No abstract

Spectrum cascade in drift wave turbulence in a magnetized plasma as well as Rossby wave turbulence in an atmospheric pressure system are studied based on a three-wave decay process derivable from the model equation applicable to both cases. The decay in the three-way interaction occurs to smaller and larger values of ‖k‖. In a region of large wavenumbers this leads to the dual cascade; the energy spectrum cascades to smaller ‖k‖ and the enstrophy spectrum to larger ‖k‖, similar to the case of two-dimensional Navier–Stokes turbulence. In a small wavenumber region a resonant three-wave decay process dominates the cascade process, and an anisotropic spectrum develops. As a consequence of the cascade, zonal flows in the direction perpendicular to the direction of inhomogeneity appear which presents a potential implication for the particle confinement in a turbulent plasma.

This paper documents a series of brief, strong (Δp/p = 1), dynamic pressure oscillations that occurred in the region upstream of the Earth's bow shock during a period of radial interplanetary magnetic field (IMF). The analyzed set of oscillations, which may be either intrinsic solar wind or bow shock‐related phenomena, recur approximately every 8–10 min, and their magnetic field signatures occur nearly simultaneously over great distances transverse to the Earth‐Sun line. The pressure oscillations appear to drive tailward‐moving magnetopause surface wavelets. In turn, the surface wavelets can be identified as hydromagnetic waves with strong compressional components in the outer magnetosphere and as quasi‐periodic variations in electron precipitation and high‐latitude ground pulsations. We use observations by spacecraft in the outer dayside magnetosphere to predict geosynchronous and subsolar magnetic field strengths, the location of the subsolar magnetopause, the solar wind dynamic pressure, and variations in the energetic magnetospheric ion flux.

Magnetic impulse events were selected by a computer algoffihm procedure from magnetic records obtained at the near cusp latitude conjugate stations Iqaluit, Northwest Territories, Canada, and South Pole Station, Antarctica. The algorithm was constructed to select large (> 50 nT in the vertical component of the magnetic field), short lived (6 to 12 min) events. These events were found to be highly localized in the 06 to 18 LT sector at the two stations. A strong minimum in occurrence was found during hour 11 LT. The field changes associated with these events can be interpreted as due to an approximately half-cycle, odd-mode, Alfx•en wave along a nearmagnetopause flux tube. From the vertical magnetic deflections of the impulse events the directions of field-aligned currents into the conjugate ionospheres were inferred. In the morning LT sector, field-aligned currents were directed into the ionospheres, while in the afternoon LT sector, field-aligned currents were directed out of the ionospheres. These findings are comparable with the statistical results for quasi-stationary field-aligned currents and suggest that at the times of these events, Iqaluit and South Pole are at a higher effective magnetic latitude. The average deflection in the vertical component for the events was measured to be -95 nT. From this the magnitude of the average field-aligned currents was calculated to be JII -2 x 10 -7 A/m 2. Paper number 91JA00567. 0148-0227/91/91 JA-00567505.00 information on plasma parameters involved with possible sporadic reconnection. Indeed, early work by Holzer and Reid [1975] on reconnection processes at the magnetopause pointed out the role that the ionospheric plasma would have in providing boundary conditions for dayside magnetic flux tubes. The publication of several important theoretical and observation-based papers [Lee and Fu, 1985; Lee, 1986; Southwood, 1985, 1987.; Saunders et al., 1984; Zhu and Kan, 1989; Crooker and Siscoe, 1990; Wei and Lee, 1990] stimulated a flurry of additional observational efforts to ascertain the validity of the theoretical ideas as well as investigations of the actual possibility of determining the "ionospheric signature" of possible sporadic dayside reconnection processes [e.g., Goertz et al., 1985; Todd et al., 1986; Lanzerotti et al., 1986, 1987; Friis-Christensen et al., 1988; Fukunishi and Lanzerotti, 1989; Sandholt et al., 1986, 1989; Mende et al., 1990]. A number of the cited papers did provide evidence of high-latitude ionospheric signatures that were consistent with theoretical ideas at the time the work was done.However, there were some disquieting concerns in several of the papers. In part these concerns were related to the difficulty (inability?) of detecting an expected ionospheric signature at the time a spacecraft FTE was observed [Lanzerotti, 1988;Elphic, 1990]. Heikkila et al. [1989] showed convincingly that one such event began on closed field lines (see also Lanzerotti et al. [1987, who discussed the implications of their conjugate measurements), a factor wh...

We present magnetic field data from the cusp‐latitude South Pole station that exhibit, under appropriate local time and interplanetary magnetic field conditions, the signature expected in the ionosphere from a flux transfer event (FTE) at the magnetopause. In particular, the model of multiple X‐line reconnection at the magnetopause predicts field‐aligned currents in helical flux tubes, with transverse magnetic fields propagating as Alfvén waves toward the ionosphere. The distinctive magnetic signature at a polar cap magnetic station, particularly in the vertical component, can be used to infer the signs of the By and Bz components of the interplanetary magnetic field.