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The nonlinear response of the cross polar cap potential (CPCP) to solar wind driving electric field is a well-known phenomenon. The reasons behind this saturation, however, are still under debate. We have performed a statistical s...
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The nonlinear response of the cross polar cap potential (CPCP) to solar wind driving electric field is a well-known phenomenon. The reasons behind this saturation, however, are still under debate. We have performed a statistical study of the coupling efficiency between the solar wind and the northern polar cap index (PCN). PCN is used as a proxy for the CPCP. Our main focus is in quantifying how the solar wind dynamic pressure alters the efficiency. We show that the saturation of PCN occurs both during low and moderate upstream M-A conditions. We also show that the increasing dynamic pressure is associated with increasing PCN. In addition, we find that the coupling is different depending on which parameter, the velocity or the magnetic field, increases the solar wind driving electric field: the higher the velocity the higher the coupling efficiency.
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The effect of curvature of open magnetic-field tubes on the death lines of radio pulsars is studied. The solution is obtained in the framework of a Goldreich-Julian model for both dipolar and asymmetric magnetic fields. The tube-a...
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The effect of curvature of open magnetic-field tubes on the death lines of radio pulsars is studied. The solution is obtained in the framework of a Goldreich-Julian model for both dipolar and asymmetric magnetic fields. The tube-axis curvature can shift the death line appreciably toward either longer or shorter periods. If the field is dipolar and gamma rays are generated by the inverse Compton effect, the formation of secondary plasma is more efficient near the death line. In the case of an asymmetric magnetic field, the generation of radio emission beyond the tube of open field lines is possible. (C) 2004 MAIK "Nauka/Interperiodica".
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Based on in situ and ground‐based observations, a new type of “polar cap hot patch” has been identified that is different from the classical polar cap enhanced density structure (cold patches). Comparing
Based on in situ and ground‐based observations, a new type of “polar cap hot patch” has been identified that is different from the classical polar cap enhanced density structure (cold patches). Comparing with the classical polar cap patches, which are transported from the dayside sunlit region with dense and cold plasma, the polar cap hot patches are associated with particle precipitations (therefore field‐aligned currents), ion upflows, and flow shears. The hot patches may have the same order of density enhancement as classical patches in the topside ionosphere, suggesting that the hot patches may be produced by transported photoionization plasma into flow channels. Within the flow channels, the hot patches have low‐energy particle precipitation and/or ion upflows associated with field‐aligned currents and flow shears. Corresponding Global Navigation Satellite System (GNSS) signal scintillation measurements indicate that hot patches may produce slightly stronger radio signal scintillation in the polar cap region than classical patches. A new type of polar cap patches, “polar cap hot patches,” is identified to differentiate enhanced density structures from classical patches. Hot patches are associated with particle precipitations, ion upflows, field‐aligned currents, and shear flows in the polar cap. Hot patches may lead to slightly stronger ionospheric scintillations of GNSS signals in the polar cap region than classical patches.
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We examined polar rain flux observed by STSAT-1 in the northern polar cap and compared it with solar wind parameters. We found that the differential energy spectrum of polar rain was similar to that of the solar wind for the energ...
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We examined polar rain flux observed by STSAT-1 in the northern polar cap and compared it with solar wind parameters. We found that the differential energy spectrum of polar rain was similar to that of the solar wind for the energy range 100 eV - 1 keV, although we cannot rule out the possibility of a small amount of acceleration. On the other hand, the low-energy component of the solar wind showed no correlation and, naturally, the solar wind density had only a weak correlation with the polar rain flux. Polar rain flux in the northern hemisphere is most significant for the condition of the interplanetary magnetic field components Bz < 0, Bx < 0, and By > 0, and in this case it correlated well with the magnitude of By and Bz. For other interplanetary magnetic field conditions, the correlation was insignificant. The results are consistent with those reported previously.
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Energetic protons can penetrate into the ionosphere increasing ionization in the D region causing polar cap absorption that may potentially block high-frequency radio communications for transpolar flights. The protons are guided b...
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Energetic protons can penetrate into the ionosphere increasing ionization in the D region causing polar cap absorption that may potentially block high-frequency radio communications for transpolar flights. The protons are guided by the geomagnetic field into the high-latitude polar cap region. Riometers monitor variations in ionospheric absorption by observing the level of background cosmic radio noise. Current polar cap absorption modeling techniques are based on the linear relationship between absorption and the square root of the integral proton flux, which has previously only been demonstrated using data from a single high-latitude polar station. The proportionality constant describing this relationship is evaluated for two different polar cap absorption events occurring 7–11 March 2012 and 23 January 2012 to 1 February 2012. Examination of the proportionality constant using data from riometers distributed between 60° and 90° magnetic latitude reveals a previously unreported latitudinal dependence for data at magnetic latitudes of ≤66.8° on the dayside and ≤70.8° on the nightside. Incorporating the latitudinal dependence into the current D Region Absorption Prediction absorption model improves the agreement between measurement-derived and modeled parameters by increasing the correlation coefficient between data sets, reducing the root-mean-square error, and reducing the bias.
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We present high-resolution Resolute Bay Incoherent Scatter Radar (RISR) measurements in the cusp region during an IMF southward turning. The simultaneous RISR-N and RISR-C operation provided 3-D observations of the dayside polar r...
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We present high-resolution Resolute Bay Incoherent Scatter Radar (RISR) measurements in the cusp region during an IMF southward turning. The simultaneous RISR-N and RISR-C operation provided 3-D observations of the dayside polar region, and offered an opportunity to identify the cusp dynamics and polar cap patch formation. Associated with the IMF southward turning, the F-region density and temperature increased in the cusp, and the increase was particularly evident in the topside ionosphere. The high-density plasma drifted into the polar cap by an enhanced poleward convection, and became a polar cap patch. The patch plasma was initially dominated by density originating in the cusp,and then later the subauroral ionospheric plasma also contributed to the density enhancement. Weak upflows were present but their contribution within the RISR altitude range was minor. We suggest that the patch source region switches due to dynamic variations of the cusp precipitation and convection from lower latitudes. RISR also detected a flow vortex embedded in the large-scale convection, which is likely a poleward moving auroral form (PMAF) signature. Joule heating peaked in the cusp E and lower F-regions. The F-region Pedersen conductivity increased more than the Hall conductivity, and the high conductivity region extended poleward associated with the patch density enhancement. A 1-D cusp simulation reproduced the density and temperature enhancements by soft electron precipitation, indicating the importance of soft electron precipitation for the cusp dynamics and the initial part of the patch formation.
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Spring sublimation of the seasonal CO_2 northern polar cap is a dynamic process in the current Mars climate. Phenomena include dark fans of dune material propelled out onto the seasonal ice layer, polygonal cracks in the seasonal ...
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Spring sublimation of the seasonal CO_2 northern polar cap is a dynamic process in the current Mars climate. Phenomena include dark fans of dune material propelled out onto the seasonal ice layer, polygonal cracks in the seasonal ice, sand flow down slipfaces, and outbreaks of gas and sand around the dune margins. These phenomena are concentrated on the north polar erg that encircles the northern residual polar cap. The Mars Reconnaissance Orbiter has been in orbit for three Mars years, allowing us to observe three northern spring seasons. Activity is consistent with and well described by the Kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere. Three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer: the crest of the dune, the interface of the dune with the interdune substrate, and through polygonal cracks in the ice. Pressurized gas flows through these vents and carries out material entrained from the dune. Furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially-organized channels ("araneiform" terrain), albeit not permanent. Properties of the seasonal CO_2 ice layer are derived from timing of seasonal events such as when final sublimation occurs. Modification of dune morphology shows that landscape evolution is occurring on Mars today, driven by seasonal activity associated with sublimation of the seasonal CO_2 polar cap.
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The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) has imaged the sublimation of Mars' seasonal CO_2 polar cap with unprecedented detail for one complete martian southern spring. In so...
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The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) has imaged the sublimation of Mars' seasonal CO_2 polar cap with unprecedented detail for one complete martian southern spring. In some areas of the surface, beneath the conformal coating of seasonal ice, radially-organized channels are connected in spidery patterns. The process of formation of this terrain, erosion by gas from subliming seasonal ice, has no earthly analog. The new capabilities (high resolution, color, and stereo images) of HiRISE enable detailed study of this enigmatic terrain. Two sites are analyzed in detail, one within an area expected to have translucent seasonal CO_2 ice, and the other site outside that region. Stereo anaglyphs show that some channels grow larger as they go uphill - implicating gas rather than liquid as the erosive agent. Dark fans of material from the substrate are observed draped over the seasonal ice, and this material collects in thin to thick layers in the channels, possibly choking off gas flow in subsequent years, resulting in inactive crisscrossing shallow channels. In some areas there are very dense networks of channels with similar width and depth, and fewer fans emerging later in the season are observed. Subtle variations in topography affect the channel morphology. A new terminology is proposed for the wide variety of erosional features observed.
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Using data from the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter, we reassess the methods by which layers within the north polar layered deposits (NPLD) can be delineated and their thi...
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Using data from the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter, we reassess the methods by which layers within the north polar layered deposits (NPLD) can be delineated and their thicknesses measured. Apparent brightness and morphology alone are insufficient for this task; high resolution topographic data are necessary. From these analyses, we find that the visible appearance of layers depends to a large degree on the distribution of younger, mantling deposits (which in turn is partially influenced by inherent layer properties) and on the shape and location of the particular outcrop. This younger mantle partially obscures layer morphology and brightness and is likely a cause of the gradational contacts between individual layers at this scale. High resolution images reveal that there are several layers similar in appearance to the well-known marker bed discovered by Malin, M., Edgett, K., 2001. J. Geophys. Res. 106, 23429-23570. The morphology, thicknesses (4 - 8 ± sqrt(2) m), and separation distances (5 - 32 ± sqrt(2) m) of these marker beds, as gleaned from a high resolution stereo digital elevation model, lend insight into the connection between stratigraphy and climate.
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We have experimentally investigated CO2 ice condensation under conditions similar to those expected in the Martian polar areas using the Environmental Wind Tunnel of Aarhus University in the framework of Trans-National Access oppo...
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We have experimentally investigated CO2 ice condensation under conditions similar to those expected in the Martian polar areas using the Environmental Wind Tunnel of Aarhus University in the framework of Trans-National Access opportunities within the EuroPlanet Research Infrastructure. Our goal was to condense CO2 directly from the chamber's atmosphere onto a specially designed cooling plate. We investigated ranges of temperatures and pressures similar to those in Martian polar areas, observed the texture of the created CO2 ice layer, and measured its optical properties. Most importantly, we find that under conditions usual for Martian polar areas in fall and winter, CO2 ice always deposits as a translucent slab. The maximum thickness of the ice that we have achieved approached 2 cm and this CO2 slab ice layer was either transparent or highly translucent. Under significantly lower temperatures or in states away from equilibrium (for example, when CO2 gas input into the chamber was fast and created over-pressure) CO2 deposited as different crystalline structures. In this case, when a thick layer was created, it was not visually transparent. However, even in those cases it still retains some level of translucency. Our results will advance the analysis of remote-sensing data related to CO2 ice, Mars' seasonal cycles, and various models considering CO2 ice condensation-sublimation related processes. (C) 2018 Elsevier Inc. All rights reserved.
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