Publications

2026

• Nonlinear phase synchronization and the role of spacing in shell models
  
  • Manfredini L.
  • Gürcan Ö D
  Physical Review E, American Physical Society (APS), 2026, 113 (1), pp.015101. A shell model can be considered as a self-similar chain of interacting triads, where each triad can be interpreted as a nonlinear oscillator that can be mapped to a spinning top. Investigating the relation between phase dynamics and intermittency in such a chain of nonlinear oscillators, it is found that synchronization is linked to increased energy transfer. In particular, our results indicate that the observed systematic increase of intermittency, as the shell spacing is decreased, is associated with strong phase alignment among consecutive triadic phases, facilitating the energy cascade. It is shown that while the overall level of synchronization can be quantied using a Kuramoto order parameter for the global phase coherence in the inertial range, a local, weighted Kuramoto parameter can be used for the detection of burst-like events propagating across shells in the inertial range. This novel analysis reveals how locally phase-locked states are associated with the passage of extreme events of energy ux. Applying this method to helical shell models ( i.e. for a class of helical interactions that couple the two helicities in a non separable topology) reveals that a reduction in phase coherence correlates with suppression of intermittency. When inverse cascade scenarios are considered using two dierent shell models including a non local helical shell model, and a local standard shell model with a modied conservation law, it was shown that a particular phase organization is needed in order to sustain the inverse energy cascade. It was also observed that the PDFs of the triadic phases were peaked in accordance with the basic considerations of the form of the ux, which suggests that a triadic phase of π/2 and -π/2 maximizes the forward and the inverse energy cascades respectively. (10.1103/2vxp-1k2t)
  DOI : 10.1103/2vxp-1k2t
• Disturbed and quiet days ∑O/N₂ variations at low and mid-latitudes during solar cycles 23 and 24
  
  • Khan Jahan Zeb
  • Younas Waqar
  • Amory-Mazaudier Christine
  • Khan Majid
  Advances in Space Research, Elsevier, 2026, 77 (5), pp.6295-6314. We analyzed the column density ratio of thermospheric compositions (∑O/N₂) using data from the Global Ultraviolet Imager (GUVI) onboard the TIMED satellite from 2002 to 2020. Daily ∑O/N 2 values for the three most geomagnetically disturbed and quietest days each month were used to compute monthly means at low and mid-latitudes across both hemispheres. These variations were also examined across various longitudinal sectors, including Asia, Africa, and the Americas. The fluctuations in ∑O/N₂ were more pronounced at mid-latitudes than at low latitudes, with low latitude values in both hemispheres peaking near the equinoxes. At midlatitudes, the highest values occurred during local winter, with stronger peaks in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). The winter and equinoctial maxima are also observed in all longitudinal sectors. Besides this, the distinct longitudinal asymmetries over Asian, African, and American regions at mid-latitudes, influenced by geomagnetic field geometry, are also observed. The downwelling of ∑O/N₂ in local winter is stronger, while upwelling in local summer is weaker in the longitudinal sectors containing the magnetic pole. Annual (AV) and semiannual variations (SAV) were extracted using a bandpass filter. AV was stronger at mid-latitudes, peaking in local winter and highlighting the winter anomaly in both hemispheres. SAV were dominant at low latitudes, with positive peaks at equinoxes and negative dips at solstices, generally in phase across hemispheres and longitude sectors. The amplitudes of AV and SAV are stronger during solar maximum periods, justifying the solar cycle trend. Analysis also revealed that during geomagnetically disturbed periods, ∑O/N₂ typically decreased (≤ -10%) at mid-latitudes and increased (≥10%) at low latitudes compared to quiet periods. Although opposite trends-enhancement at mid-latitudes and depletion at low latitudes -were occasionally observed, they were less significant. This study aims to provide valuable insights into the dynamics of thermospheric composition, thereby contributing to the improved modeling of ionospheric behavior and space weather forecasting. (10.1016/j.asr.2025.12.115)
  DOI : 10.1016/j.asr.2025.12.115
• Properties of Magnetic Switchbacks in the Near-Sun Solar Wind
  
  • Badman Samuel T.
  • Fargette Naïs
  • Matteini Lorenzo
  • Agapitov Oleksiy V.
  • Akhavan-Tafti Mojtaba
  • Bale Stuart D.
  • Bharati Das Srijan
  • Bizien Nina
  • Bowen Trevor A.
  • Dudok de Wit Thierry
  • Froment Clara
  • Horbury Timothy
  • Huang Jia
  • Jagarlamudi Vamsee Krishna
  • Larosa Andrea
  • Madjarska Maria S.
  • Panasenco Olga
  • Pariat Etienne
  • Raouafi Nour E.
  • Rouillard Alexis P.
  • Ruffolo David
  • Sioulas Nikos
  • Soni Shirsh Lata
  • Sorriso-Valvo Luca
  • Suen Gabriel Ho Hin
  • Velli Marco
  • Verniero Jaye
  Space Science Reviews, Springer Verlag, 2026, 222. Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into "patches". We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies. (10.1007/s11214-026-01267-w)
  DOI : 10.1007/s11214-026-01267-w
• Weibel-mediated filamentary structures observed in the ICF context
  
  • Ruyer C
  • Bolaños S
  • Laborde P.E. Masson
  • Gremillet L
  • Blanchot N
  • Boutoux G
  • Cayzac W
  • Courtois C
  • Dannhoff S.G
  • Denis V
  • Le Deroff L
  • Li C.K
  • Fuchs J
  • Grisollet A
  • Lantuéjoul I
  • Riquier R
  • Smets R
  • Sutcliffe G.D
  • Vauzour B
  Phys.Plasmas, 2026, 33 (5), pp.052113. In light of novel and past experimental results, we demonstrate how Weibel-mediated filamentary structures can develop in the expanding plasma plume of a laser-irradiated foil. The transverse ballistic cooling that occurs during the quasi-spherical plasma expansion naturally drives an electron pressure anisotropy, resulting in the growth of electron current filaments. This effect competes with electron-ion Coulomb collisions which tend to isotropize the electron distribution function. Based on theoretical and particle-in-cell modeling, we provide estimates of the dominant wavelength and amplitude of the self-generated magnetic fluctuations, which are found to explain experimental data obtained at the OMEGA and Laser Megajoule facilities. (10.1063/5.0321057)
  DOI : 10.1063/5.0321057