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...

Electromagnetic ion cyclotron (EMIC) waves are potentially important drivers of the loss of energetic electrons from the radiation belts. Numerous theoretical calculations exist with conflicting predictions of one of the key parameters: the minimum resonance energy of electrons precipitated into the atmosphere by EMIC waves. In this study we initially analyze an EMIC electron precipitation event using data from two different spacecraft instruments to investigate the energies involved. Combining observations from these satellites, we find that the electron precipitation has a peak flux at ∼250 keV. Extending the analysis technique to a previously published database of similar scattering events, we find that the peak electron precipitation flux occurs predominantly around 300 keV, with only ∼11% of events peaking in the 1–4 MeV range. Such a significant population of low‐energy EMIC‐driven electron precipitation events highlights the possibility for EMIC waves to be significant drivers of radiation belt electron losses.

On 31 May 2013 several rising tone electromagnetic ion cyclotron (EMIC) waves with intervals of pulsations of diminishing periods were observed in the magnetic local time afternoon and evening sectors during the onset of a moderate/large geomagnetic storm. The waves were sequentially observed in Finland, Antarctica, and western Canada. Coincident electron precipitation by a network of ground‐based Antarctic Arctic Radiation‐belt Dynamic Deposition VLF Atmospheric Research Konsortia and riometer instruments, as well as the Polar‐orbiting Operational Environmental Satellite (POES) electron telescopes, was also observed. At the same time, POES detected 30–80 keV proton precipitation drifting westward at locations that were consistent with the ground‐based observations, indicating substorm injection. Through detailed modeling of the combination of ground and satellite observations, the characteristics of the EMIC‐induced electron precipitation were identified as latitudinal width of 2–3° or ΔL = 1 Re, longitudinal width ~50° or 3 h magnetic local time, lower cutoff energy 280 keV, typical flux 1 × 104 el cm−2 sr−1 s−1 > 300 keV. The lower cutoff energy of the most clearly defined EMIC rising tone in this study confirms the identification of a class of EMIC‐induced precipitation events with unexpectedly low‐energy cutoffs of <400 keV.

Electromagnetic ion cyclotron (EMIC) waves are believed to be an important source of pitch angle scattering driven relativistic electron loss from the radiation belts. To date, investigations of this precipitation have been largely theoretical in nature, limited to calculations of precipitation characteristics based on wave observations and small‐scale studies. Large‐scale investigation of EMIC wave‐driven electron precipitation has been hindered by a lack of combined wave and precipitation measurements. Analysis of electron flux data from the POES (Polar Orbiting Environmental Satellites) spacecraft has been suggested as a means of investigating EMIC wave‐driven electron precipitation characteristics, using a precipitation signature particular to EMIC waves. Until now the lack of supporting wave measurements for these POES‐detected precipitation events has resulted in uncertainty regarding the driver of the precipitation. In this paper we complete a statistical study comparing POES precipitation measurements with wave data from several ground‐based search coil magnetometers; we further present a case study examining the global nature of this precipitation. We show that a significant proportion of the precipitation events correspond with EMIC wave detections on the ground; for precipitation events that occur directly over the magnetometers, this detection rate can be as high as 90%. Our results demonstrate that the precipitation region is often stationary in magnetic local time, narrow in L, and close to the expected plasmapause position. Predominantly, the precipitation is associated with helium band rising tone Pc1 waves on the ground. The success of this study proves the viability of POES precipitation data for investigating EMIC wave‐driven electron precipitation.

Electromagnetic ion cyclotron (EMIC) waves are thought to be important drivers of energetic electron losses from the outer radiation belt through precipitation into the atmosphere. While the theoretical possibility of pitch angle scattering‐driven losses from these waves has been recognized for more than four decades, there have been limited experimental precipitation observations to support this concept. We have combined satellite‐based observations of the characteristics of EMIC waves, with satellite and ground‐based observations of the EMIC‐induced electron precipitation. In a detailed case study, supplemented by an additional four examples, we are able to constrain for the first time the location, size, and energy range of EMIC‐induced electron precipitation inferred from coincident precipitation data and relate them to the EMIC wave frequency, wave power, and ion band of the wave as measured in situ by the Van Allen Probes. These observations will better constrain modeling into the importance of EMIC wave‐particle interactions.

In recent years, experimental results have consistently shown evidence of electromagnetic ion cyclotron (EMIC) wave‐driven electron precipitation down to energies as low as hundreds of keV. However, this is at odds with the limits expected from quasi‐linear theory. Recent analysis using nonlinear theory has suggested energy limits as low as hundreds of keV, consistent with the experimental results, although to date this has not been experimentally verified. In this study, we present concurrent observations from Polar‐orbiting Operational Environmental Satellite, Radiation Belt Storm Probes, Global Positioning System, and ground‐based instruments, showing concurrent EMIC waves and sub–MeV electron precipitation, and a global dropout in electron flux. We show through test particle simulation that the observed waves are capable of scattering electrons as low as hundreds of keV into the loss cone through nonlinear trapping, consistent with the experimentally observed electron precipitation.

Abstract. This paper describes the solar forcing dataset for CMIP6 and highlights in particular changes with respect to the CMIP5 recommendation. The solar forcing is provided for radiative properties, i.e., total solar irradiance (TSI) and solar spectral irradiance (SSI), and F10.7 cm radio flux, as well as particle forcing, i.e., geomagnetic indices Ap and Kp, and ionisation 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 is provided for a CMIP exercise. The solar forcing dataset is provided at daily and monthly resolution separately for the CMIP6 Historical Simulation (1850–2014), for the future (2015–2300), including an additional extreme Maunder Minimum-like sensitivity scenario, as well as for a constant and a time-varying forcing for the preindustrial control simulation. The paper not only describes the forcing dataset, but also provides detailed recommendations for how to implement the different forcing components in climate models. The TSI and SSI time series are defined as averages of two (semi-) empirical solar irradiance models, namely the NRLTSI2/NRLSSI2 and SATIRE-TS. A new and lower TSI value is recommended: the contemporary solar cycle-average is now 1361.0 W/m2. The slight negative trend in TSI during the last three solar cycles in CMIP6 is statistically indistinguishable from available observations and only leads to a small global radiative forcing of −0.04 W/m2. In the 200–400 nm range, which is also important for ozone photochemistry, CMIP6 shows a larger solar cycle variability contribution to TSI than CMIP5 (50 % as compared to 35 %). The CMIP6 dataset is tested and compared to its CMIP5 predecessor using timeslice experiments of two chemistry-climate models and a reference radiative transfer model. The changes in the background SSI in the CMIP6 dataset, as compared to CMIP5, impact on climatological stratospheric conditions (lower shortwave heating rates (−0.35 K/day 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 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 with a well-resolved shortwave radiation scheme are encouraged to use SSI, as well as solar-induced ozone signals, in order to better represent solar climate variability compared to models that only prescribe TSI and/or exclude the solar-ozone response. Monthly mean solar-induced ozone variations will also be incorporated into the CCMI CMIP6 Ozone Database for climate models that do not calculate ozone interactively. CMIP6 models with interactive chemistry are encouraged to use the particle forcing which will allow the potential long-term effect of particles to be addressed for the first time. The consideration of particle forcing has been shown to significantly improve the representation of reactive nitrogen and ozone variability in the polar middle atmosphere, eventually resulting in further improvements of the representation of solar climate variability.

Recent studies have shown how trapped energetic radiation belt electron fluxes rapidly "drop out" during small geomagnetic disturbances triggered by the arrival of a Solar Wind Stream Interface (SWSI). In the current study we use satellite and ground-based observations to describe the significance of energetic electron precipitation (EEP) and direct magnetopause shadowing loss mechanisms, both of which have been suggested as possible causes of the dropouts. Superposed epoch analysis of low-Earth orbiting POES spacecraft observations indicate that neither "classic" magnetopause shadowing or EEP appear able to explain the dropouts. However, SWSI-triggered dropouts in trapped flux are followed ~3 hours later by large increases of EEP, which start as the trapped electron fluxes begin to recover, and may be signatures of the acceleration process which rebuilds the trapped fluxes. Ground based observations indicate typical >30 keV EEP flux magnitudes of ~8×10 5 Tuesday, 31 July, 2012 2 electrons cm-2 sr-1 s-1. While these are ~10 times larger than the equivalent precipitating fluxes measured by POES, that is consistent with the small viewing window of the POES telescopes.