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Active region (AR) outflows have been studied in detail since the launch of textit{Hinode}/EIS and are believed to provide a possible source of mass and energy to the slow solar wind. In this work, we investigate the lower atmospheric counterpart of AR outflows using observations from the textit{Interface Region Imaging Spectrograph} (textit{IRIS}). We find that the textit{IRIS} siiv, cii and mgii transition region (TR) and chromospheric lines exhibit different spectral features in the outflows as compared to neighboring regions at the footpoints (moss) of hot AR loops. The average redshift of siiv in the outflows region ($approx$ 5.5~km s$^{-1}$) is smaller than typical moss ($approx$ 12--13 km~s$^{-1}$) and quiet Sun ($approx$ 7.5 km~s$^{-1}$) values, while the cii~line is blueshifted ($approx$ -1.1--1.5 km~s$^{-1}$), in contrast to the moss where it is observed to be redshifted by about $approx$ 2.5 km~s$^{-1}$. Further, we observe that the low atmosphere underneath the coronal outflows is highly structured, with the presence of blueshifts in siiv and positive mgii k2 asymmetries (which can be interpreted as signatures of chromospheric upflows) which are mostly not observed in the moss. These observations show a clear correlation between the coronal outflows and the chromosphere and TR underneath, which has not been shown before. Our work strongly suggests that these regions are not separate environments and should be treated together, and that current leading theories of AR outflows, such as the interchange reconnection model, need to take into account the dynamics of the low atmosphere.
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Recent observations from the Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode have shown that low density areas on the periphery of active regions are characterized by strong blue-shifts at 1 MK. These Doppler shifts have been associated with outward propagating disturbances observed with Extreme-ultraviolet and soft X-ray imagers. Since these instruments can have broad temperature responses we investigate these intensity fluctuations using the monochromatic imaging capabilities of EIS and confirm their 1 MK nature. We also find that the Fe XII 195.119 A blue shifted spectral profiles at their footpoints exhibit transient blue wing enhancements on timescales as short as the 5 minute cadence. We have also looked at the fan peripheral loops observed at 0.6 MK in Si VII 275.368 A in those regions and find no sign of the recurrent outward propagating disturbances with velocities of 40 - 130 km/s seen in Fe XII. We do observe downward trends (15 - 20 km/s) consistent with the characteristic red-shifts measured at their footpoints. We, therefore, find no evidence that the structures at these two temperatures and the intensity fluctuations they exhibit are related to one another.
The origin of the slow solar wind is still an open issue. It has been suggested that upflows at the edge of active regions (AR) can contribute to the slow solar wind. Here, we compared the upflow region and the AR core and studied how the plasma properties change from the chromosphere via the transition region to the corona. We studied limb-to-limb observations NOAA 12687 (14th - 25th Nov 2017). We analysed spectroscopic data simultaneously obtained from IRIS and Hinode/EIS in six spectral lines. We studied the mutual relationships between the plasma properties for each emission line, as well as comparing the plasma properties between the neighbouring formation temperature lines. To find the most characteristic spectra, we classified the spectra in each wavelength using the machine learning technique k-means. We found that in the upflow region the Doppler velocities of the coronal lines are strongly correlated, but the transition region and coronal lines show no correlation. However, their fluxes are strongly correlated. The upflow region has lower density and lower temperature than the AR core. In the upflow region, the Doppler and non-thermal velocity show a strong correlation in the coronal lines, but the correlation is not seen in the AR core. At the boundary between the upflow region and the AR core, the upflow region shows an increase in the coronal non-thermal velocity, the emission obtained from the DEM, and the domination of the redshifted regions in the chromosphere. The obtained results suggest that at least three parallel mechanisms generate the plasma upflow: (1) the reconnection between closed loops and open magnetic field lines in the lower corona or upper chromosphere; (2) the reconnection between the chromospheric small-scale loops and open magnetic field; (3) the expansion of the magnetic field lines that allows the chromospheric plasma to escape to the solar corona.
The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a long standing problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, low lying loops or loop segments at transition-region temperatures that vary rapidly, on the timescales of minutes. We argue that the existence of these loops solves a long standing observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle.
Plasma outflows from the edges of active regions have been suggested as a possible source of the slow solar wind. Spectroscopic measurements show that these outflows have an enhanced elemental composition, which is a distinct signature of the slow wind. Current spectroscopic observations, however, do not have sufficient spatial resolution to distinguish what structures are being measured or to determine the driver of the outflows. The High-resolution Coronal Imager (Hi-C) flew on a sounding rocket in May, 2018, and observed areas of active region outflow at the highest spatial resolution ever achieved (250 km). Here we use the Hi-C data to disentangle the outflow composition signatures observed with the Hinode satellite during the flight. We show that there are two components to the outflow emission: a substantial contribution from expanded plasma that appears to have been expelled from closed loops in the active region core, and a second contribution from dynamic activity in active region plage, with a composition signature that reflects solar photospheric abundances. The two competing drivers of the outflows may explain the variable composition of the slow solar wind.
Active regions are thought to be one contributor to the slow solar wind. Upflows in EUV coronal spectral lines are routinely osberved at their boundaries, and provide the most direct way for upflowing material to escape into the heliosphere. The mechanisms that form and drive these upflows, however, remain to be fully characterised. It is unclear how quickly they form, or how long they exist during their lifetimes. They could be initiated low in the atmosphere during magnetic flux emergence, or as a response to processes occuring high in the corona when the active region is fully developed. On 2019, March 31, a simple bipolar active region (AR 12737) emerged and upflows developed on each side. We used observations from Hinode, SDO, IRIS, and Parker Solar Probe (PSP) to investigate the formation and development of the upflows from the eastern side. We used the spectroscopic data to detect the upflow, and then used the imaging data to try to trace its signature back to earlier in the active region emergence phase. We find that the upflow forms quickly, low down in the atmosphere, and that its initiation appears associated with a small field-opening eruption and the onset of a radio noise storm detected by PSP. We also confirmed that the upflows existed for the vast majority of the time the active region was observed. These results suggest that the contribution to the solar wind occurs even when the region is small, and continues for most of its lifetime.
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