97 research outputs found
A semi-analytical solution for transient streaming potentialsassociated with confined aquifer pumping tests
We consider the transient streaming potential response due to pumping from a confined aquifer through a fully penetrating line sink. Confined aquifer flow is assumed to occur without fluid leakage from the confining units. However, since confining units are typically clayey, and hence more electrically conductive than the aquifer, they are treated as non-insulating in our three-layer conceptual model. We develop a semi-analytical solution for the transient streaming potentials response of the aquifer and the confining units to pumping of the aquifer. The solution is fitted to field measurements of streaming potentials associated with an aquifer test performed at a site located near Montalto Uffugo, in the region of Calabria in Southern Italy. This yields an average hydraulic conductivity that compares well to the estimate obtained using only hydraulic head data. Specific storage is estimated with greater estimation uncertainty than hydraulic conductivity and is significantly smaller than that estimated from hydraulic head data. This indicates that specific storage may be a more difficult parameter to estimate from streaming potential data. The mismatch may also be due to the fact that only recovery streaming potential data were used here whereas head data for both production and recovery were used. The estimate from head data may also constitute an upper bound since head data were not corrected for pumping and observation wellbore storage. Estimated values of the electrical conductivities of the confining units compare well to those estimated using electrical resistivity tomography. Our work indicates that, where observation wells are unavailable to provide more direct estimates, streaming potential data collected at land surface may, in principle, be used to provide preliminary estimates of aquifer hydraulic conductivity and specific storage, where the latter is estimated with greater uncertainty than the former
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
Effect of the heliospheric interface on the distribution of interstellar hydrogen atom inside the heliosphere
This paper deals with the modeling of the interstellar hydrogen atoms (H
atoms) distribution in the heliosphere. We study influence of the heliospheric
interface, that is the region of the interaction between solar wind and local
interstellar medium, on the distribution of the hydrogen atoms in vicinity of
the Sun. The distribution of H atoms obtained in the frame of the
self-consistent kinetic-gasdynamic model of the heliospheric interface is
compared with a simplified model which assumes Maxwellian distribution of H
atoms at the termination shock and is called often as 'hot' model. This
comparison shows that the distribution of H atoms is significantly affected by
the heliospheric interface not only at large heliocentric distances, but also
in vicinity of the Sun at 1-5 AU. Hence, for analysis of experimental data
connected with direct or undirect measurements of the interstellar atoms one
necessarily needs to take into account effects of the heliospheric interface.
In this paper we propose a new model that is relatively simple but takes into
account all major effects of the heliospheric interface. This model can be
applied for analysis of backscattered Ly-alpha radiation data obtained on board
of different spacecraft.Comment: published in Astronomy Letter
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
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