Chromospheric Network Research Articles

The origin of interplanetary switchbacks in reconnection at chromospheric network boundaries

There is renewed interest in heliospheric physics following the recent exploration of the pristine solar wind by the Parker Solar Probe. Magnetic switchback structures are frequently observed in the inner heliosphere, but there are open questions about their origin. Many researchers are investigating the statistical properties of switchbacks and their relationships with wave modes, stream types and solar activity, but the sources of switchbacks remain elusive. Here we report that interplanetary switchbacks originate from magnetic reconnection on the Sun that occurs at chromospheric network boundaries and launch solar jet flows. We link in situ interplanetary measurements and remote-sensing solar observations to establish a connection between interplanetary switchbacks and their solar source region, featuring solar jets, chromospheric network boundaries and photospheric magnetic field evolution. Our findings suggest that joint observations of switchbacks and solar jets provide a better estimate of the contribution of magnetic reconnection to coronal heating and solar wind acceleration.

Rome Precision Solar Photometric Telescope: precision solar full-disk photometry during solar cycles 23–25

The Rome Precision Solar Photometric Telescope (Rome/PSPT) is a ground-based telescope engaged in precision solar photometry. It has a 27-year database of full-disk images of the photosphere and chromosphere beginning in 1996 and continuing to 2022. The solar images have been obtained daily, weather permitting, with approximately 2 arcsec/pixel scale in Ca II K line at 393.3 nm, G-band at 430.6 nm, and continuum in the blue and red parts of the spectrum at 409.4 nm and 607.2 nm, respectively. Regular observations were also performed at the green continuum at 535.7 nm for a period of about 18 months. Since the first-light, Rome/PSPT operations have been directed at understanding the source of short-and long-term solar irradiance changes, spanning from 1 min to several months, and from 1 year to a few solar cycles, respectively. However, Rome/PSPT data have also served to study a variety of other topics, including the photometric properties of solar disk features and of the supergranulation manifested by the chromospheric network. Moreover, they have been unique in allowing to connect series of historical and modern full-disk solar observations, especially the Ca II K line data. Here, we provide an overview of the Rome/PSPT telescope and of the solar monitoring carried out with it from its first light to the present, across solar cycles 23–25. We also briefly describe the main results achieved with Rome/PSPT data, and give an overview of new results being derived with the whole time series of observations covering the period 1996–2022.

The quiet sun at mm wavelengths as seen by ALMA

Solar observations at sub-mm, mm and cm wavelengths offer a straightforward diagnostic of physical conditions in the solar atmosphere because they yield measurement of brightness temperature which, for optically thick features, equals intrinsic temperature - much unlike solar diagnostics in other spectral ranges. The Atacama Large Millimeter and sub-millimeter Array (ALMA) has therefore opened a new, hitherto underexplored, spectral window for studying the enigmatic solar chromosphere. In this review we discuss initial ALMA studies of the quiet chromosphere that used both single-dish and compact-array interferometric observing modes. We present results on the temperature structure of the chromosphere, comparison with classic empirical models of the chromosphere, and observations of the chromospheric network and spicules. Furthermore, we discuss what may be expected in the future, since the ALMA capabilities continuously expand and improve towards higher angular resolution, wavelength coverage, and polarization measurement for magnetometry.

Solar Chromospheric Network as a Source for Solar Wind Switchbacks

Recent studies suggest that the magnetic switchbacks (SBs) detected by the Parker Solar Probe carry information on the scales of solar supergranulation (large scale) and granulation (medium scale). We test this claim using high-resolution Hα images obtained with the visible spectropolarimeters of the Goode Solar Telescope in Big Bear Solar Observatory. As possible solar sources, we count all the spicule-like features standing along the chromospheric networks near the coronal hole boundary visible in the Hα blue-wing but absent in the red-wing images and measure the geometric parameters of dense sections of individual flux tubes. Intervals between adjacent spicules located along the chromospheric networks are found in the range of 0.4–1.5 Mm (0.°03–0.°12) tending to be smaller than the medium scale of SBs. Interdistances between all pairs of the flux tubes are also counted and they appear in a single peak distribution around 0.7 Mm (0.°06) unlike the waiting-time distribution of SBs in a scale-free single power-law form. The length-to-diameter ratio of the dense section of flux tubes is as high as 6–40, similar to the aspect ratio of SBs. The number of spicules along a network can be as high as 40–100, consistent with numerous SBs within a patch. With these numbers, it is argued that the medium scale of SBs can be understood as an equilibrium distance resulting from a random walk within each diverging magnetic field funnel connected to the chromospheric networks.

Solar Observations with Single-Dish INAF Radio Telescopes: Continuum Imaging in the 18 – 26 GHz Range

We present a new solar radio imaging system implemented through the upgrade of the large single-dish telescopes of the Italian National Institute for Astrophysics (INAF), not originally conceived for solar observations.During the development and early science phase of the project (2018 – 2020), we obtained about 170 maps of the entire solar disk in the 18 – 26 GHz band, filling the observational gap in the field of solar imaging at these frequencies. These solar images have typical resolutions in the 0.7 – 2 arcmin range and a brightness temperature sensitivity <10 K. Accurate calibration adopting the Supernova Remnant Cas A as a flux reference provided typical errors <3% for the estimation of the quiet-Sun level components and active regions flux measurements.As the first early scientific result of the project, we present a catalog of radio continuum solar imaging observations with Medicina 32-m and SRT 64-m radio telescopes, including the multi-wavelength identification of active regions, their brightness and spectral characterization. The interpretation of the observed emission as thermal bremsstrahlung components combined with gyro-magnetic variable emission paves the way for the use of our system for long-term monitoring of the Sun. We also discuss useful outcomes both for solar physics (e.g., study of the chromospheric network dynamics) and space weather applications (e.g., flare precursors studies).

Extreme-UV quiet Sun brightenings observed by the Solar Orbiter/EUI

Context. The heating of the solar corona by small heating events requires an increasing number of such events at progressively smaller scales, with the bulk of the heating occurring at scales that are currently unresolved. Aims. The goal of this work is to study the smallest brightening events observed in the extreme-UV quiet Sun. Methods. We used commissioning data taken by the Extreme Ultraviolet Imager (EUI) on board the recently launched Solar Orbiter mission. On 30 May 2020, the EUI was situated at 0.556 AU from the Sun. Its High Resolution EUV telescope (HRIEUV, 17.4 nm passband) reached an exceptionally high two-pixel spatial resolution of 400 km. The size and duration of small-scale structures was determined by the HRIEUV data, while their height was estimated from triangulation with simultaneous images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory mission. This is the first stereoscopy of small-scale brightenings at high resolution. Results. We observed small localised brightenings, also known as ‘campfires’, in a quiet Sun region with length scales between 400 km and 4000 km and durations between 10 s and 200 s. The smallest and weakest of these HRIEUV brightenings have not been previously observed. Simultaneous observations from the EUI High-resolution Lyman-α telescope (HRILya) do not show localised brightening events, but the locations of the HRIEUV events clearly correspond to the chromospheric network. Comparisons with simultaneous AIA images shows that most events can also be identified in the 17.1 nm, 19.3 nm, 21.1 nm, and 30.4 nm pass-bands of AIA, although they appear weaker and blurred. Our differential emission measure analysis indicated coronal temperatures peaking at log T ≈ 6.1 − 6.15. We determined the height for a few of these campfires to be between 1000 and 5000 km above the photosphere. Conclusions. We find that ‘campfires’ are mostly coronal in nature and rooted in the magnetic flux concentrations of the chromospheric network. We interpret these events as a new extension to the flare-microflare-nanoflare family. Given their low height, the EUI ‘campfires’ could stand as a new element of the fine structure of the transition region-low corona, that is, as apexes of small-scale loops that undergo internal heating all the way up to coronal temperatures.

Transient small-scale brightenings in the quiet solar corona: A model for campfires observed with Solar Orbiter

Context. Recent observations by the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter have characterized prevalent small-scale transient brightenings in the corona above the quiet Sun termed campfires. Aims. In this study we search for comparable brightenings in a numerical model and then investigate their relation to the magnetic field and the processes that drive these events. Methods. We used the MURaM code to solve the 3D radiation magnetohydrodynamic equations in a box that stretches from the upper convection zone to the corona. The model self-consistently produces a supergranular network of the magnetic field and a hot corona above this quiet Sun. For the comparison with the model, we synthesized the coronal emission as seen by EUI in its 174 Å channel, isolated the seven strongest transient brightenings, and investigated the changes of the magnetic field in and around these in detail. Results. The transients we isolated have a lifetime of about 2 min and are elongated loop-like features with lengths around 1 Mm to 4 Mm. They tend to occur at heights of about 2 Mm to 5 Mm above the photosphere, a bit offset from magnetic concentrations that mark the bright chromospheric network, and they reach temperatures of above 1 MK. As a result, they very much resemble the larger campfires found in observations. In our model most events are energized by component reconnection between bundles of field lines that interact at coronal heights. In one case, we find that untwisting a highly twisted flux rope initiates the heating. Conclusions. Based on our study, we propose that the majority of campfire events found by EUI are driven by component reconnection and our model suggests that this process significantly contributes to the heating of the corona above the quiet Sun.

Asymmetry in the Length Scales of the Solar Supergranulation Network

Abstract Supergranulation is the horizontal velocity pattern on the solar surface with a typical size of 30,000 km and a lifetime of 24 hr. The network structure seen in chromospheric lines, such as Ca ii K 3934 Å, is the manifestation of supergranulation. The network seen in the extreme-ultraviolet lines like He ii 304 Å is the extension of the chromospheric network into the upper solar atmosphere. We have obtained the length scales of the supergranulation network from the autocorrelation function of calcium ii K spectroheliograms from the Kodaikanal archival data. The behavior of the length scales in the horizontal (parallel to the direction of rotation) and vertical (perpendicular to the direction of rotation) have been obtained in different latitudes for a period of about 100 yr. The time-averaged length scales show a nearly symmetric variation in the northern and southern hemispheres. The length scales also show a profound asymmetry in the horizontal and vertical directions, which is dependent on solar latitude. A comparison reveals that both length scales are almost equal near the equatorial latitudes, but the vertical length scales relatively become smaller toward higher latitudes. The asymmetry is independently verified from He ii 304 Å images from the Solar Dynamic Observatory/Atmospheric Imaging Assembly. As the length scales are related to the width of the network, the results point to the asymmetry in the supergranular cell boundary. Supergranulation is one of the basic length scales of solar convection, hence these results can have implications for the convection in Sun-like stars.

Waves propagation in network and inter-network bright points channels between the chromosphere and transition regions with IRIS observations

The significance increase of the plasma temperature from the solar photosphere to the corona up to 1MK is still unresolved. One of the candidates for this issue is waves and instabilities in the solar plasma. It was suggested that the energy of these waves could heat the solar atmosphere to transition-region (TR) and corona. Despite many recent kind of researches about waves in the various solar dynamic structures, the reasons for the sudden rise of solar atmospheric temperature are still not enough. By using the Interface Region Imaging Spectrograph (IRIS) telescope observations, we investigate the waves in magnetic tubes such as UV bright points (BPs) at the boundary and inside the supper-granules. The Study of these dynamic structures, between the chromosphere and transition region, will impressively increase our information of mass and energy transportation through interface region between the chromosphere and inner corona. The magnetic BPs are the faces of magnetic flux tubes that are associated with magnetic elements. The magnetic flux tubes expand upward and appear as bright grains that make up the chromospheric network. For investigating periodical behavior of these structures and various aspect of these oscillations, we analyze intensity oscillations individually in IRIS slit-jaw images at three filters included 2796 A, 1400 A and 1330 A by the wavelet analysis method. The wavelet analysis of the intensity fluctuations of these points showed periods from 2 to 8 min, which are in order of the frequencies of the atmospheric pressure modes. For investigating wave propagation in these layers we also study the correlation of oscillations between chromosphere (2796 A) and TR (1400 A and 1330 A) heights by cross wavelet method, and found that these heights correlate with periods between 2.5 and 5.5 min, with wave speeds from 30 to 200 km s−1. Also, by extracting Si IV line, we determined the Doppler velocity of BPs in the network and inter-network as about −20 to +30 km s−1 and −21 to +21 km s−1, respectively. Our results suggest that the wave propagation along the magnetic flux tubes of upward-moving plasma in BPs have an important role in solar atmosphere heating.

Observations of solar chromospheric oscillations at 3 mm with ALMA

Aims. We aim to study spatially resolved chromospheric oscillations of the quiet Sun (QS) in the mm-domain at a resolution of a few arcsec, typically 2.4″ × 4.5″. Methods. We used Atacama Large millimeter and submillimeter Array (ALMA) time series of interferometric observations of the QS obtained at 3 mm with a 2-s cadence and a spatial resolution of a few arcsec. The observations were performed on March 16, 2017 and seven 80″ × 80″ fields of view (FoV) going from disk center to limb were covered, each one observed for 10 min, therefore limiting the frequency resolution of the power spectra to 1.7 mHz. For each FoV, masks for cell and network were derived, and the averaged power spectral densities (PSDs) for the entire FoV, cell, and network were computed. The resulting power spectra were fit with an analytical function in order to derive the frequency and the root-mean-square (rms) power associated with the peaks. The same analysis, over the same FoVs and for the same intervals, was performed for simultaneous Atmospheric Imaging Assembly (AIA) image sequences in 1600 Å. Results. Spatially resolved chromospheric oscillations at 3 mm, with frequencies of 4.2 ± 1.7 mHz are observed in the QS, in both cell and network. The coherence length-scale of the oscillations is commensurate with the spatial resolution of our ALMA observations. Brightness-temperature fluctuations in individual pixels could reach up to a few hundred K, while the spatially averaged PSDs yield rms in the range ≈55–75 K, i.e., up to ≈1% of the averaged brightness temperatures and exhibit a moderate increase towards the limb. For AIA 1600 Å, the oscillation frequency is 3.7 ± 1.7 mHz. The relative rms is up to 6% of the background intensity, with a weak increase towards the disk center (cell, average). ALMA 3 mm time-series lag AIA 1600 Å by ≈100 s, which corresponds to a formation-height difference of ≈1200 km, representing a novel determination of this important parameter. Conclusions. The ALMA oscillations that we detected exhibit higher amplitudes than those derived from previous lower (≈10″) resolution observations at 3.5 mm by the Berkeley-Illinois-Maryland Array. Chromospheric oscillations are, therefore, not fully resolved at the length-scale of the chromospheric network, and possibly not even at the spatial resolution of our ALMA observations. Any study of transient brightenings in the mm-domain should take into account the oscillations.

Emergence of small-scale magnetic flux in the quiet Sun

Context. We study the evolution of a small-scale emerging flux region (EFR) in the quiet Sun, from its emergence in the photosphere to its appearance in the corona and its decay. Aims. We track processes and phenomena that take place across all atmospheric layers; we explore their interrelations and compare our findings with those from recent numerical modelling studies. Methods. We used imaging as well as spectral and spectropolarimetric observations from a suite of space-borne and ground-based instruments. Results. The EFR appears in the quiet Sun next to the chromospheric network and shows all morphological characteristics predicted by numerical simulations. The total magnetic flux of the region exhibits distinct evolutionary phases, namely an initial subtle increase, a fast increase with a Co-temporal fast expansion of the region area, a more gradual increase, and a slow decay. During the initial stages, fine-scale G-band and Ca II H bright points coalesce, forming clusters of positive- and negative-polarity in a largely bipolar configuration. During the fast expansion, flux tubes make their way to the chromosphere, pushing aside the ambient magnetic field and producing pressure-driven absorption fronts that are visible as blueshifted chromospheric features. The connectivity of the quiet-Sun network gradually changes and part of the existing network forms new connections with the newly emerged bipole. A few minutes after the bipole has reached its maximum magnetic flux, the bipole brightens in soft X-rays forming a coronal bright point. The coronal emission exhibits episodic brightenings on top of a long smooth increase. These coronal brightenings are also associated with surge-like chromospheric features visible in Hα, which can be attributed to reconnection with adjacent small-scale magnetic fields and the ambient quiet-Sun magnetic field. Conclusions. The emergence of magnetic flux even at the smallest scales can be the driver of a series of energetic phenomena visible at various atmospheric heights and temperature regimes. Multi-wavelength observations reveal a wealth of mechanisms which produce diverse observable effects during the different evolutionary stages of these small-scale structures.

Polar Activity of the Sun and Latitudinal Activity Drifts in Cycles 15–24

The solar activity at different latitudes is analyzed based on daily observations at Kodaikanal, Mount Wilson, Sacramento Peak, and Meudon observatories in the CaIIK line. Activity elements of various sizes, from the elements of the chromospheric network to the flocculi, are identified. A joint database of observation results that provides information on solar activity for 1905–2018 is created. Bright elements at middle and high latitudes are distinguished in the CaIIK line in daily images, in addition to the low-latitude activity that accompanies the appearance of sunspots. The activity can be represented as a single process that begins at high latitudes during the decline phase of the previous solar cycle and continues at low latitudes as sunspot activity. The activity-drift pattern is studied for Cycles 14–24. It is more consistent with the hypothesis of an extended solar cycle than the concept of two activity waves from the midlatitudes to poles and equator obtained from the processing of faculae in white light.

Measurement of the Height of the Chromospheric Network Emission from Solar Dynamics Observatory Images

We measured the height of the chromospheric network in the 1700, 1600, and 304 A wavelength bands of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) from the shift of features on the disk with respect to corresponding features in SDO/Helioseismic and Magnetic Imager (HMI) images of the absolute value of the longitudinal magnetic field. We found that near the limb the 304 A network emission forms 3.60$\pm$0.24 Mm above the 1600 A emission, which, in turn, forms 0.48$\pm$0.10 Mm above the HMI (6173 A) level. At the center of the disk the corresponding height differences are 2.99$\pm$0.02 Mm and 0.39$\pm$0.06 Mm respectively. We also found that the 1600 A network emission forms 0.25$\pm$0.02 Mm above the 1700 A emission near the limb and 0.20$\pm$0.02 Mm at the disk center. Finally, we examined possible variations with the solar cycle. Our results can help to check and refine atmospheric models.

Temporal variations of the solar EUV network properties

The chromospheric network extended to the transition region as the solar EUV network disperses at the coronal level. The EUV emission lines from the transition region give information about different atmospheric heights. The network properties have been obtained from the daily spectroscopic data from the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO) in two lines He i 584.5 A and O v 630 A. The synoptic changes in the line intensity, skewness of intensity distribution, mean contrast and network index with respect to the sunspot cycle were studied for a period of 11 years from 1996 to 2006. We have obtained the cross correlation of the monthly average of these quantities with the monthly sunspot number. The mean intensity and skewness of the two lines generally show a positive correlation with the sunspot cycle. The network contrast and network index of the He i shows a definite negative correlation with the sunspot cycle. The negative correlations shown by the He i line are unexpected which could be due to its anomalous behaviour. There are differences in the behaviour of the two lines regarding the time lag with the sunspot cycle and the magnitude of the correlation which is always higher for the He i line. The results have implications to the studies of solar irradiance, magnetic flux transfer and solar atmospheric dynamics.

Unraveling the Links among Sympathetic Eruptions

Abstract Solar eruptions occurring at different places within a relatively short time interval are considered to be sympathetic. However, it is difficult to determine whether there exists a cause and effect between them. Here we study a failed and a successful filament eruption following an X1.8-class flare on 2014 December 20, in which slipping-like magnetic reconnections serve as a key causal link among the eruptions. Reconnection signatures and effects are identified as follows: at both sides of the filament experiencing the failed eruption, serpentine ribbons extend along the chromospheric network to move away from the filament, while a hot loop apparently grows above it; at the filament undergoing the successful eruption, overlying cold loops contract, while coronal dimming appears at both sides even before the filament eruption. These effects are understood by reconnections continually transforming magnetic fluxes overlying one filament to the other, which adjusts how the magnetic field decays with increasing height above the filaments in opposite trends, therefore either strengthening or weakening the magnetic confinement of each filament.

Solar wind and kinetic heliophysics

Abstract. This paper reviews recent aspects of solar wind physics and elucidates the role Alfvén waves play in solar wind acceleration and turbulence, which prevail in the low corona and inner heliosphere. Our understanding of the solar wind has made considerable progress based on remote sensing, in situ measurements, kinetic simulation and fluid modeling. Further insights are expected from such missions as the Parker Solar Probe and Solar Orbiter. The sources of the solar wind have been identified in the chromospheric network, transition region and corona of the Sun. Alfvén waves excited by reconnection in the network contribute to the driving of turbulence and plasma flows in funnels and coronal holes. The dynamic solar magnetic field causes solar wind variations over the solar cycle. Fast and slow solar wind streams, as well as transient coronal mass ejections, are generated by the Sun's magnetic activity. Magnetohydrodynamic turbulence originates at the Sun and evolves into interplanetary space. The major Alfvén waves and minor magnetosonic waves, with an admixture of pressure-balanced structures at various scales, constitute heliophysical turbulence. Its spectra evolve radially and develop anisotropies. Numerical simulations of turbulence spectra have reproduced key observational features. Collisionless dissipation of fluctuations remains a subject of intense research. Detailed measurements of particle velocity distributions have revealed non-Maxwellian electrons, strongly anisotropic protons and heavy ion beams. Besides macroscopic forces in the heliosphere, local wave–particle interactions shape the distribution functions. They can be described by the Boltzmann–Vlasov equation including collisions and waves. Kinetic simulations permit us to better understand the combined evolution of particles and waves in the heliosphere.

First high-resolution look at the quiet Sun with ALMA at 3mm

We present an overview of high-resolution quiet Sun observations, from disk center to the limb, obtained with the Atacama Large millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun regions were observed at a resolution of up to 2.5″ by 4.5″. We produced both average and snapshot images by self-calibrating the ALMA visibilities and combining the interferometric images with full-disk solar images. The images show well the chromospheric network, which, based on the unique segregation method we used, is brighter than the average over the fields of view of the observed regions by ∼305 K while the intranetwork is less bright by ∼280 K, with a slight decrease of the network/intranetwork contrast toward the limb. At 3 mm the network is very similar to the 1600 Å images, with somewhat larger size. We detect, for the first time, spicular structures, rising up to 15″ above the limb with a width down to the image resolution and brightness temperature of ∼1800 K above the local background. No trace of spicules, either in emission or absorption, is found on the disk. Our results highlight the potential of ALMA for the study of the quiet chromosphere.

Are Starspots and Plages Co-located on Active G and K Stars?

Abstract We explore the connection between starspots and plages of three main-sequence stars by studying the chromospheric and photospheric activity over several rotation periods. We present simultaneous photometry and high-resolution (R ∼ 31500) spectroscopy of KIC 9652680, a young, super-flare-producing G1 star with a rotation period of 1.4 days. Its Kepler light curve shows rotational modulation consistent with a bright hemisphere followed by a relatively dark hemisphere, generating photometric variability with a semi-amplitude of 4%. We find that KIC 9652680 is darkest when its S-index of Ca ii H &amp; K emission is at its maximum. We interpret this anti-correlation between flux and S to indicate that dark starspots in the photosphere are co-located with the bright plages in the chromosphere, as they are on the Sun. Moving to lower masses and slower rotators, we present K2 observations with simultaneous spectroscopy of EPIC 211928486 (K5V) and EPIC 211966629 (K4V), two active stars in the 650 Myr old open cluster Praesepe. The K2 photometry reveals that both stars have rotation periods of 11.7 days; while their flux varies by 1 and 2% respectively, their Ca ii H &amp; K S-indices seem to hold relatively constant as a function of rotational phase. This suggests that extended chromospheric networks of plages are not concentrated into regions of emission centered on the starspots that drive rotational modulation, unlike KIC 9652680. We also note that the Ca ii emission of EPIC 211928486 dipped and recovered suddenly over the duration of one rotation, suggesting that the evolution timescale of plages may be of order the rotation period.

Temporal and latitudinal variations of the length-scales and relative intensities of the chromospheric network

Temporal and latitudinal variations of the length-scales and relative intensities of the chromospheric network

Variation in the Width of Transition Region Network Boundaries

The transition region network seen in solar extreme ultraviolet (EUV) lines is the extension of the chromospheric network. The network appears as an irregular web-like pattern over the solar surface outside active regions. The average width of transition region network boundaries is obtained from the two-dimensional autocorrelation function of SOlar and Heliospheric Observatory (SOHO)/Coronal Diagnostic Spectrometer (CDS) synoptic images of the Sun in two emission lines, He i 586 A and O v 630 A during 1996 – 2012. The width of the network boundaries is found to be roughly correlated with the solar cycle variation with a lag of about ten months. A comparison of the widths in the two emission lines shows that they are larger for the He i line. The SOHO/CDS data also show large asymmetry in boundary widths in the horizontal (x) and vertical (y) image directions, which is shown to be caused by image distortions that are due to instrumental effects. Since the network boundary widths are related to the magnetic flux concentration along the boundaries, the results are expected to have implications on the flux transport on the solar surface, solar cycle, and the mass and energy budget of network loops and jets.