224 research outputs found
The ionospheric outflow feedback loop
AbstractFollowing a long period of observation and investigation beginning in the early 1970s, it has been firmly established that Earth׳s magnetosphere is defined as much by the geogenic plasma within it as by the geomagnetic field. This plasma is not confined to the ionosphere proper, defined as the region within a few density scale heights of the F-region plasma density peak. Rather, it fills the flux tubes on which it is created, and circulates throughout the magnetosphere in a pattern driven by solar wind plasma that becomes magnetically connected to the ionosphere by reconnection through the dayside magnetopause. Under certain solar wind conditions, plasma and field energy is stored in the magnetotail rather than being smoothly recirculated back to the dayside. Its release into the downstream solar wind is produced by magnetotail disconnection of stored plasma and fields both continuously and in the form of discrete plasmoids, with associated generation of energetic Earthward-moving bursty bulk flows and injection fronts. A new generation of global circulation models is showing us that outflowing ionospheric plasmas, especially O+, load the system in a different way than the resistive F-region load of currents dissipating energy in the plasma and atmospheric neutral gas. The extended ionospheric load is reactive to the primary dissipation, forming a time-delayed feedback loop within the system. That sets up or intensifies bursty transient behaviors that would be weaker or absent if the ionosphere did not “strike back” when stimulated. Understanding this response appears to be a necessary, if not sufficient, condition for us to gain accurate predictive capability for space weather. However, full predictive understanding of outflow and incorporation into global simulations requires a clear observational and theoretical identification of the causal mechanisms of the outflows. This remains elusive and requires a dedicated mission effort
The Challenges and Rewards of Running a Geospace Environment Modeling Challenge
Geospace Environment Modeling (GEM) is a community-driven, National Science Foundation-sponsored research program investigating the physics of the Earth's magnetosphere and its coupling to the solar wind and the atmosphere. This commentary provides an introduction to a Special Issue collating recent studies related to a GEM Challenge on kinetic plasma processes in the dayside magnetosphere during southward interplanetary magnetic field conditions. We also recount our experiences of organizing such a collaborative activity, where modelers and observers compare their results, that is, of the human side of bringing researchers together. We give suggestions on planning, managing, funding, and documenting these activities, which provide valuable opportunities to advance the field.Plain Language Summary Geospace Environment Modeling (GEM) is a community-driven, National Science Foundation-sponsored research program investigating the physics of the Earth's magnetosphere and its coupling to the solar wind and the atmosphere. An integral part of the program is the so-called "Challenges", which bring people together to compare models and observations in order to advance our understanding of the near-Earth space environment. This commentary provides an introduction to a Special Issue collating recent studies related to one such collaborative effort. We also share our experiences as early-career scientists organizing such an activity, to aid those who might take part in such endeavors in the future. We give suggestions on planning, managing, funding, and documenting the activities
Hydrodynamic Simulations for the Nuclear Morphology of NGC 4314
We performed SPH simulations to study the nuclear morphology of a barred
galaxy NGC 4314. We have constructed the mass models based on the results of a
profile decomposition into disk, bulge, and bar components. Our models have
three different nuclear structures according to the assumption about the
nuclear bar: no nuclear bar, a synchronous nuclear bar and a fast nuclear bar.
Our SPH simulations show that the morphology of the nuclear region of NGC 4314
which is characterized by an elongated ring/spiral of newly formed stars and
HII regions, aligned nearly parallel to the primary bar can be understood in
terms of the secular evolution driven by the non-axisymmetric potential. The
slightly elongated and aligned nuclear ring of NGC 4314 can be formed by the
strong barred potential and the moderate central concentration of the bulge
mass with and without a nuclear bar. However, the nuclear spiral pattern can
not be developed without a nuclear bar. The nuclear bar of NGC 4314 seems to
rotate faster than the primary bar since the nuclear morphology induced by the
synchronous nuclear bar is much different from the observed one.Comment: 9 page
Impact of Space Weather on Climate and Habitability of Terrestrial Type Exoplanets
The current progress in the detection of terrestrial type exoplanets has
opened a new avenue in the characterization of exoplanetary atmospheres and in
the search for biosignatures of life with the upcoming ground-based and space
missions. To specify the conditions favorable for the origin, development and
sustainment of life as we know it in other worlds, we need to understand the
nature of astrospheric, atmospheric and surface environments of exoplanets in
habitable zones around G-K-M dwarfs including our young Sun. Global environment
is formed by propagated disturbances from the planet-hosting stars in the form
of stellar flares, coronal mass ejections, energetic particles, and winds
collectively known as astrospheric space weather. Its characterization will
help in understanding how an exoplanetary ecosystem interacts with its host
star, as well as in the specification of the physical, chemical and biochemical
conditions that can create favorable and/or detrimental conditions for
planetary climate and habitability along with evolution of planetary internal
dynamics over geological timescales. A key linkage of (astro) physical,
chemical, and geological processes can only be understood in the framework of
interdisciplinary studies with the incorporation of progress in heliophysics,
astrophysics, planetary and Earth sciences. The assessment of the impacts of
host stars on the climate and habitability of terrestrial (exo)planets will
significantly expand the current definition of the habitable zone to the
biogenic zone and provide new observational strategies for searching for
signatures of life. The major goal of this paper is to describe and discuss the
current status and recent progress in this interdisciplinary field and to
provide a new roadmap for the future development of the emerging field of
exoplanetary science and astrobiology.Comment: 206 pages, 24 figures, 1 table; Review paper. International Journal
of Astrobiology (2019
Universal Vectorial and Ultrasensitive Nanomechanical Force Field Sensor
Miniaturization of force probes into nanomechanical oscillators enables
ultrasensitive investigations of forces on dimensions smaller than their
characteristic length scale. Meanwhile it also unravels the force field
vectorial character and how its topology impacts the measurement. Here we
expose an ultrasensitive method to image 2D vectorial force fields by
optomechanically following the bidimensional Brownian motion of a singly
clamped nanowire. This novel approach relies on angular and spectral tomography
of its quasi frequency-degenerated transverse mechanical polarizations:
immersing the nanoresonator in a vectorial force field does not only shift its
eigenfrequencies but also rotate eigenmodes orientation as a nano-compass. This
universal method is employed to map a tunable electrostatic force field whose
spatial gradients can even take precedence over the intrinsic nanowire
properties. Enabling vectorial force fields imaging with demonstrated
sensitivities of attonewton variations over the nanoprobe Brownian trajectory
will have strong impact on scientific exploration at the nanoscale
Cultivating a Culture of Inclusivity in Heliophysics
A large number of heliophysicists from across career levels, institution types, and job titles came together to support a poster at Heliophysics 2050 and the position papers for the 2024 Heliophysics decadal survey titled “Cultivating a Culture of Inclusivity in Heliophysics,” “The Importance of Policies: It’s not just a pipeline problem,” and “Mentorship within Heliophysics.” While writing these position papers, the number of people who privately shared disturbing stories and experiences of bullying and harassment was shocking. The number of people who privately expressed how burned out they were was staggering. The number of people who privately spoke about how they considered leaving the field for their and their family’s health was astounding. And for as much good there is in our community, it is still a toxic environment for many. If we fail to do something now, our field will continue to suffer. While acknowledging the ongoing growth that we as individuals must work toward, we call on our colleagues to join us in working on organizational, group, and personal levels toward a truly inclusive culture, for the wellbeing of our colleagues and the success of our field. This work includes policies, processes, and commitments to promote: accountability for bad actors; financial security through removing the constant anxiety about funding; prioritization of mental health and community through removing constant deadlines and constant last-minute requests; a collaborative culture rather than a hyper-competitive one; and a community where people can thrive as whole persons and do not have to give up a healthy or well-rounded life to succeed
Atmospheric Escape Processes and Planetary Atmospheric Evolution
The habitability of the surface of any planet is determined by a complex
evolution of its interior, surface, and atmosphere. The electromagnetic and
particle radiation of stars drive thermal, chemical and physical alteration of
planetary atmospheres, including escape. Many known extrasolar planets
experience vastly different stellar environments than those in our Solar
system: it is crucial to understand the broad range of processes that lead to
atmospheric escape and evolution under a wide range of conditions if we are to
assess the habitability of worlds around other stars. One problem encountered
between the planetary and the astrophysics communities is a lack of common
language for describing escape processes. Each community has customary
approximations that may be questioned by the other, such as the hypothesis of
H-dominated thermosphere for astrophysicists, or the Sun-like nature of the
stars for planetary scientists. Since exoplanets are becoming one of the main
targets for the detection of life, a common set of definitions and hypotheses
are required. We review the different escape mechanisms proposed for the
evolution of planetary and exoplanetary atmospheres. We propose a common
definition for the different escape mechanisms, and we show the important
parameters to take into account when evaluating the escape at a planet in time.
We show that the paradigm of the magnetic field as an atmospheric shield should
be changed and that recent work on the history of Xenon in Earth's atmosphere
gives an elegant explanation to its enrichment in heavier isotopes: the
so-called Xenon paradox
Activation of NF-kB Pathway by Virus Infection Requires Rb Expression
The retinoblastoma protein Rb is a tumor suppressor involved in cell cycle control, differentiation, and inhibition of oncogenic transformation. Besides these roles, additional functions in the control of immune response have been suggested. In the present study we investigated the consequences of loss of Rb in viral infection. Here we show that virus replication is increased by the absence of Rb, and that Rb is required for the activation of the NF-kB pathway in response to virus infection. These results reveal a novel role for tumor suppressor Rb in viral infection surveillance and further extend the concept of a link between tumor suppressors and antiviral activity
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