Revision of the Sun’s Spectral Irradiance as Measured by SORCE SIM

The stability and longevity of the Ozone Monitoring Instrument (OMI), flying on board the (active) Aura Earth-observing satellite since July 2004, facilitates creation of accurate, long-term record of relative (normalized to a solar minimum) solar spectral irradiances (SSIs). Here we discuss technical details of the most recent version (V3) of the SSI product that provides approximately daily measurements for the period July 2006 to April 2018 in the 265-to 500-nm domain with average 0.5-nm resolution. We compare OMI SSIs with concurrent independent observations and model estimates. The short-term (solar rotational cycle) observations and model predictions mostly agree to ∼0.1-0.2% in the ultraviolet domain, with an excellent, down to ∼0.01% agreement in the visible range. The long-term (solar cycle) comparisons pose more challenges in the ultraviolet domain, where the differences between observations and models frequently exceed the rather conservative ∼0.1% (both point-to-point and long-term) OMI uncertainties. In the visible range, these differences gradually diminish to <0.05% yet again pointing to reliability and robustness of the amassed SSI data in this domain. Key Points: • We describe the new version (V3) of the OMI solar spectral irradiances that provides a record of Solar Cycle 24 variability in the 265-to 500-nm range • The short-term (solar rotation) SSI variations: Comparison with the concurrent independent observations and model predictions show good-to-excellent (predominantly, to ∼0.1% in UV, and down to ∼0.01% in the visible) agreement between the various data sets • The long-term (solar cycle) SSI variations in the UV domain pose serious challenges, with model-observation and observation-observation disagreements frequently exceeding 0.5%. In the visible the inter-comparisons show good agreement, down to ∼0.05%

Section: The Datamentioning

confidence: 99%

Improved Aura/OMI Solar Spectral Irradiances: Comparisons With Independent Data Sets and Model Predictions

Марченко

Woods

DeLand

et al. 2019

“…Harder et al, 2005) and SOLSTICE , a reanalysis of the SORCE SIM data set between 2004 and 2012, called constrained SIM (SIMc), that applies an alternative degradation model and differs from SORCE SIM data in long-term behavior (Mauceri et al, 2018), the OMI (Levelt et al, 2018;Marchenko & DeLand, 2014), and the Solar Irradiance Data Exploitation (SOLID) project SSI composite (Haberreiter et al, 2017). All models tend, in general, to show similar structure in spectral irradiance variability at rotational variability and solar cycle timescales reflecting temporal changes in the overall emergence, evolution, rotation across the Sun's disk projected to Earth, and disappearance of active regions during an approximate 11-year solar cycle.…”

Section: Comparisons Of Ssi Variability Models and Measurementsmentioning

confidence: 99%

“…The differences reflect the challenge in measuring the spectrum of the Sun over long time periods where the level of corrections for instrument artifacts, such as degradation, may exceed solar cycle variability. The SIMc data set uses SORCE TIM observations to construct an alternative degradation model to the duty-cycle approach of the direct integrated SORCE SIM observations (Mauceri et al, 2018). The time-dependent degradation in the OMI SSI record is detected and corrected according to an assumption that any trends in the irradiance record during minima in solar activity are instrumental artifacts (Marchenko & DeLand, 2014).…”

Section: Solar Irradiance Variations On Solar Cycle Timescalesmentioning

confidence: 99%

“…For example, the competitively selected SIST teams are reprocessing and recalibrating SSI observations from the Ozone Monitoring Instrument (OMI) , the Solar Mesosphere Explorer, the Active Cavity Radiometer Irradiance Monitor (ACRIM), and the SORCE mission, including developing an alternative approach for correcting SORCE SIM degradation (Mauceri et al, 2018); improving and extending an existing SSI composite ; developing a SORCE SSI record for chemistry-climate studies (Harder et al, 2019); developing a new TSI observational composite using modern composite methodology approaches; improving observational composites of Lyman-alpha irradiance (Machol et al, 2019) and the magnesium (Mg) II index; and developing new versions of the NRL solar variability models (i.e., NRLTSI3 and NRLSSI3) that incorporates knowledge gained from these activities. The National Aeronautics and Space Administration (NASA) established a Solar Irradiance Science Team (SIST) based on a 2014 ROSES solicitation with the aim of providing to the Earth science community the most reliable specification of solar irradiance that includes consistent multi-instrument and multiplatform spacecraft records of solar irradiance.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Solar Irradiance Variability: Comparisons of Models and Measurements

Coddington

Lean

Pilewskie

et al. 2019

The Earth system responds to solar variability on a wide range of timescales. Knowledge of total solar irradiance (TSI) and solar spectral irradiance (SSI) spanning minutes to centuries is needed by scientists studying a broad array of research applications. For these purposes, the NOAA National Centers for Environmental Information (NCEI) Climate Data Record Program established the Solar Irradiance Climate Data Record. Version 2 of the Naval Research Laboratory's solar variability models that are derived from and demonstrate consistency with irradiance observations specifies TSI and SSI for the Solar Irradiance Climate Data Record. We establish the veracity of the Naval Research Laboratory models on the timescales and over the wavelength range for which the Sun is known to vary and, thereby, specify the utility of these models. Through comparisons with irradiance observations and independent models, we validate NRLTSI2 estimates of TSI on solar rotational (~27-day), solar cycle (~11-year), and multidecadal (spacecraft era) variability timescales. Similarly, we validate NRLSSI2 estimates of SSI rotational variability in the ultraviolet through the mid-visible spectrum. Validation of NRLSSI2 estimates at longer wavelengths, particularly in the near-infrared, and for the full spectrum at solar cycle timescales and longer is not possible with the current observational record due to instrumental noise and instrument instability. We identify where key new data sets, such as observations from the Total and Spectral Solar Irradiance Sensor-1, are expected to provide a fuller understanding of total and spectral solar irradiance variability on multiple timescales. Plain Language Summary An understanding of total and spectral solar irradiance is essential forEarth atmospheric and climate studies because the Sun's energy incident at the top of Earth's atmosphere is the dominant energy source driving a myriad of interactions that establish Earth's climate. We describe how the National Oceanographic and Atmospheric Administration's Solar Irradiance Climate Data Record is meeting the goal to model variability in the Sun's irradiance, identify limitations in our current understanding of solar irradiance variability on multiple timescales and over a broad spectral range, and highlight where new observations are expected to provide a fuller understanding.

“…Objective degradation corrections require designed-in onboard equipment and instrument operation schemes that are able to account for the myriad sources of signal loss (BenMoussa et al, 2013). Furthermore, in the absence of instrumentonly corrections, ad hoc corrections based on curve fitting (Wehrli et al, 2013), level shifting , imposing agreement with the TSI (Mauceri et al, 2018), and reliance on linear scaling through solar minimum (Marchenko & DeLand, 2014) cannot objectively discriminate between real solar variability and some arbitrarily specified notion of degradation. Furthermore, in the absence of instrumentonly corrections, ad hoc corrections based on curve fitting (Wehrli et al, 2013), level shifting , imposing agreement with the TSI (Mauceri et al, 2018), and reliance on linear scaling through solar minimum (Marchenko & DeLand, 2014) cannot objectively discriminate between real solar variability and some arbitrarily specified notion of degradation.…”

Section: Introductionmentioning

confidence: 99%

SORCE‐Based Solar Spectral Irradiance (SSI) Record for Input Into Chemistry‐Climate Studies

Harder

Béland

Snow

2019

Whole atmosphere chemistry-climate model (CCM) transient studies require a solar spectral irradiance (SSI) time series with very broad wavelength coverage with an uninterrupted daily cadence over a full solar cycle time period. Herein is described the construction of a SSI record valid over Solar Cycles 23 and 24 (SC23 and SC24) specifically designed to provide: (1) a daily solar spectrum from SORCE (Solar Radiation and Climate Experiment) observations from 208-2400 nm over the 2003 to 2015 time frame, (2) a wavelength extension of this spectrum out to 10000 nm from daily spectral synthesis from the Solar Radiation Physical Model (SRPM), (3) SRPM gap-filled spectra during the extended SORCE safe-hold time period (Aug 2013-March 2014) and back to Solar Cycle 23 maximum conditions in 2001 and 2002, (4) analysis of solar images generated by the Precision Solar Photometric Telescope (PSPT) network from the Mauna Loa Solar Observatory (MLSO) and Rome Observatory (OAR) (These images act both as input to the SRPM model and as a stand-alone proxy of solar variability.), (5) documentation of uncertainties and biases in the time series as a function of wavelength, and (6) comparative analysis of the SORCE time series with SRPM over the full wavelength range of the data set. Plain Language SummaryThe Sun delivers about 10,000 times more energy to the Earth climate system than any other source of energy. In spite of its overwhelming dominance in energy delivery, the Sun exerts a very benevolent influence on our climate compared to how other observable stars might behave. Nonetheless, the Sun is still a variable star, and its subtle variability is an important ingredient to understanding the evolution of the Earth climate system. For Earth chemistry-climate models to discriminate between natural and anthropogenic contributions to climate change, a high-quality data record of the variability of the Sun is needed both on a daily basis and over a full 11-year solar cycle. The construction of such a record requires a unification of available observations of the radiant power of the Sun and a solar physics model to fill in where our observation systems are lacking. We describe here a way of producing such a data record for the Earth science community.