The SWAP Filter: A Simple Azimuthally Varying Radial Filter for Wide-Field EUV Solar Images

We present the SWAP Filter: an azimuthally varying, radial normalizing filter specifically developed for EUV images of the solar corona, named for the Sun Watcher with Active Pixels and Image Processing (SWAP) instrument on the Project for On-Board Autonomy 2 spacecraft. We discuss the origins of our technique, its implementation and key user-configurable parameters, and highlight its effects on data via a series of examples. We discuss the filter's strengths in a data environment in which wide field-of-view observations that specifically target the low signal-to-noise middle corona are newly available and expected to grow in the coming years.Comment: Contact D. B. Seaton for animations referenced in figure caption

Slow Solar Wind Connection Science during Solar Orbiter’s First Close Perihelion Passage

The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilize the extensive suite of remote-sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote-sensing and in situ measurements of slow wind originating at open–closed magnetic field boundaries. The SOOP ran just prior to Solar Orbiter’s first close perihelion passage during two remote-sensing windows (RSW1 and RSW2) between 2022 March 3–6 and 2022 March 17–22, while Solar Orbiter was at respective heliocentric distances of 0.55–0.51 and 0.38–0.34 au from the Sun. Coordinated observation campaigns were also conducted by Hinode and IRIS. The magnetic connectivity tool was used, along with low-latency in situ data and full-disk remote-sensing observations, to guide the target pointing of Solar Orbiter. Solar Orbiter targeted an active region complex during RSW1, the boundary of a coronal hole, and the periphery of a decayed active region during RSW2. Postobservation analysis using the magnetic connectivity tool, along with in situ measurements from MAG and SWA/PAS, showed that slow solar wind originating from two out of three of the target regions arrived at the spacecraft with velocities between ∼210 and 600 km s−1. The Slow Wind SOOP, despite presenting many challenges, was very successful, providing a blueprint for planning future observation campaigns that rely on the magnetic connectivity of Solar Orbiter

Linear Alfvén and fast magnetosonic waves in coronal loops driven by random footpoint motions

nrpages: 173status: publishe

Resonant absorption in randomly driven coronal loops

status: publishe

Randomly driven fast waves in coronal loops

We study the time evolution of fast magnetosonic and Alfven waves in a coronal loop driven by random foot-point motions. The footpoint motions are assumed to be polarized normal to the magnetic flux surfaces in linear ideal MHD. De Groof et al. (1998) (Paper I) revealed for the case, in which the fast waves are decoupled from the Alfven waves, that the input energy is mainly stored in the body modes. Hence driving at the loop's feet forms a good basis for resonant absorption as heating mechanism. In order to determine the efficiency of resonant absorption, we therefore study the energy transfer from the body modes to the resonant Alfven waves in the case of coupling. We find that the growth of Alfven mode energy depends on several parameters. Subsequently we check whether the necessary small lengthscales are created on a realistic time scale for the coronal loop. We find that Alfven resonances are built up at the magnetic surfaces, where the local Alfven frequency equals the quasi-mode frequency, on time scales comparable to the lifetime of the loop. Finally we conclude that a random footpoint driving can produce enough resonances to give rise to a globally heated coronal loop.status: publishe

Coronal MHD Waves and Theoretical Constraints of Wave Heating

Magnetohydrodynamic (MHD) waves play an important role in the solar atmosphere both directly (or intrinsically) and indirectly. Numerous theoretical studies contributed to the development of a theoretical framework and continue to do so. As a matter of fact, magnetic waves and oscillations seem to be present in all magnetic structures as they are observed in coronal loops, plumes, prominences, sunspots, arcades, etc. This omnipresence of MHD waves in combination with the possibility to observe them with sufficiently high spatial and time resolution enables coronal seismology. The theory of the different generation mechanisms, the propagation and evolution, and the dissipation and/or 'leakage' of the different types of linear MHD waves will be briefly reviewed in the context of the inhomogeneous, magnetically structured solar atmosphere. Particular attention will be given to the intriguing problem of the dissipation of waves and its possible role in coronal heating.status: publishe

Randomly driven fast waves in coronal loops II. with coupling to Alfvén waves

We study the time evolution of fast magnetosonic and Alfven waves in a coronal loop driven by random footpoint motions. The footpoint motions are assumed to be polarized normal to the magnetic flux surfaces in Linear ideal MHD. De Groof et al. (1998) (Paper I) showed that the input energy is mainly stored in the body modes when the fast waves are decoupled from the Alfven waves. Hence driving at the loop's feet forms a good basis for resonant absorption as heating mechanism.status: publishe

Resonant absorption in randomly driven coronal loops

De Groof et al. '98 [1] and '00 [2] studied the time evolution of fast magnetosonic and Alfven waves in a coronal loop driven by radially polarized footpoint motions in linear ideal MHD. Footpoint driving seems to be an efficient way of generating resonant absorption since the input energy is mainly stored in body modes which keep the energy in the loop. The most important feature in this study is the stochastic driving of the loop. While in earlier models with a periodic driver or a single pulse, the loop is only heated at one single layer, we now find multiple resonance layers which results in a more globally heated loop. Moreover, these resonances (created on a realistic time scale) have lengthscales which are small enough to explain energy dissipation. An important aspect to take into account is the mass transfer between corona and chromosphere since the density becomes time dependent and consequently, the resonant surfaces shift throughout the loop [3]. Combined with the multiple resonances we found in the previous study, this result can lead to the globally heated coronal loops we observe.status: publishe