# Focus Meeting 9 - Poster Abstracts

## X-class flares released during the peak of the decline phase of SC24, a descriptive study

Eruptive X-class flares occurring during the peak and decline phases of the solar cycle 24 are stronger than those of the solar cycle 23. We notice that the solar cycle 24 is the weakest in the last 100 years. The last two cycles are very weak compared to other cycles, except for the Dalton Minimum cycles 4, 5, 6 and 7; which indicates the appearance of a new Dalton minimum during 23, 24, 25 and 26. During the last 5 solar cycles, a new peak has appeared releasing high energetic particles and X-class solar flares which are called the secondary peak or the double peak of the solar cycle.The aim of this descriptive study is to follow the X-class flares released during the peak and decline phase of SC24, once they are released, to compare it with other solar cycles.The causes of the release of such eruptive storms, through the year 2014, during the double peak of the solar cycle 24 are also discussed.

## Double maximum of solar cycle

Krivodubskij, Valery

We propose a new scenario to explain the observed phenomenon of the double maximum of the sunspot cycle. This scenario includes the generation of the magnetic field near the bottom of the solar convection zone (SCZ) and its subsequent removal from the deep layers to the surface in the “royal zone". We take into account the five processes of magnetic field reconstructing during solar cycle: omega-effect, meridional circulation, magnetic buoyancy, macroscopic radial turbulent diamagnetism and magnetic pumping due to matter density radial inhomogeneity (the MPDI-effect). It was found that there are different conditions for the reconstruction of magnetism in the near-polar and the near-equatorial domains of the SCZ. The radial differential rotation generates a strong toroidal field near tachocline by affecting the poloidal field of the previous cycle. In the near-equatorial domain, magnetic buoyancy, turbulent diamagnetism, and the MPDI-effect act together to transport this deep strong toroidal field to the solar surface, where its fragments can be observed after a while as bipolar sunspot groups at the middle latitudes of the “royal zone”. This upward directed first wave of toroidal field is responsible for the main maximum of sunspot activity. At the same time the toroidal fields in the high-latitude polar domains are blocked at the beginning of the cycle near the SCZ bottom by two “negative buoyancy” effects: the downward turbulent diamagnetic transfer and the downward magnetic pumping due to matter density inhomogeneity. After only 1–2 years the deep equatorward meridional flow will push these magnetic fields into low-latitude areas of the near-equatorial domain. Due to directed upward magnetic pumping caused by the MPDI-effect these belated magnetic fields rise to the surface. These second waves of belated toroidal fields come to the surface at somewhat lower latitudes of the “royal zone” and produce the repeated maximum of sunspot activity.

## Solar disk radius determined from Sun occultation by the Moon using bolometric and photometric instruments onboard the PICARD satellite

Thuillier, Gerard

Despite the importance of having an accurate measurement of the solar disk radius, there are large uncertainties of its value due to the use of different measurement techniques and instrument calibration. Measurements of the solar disk radius is a basic metrological quantity of the solar system. Furthermore, is the solar radius constant or changing with time in particular with solar activity. The solar radius value depends on the solar atmosphere opacity, which allows solar model validation by comparing model predictions with the observations.Three instruments onboard the PICARD spacecraft, the Bolometric Oscillations Sensor (BOS), the PREcision MOnitoring Sensor (PREMOS), and a solar sensor (SES), are used to derive the solar disk radius using the light curves produced when the Sun is occulted by the Moon. Nine eclipses from 2010 to 2013, resulted in 17 occultations. The calculation of the solar disk radius uses a simulation of the light curve taking into account the center to limb variation provided by the Non local thermodynamic Equilibrium Spectral SYnthesis (NESSY) code and the relative positions of Sun, Moon and spacecraft. The solar disk radius for each occultation was obtained for 4 spectral domains in the visible and IR solar continuum and two in UV. No relation with solar activity being found, we derived a more precise radius value by averaging these values. At one astronomical unit, we obtain 959.79” from the bolometric experiment; from PREMOS measurements, we obtain 959.78” at 782nm; 959.76” at 535nm. We found 960.07” at 210nm, which is a larger value than the others given the photons at this wavelength originate from the upper photosphere and lower chromosphere. The minimum solar disk radius is found around 600nm.We point out that the Moon provides a stable reference for instruments in space allowing long term studies by using simple photometers, which are robust instruments able to survive without significant aging in the harsh orbital environment.

## Revisiting the solar flux predicted by model photospheres

Allende Prieto, Carlos

One of the big successes of the theory of model atmospheres is the ability of models to approximately reproduce the observed disk-integrated solar flux from the near-UV to the mid-infrared. In this presentation I will present recent calculations to quantify how good this agreement is for state-of-the art theoretical models of the solar photosphere.

## Cycle-dependent and cycle independent surface tracers of solar magnetic activity

Sokoloff, Dmitry

We consider several tracers of magnetic activity that separate cycle-dependent contributions to the background solar magnetic field from those that are independent of the cycle. The main message is that background fields include two relative separate populations. The background fields with a strength up to 100 Mx cm$^{-2}$ are very poorly correlated with the sunspot numbers and vary little with the phase of the cycle. In contrast, stronger magnetic fields demonstrate pronounced cyclic behaviour. We discuss how this result can be included in the above-mentioned concepts of solar dynamo studies. Small-scale solar magnetic fields demonstrate features of fractal intermittent behavior, which requires quantification. We investigate how the observational estimate of the solar magnetic flux density B depends on resolution D in order to obtain the scaling $\ln BD = - k \ln D +a$ in a reasonably wide range. The quantity k demonstrates cyclic variations typical of a solar activity cycle. $k$ depends on the magnetic flux density, i.e. the ratio of the magnetic flux to the area over which the flux is calculated, at a given instant. The quantity a demonstrates some cyclic variation, but it is much weaker than in the case of $k$. The scaling is typical of fractal structures. The results obtained trace small-scale action in the solar convective zone and its _x000D_ coexistence with the conventional large-scale solar dynamo based on differential rotation and mirror-asymmetric convection. The research is supported by RFBR projects 18-02-00085 and 17-02-00300. By D.D.Sokoloff, V.N.Obridko, I.M.Livshits, A.S.Shibalova.

## Origin and early development stage of solar active regions

Getling, Alexander

The early development stage of active region (AR) 12548 is investigated using observational data of 20–26 May 2016 from the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). In view of our “strategic” aim of comprehending the sunspot-formation processes, we discuss here the adequacy of the model of the rising loop of a strong-magnetic-flux tube. To this end, we compare the simultaneously measured full-vector magnetic and velocity fields using a Spaceweather HMI Active Region Patch (SHARP).We managed to pick up the very conception of the bipolar magnetic region (BMR) to within a time interval of about 20 min. The leading polarity is found to originate as a compact, isolated feature with a fountainlike magnetic-field structure against the background of a distributed trailing-polarity field and a downflow. The leading and the trailing polarity exhibit a strong asymmetry between their evolution patterns: the leading magnetic element starts developing from a noise-level field strength and reaches a strength of about 2500 G in one day and a half, while the trailing-polarity magnetic element, which had initially a strength of almost 1000 G, grows more slowly and becomes weaker than the leading element. The magnetic fluxes of the two polarities vary in a similar way. No strong horizontal magnetic field is observed in the BMR between the growing leading and following magnetic elements. Also, neither clear-cut material upflows between these sunspots nor remarkably strong horizontal divergent flow is noted. Moreover, small-scale upflows and downflows are mixed, and downflows even dominate at the early evolutionary stage. An intact pattern of supergranulation and mesogranulation is observed over the location area of the growing BMR and around it. Thus, as in the previously analysed AR 11313 (9–10 October 2011), the evolution pattern of AR 12548 strongly disagrees with that definitely predictable based on the rising-tube model.

## Multiscale structure of convection due to particularities of thermal stratification

Getling, Alexander

Solar convection controls the processes of magnetic-field structuring, thus affecting the variety of active phenomena. A superposition of cellular convection structures widely differing in their scales (granules, mesogranules, supergranules, giant cells and possibly mini-granules) is characteristic of the solar convection zone, understanding the nature of structural organization of solar convection being thus an important problem of solar physics. In view of the ultimate aim of finding physical factors responsible for the multiscale structure of solar convection, we consider only one of such conceivable factors – the thermal stratification due to a temperature-dependent thermal diffusivity. We carry out three-dimensional numerical simulations of convection in a horizontal fluid layer based on an extended Boussinesq approximation admissive of thermal-diffusivity variations. These variations are assumed to be of a form producing a specific static temperature profile, with the temperature gradient being much greater in its magnitude near the upper layer surface than in the remaining portion of the layer; however, the layer is everywhere convectively unstable. Both free-slip and no-slip boundary conditions at the top layer surface are considered; the bottom boundary is assumed to be rigid. The simulated velocity and temperature fields are analysed using Fourier techniques and computational-homology methods. For both boundary-condition types, the well-developed flow appears as a superposition of cellular convection motions of three scales. In contrast to the largest cells filling the whole layer thickness, smaller cells are localised near the top layer boundary and advected by the larger-scale flows. On the whole, the flow pattern is qualitatively similar to solar-convection pattern formed by supergranules, mesogranules and granules.

## Solar variability and climate change – an Empirical Analysis

bhargawa, asheesh

Sun in the main source of energy for our planet therefore even a slight change in its output energy can make a huge difference in the climatic conditions of the Earth. The rate of energy coming from the Sun (solar irradiance) might affect our climate directly by changing the rate of solar heating of the Earth and atmosphere and indirectly by changing cloud forming processes. In the present paper, based on stability test of the Vector autoregressive (VAR) model, we have used impulse response functions and variance decomposition method for the analysis of climate variability. We have examined the possible connection between the solar irradiance and some climate indicators, viz., the global temperature anomaly, the global mean sea level, global sea ice extent and the global precipitation anomaly since last forty years (1978-2017). We have noticed that these parameters have shown changing patterns during the last few decades. In addition, we have also tried to find the role of atmospheric carbon dioxide as a greenhouse gas in the climate change. Considering global surface temperature anomaly (land + sea) as the most important indicator of clime change and using the impulse response function analysis and variance decomposition method, we have tried to answer the questions whether the climate system is subjecting to a solar irradiance shock or what is the contribution of rise in CO2, etc?

## Superflares on Solar-Type Stars

Nogami, Daisaku

Super?ares are de?ned as ?ares which are over 10 times more energetic (=1033 erg) than largest ?ares ever observed on the Sun, and many super?ares have been found on many solar-type stars, i.e. G-type main sequence stars in the Kepler-spacecraft data. Statistical analyses indicate that the frequency distribution to the ?are energy of the super?are is almost consistent with that of the Sun. Many of super?are stars show quasi-periodic variations with timescales of about 1 to 30 days. Spectroscopic measurements of the projected rotation velocity suggest that these variations are due to rotation of super?are stars with large starspots. The size distribution of starspots shows the power-law distribution which is on the same line of the size distribution of relatively large sunspots. The frequency-energy distributions for ?ares originating from spots with various sizes are the same for solar-type stars with super?ares and the Sun. These results suggest that the magnetic activity on solar-type stars with super?ares and that on the Sun is caused by the same physical processes. Long term monitoring of the chromospheric activity and research on possible coronal mass ejections accompanying with super?ares will give us an insight on the e?ects of super?ares on the planetary environment, and possible extreme space weather events on the Earth.

## Realistic 3D simulations of solar and stellar surface convection covering several days

Kupka, Friedrich

We present results from 3D radiation hydrodynamical simulations forthe Sun and a few other Sun-like stars. These are performed over relatively long time scales of several days to study p-mode excitation and damping processes. While the focus of our study is on helio- and asteroseismology, the same simulation data can also be used to investigate the stability of solar and stellar irradiance over these time scales. To this end, we show results from a first analysis of our simulation data.

## Association of Radio Polar Cap Brightening with Bright Patches and Coronal Holes

Selhorst, Caius

Radio-bright regions near the solar poles are frequently observed in Nobeyama Radioheliograph (NoRH) maps at 17 GHz, and often in association with coronal holes. However, the origin of these polar brightenings has not been established yet. We propose that small magnetic loops are the source of these bright patches, and present modeling results that reproduce the main observational characteristics of the polar brightening within coronal holes at 17 GHz. The simulations were carried out by calculating the radio emission of the small loops, with several temperature and density profiles, within a 2D coronal hole atmospheric model. If located at high latitudes, the size of the simulated bright patches are much smaller than that of the beam size and they present the instrument beam size when observed. The larger bright patches can be generated by a great number of small magnetic loops unresolved by the NoRH beam. Loop models that reproduce bright patches contain denser and hotter plasma near the upper chromosphere and lower corona. On the other hand, loops with increased plasma density and temperature only in the corona do not contribute to the emission at 17 GHz. This could explain the absence of a one-to-one association between the 17 GHz bright patches and those observed in extreme ultraviolet. Moreover, the emission arising from small magnetic loops located close to the limb may merge with the usual limb brightening profile, increasing its brightness temperature and width.

## Comparison of solar radio and extreme ultraviolet synoptic limb charts during the present solar maximum

Selhorst, Caius

We analyze daily images at 304 and 171 Å obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The 17 GHz maps were obtained by the Nobeyama Radioheliograph (NoRH). To construct synoptic limb charts, we calculated the mean emission of delimited limb areas with 100'' wide and angular separation of 5o. At the equatorial region, the results show a hemispheric asymmetry of the solar activity. The northern hemisphere dominance is coincident with the first sunspot number peak, whereas the second peak occurs concurrently with the increase in the activity at the south. The polar emission reflects the presence of coronal holes at both EUV wavelengths, moreover, the 17 GHz polar brightenings can be associated with the coronal holes. Until 2013, both EUV coronal holes and radio polar brightenings were more predominant at the south pole. Since then they have not been apparent in the north, but thus appear in the beginning of 2015 in the south as observed in the synoptic charts. This work strengthens the association between coronal holes and the 17 GHz polar brightenings as it is evident in the synoptic limb charts in agreement with previous case study papers. The enhancement of the radio brightness in coronal holes is explained by the presence of bright patches closely associated with the presence of intense unipolar magnetic fields. However, observations with better spatial resolution and also at different radio wavelengths will be necessary to fully understand the physical mechanisms that link these features.

## Synoptic maps of high-latitude filaments for solar cycle 24 observed by the Chromospheric Telescope

Diercke, Andrea

The Chromospheric Telescope (ChroTel) at the Observatorio del Teide, Tenerife, Spain observes the entire solar disk since 2011 in three different chromospheric wavelengths: Ha, Ca II line, and He I. The instrument records full-disk images of the Sun every three minutes in these different spectral ranges. In addition, the telescope records filtergrams in He I, scanning the line at seven different wavelength points so that chromospheric Doppler velocities can be measured. Although, ChroTel does not observe the Sun daily, a long data set of 746 days (2012-2016) with observations is publicly available in the data archive. This covers the rising and decaying phase of solar cycle 24. We started analyzing the ChroTel time-series and created synoptic maps of the entire observational period in all three wavelength bands. The synoptic maps contain, among others, information about the number, location, area, and orientation of the filaments. The number and the location of filaments follows the solar activity cycle. We focus in our study on large-scale filaments, polar crown filaments, and high-latitude filaments and their propagation towards the pole, which is known as 'dash-to-the-pole'. Furthermore, other properties of the filament can be determined from this data set such as length, width, and lifetime, which can be statistically analyzed throughout the cycle.

## A multiwavelength analysis of the long duration flare observed on 2002 April 15

Kepa, Anna

We present a multiwavelength analysis of the long duration flare observed on 2002 April 15 (soft X-ray peak time at 03:55 UT).  This flare occurred  in NOAA 9906 and was observed by a number of space instruments including EIT/SOHO,  RESIK, and RHESSI. We have performed a complex analysis of available measurements and studied the morphology and physical parameters characterizing the conditions in the flaring plasmas. The EIT images have been used to study evolution of flaring loops.  RHESSI data provided opportunity of detailed analysis o HXR emission with a high energy resolution. The temperature diagnostics of flaring plasma have been carried out by means of a differential emission measure (DEM) analysis based on RESIK X-ray spectra and GOES.

## Generating magnetograms from Ca II K observations for irradiance reconstructions since the early 20th century

Chatzistergos, Theodosios

Models of irradiance reconstruction rely on data providing information about the evolution of the surface magnetism of the Sun. Magnetograms of the Sun are well suited for that purpose, however they exist for almost the same period as the direct measurements of irradiance.Full-disc observations made in the Ca II K line can potentially be used to reconstruct magnetograms since the early 20th century due to the corresponence of bright regions in Ca II K observations and magnetically strong regions found in magnetograms.Such a relation has been investigated by many studies, reporting however disparate results.Here we examine the relation between the magnetic field strength and the Ca II K emission with high-quality full-disc and near co-temporal SDO/HMI magnetograms and Rome PSPT Ca II K observations. These observations span half a solar cycle, enabling us to study the relation for different features and positions on the disc, as well as effects of solar activity on the relation.This obtained relation is then used to reconstruct unsigned magnetograms from the PSPT observations, which we can use to directly estimate the accuracy of the conversion.

## Modeling of Century-Scale Solar Activity and a Prediction for Cycle 25

Nandi, Dibyendu

It is now believed that variations in the Sun's irradiance are primarily governed by surface magnetic flux emergence and evolution -- at least over centennial timescales. Observations show that this flux emergence is cyclic with significant variations in the amount of magnetic flux from one cycle to another. This magnetic variability is driven by a magnetohydrodynamic dynamo mechanism operating in the Sun’s interior. Based on recent advances in our understanding we utilize a solar surface flux transport model and a solar internal dynamo model to perform the first ever century-scale calibrated, data driven simulation of solar activity to predict the strength and timing of the upcoming sunspot cycle 25. Our simulation results are further interpreted to provide insights on the processes that govern long-term solar variability over centennial timescales.

## Prediction of Limb Flares Based on Coronal Images

Priyatikanto, Rhorom

Disregarding the existence of active longitudes in dynamical Carrington frame of reference, solar flares can be considered as isotropic phenomenon in heliographic longitude space. Flares may occur on any heliographical longitude and modern society requires ample capability to forecast their occurrence and their subsequent effects to Earth's space weather.This work aims to characterize solar active region based on the extreme ultraviolet coronal images. Photometric and geometric properties will be cultivated to characterize the active region. Characterization of emerging active region on the far east region will be the ultimate goal in this context. Flare probability model based on the observed brightness of solar corona above any active region will be established according to that charaterization.

## Features of Long-Term Changes in Areas of Large Sunspots Groups in Solar Activity Cycles 12-24

Efimenko, Volodymyr

We analyze the Greenwich catalog data on areas of sunspots in the thirteen last cycles of solar activity (http://solar.science.msfc.nasa.gov/greenwich/). Namely such parameter was analyzed in papers by Babij et al. [2011], Efimenko and Lozitsky [2016], Nagovitsyn and Pevtsov [2016], and  Mandal and Banerjee [2016]. This conclusion follows from consideration of integral distributions for diameters of great sunspots (50-90 Mm) for cycles Nos. 12-24.The main results are following: (a) the average value of the index of the power-law approximation is 5.4 for the last 13 cycles; (b) there is no secular trend of index changes, and (c) there is reliable evidence of Hale's double cycle (about 44 years). Since this indicator reflects the dispersion of the spot diameters, the results obtained show that the convective zone of the sun generates embryos of active regions in different statistical regimes which change with a cycle of about 44 years.ReferensesBabij V.P., Efimenko V.M., Lozitsky V.G.  Kinematics and Physics of Celestial Bodies. V. 27, ?4, P.191-196. 2011.Efimenko V., Lozitsky V. Bull. Kyiv. Nation. Univ., Astronomiya. ? 53. ?. 52-55.  2016.Nagovitsyn Yu.A., Pevtsov A.A. Astrophys. J. V. 833, ? 1. id. 94. 6 pp. 2016.Mandal S., Banerjee D. Sunspot sizes and the solar cycle: analysis using Kodaikanal white-light digitized data // The Astrophys. J. Lett. V. 830, ? 2. article id. L33, 6 pp. 2016.

## Re-analysis of highest-resolution Solar Maximum Mission X-ray spectra using Bayesian deconvolution

Sylwester, Janusz

Spectra collected in early 1980s by the Bent Crystal Spectrometer (BCS) aboard Solar Maximum Mission still constitute the highest resolution astrophysical database in the X-ray range 1.7 – 3.2 Å. More than 100,000 raw flare spectra are available from NASA archives (ftp://umbra.nascom.nasa.gov/pub/smm/xrp/data/). These spectra were mostly emitted by hot plasmas associated with flares observed in the periods 1980 and 1984-1989. Early analysis of BCS spectra indicated a number of effects previously unseen, like turbulent line broadening and the presence of blue-shifted line components. More recently, substantial progress has been made for both the theory of spectra formation in hot, possibly non-equilibrium flaring plasmas and spectral data reduction and interpretation using new BCS instrument parameters (Rapley, Sylwester and Phillips, 2017, Solar Physics, 292: 50). Using synthetic and observed BCS spectra, we show here how these advances contribute to a better understanding of the physical processes in flare plasmas. In particular, we will illustrate how advanced Bayesian methods can be used to derive physical line profiles and to detect weak line components.

## Is a hot plasma component present in the solar corona during periods of the lowest activity?

Sylwester, Barbara

Using spectra collected by the Polish spectrophotometer SphinX, we address the intriguing question of whether a ~10 MK plasma exists in the corona when no active regions ("no-AR") are present on the disk. SphinX observed the integrated soft X-ray radiation ("Sun as a star") throughout most of 2009. This included times of exceptionally low activity when not even small ARs were apparent in X-ray and EUV images and no sunspots in visible light. The SphinX instrument had the highest sensitivity in the spectral range above 1.2 keV of any instrument then in orbit and also good spectral resolution (FWHM = 460 eV). SphinX spectra were recorded over numerous no-AR times lasting up to a few consecutive days. We analysed these spectra on an isothermal and multi-temperature assumption (covering a temperature range 1 MK to 15 MK). For the multi-temperature modelling, we used Bayesian differential emission measure (DEM) deconvolution tested on appropriate sample spectra. We first discuss results of these tests showing the capability of this DEM inversion, and then the DEM inversion as applied to SphinX measurements, in particular no-AR spectra summed over time periods (ensuring that the total number of photon counts in the spectrum above 1.2 keV exceeded ~106). We discuss the derived DEM distributions in terms of the heating mechanisms involved in the Sun's quiet corona.

## Monitoring Solar Activity Variations with High-Resolution Sun-as-a-star Spectroscopy

Dineva, Ekaterina

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) is a state-of-the-art, thermally stabilized, fiber-fed, high-resolution spectrograph for the Large Binocular Telescope (LBT) at Mt. Graham, Arizona. Typically theLBT with its large light-gathering power feeds starlight to PEPSI. However, the spectrograph can also be fed with sunlight from the Solar Disk-Integrated (SDI) telescope. Synoptic solar observations with PEPSI/SDI produce daily spectra with high signal-to-noise ratio, providing access to unprecedented, quasi-continuous, long-term, disk-integrated spectra of the Sun with high spectral and temporal resolution. The observed spectra contain a multitude of photospheric and chromospheric spectral lines in the wavelength range of 380-910 nm. We develop tools to monitor and study solar activity on different time-scales ranging from daily changes, over periods related to solar rotation, to annual and decadal trends. Strong chromospheric absorption lines, like the Ca II K & H lines, are powerful diagnostic tools for solar activity studies, since they trace the variations of the solar magnetic field. Currently, we are  developing a data pipeline for extraction, calibration, and analysis of the PEPSI/SDI data. We compare the SDI data with daily spectra from the Integrated Sunlight Spectrometer (ISS), which is part of the NSO Synoptic Optical Long-Term Investigation of the Sun (SOLIS) facility. This allows us to validate SDI data quality and precision. We present result for the Ca II K & H lines, including details of the wavelength and flux calibration. First results combined with Ca II K line activity index are discussed in the context of synoptic full-disk images and magnetograms.

## Study of cavities geometry for absolute radiometer

Carlesso, Franciele

The measurement of the Total Solar Irradiance (TSI) and its variations are very important to understand the influence of Sun’s radiant output on the Earth’s climate. Space-borne instruments have made TSI measurements continually and allowed advances in the TSI understanding.  These measurements rely on active cavity radiometers, which use black interior surfaces to absorb incident sunlight. Black Ni-P was firstly applied in active cavity radiometers for measuring solar irradiance in TIM (Total Irradiance Monitor) instrument [1]. The development of an absolute radiometer is currently been done at INPE. We obtained black Ni-P by electroless deposition for application in the interior of the silver cavities. We used bidirectional reflectance distribution function (BRDF) data to describe the surface reflectance properties of the Ni-P film. The BRDF data were used in the geometry study of the absorber cavity in a ray tracing software - ZEMAX. These measures allowed cavities geometries optimization considering the characteristics of the black Ni-P produced at INPE. We intend to use this cavity in a bench prototype radiometer under development. The current status of the study and obtained results are presented in detail.[1] G. Kopp, Journal of Space Weather and Space Climate, 4, A14 (2014).

## GENERAL FEATURES OF THE SOLAR CYCLE 24

Gursoy, Fulin

In this study, using the data of Istanbul University Observatory, general features of the Solar Cycle 24 are presented.

Kopp, Greg

Variations in the total solar irradiance (TSI) over long periods of time potentially provide natural Earth-climate forcing and are thus important to measure. Variations over a solar cycle are at the 0.1% level. Variations on multi-decadal to century timescales, if extant, are fortunately very small, which thus drives the need for highly-accurate and stable measurements over correspondingly long periods of time. Advances to TSI-measuring space-borne instruments are striving to achieve the desired climate-driven measurement accuracies and stabilities. I will present a summary of the modern-instrument improvements intended to enable these measurements and show some of the solar-variability measurement results recent space-borne instruments have acquired, including solar variability from solar-flare and solar-convection to solar-cycle timescales.

Remesal Oliva, Alberto

The degradation of the on-orbit TSI radiometer detectors must be studied on ground to understand the evolution of the irradiance data that we measure. Between the different processes that might induce degradation, UV radiation is most likely one of the most significant contributors. In order to estimate the effect of this radiation on the black paints applied to the radiometer detectors, we simulate with a Hg-Xe lamp the UV radiation that would hit on the detectors in a full life-time mission.We performed this experiment in two different coatings that might be used in future missions. The first one is a sprayable Carbon Nanotubes coating from Surrey NanoSystems and the second one is a glossy silicon base black paint.We study the reflectance of these detectors before and after the experiment, we evaluate the consequences of the radiation and estimate the degradation.

## Update to the Whole Heliosphere Interval (WHI) Solar Reference Spectrum

Béland, Stéphane

As part of the 2008 Whole Heliosphere Interval (WHI) efforts, a new Solar Irradiance Reference Spectra (SIRS,) near solar minimum, was determined from 0.1 nm to 2400 nm using a combination of satellite and sounding rocket observations. The WHI campaign covered the solar Carrington Rotation 2068 (20 March to 16 April 2008) and included a Quiet Sun period (10 - 16 April 2008).We are presenting an update to the SIRS using the latest version of the various data products used initially as well as a different time range for the Quiet Sun to reflect the observed period of Solar minimum.

## Sunspot group tilt angles for cycles 19-24

Isik, Seda

The tilt angle of sunspot groups is an important quantity, as it determines the amount of signed flux transported to the solar poles. To date, however, there has been only a few observational studies on cycle-averaged tilt angles. Using the digitised archive of sunspot drawings produced at Kandilli Observatory, we measured group tilt angles for the period 1958-2017, and compared our results with the Mount Wilson (MWO), Kodaikanal (KSO) and Debrecen Photoheliographic (DPD) databases. The average shape of Joy's law as well as cycle-averaged tilt angles show similar trends with DPD. We found a much weaker anti-correlation of the mean tilt angle (normalised to latitude) with cycle strength than was reported using MWO and KSO data.

## Emergence and surface transport of magnetic flux in Sun-like stars

Isik, Emre

Forward modelling of surface magnetism can be highly useful when interpreting photometric time series of Sun-like stars, as well as when reconstructing solar irradiance. We set up a theoretical framework based on the solar butterfly diagram, to study processes of flux emergence and transport on Sun-like stars. We take a semi-synthetic solar butterfly diagram of sunspot group emergence and map the emergence latitudes back to the base of the convection zone, using numerical simulations of rising flux tubes under the effects of stratification, drag force, and internal differential rotation. Transforming the base distribution to the surface for a given rotation rate, we determine the emergence latitudes and tilt angles of flux loops for the input rotation rate and activity level. Running a surface flux transport (SFT) model, we simulate the diffusive-advective evolution of the radial field at the surface. As the rotation rate increases, an inactive gap opens around the equator, reaching a half-width of 20º for 4 and 8 times the solar rotation rate. Between these two rotation rates, we find that polar spots start to form by accumulation of follower polarity flux. For 4 and 8 times the solar rotation rate, the cycle-averaged spot coverage becomes 2% and 10%, respectively, compared to the solar value of 0.2%, compatible with stellar observations.

## Spatially resolved solar spectral irradiance in NUV with Solar Ultraviolet Imaging Telescope (SUIT) on board Aditya-L1 mission

Tripathi, Durgesh

In order to fully comprehend the Sun-climate relations, it is of paramount importance to measure and monitor spatially resolved solar spectral irradiance in the wavelength range of 200 - 400 nm. The solar radiation emitted in within this wavelength range is known to play important role in the chemistry of Oxygen and Ozone in the stratosphere of the Earth’s atmosphere. The Solar Ultraviolet Imaging Telescope (SUIT) on board the first Indian solar mission Aditya-L1 aims to perform such measurements. SUIT will provide near-simultaneous full disk images of the Sun with a spatial resolution of 1.4 arcsec using 11 filters sensitive to different wavelengths within 200-400 nm. Three out of 11 filters cover the wavelength range of 200-242 nm, 242 - 300 nm and 320-360 nm. The other 8 filters are chosen such that they slice through different heights in the solar atmosphere, thereby providing an opportunity to study the processes involved in the transfer of mass and energy within the lower solar atmosphere.