Nawin Ngampoopun

The Sun continuously releases a stream of charged particles known as the solar wind, threaded by magnetic field lines that occasionally fold back on themselves in sharp reversals called magnetic switchbacks. These structures are frequently observed by spacecraft near the Sun, but their formation mechanism remains an open question. Using measurements from Solar Orbiter at 0.55 AU, we report heavy ion observations within a magnetic switchback that provide direct evidence of its solar source. Elevated charge-state ratios of oxygen and carbon, combined with a depletion of helium relative to protons, indicate that the switchback plasma originated from hot, closed coronal loop structures. A semi-empirical coronal model, constrained by electron temperature and density measurements from the Solar Dynamics Observatory, traces the ion signatures to either a coronal hole boundary or loops within the coronal hole, implicating the source mechanism as interchange reconnection, where closed loops reconnect with open magnetic field and eject plasma. The proton velocity and magnetic field fluctuations of the switchback are in accordance with an outward-propagating Alfvén wave. These findings suggest that interchange reconnection and wave or turbulence mechanisms jointly govern switchback origin and propagation, respectively. Most importantly, we show that switchbacks preserve measurable signatures, carrying information about the physical processes that heat the solar atmosphere and accelerate the solar wind.

Coronal hole boundaries are the interfaces between closed and open magnetic field regions in the solar atmosphere. Many fundamental processes take place at these regions, including magnetic reconnection that is responsible for solar wind release and restructuring of the solar magnetic field. In this paper, we present a case study in which we investigate the physical properties of the boundary of a large low-latitude coronal hole. Differential Emission Measure analysis is used to derive the plasma properties of these regions. We also apply correlation dimension mapping analysis to measure the irregularities of the coronal hole boundary. We find that the leading boundary of this coronal hole has a slightly higher average plasma temperature, is associated with a stronger and more unipolar magnetic field, and has a smoother boundary line than the trailing counterpart. These differences are hypothesised to be direct consequences of the local magnetic field configurations of the coronal hole boundary: the leading boundary corresponds to large, well-organised coronal loops, and the trailing boundary corresponds to more dispersed, randomly orientated small magnetic bipoles. Hence, we suggest that the surrounding magnetic field structure and the nature of magnetic reconnection influence the properties of coronal hole boundaries.

ESA/NASA’s Solar Orbiter (SO) enables us to study the solar corona at closer distances and from different perspectives, which helps us to gain significant insights into the origin of the solar wind. In this work, we present the analysis of solar wind outflows from two locations: a narrow open-field corridor and a small, mid-latitude coronal hole. These outflows were observed off-limb by the Metis coronagraph onboard SO and on-disk by the Extreme Ultraviolet Imaging Spectrometer (EIS) onboard Hinode. Magnetic field extrapolations suggest that the upflow regions seen in EIS were the sources of the outflowing solar wind observed with Metis. We find that the plasma associated with the narrow open-field corridor has higher electron densities and lower outflow velocities compared to the coronal hole plasma in the middle corona, even though the plasma properties of the two source regions in the low corona are found to be relatively similar. The speed of the solar wind from the open-field corridor also shows no correlation with the magnetic field expansion factor, unlike the coronal hole. These pronounced differences at higher altitudes may arise from the dynamic nature of the low-middle corona, in which reconnection can readily occur and may play an important role in driving solar wind variability.

Magnetic field reversals, where the radial component of the heliospheric magnetic field changes direction, are frequently observed in the near-Sun region. Theory and numerical simulations regarding these reversals suggest that possible generation mechanisms include interchange reconnection in the solar corona, or solar wind expansion and turbulence. Magnetic field reversals thus provide information about both the solar corona and solar wind acceleration and propagation. Previous observations, including magnetic field structure, He2+- abundance, and the so-called patchy-ness are not conclusive in revealing their origin. In this presentation we discuss in situ observations of protons, electrons, He2+, and heavy ions from Solar Orbiter's Solar Wind Analyser instrument , together with the magnetic field from the MAG instrument, during a long-duration magnetic field reversal. We identify the origin of the reversal using the in situ heavy ion data, magnetic connectivity tools, and plasma emission measurements from the Solar Dynamic Observatory. In addition, we study kinetic properties of the electrons, protons and heavy ions, in order to provide readily employable observational tests to help discern the origin of the magnetic field reversals.

The ambient solar wind that fills the heliosphere originates from multiple sources in the solar corona and is highly structured. It is often described as high-speed, relatively homogeneous, plasma streams from coronal holes and slow-speed, highly variable, streams whose source regions are under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify solar wind sources and understand what drives the complexity seen in the heliosphere. By combining magnetic field modelling and spectroscopic techniques with high-resolution observations and measurements, we show that the solar wind variability detected in situ by Solar Orbiter in March 2022 is driven by spatio-temporal changes in the magnetic connectivity to multiple sources in the solar atmosphere. The magnetic field footpoints connected to the spacecraft moved from the boundaries of a coronal hole to one active region (12961) and then across to another region (12957). This is reflected in the in situ measurements, which show the transition from fast to highly Alfvénic then to slow solar wind that is disrupted by the arrival of a coronal mass ejection. Our results describe solar wind variability at 0.5 au but are applicable to near-Earth observatories.

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.

We report on the merging between the southern polar coronal hole and an adjacent coronal dimming induced by a coronal mass ejection on 2022 March 18, resulting in the merged region persisting for at least 72 hr. We use remote sensing data from multiple co-observing spacecraft to understand the physical processes during this merging event. The evolution of the merger is examined using Extreme-UltraViolet (EUV) images obtained from the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory and Extreme Ultraviolet Imager, which is on board the Solar Orbiter spacecraft. The plasma dynamics are quantified using spectroscopic data obtained from the EUV Imaging Spectrometer on board Hinode. The photospheric magnetograms from the Helioseismic and Magnetic Imager are used to derive the magnetic field properties. To our knowledge, this work is the first spectroscopical analysis of the merging of two open-field structures. We find that the coronal hole and the coronal dimming become indistinguishable after the merging. The upflow speeds inside the coronal dimming become more similar to that of a coronal hole, with a mixture of plasma upflows and downflows observable after the merging. The brightening of the bright points and the appearance of coronal jets inside the merged region further imply ongoing reconnection processes. We propose that component reconnection between the coronal hole and coronal dimming fields plays an important role during this merging event because the footpoint switching resulting from the reconnection allows the coronal dimming to intrude onto the boundary of the southern polar coronal hole.

We report a partial filament eruption in the southern solar hemisphere that occurred on 18 March 2022 during the first science perihelion of Solar Orbiter. The filament erupted into a coronal mass ejection (CME), producing coronal dimmings at the footpoints of the erupting structure. The expanding dimming then merged with the adjacent southern polar coronal hole. This merging of two open magnetic structures is observationally rare and poorly understood. We use remote sensing data from multiple co-observing spacecraft to understand the physical processes during this merging event. The evolution of the merger is examined using Extreme-UltraViolet (EUV) images obtained from the instruments onboard the Solar Orbiter and Solar Dynamic Observatory spacecraft. The plasma dynamics are quantified using spectroscopic data obtained from the EUV Imaging Spectrometer onboard Hinode. The preliminary results show that the coronal hole and coronal dimming become indistinguishable from each other after the merging. Several plasma upflow regions were observed throughout the merging event, suggesting the opening of magnetic field lines. The brightening of bright points and coronal jets inside the merged region further imply ongoing reconnection processes. This work also has implications for the formation of coronal hole/open field regions and the origin of solar wind from coronal dimming and coronal hole boundaries.

We report on the merging between the southern polar coronal hole and an adjacent coronal dimming induced by a coronal mass ejection on 2022 March 18, resulting in the merged region persisting for at least 72 hrs. We use remote sensing data from multiple co-observing spacecraft to understand the physical processes during this merging event. The evolution of the merger is examined using Extreme-UltraViolet (EUV) images obtained from the Atmospheric Imaging Assembly onboard the Solar Dynamic Observatory and Extreme Ultraviolet Imager onboard the Solar Orbiter spacecraft. The plasma dynamics are quantified using spectroscopic data obtained from the EUV Imaging Spectrometer onboard Hinode. The photospheric magnetograms from the Helioseismic and Magnetic Imager are used to derive magnetic field properties. To our knowledge, this work is the first spectroscopical analysis of the merging of two open-field structures. We find that the coronal hole and the coronal dimming become indistinguishable after the merging. The upflow speeds inside the coronal dimming become more similar to that of a coronal hole, with a mixture of plasma upflows and downflows observable after the merging. The brightening of bright points and the appearance of coronal jets inside the merged region further imply ongoing reconnection processes. We propose that component reconnection between the coronal hole and coronal dimming fields plays an important role during this merging event, as the footpoint switching resulting from the reconnection allows the coronal dimming to intrude onto the boundary of the southern polar coronal hole.

Coronal jets are short-lived eruptive features commonly observed in polar coronal holes and are thought to play a key role in the transfer of mass and energy into the solar corona. We describe unique contemporaneous observations of a coronal blowout jet seen by the Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter (SO) spacecraft and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The coronal jet erupted from the south polar coronal hole, and was observed with high spatial and temporal resolution by both instruments. This enabled identification of the different stages of a breakout reconnection process producing the observed jet. We find bulk plasma flow kinematics of ∼100–200 km s⁻¹ across the lifetime of its observed propagation, with a distinct kink in the jet where it impacted and was subsequently guided by a nearby polar plume. We also identify a faint faster feature ahead of the bulk plasma motion propagating with a velocity of ∼715 km s⁻¹, which we attribute to untwisting of newly reconnected field lines during the eruption. A differential emission measure (DEM) analysis using the SDO/AIA observations revealed a very weak jet signal, indicating that the erupting material was likely much cooler than the coronal passbands used to derive the DEM. This is consistent with the very bright appearance of the jet in the Lyα passband observed by SO/EUI. The DEM was used to estimate the radiative thermal energy of the source region of the coronal jet, finding a value of ∼2 × 10²⁴ erg, comparable to the energy of a nanoflare.