Our ground ball is warming because it gets more light from the Sun than it sends out to space. Our ground ball is sending out less light now than it did a few years ago, and less than we expected, which is concerning because this means that the ground ball will keep warming for longer.It is important to understand the light going in and out, and to continue looking at it to see how it changes over time. There are space boxes that look at the light right now, but these boxes will stop looking in a few years, so there are plans for new space boxes that will look later.We are working on a new space box called the long-time ground-ball-looker ('ECO'). By looking up and down at the same time, this box will help us know how much light is going in and out every year. This will help us understand how quickly our ground ball is warming, and make it easier to figure out when it will stop warming.

The Earth's energy imbalance is the difference between incoming solar radiation and outgoing reflected and emitted radiation from the Earth, and quantifies the current ongoing accumulation of energy in the Earth's climate system. There are indications that the imbalance is growing, and it is important to be able to measure and monitor this quantity to better constrain future changes. The reflected shortwave component of the outgoing radiation depends on surface and atmospheric properties, which leads to strong directional variations associated with the angular geometry relative to the incoming sunlight and the observer. The effect of this anisotropy on global average measurements from wide-field-of-view radiometers has been the topic of some investigation in the past, and results from an earlier study suggest that this effect could potentially lead to substantial systematic biases in the context of the global mean reflected shortwave radiation. Here we simulate wide-field-of-view instruments on satellites in polar, sun-synchronous and precessing orbits, as well as constellations of these types of satellite orbits, with both Lambertian and anisotropic shortwave reflection. Reference top-of-atmosphere radiative fluxes are taken from the Clouds and the Earth's Radiant Energy System synoptic data product and combined with angular dependence models that were developed for the Earth Radiation Budget Experiment. We find that the polar regions appear brighter and the midlatitudes appear dimmer with anisotropic reflection, but both the estimated global annual mean and the estimated interannual trend only exhibit limited sensitivity to whether Lambertian or anisotropic reflection is assumed. With anisotropic reflection, the estimated global annual mean root-mean-square sampling error is at most 0.11 Wm-2 provided that at least two complementary satellites are used, compared with at most 0.09 Wm-2 in the case of Lambertian reflection. The magnitude of the difference in the estimated interannual trend is at most 0.07 Wm-2 per decade, and typically only similar to 0.01 Wm-2 per decade. Analysis of the angular sampling of these satellites reveals that the anisotropic reflection requires sufficient sampling of viewing zenith angle and relative azimuth angle, in addition to the solar zenith angle. However, we conclude that it is possible to choose satellite orbits so that the sampling error is not substantially affected by reflected shortwave anisotropy.

A transatlantic scientific balloon flight (TRANSAT) was conducted between 22 and 26 June 2024. The TRANSAT balloon, operated by the French Space Agency (CNES), floated in the stratosphere at approximately 40 km altitude between Esrange (Sweden) and Baffin Island (Canada) for about 3.8 d. The scientific payload comprised nine instruments, including an optical imager for noctilucent cloud (NLC) studies from the Swedish Institute of Space Physics. The NLC imager consisted of three identical visible-range optical cameras, one of which operated successfully throughout the entire flight, capturing thousands of NLC images. The TRANSAT balloon campaign was supported by ground-based lidar measurements and spaceborne observations from the Swedish MATS satellite. Here, we describe the technical characteristics of the balloon experiment and present early results. Nearly continuous observations of NLC were obtained during the entire flight. A localized warm region in the mesopause was identified as the cause of temporary NLC disappearance, while complex NLC structures exhibiting different motions were found to probably result from horizontal wind rotation with altitude within the mesopause region.

The MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) mission is a Swedish satellite mission designed to study atmospheric gravity waves the mesopause region. MATS was launched in November 2022 and carries a limb-imaging instrument that observes the Earth’s atmosphere in the altitude range from approximately 70 to 110 km and a nadir camera. The primary observables are airglow emissions in the O₂ A-band and ultraviolet light scattered by noctilucent clouds.The limb instrument is a telescope that continuously images the atmospheric limb in six spectral channels: four channels in the near-infrared targeting the airglow, and two ultraviolet channels dedicated to noctilucent cloud observations. By exploiting limb geometry and multi-view sampling along the orbit, MATS enables tomographic reconstruction of three-dimensional atmospheric structures. The airglow measurements yield a high–vertical-resolution 3-D temperature product, allowing characterization of individual gravity waves, while the ultraviolet observations enable reconstruction of the spatial distribution and characteristics of noctilucent clouds.This presentation will focus on the newly completed 3-D mesospheric temperature data set derived from the MATS airglow measurements. We will describe the tomographic retrieval, the characteristics and coverage of the temperature product. If available, early validation results will be presented.The presentation will also provide an update on the current status of the MATS mission, which after severe technical and regulatory challenges since 2023, is expected to resume operations in February 2026.

This study conducts a statistical analysis of the aurora observed by the Swedish satellite MATS. MATS' main instrument is a telescope that performs limb imaging at six different wavelength intervals, among them the 762 nm wavelength emission in the O2 atmospheric band. This emission, even though it can not be observed from the ground, is important at mesosphere/lower thermosphere altitudes for both atmospheric airglow and aurora. Here, some auroral properties of this emission, such as peak altitude, geomagnetic location, and auroral intensity, are examined and compared to the SME and Kp geomagnetic indices. A total of 378 events are analyzed. An average geomagnetic latitude of 67.7° is found in both hemispheres, and an average peak altitude of 103 km is obtained. The peak altitude shows dependence on the magnetic local time. Auroral intensities of the order of 102–103 kR are observed.

The Mesospheric Airglow/Aerosol Tomography and Spectroscopy (MATS) satellite was launched in November 2022, carrying as its main instrument a limb-viewing telescope with six spectral channels designed to image atmospheric O2 airglow and noctilucent clouds. Although the main objective of the satellite mission is to observe structures in the airglow introduced by propagating smaller-scale waves, the airglow emissions are also subjected to large-scale dynamic disturbances, such as atmospheric tides and planetary waves. This work presents large-scale structures in the airglow field, as observed by the MATS limb imager from February 2023 to April 2023. The ascending (north-going) node in the satellite orbit, corresponding to the local sunset, is dominated by a strong equatorial maximum in the dayglow. In contrast, the descending (south-going) node, corresponding to the local sunrise, indicates an accompanying equatorial minimum. These characteristics align with the expected behaviour of atmospheric tidal movements. Specifically, a downwelling of atomic oxygen is expected over the Equator at local sunset, contributing to airglow chemistry and enhancing the emissions. Another distinct feature in the data is a westward propagating disturbance observed at high latitudes in the northern hemisphere, maximising in February, interpreted as the quasi-10 d planetary wave of zonal wavenumber 1.

Global warming results from anthropogenic greenhouse gas emissions which upset the delicate balance between the incoming sunlight, and the reflected and emitted radiation from Earth. The imbalance leads to energy accumulation in the atmosphere, oceans and land, and melting of the cryosphere, resulting in increasing temperatures, rising sea levels, and more extreme weather around the globe. Despite the fundamental role of the energy imbalance in regulating the climate system, as known to humanity for more than two centuries, our capacity to observe it is rapidly deteriorating as satellites are being decommissioned.

The MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) satellite was launched in November 2022 and began collecting scientific measurements of the mesosphere and lower thermosphere (MLT) in early 2023. The satellite utilises a multichannel limb-viewing instrument designed to gather images across six distinct spectral bands, each selected to capture atmospheric airglow from O2 atmospheric band emissions and light scattered by noctilucent clouds (NLC). This article presents a comparison between the MATS limb measurements and the observations made by the OSIRIS spectrograph on the Odin satellite. Specifically, airglow signals from excited O2, as recorded by MATS infrared (IR) channels and OSIRIS, are analysed over the polar regions under temporally and spatially aligned conditions. From December 2022 to February 2023, 36 close encounters of the two satellites were identified and analysed. The results show that the two instruments agree well on the overall structure but that the MATS signals generally exceed OSIRIS by similar to 20 % in magnitude. OSIRIS measurements are also compared to the radiative transfer model SASKTRAN to investigate stray light impact on the measurements.

MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) is a Swedish satellite mission designed to investigate atmospheric gravity waves. In order to observe wave patterns, MATS observes structures in the O2 atmospheric band airglow (light emitted by oxygen molecules in the mesosphere and lower thermosphere), as well as structures in noctilucent clouds (NLCs) which form around the mesopause. The main instrument is a telescope that continuously captures high-resolution images of the atmospheric limb. Using tomographic analysis of the acquired images, the MATS mission can reconstruct waves in three dimensions and provide a comprehensive global map of the properties of gravity waves. The data provided by the MATS satellite will thus be three-dimensional fields of airglow and NLC properties in 200 km-wide (across track) strips along the orbit at altitudes of 70 to 110 km. By adding spectroscopic analysis, by separating light into six distinct wavelength channels, it also becomes possible to derive temperature and microphysical NLC properties. Based on those data fields, further analysis will yield gravity wave parameters, such as the wavelengths, amplitudes, phase, and direction of the waves, on a global scale. The MATS satellite, funded by the Swedish National Space Agency, was launched in November 2022 into a 580 km sun-synchronous orbit with a 17.25 local time of the ascending node (LTAN). This paper accompanies the public release of the Level 1b (v. 1.0) dataset from the MATS limb imager. The purpose of the paper is to provide background information in order to assist users to correctly and efficiently handle the data. As such, it details the image processing and how instrumental artefacts are handled. It also describes the calibration efforts that have been carried out on the basis of laboratory and in-flight observations, and it discusses uncertainties that affect the dataset.

MATS (Mesospheric airglow/Aerosol Tomography and Spectroscopy) is as Swedish satellite launched in November 2022. It observes O2 A-band airglow in near-infrared and UV light scattered from noctilucent clouds (NLCs) in limb imaging geometry and provides global 3-D temperature and NLC data products. These data sets can be used to characterise individual gravity waves (GWs) by determining their amplitudes, wavelengths and propagation directions (i.e. determining the 3-D wave vector for each wave). This enables determination of GW momentum fluxes in the MLT region, as well as detailed studies on GW spectra, propagation and interactions with the mean flow. MATS data, in combination with some GW modelling, can also be used to study GW sources and dissipation. This presentation will provide an overview of the MATS mission and the 3-D data products with the focus on GW observations. We will include examples of data along with some initial GW analysis, instrument sensitivity estimates and data quality evaluation.

MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) is a Swedish research satellite launched in 2022 targeting gravity wave activity in the mesosphere and lower thermosphere (MLT). Infrared measurements of MLT O2 A-band airglow conducted by the MATS satellite during February, March, and April reveal large-scale, global structures that significantly impact this region's dynamics. An analysis of atmospheric A-band emissions between 70 and 110 km reveals that atmospheric tides greatly influence the radiance produced in the airglow layer. This is evidenced by an equatorial maximum at local sunset and minima at 30°N and 30°S, which correspond to the various phases of the tides. Meanwhile - in the vicinity of the poles, westward propagating planetary waves dominate the measurements, including strong signals from the 16-day wave in the northern hemisphere, and the 5.5-day wave in the southern hemisphere. In this talk, we take a closer look at the individual measurements made by the satellite, illustrating the smaller-scale atmospheric structures they contain, as well as the global picture that the images make up together.

Monitoring the Earth Energy Imbalance (EEI) is of prime importance for a predictive understanding of climate change. Furthermore, monitoring of the EEI gives an early indication on how well mankind is doing in implementing the Paris Climate Agreement. EEI is defined as the small difference between the incoming energy the Earth receives from the Sun and the outgoing energy lost by Earth to space. The EEI is cumulated in the Earth climate system, particularly in the oceans, due to their substantial heat capacity, and results in global temperature rise. Currently the best estimates of the absolute value of the EEI, and of its long term variation are obtained from in situ observations, with a dominant contribution of the time derivative of the Ocean Heat Content (OHC). These in situ EEI observations can only be made over long time periods, typically a decade or longer. In contrast, with direct observations of the EEI from space, the EEI can be measured at the annual mean time scale. However, the EEI is currently poorly measured from space, due to two fundamental challenges. The first fundamental challenge is that the EEI is the difference between two opposing terms of nearly equal amplitude. Currently, the incoming solar radiation and outgoing terrestrial radiation are measured with separate instruments, which means that their calibration errors are added and overwhelm the signal to be measured. To make significant progress in this challenge, a differential measurement using identical intercalibrated instruments to measure both the incoming solar radiation and the outgoing terrestrial radiation is needed. The second fundamental challenge is that the outgoing terrestrial radiation has a systematic diurnal cycle. Currently, the outgoing terrestrial radiation is sampled from the so-called morning and afternoon Sun-synchronous orbits, complemented by narrow band geostationary imagers. Recently the sampling from the morning orbit was abandoned. The sampling of the diurnal cycle can be improved, for example, by using two orthogonal 90° inclined orbits which give both global coverage, and a statistical sampling of the full diurnal cycle at seasonal time scale. For understanding the radiative forcing – e.g. aerosol radiative forcing - and climate feedback – e.g. ice albedo feedback - mechanisms underlying changes in the EEI, and for climate model validation, it is necessary to separate the Total Outgoing Radiation (TOR) spectrally into the two components of the Earth Radiation Budget (ERB), namely the Reflected Solar radiation (RSR) and Outgoing Longwave Radiation (OLR) and to map them at relatively high spatial resolution. The Earth Climate Observatory (ECO) mission concept was recently selected by the European Space Agency as one of the 4 candidate Earth Explorer 12 missions, that will be further studied in Phase 0 until mid 2026. The current paper provides a broad overview of the ECO mission objectives, the mission requirements, and the key elements of a baseline mission concept. During Phase 0, the ECO mission concept will be further elaborated in two parallel industrial studies, which may or may not adopt or refine the elements of the baseline concept.

MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) is a Swedish satellite designed to investigate atmospheric dynamics in the mesosphere and lower thermosphere (MLT). By observing structures in noctilucent clouds over polar regions and oxygen atmospheric-band (A-band) emissions globally, MATS will provide the research community with properties of the MLT atmospheric wave field. Individual A-band images taken by MATS's main instrument, a six-channel limb imager, are transformed through tomography and spectroscopy into three-dimensional temperature fields, within which the wave structures are embedded. To identify wave properties, particularly the gravity wave momentum flux, from the temperature field, smaller-scale perturbations (associated with the targeted waves) must be separated from large-scale background variations using a method of scale separation. This paper investigates the possibilities of employing a simple method based on smoothing polynomials to separate the smaller and larger scales. Using using synthetic tomography data based on the HIAMCM (HIgh Altitude Mechanistic general Circulation Model), we demonstrate that smoothing polynomials can be applied to MLT temperatures to obtain fields corresponding to global-scale separation at zonal wavenumber 18. The simplicity of the method makes it a promising candidate for studying wave dynamics in MATS temperature fields.

The Earth’s energy imbalance (EEI), i.e. the difference between incoming solar radiation and outgoing reflected and emitted radiation, is the one quantity that ultimately controls the evolution of our climate system. Despite its importance, the exact magnitude of the energy imbalance is not well known, and because it is a small net difference of about 1 Wm−2 between two large fluxes (approximately 340 Wm−2), it is difficult to measure directly. There has recently been a renewed interest in applying wide-field-of-view radiometers onboard satellites to measure the outgoing radiation, and hence deduce the global annual mean energy imbalance. Here we investigate how to sample with a limited number of satellite orbits, in order to correctly determine the global annual mean imbalance. Using observational and model data, we have investigated the importance of the local and global diurnal cycles, as they are observed by a satellite, in the determination of the EEI. We simulate satellites in polar (90° inclination), sun-synchronous (98°) and precessing orbits (73°, 82°), as well as constellations of these types of satellite orbits. We present the results of ongoing work concerning different orbits, and how they affect the estimated global annual mean EEI.

Global three-dimensional data are a key to understanding gravity waves in the mesosphere and lower thermosphere. MATS is a small Swedish satellite that aims at providing such fields using tomographic measurements of oxygen A-band airglow and noctilucent clouds. MATS was successfully launched from Mahia, New Zealand, on November 4, 2022. Data collection started in December 2022, and MATS is projected to have collected over 3 million images of the MLT region by April 2023.This presentation will provide an overview over first results from the MATS data. This includes analysis of in-flight performance of the instruments, an overview of data availability, and some examples of possible usage of the data. We will discuss data quality as well as possible biases and uncertainties that need to be considered when using this new and unique dataset for mesospheric studies.

The mesospheric polar vortex (MPV) plays a critical role in coupling the atmosphere-ionosphere system, so its accurate simulation is imperative for robust predictions of the thermosphere and ionosphere. While the stratospheric polar vortex is widely understood and characterized, the mesospheric polar vortex is much less well-known and observed, a short-coming that must be addressed to improve predictability of the ionosphere. The winter MPV facilitates top-down coupling via the communication of high energy particle precipitation effects from the thermosphere down to the stratosphere, though the details of this mechanism are poorly understood. Coupling from the bottom-up involves gravity waves (GWs), planetary waves (PWs), and tidal interactions that are distinctly different and important during weak vs. strong vortex states, and yet remain poorly understood as well. Moreover, generation and modulation of GWs by the large wind shears at the vortex edge contribute to the generation of traveling atmospheric disturbances and traveling ionospheric disturbances. Unfortunately, representation of the MPV is generally not accurate in state-of-the-art general circulation models, even when compared to the limited observational data available. Models substantially underestimate eastward momentum at the top of the MPV, which limits the ability to predict upward effects in the thermosphere. The zonal wind bias responsible for this missing momentum in models has been attributed to deficiencies in the treatment of GWs and to an inaccurate representation of the high-latitude dynamics. In the coming decade, simulations of the MPV must be improved.

We present optical characterization, calibration, and performance tests of the Mesospheric Airglow/Aerosol Tomography Spectroscopy (MATS) satellite, which for the first time, to the best of our knowledge, for a satellite, applies a linear-astigmatism-free confocal off-axis reflective optical design. Mechanical tolerances of the telescope were investigated using Monte Carlo methods and single-element perturbations. The sensitivity analysis results indicate that tilt errors of the tertiary mirror and a surface RMS error of the secondary mirror mainly degrade optical performance. From the Monte Carlo simulation, the tolerance limits were calculated to ±0.5mm, ±1mm, and ±0.15∘ for decenter, despace, and tilt, respectively. We performed characterization measurements and optical tests with the flight model of the satellite. Multi-channel relative pointing, total optical system throughput, and distortion of each channel were characterized for end-users. Optical performance was evaluated by measuring the modulation transfer function (MTF) and point spread function (PSF). The final MTF performance was 0.25 MTF at 20 lp/mm for the ultraviolet channel (304.5 nm), and 0.25-0.54 MTF at 10 lp/mm for infrared channels. The salient fact of the PSF measurement of this system is that there is no noticeable linear astigmatism detected over a wide field of view (5.67∘×0.91∘). All things considered, the design method showed great advantages in wide field of view observations with satellite-level optical performance.

Global three-dimensional data are a key to understanding gravity waves in the mesosphere and lower thermosphere. MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) is a new Swedish satellite mission that addresses this need. It applies space-borne limb imaging in combination with tomographic and spectroscopic analysis to obtain gravity wave data on relevant spatial scales. Primary measurement targets are O2 atmospheric band dayglow and nightglow in the near infrared, and sunlight scattered from noctilucent clouds in the ultraviolet. While tomography provides horizontally and vertically resolved data, spectroscopy allows analysis in terms of mesospheric temperature, composition, and cloud properties. Based on these dynamical tracers, MATS will produce a climatology on wave spectra during a 2-year mission. Major scientific objectives include a characterization of gravity waves and their interaction with larger-scale waves and mean flow in the mesosphere and lower thermosphere, as well as their relationship to dynamical conditions in the lower and upper atmosphere. MATS is currently being prepared to be ready for a launch in 2020. This paper provides an overview of scientific goals, measurement concepts, instruments, and analysis ideas.

In my article "Minimal impact on condensation nuclei properties on observable mesospheric ice properties" (Megner, 2011, https://doi.org/10.1016/j.jastp.2010.08.006) I show that the observable bulk quantities of Noctilucent clouds are much less sensitive to the concentration of condensation nuclei than what previously has been believed. These results were challenged by Wilms et al. (2016, https://doi.org/10.1002/2015JA021764), who studied the effect of nucleation rate on cloud properties and find a sensitivity. In this comment I argue that the differences between the studies are less than they first appear: Both studies show a very limited sensitivity to ice condensation nuclei, especially when there are more than roughly 100 condensation nuclei per cubic centimeter. Observations do indicate that under normal conditions, there are at least around 100 particles per cubic centimeter in the region of formation, and thus that we are in the insensitive regime.

Nitric oxide (NO) produced in the polar middle and upper atmosphere by energetic particle precipitation depletes ozone in the mesosphere and, following vertical transport in the winter polar vortex, in the stratosphere. Medium‐energy electron (MEE) ionization by 30–1,000 keV electrons during geomagnetic storms may have a significant role in mesospheric NO production. However, questions remain about the relative importance of direct NO production by MEE at altitudes ~60–90 km versus indirect NO originating from auroral ionization above 90 km. We investigate potential drivers of NO variability in the southern‐hemisphere mesosphere and lower thermosphere during 2013–2014. Contrasting geomagnetic activity occurred during the two austral winters, with more numerous moderate storms in the 2013 winter. Ground‐based millimeter‐wave observations of NO from Halley, Antarctica, are compared with measurements by the Solar Occultation For Ice Experiment (SOFIE) spaceborne spectrometer. NO partial columns over the altitude range 65–140 km from the two observational data sets show large day‐to‐day variability and significant disagreement, with Halley values on average 49% higher than the corresponding SOFIE data. SOFIE NO number densities, zonally averaged over geomagnetic latitudes −59° to −65°, are up to 3 × 10 8 /cm 3 higher in the winter of 2013 compared to 2014. Comparisons with a new version of the Whole Atmosphere Community Climate Model, which includes detailed D ‐region ion chemistry (WACCM‐SIC) and MEE ionization rates, show that the model underestimates NO in the winter lower mesosphere whereas thermospheric abundances are too high. This indicates the need to further improve and verify WACCM‐SIC with respect to MEE ionization, thermospheric NO chemistry, and vertical transport.