On impulse excitation of the global poloidal modes in the magnetosphere

International audienceThrough the combined action of the field line curvature and finite plasma pressure in some regions of the magnetosphere (plasmapause, ring current) there can exist global poloidal Alfvén modes standing both along field lines and across magnetic shells and propagating along azimuth. In this paper we investigate the spatio-temporal structure of such waves generated by an impulsive source. In general, the mode is the sum of radial harmonics whose structure is described by Hermitian polynomials. For the usually observed second harmonic structure along the background field, frequencies of these radial harmonics are very close to each other; therefore, the generated wave is almost a monochromatic oscillation. But mixing of the harmonics with different radial structure causes the evolution of the initially poloidal wave into the toroidal one. This casts some doubts upon the interpretation of observed high-m poloidal waves as global poloidal modes

Pc5 waves generated by substorm injection: a case study

We analyzed the spectral-polarized characteristics of Pc5 ULF waves observed on 17 September 2000 after the 03:20:25 UT substorm onset with the satellites GOES 8 and 10 located east and west of the onset location. In the course of the event, the wave polarization changed from mixed (between toroidal and poloidal) to poloidal, and then to mixed again. The hodogram of magnetic field oscillations rotated counterclockwise at GOES 8, and clockwise at GOES 10. It is suggested that the satellites detected the waves generated by the substorm injected clouds of the charged particles drifting in the magnetosphere in the opposite azimuthal directions: GOES 8 (located east of the substorm onset) detected the wave generated by an electron cloud, and GOES 10 (west of the onset) detected the wave generated by a positive ion cloud. This interpretation is confirmed by the energetic particles data recorded by LANL satellites

Definition of the Alfvén mode in inhomogeneous magnetic field

The article is methodological and defines the concept of the linear Alfvén mode. There are two definitions — electrodynamic and hydrodynamic. In the former, the Alfvén mode is considered a wave with a potential transverse electric field. In the latter, waves are more often identified with the Alfvén mode, plasma motion in which is purely vortex. While these definitions are equivalent for homogeneous plasma, they are incompatible if the field line curvature is taken into account: if the transverse electric field is purely potential, the plasma speed has not only a vortex component, but also a potential one, and vice versa. The electrodynamic and hydrodynamic definitions are equivalent only if the wave electric field completely lacks a component along the binormal to the external magnetic field. However, such waves do not exist in nature

Corrugation instability of a coronal arcade

AbstractWe analyse the behaviour of linear magnetohydrodynamic perturbations of a coronal arcade modelled by a half-cylinder with an azimuthal magnetic field and non-uniform radial profiles of the plasma pressure, temperature, and the field. Attention is paid to the perturbations with short longitudinal (in the direction along the arcade) wavelengths. The radial structure of the perturbations, either oscillatory or evanescent, is prescribed by the radial profiles of the equilibrium quantities. Conditions for the corrugation instability of the arcade are determined. It is established that the instability growth rate increases with decreases in the longitudinal wavelength and the radial wave number. In the unstable mode, the radial perturbations of the magnetic field are stronger than the longitudinal perturbations, creating an almost circularly corrugated rippling of the arcade in the longitudinal direction. For coronal conditions, the growth time of the instability is shorter than one minute, decreasing with an increase in the temperature. Implications of the developed theory for the dynamics of coronal active regions are discussed

First comparison of retroperitoneal versus transperitoneal robot-assisted nephroureterectomy with bladder cuff : a single center study

Introduction. After recent presentation of the first complete robot-assisted retroperitoneal nephroureterectomy with bladder cuff (RRNU) for patients with upper tract urothelial cancer (UTUC), we aimed to compare this new surgical technique with robot-assisted transperitoneal nephroureter ectomy (TRNU) representing the current standard of care. Methods. Robot-assisted nephroureterectomies (NUs) were retrospectively analyzed and compared based on two groups: transperitoneal versus retroperitoneal approach. Baseline data were collected for patient demographics, tumor characteristics, intra- (EAUiaiC) and postoperative (Clavien-Dindo) complications, and perioperative variables. Tumor characteristics included grade of malignancy, clinical stage, and surgical margin status. Short-term follow-up data including 30-day readmission rates were collected. Statistical analyses were performed assuming a significant p-value of < 0.05. Results. The analysis includes perioperative patient data after proven UTUC of 24 TRNU versus 12 RRNU (mean age: 70 versus 71 years; BMI: 25.9 versus 26.1 kg/m 2 ; CCI score ≥ 4: 83% versus 75%; ASA score ≥ 3: 37% vs 33%). Intraoperative (16.4% vs 0%, p = 0.35) and postoperative (25% vs 12.5%, p = 0.64) complications demonstrated no significant discrepancy. Notably, RRNU demonstrated significantly shorter surgery time (p < 0.05) and length of stay (p < 0.05). There was no significant difference in histopathological tumor characteristics, whereas significantly more lymph nodes were removed through RRNU (11.0±3.3 vs. 6.4±5.1, p < 0.05). Finally, no statistical difference was shown in short-term follow-up. Conclusion. We report the first head-to-head comparison between RRNU and TRNU. RRNU proves to be a safe and feasible approach which appears to be non-inferior to TRNU. RRNU expands the spectrum of minimally invasive treatment options, particularly for patients with major previous abdominal surgery