On the generation of low-frequency waves in the solar wind in the front of the bow shock

Kovner, M. S.; Лебедев, В. В.; Plyasova-Bakounina, T.A.; Troitskaya, V. A.

doi:10.1016/0032-0633(76)90022-2

Cited by 51 publications

(24 citation statements)

References 7 publications

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“…For comparison, the dependence of the observed Pc3ind on cos 2 ϑ Bx can not be described by a linear equation, but by a quadratic formula (Pc3ind = −147.20cos 4 ϑ Bx + 185.56cos 2 ϑ Bx + 42.0 pT, R = 0.97) with a maximum at 37 • . This is in agreement with the theoretical prediction of Kovner et al (1976), who found that the ion-cyclotron instability near the nose of the bow shock is the most efficient when the cone angle is around 30 • . The order of normalisation and the reference levels chosen are all arbitrary.…”

Section: Separation Of the Influences Of Solar Wind Parameterssupporting

confidence: 93%

Empirically modelled Pc3 activity based on solar wind parameters

et al. 2010

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Abstract. It is known that under certain solar wind (SW)/interplanetary magnetic field (IMF) conditions (e.g. high SW speed, low cone angle) the occurrence of groundlevel Pc3-4 pulsations is more likely. In this paper we demonstrate that in the event of anomalously low SW particle density, Pc3 activity is extremely low regardless of otherwise favourable SW speed and cone angle. We re-investigate the SW control of Pc3 pulsation activity through a statistical analysis and two empirical models with emphasis on the influence of SW density on Pc3 activity. We utilise SW and IMF measurements from the OMNI project and groundbased magnetometer measurements from the MM100 array to relate SW and IMF measurements to the occurrence of Pc3 activity. Multiple linear regression and artificial neural network models are used in iterative processes in order to identify sets of SW-based input parameters, which optimally reproduce a set of Pc3 activity data. The inclusion of SW density in the parameter set significantly improves the models. Not only the density itself, but other density related parameters, such as the dynamic pressure of the SW, or the standoff distance of the magnetopause work equally well in the model. The disappearance of Pc3s during lowdensity events can have at least four reasons according to the existing upstream wave theory: 1. Pausing the ion-cyclotron resonance that generates the upstream ultra low frequency waves in the absence of protons, 2. Weakening of the bow shock that implies less efficient reflection, 3. The SW becomes sub-Alfvénic and hence it is not able to sweep back the waves propagating upstream with the Alfvén-speed, and 4. The increase of the standoff distance of the magnetopause (and of the bow shock). Although the models cannot account Correspondence to: B. Heilig (heilig@elgi.hu) for the lack of Pc3s during intervals when the SW density is extremely low, the resulting sets of optimal model inputs support the generation of mid latitude Pc3 activity predominantly through upstream waves.

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Section: Separation Of the Influences Of Solar Wind Parameterssupporting

confidence: 93%

Empirically modelled Pc3 activity based on solar wind parameters

et al. 2010

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“…In this area the bow shock is close to perpendicular to the solar wind flow and so the backscattered ions have an initial velocity almost parallel to the Sun-Earth line. A zero cone angle (Russell et al, 1983;Yumoto et al, 1984;Greenstadt and Russell, 1994), or a small but not zero angle (∼30 • ) between the stream of backscattered ions and the IMF is thought to be the most favourable condition for UW generation (Kovner et al, 1976;Verő and Holló, 1978) and UW transfer through the magnetosheath (Russell et al, 1983). The resulting waves propagate upstream, but since the solar wind is super Alfvénic, i.e.…”

Section: Introductionmentioning

confidence: 99%

“…These Doppler-shifted waves become left-hand polarized in the spacecraft frame (Yumoto et al, 1984). The efficiency of the wave transfer process (Popatov and Mazur, 1994) and the penetration of UWs through the magnetopause (Kovner et al, 1976), i.e. the power of these waves in the magnetosphere should also depend on the solar wind speed.738 B.…”

Section: Introductionmentioning

confidence: 99%

Comprehensive study of ULF upstream waves observed in the topside ionosphere by CHAMP and on the ground

2007

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Abstract. Based on magnetic field measurements from the satellite CHAMP, a detailed picture could be obtained of the upstream wave (UW) distribution in the topside ionosphere. The low, near-polar orbit of CHAMP, covering all local times, allows the global distribution of this type of pulsation to be revealed. The observations from space are compared to recordings of the ground-based MM100 meridional array covering the latitude range 66 • to 42 • in magnetic coordinates. UWs show up very clearly in the compressional component of the satellite magnetic field data, whereas on the ground, their signature is found in the H component, but it is mixed with oscillations from field line resonant pulsations. Here we first introduce a procedure for an automated detection of UW signatures, both in ground and space data. Then a statistical analysis is presented of UW pulsations recorded during a 132-day period, centred on the autumn 2001 equinox. Observations in the top-side ionosphere reveal a clear latitudinal distribution of the amplitudes. Largest signals are observed at the equator. Minima show up at about 40 • latitude. The coherence between ground and satellite wave signatures is high over wide latitude and longitude ranges. We make suggestions about the entry mechanism of UWs from the foreshock region into the magnetosphere. The clear UW signature in satellite recordings between −60 • and 60 • latitude allows for detailed investigations of the dependence on solar wind conditions. We test the control of solar wind speed, interplanetary magnetic field strength and cone angle on UWs. For the first time, it is possible to derive details of the Doppler-shift effect by modifying the UW frequency from direct observations. The results reconcile foreshock wave generation predictions with near-Earth observations.

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“…As a matter of fact, the relationship between the pulsation power and the SW speed has been often interpreted in terms of a dominant role of the KHI; we would rather interpret the higher correlation with the SW speed at dawn and dusk, and the higher percentages of polarized events in the same time sectors in terms of a more significant role of KHI along the magnetopause flanks in the amplification of already existing waves. On the other hand, it is well known that the SW speed is a key factor for determining the general level of the magnetospheric activity: in particular, it might also determine an increasing efficiency of the ion-cyclotron instability mechanism for producing upstream waves (Kovner et al, 1976). 3.…”

Section: Discussionmentioning

confidence: 99%

Experimental Aspects of Mid-Frequency Pulsations (f≈10–100 mHz) in the Southern Polar Cap

et al. 2006

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We review the results obtained in the frequency range of Pc3 (22-100 mHz) and Pc4 (7-22 mHz) pulsations at Italian Antarctic stations in the southern polar cap ("Mario Zucchelli", at Terra Nova Bay, TNB, 80 • S; "Concordia", the Italian/French base at Dome C, DMC, 89 • S). The absence of a midnight enhancement in the pulsation power suggests a negligible substorm influence at extreme latitudes, while the sharp noon enhancement, which appears only at TNB, is determined by the closer proximity of the station to cusp related phenomena. The relationship between the frequency of the band-limited signals and the interplanetary magnetic field strength, the cone angle influence, and the higher correlation of the Pc3 power with the solar wind speed in the morning hours suggest a global scenario in which upstream waves would be mainly responsible for the mid-frequency activity in the polar cap. However, the polarization pattern is odd with respect to the predictions for tailward propagating modes.

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On the generation of low-frequency waves in the solar wind in the front of the bow shock

Cited by 51 publications

References 7 publications

Empirically modelled Pc3 activity based on solar wind parameters

Empirically modelled Pc3 activity based on solar wind parameters

Comprehensive study of ULF upstream waves observed in the topside ionosphere by CHAMP and on the ground

Experimental Aspects of Mid-Frequency Pulsations (f≈10–100 mHz) in the Southern Polar Cap

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