Coronal hole evolution from multi-viewpoint data as input for a STEREO solar wind speed persistence model

Temmer, Manuela; Hinterreiter, Jürgen; Reiss, Martin A.

doi:10.1051/swsc/2018007

Cited by 26 publications

(24 citation statements)

References 29 publications

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“…For example, if the continuous outflow in some funnels is disrupted and starts to weaken in a non-uniform or unsynchronized manner and at a higher rate than the increase in other funnels, we would expect a non-linear relation between CH area and solar wind outflow speed (which has been shown statistically, e.g. by Temmer et al 2018).…”

Section: Discussionmentioning

confidence: 99%

Three-phase Evolution of a Coronal Hole. II. The Magnetic Field

Heinemann

Hofmeister

Veronig

et al. 2018

ApJ

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We investigate the magnetic characteristics of a persistent coronal hole (CH) extracted from EUV imagery using HMI filtergrams over the timerange February 2012 − October 2012. The magnetic field, its distribution as well as the magnetic fine structure in form of flux tubes (FT) are analyzed in different evolutionary states of the CH. We find a strong linear correlation between the magnetic properties (e.g. signed/unsigned magnetic field strength) and area of the CH. As such, the evolutionary pattern in the magnetic field clearly follows the three-phase evolution (growing, maximum and decaying phase) as found from EUV data (Part I). This evolutionary process is most likely driven by strong FTs with a mean magnetic field strength exceeding 50 G. During the maximum phase they entail up to 72% of the total signed magnetic flux of the CH, but only cover up to 3.9% of the total CH area, whereas during the growing and decaying phase, strong FTs entail 54 − 60% of the signed magnetic flux and cover around 1 − 2% of the CHs total area. We conclude that small scale-structures of strong unipolar magnetic field are the fundamental building blocks of a CH and govern its evolution.

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Section: Discussionmentioning

confidence: 99%

Three-phase Evolution of a Coronal Hole. II. The Magnetic Field

Heinemann

Hofmeister

Veronig

et al. 2018

ApJ

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“…Reliably defining CH boundaries is not only relevant for studying coronal and photospheric properties and their evolution but is also of major scientific importance towards space weather research. Empirical relations between CH area and measured solar wind speed at 1 AU (e.g., Nolte et al, 1976;Vršnak, Temmer, and Veronig, 2007;Tokumaru et al, 2017;Hofmeister et al, 2018) are used for forecasting purposes (e.g., Rotter et al, 2012Rotter et al, , 2015Reiss et al, 2016;Temmer, Hinterreiter, and Reiss, 2018). Moreover, the distance to CH boundary is an important parameter for MHD models simulating the solar wind distribution in interplanetary space (e.g., ENLIL: Odstrčil and Pizzo 1999, EUHFORIA: Pomoell and Poedts 2018and CORHEL: Riley et al 2012.…”

Section: Introductionmentioning

confidence: 99%

Statistical Analysis and Catalog of Non-polar Coronal Holes Covering the SDO-Era Using CATCH

et al. 2019

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Coronal holes are usually defined as dark structures seen in the extreme ultraviolet and X-ray spectrum which are generally associated with open magnetic fields. Deriving reliably the coronal hole boundary is of high interest, as its area, underlying magnetic field, and other properties give important hints as regards high speed solar wind acceleration processes and compression regions arriving at Earth. In this study we present a new threshold-based extraction method, which incorporates the intensity gradient along the coronal hole boundary, which is implemented as a user-friendly SSW-IDL GUI. The Collection of Analysis Tools for Coronal Holes (CATCH) enables the user to download data, perform guided coronal hole extraction and analyze the underlying photospheric magnetic field. We use CATCH to analyze non-polar coronal holes during the SDO-era, based on 193 Å filtergrams taken by the Atmospheric Imaging Assembly (AIA) and magnetograms taken by the Heliospheric and Magnetic Imager (HMI), both on board the Solar Dynamics Observatory (SDO). Between 2010 and 2019 we investigate 707 coronal holes that are located close to the central meridian. We find coronal holes distributed across latitudes of about ± 60 • , for which we derive sizes between 1.6 × 10 9 and 1.8 × 10 11 km 2. The absolute value of the mean signed magnetic field strength tends towards an average of 2.9 ± 1.9 G. As far as the abundance and size of coronal holes is concerned, we find no distinct trend towards the northern or southern hemisphere. We find that variations in local and global conditions may significantly change Electronic supplementary material The online version of this article (

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“…Data assimilation (DA) is the mathematically rigorous process of Topical Issue -Space Weather research in the Digital Age and across the full data lifecycle combining models and observations, taking account of their individual uncertainties (Kalnay, 2002;Asch et al, 2016). This methodology has long been used in atmospheric and oceanic sciences (Sasaki, 1970;Ghil & Malanotte-Rizzoli, 1991;Rabier, 2005) and has more recently been adopted in relatively data-rich areas of space physics (Bust & Mitchell, 2008;Hickmann et al, 2015;Glauert et al, 2018;Temmer et al, 2018;Aseev & Shprits, 2019;Elvidge & Angling, 2019). In the heliosphere, we have recently demonstrated assimilation of in situ solar wind observations (Lang et al, 2017;Lang & Owens, 2019), though the same methods should be broadly applicable to other remote observing techniques in the future (e.g., Manoharan, 2012;Barnard et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Quantifying the latitudinal representivity of in situ solar wind observations

Owens

Lang

Riley

et al. 2020

J. Space Weather Space Clim.

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Advanced space-weather forecasting relies on the ability to accurately predict near-Earth solar wind conditions. For this purpose, physics-based, global numerical models of the solar wind are initialized with photospheric magnetic field and coronagraph observations, but no further observation constraints are imposed between the upper corona and Earth orbit. Data assimilation (DA) of the available in situ solar wind observations into the models could potentially provide additional constraints, improving solar wind reconstructions, and forecasts. However, in order to effectively combine the model and observations, it is necessary to quantify the error introduced by assuming point measurements are representative of the model state. In particular, the range of heliographic latitudes over which in situ solar wind speed measurements are representative is of primary importance, but particularly difficult to assess from observations alone. In this study we use 40+ years of observation-driven solar wind model results to assess two related properties: the latitudinal representivity error introduced by assuming the solar wind speed measured at a given latitude is the same as that at the heliographic equator, and the range of latitudes over which a solar wind measurement should influence the model state, referred to as the observational localisation. These values are quantified for future use in solar wind DA schemes as a function of solar cycle phase, measurement latitude, and error tolerance. In general, we find that in situ solar wind speed measurements near the ecliptic plane at solar minimum are extremely localised, being similar over only 1° or 2° of latitude. In the uniform polar fast wind above approximately 40° latitude at solar minimum, the latitudinal representivity error drops. At solar maximum, the increased variability of the solar wind speed at high latitudes means that the latitudinal representivity error increases at the poles, though becomes greater in the ecliptic, as long as moderate speed errors can be tolerated. The heliospheric magnetic field and solar wind density and temperature show very similar behaviour.

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Coronal hole evolution from multi-viewpoint data as input for a STEREO solar wind speed persistence model

Cited by 26 publications

References 29 publications

Three-phase Evolution of a Coronal Hole. II. The Magnetic Field

Three-phase Evolution of a Coronal Hole. II. The Magnetic Field

Statistical Analysis and Catalog of Non-polar Coronal Holes Covering the SDO-Era Using CATCH

Quantifying the latitudinal representivity of in situ solar wind observations

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