Abstract. This paper describes the recommended solar forcing dataset for CMIP6 and highlights changes with respect to CMIP5. The solar forcing is provided for radiative properties, namely total solar irradiance (TSI), solar spectral irradiance (SSI), and the F10.7 index as well as particle forcing, including geomagnetic indices Ap and Kp, and ionization rates to account for effects of solar protons, electrons, and galactic cosmic rays. This is the first time that a recommendation for solar-driven particle forcing has been provided for a CMIP exercise. The solar forcing datasets are provided at daily and monthly resolution separately for the CMIP6 preindustrial control, historical (1850CMIP6 preindustrial control, historical ( -2014, and future (2015-2300) simulations. For the preindustrial control simulation, both constant and time-varying solar forcing components are provided, with the latter including variability on 11-year and shorter timescales but no long-term changes. For the future, we provide a realistic scenario of what solar behavior could be, as well as an additional extreme Maunderminimum-like sensitivity scenario. This paper describes the forcing datasets and also provides detailed recommendations as to their implementation in current climate models.For the historical simulations, the TSI and SSI time series are defined as the average of two solar irradiance models that are adapted to CMIP6 needs: an empirical onePublished by Copernicus Publications on behalf of the European Geosciences Union. A new and lower TSI value is recommended: the contemporary solar-cycle average is now 1361.0 W m −2 . The slight negative trend in TSI over the three most recent solar cycles in the CMIP6 dataset leads to only a small global radiative forcing of −0.04 W m −2 . In the 200-400 nm wavelength range, which is important for ozone photochemistry, the CMIP6 solar forcing dataset shows a larger solar-cycle variability contribution to TSI than in CMIP5 (50 % compared to 35 %).We compare the climatic effects of the CMIP6 solar forcing dataset to its CMIP5 predecessor by using timeslice experiments of two chemistry-climate models and a reference radiative transfer model. The differences in the long-term mean SSI in the CMIP6 dataset, compared to CMIP5, impact on climatological stratospheric conditions (lower shortwave heating rates of −0.35 K day −1 at the stratopause), cooler stratospheric temperatures (−1.5 K in the upper stratosphere), lower ozone abundances in the lower stratosphere (−3 %), and higher ozone abundances (+1.5 % in the upper stratosphere and lower mesosphere). Between the maximum and minimum phases of the 11-year solar cycle, there is an increase in shortwave heating rates (+0.2 K day −1 at the stratopause), temperatures (∼ 1 K at the stratopause), and ozone (+2.5 % in the upper stratosphere) in the tropical upper stratosphere using the CMIP6 forcing dataset. This solar-cycle response is slightly larger, but not statistically significantly different from that for the CMIP5 forcing dataset.CMIP6 models wi...

Context. Solar flares radiate energy at all wavelengths, but the spectral distribution of this energy is still poorly known. White-light continuum emission is sometimes observed, and these flares are then called "white-light flares" (WLFs). Aims. We investigate if all flares are WLFs and how the radiated energy is distributed spectrally. Methods. We perform a superposed epoch analysis of spectral and total irradiance measurements obtained since 1996 by the SOHO and GOES spacecraft at various wavelengths, from soft X-rays to the visible domain.Results. The long-term record of solar irradiance and the excellent duty cycle of the measurements allow us to detect a signal in visible irradiance even for moderate (C-class) flares mainly during the impulsive phase. We identify this signal as continuum emission emitted by WLFs and find that it is consistent with a blackbody emission at ∼9000 K. We estimate the contribution of the WL continuum for several sets of flares and find it to be about 70% of the total radiated energy. We re-analyse the X17 flare that occurred on 28 October 2003 and find similar results. Conclusions. We show that most of the flares -if not all -are WLFs and that the white-light continuum is the main contributor to the total radiated energy; this continuum is consistent with a blackbody spectrum at ∼9000 K. These observational results are important for understanding the physical mechanisms during flares and possibly suggest a contribution of flares to the variations of the total solar irradiance (TSI).

In this study we synthesize the results of four previous studies on the global energetics of solar flares and associated coronal mass ejections (CMEs), which include magnetic, thermal, nonthermal, and CME energies in 399 solar Mand X-class flare events observed during the first 3.5 yr of the Solar Dynamics Observatory (SDO) mission. Our findings are as follows. (1) The sum of the mean nonthermal energy of flare-accelerated particles (E nt ), the energy of direct heating (E dir ), and the energy in CMEs (E CME ), which are the primary energy dissipation processes in a flare, is found to have a ratio of ( ), compared with the dissipated magnetic free energy E mag , which confirms energy closure within the measurement uncertainties and corroborates the magnetic origin of flares and CMEs. (2) The energy partition of the dissipated magnetic free energy is: 0.51±0.17 in nonthermal energy of 6 keV electrons, 0.17±0.17 in nonthermal 1 MeV ions, 0.07±0.14 in CMEs, and 0.07±0.17 in direct heating. (3) The thermal energy is almost always less than the nonthermal energy, which is consistent with the thick-target model. (4) The bolometric luminosity in white-light flares is comparable to the thermal energy in soft X-rays (SXR). (5) Solar energetic particle events carry a fraction »0.03 of the CME energy, which is consistent with CME-driven shock acceleration. (6) The warm-target model predicts a lower limit of the low-energy cutoff at » e 6 keV c , based on the mean peak temperature of the differential emission measure of T e =8.6 MK during flares. This work represents the first statistical study that establishes energy closure in solar flare/CME events.

We present the lessons learned about the degradation observed in several space solar missions, based on contributions at the Workshop about OnOrbit Degradation of Solar and Space Weather Instruments that took place at the Solar Terrestrial Centre of Excellence (Royal Observatory of Belgium) in Brussels on 3 May 2012. The aim of this workshop was to open discussions related to the degradation observed in Sun-observing instruments exposed to the effects of the space environment. This article summarizes the various lessons learned and offers recommendations to reduce or correct expected degradation with the goal of increasing the useful lifespan of future and ongoing space missions.

International audienceThe Large Yield Radiometer (LYRA) is an XUV-EUV-MUV (soft X-ray to mid-ultraviolet) solar radiometer onboard the European Space Agency Project for On-Board Autonomy 2 (PROBA2) mission, which was launched in November 2009. LYRA acquires solar-irradiance measurements at a high cadence (nominally 20 Hz) in four broad spectral channels, from soft X-ray to MUV, which have been chosen for their relevance to solar physics, space weather, and aeronomy. We briefly review the design of the instrument, give an overview of the data products distributed through the instrument website, and describe how the data are calibrated. We also briefly present a summary of the main fields of research currently under investigation by the LYRA consortium

International audienceWe discuss the implications of the first systematic observations of solar flares at submillimeter wavelengths, defined here as observing wavelengths shorter than 3 mm (frequencies higher than 0.1 THz). The events observed thus far show that this wave band requires a new understanding of high-energy processes in solar flares. Several events, including observations from two different observatories, show during the impulsive phase of the flare a spectral component with a positive (increasing) slope at the highest observable frequencies (up to 405 GHz). To emphasize the increasing spectra and the possibility that these events could be even more prominent in the THz range, we term this spectral feature a "THz component". Here we review the data and methods, and critically assess the observational evidence for such distinct component(s). This evidence is convincing. We also review the several proposed explanations for these feature(s), which have been reported in three distinct flare phases. These data contain important clues to flare development and particle acceleration as a whole, but many of the theoretical issues remain open. We generally have lacked systematic observations in the millimeter-wave to far-infrared range that are needed to complete our picture of these events, and encourage observations with new facilities

No abstract

[1] Solar UV emission has a profound impact on the upper terrestrial atmosphere. Because of instrumental constraints, however, solar proxies often need to be used as substitutes for the solar spectral variability. Finding proxies that properly reproduce specific spectral bands or lines is an ongoing problem. Using daily observations from 2003 to 2008 and a multiscale statistical approach, we test the performance of 9 proxies for the UV solar flux. Their relevance is evaluated at different time-scales and a novel representation allows all quantities to be compared simultaneously. This representation reveals which proxies are most appropriate for different spectral bands and for different time scales. Citation: Dudok de Wit, T., M. Kretzschmar, J. Lilensten, and T. Woods (2009), Finding the best proxies for the solar UV irradiance, Geophys. Res. Lett., 36, L10107, doi:10.1029/2009GL037825. Why Are Solar Proxies Needed?[2] The solar irradiance in wavelengths shortward of 300 nm is a key parameter for the specification of the upper terrestrial atmosphere [Floyd et al., 2002]. Variations are observed on time-scales ranging from seconds to years and can impact radio wave propagation, satellite orbits through increased air-drag but also global Earth climate. Unfortunately, there has been no long-term and continuous measurement of the full solar UV spectrum until Feb. 2002, when the TIMED satellite started operating. Even today, the continuous measurement of solar irradiance with sufficient temporal resolution and radiometric accuracy remains a major instrumental challenge [Woods et al., 2005a]. A important issue is the identification of proper substitutes (i.e., proxies) of the solar UV flux for upper atmospheric modeling .[3] Here, we test the performance of nine proxies for various UV spectral bands that encompass emissions coming from the solar corona down to the photosphere. The variability should therefore be strongly wavelength dependent, even though different solar layers are coupled. The solar UV radiation mostly affects the terrestrial atmosphere through photoionization and photochemistry, which are again wavelength-dependent processes [Floyd et al., 2002;Lilensten et al., 2008]. The radiation in the MUV range (200 -300 nm) mostly affects the stratospheric O 3 concentration; the FUV range (122-200 nm) affects the upper mesospheric O 2 excitation production and the lower thermospheric O 2 dissociation; the EUV range (10 -120 nm) affects the thermospheric O, O 2 and N 2 ionization and excitation productions. Other effects include the impact of the intense H I Lyman-a line at 121.57 nm on nitric oxides, which are important for climatological considerations. The altitude of strongest absorption is shown in Figure 1, together with the average spectral irradiance. No single proxy can reproduce the solar variability over the whole UV spectrum. Our prime objective therefore is to compare the measured irradiance in these bands to various proxies that are measured by independent means, partly from ground instruments. Se...