100 research outputs found
Scatter-free pickup ions beyond the heliopause as a model for the Interstellar Boundary Explorer (IBEX) ribbon
We present new kinetic-gasdynamic model of the solar wind interaction with
the local interstellar medium. The model incorporates several processes
suggested by McComas et al. (2009) for the origin of the heliospheric ENA
ribbon -- the most prominent feature seen in the all sky maps of heliospheric
ENAs discovered by the Interstellar Boundary Explorer (IBEX). The ribbon is a
region of enhanced fluxes of ENAs crossing almost the entire sky. Soon after
the ribbon's discovery it was realized (McComas et al., 2009) that the
enhancement of the fluxes could be in the directions where the radial component
of the interstellar magnetic field around the heliopause is close to zero
(Schwadron et al., 2009). Our model includes secondary charge exchange of the
interstellar H atoms with the interstellar pickup protons outside the
heliopause and is a further advancement of the kinetic-gasdynamic model by
Malama et al. (2006) where pickup protons were treated as a separate kinetic
component. Izmodenov et al. (2009) have shown in the frame of Malama's model
that the interstellar pickup protons outside the heliopause maybe a significant
source of ENAs at energies above 1 keV. The difference between the current work
and that of Izmodenov et al. (2009) is in the assumption of no-scattering for
newly created pickup protons outside the heliopause. In this limit the model
produces a feature qualitatively similar to the ribbon observed by IBEX.Comment: submitted to ApJ
Solar cycle influence on the interaction of the solar wind with Local Interstellar Cloud
We present results of a new time-dependent kinetic model of the H atom penetration through the solar wind - interstellar medium interaction region. A kinetic 6D (time, two dimensions in space, and three dimensions in velocity-space) equation for interstellar H atoms was solved self-consistently with time-dependent Euler equations for the solar wind and interstellar charged components. We study the response of the interaction region to 11-year solar cycle variations of the solar wind dynamic pressure. It is shown that the termination shock location varies within ±7 AU, the heliopause variation is ~4 AU, and the bow shock variation is negligible. At large heliocentric distances, the solar cycle induces 10-12% fluctuations in the number density of both primary and secondary interstellar H atoms and atoms created in the inner heliosheath. We underline the kinetic behavior of the fluctuations of the H atom populations. Closer to the Sun the fluctuations increase up to 30-35% at 5 AU due to solar cycle variation of the charge exchange rate. Solar cycle variations of interstellar H atoms in the heliospheric interface and within the heliosphere may have major importance for the interpretation of H atom observations inside the heliosphere
Neutral interstellar hydrogen in the inner heliosphere under the influence of wavelength-dependent solar radiation pressure
With the plethora of detailed results from heliospheric missions and at the
advent of the first mission dedicated IBEX, we have entered the era of
precision heliospheric studies. Interpretation of these data require precision
modeling, with second-order effects quantitatively taken into account. We study
the influence of the non-flat shape of the solar Ly-alpha line on the
distribution of neutral interstellar H in the inner heliosphere. Based on
available data, we (i) construct a model of evolution for the solar Ly-alpha
line profile with solar activity, (ii) modify an existing test-particle code
used to calculate the distribution of neutral interstellar H in the inner
heliosphere so that it takes the dependence of radiation pressure on radial
velocity into account, and (iii) compare the results of the old and new
version. Discrepancies between the classical and Doppler models appear between
~5 and ~3 AU and increase towards the Sun from a few percent to a factor of 1.5
at 1 AU. The classical model overestimates the density everywhere except for a
~60-degr cone around the downwind direction, where a density deficit appears.
The magnitude of the discrepancies appreciably depends on the phase of the
solar cycle, but only weakly on the parameters of the gas at the termination
shock. For in situ measurements of neutral atoms performed at ~1 AU, the
Doppler correction will need to be taken into account, because the
modifications include both the magnitude and direction of the local flux by a
few km/s and degrees, respectively, which, when unaccounted for, would
introduce an error of a few km/s and degrees in determination of the magnitude
and direction of the bulk velocity vector at the termination shock.Comment: 10 pages, 13 figures, accepted by A&
Effects of interstellar and solar wind ionized helium on the interaction of the solar wind with the local interstellar medium
The Sun is moving through a warm (6500 K) and partly ionized local
interstellar cloud (LIC) with a velocity of 26 km/s. Recent measurements
of the ionization of the LIC (Wolff et al., 1999) suggest that interstellar
helium in the vicinity of the Sun is 30-40 % ionized, while interstellar
hydrogen is less ionized. Consequently, interstellar helium ions contribute up
to 50% of the total dynamic pressure of the ionized interstellar component. Up
to now interstellar helium ions have been ignored in existing models of the
heliospheric interface. In this paper we present results of a new model of the
solar wind interaction with the interstellar medium, which takes into account
interstellar helium ions. Using results of this model we find that the
heliopause, termination and bow shocks are closer to the Sun when compared to
the model results that ignore ions. The influence of interstellar helium
ions is partially compensated by solar wind alpha particles, which are taken
into account in our new model as well. Finally, we apply our new model to place
constraints on the plausible location of the termination shock.Comment: accepted for publication in Astrophys. J. Letter
Modeling of the heliospheric interface: multi-component nature of the heliospheric plasma
We present a new model of the heliospheric interface - the region of the
solar wind interaction with the local interstellar medium. This new model
performs a multi-component treatment of charged particles in the heliosphere.
All charged particles are divided into several co-moving types. The coldest
type, with parameters typical of original solar wind protons, is considered in
the framework of fluid approximation. The hot pickup proton components created
from interstellar H atoms and heliospheric ENAs by charge exchange, electron
impact ionization and photoionization are treated kinetically. The charged
components are considered self-consistently with interstellar H atoms, which
are described kinetically as well. To solve the kinetic equation for H atoms we
use the Monte Carlo method with splitting of trajectories, which allows us 1)
to reduce statistical uncertainties allowing correct interpretation of
observational data, 2) to separate all H atoms in the heliosphere into several
populations depending on the place of their birth and on the type of parent
protons.Comment: A&A accepte
Neutral H density at the termination shock: a consolidation of recent results
We discuss a consolidation of determinations of the density of neutral
interstellar H at the nose of the termination shock carried out with the use of
various data sets, techniques, and modeling approaches. In particular, we focus
on the determination of this density based on observations of H pickup ions on
Ulysses during its aphelion passage through the ecliptic plane. We discuss in
greater detail a novel method of determination of the density from these
measurements and review the results from its application to actual data. The H
density at TS derived from this analysis is equal to 0.087 \pm 0.022 cm-3, and
when all relevant determinations are taken into account, the consolidated
density is obtained at 0.09 \pm 0.022 cm-3. The density of H in CHISM based on
literature values of filtration factor is then calculated at 0.16 \pm 0.04
cm-3.Comment: Submitted to Space Science Review
Unconfined Aquifer Flow Theory - from Dupuit to present
Analytic and semi-analytic solution are often used by researchers and
practicioners to estimate aquifer parameters from unconfined aquifer pumping
tests. The non-linearities associated with unconfined (i.e., water table)
aquifer tests makes their analysis more complex than confined tests. Although
analytical solutions for unconfined flow began in the mid-1800s with Dupuit,
Thiem was possibly the first to use them to estimate aquifer parameters from
pumping tests in the early 1900s. In the 1950s, Boulton developed the first
transient well test solution specialized to unconfined flow. By the 1970s
Neuman had developed solutions considering both primary transient storage
mechanisms (confined storage and delayed yield) without non-physical fitting
parameters. In the last decade, research into developing unconfined aquifer
test solutions has mostly focused on explicitly coupling the aquifer with the
linearized vadose zone. Despite the many advanced solution methods available,
there still exists a need for realism to accurately simulate real-world aquifer
tests
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