Local Time Asymmetries in Jupiter's Magnetodisc Currents Lorch, C. T. S.; Ray, L. C.; Arridge, C. S. ...
Journal of geophysical research. Space physics,
February 2020, 2020-02-00, 20200201, Letnik:
125, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present an investigation into the currents within the Jovian magnetodisc using all available spacecraft magnetometer data up until 28 July 2018. Using automated data analysis processes as well as ...the most recent intrinsic field and current disk geometry models, a full local time coverage of the magnetodisc currents using 7,382 lobe traversals over 39 years is constructed. Our study demonstrates clear local time asymmetries in both the radial and azimuthal height‐integrated current densities throughout the current disk. Asymmetries persist within 30 R
J where most models assume axisymmetry. Inward radial currents are found in the previously unmapped dusk and noon sectors. Azimuthal currents are found to be weaker in the dayside magnetosphere than the nightside, in agreement with global magnetohydrodynamic simulations. The divergence of the azimuthal and radial currents indicates that downward field‐aligned currents exist within the outer dayside magnetosphere. The presence of azimuthal currents is shown to highly influence the location of the field‐aligned currents, which emphasizes the importance of the azimuthal currents in future magnetosphere‐ionosphere coupling models. Integrating the divergence of the height‐integrated current densities, we find that 1.87 MA R
J−2 of return current density required for system closure is absent.
Key Points
Radial and azimuthal current densities exhibit local time asymmetries throughout the current disk
Radial currents flow planetward in noon‐dusk sectors and azimuthal currents are weakest through noon
Downward field‐aligned currents are identified in the noon‐dusk magnetosphere
Using a combination of Juno magnetometer and plasma data, we show evidence of Alfvénic turbulence within the mid‐to‐high latitude magnetosphere with sufficient conditions to trigger auroral particle ...acceleration. We analyze 12 events that, in agreement with theoretical results, are found to be dissipative at the electron inertial scale. Furthermore, these events contain significant Poynting flux in the range ∼0.8–20 mW/m2 at ionospheric altitudes. This is sufficient to generate auroral emissions. We confirm that such events are incompressible, confirming their Alfvénicity, occur at dissipative scales, have intermittent features present and are multifractal in nature. These results illustrate the importance of turbulence in the mid‐to‐high latitudes of Jupiter's magnetosphere as a driver of particle acceleration.
Plain Language Summary
Jupiter's aurora is the most powerful in the solar system. Electrons entering the upper atmosphere create these auroral displays, which were originally thought to be generated through a similar mechanism to those at Earth, via semi‐stationary electric fields aligned with the magnetic field close to the planet. However the Juno spacecraft in orbit around Jupiter, found much less instances of inverted V electron precipitation (driven by quasi‐static potential drops) than expected, therefore other mechanisms are needed along the magnetic field to provide electrons with the necessary energy to enter the planetary atmosphere. Before Juno it was not possible to gather in situ data in these regions. In this paper, we use Juno data to look in these regions for possible acceleration mechanisms and find that turbulence in the magnetic field has the potential to supply the required energy for auroral particle excitation. These results illustrate the importance of magnetic turbulence in Jupiter's space environment.
Key Points
New observations of Alfvénic activity in mid‐high latitude regions of Jupiter's magnetosphere
Events are turbulent in nature and are energy dissipative at the electron inertial scale
Calculated Poynting flux of turbulent perturbations is sufficient to drive auroral emissions
Ionospheric outflow is the flow of plasma initiated by a loss of equilibrium along a magnetic field line, which induces an ambipolar electric field due to the separation of electrons and ions in a ...gravitational field and other mass‐dependent sources. We have developed an ionospheric outflow model using the transport equations to determine the number of particles that flow into the outer magnetosphere of Jupiter. The model ranges from 1,400 km in altitude above the 1 bar level to 2.5 RJ along the magnetic field line and considers H+ and
H3+ as the main ion constituents. Previously, only pressure gradients and gravitational forces were considered in modeling polar wind. However, at Jupiter we need to evaluate the effect of field‐aligned currents present in the auroral regions due to the breakdown of corotation in the magnetosphere, along with the centrifugal force exerted on the particles due to the fast planetary rotation rate. The total number flux from both hemispheres is found to be 1.3–1.8 × 1028 s−1 comparable in total number flux to the Io plasma source. The mass flux is lower due to the difference in ion species. This influx of protons from the ionosphere into the inner and middle magnetosphere needs to be included in future assessments of global flux tube dynamics and composition of the magnetosphere system.
Key Points
An ionospheric outflow model is developed for use at Jupiter's auroral regions
The model evaluates the effect of field‐aligned currents and centrifugal forces
A total number flux of 1.3 – 1.8 × 1028 s−1 is found, which is comparable to number flux from Io
Why is the H3+ hot spot above Jupiter's Great Red Spot so hot? Ray, L C; Lorch, C T S; O'Donoghue, J ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
09/2019, Letnik:
377, Številka:
2154
Journal Article
Recenzirano
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Recent observations of Jupiter's Great Red Spot indicate that the thermosphere above the storm is hotter than its surroundings by more than 700 K. Possible suggested sources for this heating have ...thus far included atmospheric gravity waves and lightning-driven acoustic waves. Here, we propose that Joule heating, driven by Great Red Spot vorticity penetrating up into the lower stratosphere and coupling to the thermosphere, may contribute to the large observed temperatures. The strength of Joule heating will depend on the local inclination angle of the magnetic field and thus the observed emissions and inferred temperatures should vary with planetary longitude as the Great Red Spot tracks across the planet.
This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H
3
+
, H
5
+
and beyond’.
Ionospheric outflow is driven by an ambipolar electric field induced due to the separation of electrons and ions in a gravitational field when equilibrium along a magnetic field line is lost. A model ...of ionospheric outflow at Saturn was developed using transport equations to estimate the number of charged particles that flow from the auroral regions into the magnetosphere. The model evaluates the outflow from 1,400 km in altitude above the 1 bar level, to 3 RS along the field line. The main ion constituents evaluated are R+ and
R3+. We consider the centrifugal force exerted on the particles due to a fast rotation rate, along with the effects of field‐aligned currents present in the auroral regions. The total number flux from both auroral regions is found to be 5.5–13.0×1027 s−1, which relates to a total mass source of 5.5–17.7 kg s−1. These values are on average an order of magnitude higher than expected without the additional effects of centrifugal force and field‐aligned currents. We find the ionospheric outflow rate to be comparable to the lower estimates of the mass loading rate from Enceladus and are in agreement with recent Cassini observations. This additional mass flux into the magnetosphere can substantially affect the dynamics and composition of the inner and middle magnetosphere of Saturn.
Key Points
An ionospheric outflow model is developed for use at Saturn's auroral regions
The presence of field‐aligned currents and centrifugal forces enhances outflow by an order of magnitude
Predicted total outflow flux rate of 5.5–13.0×1027 s−1 is comparable to flux calculated from Cassini data
Why is the H 3 + hot spot above Jupiter's Great Red Spot so hot? Ray, L C; Lorch, C T S; O'Donoghue, J ...
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
2019-Sep-23, 2019-09-23, Letnik:
377, Številka:
2154
Journal Article
Recenzirano
Odprti dostop
Recent observations of Jupiter's Great Red Spot indicate that the thermosphere above the storm is hotter than its surroundings by more than 700 K. Possible suggested sources for this heating have ...thus far included atmospheric gravity waves and lightning-driven acoustic waves. Here, we propose that Joule heating, driven by Great Red Spot vorticity penetrating up into the lower stratosphere and coupling to the thermosphere, may contribute to the large observed temperatures. The strength of Joule heating will depend on the local inclination angle of the magnetic field and thus the observed emissions and inferred temperatures should vary with planetary longitude as the Great Red Spot tracks across the planet. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H
, H
and beyond'.
The COVID-19 pandemic highlights the substantial public health, economic, and societal consequences of virus spillover from a wildlife reservoir. Widespread human transmission of severe acute ...respiratory syndrome coronavirus 2 (SARS-CoV-2) also presents a new set of challenges when considering viral spillover from people to naïve wildlife and other animal populations. The establishment of new wildlife reservoirs for SARS-CoV-2 would further complicate public health control measures and could lead to wildlife health and conservation impacts. Given the likely bat origin of SARS-CoV-2 and related beta-coronaviruses (β-CoVs), free-ranging bats are a key group of concern for spillover from humans back to wildlife. Here, we review the diversity and natural host range of β-CoVs in bats and examine the risk of humans inadvertently infecting free-ranging bats with SARS-CoV-2. Our review of the global distribution and host range of β-CoV evolutionary lineages suggests that 40+ species of temperate-zone North American bats could be immunologically naïve and susceptible to infection by SARS-CoV-2. We highlight an urgent need to proactively connect the wellbeing of human and wildlife health during the current pandemic and to implement new tools to continue wildlife research while avoiding potentially severe health and conservation impacts of SARS-CoV-2 "spilling back" into free-ranging bat populations.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Energetic Particle Signatures Above Saturn's Aurorae Bader, A.; Badman, S. V.; Ray, L. C. ...
Journal of geophysical research. Space physics,
January 2020, 2020-01-00, 2020, Letnik:
125, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Near the end of its mission, NASA's Cassini spacecraft performed several low‐altitude passes across Saturn's auroral region. We present ultraviolet auroral imagery and various coincident particle and ...field measurements of two such passes, providing important information about the structure and dynamics of Saturn's auroral acceleration region. In upward field‐aligned current regions, upward proton beams are observed to reach energies of several tens of keV; the associated precipitating electron populations are found to have mean energies of about 10 keV. With no significant wave activity being apparent, these findings indicate strong parallel potentials responsible for auroral acceleration, about 100 times stronger than at Earth. This is further supported by observations of proton conics in downward field‐aligned current regions above the acceleration region, which feature a lower energy cutoff above
∼50 keV—indicating energetic proton populations trapped by strong parallel potentials while being transversely energized until they can overcome the trapping potential, likely through wave‐particle interactions. A spacecraft pass through a downward current region at an altitude near the acceleration region reveals plasma wave features, which may be driving the transverse proton acceleration generating the conics. Overall, the signatures observed resemble those related to the terrestrial and Jovian aurorae, the particle energies and potentials at Saturn appearing to be significantly higher than at Earth and comparable to those at Jupiter.
Plain Language Summary
NASA's Cassini spacecraft orbited closer to Saturn than ever before during the last stage of its mission, the “Grand Finale”. This allowed the onboard instruments to measure charged particles and plasma waves directly above the auroral region while simultaneously providing high‐resolution imagery of the ultraviolet aurorae. Based on observations of highly energetic ions streaming away from the planet in regions of low plasma wave activity, we infer the existence of strong electric fields which act to accelerate electrons down into the atmosphere, driving the bright auroral emissions. Our estimates of the average energy of the precipitating electrons support this finding. Charged ions sometimes seem to be energized by plasma waves above the aurorae before they can escape, but the exact process in which this happens is not fully understood. Most signatures presented here resemble those observed in relation to Earth's aurorae, suggesting that the mechanisms acting at both planets are quite similar although Saturn's acceleration mechanism is significantly stronger.
Key Points
Low‐altitude orbits of Cassini reveal energetic proton and related plasma wave signatures within/above Saturn's auroral acceleration region
Observations of proton conics in downward current regions indicate strong parallel electric potentials and transverse heating
Observed energies are much higher at Saturn than above the terrestrial aurorae, but the acceleration mechanisms may be of a similar nature
Why is the H 3 + hot spot above Jupiter’s Great Red Spot so hot? Ray, L. C.; Lorch, C. T. S.; O’Donoghue, J. ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
09/2019, Letnik:
377, Številka:
2154
Journal Article
Recenzirano
Recent observations of Jupiter’s Great Red Spot indicate that the thermosphere above the storm is hotter than its surroundings by more than 700 K. Possible suggested sources for this heating have ...thus far included atmospheric gravity waves and lightning-driven acoustic waves. Here, we propose that Joule heating, driven by Great Red Spot vorticity penetrating up into the lower stratosphere and coupling to the thermosphere, may contribute to the large observed temperatures. The strength of Joule heating will depend on the local inclination angle of the magnetic field and thus the observed emissions and inferred temperatures should vary with planetary longitude as the Great Red Spot tracks across the planet.
This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions:
H
3
+
,
H
5
+
and beyond’.
Desde 2007, se produjeron dos rondas de picos de los precios de los alimentos que han contribuido a que al hambre y la malnutrición de millones de personas. Los mismos factores que contribuyeron a la ...crisis de los precios de los alimentos de 2007-08 dispararon picos de precios similares en 2011; entre tales factores se incluyen la caída de la tasa de crecimiento agrícola, los altos precios de la energía que impulsan la expansión de la producción de biocombustibles, la depreciación del dólar estadounidense, una fuerte demanda de productos agrícolas por parte de las economías emergentes, y las crisis climáticas. Dada esta combinación de fuerzas complejas, resulta claro que las políticas alimentarias necesarias para garantizar que todas las personas tengan acceso a alimentos sanos, suficientes, nutritivos y cultivados de manera sostenible deben ir más allá de la producción agrícola tradicional. Por consiguiente, no resulta sorprendente que la demanda de investigación capaz de fundamentar con datos empíricos dichas políticas sea más alta que nunca, y el Instituto internacional de investigación sobre políticas alimentarias (IFPRI) produce bienes públicos mundiales para responder a esa necesidad.
DGO; EPTD; MTID; DSGD; PHND; COM
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