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Advances in Geosciences. Across the discontinuity the plasma is compressed and heated and the magnetic field B rotates of a negligible angle whereas its magnitude B jumps. The estimated propagation time, from Wind to the Cluster SC3 position, results to be Therefore, a causal connection is established between the arrival of the IP shock and the observed perturbation of the magnetosheath.
The first of them coincides with the transmitted IP shock, the second one is given by a slight increase of n and a more clear decrease of T whereas the last one is characterized by an n decrease and a T increase. In this regard a clarification is necessary.
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However, they do not play any role in the perturbation under study. Therefore, they are surely distinct objects from the discontinuities discussed here. Moreover, it is even possible to rule out that they can somehow affect the magnetosheath perturbation. Actually, those two discontinuities are observed in the solar wind, at a distance from the Earth of The reason stands in the absence of an appreciable bidimensional variation of the magnetic field through both discontinuities. Also, the multispacecraft timing analysis [ Schwartz , ] is not applicable on those data set, which are available for all Cluster spacecraft in the present event, that is magnetic field FGM and the electrons PEACE data.
In this case the drawback is that the expected time delays of the discontinuities arrival to the four Cluster spacecraft positions are quite short, at maximum a few spin periods, and that the discontinuities signatures are blurred by other fluctuations with not negligible amplitudes. This fact leads to errors on the timing, which are of the order of the magnitude of the estimated values. The assertion is based on the good agreement existing between the observations and some results issuing from the basic equations of the nonlinear magnetosonic waves here recalled in Appendix A.
In this regard, the first annotation concerns the fact that B has a nearly bidimensional geometry. As is easy to note, equation A7 is successful to catch the trend of the time variation of the measured B 1. Equations A4 and A6 provide additional support to the attempt of understanding the present observations in terms of a fast magnetosonic wave.
An estimate of the statistical uncertainty associated with the minimum variance technique [e. Despite this uncertainty, therefore, the propagation direction is still definitely sunward as can be easily verified. The agreement between theory and observations is quite satisfactory for both V 1 and V 3 although the time derivative of theoretical V 3 is slightly greater than the observed one.
It is known that two discontinuities, here the transmitted shock I and the discontinuity basically characterized by a drop of T II , are generated and launched through the magnetosheath by the interaction between the IP shock and the bow shock [ Samsonov et al. Differently from the first two discontinuities, which have been observed several times, a discontinuity like III has been identified in the inner magnetosheath just in the event analyzed by [ Pallocchia et al.
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Therefore, without the present experimental confirmation, the presence of such discontinuity in the Pallocchia et al. Here we have for the first time identified a reverse compressional fast magnetosonic wave, which comes before discontinuity III at the spacecraft location. In principle, this outward fast wave is able to climb up the inward plasma bulk flow which is subfast and, therefore, to impinge on the bow shock somewhere in the outer magnetosheath. Therefore, the present observations support the mechanism proposed by Pallocchia et al. At the end of the section we will formulate a hypothesis about the nature and the origin of the observed reverse wave.
Moreover, a decrease of V is observed in that same interval. In the Pallocchia et al. As well as in the above events, signatures of a reverse wave can be recognized also in Samsonov et al. All the above indications lead us to think that probably a reverse fast wave is always a noticeable part of the inner magnetosheath perturbation triggered by the IP shock impact on the bow shock. In fact, the impact of a fast shock on the magnetopause, considered as a tangential discontinuity, produces a reverse fast rarefaction wave rather than a compressional one [ Grib et al. Differently, an inward rarefaction wave can generate a sunward fast compressional wave in the magnetosheath through the reflection on the magnetopause [ Grib et al.
Taking into account the theoretical finding that an earthward slow expansion wave is created when an IP shock hits the bow shock [ Grib , ], the reflection of such a secondary wave could be a good candidate to explain the observation of a reverse wave in the magnetosheath. Nevertheless, our data do not support the above mechanism because an inward slow rarefaction wave is not found in the incident plasma following the transmitted shock. We do not have any evidence that a magnetosonic wave is associated to that rarefaction. Anyway, even if that were the case, the fact that the magnitude of the magnetic field is positively correlated with the density would indicate that the rarefaction is a fast wave and not a slow one as noted in Appendix A.
As a matter of fact, the solar wind conditions are considerably modified by the IP shock passage and, therefore, a global reconfiguration of the plasma flow around the obstacle magnetopause is expected on the basis of elementary physics reasons. Therefore, under the hypothesis that in the above HO run is really present a reverse wave, an obvious inference is that such reverse wave is produced in the magnetosheath.
In fact, the Samsonov et al. Obviously, further observational and theoretical studies are necessary to confirm or reject the above conjecture. Our results are summarized as follows:  The interaction of the IP shock with the bow shock launches in the magnetosheath a transmitted shock, which is slightly weaker and slower in the Earth's reference frame than the incident one. The transmitted shock is followed by other two discontinuities.
Systematic changes in the latitudinal location and in the intensity of the LPJs were observed in the 2 min time resolution data of the SuperDARN radars. The effect of the abrupt changes in the LPJs location is to create regions containing dayside plasma almost detached from the rest of the oval density. One of these density features was seen by the Sondrestrom radar at UT.
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The data presented here suggest that two plasma structuring mechanisms TCVs and LPJs can act tens of minutes apart to produce higher levels of density structures in the near noon F-region ionosphere. Unable to display preview. Download preview PDF.
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Skip to main content. Advertisement Hide. Observations of plasma density structures in association with the passage of traveling convection vortices and the occurrence of large plasma jets. Authors Authors and affiliations C. Valladares D.