<p>Total solar irradiance (TSI) has been measured by satellites for more than four decades, which provides an estimate of the amount of TSI variation over this time interval. Satellite measurements have established the variation of TSI in phase with sunspots by roughly 1000 ppm. This variation has slightly decreased during the last decades, following the related decrease of sunspot cycle amplitudes. However, opposing results have been found for a longer-term trend of TSI between recent cycle minima. In addition to TSI, some composite sets have been constructed to cover mainly the high-frequency part of the spectrum over several decades. A number of spectral lines have been observed for more than a century, yielding information on the centennial evolution of limited parts of the solar spectrum. However, the full solar spectrum has been measured only for about 20 years, first by the SORCE satellite from 2003 until 2020 and, more recently, by the TSIS-1 satellite since 2018. These observations allow to study not only by how much the different parts of the spectrum contribute to the TSI, but also their temporal evolution during the last 20 years.</p><p>We use here the TSIS-1 SIM (version 7) data and the SORCE SIM TSIS-1 adjusted SSI values (version 2, TAV2) to study the temporal evolution of several bands of the solar spectrum. We note that, according to TAV2, the contribution of the visual band of the spectrum to TSI (vis-TSI) depicts a curious, almost systematic increase from the late declining phase of solar cycle 23, through the ascending to maximum phase of solar cycle 24. Vis-TSI increases by about 1000 ppm during this time, reaching its maximum in 2015, at the same time as TSI has its cycle maximum. However, the subsequent decrease of vis-TSI is relatively smaller than that of TSI, with vis-TSI remaining some 0.4W/m**2 higher during the sunspot minimum of 2018 than during the previous minimum. TSIS-1 observations since 2018 show the continuing increase of vis-TSI in the ascending phase of cycle 25 roughly at the same rate as in the ascending phase of cycle 24. These observations exclude a purely solar cycle related variation of vis-TSI and indicate a curious longer-term increase.</p>
[1] The measurement of cloud absorption from aircraft has been a controversial subject largely because broadband measurements provide little insight into the physical mechanisms underlying the absorption. To partition and quantify the various mechanisms of cloud absorption, spectrally resolved measurements are required. Measurements of cloud solar spectral (400–2150 nm) absorption from airborne spectroradiometers are presented from two cases of extensive tropical marine stratus cloud fields. Radiative transfer modeling was used to retrieve the cloud optical thickness and cloud droplet effective radius from a best fit with the measured cloud spectral albedo. These values were used to estimate the cloud spectral absorptance. For the higher optical thickness case, the measurement-model agreement in absorptance across the spectrum is better than 0.05 and substantially better (within 0.01) at visible wavelengths unaffected by cloud absorption. For an optically thinner and more heterogeneous cloud field, the differences were higher, up to 0.07 in the near infrared. The standard deviations of cloud absorptance spectra show that the integrated absorbed irradiances, usually measured by broadband radiometers, are strongly affected by variations in the water vapor amount. Radiative transfer modeling is used to illustrate the spectral dependence of the absorption from radiatively important gases (e.g., water vapor), cloud liquid water, and absorbing aerosol particles. A novel sampling strategy, based on single aircraft measurements, is demonstrated, as is the value of spectrally resolved measurements in partitioning the various mechanisms of cloud absorption including the possible effects of absorbing aerosols embedded in clouds.
Abstract This work describes two achievements to a key data set. First, we present version 2 of the Total and Spectral Solar Irradiance Sensor‐1 Hybrid Solar Reference Spectrum (TSIS‐1 HSRS), which has recently been recognized as a new solar irradiance reference standard ( https://calvalportal.ceos.org/ ). Second, we present a new “full spectrum extension” of the TSIS‐1 HSRS. The TSIS‐1 HSRS observational composite solar irradiance reference spectrum spans 0.202–2.730 μm and encompasses more than 97% of the energy in the total solar irradiance (TSI). Version 2 is an incremental update that corrects the radiometric baseline between 0.202 and 0.210 μm and updates the solar lines at wavelengths longward of 0.743 μm to those listed in the most recent database. The full spectrum extension builds off version 2 of the TSIS‐1 HSRS and supports applications that require a solar spectrum encompassing nearly 100% of the energy in the TSI. It spans 0.115–200 μm and was developed by incorporating additional observations and theoretical knowledge where no direct observations currently exist.
The Sun is Earth's primary source of energy. In this paper, we compare the magnitude of the Sun to all other external (to the atmosphere) energy sources. These external sources were previously identified in Sellers (1965); here, we quantify and update them. These external sources provide a total energy to the Earth that is more than 3700 times smaller than that provided by the Sun, a vast majority of which is provided by heat from the Earth's interior. After accounting for the fact that 71% of incident solar radiation is deposited into the earth system, the Sun provides a total energy to Earth that is still more than 2600 times larger than the sum of all other external sources.
Abstract 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.
