ALBERT

Description: Context. Since April 5, 2008 and up to February 15, 2017, the SOLar SPECtrometer (SOLSPEC) instrument of the SOLAR payload on board the International Space Station (ISS) has performed accurate measurements of solar spectral irradiance (SSI) from the middle ultraviolet to the infrared (165 to 3088 nm). These measurements are of primary importance for a better understanding of solar physics and the impact of solar variability on climate. In particular, a new reference solar spectrum (SOLAR-ISS) is established in April 2008 during the solar minima of cycles 23–24 thanks to revised engineering corrections, improved calibrations, and advanced procedures to account for thermal and aging corrections of the SOLAR/SOLSPEC instrument. Aims. The main objective of this article is to present a new high-resolution solar spectrum with a mean absolute uncertainty of 1.26% at 1σ from 165 to 3000 nm. This solar spectrum is based on solar observations of the SOLAR/SOLSPEC space-based instrument.Methods. The SOLAR/SOLSPEC instrument consists of three separate double monochromators that use concave holographic gratings to cover the middle ultraviolet (UV), visible (VIS), and infrared (IR) domains. Our best ultraviolet, visible, and infrared spectra are merged into a single absolute solar spectrum covering the 165–3000 nm domain. The resulting solar spectrum has a spectral resolution varying between 0.6 and 9.5 nm in the 165–3000 nm wavelength range. We build a new solar reference spectrum (SOLAR-ISS) by constraining existing high-resolution spectra to SOLAR/SOLSPEC observed spectrum. For that purpose, we account for the difference of resolution between the two spectra using the SOLAR/SOLSPEC instrumental slit functions.Results. Using SOLAR/SOLSPEC data, a new solar spectrum covering the 165–3000 nm wavelength range is built and is representative of the 2008 solar minimum. It has a resolution better than 0.1 nm below 1000 nm and 1 nm in the 1000–3000 nm wavelength range. The new solar spectrum (SOLAR-ISS) highlights significant differences with previous solar reference spectra and with solar spectra based on models. The integral of the SOLAR-ISS solar spectrum yields a total solar irradiance of 1372.3 ± 16.9 Wm−2 at 1σ, that is yet 11 Wm−2 over the value recommended by the International Astronomical Union in 2015.

Description: Springtime stratospheric final warming (SFW) variability has been suggested to be linked to the tropospheric circulation, particularly over the North Atlantic sector. These findings, however, are based on reanalysis data that cover a rather short period of time (1979 to present). The present work aims to improve the understanding of drivers, trends and surface impact of dynamical variability of boreal SFWs using chemistry-climate models. We use multidecadal integrations of the fully coupled chemistry-climate models Community Earth System Model version 1 (Whole Atmosphere Community Climate Model) and ECHAM/Modular Earth Submodel System Atmospheric Chemistry-O. Four sensitivity experiments are analyzed to assess the impact of external factors; namely, the quasi-biennial oscillation, sea surface temperature (SST) variability, and anthropogenic emissions. SFWs are classified into two types with respect to their vertical development; that is, events which occur first in the midstratosphere (10-hPa first SFWs) or first in the upper stratosphere (1-hPa first SFWs). Our results confirm previous reanalysis results regarding the differences in the time evolution of stratospheric conditions and near-surface circulation between 10 and 1-hPa first SFWs. Additionally, a tripolar SST pattern is, for the first time, identified over the North Atlantic in spring months related to the SFW variability. Our analysis of the influence of remote modulators on SFWs revealed that the occurrence of major warmings in the previous winter favors the occurrence of 10-hPa first SFWs later on. We further found that quasi-biennial oscillation and SST variability significantly affect the ratio between 1-hPa first and 10-hPa first SFWs. Finally, our results suggest that ozone recovery may impact the timing of the occurrence of 1-hPa first SFWs. ©2019. American Geophysical Union. All Rights Reserved.

Description: Global Ozone Monitoring by Occultation of Stars (GOMOS) satellite data are analyzed to estimate the first observation-based nighttime (22:00 median local time) ozone response to the 27-day solar rotational cycle in the tropical mesosphere/lower thermosphere (50–110 km altitude). The ozone response to solar rotational variability is derived from linear correlation and regressions using Lyman-α line (121.6 nm) as solar index that varies by about 10–15% over solar rotational cycles. In the lower mesosphere (50–70 km), the GOMOS ozone is found to be correlated with the solar fluctuations and exhibits a sensitivity of ~0.1 (expressed in percent change of ozone for 1% change in Lyman-α). In the upper mesosphere/lower thermosphere (above 80 km), ozone variations become anticorrelated with solar rotational variations. In this region, the vertical profile of ozone sensitivity to the 27-day solar cycle exhibits a maximum of 1.8 at 81 km, a minimum of 0.3 at 100 km, and a sharp increase above. Such high ozone sensitivities are observed for the first time. The observed ozone response is compared with chemistry-climate simulations from the Hamburg model of the neutral and ionized atmosphere (HAMMONIA) that is forced with an idealized 27-day solar spectral irradiance time series. Although observational and model results share some common features, substantial discrepancies are found. Namely, the altitude of transition from positive to negative solar ozone correlation signal in the model simulation is found about 10 km below the altitude of the observations and the amplitude of the ozone sensitivity is generally vastly underestimated by the model. ©2018. American Geophysical Union. All Rights Reserved.

Description: The impact of changes in incoming solar ultraviolet irradiance on stratospheric ozone forms an important part of the climate response to solar variability. To realistically simulate the climate response to solar variability using climate models, a minimum requirement is that they should include a solar cycle ozone component that has a realistic amplitude and structure, and which varies with season. For climate models that do not include interactive ozone chemistry, this component must be derived from observations and/or chemistry–climate model simulations and included in an externally prescribed ozone database that also includes the effects of all major external forcings. Part 1 of this two part study presents the solar-ozone responses in a number of updated satellite datasets for the period 1984–2004, including the Stratospheric Aerosol and Gas Experiment (SAGE) II version 6.2 and version 7.0 data, and the Solar Backscatter Ultraviolet Instrument (SBUV) version 8.0 and version 8.6 data. A number of combined datasets, which have extended SAGE II using more recent satellite measurements, are also analysed for the period 1984–2011. It is shown that SAGE II derived solar-ozone signals are sensitive to the independent temperature measurements used to convert ozone number density to mixing ratio units. A change in these temperature measurements in the recent SAGE II v7.0 data leads to substantial differences in the mixing ratio solar-ozone response compared to the previous v6.2, particularly in the tropical upper stratosphere. We also show that alternate satellite ozone datasets have issues (e.g., sparse spatial and temporal sampling, low vertical resolution, and shortness of measurement record), and that the methods of accounting for instrument offsets and drifts in merged satellite datasets can have a substantial impact on the solar cycle signal in ozone. For example, the magnitude of the solar-ozone response varies by around a factor of two across different versions of the SBUV VN8.6 record, which appears to be due to the methods used to combine the separate SBUV timeseries. These factors make it difficult to extract more than an annual-mean solar-ozone response from the available satellite observations. It is therefore unlikely that satellite ozone measurements alone can be applied to estimate the necessary solar cycle ozone component of the prescribed ozone database for future coupled model intercomparison projects (e.g., CMIP6).

Description: The 11 year solar-cycle component of climate variability is assessed in historical simulations of models taken from the Coupled Model Intercomparison Project, phase 5 (CMIP-5). Multiple linear regression is applied to estimate the zonal temperature, wind and annular mode responses to a typical solar cycle, with a focus on both the stratosphere and the stratospheric influence on the surface over the period approximately 1850-2005. The analysis is performed on all CMIP-5 models but focuses on the 13 CMIP-5 models that resolve the stratosphere (high-top models) and compares the simulated solar cycle signature with reanalysis data. The 11 year solar cycle component of climate variability is found to be weaker in terms of magnitude and latitudinal gradient around the stratopause in the models than in the reanalysis. The peak in temperature in the lower equatorial stratosphere (approximately 70 hPa) reported in some studies is found in the models to depend on the length of the analysis period, with the last 30 years yielding the strongest response. A modification of the Polar Jet Oscillation (PJO) in response to the 11 year solar cycle is not robust across all models, but is more apparent in models with high spectral resolution in the short-wave region. The PJO evolution is slower in these models, leading to a stronger response during February, whereas observations indicate it to be weaker. In early winter, the magnitude of the modeled response is more consistent with observations when only data from 1979-2005 are considered. The observed North Pacific high-pressure surface response during the solar maximum is only simulated in some models, for which there are no distinguishing model characteristics. The lagged North Atlantic surface response is reproduced in both high- and low-top models, but is more prevalent in the former. In both cases, the magnitude of the response is generally lower than in observations.

Description: The surface response to the 11-yr solar cycle is assessed in ensemble simulations of the 20th century climate performed in the framework of the 5th phase of the Coupled Model Inter-Comparison Project (CMIP5). A lead/lag multiple linear regression analysis identifies a multi-model mean (MMM) global mean surface warming of about 0.07 K lagging the solar cycle by one to two years on average. The anomalous warming penetrates to approximately the first 80–100 m depth in the ocean. Solar signals in the troposphere show a similar time lag of one to two years and the strongest MMM warming is simulated in the tropics above 300 hPa. At the surface, the MMM response in a subset of models that show statistically significant global mean warming (CMIP5-SIG95) is characterized by an anomalous warming in the west equatorial Pacific Ocean and the Arctic, at one to two years after solar maximum. The Arctic warming is twice as strong as the global mean response and appears in winter months only. The surface warming in the equatorial Pacific Ocean is related to dynamical/thermodynamical processes. Different increase rates of global mean precipitation and atmospheric water vapor in response to a warmer surface lead to a weaker Walker circulation and anomalous westerly winds over the equatorial Pacific in years following solar maximum. Owing to atmosphere–ocean coupling, the anomalous westerly winds cool the subsurface and warm the surface in the western equatorial Pacific by ∼ 0.14 K. The CMIP5-SIG95 MMM surface warming in the equatorial Pacific and Arctic is weak but qualitatively similar compared to solar signals in the HadCRUT4 dataset.

Description: Springtime stratospheric final warming (SFW) variability has been suggested to be linked to the tropospheric circulation, particularly over the North Atlantic sector. These findings, however, are based on reanalysis data that cover a rather short period of time (1979 to present). The present work aims to improve the understanding of drivers, trends and surface impact of dynamical variability of boreal SFWs using chemistry‐climate models. We use multidecadal integrations of the fully coupled chemistry‐climate models Community Earth System Model version 1 (Whole Atmosphere Community Climate Model) and ECHAM/Modular Earth Submodel System Atmospheric Chemistry‐O. Four sensitivity experiments are analyzed to assess the impact of external factors; namely, the quasi‐biennial oscillation, sea surface temperature (SST) variability, and anthropogenic emissions. SFWs are classified into two types with respect to their vertical development; that is, events which occur first in the midstratosphere (10‐hPa first SFWs) or first in the upper stratosphere (1‐hPa first SFWs). Our results confirm previous reanalysis results regarding the differences in the time evolution of stratospheric conditions and near‐surface circulation between 10 and 1‐hPa first SFWs. Additionally, a tripolar SST pattern is, for the first time, identified over the North Atlantic in spring months related to the SFW variability. Our analysis of the influence of remote modulators on SFWs revealed that the occurrence of major warmings in the previous winter favors the occurrence of 10‐hPa first SFWs later on. We further found that quasi‐biennial oscillation and SST variability significantly affect the ratio between 1‐hPa first and 10‐hPa first SFWs. Finally, our results suggest that ozone recovery may impact the timing of the occurrence of 1‐hPa first SFWs.