The solar spectrum at the top of the atmosphere contains crucial data for solar physics, astronomy, and geophysics. Accurately determining high-resolution solar reference spectra, whether they are ...disk-integrated, disk-center, or intermediate cases, represents a new challenge and is of primary importance for all applications where spectral solar radiation needs to be evaluated. These spectra are also essential for interpreting remote sensing measurements that rely on sunlight, such as those obtained by Earth observation satellites or spacecraft exploring other planets. This paper lays a foundation for the implementation of multiple new solar irradiance reference spectra that have high resolution and are representative of solar minimum conditions. We developed the SOLAR high-resolution extraterrestrial reference spectra (SOLAR-HRS disk-integrated spectra) by normalizing high-spectral-resolution solar line data to the absolute irradiance scale of the SOLAR-ISS reference spectrum. The resulting one-of-a-kind SOLAR-HRS disk-integrated spectrum has a spectral resolution varying between 0.001 and 1 nm in the 0.5–4400 nm wavelength range. We also implemented a new high-resolution solar spectrum at the disk-center, covering a range of 650–4400 nm with a spectral resolution of 0.001 to 0.02 nm. We further expanded our analysis by producing several solar spectra for ten different solar view angles ranging from μ = 0.9 to μ = 0.05 (SOLAR-HRS intermediate cases). Finally, we developed new Merged Parallelised Simplified ATLAS spectra (MPS-ATLAS) based on solar modeling with Kurucz and Vald3 solar linelists for both the disk-integrated and disk-center spectra. One of the objectives of implementing all these new solar spectra is to fulfill the requirements of the MicroCarb space mission, which focuses on measuring greenhouse gas emissions. The solar data of this study are openly available.
To advance our understanding of the stratosphere, high-quality observational datasets of the stratosphere are needed. It is commonplace that reanalysis datasets are used to conduct stratospheric ...studies. However, the accuracy of these reanalyses at these heights is hard to infer due to a lack of in situ measurements. Satellite measurements provide one source of temperature information. As some satellite information is already assimilated into reanalyses, the direct comparison of satellite temperatures to the reanalysis is not truly independent. Stratospheric lidars use Rayleigh scattering to measure density in the middle and upper atmosphere, allowing temperature profiles to be derived for altitudes from 30 km (where Mie scattering due to stratospheric aerosols becomes negligible) to 80–90 km (where the signal-to-noise ratio begins to drop rapidly). The Network for the Detection of Atmospheric Composition Change (NDACC) contains several lidars at different latitudes that have measured atmospheric temperatures since the 1970s, resulting in a long-running upper-stratospheric temperature dataset. These temperature datasets are useful for validating reanalysis datasets in the stratosphere, as they are not assimilated into reanalyses. Here, stratospheric temperature data from lidars in the Northern Hemisphere between 1990–2017 were compared with the
European Centre for Medium-Range Weather Forecasts ERA-Interim and ERA5 reanalyses. To give confidence to any bias found, temperature data from NASA's EOS Microwave Limb Sounder were also compared to ERA-Interim and ERA5 at points over the lidar sites. In ERA-Interim a cold bias of −3 to −4 K between 10 and 1 hPa was found when compared to both measurement systems. Comparisons with ERA5 found a small bias of magnitude 1 K which varies between cold and warm bias with height between 10 and 1 hPa, indicating a good thermal representation of the middle atmosphere up to 1 hPa. A further comparison was undertaken looking at the temperature bias by year to see the effects of the assimilation of the Advanced Microwave Sounding Unit-A (AMSU-A) satellite data and the Constellation Observing System for Meteorology, Ionosphere, and Climate GPS Radio Occultation (COSMIC GPSRO) data on stratospheric temperatures within the aforementioned ERA analyses. It was found that ERA5 was sensitive to the introduction of COSMIC GPSRO in 2007 with the reduction of the cold bias above 1 hPa. In addition to this, the introduction of AMSU-A data caused variations in the temperature bias between 1–10 hPa between 1997–2008.
The strong interest in Sudden Stratospheric Warmings (SSWs) is motivated by their role in the two‐way stratospheric‐tropospheric dynamical coupling. While most studies only investigate major SSWs ...(vortex breakdown), the minor ones (strong vortex deceleration) are overlooked. This work aims at overcoming this gap by providing a comprehensive description of stratospheric warming events without a priori distinctions between major and minor SSWs, leading to a more complete estimate of the stratospheric variability. Warming events are extracted from reanalysis data sets by means of a midstratospheric polar cap temperature daily index. Events are characterized by a bimodal distribution in amplitude, with a broad peak at small amplitudes (inferior to 5K) and a sharp peak at around 9K. Due to the intrinsic polar vortex dynamics, the warming amplitude presents a distinct seasonal distribution. Small amplitude warmings mainly occur during early and late wintertime by contrast with the larger‐amplitude ones occurring during midwintertime. From mid‐November to mid‐March, the large‐amplitude warmings (i.e., strong warming events, SWEs) include both major and minor SSWs, as well as Canadian and Final warmings. Although major SSWs belong to the tail of the SWEs distribution, there is no clear distinction between the major and minor SSWs according to the considered properties of the events. Such result brings out the idea of “warming continuum.” Furthermore, diagnostics of heat flux reveal that there is no statistical difference between SWEs with regard to their feedbacks on the planetary waves and hence on their potential influence into the troposphere.
Key Points
Characterization of stratospheric warming events during wintertime
Stratospheric warming continuum
Polar stratospheric variability analysis
The long-term evolution of total ozone column inside the Antarctic polar
vortex is investigated over the 1980–2017 period. Trend analyses are
performed using a multilinear regression (MLR) model ...based on various proxies
for the evaluation of ozone interannual variability (heat flux,
quasi-biennial oscillation, solar flux, Antarctic oscillation and aerosols).
Annual total ozone column measurements corresponding to the mean monthly values inside the
vortex in September and during the period of maximum ozone depletion from
15 September to 15 October are used. Total ozone columns from
the Multi-Sensor Reanalysis version 2 (MSR-2) dataset and from a combined record based
on TOMS and OMI satellite datasets with gaps filled by MSR-2 (1993–1995)
are considered in the study. Ozone trends are computed by a piece-wise
trend (PWT) proxy that includes two linear functions before and after the
turnaround year in 2001 and a parabolic function to account for the
saturation of the polar ozone destruction. In order to evaluate average total
ozone within the vortex, two classification methods are used, based on the
potential vorticity gradient as a function of equivalent latitude. The first
standard one considers this gradient at a single isentropic level (475 or
550 K), while the second one uses a range of isentropic levels between 400
and 600 K. The regression model includes a new proxy (GRAD) linked to the
gradient of potential vorticity as a function of equivalent latitude and
representing the stability of the vortex during the studied month. The
determination coefficient (R2) between observations and modelled values
increases by ∼ 0.05 when this proxy is included in the MLR
model. Highest R2 (0.92–0.95) and minimum residuals are obtained for the
second classification method for both datasets and months. Trends in September over the 2001–2017 period are statistically
significant at 2σ level with values ranging between 1.84 ± 1.03
and 2.83 ± 1.48 DU yr−1 depending on the methods and considered
proxies. This result confirms the recent studies of Antarctic ozone healing
during that month. Trends from 2001 are 2 to 3 times smaller than before the
turnaround year, as expected from the response to the slowly ozone-depleting
substances decrease in polar regions. For the first time, significant trends are found for the period of maximum
ozone depletion. Estimated trends from 2001 for the 15 September–15 October period over
2001–2017 vary from 1.21 ± 0.83 to 1.96 DU ± 0.99 yr−1 and
are significant at 2σ level. MLR analysis is also applied to the ozone mass deficit (OMD) metric for both
periods, considering a threshold at 220 DU and total ozone columns south of
60∘ S. Significant trend values are observed for all cases and
periods. A decrease of OMD of 0.86 ± 0.36 and 0.65 ± 0.33 Mt yr−1
since 2001 is observed in September and 15 September–15 October,
respectively. Ozone recovery is also confirmed by a steady decrease of the relative area
of total ozone values lower than 175 DU within the vortex in the
15 September–15 October period since 2010 and a delay in the occurrence of ozone levels
below 125 DU since 2005.
Abstract
In early spring the stratospheric zonal circulation reverses from westerly to easterly. The transition, called Stratospheric Final Warming (SFW), may be smooth and late, mainly controlled by ...the solar radiative heating of the polar region, or early and abrupt with rapid increase of polar temperature and deceleration of the zonal wind, forced by the planetary wave activity. Here we present a study, based on 71 years meteorological reanalysis data. Two composites of radiative and dynamical SFWs have been built. There is a very significant difference in the evolution during the year of polar temperature and 60°N zonal wind between the two composites. The state of the polar vortex on given month is anticorrelated with its state 2 to 3 months earlier. Early winter is anticorrelated with mid-winter and mid-winter with late winter/early spring. The summer stratosphere keeps a memory of its state in April–May after the SFW until late June.
To better extract the tides represented in the European meteorological analysis ERA5, an analysis of the histograms of the diurnal and semi-diurnal modes as a function of longitudes was performed. ...This analysis revealed that modes with different characteristics appeared regionally along a single longitude. Retrieved migrating tides were compared with a tidal model showing global agreement below 60 km and twice the amplitude in meteorological analyses at mid-latitude. Non-migrating tidal modes have been identified along the tropical band. They logically appear above the convective zones, probably due to water vapor excess. Their characteristics are different from migrating components. This preliminary study has shown that it is necessary to develop additional observations allowing for more frequent sampling to retrieve migrating and non-migrating tides that can only be achieved with satellite constellations from space.
Stratospheric temperature trends for the period 2002–2014 have been estimated using NOAA's Integrated Microwave Inter‐calibration Approach (IMICA) version of advanced microwave sounding unit (AMSU) ...on AQUA satellite. In this period the stratosphere continued cooling over most of the globe with a rate ranging from −0.4 ± 0.3 to −0.5 ± 0.4 K/decade above 25 km. Considering specific latitude bands, trends are highly variable with height. In the tropical region, trends vary from −0.5 ± 0.3 K/decade for channel 12 (∼30 km) to −0.7 ± 0.3 K/decade for higher channels and present small seasonal variability in the intensity of cooling. In the polar regions and in the midlatitudes, trends for all channels are negative but not significant; uncertainties are large due to the high dynamical variability particularly in high latitudes. There is also large seasonal variability, with southern midlatitudes seasonal trends significant during summer (December, January, February) and autumn (March, April, May) above ∼25 km, with values ranging from −1.0 ± 0.5 to −0.6 ± 0.5 K/decade. Regional trends estimated with AMSU and long‐term lidar measurements (over two decades) confirm stratospheric cooling in the northern midlatitudes and tropical regions. The effect of the length of the short series on trends was found to be small outside polar regions. It was found to be large in polar regions with about 1 K changes in trend depending on start dates of the time series.
Key Points
Stratosphere cooled at a global mean rate of ‐0.2 ± 0.3 to ‐0.5 ± 0.4 K/decade in the 2002–2014 period
Trends range from ‐0.5 ± 0.3 to ‐0.7 ± 0.3 K/decade above 30 km in the tropics
Regional trends by AMSU (2002–2014) and lidars (greater than two decades) confirm continuous stratospheric cooling
Monitoring atmospheric concentrations of greenhouse gases (GHGs) like carbon dioxide and methane in near real time and with good spatial resolution is crucial for enhancing our understanding of the ...sources and sinks of these gases. A novel approach can be proposed using a constellation of small satellites equipped with miniaturized spectrometers having a spectral resolution of a few nanometers. The objective of this study is to describe expected results that can be obtained with a single satellite named Uvsq-Sat NG. The SolAtmos end-to-end simulator and its three tools (IRIS, OptiSpectra, and GHGRetrieval) were developed to evaluate the performance of the spectrometer of the Uvsq-Sat NG mission, which focuses on measuring the main GHGs. The IRIS tool was implemented to provide Top-Of-Atmosphere (TOA) spectral radiances. Four scenes were analyzed (pine forest, deciduous forest, ocean, snow) combined with different aerosol types (continental, desert, maritime, urban). Simulated radiance spectra were calculated based on the wavelength ranges of the Uvsq-Sat NG, which spans from 1200 to 2000 nm. The OptiSpectra tool was used to determine optimal observational settings for the spectrometer, including Signal-to-Noise Ratio (SNR) and integration time. Data derived from IRIS and OptiSpectra served as input for our GHGRetrieval simulation tool, developed to provide greenhouse gas concentrations. The Levenberg–Marquardt algorithm was applied iteratively to fine-tune gas concentrations and model inputs, aligning observed transmittance functions with simulated ones under given environmental conditions. To estimate gas concentrations (CO2, CH4, O2, H2O) and their uncertainties, the Monte Carlo method was used. Based on this analysis, this study demonstrates that a miniaturized spectrometer onboard Uvsq-Sat NG is capable of observing different scenes by adjusting its integration time according to the wavelength. The expected precision for each measurement is of the order of a few ppm for carbon dioxide and less than 25 ppb for methane.
The article presents new high-quality continuous stratospheric aerosol observations spanning 1994–2015 at the French Observatoire de Haute-Provence (OHP, 44° N, 6° E) obtained by two independent, ...regularly maintained lidar systems operating within the Network for Detection of Atmospheric Composition Change (NDACC). Lidar series are compared with global-coverage observations by Stratospheric Aerosol and Gas Experiment (SAGE II), Global Ozone Monitoring by Occultation of Stars (GOMOS), Optical Spectrograph and InfraRed Imaging System (OSIRIS), Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and Ozone Mapping Profiling Suite (OMPS) satellite instruments, altogether covering the time span of OHP lidar measurements. Local OHP and zonal-mean satellite series of stratospheric aerosol optical depth are in excellent agreement, allowing for accurate characterization of stratospheric aerosol evolution and variability at northern midlatitudes during the last 2 decades. The combination of local and global observations is used for a careful separation between volcanically perturbed and quiescent periods. While the volcanic signatures dominate the stratospheric aerosol record, the background aerosol abundance is found to be modulated remotely by the poleward transport of convectively cleansed air from the deep tropics and aerosol-laden air from the Asian monsoon region. The annual cycle of background aerosol at midlatitudes, featuring a minimum during late spring and a maximum during late summer, correlates with that of water vapor from the Aura Microwave Limb Sounder (MLS). Observations covering two volcanically quiescent periods over the last 2 decades provide an indication of a growth in the nonvolcanic component of stratospheric aerosol. A statistically significant factor of 2 increase in nonvolcanic aerosol since 1998, seasonally restricted to late summer and fall, is associated with the influence of the Asian monsoon and growing pollution therein.
A mesospheric model of the airglow emission is developed to recover the night variations observed at ground level. The model is based on a 1D vertical photochemical model, including the ...photodissociation and heating processes. The spectral radiation is calculated at high altitude and propagated through the atmosphere to the ground. We also include short scale vertical dynamic such as turbulences and the molecular diffusion. Simulations reveal realistic emissions when compared with space observations. In addition, we estimate the impact of changes associated with parameterized atmospheric tides. The comparison with observations is performed over high altitude and ground level. We confront the model outputs at high altitude with satellite observations (SABER and GOMOS) and the simulations propagated at ground level are compared to local measurements campaigns performed in France and India. Biases between observed and simulated radiances and volume emission rates are suspected to be due to the impact of gravity waves or the large scale dynamic.
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