Synoptic Maps Research Articles

The Solar Activity Monitor Network – SAMNet

The Solar Activity Magnetic Monitor (SAMM) Network (SAMNet) is a future UK-led international network of ground-based solar telescope stations. SAMNet, at its full capacity, will continuously monitor the Sun’s intensity, magnetic, and Doppler velocity fields at multiple heights in the solar atmosphere (from photosphere to upper chromosphere). Each SAMM sentinel will be equipped with a cluster of identical telescopes each with a different magneto-optical filter (MOFs) to take observations in K I, Na D, and Ca I spectral bands. A subset of SAMM stations will have white-light coronagraphs and emission line coronal spectropolarimeters. The objectives of SAMNet are to provide observational data for space weather research and forecast. The goal is to achieve an operationally sufficient lead time of e.g., flare warning of 2–8 h and provide many sought-after continuous synoptic maps (e.g., LoS magnetic and velocity fields, intensity) of the lower solar atmosphere with a spatial resolution limited only by seeing or diffraction limit, and with a cadence of 10 min. The individual SAMM sentinels will be connected to their master HQ hub where data received from all the slave stations will be automatically processed and flare warning issued up to 26 h in advance.

ЦИРКУЛЯЦИОННЫЕ ФАКТОРЫ ЛЕСНЫХ ПОЖАРОВ НА ТЕРРИТОРИИ СИБИРИ И ЯКУТИИ В НАЧАЛЕ XXI В

Natural fires in the northern underdeveloped regions of Russia constitute a significant part of natural emergencies, while about 70-90% of all forest areas covered by fire are recorded in Siberia and Yakutia. These are the regions where the bulk of the boreal forests of Russia are concentrated, which play an important role in the absorption and sequestration of carbon. Global changes, which are seen as an integral result of climate change and anthropogenic activities, are rapidly changing the environment of the boreal forest. In this regard, studies of climatic and circulation factors for the occurrence and spread of forest fires are relevant. The territories of the Krasnoyarsk Territory, the Irkutsk Region, the Republic of Buryatia, the Republic (Sakha) of Yakutia and Transbaikalia, which make a significant contribution to the dynamics of forest fires in Russia as a whole, were chosen as objects of study. According to the daily data of FBU "Avialesohrana", the percentage contribution of these regions to the number and area of forest fires that were recorded in Russia from June 1 to September 30 was calculated using the example of 2020 and 2021. Based on the typification of synoptic processes near the Earth's surface and the middle troposphere, according to the daily synoptic maps of the Hydrometeorological Center of Russia, the prevailing types of weather conditions of a high level of fire danger in Siberia and Yakutia were established.

Development of a Deep Learning Model for Inversion of Rotational Coronagraphic Images Into 3D Electron Density

Abstract We present, for the first time, a deep learning model that returns the three-dimensional (3D) coronal electron density from coronagraphic images. The intensity of coronagraphic observations arises from the Thomson scattering of photospheric light by the coronal electrons. We use MHD numerical simulations to obtain realistic 3D electron density and construct error-free training sets consisting of input (observation) and target (electron density) images. In the training sets, the input images are directly synthesized from the target 3D electron density by applying the Thomson scattering theory. The input and target images are in the form of latitude–longitude maps given at a radius, often referred to as synoptic maps. Using synoptic maps reduces a tomographic method to an image translation problem. We use pix2pixHD, one of the well-established supervised image translation methods and develop models for six selected heights: 2.0, 2.2, 2.5, 4.0, 6.0, and 12.0 solar radii. All six models have similar performance and the mean absolute percent error of the generated density images is less than 7% with respect to the ground-truth simulated data sets.

Inferring magnetic helicity spectrum in spherical domains: Method and example applications

Context. Obtaining observational constraints on the role of turbulent effects for the solar dynamo is a difficult, yet crucial, task. Without such knowledge, the full picture of the operation mechanism of the solar dynamo cannot be formed. Aims. The magnetic helicity spectrum provides important information about the α effect. Here we demonstrate a formalism in spherical geometry to infer magnetic helicity spectra directly from observations of the magnetic field, taking into account the sign change of magnetic helicity across the Sun’s equator. Methods. Using an angular correlation function of the magnetic field, we develop a method to infer spectra for magnetic energy and helicity. The retrieval of the latter relies on a fundamental definition of helicity in terms of linkage of magnetic flux. We apply the two-scale approach, previously used in Cartesian geometry, to spherical geometry for systems where a sign reversal of helicity is expected across the equator on both small and large scales. Results. We test the method by applying it to an analytical model of a fully helical field, and to magneto-hydrodynamic simulations of a turbulent dynamo. The helicity spectra computed from the vector potential available in the models are in excellent agreement with the spectra computed solely from the magnetic field using our method. In a next test, we use our method to obtain the helicity spectrum from a synoptic magnetic field map corresponding to a Carrington rotation. We observe clear signs of a bihelical spectrum of magnetic helicity, which is in complete accordance to the previously reported spectra in literature from the same map. Conclusions. Our formalism makes it possible to infer magnetic helicity in spherical geometry, without the necessity of computing the magnetic vector potential. It has many applications in solar and stellar observations, but can also be used to analyse global magnetoconvection models of stars and to compare them with observations.

Solar Cycle Evolution of Filaments over a Century: Investigations with the Meudon and McIntosh Hand-drawn Archives

Abstract Hand-drawn synoptic maps from the Meudon Observatory (1919 onwards) and the McIntosh archive (1967 onwards) are two important sources of long-term, manually recorded filament observations. In this study, we calibrate the Meudon maps and subsequently identify filaments through an automated method. We extract physical parameters from this filament database and perform a comparative study of their long-term evolution focusing on the cotemporal period of the McIntosh and Meudon observations. The spatiotemporal evolution of filaments manifests in the form of a filament butterfly diagram, further indicating that they are intimately related to the large-scale solar cycle. Physical descriptors such as the number and length of filaments, which are tracers of the solar surface magnetic field, have cycles which are phase locked with the ∼11 yr sunspot cycle. The tilt-angle distribution of filaments—both near to or distant from active region locations—indicates that their origin is due to either large-scale surface magnetic field or inter-active-region field evolution. This study paves the way for constructing a composite series of hand-drawn filament data with minimal gaps stretching over the time span of solar filament observations up to a century. On the one hand, this would serve as a useful constraint for models of magnetic field emergence and evolution on the Sun’s surface over multiple solar cycles, and on the other hand, this filament database may be used to guide the reconstruction of filament/prominence associated eruptive events before the space age.

Formation factors of the most electrically active thunderstorm days over Poland (2002–2020)

This research documents atmospheric conditions and development of high electrically active thunderstorm days that occurred over Poland in period 2002–2020. The 8 days with the highest number of detected cloud-to-ground flashes during one storm cell life cycle were analyzed. The study used data from the PERUN lightning detection and location system, ERA5-reanalysis, vertical atmospheric soundings, and synoptic maps as well. As a result of the analysis, it can be concluded that the development of thunderstorms is positively influenced by the low-pressure area above the North Sea and the atmospheric fronts with zone of wind convergence in the lower troposphere. The analyzed storm systems on the analyzed days were created in the atmosphere of a high vertical wind shear (from 10 to 18 m s−1), lifted index (from +0.04 to –8.22), thermodynamic instability (CAPE 1000–3700 J kg−1), rich boundary layer moisture (mixing ratio: 12–14 g kg−1), and high tropospheric moisture (total column water vapour >50 kg m−2). Very moist air masses ahead of the storm systems provided consistent access to large amounts of latent heat released into the clouds and intensified upward mass fluxes and development of intense lightning activity from Cumulonimbus cloud.

Moisture sources and transport during an extreme rainfall event over the Limpopo River Basin, southern Africa

Intermittent heavy rainfall over an eleven day period (11–21 January 2013) led to devastating floods over parts of South Africa and southern Mozambique, with regions within the Limpopo River Basin (LRB) being the worst affected. Previous observational work, based on an Eulerian analysis and low resolution data, indicated that moisture emanating from anomalously warm waters off the Angolan coast played a very important role in the evolution of this heavy rainfall event. However, there has been some debate about this moisture source and the general synoptic settings of the event that produced the heavy rainfall in the LRB. In this study, an analysis of the event using WRF model (12 km resolution) simulations, reanalyses, SAWS synoptic maps and NASA satellite images indicated that a tropical low was largely responsible for the floods which occurred over the LRB, particularly between 17 and 21 January. Moisture sources and transport are determined using the HYSPLIT model forced with WRF output and reveal a new perspective on the complex evolution of the event. During the early parts of the event, there were two core moisture source regions: i) a continental source with moisture being supplied from the Congo Basin region and, ii) a local oceanic region with moisture originating from the Agulhas Current and the Mozambique Channel. As the event progressed, the dominant moisture input was from parts of the South Indian Ocean including off the coast of Tanzania/Mozambique and to the east of Madagascar. Two days showed a moisture contribution from the tropical South Atlantic Ocean. A WRF sensitivity study with the observed warm SST anomaly off Angola replaced by climatological SST there indicated a reduction of moisture from the tropical South East Atlantic Ocean in the beginning and towards the end of the event, when there was some of the heaviest rainfall over the LRB, thereby reinforcing the suggestion that there was also some moisture being sourced from the tropical South East Atlantic during part of the observed event. When calculated over the entire 11–21 January 2013 event, there were four moisture sources, the largest contribution of which was from the Agulhas Current/Mozambique Channel and the South Indian Ocean, accounting for 53% of the moisture, followed by the continental source (25%). The tropical western Indian Ocean had the third largest contribution, at 17%, and the midlatitude South Atlantic Ocean (5%) contributed the least.

Evaluation of Version 3 Total and Tropospheric Ozone Columns From Earth Polychromatic Imaging Camera on Deep Space Climate Observatory for Studying Regional Scale Ozone Variations

Discrete wavelength radiance measurements from the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) allows derivation of global synoptic maps of total and tropospheric ozone columns every hour during Northern Hemisphere (NH) Summer or 2 hours during Northern Hemisphere winter. In this study, we present version 3 retrieval of Earth Polychromatic Imaging Camera ozone that covers the period from June 2015 to the present with improved geolocation, calibration, and algorithmic updates. The accuracy of total and tropospheric ozone measurements from EPIC have been evaluated using correlative satellite and ground-based total and tropospheric ozone measurements at time scales from daily averages to monthly means. The comparisons show good agreement with increased differences at high latitudes. The agreement improves if we only accept retrievals derived from the EPIC 317 nm triplet and limit solar zenith and satellite looking angles to 70°. With such filtering in place, the comparisons of EPIC total column ozone retrievals with correlative satellite and ground-based data show mean differences within ±5-7 Dobson Units (or 1.5–2.5%). The biases with other satellite instruments tend to be mostly negative in the Southern Hemisphere while there are no clear latitudinal patterns in ground-based comparisons. Evaluation of the EPIC ozone time series at different ground-based stations with the correlative ground-based and satellite instruments and ozonesondes demonstrated good consistency in capturing ozone variations at daily, weekly and monthly scales with a persistently high correlation (r2 > 0.9) for total and tropospheric columns. We examined EPIC tropospheric ozone columns by comparing with ozonesondes at 12 stations and found that differences in tropospheric column ozone are within ±2.5 DU (or ∼±10%) after removing a constant 3 DU offset at all stations between EPIC and sondes. The analysis of the time series of zonally averaged EPIC tropospheric ozone revealed a statistically significant drop of ∼2–4 DU (∼5–10%) over the entire NH in spring and summer of 2020. This drop in tropospheric ozone is partially related to the unprecedented Arctic stratospheric ozone losses in winter-spring 2019/2020 and reductions in ozone precursor pollutants due to the COVID-19 pandemic.

Reconstructing solar magnetic fields from historical observations

Context. The evolution of the photospheric magnetic field can be simulated with surface flux transport (SFT) simulations, which allow for the study of the evolution of the entire field, including polar fields, solely using observations of the active regions. However, because only one side of the Sun is visible at a time, active regions that emerge and decay on the far-side are not observed and not included in the simulations. As a result, some flux is missed. Aims. We construct additional active regions and apply them to the far-side of the Sun in an SFT simulation to assess the possible effects and the magnitude of error that the missing far-side flux causes. We estimate how taking the missing far-side flux into account affects long-term SFT simulations. Methods. We identified active regions from synoptic maps of the photospheric magnetic field between 1975 and 2019. We divided them into solar cycle wings and determined their lifetimes. Using the properties of observed active regions with sufficiently short lifetimes, we constructed additional active regions and inserted them into an SFT simulation. Results. We find that adding active regions with short lifetimes to the far-side of the Sun results in significantly stronger polar fields in minimum times and slightly delayed polarity reversals. These results partly remedy the earlier results, which show overly weak polar fields and polarity reversals that are slightly too early when far-side emergence is not taken into account. The far-side active regions do not significantly affect poleward flux surges, which are mostly caused by larger long-living active regions. The far-side emergence leads to a weak continuous flow of flux, which affects polar fields over long periods of time.

On Using Lagrangian Drift Simulations to Aid Interpretation of in situ Monitoring Data

One key challenge of marine monitoring programs is to reasonably combine information from different in situ observations spread in space and time. In that context, we suggest the use of Lagrangian transport simulations extending both forward and backward in time to identify the movements of water bodies from the time they were observed to the time of their synopsis. We present examples of how synoptic maps of salinity generated by this method support the identification and tracing of river plumes in coastal regions. We also demonstrate how we can use synoptic maps to delineate different water masses in coastal margins. These examples involve quasi-continuous observations of salinity taken along ferry routes. A third application is the synchronization of measurements between fixed stations and nearby moving platforms. Both observational platforms often see the same water body, but at different times. We demonstrate how the measurements from a fixed platform can be synchronized to measurements from a moving platform by taking into account simulation-based time shifts.

Marine storms in coastal tourist areas of the Canary Islands

The small island areas oriented to coastal tourism are highly vulnerable to marine storms, given the fluctuation of this economic sector and the increase in its exposure due to the increasing anthropogenic presence on the coastline. In this context, the storms between 1958 and 2017 are studied here in the most important tourist enclaves of Tenerife and Gran Canaria, located in the municipalities of Arona and Adeje (SW of Tenerife) and in San Bartolomé de Tirajana and Mogán (S-SW of Gran Canaria). In order to perform the analysis, wave data from State Ports (Spain) (SIMAR-44 nodes, Ministry of Transport, Mobility and Urban Agenda of Spain) are used. A statistical study of the phenomena can help establish a threshold for the identification of a marine storm based on a significant wave height (Hs) of 2.7 m in Arona and Adeje and 1.7 m in San Bartolomé de Tirajana and Mogán. The application of this threshold identified 144 episodes in the SW of Tenerife and 154 in the S-SW of Gran Canaria. Their behavior is examined from, on the one hand, the duration, seasonality, type of waves and degree of severity that characterizes them; and, on the other, from the state of the atmosphere that concurs in its genesis by means of the Wetterzentrale synoptic maps. Finally, a first assessment of the effects of these stormy phenomena is made using local press reports on drowning, damage to urban furniture and port infrastructures and loss of sand on the beaches.

Heavy versus extreme rainfall events in southeast Australia

AbstractFocussing on the major cities of Brisbane, Sydney, and Melbourne in southeast Australia, this study seeks to determine the environmental factors that distinguish between heavy rainfall events (HREs) and extreme rainfall events (EREs). Using daily rain gauge observations, HREs and EREs are defined for each domain based, respectively, on the 95th and 99th percentiles of wet‐day rainfall for the period 1979–2018. K‐means clustering is applied to mean sea‐level pressure, data from ERA5 to obtain a set of representative large‐scale circulation patterns associated with these events. Composite synoptic maps, mean vertical profiles, and a series of column‐integrated diagnostics are then examined for each cluster and used to compare the environmental characteristics of HREs and EREs. For all three cities, HREs are associated with an upper‐level trough to the west, with large‐scale ascent, positive column water vapour (CWV) anomalies, and strong moisture transport over the analysis domain. For Brisbane and Sydney, the clusters are characterised by a coastal trough/low with moist onshore flow from the Tasman and Coral Seas. For Melbourne, circulation patterns are more distinct, with clusters characterised by a front, a cut‐off low, and an inland trough. Compared with HREs, EREs show a more amplified upper‐level trough, with stronger vertical motion and larger CWV anomalies over the analysis domain. In Brisbane and Sydney, EREs also feature stronger and deeper onshore flow, promoting enhanced moisture transport. A diagnostic termed upward vapour transport, which combines the key ingredients of high CWV and large‐scale ascent, is shown to discriminate well between HREs and EREs in all three domains. In contrast, surface temperature, which is frequently linked to rainfall extremes via Clausius–Clapeyron scaling, shows significant overlap between the different event categories, particularly for Brisbane and Sydney.

Теміртау қаласы ауа алабының ластануының синоптикалық жағдайлары

Мақалада Қарағанды облысының Теміртау қаласының атмосфералық ауасының ластану жағдайы және атмосфераның ластану индексінің (АЛИ) динамикасы қарастырылған. АЛИ қаладағы негізгі 5 ластаушы заттар бойынша, яғни олардың ішінде: қалқыма бөлшектер, азот диоксиді, көміртек оксиді, фенол және аммиак заттарының концентрациялары арқылы есептелген. Автор Теміртау қаласының ауа алабының ластануының синоптикалық жағдайларын, яғни циклон және антициклон, жыра және жота сияқты барикалық құрылымдардың қала ауасындағы зиянды заттардың шекті мүмкіндік концентрацияларын, сақталу мерзіміне әсерін қарастырған. Сонымен қатар ауа алабының ластануына қолайлы метеорологиялық шамалар, әсіресе, ластаушы заттардың тасымалдануына себепші жел сияқты шаманың ластану мәселесіне әсері және ластануда трансшекаралық тасымалдауды ескеру мақсатымен оның берілген мерзім бойынша қаладағы бағытының қайталанушылығының диаграммасы ұсынылған. Мақала материалдарында арнайы берілген мерзім бойынша барикалық топография карталары, синоптикалық жер карталары пайдаланылып, оларға талдау жасалған. Мақалада карталардың талдауы бойынша арнайы мерзімдегі қала бойынша зиянды заттардың концентрацияларының үлкен мөлшерде жиналуына қолайлы синоптикалық жағдайлардың орын алу мәселесі және шарттары сипатталған. Зерттелген сұрақтар біздің еліміздің экологиясына, әсіресе Теміртау қаласы сияқты үлкен өндірістік кешені бар қалалардың экологиялық жүйесіне, оның ішінде атмосфералық ауаның сапалық жағдайына көз салатын, өткір жаһандық мәселелеріне назар аударатын жаратылыстану саласындағы мамандарға, саясаткерлер мен қоғам қайраткерлеріне қызығушылық танытады.

Exploiting White-Light Observations to Improve Estimates of Magnetic Connectivity

TheSolar Orbiter(SolO) andParker Solar Probemissions have opened up new challenges for the heliospheric scientific community. Their proximity to the Sun and their high quality measurements allow us to investigate, for the first time, potential sources for the solar wind plasma measuredin situ. More accurate estimates of magnetic connectivities from spacecraft to the Sun are required to support science and operations for these missions. We present a methodology to systematically compare coronal and heliospheric models against white-light (WL) observations. WL images from the SOlar and Heliospheric Observatory (SoHO) are processed to unveil the faint structures of the K-corona. Images are then concatenated over time and are projected into a Carrington synoptic map. Features of interest such as the Streamer Belt (SB) are reduced to simplified geometric objects. Finally, a metric is defined to rank models according to their performance against WL observations. The method has been exploited to reproduce magnetic sectors from WL observations. We tested our results against one year ofin situmagnetic polarity measurements taken at near one AU from theAdvanced Composition Explorer(ACE) and theSolar TErrestrial RElations Observatory(STEREO-A). We obtained a good correlation that emphasizes the relevance of using WL observations to infer the shape of the sector structure. We show that WL observations provide additional constraints to better select model parameters such as the input photospheric magnetic map. We highlight the capability of this technique to systematically optimize coronal and heliospheric models using continuous and near-real-time WL observations. Several relevant practical applications are discussed, which should allow us to improve connectivity estimates.

Quantifying the Impact of Synoptic Weather Systems on High PM2.5 Episodes in the Seoul Metropolitan Area, Korea

AbstractVariations in concentrations of PM2.5, particulate matters of diameters below 2.5 μm, vary following both meteorological conditions and emissions controls. Meteorological conditions particularly affect short‐term high PM2.5 episodes through accumulations, transports, and secondary formations. This study quantifies the meteorological impacts on high PM2.5 episodes in the Seoul Metropolitan Area (SMA), Korea, for the period 2016–2018 using empirical and statistical methods. Synoptic weather maps of 77 high PM2.5 episodes in 2016 are grouped into two synoptic types: onshore winds associated with migratory pressure systems over the SMA and offshore winds from continental high pressure extending toward the SMA. We applied principal component analysis and regression to extract the dominant synoptic types controlling PM2.5 variability. It identifies two major principal components (PCs) from 12 surface and upper‐air meteorological variables for 2017–2018. Weather patterns in 49 examples of the high‐positive PCs show that the two PCs are capable of reproducing the synoptic weather patterns relevant for high PM2.5 episodes. To quantify the relationship between the synoptic weather patterns and PM2.5 levels, the two PCs are further classified into four groups according to their signs. Positive‐ and negative‐PC groups are associated with about 82% and 73% of high‐ and low‐PM2.5 episodes, respectively, suggesting that most of the high/low PM2.5 episodes in the SMA can occur under the two PCs‐dominant weather conditions. The results can be utilized as a reference for daily predictions of high PM2.5 episodes, as well as for quantitative analysis of the climatic influence on the long‐term PM2.5 variability.

Warunki powstania zjawiska downburst nad Wrocławiem w dniu 30 VI 2016

The article presents the issue of downburst over Poland. Strong downdrafts are a great danger in aviation, but can also cause damage on the surface of the Earth. On the basis of synoptic maps, aerological and radar data the analysis of synoptic and thermodynamic conditions of the atmosphere in which the phenomenon occurred was conducted. The appearance of the cold front over Lower Silesia and the occurrence of V-notch radar signature over Wroclaw may have suggested the formation of a storm and the associated downburst.

Synoptic Climatology of Lake-Effect Snow Events off the Western Great Lakes

As the mesoscale dynamics of lake-effect snow (LES) are becoming better understood, recent and ongoing research is beginning to focus on the large-scale environments conducive to LES. Synoptic-scale composites are constructed for Lake Michigan and Lake Superior LES events by employing an LES case repository for these regions within the U.S. North American Regional Reanalysis (NARR) data for each LES event were used to construct synoptic maps of dominant LES patterns for each lake. These maps were formulated using a previously implemented composite technique that blends principal component analysis with a k-means cluster analysis. A sample case from each resulting cluster was also selected and simulated using the Advanced Weather Research and Forecast model to obtain an example mesoscale depiction of the LES environment. The study revealed four synoptic setups for Lake Michigan and three for Lake Superior whose primary differences were discrepancies in a surface pressure dipole structure previously linked with Great Lakes LES. These subtle synoptic-scale differences suggested that while overall LES impacts were driven more by the mesoscale conditions for these lakes, synoptic-scale conditions still provided important insight into the character of LES forcing mechanisms, primarily the steering flow and air–lake thermodynamics.

Comparison of Synoptic Maps and PFSS Solutions for The Declining Phase of Solar Cycle 24

AbstractThe global distributions of photospheric magnetic field are routinely provided by synoptic maps, which often serve as fundamental observational input for coronal and heliospheric models. In this paper, we compare synoptic maps and PFSS‐derived magnetic field results obtained during 2017/12/06–2018/12/06, a period at the declining phase of solar cycle 24. We use four kinds of synoptic maps, the Helioseismic and Magnetic Imager (HMI) maps, the Air Force Data Assimilative Photospheric Flux Transport (ADAPT) maps, the Global Oscillation Network Group (GONG) maps with their zero‐point uncertainty corrected (GONGz maps) or uncorrected (GONGb maps). Qualitatively similarity among the four maps are found in the low‐latitude region, but the polar fields have notable differences. While the polar fields of HMI, ADAPT and GONGz maps are unipolar and relative stable in large scale, those of the GONGb maps are variable. The PFSS results of HMI, ADAPT, and GONGz compare reasonably with coronal remote observations and near‐Earth in situ data, and the HMI maps perform slightly better. There is generally no significant difference among results of the 12 ADAPT ensemble maps, but exceptions are also found. The PFSS results of GONGb maps deviate from observation significantly. The deviations are attributed to the problematic polar field, and the source of the problem may be the zero‐point uncertainty of the magnetograms. As GONGb maps perform well in the declining phase of solar cycle 23, results in this study highlight the importance of continuous assessment of synoptic map data quality.

Modified Path-conservative HLLEM Scheme for Magnetohydrodynamic Solar Wind Simulations

Abstract The goal of the present work is to solve the magnetohydrodynamic (MHD) system of extended generalized Lagrange multiplier (EGLM) formulation with Galilean invariance (G-EGLM MHD equations) through a modified path-conservative HLLEM finite-volume method. A second-order least-squares reconstruction with Venkatakrishnan limiter is employed for state variables, and a solenoidality-preserving condition is considered for the magnetic field with the purpose of magnetic divergence cleaning. The two-stage Runge–Kutta time-integration method is utilized to advance the MHD governing equations. Compared with the original path-conservative HLLEM method, the modified method in this paper is shock stable and is able to adjust the diffusion according to the smoothness of the physical flow so as to automatically apply more diffusion near strong shocks and less in smooth regions near rarefaction waves and at contact discontinuities. Meanwhile, it can be robustly defined in the low plasma-β region. After several tests of smooth Alfvén wave, strong Lax, odd–even perturbation, and blast-wave problems, the large-scale structures of the solar corona for Carrington Rotation 2185 are numerically modeled in a six-component grid system of spherical coordinates with input from a Carrington rotation synoptic map provided by the Helioseismic and Magnetic Imager. Numerical results show the model’s capability of producing a structured solar wind in agreement with the observations.

24 synoptic maps of average magnetic field in 296 prominences measured by the Hanle effect during the ascending phase of solar cycle 21

Aims. We present 24 synoptic maps of solar filaments, in which the average unambiguous magnetic field vectors of 296 prominences were determined with Pic-du-Midi observations between 1974 and 1982. This was the ascending phase of cycle 21. Methods. The magnetic field was determined by interpreting the Hanle effect, which is observed in the He I D3 line. Previous results for the prominence field polarity and prominence chirality were applied to solve the fundamental ambiguity. The measurements were averaged in each prominence for accuracy reasons. Results. The result is twofold. First, alternating field directions can be observed from one neutral line to the next. Second, a general field alignment is found along a solar north-south field that is distorted by the differential rotation effect.