.D. are as small as 16.9°. There are differences seen in the backazimuth estimation capabilities of ARCESS and NORESS with specific parameter combinations. The larger aperture configurations (10- and 17-elements) have smaller means at ARCESS, although the precision is about the same. The estimates using unfiltered data at ARCESS are poor, because of local noise conditions that increase the level of background noise at low frequencies. Overall the precision is better at NORESS, but both regional arrays have the best results using the 13-element configuration and filtering the data in the middle frequency range (3 to 10 Hz). Other factors investigated include SNR and source region. Backazimuth estimation statistics improve if only events with 5 dB of SNR are included in the data set at both ARCESS and NORESS. The mean errors move closer to zero and standard deviations decrease. The differences between the two arrays are not as pronounced. There are some path effects from different source regions around the ARCESS array. However, combinations of small aperture configurations and middle (3 to 10 Hz) frequency bands work well for events over the entire distance range of 30 to 1200 km. ARCESS and NORESS have similar backazimuth estimation capabilities even though there are differences in the local geology and noise conditions. Because a 13-element configuration produces reliable results for both arrays, it would be reasonable to reduce the number of elements in a regional array. This in turn will reduce the costs associated with building and deploying small regional arrays.

Determine the Physical Mechanism and Source Region of Beat Wave Modulation by Changing the Frequency of HF Waves

2021 ◽  
Author(s):  
Zhe Guo ◽  
Hanxian Fang ◽  
Farideh Honary
Keyword(s):  
Physical Mechanism ◽  
Source Region ◽  
Low Frequency ◽  
Signal Amplitude ◽  
New Approach ◽  
Wave Modulation ◽  
F Region ◽  
Source Regions ◽  
High Modulation ◽  
E Region

Abstract This paper introduces a new approach for the determination of the source region of BW (beat wave) modulation. This type of modulation is achieved by transmitting HF continuous waves with a frequency difference of f, where f is the frequency of modulated ELF/VLF (extremely low frequency/very low frequency) waves from two sub-arrays of a high power HF transmitter. Despite the advantages of BW modulation in terms of generating more stable ELF/VLF signal and high modulation efficiency, there exists a controversy on the physical mechanism of BW and its source region. In this paper, the two controversial theories, i.e. BW based on D-E region thermal nonlinearity and BW based on F region ponderomotive nonlinearity are examined for cases where each of these two theories exists exclusively or both of them exist simultaneously. According to the analysis and the simulation results presented in this paper, it is found that the generated VLF signal amplitude exhibits significant variation as a function of HF frequency in different source regions. Therefore, this characteristic can be utilised as a potential new approach to determine the physical mechanism and source location of BW.

scholarly journals Differentiating between Inherited and Autocrystic Zircon in Granitoids

2020 ◽  
Vol 61 (8) ◽  
Author(s):  
Hugo K H Olierook ◽  
Christopher L Kirkland ◽  
Kristoffer Szilas ◽  
Julie A Hollis ◽  
Nicholas J Gardiner ◽  
...  
Keyword(s):  
Trace Element ◽  
Source Region ◽  
Wall Rock ◽  
Magma Source ◽  
Trace Element Data ◽  
Element Data ◽  
Age Constraints ◽  
Erroneous Interpretation ◽  
Zircon Fraction

Abstract Inherited zircon, crystals that did not form in situ from their host magma but were incorporated from either the source region or assimilated from the wall-rock, is common but can be difficult to identify. Age, chemical and/or textural dissimilarity to the youngest zircon fraction are the primary mechanisms of distinguishing such grains. However, in Zr-undersaturated magmas, the entire zircon population may be inherited and, if not identifiable via textural constraints, can lead to erroneous interpretation of magmatic crystallization age and magma source. Here, we present detailed field mapping of cross-cutting relationships, whole-rock geochemistry and zircon textural, U–Pb and trace element data for trondhjemite, granodiorite and granite from two localities in a complex Archean gneiss terrane in SW Greenland, which reveal cryptic zircon inheritance. Zircon textural, U–Pb and trace element data demonstrate that, in both localities, trondhjemite is the oldest rock (3011 ± 5 Ma, 2σ), which is intruded by granodiorite (2978 ± 4 Ma, 2σ). However, granite intrusions, constrained by cross-cutting relationships as the youngest component, contain only inherited zircon derived from trondhjemite and granodiorite based on ages and trace element concentrations. Without age constraints on the older two lithologies, it would be tempting to consider the youngest zircon fraction as recording crystallization of the granite but this would be erroneous. Furthermore, whole-rock geochemistry indicates that the granite contains only 6 µg g–1 Zr, extremely low for a granitoid with ∼77 wt% SiO2. Such low Zr concentration explains the lack of autocrystic zircon in the granite. We expand on a differentiation tool that uses Th/U ratios in zircon versus that in the whole-rock to aid in the identification of inherited zircon. This work emphasizes the need for field observations, geochemistry, grain characterization, and precise geochronology to accurately determine igneous crystallization ages and differentiate between inherited and autocrystic zircon.

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