First results of the high-resolution multibeam ULF wave experiment at the Ekaterinburg SuperDARN radar: Ionospheric signatures of coupled poloidal Alfvén and drift-compressional modes

Abstract. As shown within the gyrokinetic framework, drift-compressional waves can propagate in the magnetosphere in the direction of energetic electron drift. The plasma is assumed to be composed of cold particles with an admixture of hot protons with a Maxwell distribution and electrons with an inverted distribution. The conditions of existence of such waves and their intensification due to resonance interaction with energetic electrons (drift instability) have been determined. The results can be helpful in interpreting observation of wave phenomena in the magnetosphere with frequencies in the range of geomagnetic pulsations Pc5 and below.

Section: Introductionsupporting

confidence: 84%

Drift-compression waves propagating in the direction of energetic electron drift in the magnetosphere

Kostarev¹,

Mager²

2017

“…Technical characteristics of the radar are given on the website http://sdrus.iszf.irk.ru/; the basic principles of its operation and data processing techniques, in articles Mager et al, 2015]. On the days considered, the YeKB radar operated at ~ 11 MHz in the normal mode along 0-15 beams providing spatial resolution of 45 km and temporal resolution of 1-2 minutes.…”

Section: Datamentioning

confidence: 99%

“…characterized by gradual decrease in the range from maximum nighttime R g = 2500-3000 km to minimum daytime R g = 800-1500 km and by an increase in R g in the evening [Bland et al, 2014.;Mager et al, 2015]. This diurnal variation in R g is due to diurnal variations in N m F2 and the F2-layer peak height Considering data from Table 2, we believe that the compression of the magnetosphere in the initial phase and within the first two hours of the main phase along with the reconnection on the daytime magnetopause [Le et al, 2016] caused an increase in the critical frequency of the F2 layer at 74-77° N in the sector 08:00-13:00 LT.…”

Section: Backscattering Dynamics During Intense Geomagnetic Storm…mentioning

confidence: 99%

Backscattering dynamics during intense geomagnetic storm as deduced from Yekaterinburg radar data: March 17–22, 2015

Золотухина¹,

Kurkin²,

Полех³

et al. 2017

“…SuperDARN radars have repeatedly observed excitation of ULF waves such as drift-compressional waves by energetic protons. Let us focus on recent observations made by SuperDarn radars in Russia [Mager et al, 2015;Chelpanov et al, 2016]. Note that James et al [James et al, 2016] employed several radars to observe different frequencies in one event at the same geomagnetic latitude; Bland and McDonald [Bland, McDonald, 2016] Walker et al [Walker et al, 1979] stated that the plasma density in the outer magnetosphere estimated at frequencies they found was overestimated.…”

Section: Introductionmentioning

confidence: 99%

Resonant ULF absorption in storm time conditions

Бадин¹

2017

_____________________________________________________________________________________________ INTRODUCTIONThe origin of ultralow-frequency (ULF) oscillations of magnetic and electric fields is often associated with the excitation of magnetohydrodynamic (MHD) resonances in near-Earth plasma frozen in the geomagnetic field. In [Chen, Hasegawa, 1974;Southwood, 1974], the authors theoretically analyze the excitation of resonant ULF oscillations of magnetic field lines by surface MHD waves in the magnetosphere. Resonant frequencies of such oscillations have been repeatedly calculated by numerical methods for both dipole [Lee, Lysak, 1989] and nondipole geomagnetic field models [Cheng, Zaharia, 2003]. The numerical calculations established typical values of minimum resonant frequencies 3-5 mHz (in the dayside magnetosphere) for quiet geomagnetic conditions. A significant limitation of such studies was the approximation of infinitely large ionospheric conductivity. This approximation restricts field line resonances only to eigenoscillations of the so-called classical half-wave mode, i.e. to standing waves for which an integer of half-waves fits between conjugated ionospheres along magnetic field lines. In this case, resonant oscillations of the magnetic field line are analogous to acoustic oscillations of a string whose ends are fixed in the E layer of the conjugated ionospheres [Nishida, 1980]. Taking the finite ionospheric conductivity into account revealed first and foremost a significant damping decrement of the fundamental harmonic of the half-wave mode for sufficiently low ionospheric conductivity [Newton et al., 1978]. In addition, the finite ionospheric conductivity supplemented field line resonances with quarter-wave oscillations, for which an odd number of quarter wavelengths fits between the conjugated ionospheres [Allan, Knox, 1979]. Such oscillations are similar to acoustic oscillations of a pipe whose one end is fixed and the The differences between the experimental and theoretical estimates can be explained by a strong effect of nondissipative energy losses on the Q factor of the resonator [Poulter, Allan, 1985]. At high latitudes, i.e. at L~10 and at low ionospheric conductivity under polar winter conditions, the theoretical Q-factor estimate taking into account only ohmic dissipation [Yumoto et al., 1995] gives Q 1~1 . At high latitudes, there appear additional non-dissipative losses produced, for example, by magnetospheric convection. Indeed, convection trajectories in the general case do not coincide with constant-period magnetic surfaces of the field line resonance. In the drift motion, magnetospheric plasma along with field-aligned currents leaves the resonance region. This causes additional losses of resonator energy and reduces the Q factor. With a low Q factor of the resonator, the eigenoscillation amplitude does not exceed the amplitude of background waves; this hinders the observation of resonant ULF oscillations at high latitudes.High oscillation amplitudes at 2.7, 3.5, and 3.9 mHz, found in...