Comparison of solar soft X-ray irradiance from broadband photometers to a high spectral resolution rocket observation

The solar soft X-ray (XUV; 1–30 nm) radiation is highly variable on all time scales and strongly affects the ionosphere and upper atmosphere of Earth, Mars, as well as the atmospheres and surfaces of other planets and moons in the solar system; consequently, the solar XUV irradiance is important for atmospheric studies and for space weather applications. While there have been several recent measurements of the solar XUV irradiance, detailed understanding of the solar XUV irradiance, especially its variability during flares, has been hampered by the lack of high spectral resolution measurements in this wavelength range. The conversion of the XUV photometer signal into irradiance requires the use of a solar spectral model, but there has not been direct validation of these spectral models for the XUV range. For example, the irradiance algorithm for the XUV Photometer System (XPS) measurements uses multiple CHIANTI spectral models, but validation has been limited to other solar broadband measurements or with comparisons of the atmospheric response to solar variations. A new rocket observation of the solar XUV irradiance with 0.1 nm resolution above 6 nm was obtained on 14 April 2008, and these new results provide a first direct validation of the spectral models used in the XPS data processing. The rocket observation indicates very large differences for the spectral model for many individual emission features, but the differences are significantly smaller at lower resolution, as expected since the spectral models are scaled to match the broadband measurements. While this rocket measurement can help improve a spectral model for quiet Sun conditions, many additional measurements over a wide range of solar activity are needed to fully address the spectral model variations. Such measurements are planned with a similar instrument included on NASA’s Solar Dynamics Observatory (SDO), whose launch is expected in 2009.     

Recent advances in observations and modeling of the solar ultraviolet and X-ray spectral irradiance

There have been significant, recent advances in understanding the solar ultraviolet (UV) and X-ray spectral irradiance from several different satellite missions and from new efforts in modeling the variations of the solar spectral irradiance. The recent satellite missions with solar UV and X-ray spectral irradiance observations include the X-ray Sensor (XRS) aboard the series of NOAA GOES spacecraft, the Upper Atmosphere Research Satellite (UARS), the SOHO Solar EUV Monitor (SEM), the Solar XUV Photometers (SXP) on the Student Nitric Oxide Explorer (SNOE), the Solar EUV Experiment (SEE) aboard the Thermosphere, Ionosphere, Mesosphere, Dynamics, and Energetics (TIMED) satellite, and the Solar Radiation and Climate Experiment (SORCE) satellite. The combination of these measurements is providing new results on the variability of the solar ultraviolet irradiance throughout the ultraviolet range shortward of 200 nm and over a wide range of time scales ranging from years to seconds. The solar UV variations of flares are especially important for space weather applications and upper atmosphere research, and the period of intense solar storms in October–November 2003 has provided a wealth of new information about solar flares. The new efforts in modeling these solar UV spectral irradiance variations range from simple empirical models that use solar proxies to more complicated physics-based models that use emission measure techniques. These new models provide better understanding and insight into why the solar UV irradiance varies, and they can be used at times when solar observations are not available for atmospheric studies.     

New flare model using recent measurements of the solar ultraviolet irradiance

The solar photon output from the Sun, which was once thought to be constant, varies considerably over time scales from seconds during solar flares to years due to the solar cycle. This is especially true in the wavelengths shorter than 190 nm. These variations cause significant deviations in the Earth and space environment on similar time scales, which then affects many things including satellite drag, radio communications, atmospheric densities and composition of particular atoms, molecules, and ions of Earth and other planets, as well as the accuracy in the Global Positioning System (GPS). The Flare Irradiance Spectral Model (FISM) is an empirical model that estimates the solar irradiance at wavelengths from 0.1 to 190 nm at 1 nm resolution with a time cadence of 60 s. This is a high enough temporal resolution to model variations due to solar flares, for which few accurate measurements at these wavelengths exist. This model also captures variations on the longer time scales of solar rotation (days) and solar cycle (years). Daily average proxies used are the 0–4 nm irradiance, the Mg II c/w, F10.7, as well as the 1 nm bins centered at 30.5 nm, 121.5 (Lyman Alpha), and 36.5 nm. The GOES 0.1–0.8 nm irradiance is used as the flare proxy. The FISM algorithms are given, and results and comparisons are shown that demonstrate the FISM estimations agree within the stated uncertainties to the various measurements of the solar Vacuum Ultraviolet (VUV) irradiance.     

Influence of Fast Global Variations of Solar Magnetic Fields on Space Weather in Cycle 23

It is established that the large-scale and global magnetic fields in the Sun's atmosphere do not change smoothly, and long-lasting periods of gradual variations are superseded by fast structural changes of the global magnetic field. Periods of fast global changes on the Sun are accompanied by anomalous manifestations in the interplanetary space and in the geomagnetic field. There is a regular recurrence of these periods in each cycle of solar activity, and the periods are characterized by enhanced flaring activity that reflects fast changes in magnetic structures. Is demonstrated, that the fast changes have essential influencing on a condition of space weather, as most strong geophysical disturbances are connected to sporadic phenomena on the Sun. An explanation has been offered for the origin of anomalous geomagnetic disturbances that are unidentifiable in traditionally used solar activity indices. Is shown, main physical mechanism that leads to fast variations of the magnetic fields in the Sun's atmosphere is the reconnection process.     

Sun CubE OnE: A multi-wavelength synoptic solar micro satellite

The Sun cubE onE (SEE) is a 12U CubeSat mission proposed for a phase A/B study to the Italian Space Agency that will investigate Gamma and X-ray fluxes and ultraviolet (UV) solar emission to support studies in Sun-Earth interaction and Space Weather from LEO. More in detail, SEE’s primary goals are to measure the flares emission from soft-X to Gamma ray energy range and to monitor the solar activity in the Fraunhofer Mg II doublet at 280 nm, taking advantage of a full disk imager payload. The Gamma and X-ray fluxes will be studied with unprecedented temporal resolution and with a multi-wavelength approach thanks to the combined use of silicon photodiode and silicon photomultiplier (SiPM) -based detectors. The flare spectrum will be explored from the keV to the MeV range of energies by the same payload, and with a cadence up to 10 kHz and with single-photon detection capabilities to unveil the sources of the solar flares. The energy range covers the same bands used by GOES satellites, which are the standard bands for flare magnitude definition. At the same time SiPM detectors combined with scintillators allow to cover the non-thermal bremsstrahlung emission in the gamma energy range. Given its UV imaging capabilities, SEE will be a key space asset to support detailed studies on solar activity, especially in relation to ultraviolet radiation which strongly interacts with the upper layers of the Earth’s atmosphere, and in relation to space safety, included in the field of human space exploration. The main goal for the UV payload is to study the evolution of the solar UV emission in the Mg II band at two different time scales: yearly variations along the solar cycle and transient variations during flare events. The Mg II index is commonly used as a proxy of the solar activity in the Sun-as-a-star paradigm, in which solar irradiance variations in the UV correlate with the variations in stratospheric ozone concentrations and other physical parameters of the Earth high atmosphere. SEE data will be used together with space and ground-based observatories that provide Solar data (e.g. Solar Orbiter, IRIS, GONG, TSST), high energy particle fluxes (e.g. GOES, MAXI, CSES) and geomagnetic data in a multi-instrument/multi-wavelength/multi-messenger approach.     

The method for predicting solar proton events

Dynamic processes in the interplanetary space have been investigated using time variations in time parameters of the cosmic-ray rigidity spectrum. Change of heliosphere electromagnetic characteristics has been found out to precede sporadic phenomena on the Sun. In particular, it is shown that sporadic phenomena are followed by generation of local polarization electric fields, decrease of the magnetic-field strength in small-scale heliospheric structures, and increase of the potential difference between the pole and the plane of the ecliptic. These features allow prediction of solar proton events in advance (from several hours to several tens of hours) with a high degree of confirmation.     

Results of solar observations by the CORONAS-F payload

The CORONAS-F mission experiments and results have been reviewed. The observations with the DIFOS multi-channel photometer in a broad spectral range from 350 to 1500 nm have revealed the dependence of the relative amplitudes of p-modes of the global solar oscillations on the wavelength that agrees perfectly well with the earlier data obtained in a narrower spectral ranges. The SPIRIT EUV observations have enabled the study of various manifestations of solar activity and high-temperature events on the Sun. The data from the X-ray spectrometer RESIK, gamma spectrometer HELICON, flare spectrometer IRIS, amplitude–temporal spectrometer AVS-F, and X-ray spectrometer RPS-1 have been used to analyze the X- and gamma-ray emission from solar flares and for diagnostics of the flaring plasma. The absolute and relative content of various elements (such as potassium, argon, and sulfur) of solar plasma in flares has been determined for the first time with the X-ray spectrometer RESIK. The Solar Cosmic Ray Complex monitored the solar flare effects in the Earth’s environment. The UV emission variations recorded during solar flares in the vicinity of the 120-nm wavelength have been analyzed and the amplitude of relative variations has been determined.     

Irradiance models

Measurements of solar irradiance have revealed variations at all the sampled time scales (ranging from minutes to the length of the solar cycle). One important task of models is to identify the causes of the observed (total and spectral) irradiance variations. Another major aim is to reconstruct irradiance over time scales longer than sampled by direct measurements in order to consider if and to what extent solar irradiance variations may be responsible for global climate change. Here, we describe recent efforts to model solar irradiance over the current and the previous two solar cycles. These irradiance models are remarkably successful in reproducing the observed total and spectral irradiance, although further improvements are still possible.     

Reconstruction of the solar UV irradiance back to 1974

The variability of the solar UV irradiance has strong effects on the terrestrial atmosphere. In order to study the solar influence for times when no UV observations are available, it is necessary to reconstruct the variation of the UV irradiance with time on the basis of proxies. We present reconstructions of the solar UV irradiance based on the analysis of space-based and ground-based magnetograms of the solar disk going back to 1974. With COde for Solar Irradiance (COSI) we calculate solar intensity spectra for the quiet Sun and different active regions and combine them according to their fractional area on the solar disk, whereby their time-dependent contributions over the solar cycle lead to a variability in radiation. COSI calculates the continuum and line formation under conditions which are out of local thermodynamic equilibrium (non-LTE). The applied temperature and density structures include the chromosphere and transition region, which is particularly important for the UV. The reconstructions are compared with observations.     

Distinct EUV minimum of the solar irradiance (16–40 nm) observed by SolACES spectrometers onboard the International Space Station (ISS) in August/September 2009

In the field of terrestrial climatology the continuous monitoring of the solar irradiance with highest possible accuracy is an important goal. SolACES as a part of the ESA mission SOLAR on the ISS is measuring the short-wavelength solar EUV irradiance from 16–150 nm. This data will be made available to the scientific community to investigate the impact of the solar irradiance variability on the Earth’s climate as well as the thermospheric/ionospheric interactions that are pursued in the TIGER program. Since the successful launch with the shuttle mission STS-122 on February 7th, 2008, SolACES initially recorded the low EUV irradiance during the extended solar activity minimum. Thereafter it has been observing the EUV irradiance during the increasing solar activity with enhanced intensity and changing spectral composition. SolACES consists of three grazing incidence planar grating spectrometers. In addition there are two three-signal ionisation chambers, each with exchangeable band-pass filters to determine the absolute EUV fluxes repeatedly during the mission. One important problem of space-borne instrumentation recording the solar EUV irradiance is the degradation of the spectrometer sensitivity. The two double ionisation chambers of SolACES, which could be re-filled with three different gases for each recording, allow the recalibration of the efficiencies of the three SolACES spectrometers from time to time.     

Flight performance of a high resolution,high data rate solar ultraviolet telescope and spectrograph

The High Resolution Telescope and Spectrograph (HRTS) instrument has been flown three times on sounding rockets and has dramatically demonstrated the value of high resolution (spectral, spatial, and temporal) coupled with wide spectral and spatial coverage. Through the use of film as a detector, the HRTS can capture a large spectral and spatial range simultaneously. Because of the high spectral and spatial resolution, each exposure contains 10 million data points. After digitizing, this equates to a data collection rate of four megabits per second for a 20 second exposure. Because of the large film format, a set of HRTS exposures has recorded complete profiles of over 2800 emission lines simultaneously at 1000 different locations on the Sun. These emission lines originate in temperature regimes ranging from the temperature minimum to the corona. This allows a statistical analysis of temperature, pressure, density and velocity in many layers of the solar atmosphere.     

Thermospheric neutral density response to solar forcing

Recent measurements by the Solar EUV (Extreme Ultra Violet) Experiment (SEE) aboard the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics satellite (TIMED) provide solar EUV spectral irradiance with adequate spectral and temporal resolution, and thus the opportunity to use solar measurements directly in upper atmospheric general circulation models. Thermospheric neutral density is simulated with the NCAR Thermosphere–Ionosphere–Electrodynamic General Circulation Model (TIEGCM) using TIMED/SEE measurements and using the EUVAC solar proxy model. Neutral density is also calculated using the NRLMSISE-00 empirical model. These modeled densities are then compared to density measurements derived from satellite drag data. It is found that using measured solar irradiance in the general circulation model can improve density calculations compared to using the solar proxy model. It is also found that the general circulation model can improve upon the empirical model in simulating geomagnetic storm effects and the solar cycle variation of neutral density.     

The coronal dynamics imagers for the KuaFu mission

The Space Weather Explorer – KuaFu mission will provide simultaneous, long-term, and synoptic observations of the complete chain of disturbances from the solar atmosphere to the geospace. KuaFu-A (located at the L1 liberation point) includes Coronal Dynamics Imagers composed of a Lyman-α coronagraph (from 1.15 to 2.7 solar radii) and a white light coronagraph (out to 15 solar radii), in order to identify the initial sources of Coronal Mass Ejections (CMEs) and their acceleration profiles. The difficulty of observing the lower corona should not be underestimated since instrumental stray light remains a critical issue in the visible because of the low contrast of the corona with respect to the Sun. Observing the corona in the Lyman-α line is a valid alternative to white light observations. This approach takes advantage of both the intrinsic higher contrast of the corona with respect to the solar disk in this line compared to the visible, and the absence of F-corona at 121.6 nm. Furthermore, it has been convincingly shown that the coronal structures seen in Lyman-α correspond to those seen in the visible and which result from Thomson scattering of the coronal ionized gas. This is because the plasma is still collisional in the lower corona so that the hydrogen neutral atoms are coupled to the protons. A classical, all-reflecting internally-occulted Lyot coronagraph is required so as to preserve the image quality down to the inner limit of the field-of-view. A narrow band interference filter located in a collimated beam allows isolating the Lyman-α line. The visible coronagraph will adopt the approach of a single instrument having a large field-of-view extending from 2.5 to 15 solar radii. Such a design is based on refractive externally-occulted coronagraphs built for recent past missions, essentially the LASCO-C2 and C3 instruments and the SECCHI/COR 2 of the STEREO mission, which is itself a combination of the C2 and C3 instruments.     

Climatology of extreme upper atmospheric heating events

We use a trio of empirical models to estimate the relative contributions of solar extreme ultraviolet heating, Joule heating and particle heating to the global energy budget of the earth’s upper atmosphere. Daily power values are derived from the models for the three heat sources. The SOLAR2000 solar irradiance specification model provides estimates of the daily extreme EUV solar power input. Geomagnetic power comes from a combination of satellite-derived electron precipitation power and an empirical model of Joule power derived from hemispherically integrated estimates of high-latitude heating, which we discuss in this paper. From 1975 to mid-2002, the average daily contributions were electrons: 51 GW, Joule: 95 GW and solar: 784 GW. Joule and particle heating combine to provide more than 17% of the total global upper atmospheric heating. For the top 10% and 1% of heating events, contributions rise to 20% and 25%, respectively. In the top 15 heating events, geomagnetic power contributed more than 50% of the total power budget. During three events, the Joule power alone exceeded solar power.     

Which solar EUV indices are best for reconstructing the solar EUV irradiance?

The solar EUV irradiance is of key importance for space weather. Most of the time, however, surrogate quantities such as EUV indices have to be used by lack of continuous and spectrally resolved measurements of the irradiance. The ability of such proxies to reproduce the irradiance from different solar atmospheric layers is usually investigated by comparing patterns of temporal correlations. We consider instead a statistical approach. The TIMED/SEE experiment, which has been continuously operating since February 2002, allows for the first time to compare in a statistical manner the EUV spectral irradiance to five EUV proxies: the sunspot number, the f10.7, Ca K, and Mg II indices, and the He I equivalent width.     

基于太阳模拟器法的钙钛矿太阳电池测量方法研究

阐述了基于太阳模拟器法的钙钛矿太阳电池测量方法,包括对太阳模拟器性能、光源辐照度、光谱失配、电池温度、有效面积、I-V扫描时间设定等影响因素的规范,解决了钙钛矿太阳电池测量样品面积小、电容效应高、热稳定性差以及缺少光谱响应匹配度较好的标准电池和有效温控手段缺失等测量问题;并对测量结果的不确定度进行了评定,为国产钙钛矿太阳电池的精确测量奠定基础。     

Small-scale solar jet formation and their associated waves and instabilities

Studies on small-scale jets’ formation, propagation, evolution, and role, such as type I and II spicules, mottles, and fibrils in the lower solar atmosphere’s energetic balance, have progressed tremendously thanks to the combination of detailed observations and sophisticated mathematical modelling. This review provides a survey of the current understanding of jets, their formation in the solar lower atmosphere, and their evolution from observational, numerical, and theoretical perspectives. First, we review some results to describe the jet properties, acquired numerically, analytically and through high-spatial and temporal resolution observations. Further on, we discuss the role of hydrodynamic and magnetohydrodynamic instabilities, namely Rayleigh–Taylor and Kelvin–Helmholtz instabilities, in jet evolution and their role in the energy transport through the solar atmosphere in fully and partially ionised plasmas. Finally, we discuss several mechanisms of magnetohydrodynamic wave generation, propagation, and energy transport in the context of small-scale solar jets in detail. This review identifies several gaps in the understanding of small-scale solar jets and some misalignments between the observational studies and knowledge acquired through theoretical studies and numerical modelling. It is to be expected that these gaps will be closed with the advent of high-resolution observational instruments, such as Daniel K. Inouye Solar Telescope, Solar Orbiter, Parker Solar Probe, and Solar CubeSats for Linked Imaging Spectropolarimetry, combined with further theoretical and computational developments.     

Active region properties and irradiance variations

Total Solar Irradiance (TSI) has been measured for more than three decades. These observations demonstrate that total irradiance changes on time scales ranging from minutes to years and decades. Considerable efforts have been made to understand the physical origin of irradiance variations and to model the observed changes using measures of sunspots and faculae. In this paper, we study the short-term variations in TSI during the declining portion and minimum of solar cycle 22 and the rising portion of cycle 23 (1993–1998). This time interval of low solar activity allows us to study the effect of individual sunspot groups on TSI in detail. In this paper, we indicate that the effect of sunspot groups on total irradiance may depend on their type in the Zürich classification system and/or their evolution, and on their magnetic configuration. Some uncertainties in the data and other effects are also discussed.     

Solar spectral irradiance variability in the ultraviolet from SORCE and UARS SOLSTICE

The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) on the SOlar Radiation and Climate Experiment (SORCE) has been measuring the solar spectral irradiance on a daily basis since early 2003. This time period includes near-solar maximum conditions, the Halloween storms of 2003, and solar minimum conditions. These results can be compared to observations from the SOLSTICE I experiment that flew on the Upper Atmosphere Research Satellite (UARS) during the decline of the previous solar cycle as well as with currently operating missions. We will discuss similarities and differences between the two solar cycles in the long-term ultraviolet irradiance record.     

Integration and calibration of a multi slit spectropolarimeter

Multi-slit spectropolarimeter is a next-generation spectropolarimeter to obtain vector magnetic field information at high spatial, spectral, and temporal resolution for studying the magnetic structures on the Sun. Once developed, it can be used as ground based instrument at solar observatories, also as a space payload for various solar missions. A high spectral resolution is invariably an important parameter for accurate vector magnetic field measurements and faster cadence is required for the study of dynamical evolution of structures (e.g., solar flares, sunspots etc.) on the Sun and hence better understanding on the physics behind their evolution.