Solar irradiance spectra from the compact SOLSTICE (CSOL) experiment: Instrument design, FUV calibration, measurements, and comparison of the 2018 rocket flight

The Compact SOLSTICE, a compact far and mid ultraviolet (FUV and MUV) spectrograph, flew on a sounding rocket on 18 June 2018 to validate and potentially calibrate the SOLar STellar Irradiance Comparison Experiment (SOLSTICE) onboard the Solar Radiation Climate Experiment (SORCE) spacecraft. This article reports the instrument design, the calibration of the FUV channel, and the FUV irradiance measurements. Irradiance measurements are compared to SOLSTICE showing agreement within the combined instrumental uncertainties at most wavelengths, including the H Lyman-α emission at 121.6 nm. Some unexplained differences in line ratios between 130.5 nm and 147.5 nm are observed

Solar irradiance spectra from the compact SOLSTICE (CSOL) experiment: instrument design, FUV calibration, measurements, and comparison of the 2018 rocket flight

The Compact SOLSTICE, a compact far and mid ultraviolet (FUV and MUV) spectrograph, flew on a sounding rocket on 18 June 2018 to validate and potentially calibrate the SOLar STellar Irradiance Comparison Experiment (SOLSTICE) onboard the Solar Radiation Climate Experiment (SORCE) spacecraft. This article reports the instrument design, the calibration of the FUV channel, and the FUV irradiance measurements. Irradiance measurements are compared to SOLSTICE showing agreement within the combined instrumental uncertainties at most wavelengths, including the H Lyman-α emission at 121.6 nm. Some unexplained differences in line ratios between 130.5 nm and 147.5 nm are observed

Spectral irradiance variations: Comparison between observations and the SATIRE model on solar rotation time scales

Aims: We test the reliability of the observed and calculated spectral irradiance variations between 200 and 1600 nm over a time span of three solar rotations in 2004. Methods: We compare our model calculations to spectral irradiance observations taken with SORCE/SIM, SoHO/VIRGO and UARS/SUSIM. The calculations assume LTE and are based on the SATIRE (Spectral And Total Irradiance REconstruction) model. We analyse the variability as a function of wavelength and present time series in a number of selected wavelength regions covering the UV to the NIR. We also show the facular and spot contributions to the total calculated variability. Results: In most wavelength regions, the variability agrees well between all sets of observations and the model calculations. The model does particularly well between 400 and 1300 nm, but fails below 220 nm as well as for some of the strong NUV lines. Our calculations clearly show the shift from faculae-dominated variability in the NUV to spot-dominated variability above approximately 400 nm. We also discuss some of the remaining problems, such as the low sensitivity of SUSIM and SORCE for wavelengths between approximately 310 and 350 nm, where currently the model calculations still provide the best estimates of solar variability.Comment: 15 pages, 11 figures, accepted by A&

2010 Solar and Space Physics Decadal Survey White Paper: Next Steps in Solar Spectral Irradiance Studies

Understanding the physical causes underlying solar spectral irradiance variations and the impact of these variations on terrestrial climate remain critical compelling challenges. On the solar side, the most fundamental unknown is the role of the “quiet-sun7 ,” a question brought into focus by spectral irradiance observations during the recent deep minimum, which show opposing trends in the infrared and ultraviolet portions of the spectrum (Harder et al. 2009). On the terrestrial side, while it is clear that the Sun played only a small role in late twentieth century warming, the signature of solar cycle variations in climate are now quite well established (Gray et al. 2010). How this coupling occurs is not fully understood, suggesting something incomplete in our understanding of the climate system. We suggest that in the coming decade, through the focused efforts outlined below, we can successfully address both of these scientific challenges and emerge with a new more complete understanding of the Sun and its influence on Earth. The essential ingredients in this effort are poised at the edge of our abilities, challenging but not risky, and take full advantage of current technological capabilities

SORCE and TSIS-1 SIM Comparison: Absolute Irradiance Scale Reconciliation

The Solar Radiation and Climate Experiment (SORCE) and Total and Spectral Irradiance Sensor (TSIS-1) conducted an intercomparison for the two Spectral Irradiance Monitors (SIM) spanning 704&nbsp;days from 23 March 2018 to 25 February 2020 and permitted 554 time-matched pairs of observations. This comparison was conducted during the extremely quiescent Solar Cycle 24 minimum, so all observed differences and drifts between the two sensors are instrumental in nature. The TSIS-1 SIM benefitted from advanced calibration capabilities based on SI standards that were not available during the preflight calibration time period of SORCE. For this reason, a revision of the SORCE SIM absolute scale is appropriate. As expected, wavelength dependent differences in absolute agreement are a function of detector sensitivity and local changes in spectral slope. At the time of the comparison SORCE SIM has been on-orbit for 17&nbsp;years while TSIS-1 observations commenced immediately after a 100-day outgassing and commissioning period. Peak-to-peak absolute scale differences are about 12% with a mean fractional difference of 0.7%&nbsp;&plusmn;&nbsp;2.9%. The greatest scale differences occur at the change-over between the UV and visible photodiodes in the 310&nbsp;nm region, and a systematic disagreement is present in the 850&ndash;1,600&nbsp;nm range. A multiplicative scale correction factor has been developed to reconcile the TSIS-1 and SORCE difference with a wavelength dependent error on the mean typically less than 0.01% derived from every matched pair of observations. &nbsp;</p

Regional climate impacts of a possible future grand solar minimum.

This is the final published version. It first appeared at http://www.nature.com/ncomms/2015/150623/ncomms8535/full/ncomms8535.html.Any reduction in global mean near-surface temperature due to a future decline in solar activity is likely to be a small fraction of projected anthropogenic warming. However, variability in ultraviolet solar irradiance is linked to modulation of the Arctic and North Atlantic Oscillations, suggesting the potential for larger regional surface climate effects. Here, we explore possible impacts through two experiments designed to bracket uncertainty in ultraviolet irradiance in a scenario in which future solar activity decreases to Maunder Minimum-like conditions by 2050. Both experiments show regional structure in the wintertime response, resembling the North Atlantic Oscillation, with enhanced relative cooling over northern Eurasia and the eastern United States. For a high-end decline in solar ultraviolet irradiance, the impact on winter northern European surface temperatures over the late twenty-first century could be a significant fraction of the difference in climate change between plausible AR5 scenarios of greenhouse gas concentrations.This work was supported by the Joint DECC/Defra Met Office Hadley Centre Climate Programme (GA01101) and also by the EU project SPECS funded by the European Commission’s Seventh Framework Research Programme under the grant agreement 308378 (Met Office Hadley Centre authors), by the NERC National Centre for Atmospheric Science (NCAS) Climate directorate (L.J.G. and A.C.M.), an ERC ACCI grant (A.C.M) and an AXA Postdoctoral Fellowship (A.C.M.)

Midlatitude atmospheric OH response to the most recent 11-y solar cycle

The hydroxyl radical (OH) plays an important role in middle atmospheric photochemistry, particularly in ozone (O_3) chemistry. Because it is mainly produced through photolysis and has a short chemical lifetime, OH is expected to show rapid responses to solar forcing [e.g., the 11-y solar cycle (SC)], resulting in variabilities in related middle atmospheric O_3 chemistry. Here, we present an effort to investigate such OH variability using long-term observations (from space and the surface) and model simulations. Ground-based measurements and data from the Microwave Limb Sounder on the National Aeronautics and Space Administration’s Aura satellite suggest an ∼7–10% decrease in OH column abundance from solar maximum to solar minimum that is highly correlated with changes in total solar irradiance, solar Mg-II index, and Lyman-α index during SC 23. However, model simulations using a commonly accepted solar UV variability parameterization give much smaller OH variability (∼3%). Although this discrepancy could result partially from the limitations in our current understanding of middle atmospheric chemistry, recently published solar spectral irradiance data from the Solar Radiation and Climate Experiment suggest a solar UV variability that is much larger than previously believed. With a solar forcing derived from the Solar Radiation and Climate Experiment data, modeled OH variability (∼6–7%) agrees much better with observations. Model simulations reveal the detailed chemical mechanisms, suggesting that such OH variability and the corresponding catalytic chemistry may dominate the O_3 SC signal in the upper stratosphere. Continuing measurements through SC 24 are required to understand this OH variability and its impacts on O_3 further