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Effects of the extreme-ultraviolet (EUV) late phase of solar flares on the ionosphere were rarely studied. Here we simulated such effects on the ionospheric electron density using an ionosphere−thermosphere coupled model driven by the realistic solar spectrum observed during the X1.8 flare on 2012 October 23. Global total electron content (TEC) observations and simulations showed that the dayside ionospheric TEC during the EUV late phase increased more than that of the flare's main phase. We examined the performance of the model for flares with EUV late phase. The results showed that the F-region electron density enhancement and recovery did not vary in the same pace as the temporal variations of the EUV late phase, and the presence of the EUV late phase prolonged the recovery of electron density by ∼9 hr. We also found that the enhancement in electron density was mainly determined by the chemical production, while the recovery of electron density was primarily controlled by the electric field transport effects. This study enhanced understanding of the intricate physical and photochemical processes governing Earth's space environment and similar planetary systems during solar flare events with EUV late phase. [ABSTRACT FROM AUTHOR]

This work reports the development of the first version of the E‐region Prompt Radio Occultation Based Electron Density (E‐PROBED) Model. This is an empirical model of E‐region electron density (Ne) between 90 and 120 km developed using radio occultation measurements from the COSMIC‐1 mission. This first version captures more than 80% of the observed variability in monthly‐mean latitude‐local time‐altitude E‐region Ne profiles but it does not account for longitudinal variability at constant local‐time. This work also reports a validation of E‐PROBED simulations through comparisons with ionosondes and incoherent scatter radar (ISR) E‐region Ne profiles. E‐PROBED generally agrees with these ground‐based observations during day‐time. During night‐time, there is a large disparity between E‐PROBED and ISR values. Finally, this work compares E‐PROBED with E‐region Ne simulated by the International Reference Ionosphere (IRI) and the Specified Dynamics—Whole Atmosphere Community Climate Model with Ionosphere/Thermosphere eXtension (SD‐WACCM‐X). One of the main differences amongst these models is on the simulation of variabilities that cannot be attributed to photoionization. IRI barely simulates any variability not driven by photoionization. Both E‐PROBED and SD‐WACCM‐X simulates variability not driven by photoionization. Another main difference is in the absolute magnitude of night‐time E‐region Ne values. Both IRI and SD‐WACCM‐X are substantially lower than E‐PROBED. This work first concludes that E‐PROBED can conveniently provide E‐region Ne latitude—local time variabilities and structures that COSMIC‐1 observes. This work also concludes that E‐region Ne have significant non‐photoionization driven variabilities. Plain Language Summary: Navigation and communication systems reliant on sending signals into space require accurate predictions from empirical models of ionospheric electron density (Ne) values because the frequency of the appropriate signals to use are a function of Ne. Empirical models currently struggle the most with the ionospheric E‐region (between 90 and 120 km) because most of these models were constructed using sparsely sampled E‐region Ne data from ground‐based observations. Recently, E‐region Ne profiles were finally retrieved from Global Navigation Satellite Systems Radio Occultation (GNSS RO) measurements. This work reports on a new empirical model of monthly‐mean E‐region Ne that uses global observations of E‐region Ne from GNSS RO. The model is called the E‐region Prompt Radio Occultation Based Electron Density (E‐PROBED) Model, and it captures more than 80% of the observed variability in monthly‐mean latitude‐local time‐altitude E‐region Ne profiles. It agrees well with both ground‐based observations and first principles Physics‐based model simulations. These findings suggest that E‐PROBED makes a viable alternative E‐region Ne empirical model for those interested in an E‐region Ne model constrained by satellite observations. Key Points: The first version of E‐region Prompt Radio Occultation Based Electron Density Model (E‐PROBED) is developedE‐PROBED agrees with ground‐based observations during day‐time but not during night‐timeE‐PROBED agrees with SD‐WACCM‐X that E‐region Ne have significant non‐photoionization‐driven variabilities [ABSTRACT FROM AUTHOR]

In Older to solve the problem of low quality and unstable source of dissolving pulp for domestic lyocell fiber, Russian space was used as raw material and high-quality dissolving pulp was prepared for lyocell fiber by pre-hydrolyzed sulfate cooking process. The effects of pre-hydrolysis, sulfate cooking, chlorine dioxide-hydrogen peroxide bleaching and acid treatment on the key technical indexes of dissolved pulp, such as α-cellulose content, polymerization, whiteness, ash content and metal ion content, were investigated. The experimental results show that the holding time of 90 min, the temperature of 150 °C and the solid-liquid ratio of 1:4 were the optimal prehydrolysis conditions, and the alkali content of 24%, the degree of vulcanization of 30% and the holding time of 180 min were the optimal cooking conditions. The slurry prepared under the optimal prehydrolysis and cooking conditions was treated with 1.5% chlorine dioxide bleaching, 12% cold alkali extraction, 5% hydrogen peroxide bleaching and 6% acetic acid, and the resulting pulp had a α-cellulose content, a whiteness of 85%, a polymerization degree of 647, an ash content of 0.06%, an iron ion content of 6 mg/kg, and a copper ion content of 3 mg/kg. Polarizing microscopy showed that the slurry could be completely dissolved in NMMO (moisture content of 13.3%) at 90 °c for 30 s. [ABSTRACT FROM AUTHOR]

Over the past decades, various experimental and numerical model studies have indicated cooling trend in the mesosphere and lower thermosphere (MLT), while the magnitude of the trend varies noticeably. Previous studies using the lidar observations derived the temperature trends and solar responses solely from the traditional nocturnal measurements. While these archived results are more or less in agreement with modeling studies, one of the main uncertainties in these studies is the potential biases induced by the trends of the diurnal tide forced in the lower atmosphere, and that of the in situ exothermal reactions involving the photolysis. In the MLT, the diurnal tide has significant seasonal variations, considerable amplitude and is one of the dominant dynamic sources. However, its potential effects in the trend studies have rarely been discussed. In this paper, we present and compare the long‐term temperature trends in the upper mesosphere utilizing the daily mean and nightly mean temperature profiles measured by a Sodium (Na) Doppler lidar at midlatitude. The system was operating routinely in full diurnal cycles between 2002 and 2017, obtaining a unique multi‐year temperature data set. A customized multi‐linear regression (MLR) model is applied to determine the linear trends and the other fitting parameters, such as ENSO and solar F10.7 responses in the upper mesosphere. This study indicates the daily mean cooling trend between 84 and 98 km is larger than that of nightly mean trend by ∼−1 K/decade, while differences in the solar response are within the fitting uncertainties. Plain Language Summary: The upper atmosphere is sensitive to both the climate change in the lower atmosphere and the solar activity. Studies have demonstrated this region has been experiencing long‐term cooling trend over the past several decades. Most of the previous ground‐based investigations utilized nighttime temperature observations to derive the long‐term changes in the mesosphere and lower thermosphere. However, these nighttime trend results can be biased due to the lack of daytime temperature measurements, leading to the uncertainty in these achieved results. In this study, the daily mean temperatures measured by a lidar at middle latitude between 2002 and 2017 are used to determine the trend and the upper atmosphere response to solar activity. The customized algorithm includes new and important climate parameters. This investigation eliminates such potential bias in the temperature, and the results demonstrated noticeably larger cooling trend in this atmospheric region when compared with those derived from the nightly temperature observations. In addition, the solar response derived from these daily mean lidar temperatures are positive but less than those based on nightly mean observations. The revealed differences will lead to future investigations on the underlying mechanisms and, thus, uncover new aspect of the long‐term studies. Key Points: The temperature in the mesosphere and lower thermosphere is coolingThe cooling trend derived from the daily mean temperatures is noticeably larger than that revealed by the nightly average temperaturesThe WACCM‐X simulations also indicate the differences between the daily mean trend and the nightly mean trend with less magnitude [ABSTRACT FROM AUTHOR]

We investigate the interactions between medium-scale traveling ionospheric disturbances (MSTIDs) and the equatorial ionization anomaly (EIA) as well as between MSTIDs and equatorial plasma bubbles (EPBs) on the night of 13–14 May 2013, based on observations from multiple instruments (an all-sky imager, digisonde, and global positioning system (GPS)). Two dark bands (the low plasma density region) for the MSTIDs were observed moving toward each other, encountering and interacting with the EIA, and subsequently interacting again with the EIA before eventually dissipating. Then, a new dark band of MSTIDs moved in the southwest direction, drifted into the all-sky imager's field of view (FOV), and interacted with the EIA. Following this interaction, a new dark band split off from the original dark band, slowly moved in the northeast direction, and eventually faded away in a short time. Subsequently, the original southwestward-propagating dark band of the MSTIDs encountered eastward-moving EPBs, leading to an interaction between the MSTIDs and the EPBs. Then, the dark band of the MSTIDs faded away, while the EPBs grew larger with a pronounced westward tilt. The results from various observational instruments indicate the pivotal role played by the high-density region of the EIA in the occurrence of various interaction processes. In addition, this study also revealed that MSTIDs propagating into the equatorial region can significantly impact the morphology and evolution characteristics of EPBs. [ABSTRACT FROM AUTHOR]

Using the latest coupled geospace model Multiscale Atmosphere‐Geospace Environment (MAGE) and observations from Jicamarca Incoherent scatter radar (ISR) and ICON ion velocity meter (IVM) instrument, we examine the pre‐reversal enhancement (PRE) during geomagnetic quiet time period. The MAGE shows comparable PRE to both the Jicamarca ISR and ICON observations. There appears to be a discrepancy between the Jicamarca ISR and ICON IVM with the later showed PRE about two times larger (∼40 m/s). This is the first time that MAGE is used to simulate the PRE. The results show that the MAGE can simulate the PRE well and are mostly consistent with observations. Key Points: The Multiscale Atmosphere‐Geospace Environment is able to simulate the pre‐reversal enhancement (PRE) very wellThe PRE was a persistent feature on different time scales (day, hour, and minute) during this fall equinox time periodJicamarca Incoherent scatter radar observed PRE is about half of size of that by the ICON ion velocity meter [ABSTRACT FROM AUTHOR]

Motivated by numerous lower atmosphere climate model hindcast simulations, we performed simulations of the Earth's atmosphere from the surface up through the thermosphere‐ionosphere to reveal for the first time the century scale changes in the upper atmosphere from the 1920s through the 2010s using the Whole Atmosphere Community Climate Model—eXtended (WACCM‐X v. 2.1). We impose solar minimum conditions to get a clear indication of the effects of the long‐term forcing from greenhouse gas increases and changes of the Earth's magnetic field and to avoid the requirement for careful removal of the 11‐year solar cycle as in some previous studies using observations and models. These previous studies have shown greenhouse gas effects in the upper atmosphere but what has been missing is the time evolution with actual greenhouse gas increases throughout the last century, including the period of less than 5% increase prior to the space age and the transition to the over 25% increase in the latter half of the 20th century. Neutral temperature, density, and ionosphere changes are close to those reported in previous studies. Also, we find high correlation between the continuous carbon dioxide rate of change over this past century and that of temperature in the thermosphere and the ionosphere, attributed to the shorter adjustment time of the upper atmosphere to greenhouse gas changes relative to the longer time in the lower atmosphere. Consequently, WACCM‐X future scenario projections can provide valuable insight in the entire atmosphere of future greenhouse gas effects and mitigation efforts. Plain Language Summary: From seeing lower atmosphere computer climate models run for the past century, we decided to do the same for the upper atmosphere using the Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X) for the decades from the 1920s to 2010s. In this higher region, the atmosphere is affected strongly by the Sun and removing the Sun's effect is tricky in previous observation and model studies. We make the Sun's effect small to see only effects from the Earth's magnetic field and greenhouse gases. Earlier studies focused on recent decades show effects of greenhouse gas increases on the upper atmosphere but not for the early decades of the past century with greenhouse gas changes from less than 5% increase prior to the space age and the transition to the over 25% increase in the latter half of the 20th century. We cover this entire period and get results like those in studies before, with especially the temperature change matching very well with the greenhouse gas carbon dioxide change. Because WACCM‐X performs well over the past century, it will be useful to predict what will happen in the century ahead as greenhouse gases increase and humans make efforts to reverse the increase. Key Points: Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X) simulated continuous rate of climate change in the thermosphere/ionosphere over the past century follows closely that of CO2 and CH4Large CO2/thermosphere temperature correlation shows greenhouse gas impact on upper atmosphere climate is consistent over the past centuryConsistency with past century observations and model simulations gives confidence in results of WACCM‐X 21st century climate projections [ABSTRACT FROM AUTHOR]

Leveraging observations by two NASA missions—GOLD (Global‐scale Observations of the Limb and Disk) and ICON (Ionospheric Connection Explorer), we investigate concurrent responses of thermospheric composition, temperatures, and neutral winds to the geomagnetic storm on 3–4 November 2021, as well as their interplay at low and middle latitudes. The synergetic observations reveal remarkable depletions up to 60%–70% in GOLD O/N2, along with large enhancements in GOLD temperatures poleward of 30° in the middle thermosphere. Meridional winds from ICON observations are altered by ∼100 m/s equatorward of 25°N latitude and at 250 km, characterized by a reversal of prevailing northward winds to geomagnetic storm‐driven southward winds. This study fills a need, after a decade‐long gap, for observing concurrent and co‐located responses of composition, temperatures, and neutral winds in the thermosphere to geomagnetic storms. Plain Language Summary: Geomagnetic storms, arising from solar wind shocks emitted from the Sun, deposit a large portion of the absorbed solar energy into the Earth's high‐latitude atmosphere through Joule heating and high energy particle heating. Accurate prediction of the responses to geomagnetic storms in the thermosphere‐ionosphere is one of the core scientific objectives of space weather. The recently launched Global‐scale Observations of the Limb and Disk (GOLD) and Ionospheric Connection Explorer (ICON) missions provides an unparalleled opportunity to assess storm‐induced concurrent changes in multiple key parameters. During a G3 geomagnetic storm on 3 November 2021, GOLD observed the substantial changes of 60%–70% in thermosphere column density ratios of atomic oxygen to molecular nitrogen and temperatures. Exceptional meridional winds of 100–200 m/s were also seen by ICON over a broad altitude range. Such observations fill a decades‐long need for simultaneous observations of the key variables in the ionosphere‐thermosphere system. Key Points: Remarkable depletions in O/N2 and enhancements in temperature, up to 60%–70%, are seen by Global‐scale Observations of the Limb and Disk during the geomagnetic stormAveraged southward wind deviations of ∼100 m/s are observed by Ionospheric Connection Explorer, coincident with the largest gradient in O/N2 depletionsBoth O/N2 and temperatures recover rapidly from the disturbed states to pre‐storm states [ABSTRACT FROM AUTHOR]

During a minor geomagnetic storm occurring from Aug 2 (day‐of‐year (DOY) 214) to Aug 4 (DOY 216), 2021, the National Aeronautics and Space Administration Global‐scale Observations of the Limb and Disk (GOLD) mission observed different column density ratio of O to N2 (ΣO/N2) variations in storm main and recovery phases. The percentage difference of ΣO/N2 between DOY 215 (disturbed day, main phase) and DOY 213 (quiet reference day) exhibits a depletion on the east side of the GOLD field‐of‐view (FOV). However, that of ΣO/N2 between DOY 216 (recovery phase) and 213 shows depletions on the west side of GOLD FOV. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model qualitatively reproduced the observations. Analysis of the model output illustrates that the ΣO/N2 patterns in the two days are both formed due to the classical thermospheric composition theory and formed on DOY 214 and 215, respectively. Further investigation found that the ΣO/N2 depletion on DOY 214 and 215 both initially formed near 120–180°E, but the one on DOY 215 then quickly moved westward into the GOLD FOV, from local post‐midnight to pre‐midnight, near 19 UT. Then it moves equatorward and slowly westward. This results in the observed depletion structure on the west side of GOLD FOV. Model simulations show that the quick westward movement near 19 UT is due to the dominant positive Interplanetary Magnetic Field east‐west component (By) conditions. Key Points: GOLD observed two different ∑O/N2 variations during the main and recovery phase of a minor geomagnetic storm on August 3–4Numerical simulations illustrate that these two different patterns originated in almost the same longitude ranges and local midnightThe quick westward motion of ∑O/N2 depletion due to strong westward wind under dominant Interplanetary Magnetic Field By results in GOLD observed different patterns [ABSTRACT FROM AUTHOR]

As a companion study of the Part 1 (J. C. Wang et al., 2022, https://doi.org/10.1029/2022JA030948), the impact of the lower‐thermospheric circulation on atomic oxygen (O) in the mesosphere and lower thermosphere (MLT) region is investigated in this Part 2 using Specified Dynamics Configuration Runs of the Whole Atmosphere Community Climate Model eXtended (SD‐WACCMX) output. The asymmetry of the O profile in the summer and winter MLT region is mainly driven by local vertical advection, which is associated with the lower‐thermospheric winter‐to‐summer circulation and middle‐to‐upper thermospheric summer‐to‐winter circulation. It is found that meridional transport and eddy diffusion only weakly modulate the O budget within this altitude range. The globally and annually averaged transport effect due to the vertical advection is quantitatively estimated. It is shown that the vertical advection is the dominant mechanism in redistributing O at altitudes between 84 and 103 km, suggesting the vertical wind can efficiently transport O between its source and sink region within the vertical column. This study demonstrates that whole atmosphere coupling on seasonal time scales is a complex interaction involving multiple underlying mechanisms within the space‐atmosphere interaction region. Key Points: Vertical advection is the dominant mechanism acting to transport O in the mesosphere and lower thermosphere (MLT)A Hemispheric asymmetry in MLT O number density is driven by local vertical advectionInterhemispheric mass transport and eddy diffusion only play a minor role in controlling O at higher latitudes in the MLT [ABSTRACT FROM AUTHOR]