Mesosphere Research Articles

Polar mesospheric summer echo (PMSE) multilayer properties during the solar maximum and solar minimum

Abstract. Polar mesospheric summer echoes (PMSEs) are radar echoes that are measured in the upper atmosphere during the summer months and that can occur in several layers. In this study, we aimed to investigate the relationship between PMSE layers ranging from 80 to 90 km altitude and the solar cycle. We investigated 230 h of observations from the EISCAT very high frequency (VHF) radar located near Tromsø, Norway, from the years 2013, 2014 and 2015 during the solar maximum and the years 2019 and 2020 during the solar minimum and applied a previously developed classification model to identify PMSE layers. Our analysis focused on parameters such as the altitude, thickness and echo power in the PMSE layers, as well as the number of layers present. Our results indicate that the average altitude of PMSEs, the echo power in the PMSEs and the thickness of the layers are, on average, higher during the solar maximum than during the solar minimum. In the considered observations, the electron density at 92 km altitude and the echo power in the PMSEs are positively correlated with the thickness of the layers except for four multilayers at solar minimum. We infer that higher electron densities at ionospheric altitudes might be necessary to observe multilayered PMSEs. We observe that the thickness decreases as the number of multilayers increases. We compare our results with previous studies and find that similar results regarding layer altitudes were found in earlier studies using observations with other VHF radars. We also observed that the bottom layer in the different sets of multilayers almost always aligned with the noctilucent cloud (NLC) altitude reported by previous studies at 83.3 km altitude. Also, an interesting parallel is seen between the thickness of NLC multilayers and PMSE multilayers, where both NLCs and PMSEs have a similar distribution of layers greater than 1 km in thickness. Future studies that include observations over longer periods would make it possible to distinguish the influence of the solar cycle from possible other long-term trends.

Efficient Phase Step Determination Approach for Four-Quadrant Wind Imaging Interferometer

A four-quadrant wind imaging interferometer is a new generation of wind imaging interferometer with the valuable features of being monolithic, compact, light, and insensitive to temporal variations in the source. Its applications include remote sensing of the wind field of the upper atmosphere and observing important dynamical processes in the mesosphere and lower thermosphere. In this paper, we describe a new phase step determination approach based on the Lissajous figure, which provides an efficient, accurate, and visual method for the characterization and calibration of this type of instrument. Using the data from wavelength or thermal fringe scanning, the phase steps, relative intensities, and instrument visibilities of four quadrants can be retrieved simultaneously. A general model for the four-quadrant wind imaging interferometer is described and the noise sensitivity of this method is analyzed. This approach was successfully implemented with four-quadrant wind imaging interferometer prototypes, and its feasibility was experimentally verified.

Convective Magnetic Flux Emergence Simulations from the Deep Solar Interior to the Photosphere: Comprehensive Study of Flux Tube Twist

The emergence of magnetic flux from the deep convection zone plays an important role in solar magnetism, such as the generation of active regions and triggering of various eruptive phenomena, including jets, flares, and coronal mass ejections. To investigate the effects of magnetic twist on flux emergence, we performed numerical simulations of flux tube emergence using the radiative magnetohydrodynamic code R2D2 and conducted a systematic survey on the initial twist. Specifically, we varied the twist of the initial tube both positively and negatively from zero to twice the critical value for kink instability. As a result, regardless of the initial twist, the flux tube was lifted by the convective upflow and reached the photosphere to create sunspots. However, when the twist was too weak, the photospheric flux was quickly diffused and not retained long as coherent sunspots. The degree of magnetic twist measured in the photosphere conserved the original twist relatively well and was comparable to actual solar observations. Even in the untwisted case, a finite amount of magnetic helicity was injected into the upper atmosphere because the background turbulence added helicity. However, when the initial twist exceeded the critical value for kink instability, the magnetic helicity normalized by the total magnetic flux was found to be unreasonably larger than the observations, indicating that the kink instability of the emerging flux tube may not be a likely scenario for the formation of flare-productive active regions.

Impact of Tonga volcanic eruption on the ionosphere based on ground-based GNSS and COSMIC occultation data

The eruption of large volcanoes may potentially disturb the upper atmosphere, causing disturbances in ionospheric plasma and triggering irregular changes in the Total Electron Content (TEC). The GNSS ionospheric inversion method has been used to analyze ionospheric anomalies caused by the volcano, while it was limited to the spatial distribution of ground-based GNSS. The joint observation with space-based GNSS can further improve the spatio-temporal distribution of ionospheric monitoring. The Tonga volcano erupted on January 15th, 2022, is the largest volcanic eruption since the beginning of the 21st century and generated intense acoustic, atmospheric gravity waves and ionospheric disturbance. In this paper, we used the GIM products, ground-based GNSS station data around the volcanic eruption point and COSMIC occultation data to analyze the short-term TEC change. The experiments showed that: the average TEC of GIM grid data on eruption day dropped by 7.5 TECu compared to the last day which was substantially larger than other three days. The TEC extracted from nearby tracking stations was smaller than GIM and the difference was inversely proportional to the distance between the station and the volcanic eruption site. The average daily ionospheric TEC obtained from the nearest TONG station was the biggest, as much as 3.44 TECu lower. The peak electron density of COSMIC occultation data gradually diminished and then recovered with TEC about 7.32 TECu lower than GIM products. The experments showed that there was a good consistency in the TEC obtained from space-based and ground-based GNSS, the Tonga volcano produced a huge TEC change over 10 TECu or even bigger. As a global grid product, GIM underestimated ionospheric changes due to its limited spatial resolution, which needs further improvement.

Long-term changes of sodium column abundance at 24.6°S above the Atacama Desert in Chile

Aims. The utilisation of artificial laser guide star (LGS) obviates the necessity for a prominent natural guide star (NGS) within adaptive optics (AO) systems. High-power lasers are fundamental components of most AO systems today. The generation of an LGS relies on the excitation of sodium (denoted by its symbol Na) atoms situated in the upper atmosphere. Therefore, the sodium vertical column density (denoted as CNa) is a crucial parameter. Beyond ensuring the optimal and stable performance of an AO system, knowledge of the return flux from an LGS is imperative during the design phase, aiding in the accurate specification of both the LGS and the AO system. The availability of sodium in the upper atmosphere has been the focal point of diverse studies, exhibiting a pronounced dependence on the specific observatory site. Furthermore, it is well established that CNa varies across multiple timescales, including hours, nights, months, seasons, and even several years. As many of the world’s largest telescopes are located in the Atacama Desert in northern Chile, our objective is to provide CNa statistics pertinent to this specific region. Methods. We used telemetry data from the AO systems operational at the Paranal Observatory (24.6°S, 70.4°W): Ground Atmospheric Layer Adaptive Corrector for Spectroscopic Imaging (GALACSI) and Ground layer Adaptive Optics system Assisted by Lasers (GRAAL). We combined these data with measurements from two space instruments: SCanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) and Optical Spectrograph and Infrared Imaging System (OSIRIS), as well as with simulated data from the Whole Atmosphere Community Climate Model (WACCM). We carefully analysed and compared these datasets to develop a statistical model for the temporal variations of CNa. Results. We validated the use of the AO telemetry data from Paranal systems to retrieve the CNa. The near-continuous measurements encompassing the period from mid-2017 to the end of 2023 facilitated the determination of monthly and yearly abundance and variability of Na in the mesopause region. Throughout the complete years of measurement, the annual and semi-annual variations exhibit consistent characteristics that align with previously documented findings in atmospheric studies. Through meticulous comparison and the fitting of various long-term datasets, we formulated a model depicting the evolution of CNa over time. The validity of our data processing and model is scrutinised, and the results obtained for the Paranal latitude exhibit noteworthy concordance with the findings of other studies.

Biases in Exoplanet Transmission Spectra Introduced by Limb-darkening Parametrization

One of the main endeavors of the field of exoplanetary sciences is the characterization of exoplanet atmospheres on a population level. The current method of choice to accomplish this task is transmission spectroscopy, where the apparent radius of a transiting exoplanet is measured at multiple wavelengths in search of atomic and molecular absorption features produced by the upper atmosphere constituents. To extract the planetary radius from a transit light curve, it is necessary to account for the decrease in luminosity away from the center of the projected stellar disk, known as limb darkening. Physically motivated parametrizations of limb darkening, in particular of the quadratic form, are commonly used in exoplanet transit light-curve fitting. Here, we show that such parametrizations can introduce significant wavelength-dependent biases in the transmission spectra currently obtained with all instrument modes of the JWST, and thus have the potential to affect atmospheric inferences. To avoid such biases, we recommend the use of standard limb-darkening parametrizations with wide uninformative priors that allow for nonphysical stellar intensity profiles in the transit fits, and thus for a complete and symmetrical exploration of the parameter space. We further find that fitting the light curves at the native resolution results in errors on the measured transit depths that are significantly smaller compared to light curves that are binned in wavelength before fitting, thus potentially maximizing the amount of information that can be extracted from the data.

What Controls the Dawn‐Dusk Asymmetry of Dayside Alfvénic Power: Interplanetary Magnetic Field or Ionospheric Conductance?

AbstractAlfvén waves are important carriers of solar wind energy into the Earth's magnetosphere and upper atmosphere. The observed distribution of Alfvénic power at low altitude exhibits significant dawn‐dusk asymmetry with different causes and impacts on the dayside and nighside. The nightside asymmetry has been shown to be controlled by the meridional gradient in the ionospheric Hall conductance. It is not clear what controls the dayside asymmetry. Both the ionospheric conductance gradient and orientation of the y‐component of the interplanetary magnetic field (IMF) are possible factors. We examined both possibilities using global magnetohydrodynamic (MHD) simulations. Our results show: (a) The dayside distribution of Alfvénic power is very sensitive to the orientation of IMF By, with enhanced power in the dawn (dusk) sector of the northern hemisphere for positive (negative) By (and opposite in the southern hemisphere); and (b) gradients in ionospheric conductance exert a weaker influence on the dayside asymmetry.

How Increased CO2 Warms the Earth-Two Contexts for the Greenhouse Gas Effect

The widespread explanations of the greenhouse effect taught to millions of schoolchildren are misleading. The objective of this work is to clarify how increasing CO2 produces warming in current times. It is found that there are two contexts for the greenhouse gas effect. In one context, the fundamental greenhouse gas effect, one imagines a dry Earth starting with no water or CO2 and adding water and CO2. This leads to the familiar “thermal blanket” that strongly inhibits IR transmission from the Earth to the atmosphere. The Earth is much warmer with H2O and CO2. In the other context, the current greenhouse gas effect, CO2 is added to the current atmosphere. The thermal blanket on IR radiation hardly changes. But the surface loses energy primarily by evaporation and thermals. Increased CO2 in the upper atmosphere carries IR radiation to higher altitudes. The Earth radiates to space at higher altitudes where it is cooler, and the Earth is less able to shed energy. The Earth warms to restore the energy balance. The “thermal blanket” is mainly irrelevant to the current greenhouse gas effect. It is concluded that almost all discussions of the greenhouse effect are based on the fundamental greenhouse gas effect, which is a hypothetical construct, while the current greenhouse gas effect is what is happening now in the real world. Adding CO2 does not add much to a “thermal blanket” but instead, drives emission from the Earth to higher, cooler altitudes.

An Engineering Model to Represent Positive Return Strokes—An Extension of the Modified Transmission Line (MTL) Model

An engineering model to represent positive return strokes is introduced as an extension of the Modified Transmission Line model with Linear Current Decay (MTLL). This extension is grounded in experimental data on the electric fields and currents associated with positive return strokes. The core premise of the model is that once the return stroke front reaches the cloud, recoil leader-type activities within the cloud feed the lightning channel with a positive charge. This positive charge then travels to the ground in the form of an M-component, enhancing both the amplitude and duration of the impulse current in the channel and at ground level. The propagation of the return stroke current along the channel follows the MTLL model, while the M-component is treated as a current pulse traveling from the cloud to the ground. At ground level, the M-component current is fully reflected. The model successfully generates electromagnetic fields that resemble those observed from positive return strokes, and it is easily applicable to studies involving the interaction of positive return stroke fields with power lines and the Earth’s upper atmosphere.

Imaging the May 2024 Extreme Aurora With Ionospheric Total Electron Content

AbstractThe continental United States is well instrumented with facilities for mid‐latitude upper atmosphere research that operate on a continuous basis. In addition, citizen scientists provide a wealth of information when unusual events occur. We combine ionospheric total electron content (TEC) data from distributed arrays of GNSS receivers, magnetometer chains, and auroral observations obtained by citizen scientists, to provide a detailed view of the intense auroral breakup and westward surge occurring at the peak of the 10–11 May 2024 extreme geomagnetic storm. Over a 20‐min interval, vertical TEC (vTEC) increased at unusually low latitude (∼45°) and rapidly expanded azimuthally across the continent. Individual receiver/satellite data sets indicate sharp bursts of greatly elevated of vTEC (∼50 TECu). Intense red aurora was co‐located with the leading edge of the equatorward and westward TEC enhancements, indicating that the large TEC enhancement was created by extremely intense low‐energy precipitation during the rapid substorm breakup.

Science Highlights from the Kjell Henriksen Observatory on Svalbard

The Kjell Henriksen Observatory (KHO) is the world's largest optical observatory for auroral and airglow measurements, operated by the University Centre in Svalbard (UNIS). KHO is a unique site that lies underneath the dayside cusp, a funnel-shaped region where particles from the Sun can directly enter the Earth's upper atmosphere, including the ionosphere. Building on the pioneering observations of its predecessor --- the Auroral Station in Adventdalen, Svalbard --- KHO has played a pivotal role in advancing our understanding of phenomena in the polar atmosphere. The Auroral Station and KHO have amassed climatological measurements over Svalbard for an impressive 40-year period. KHO's diverse instrumentation, combined with other co-located optical and radar infrastructure and in-situ measurements from satellites and sounding rockets, has paved the way for impactful multi-instrument studies. Serving as an accessible testbed for instrument development, new types of instruments have recently been installed, both at KHO and on satellites. Beyond its scientific contributions, KHO has become an integral part of the Longyearbyen community, with students, visitors, and locals participating in tours and educational initiatives. This connection underscores KHO's multi-functional role, not only as a centre for excellent research but also as a vital hub for public outreach and engagement.

An extreme precipitation event over Dronning Maud Land, East Antarctica - A case study of an atmospheric river event using the Polar WRF Model

Extreme precipitation events (EPEs) are crucial in Antarctica, impacting the Antarctic ice sheet's surface mass balance and stability. Comprehensive case studies are essential for better understanding these events and the underlying processes driving them. Here, we investigate an extreme snowfall event in Dronning Maud Land (DML), East Antarctica on November 8 and 9, 2015. This event contributed approximately 22 % of the annual accumulation in less than two days and exhibited high spatial variability in precipitation distribution. We employed a high-resolution atmospheric model specifically optimized for the polar regions (Polar WRF) and ERA5 reanalysis data to analyze the event in detail. Our findings highlight the importance of a blocking high-pressure ridge of record strength that effectively blocked and diverted a strong extratropical cyclone into DML, ultimately leading to the heavy snowfall event. The sudden deepening of the cyclone was initiated by a ‘jet streak’ in the upper atmosphere that steered the system southeastwards towards the Antarctic coast. Notably, we observed an anomalously high poleward moisture transport in the form of a strong atmospheric river on November 7, 2015. This atmospheric river originated in the South Atlantic Ocean and tracked poleward from the 30°S-40°S latitude band. Vertical cross-sections of the model outputs indicate that most of the precipitation was concentrated in regions with steep orography along the path of the atmospheric river. This interaction between the atmospheric river and the steep terrain led to the uplift of maritime air, resulting in heavy snowfall. This study highlights the significance of extreme upper and lower atmospheric conditions in driving intense moisture transport towards coastal DML. The interaction between the atmospheric river and the steep orography contributed to heavy snowfall, underscoring the importance of considering orographic influences in understanding EPEs in Antarctica.

Effects of the internal temperature on vertical mixing and on cloud structures in ultra-hot Jupiters

The vertical mixing in hot-Jupiter atmospheres plays a critical role in the formation and spacial distribution of cloud particles in their atmospheres. This affects the observed spectra of a planet through cloud opacity, which can be influenced by the degree of cold trapping of refractory species in the deep atmosphere. We aim to isolate the effects of the internal temperature on the mixing efficiency in the atmospheres of ultra-hot Jupiters (UHJs) and the spacial distribution of cloud particles across the planet. We combined a simplified tracer-based cloud model, a picket fence radiative-transfer scheme, and a mixing length theory to the Exo-FMS general circulation model. We ran the model for five different internal temperatures at typical UHJ atmosphere system parameters. Our results show the convective eddy diffusion coefficient remains low throughout the vast majority of the atmosphere, with mixing dominated by advective flows. However, some regions can show convective mixing in the upper atmosphere for colder interior temperatures. The vertical extent of the clouds is reduced as the internal temperature is increased. Additionally, a global cloud layer gets formed below the radiative--convective boundary (RCB) in the cooler cases. Convection is generally strongly inhibited in UHJ atmospheres above the RCB due to their strong irradiation. Convective mixing plays a minor role compared to advective mixing in keeping cloud particles aloft in UHJs with warm interiors. Higher vertical turbulent heat fluxes and the advection of potential temperature inhibit convection in warmer interiors. Our results suggest that isolated upper atmosphere regions above cold interiors may exhibit strong convective mixing in isolated regions around Rossby gyres, allowing aerosols to be better retained in these areas.

On the long-term stability of the association between foF2 and EUV solar proxies

Solar extreme ultraviolet (EUV) radiation is the main source of heating and ionization of the Earth's upper atmosphere, forcing most of this system's time variability, which in annual scales corresponds to the solar activity ∼11-year cycle. Due to the difficulties in obtaining solar EUV time series covering extended periods of time or during periods without measurements available, the use of solar EUV proxies became a solution. In the case of the ionosphere, and in particular the F2-layer critical frequency (foF2), in addition to the solar activity cycle variation, it may also exhibit the effect of long-term trend forcings, like the monotonous increasing greenhouse gas concentration since the industrial revolution. To accurately detect and measure this weak trend against the solar activity variability, it is crucial to account for the solar forced variation. Traditionally, it is modeled as a linear association between foF2 and a given solar EUV proxy. However, the stability of this association has become a controversial issue. It would be reasonable to assume, in turn, that if the ionospheric environment is undergoing a trend forced by a non-solar diver, like the greenhouse gas concentration increase, the relationship between foF2 and solar proxies may be affected, ceasing to be stable if this additional driver is not introduced in the modeled association. Using rolling regressions over the period 1960–2023 to analyze this stability, our results suggest that the issue may not only lie in the steady trend expected in foF2 from a non-solar source or the need to include terms in the simple linear regression commonly used, but also in the possible deviation of the different proxies from the 'true' EUV solar flux, which is the ultimate main driver of F2 region ionization, a deviation that has been intensifying over the last two decades. We assert that it is a deviation from the actual EUV behavior because the indices diverge from one another, something that should not occur if they all reflect the same solar EUV.

Studying infrasound propagation in the middle atmosphere with ICON and UA-ICON: comparison with the IFS and ground-based remote sensing

Infrasound signals are used to monitor various anthropogenic and natural sources. In particular, infrasound is one of the four verification technologies used by the International Monitoring System (IMS) of the Comprehensive Test-Ban Treaty organisation (CTBTO). To determine accurate source locations and energies, an accurate model of wind and temperature up to the lower thermosphere is necessary, hence operational NWP products are of great importance for routine infrasound monitoring activities. However, many of these models focus on tropospheric conditions, and the middle atmosphere (MA) is not well represented. UA-ICON is an upper atmosphere version of the ICON model that provides modelled atmospheric parameters up to 150 km. First, to assess ICON and IFS operational analysis products, comparisons to lidar observations are made. The main differences between both products were analysed with respect to winds and temperatures in the MA. Second, UA-ICON simulations outputs were compared to ICON and IFS fields to demonstrate the increased wave activity above ~30 km with UA-ICON. The added value of UA-ICON with respect to ICON and IFS for infrasound propagation simulations is discussed. The comparisons between the instrumental observations and the models will be presented, as well as comparisons between modelled and measured infrasound propagation.

Deep stratospheric intrusion events in China revealed on the ground by cosmogenic 10Be/7Be

Given the impact of deep stratospheric intrusion on air quality, the development of more extensive trace substances to quantify stratospheric intrusion intensity can better distinguish between stratospheric ozone pollution and anthropogenic factors. The ratio of cosmogenic beryllium-10 to beryllium-7 (10Be/7Be), primarily generated in the stratosphere, has the potential to identify stratospheric air masses on the ground. Here we constructed a 10Be/7Be time-series (July 2020 to September 2021) in rainwater and aerosols from Xi’an, China. Combining in-situ pollutants, reanalysis data, and model calculations support a stratospheric origin for increased 10Be/7Be and identify it as a means of quantifying intrusion intensity. It was found that anticyclones formed by the Asian summer monsoon drive a sudden increase in deep stratospheric intrusion in spring, exacerbating ozone pollution beyond China’s air quality standards. Based on the sufficiently sensitive 10Be/7Be, it further indicates the process of six weak upper atmosphere intrusions in Xi’an during winter.

Changes in turbulent processes caused by atmospheric gravity waves from troposphere

We have determined that changes in temperature and wind speed recorded in the Earth‘s upper atmosphere above tropospheric sources (hurricanes) can be explained by the propagation of atmospheric gravity waves (AGW). We carried out modeling of the propagation of AGW with a period of 65 min and kx=10−5 m−1 using multi-layer methods in a non-homogeneous, non-isothermal atmosphere, taking into account viscosity and thermal conductivity. We obtained that disturbances in the horizontal component of the velocity are five times greater than the increase in the vertical component of the velocity, and temperature changes can reach 30 K. We should note that the disturbances of temperature and pressure as a result of AGW spreading are superimposed onto the usual view of changes of pressure and temperature with the altitude and reach the maximum amplitude in the range from 90 to 100 km. The obtained changes in the temperature of the upper atmosphere and the velocity with height as a result of the presence of AGW made it possible to estimate the values of the coefficients of turbulent viscosity and thermal conductivity in the upper atmosphere of the Earth above tropospheric energy sources. Intensification of turbulent processes was recorded in the range of altitudes from 75 to 100 km.

The Solar FUV-UV Spectra Measurement Experiment in the Near Space by High Altitude Balloon

An experiment measuring the solar far-ultraviolet-ultraviolet (FUV-UV) irradiance with spectral resolution better than 0.1 nm in the wavelength range from 170 to 400 nm was carried out by the “HongHu-6” high-altitude balloon that flew to the bottom region of the near-space in September 2022. This experiment was based on the fact that solar FUV-UV penetrates through a complex cross-section window of the upper atmosphere, from outer to near space. The solar FUV-UV deposits energy in the upper atmosphere, which provides a key to answer scientific questions on the most important energy contributor to overall heating sources of the near space and how the near-space environment responds to solar activities. In the wavelength range between 150 and 210 nm, irradiance maps from active regions of the solar corona, the comparative small cross-section of molecular oxygen allows certain wavelengths of the band to arrive at altitudes between 20 and 30 km above the ground, indicating solar flares could directly impact the bottom region of the near space. Solar UV irradiance in the wavelength range 210 – 400 nm is absorbed by the upper atmosphere as a function of wavelength, and energy is deposited vertically in the lower regions of the near space. This experiment historically provides measurement data to fill a gap in the wavelength shorter than 280 nm in the lower regions of the near space. The solar FUV-UV spectrometer (SUVS) is a compact instrument based on improved Roland circle optics to adapt to the “HongHu-6” balloon payload platform. In this paper, we introduce the scientific goals of the solar FUV-UV spectrum measurement experiment, provide information on the SUVS instrument preflight calibration, and present the first results from the flight data.

Inter-annual changes in transboundary air quality from KORUS-AQ 2016 to SIJAQ 2022 campaign periods and assessment of emission reduction strategies in Northeast Asia

Northeast Asia suffers from high concentrations of particulate matter (PM), prompting nations to actively implement emission reduction policies. This study evaluated the recent inter-annual changes in the chemical transformation and transboundary transport of PM over Northeast Asia, based on both ground and aircraft measurements, as well as WRF-Chem simulations, during two comprehensive campaigns: the Korea–United States Air Quality (KORUS-AQ) campaign in 2016 and the Satellite Integrated Joint Monitoring of Air Quality (SIJAQ) campaign in 2022, both conducted around the Korean Peninsula. Ground measurements in 2022 revealed significant reductions in air pollutants compared to 2016 levels. In the Beijing–Tianjin–Hebei region, PM2.5 and SO2 concentrations decreased by 47.2% and 73.9%, respectively, attributable to successful SOx and NOx emission reduction strategies. Similar trends were observed in downwind areas, including Seoul, where PM2.5 and SO2 levels declined by 30.0% and 41.4%, respectively. WRF-Chem model results indicated substantial decreases in sulfates, nitrates, and their precursors in both surface and upper atmosphere in 2022 compared to 2016. Moreover, model-calculated gas-to-particle conversion ratios, which peaked in the Yellow Sea in 2016, decreased by 15% in 2022 and shifted slightly eastward to the western Korean Peninsula. This shift suggests a potential decline in secondary PM formation processed in the Yellow Sea, coinciding with reduced long-range transport of gaseous pollutants. A comparison of model sensitivity experiments, accounting for both bottom-up emission changes and meteorological variations, revealed that while weather and climate factors such as precipitation and pressure patterns between 2016 and 2022 contributed to the overall decrease in PM concentrations, the primary driver was the reduction in emissions during this period. This study highlighted that the main driver of the substantial improvement in air quality over East Asia was the implementation of emission reduction policies targeting PM and its precursors in the main source regions in China.

Recurrent Coronal Mass Ejections and Their Geomagnetic Storms Association on 2012 January 19: Solar Surface to Upper Earth’s Atmosphere Analyses

In this study, we have conducted an analysis of space weather disruptions that occurred on 19 January 2012. Our analysis identified three coronal mass ejections (CMEs), CME1, CME2, and CME3—which were ejected at 09:48:05 universal time (UT), 14:36:05 UT, and 16:12:06 UT, respectively. Nonrecurrent disturbances in space weather, such as geomagnetic storms, result from CMEs originating from the Sun and traveling toward Earth. We assess the contribution of CME–CME interactions on 2012 January 19 and the volume emission rate of nitric oxide (NO) near the Earth's upper atmosphere in prolonging the geomagnetic disturbances observed on 2012 January 23. The findings suggest an increase in intensity at the interacting boundaries of CME1 and CME2, indicating an increase in pressure and density, leading to the compression of the magnetosphere. The 3D reconstructions of the CMEs provide evidence of unequal expansion and rotations within coronagraphic frames attributed to structural variability in the background solar wind during the eruptions. Furthermore, highlights from the in situ observations suggest that the impact of the recurrent CMEs on the geomagnetic disturbance was more pronounced within the auroral region synchronizing with a significant increase in NO volume emission rate on 2012 January 23, near the upper Earth's atmosphere. Our focus is on exploring the interactions between these CMEs to understand their potential contribution to the extended duration of the observed geomagnetic disturbance.