Solar Occultation For Ice Experiment Research Articles

Quasi-10-day waves in temperature and polar mesospheric clouds: Results of AIM/SOFIE and Aura/MLS observations

Planetary waves, including quasi-2, -5, -10, −16-day waves, play significant roles in stratospheric dynamics. However, the existing knowledge on quasi-10-day waves (Q10DWs) at high latitudes is limited. This paper investigated the interannual and seasonal variations of Q10DWs with zonal wave numbers varying from the −3 (westward propagation) to 3 (eastward propagation) modes from 2008 to 2022, using temperature data measured by the Microwave Limb Sounder instrument (316−0.001 hPa, corresponding to an altitude of approximately 8–97 km) and temperature/ice water content data measured by the Solar Occultation for Ice Experiment (SOFIE) instrument (10−100 km at latitudes >55°). The findings revealed that the amplitude of Q10DWs in winter was higher than that in other seasons. The amplitude of Q10DWs was observed to substantially decrease with an increase in wavenumber. In addition, the amplitude of stationary Q10DWs in the northern polar region exceeded that in the southern polar region. Moreover, we used observational data from the SOFIE instrument, which simultaneously measures temperature and ice water content (IWC) in the mesosphere, to examine the variations of Q10DWs with respect to the temperature and IWC. Our findings suggest that in the northern polar region, the maximum value of Q10DWs in IWC was occasionally observed earlier than the lowest value of Q10DWs in temperatures.

Planetary Wave Modulation of Gravity Waves Over the Andes in 2016

AbstractThe Andes account for the largest source of orographic gravity waves (GWs) in the middle atmosphere. This results from persistent, strong zonal winds at the surface encountering the north‐south mountain chain, producing strong orographic lift, and resulting GWs. Here, we consider GWs in the stratosphere and mesosphere above the Andes as observed by the Cloud Imaging and Particle Size instrument, the Solar Occultation for Ice Experiment on the AIM satellite, and the Sounding of the Atmosphere using Broadband Emission Radiometry instrument onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. GW variability is considered in the context of the location of the stratospheric wintertime westerly jet and planetary wave (PW) amplitude and phase. The occurrence of GWs in the middle and upper atmosphere depends not only on tropospheric sources, like the Andes, but also on the background winds through which they propagate. Results suggest that the propagation of GWs into the mesosphere is well correlated with winds throughout the middle and upper stratosphere. PWs cause the westerly jet to move over the Andes, resulting in an increase in GW amplitude throughout the middle and upper stratosphere. The evolution and variability of GWs are tied closely to the phase of the PW‐1 and are linked to PW‐2 when the PW amplitudes are sufficiently large. GW amplitude, as observed by all three data sets, increases in the upper stratosphere and lower mesosphere when the trough of the PW‐1 in the stratosphere is over the Andes.

A novel methodology to estimate pre-atmospheric dynamical conditions of small meteoroids

Recent observations using the Wind and Ulysses spacecrafts and the Solar Occultation For Ice Experiment (SOFIE) during the period between 2007 and 2020 indicate a total cosmic dust influx at Earth ranging from 22 to 32 tonnes per day. Much is still unclear about the formation, evolution, and propagation of this cosmic dust throughout our Solar System, as well as the transport and chemical interaction of such particles within our own atmosphere. Studying meteoroids, which are particles small and fast enough to ablate in the Earth’s upper atmosphere producing meteor plasma detectable by meteor radars, offers an opportunity to better understand these processes. While meteor radars provide a powerful tool to detect meteoroids, they are limited to detecting particles that produce a sufficient amount of plasma within the instrument’s field-of-view, and thus most of their trajectory remains undetected. In this work, we report a novel methodology, using new polarization measurements as well as two state-of-the art models, to determine the pre-atmosphere dynamical characteristics of the detected particles, before they suffer any significant ablation or deceleration. We present the results for 20 meteor detection case studies, and find that for the majority of particles, at least 80% (typically 95%) of the particle mass has already been lost at the time of detection. In addition, while all particles experienced deceleration by the time of detection, this was typically small (≤4% of their initial velocity). Future work will implement this new methodology to automatically determine the initial mass and velocities of individual meteors. This will help provide more precise meteor orbits and characterization of parent source populations, as well as the identification of potential interstellar particles.

Validation of Version 1.3 Ozone Measured by the SOFIE Instrument

AbstractThe Solar Occultation for Ice Experiment (SOFIE) has operated aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite since 2007. SOFIE uses solar occultation to retrieve ozone (O3) profiles from ∼20 to 100 km altitude, typically at polar latitudes. This study validates SOFIE O3 profiles, including error analysis and comparisons with independent observations. Comparisons are made to the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite instruments. SOFIE shows qualitative and quantitative agreement with both data sets between 30 and 70 km and better overall agreement in the northern hemisphere. SOFIE and ACE mean differences are typically within 20% in the 30–70 km altitude range. SOFIE and MIPAS exhibit mean difference values within 30% in the winter and 20% for all other seasons averaged, between ∼30 and 60 km. Seasonal comparisons indicate similar variations in both hemispheres and through all seasons. The comparisons indicate that SOFIE is biased 5%–10% low at 30–70 km altitudes, with greater differences at higher and lower altitudes. The comparisons are challenging due to the low O3 concentrations at high altitudes, the limited number of coincidences, and the large diurnal variation in mesospheric O3 during twilight hours.

Solar-induced 27-day modulation on polar mesospheric cloud (PMC), based on combined observations from SOFIE and MLS

Temperature and water vapor are two key variables affecting the polar mesospheric cloud (PMC). Solar radiation can increase the mesospheric temperature through UV heating. In this research, the composite solar index Y10 is used for the first time to study the influence of solar radiation on PMC variability. The ice water content (IWC) is selected to characterize the properties of PMCs. The observations of IWC are from the Solar Occultation For Ice Experiment (SOFIE) onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite, and the temperature data used are measured by both the SOFIE instrument and Microwave Limb Sounder (MLS) onboard the Aura satellite. According to the superposed epoch analysis (SEA) method, it is shown that the solar 27-day modulation can affect PMCs by changing and modulating the mesospheric temperature. The results show that the IWC responds to the Y10 later than the mesospheric temperature does. Further investigation into the relationship between the mesospheric temperature and PMCs reveals that the average time lag is 0 days in the northern hemisphere (NH) and 1 day in the southern hemisphere (SH). The differences in temperature response to the 27-day solar rotational modulation with atmospheric pressure and latitude are also analyzed on the basis of the temperature observations made from 2004 to 2020 by the MLS. The temperature time lag of NH2008 and NH2012 are 1–5 days (depending on latitude), close to the time lag of direct solar heating with 4 days. The PMC seasons with temperature time lags greater than 5 days are indicated to be modulated by atmospheric dynamics with a 27-day cycle. The temperature time lag has two distinct patterns of variation in latitude, and thus two different atmospheric modulation mechanisms may exist. Twelve PMC seasons with 27-day periodicity are distinguished, nine of which have decreasing temperature time lags with increasing altitude because of the atmospheric dynamical effects.

Decadal and Annual Variations in Meteoric Flux From Ulysses, Wind, and SOFIE Observations

AbstractOur solar system is filled with meteoric particles, or cosmic dust, which is either interplanetary or interstellar in origin. Interstellar dust (ISD) enters the heliosphere due to the relative motion of the sun and the interstellar flow. Interplanetary dust (IPD) comes primarily from asteroid collisions or comet sublimation, and comprises the bulk of material entering Earth's atmosphere. This study examines variations in ISD and the IPD flux at Earth using observations from three different satellite techniques. First are size‐resolved in situ meteoroid detections by the Ulysses spacecraft, and second are in situ indirect dust observations by Wind. Third are measurements of meteoric smoke in the mesosphere by the Solar Occultation For Ice Experiment (SOFIE). Wind and Ulysses observations are sorted into the interstellar and interplanetary components. Wind ISD show the anticipated correlation to the 22‐year solar magnetic cycle, and are consistent with model predictions of ISD. Because Wind does not discriminate particle size, the IPD measurements were interpreted using meteoric mass distributions from Ulysses observations and from different models. Wind observations during 2007–2020 indicate a total meteoric influx at Earth of 22 metric tons per day (t d−1), in reasonable agreement with long‐term averages from SOFIE (25 t d−1) and Ulysses (32 t d−1). The SOFIE and Wind influx time series both show an unexpected correlation to the 22‐year solar cycle. This relationship could be an artifact, or may indicate that IPD responds to changes in the solar magnetic field.

Mesospheric Nitric Oxide Transport in WACCM

AbstractEnergetic particle precipitation (EPP) causes ionization of the main constituents of the Earth's atmosphere which leads to the production of nitric oxide (NO) throughout the polar mesosphere and lower thermosphere (MLT). Due to the long lifetime of NO during winter, it can also be transported deeper into the atmosphere by the mesospheric residual circulation (the indirect EEP effect). This study investigates the mesospheric indirect NO response to EEP using Whole Atmosphere Community Climate Model (WACCM) version 6. In comparison to observations from the instrument Solar Occultation For Ice Experiment (SOFIE) on the AIM (Aeronomy of Ice in the Mesosphere) satellite, a wintertime underestimation is found in the modeled mesospheric NO amount. WACCM's temperature profile is found to be vertically shifted compared to observations by SOFIE and by The Sounding of the Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite (SABER). The discrepancies in NO are therefore attributed to the model's ability to simulate the dynamics responsible for the indirect EEP effect. The drivers of this transport are investigated by sensitivity runs of WACCM's gravity wave forcing. Changing the amplitude of the non‐orographic gravity waves and the Prandtl number improves the modeled vertical distribution of NO and temperature in the MLT region.

Two- and three-dimensional structures of the descent of mesospheric trace constituents after the 2013 sudden stratospheric warming elevated stratopause event

Abstract. We use the Specified Dynamics version of the Whole Atmosphere Community Climate Model Extended (SD-WACCMX) to model the descent of nitric oxide (NO) and other mesospheric tracers in the extended, elevated stratopause phase of the 2013 sudden stratospheric warming (SSW). The dynamics are specified with a high-altitude version of the Navy Global Environmental Model (NAVGEM-HA). Consistent with our earlier published results, we find that using a high-altitude meteorological analysis to nudge WACCMX allows for a realistic simulation of the descent of lower-thermospheric nitric oxide down to the lower mesosphere, near 60 km. This is important because these simulations only included auroral electrons and did not consider additional sources of NO from higher-energy particles that might directly produce ionization, and hence nitric oxide, below 80–85 km. This suggests that the so-called energetic particle precipitation indirect effect (EPP-IE) can be accurately simulated, at least in years of low geomagnetic activity, such as 2013, without the need for additional NO production, provided the meteorology is accurately constrained. Despite the general success of WACCMX in bringing upper-mesospheric NO down to 55–60 km, a detailed comparison of the WACCMX fields with the analyzed NAVGEM-HA H2O and satellite NO and H2O data from the Solar Occultation for Ice Experiment (SOFIE) and the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) reveals significant differences in the latitudinal and longitudinal distributions at lower altitudes. This stems from the tendency for WACCMX descent to maximize at sub-polar latitudes, and while such sub-polar descent is seen in the NAVGEM-HA analysis, it is more transient than in the WACCMX simulation. These differences are linked to differences in the transformed Eulerian mean (TEM) circulation between NAVGEM-HA and WACCMX, most likely arising from differences in how gravity wave forcing is represented. To attempt to compensate for the differing distributions of model vs. observed NO and to enable us to quantify the total amount of upper-atmospheric NO delivered to the stratopause region, we use potential vorticity and equivalent latitude coordinates. Preliminary results suggest both model and observations are generally consistent with NO totals in the range of 0.1–0.25 gigamoles (GM).

New Global Meteoric Smoke Observations From SOFIE: Insight Regarding Chemical Composition, Meteoric Influx, and Hemispheric Asymmetry

AbstractMeasurements from the Solar Occultation For Ice Experiment (SOFIE) in both hemispheres are used to characterize meteoric smoke in the mesosphere and to estimate the meteoric flux into Earth's atmosphere. New smoke extinction retrievals from sunrise measurements in the Northern Hemisphere (NH) are presented, which complement the previously reported sunset observations in the Southern Hemisphere (SH). The sunrise observations are in good agreement with simulations from the Whole Atmosphere Community Climate Model (WACCM), for both the seasonal and height dependence of smoke in the mesosphere. The SOFIE‐WACCM comparisons assumed that smoke in the mesosphere exists purely as Fe‐rich olivine. This is justified because olivine is detected optically by SOFIE, meteoric ablation is predicted to inject similar quantities of the most abundant elements (Fe, Mg, and Si) into the mesosphere, and olivine is anticipated by theory and laboratory experiments. In addition, the ablated meteoric influx (AMI) and total meteoric influx determined from SOFIE assuming Fe‐rich olivine is in agreement with a recent and independent investigation based on models and observations. SOFIE observations from 2007 to 2021 indicate a global AMI of 7.3 ± 2.2 metric tons per day (t d−1), which corresponds to a total influx (ablated plus surviving material) of 24.7 ± 7.3 t d−1. Finally, the results indicate stronger descent in the NH polar winter mesosphere than in the SH winter. This hemispheric asymmetry at polar latitudes is indicated by smoke and water vapor results from both SOFIE and WACCM.

Trends in the polar summer mesosphere temperature and pressure altitude from satellite observations

Time series of mesospheric temperature and pressure altitude are produced through combining observations by the Halogen Occultation Experiment (HALOE), Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER), and Solar Occultation for Ice Experiment (SOFIE) instruments. Time series of both temperature and pressure altitude are produced through the combination of HALOE/SABER providing 29 years in length and HALOE/SOFIE providing 22 years in length. The different sampling of the three instruments constrains the time series to June in the northern hemisphere and December in the southern hemisphere and 64–70° in both hemispheres. We interpret the time series by fitting them to simple descriptions of the variations including solar, intra-hemispheric, inter-hemispheric, and linear trend terms. The inferred intra- and inter-hemispheric terms show that dynamical influences rival solar variability in the mesosphere. We find a robust result that the mesosphere is in general cooling at most altitudes at approximately 1–2 K per decade in response to greenhouse gas increases. That cooling leads to a shrinking of the atmosphere on the order of 100–200 m per decade. The shrinking leads to a reduction in cooling and eventually a warming near 0.005 hPa due to hydrostatic contraction.

Spatial Distributions of Nitric Oxide in the Antarctic Wintertime Middle Atmosphere During Geomagnetic Storms

AbstractEnergetic electron precipitation leads to increased nitric oxide (NO) production in the mesosphere and lower thermosphere. NO distributions in the wintertime, high‐latitude Southern Hemisphere atmosphere during geomagnetic storms are investigated. NO partial columns in the upper mesosphere at altitudes 70–90 km and in the lower thermosphere at 90–110 km have been derived from observations made by the Solar Occultation For Ice Experiment (SOFIE) on board the Aeronomy of Ice in the Mesosphere (AIM) satellite. The SOFIE NO measurements during 17 geomagnetic storms in 2008–2014 have been binned into selected geomagnetic latitude and geographic latitude/longitude ranges. The regions above Antarctica showing the largest instantaneous NO increases coincide with high fluxes of 30–300 keV precipitating electrons from measurements by the second‐generation Space Environment Monitor (SEM‐2) Medium Energy Proton and Electron Detector (MEPED) instrument on the Polar‐orbiting Operational Environmental Satellites (POES). Significant NO increases over the Antarctic Peninsula are likely due to precipitation of >30 keV electrons from the radiation belt slot region. NO transport is estimated using Horizontal Wind Model (HWM14) calculations. In the upper mesosphere strong eastward winds (daily mean zonal wind speed ~20–30 m s−1 at 80 km) during winter transport NO‐enriched air away from source regions 1–3 days following the storms. Mesospheric winds also introduce NO‐poor air into the source regions, quenching initial NO increases. Higher up, in the lower thermosphere, weaker eastward winds (~5–10 m s−1 at 100 km) are less effective at redistributing NO zonally.

Investigating an Unusually Large 28‐Day Oscillation in Mesospheric Temperature Over Antarctica Using Ground‐Based and Satellite Measurements

AbstractThe Utah State University Advanced Mesospheric Temperature Mapper was deployed at the Amundsen‐Scott South Pole Station in 2010 to measure OH temperature at ~87 km as part of an international network to study the mesospheric dynamics over Antarctica. During the austral winter of 2014, an unusually large amplitude ~28‐day oscillation in mesospheric temperature was observed for ~100 days from the South Pole Station. This study investigates the characteristics and global structure of this exceptional planetary‐scale wave event utilizing ground‐based mesospheric OH temperature measurements from two Antarctic stations (South Pole and Rothera) together with satellite temperature measurements from the Microwave Limb Sounder on the Aura satellite and the Solar Occultation For Ice Experiment on the Aeronomy of Ice in the Mesosphere satellite. Our analyses have revealed that this large oscillation is a wintertime, high‐latitude phenomenon, exhibiting a coherent zonal wave #1 structure below 80‐km altitude. At higher altitudes, the wave was confined in longitude between 180°E and 360°E. The amplitude of this oscillation reached ~15 K at 85 km, and it was observed to grow with altitude as it extended from the stratosphere into the lower thermosphere in the Southern Hemisphere. The satellite data further established the existence of this oscillation in the Northern Hemisphere during the boreal wintertime. The main characteristics and global structure of this event as observed in temperature are consistent with the predicted 28‐day Rossby Wave (1,4) mode.

Northern hemisphere summer mesospheric gravity wave response to solar activity from nine years of AIM observation

High-latitude northern hemisphere summer mesospheric gravity wave (GW) activity at PMC altitude (82–86 km) is analyzed from nine years (2007–2015) of Aeronomy of Ice in the Mesosphere (AIM) satellite observation. GW activity is characterized in terms of potential energy per unit mass. A new method is proposed to convert the Ice Water Content (IWC) in Polar Mesospheric Cloud (PMC) observed by the Cloud Imaging and Particle Size (CIPS) experiment on the AIM satellite to temperature using a simple model. These are used with temperatures from the Solar Occultation for Ice Experiment (SOFIE, also onboard the AIM), to derive daily averaged GW potential energy in the northern hemisphere summer. July monthly averaged GW potential energy indicates no relation to the 11-year solar cycle. Daily averaged values indicate a large variability in the 27-day GW oscillation, with positive, negative or no correlation with the 27-day solar rotation during individual summer seasons. However, a superposed epoch analysis using SOFIE GW anomalies indicate a significant negative response to the 27-day solar rotation with a lag of 8–12 days. This 27-day GW response may be related to similar oscillations in the wind, but the exact cause of the 27-day signal in the GW activity is not yet understood.

Validation of Solar Occultation for Ice Experiment (SOFIE) nitric oxide measurements

Abstract. Nitric oxide (NO) measurements from the Solar Occultation for Ice Experiment (SOFIE) are validated through detailed uncertainty analysis and comparisons with independent observations. SOFIE was compared with coincident satellite measurements from the Atmospheric Chemistry Experiment (ACE) – Fourier Transform Spectrometer (FTS) instrument and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument. The comparisons indicate mean differences of less than ∼50 % for altitudes from roughly 50 to 105 km for SOFIE spacecraft sunrise and 50 to 140 km for SOFIE sunsets. Comparisons of NO time series show a high degree of correlation between SOFIE and both ACE and MIPAS for altitudes below ∼130 km, indicating that measured NO variability in time is robust. SOFIE uncertainties increase below ∼80 km due to interfering H2O absorption and signal correction uncertainties, which are larger for spacecraft sunrise compared to sunset. These errors are sufficiently large in sunrises that reliable NO measurements are infrequent below ∼80 km.

On the relative roles of dynamics and chemistry governing the abundance and diurnal variation of low-latitude thermospheric nitric oxide

Abstract. We use data from two NASA satellites, the Thermosphere Ionosphere Energetics and Dynamics (TIMED) and the Aeronomy of Ice in the Mesosphere (AIM) satellites, in conjunction with model simulations from the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) to elucidate the key dynamical and chemical factors governing the abundance and diurnal variation of lower thermospheric nitric oxide (NO) at near-solar minimum conditions and low latitudes. This analysis was enabled by the recent orbital precession of the AIM satellite which caused the solar occultation pattern measured by the Solar Occultation for Ice Experiment (SOFIE) to migrate down to low and mid-latitudes for specific periods of time. We use a month of NO data collected in January 2017 to compare with two versions of the TIME-GCM; one is driven solely by climatological tides and analysis-derived planetary waves at the lower boundary and is free running at all other altitudes, and the other is constrained by a high-altitude analysis from the Navy Global Environmental Model (NAVGEM) up to the mesopause. We also compare SOFIE data with a NO climatology from the nitric oxide empirical model (NOEM). Both SOFIE and NOEM yield peak NO abundances of around 4×107 cm−3; however, the SOFIE profile peaks about 6–8 km lower than NOEM. We show that this difference is likely a local time effect, with SOFIE being a dawn measurement and NOEM representing late morning and/or near noon. The constrained version of TIME-GCM exhibits a low-altitude dawn peak, while the model that is forced solely at the lower boundary and free running above does not. We attribute this difference to a phase change in the semi-diurnal tide in the NAVGEM-constrained model, causing the descent of high NO mixing ratio air near dawn. This phase difference between the two models arises due to differences in the mesospheric zonal mean zonal winds. Regarding the absolute NO abundance, all versions of the TIME-GCM overestimate this. Tuning the model to yield calculated atomic oxygen in agreement with TIMED data helps but is insufficient. Furthermore, the TIME-GCM underestimates the electron density (Ne) as compared with the International Reference Ionosphere (IRI) empirical model. This suggests a potential conflict with the requirements of NO modeling and Ne modeling, since one solution typically used to increase model Ne is to increase the solar soft X-ray flux, which would, in this case, worsen the NO model–data discrepancy.

Observations and Modeling of Increased Nitric Oxide in the Antarctic Polar Middle Atmosphere Associated With Geomagnetic Storm‐Driven Energetic Electron Precipitation

AbstractNitric 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 × 108/cm3 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.

Production and transport mechanisms of NO in the polar upper mesosphere and lower thermosphere in observations and models

Abstract. A reservoir of nitric oxide (NO) in the lower thermosphere efficiently cools the atmosphere after periods of enhanced geomagnetic activity. Transport from this reservoir to the stratosphere within the winter polar vortex allows NO to deplete ozone levels and thereby affect the middle atmospheric heat budget. As more climate models resolve the mesosphere and lower thermosphere (MLT) region, the need for an improved representation of NO-related processes increases. This work presents a detailed comparison of NO in the Antarctic MLT region between observations made by the Solar Occultation for Ice Experiment (SOFIE) instrument on-board the Aeronomy of Ice in the Mesosphere (AIM) satellite and simulations performed by the Whole Atmosphere Community Climate Model with Specified Dynamics (SD-WACCM). We investigate 8 years of SOFIE observations, covering the period 2007–2015, and focus on the Southern Hemisphere (SH), rather than on dynamical variability in the Northern Hemisphere (NH) or a specific geomagnetic perturbed event. The morphology of the simulated NO is in agreement with observations though the long-term mean is too high and the short-term variability is too low in the thermosphere. Number densities are more similar during winter, though the altitude of peak NO density, which reaches between 102 and 106 km in WACCM and between 98 and 104 km in SOFIE, is most separated during winter. Using multiple linear regression (MLR) and superposed epoch analysis (SEA) methods, we investigate how well the NO production and transport are represented in the model. The impact of geomagnetic activity is shown to drive NO variations in the lower thermosphere similarly across both datasets. The dynamical transport from the lower thermosphere into the mesosphere during polar winter is found to agree very well with a descent rate of about 2.2 km day−1 in the 80–110 km region in both datasets. The downward-transported NO fluxes are, however, too low in WACCM, which is likely due to medium energy electrons (MEE) and D-region ion chemistry that are not represented in the model.

Responses of Lower Thermospheric Temperature to the 2013 St. Patrick's Day Geomagnetic Storm

AbstractThe altitude‐ and latitude‐dependent responses of neutral temperature in the lower thermosphere to the 2013 St. Patrick's Day geomagnetic storm have been studied using neutral temperature measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the TIMED satellite and the Solar Occultation For Ice Experiment (SOFIE) instrument onboard the AIM satellite. Both SABER and SOFIE observations revealed that both temperature increase (having peaks of ~15–25 K) and decrease (having peak of ~15 K), which were associated with the storm, occurred in the two hemispheres. The magnitudes of temperature variations changed with latitude, altitude, and the phase of the storm. The peaks of the temperature increase occurred 0.5–1.5 days later than the peak of the AE index, depending on latitude and height. Global circulation changes initiated due to heating and ion drag in the auroral region are likely responsible for the temperature increases or decreases in the lower thermosphere.

Constraints on Meteoric Smoke Composition and Meteoric Influx Using SOFIE Observations With Models

AbstractThe composition of meteoric smoke particles in the mesosphere is constrained using measurements from the Solar Occultation For Ice Experiment (SOFIE) in conjunction with models. Comparing the multiwavelength observations with models suggests smoke compositions of magnetite, wüstite, magnesiowüstite, or iron‐rich olivine. Smoke compositions of pure pyroxene, hematite, iron‐poor olivine, magnesium silicate, and silica are excluded, although this may be because these materials have weak signatures at the SOFIE wavelengths. Information concerning smoke composition allows the SOFIE extinction measurements to be converted to smoke volume density. Comparing the observed volume density with model results for varying meteoric influx (MI) provides constraints on the ablated fraction of incoming meteoric material. The results indicate a global ablated MI of 3.3 ± 1.9 t d−1, which represents only iron, magnesium, and possibly silica, given the smoke compositions indicated here. Considering the optics and iron content of individual smoke compositions gives an ablated Fe influx of 1.8 ± 0.9 t d−1. Finally, the global total meteoric influx (ablated plus surviving) is estimated to be 30 ± 18 t d−1, when considering the present results and a recent description of the speciation of meteoric material.

Relative Importance of Nitric Oxide Physical Drivers in the Lower Thermosphere

AbstractNitric oxide (NO) observations from the Solar Occultation for Ice Experiment and Student Nitric Oxide Explorer satellite instruments are investigated to determine the relative importance of drivers of short‐term NO variability. We study the variations of deseasonalized NO anomalies by removing a climatology, which explains between approximately 70% and 90% of the total NO budget, and relate them to variability in geomagnetic activity and solar radiation. Throughout the lower thermosphere geomagnetic activity is the dominant process at high latitudes, while in the equatorial region solar radiation is the primary source of short‐term NO changes. Consistent results are obtained on estimated geomagnetic and radiation contributions of NO variations in the two data sets, which are nearly a decade apart in time. The analysis presented here can be applied to model simulations of NO to investigate the accuracy of the parametrized physical drivers.