Context. Waves offer a unique opportunity to understand and diagnose the properties of solar coronal plasma.

A new theoretical model for the study of slow standing sausage mode oscillations in hot ( MK) active region coronal loops is presented. These are observed by SUMER spectrometer on board SoHO satellite. The contains transition and upper chromosphere which enables us to entire process loop – from impulsive footpoint excitation phase rapid damping phase. It shown that acoustic waves can be excited an heat deposition at chromospheric a if duration pulse matches fundamental period. immediately...

Through reduction of a huge data set spanning 2010-2017, we compare mean global changes in temperature, emission measure (EM), and underlying photospheric magnetic field the solar corona over most last activity cycle. The quiet coronal temperature rises from 1.4 to 1.8 MK, whereas EM increases by almost factor 50% minimum maximum. An increased high-temperature component near 3 MK at maximum drives increase bulk plasma remains 1.6 throughout mean, spatially smoothed magnitude Sun G 2011 peak...

An example of hot active region loop oscillations observed by SUMER and SXT is presented. The hypothesis that a fundamental mode standing slow sausage (acoustic) wave initiated footpoint microflare tested confirmed using forward modeling approach. oscillation set up immediately after the heating pulse. duration, temporal behavior, total heat input are estimated parameters. rapid energy release followed cooling. time-distance profile rate along recovered intensity Doppler-shift time series....

Abstract The propagation of azimuthal Alfvén waves and their interaction with the solar wind are investigated using a 2.5D magnetohydrodynamic model that incorporates effects optically thin radiation, as well collisional collisionless thermal conduction. background plasma forms dipole field is extended into helmet streamer by wind, slow near equator fast at mid- high latitudes. Alfvénic wave trains, localized random heliographic latitudes, launched from coronal base moderate amplitude 9 km s...

SUMER/SoHO data taken at a coronal hole boundary show repetitive explosive event occurrence rate of around 3 min increasing to over 5 towards the end activity. We suggest that neighbouring oppositely directed closed and open field lines undergo reconnection seen as sequence events. The may be triggered by transverse oscillations flux tubes in line region. These periodically separate bring together on two sides boundary. An important indicator favouring interpretation terms kink mode is...

We present near ultraviolet (NUV:1750 - 2800Å) and far (FUV: 1350 1750Å) light-curves for flares on 4 nearby dMe-type stars (GJ 3685A, CR Dra, AF Psc SDSS J084425.9+513830.5) observed with the GALEX satellite. Taking advantage of time-tagged events recorded photon counting detectors, we high temporal resolution (<0.01 sec) analysis these UV flare data. A statistical 700 seconds pre-flare quiescence data both Dra J084425.9+513830.5 failed to reveal presence significant micro-flare activity...

Context.The nature of loops is still a matter debate with several explanations having been put forward. Simultaneous spectral and imaging data have the capacity to provide new insight into mass motions, dynamics energetics loops.

Context.Standing slow (acoustic) waves commonly observed in hot coronal loops offer a unique opportunity to understand the properties of plasma. The lack evidence for similar oscillations cooler is still puzzle.

The Kelvin–Helmholtz instability (KHI) of magnetohydrodynamic surface waves on the magnetopause is examined and resonant flow (RFI) these studied under assumption that plasma density decreases in direction from magnetosheath towards magnetosphere. It found when a finite temperature taken into account, three different kinds modes (labeled as “primary” “β” sides 1 2) may exist. β remain almost unaffected by corresponding rest frames can be excited certain velocity intervals which are...

The plasma response inside a semicircular coronal loop heated by nanoflares is examined. thermally and gravitationally stratified. losses due to thermal conduction radiation are balanced localised energy pulses randomly deposited along the loop. initial stage of evolution during which temperature gradually increases from chromospheric values completed about 20 minutes after start heating. random heating produces thin transition region in continuous motion. profiles , resonance lines, have...

Transverse oscillations of coronal magnetic loops are routinely observed during the space missions. Since first observation these were interpreted in terms kink tubes. Sometimes collective two or more observed. This makes development theory a few parallel tubes desirable. Another reason for this is that there evidences at least some not monolithic but consist many thin threads. In paper linear with density varying along developed. The asymptotic method used to derive system equations...

The resonant flow instability (RFI) and the Kelvin‐Helmholtz (KHI) are investigated as possible wave‐generating mechanisms in mantle‐like boundary layer of Earth's magnetotail where all equilibrium quantities transit continuously from magnetosheath values to more characteristic tail lobe. It is shown that case a sharp interface, KHI requiring high speeds unlikely be operative under typical conditions. RFI which physically distinct may appear at lower owing inhomogeneity layer. can important...

A new magnetohydrodynamic (MHD) instability in coronal loops is presented.It demonstrated that smallamplitude torsional Alfvénic disturbances generated by random photospheric motions are inevitably amplified asymmetrically stratified with siphon flows.The loop asymmetry and the flow speeds can be arbitrarily small.The growth rates linked increase increasing speeds.The caused over-reflection of Alfvén waves at transition region where steep variations density exist.

Context. Simulations and observations of the solar atmosphere often reveal presence torsional Alfvén waves vortices with sufficient power to heat corona accelerate wind. Aims. We challenge long-held view that low-frequency are suppressed due inhomogeneities steep spatial gradients in atmosphere. a stratified modelled aim calculating comparing their energy flux for different field line geometries. Methods. show general problem linear wave propagation along lines arbitrary geometry can be...

Context.Analysing the structure of solar coronal loops is crucial to our understanding processes which heat and maintain plasma at multimillion degree temperatures. The determination physical parameters remains both an observational theoretical challenge.

Abstract The interaction of siphon flow with an initially linear Alfvén wave within isolated chromospheric loop is investigated. modeled using 1.5D magnetohydrodynamics (MHD). undergoes a hydrodynamic (HD) shock, which allows the instability to amplify propagating waves as they interact shock and footpoints. amplification leads nonlinear processes strongly altering equilibrium. Azimuthal twists <?CDATA $50\ \mathrm{km}\,{{\rm{s}}}^{-1}$?> are generated becomes globally twisted azimuthal...

Magnetohydrodynamic surface waves are studied at an interface of finite thickness separating two homogeneous arbitrary β plasmas which in parallel motion with respect to each other and permeated by magnetic fields. It is assumed that the density decreases field strength increases across interface. The model representative mantle-like boundary layer fast flowing magnetosheath from tail region magnetosphere. All existing wave modes classified, their main properties investigated, analytical...

A major shortcoming of theories long‐period magnetic pulsations is the separate treatment problems wave excitation and resonant coupling. This could account for many substantial discrepancies between waveguide/cavity mode observations. unified approach leading to a new type field line resonance mechanism presented. It shown that in steady state direct coupling waveguide modes local oscillations provides natural very efficient transfer energy from magnetosheath flow shear Alfvén waves deep...

A new ideal magnetohydrodynamic instability is presented. It shown that linear incompressible Alfv\'enic disturbances can get over-reflected and exponentially amplified in compressible plasma flows. simple transparent stability criterion for a two-layer model derived. The does not require shear the flow may arise rather moderate sub-Alfv\'enic speeds. therefore important to be aware of Alfv\'en when dealing with laboratory or astrophysical