Global-scale Observations Of The Limb And Disk Research Articles

Investigation of Thermospheric Response to Geomagnetic Storms Using GITM‐OVATION Prime and ‐FTA Model With Comparison to GOLD and SABER Observations

AbstractGlobal Ionosphere Thermosphere Model (GITM) results have been compared with measurements from Global‐scale observations of the limb and disk (GOLD) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). For the first time, GOLD‐derived exospheric temperature and column‐integrated ratio measurements have been used to validate GITM model results. We examine two geomagnetic storm events for which we drive GITM with space weather conditions to understand how well the model reproduces the thermospheric responses to geomagnetic activity. In this paper, a recently developed auroral model, the Feature Tracking of Aurora (FTA) model, has been employed to calculate auroral electron precipitation in GITM (GITM w/FTA), and results are compared with the OVATION prime (OP) driven GITM model (GITM w/OP). GITM w/FTA simulated temperature, neutral density, and nitric oxide (NO) density are generally higher compared to the GITM w/OP model. During the geomagnetic storm, the GITM model and GOLD‐derived exospheric temperature agree between and N latitude in the equatorial region. GOLD measurements show strong peaks on either side of the equator during the geomagnetic storm period, which is also observed in our model results. The NO cooling peaks estimated by GITM models are 20 km lower than SABER observations during geomagnetic storms. GITM w/FTA better matches SABER observations than GITM w/OP except at low latitudes during storm time. Our model‐model/data comparisons show that improved auroral models are needed to better capture the thermospheric variations during geomagnetic storms.

Effects of Storm‐Time Winds on Ionospheric Pre‐Midnight Equatorial Plasma Bubbles Over South America as Observed by ICON and GOLD

AbstractThis study uses satellite measurements of plasma densities and thermospheric winds to analyze the effects of the November 2021 geomagnetic storm on ionospheric pre‐midnight topside plasma bubbles over South America. Using observations from the Ionospheric Connection Explorer (ICON) and the Global‐scale Observations of the Limb and Disk (GOLD) satellites, we find that pre‐midnight topside plasma bubbles were inhibited over eastern South America during the recovery phase of the storm. This is particularly notable because of the otherwise high occurrence rate of plasma bubbles at these longitudes during this season. This inhibition coincided with the recovery phase of the geomagnetic storm, marked by a northward turning of the z‐component of the interplanetary magnetic field (IMFBz) and quiet‐time values of the SuperMAG Auroral Electrojet Index (SME). We observed a westward turning of the zonal wind before the bubble inhibition, so we conclude the inhibition of topside plasma bubbles is likely related to a westward disturbance dynamo electric field (DDEF) causing a downward drift and suppress the growth of the instability responsible for bubble development. Contrary to theoretical predictions, we do not observe notable changes to the meridional wind during the event. These results provide new insights into the ionosphere‐thermosphere system's response to geomagnetic storms and highlight the role of wind patterns in inhibiting ionospheric irregularities, contributing to better predictive models for these phenomena.

GOLD Observations of the Merging of the Southern Crest of the Equatorial Ionization Anomaly and Aurora During the 10 and 11 May 2024 Mother's Day Super Geomagnetic Storm

AbstractUsing NASA's Global‐scale Observations of the Limb and Disk (GOLD) imager, we report nightside ionospheric changes during the G5 super geomagnetic storm of 10 and 11 May 2024. Specifically, the nightside southern crest of the Equatorial Ionization Anomaly (EIA) was observed to merge with the aurora near the southern tip of South America. During the storm, the EIA southern crest was seen moving poleward as fast as 450 m/s. Furthermore, the aurora extended to mid‐latitudes reaching the southern tips of Africa and South America. The poleward shift of the equatorial ionospheric structure and equatorward motion of the aurora means there was no mid‐latitude ionosphere in this region. These observations offer unique insights into the ionospheric response to extreme geomagnetic disturbances, highlighting the complex interplay between solar activity and Earth's upper atmosphere.

Disk Images of Neutral Temperature From the Global‐Scale Observations of the Limb and Disk (GOLD) Mission

AbstractObservations of far‐ultraviolet (FUV) dayglow by the Global‐scale Observations of Limb and Disk (GOLD) mission provide an opportunity for quantifying the global‐scale response of the thermosphere to solar extreme‐ultraviolet variability and geomagnetic activity. Relative temperature changes can be measured by monitoring changes in the rotational structure observed in molecular nitrogen Lyman‐Birge‐Hopfield (LBH) band emissions. We present a new technique for deriving effective neutral temperatures from GOLD FUV observations using optimal estimation fits to spectra containing LBH band emissions. We provide an overview of the theoretical basis for the GOLD Level 2 TDISK algorithm. Effects on derived effective neutral temperatures from instrument artifacts and particle background are reviewed. We also discuss GOLD Level 1C DAY and Level 2 TDISK data products and present representative examples of each. We show that effective neutral temperatures vary with local time, exhibit a strong dependence on season and solar zenith angle, and correlate strongly with geomagnetic and solar activity. Finally, we present results from a preliminary data product validation that show good agreement with coincident GOLD exospheric temperatures and predictions from a global reference atmospheric model.

GOLD Observations of Equatorial Plasma Bubbles Reaching Mid‐Latitudes During the 23 April 2023 Geomagnetic Storm

AbstractA coronal mass ejection erupted from the Sun on 21 April 2023 and created a G4 geomagnetic storm on 23 April. NASA's global‐scale observations of the limb and disk (GOLD) imager observed bright equatorial ionization anomaly (EIA) crests at ∼25° Mlat, ∼11° poleward from their average locations, computed by averaging the EIA crests during the previous geomagnetic quiet days (18–22 April) between ∼15°W and 5°W Glon. Reversed C‐shape equatorial plasma bubbles (EPBs) were observed reaching ∼±36° Mlat (∼40°N and ∼30°S Glat) with apex altitudes ∼4,000 km and large westward tilts of ∼52°. Using GOLD's observations EPBs zonal motions are derived. It is observed that the EPBs zonal velocities are eastward near the equator and westward at mid‐latitudes. Model‐predicted prompt penetration electric fields indicate that they may have affected the postsunset pre‐reversal enhancement at equatorial latitudes. Zonal ion drifts from a defense meteorological satellite program satellite suggest that westward neutral winds and perturbed westward ion drifts over mid‐latitudes contributed to the observed latitudinal shear in zonal drifts.

Application of the Bagged Trees Technique on Retrieving the Nighttime Ionospheric Peak Density From OI‐135.6 nm Airglow

AbstractThe NASA global‐scale observations of the limb and disk (GOLD) mission is a measurement opportunity to scan the far ultraviolet airglow at ∼134–162 nm over the American Hemisphere since October 2018. The FORMOSAT‐7/COSMIC‐2 (F7/C2) satellite mission has provided thousands of daily radio occultation soundings in the low‐ and mid‐latitude regions since July 2019. The nighttime OI–135.6 nm emission is mainly through radiative recombination, and the radiance is used to derive the peak electron density. Comparison with corresponding F7/C2 observations demonstrates good correlation in low‐latitudes, while is overestimated near mid‐latitudes in winter, induced by the photoelectrons emanating from magnetically conjugate Hemisphere. The machine learning technique Bagged Trees is implemented to develop an intensity to peak density model training from GOLD and F7/C2 observations. The validation demonstrates that Bagged Trees peak‐density has less influence from conjugate photoelectrons and indicates the power of machine learning techniques for geophysics data processing.

Occurrence Characteristics of Nighttime Merged EIA Based on NASA GOLD Observations from 2018 to 2023

The ionosphere equatorial ionization anomaly (EIA) is usually characterized by two plasma density maxima in the Earth’s equatorial region. Merged EIA (MEIA) is a unique phenomenon in the evolution of the EIA. Currently, the occurrence characteristics of MEIA are still not well understood. In this study, we investigate the occurrence characteristics of nighttime MEIA using NASA Global-scale Observations of the Limb and Disk (GOLD) observations between October 2018 and the end of 2023. We found that the occurrence of nighttime MEIA exhibits solar cycle, seasonal, and local time variations. The occurrence rate of the MEIA is inversely dependent on solar activity. Occurrence of the MEIA maximizes near the equinoxes, with a primary (secondary) low occurrence rate near the June (December) solstice. In addition, occurrences of the MEIA are suppressed during the pre-reversal enhancement (PRE), resulting in relatively fewer events. Furthermore, it was found that the occurrence of the MEIA is not significantly dependent on the strength of geomagnetic activity. As far as we know, this study represents the first instance of utilizing observations from GOLD observations to investigate the characteristics of MEIA occurrences and their correlations with solar activity, season, and local time.

A 2‐Dimensional Data Detrending Technique for Equatorial Plasma Bubble Studies Using GOLD Far Ultraviolet Observations

AbstractWe formulate a numerical data detrending technique that can be used to help reveal large‐scale equatorial plasma bubble (EPB) structures in 2‐dimensional data from the Global‐scale Observations of the Limb and Disk (GOLD) mission. This GOLD data detrending technique is inspired by and is a generalization of a previous rolling‐barrel data detrending method for 1‐dimensional total electron content (TEC) observations on individual global positioning system (GPS) satellite passes. This 2‐dimensional GOLD data detrending technique treats the observed 135.6 nm radiance as a function of longitude and latitude as an uneven terrain, where EPBs appear as deep but narrow elongated valleys. The unperturbed background radiance is inferred by rolling a ball on the 2‐dimensional terrain to skip over the EPB valleys. The two degrees‐of‐freedom possessed by the rolling ball allow it to smoothly trace the edges of EPB depletions, without falling into the deep valleys. Surface interpolation of radiance values at the ball's contact points onto the whole domain produces the baseline radiance. Subtracting the baseline from the original radiance data yields the net detrended radiance. As a result of the detrending, sharper contrast is present between EPB depletions and the ambient surroundings. As such, this new 2‐dimensional GOLD data detrending may potentially open the door to the development of other more advanced techniques for automated EPB detection and tracking, or data assimilation into low‐latitude space domain awareness (SDA) information ecosystems.

Semidiurnal Non‐Migrating Tides in the Middle Thermosphere From Far Ultraviolet Observations

AbstractMuch of the longitude/local time dependence of the thermosphere is controlled by non‐migrating tides. Observations of semidiurnal (12‐hr) tides between 120 and 200 km altitude, that is, the middle thermosphere, are rare owing to the lack of systematic measurements in this region. Since late 2018, the Global‐scale Observations of the Limb and Disk (GOLD) Mission has provided unique measurements of thermospheric disk temperature and the column density ratio of atomic oxygen to molecular nitrogen ratio (ΣO/N2) from geostationary orbit. In this paper, we present an approach to deduce the strongest semidiurnal non‐migrating tides in the middle thermosphere by adapting the method of Krier et al. (2021, https://doi.org/10.1029/2021ja029563) that deduces diurnal non‐migrating tides in simultaneous observations of temperature and ΣO/N2 made by GOLD. Testing of this approach suggests that the principal sources of uncertainties in the derived semidiurnal non‐migrating tides are the limitation on the longitudes sampled, such that uncertainties are higher for tides with longer horizontal wavelength, and contamination of the local time sums by stationary planetary waves, which causes amplitudes to be overestimated. Our approach is applied to GOLD data during solstice conditions in 2019–2021. Comparison to models yield disagreements which are likely due to uncertainties intrinsic to the method and/or misrepresentation of tidal dynamics in the models. These results are the first observations of semidiurnal non‐migrating tides in the middle thermosphere from a geostationary observational platform.

Retrieval of Thermospheric O and N2 Densities From ICON EUV

AbstractAs activity in Earth orbit continues to grow, it is important to characterize the environment of near‐Earth space. One means of remotely sensing lower thermospheric neutrals is by measurement of O and N2 density through the observation of far‐ultraviolet (FUV) airglow of atomic oxygen at 135.6 nm and the N2 Lyman‐Birge‐Hopfield (LBH) bands (~130–180 nm), as has been done on the Ionospheric Connection Explorer (ICON), Global‐scale Observations of the Limb and Disk (GOLD), and Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) missions. This technique is not without limitations, however, as the FUV measurements suffer from contamination by ionospheric emissions at low latitudes and auroral emissions excited by precipitating energetic electrons and protons at high latitudes. Previous work has shown the potential for making measurements of O and N2 density in the lower‐middle thermosphere using observations of extreme‐ultraviolet (EUV) airglow. This measurement approach has a potential advantage in that it does not have an inherent ionospheric emission that must be accounted for. Additionally, these emissions are primarily excited directly by solar UV rather than electron impact and thus have the potential to enable expansion of neutral density observations into the auroral zone and polar cap where the FUV measurement cannot be applied. This article demonstrates a new approach and algorithm designed to retrieve thermospheric O and N2 density from 150 to 400 km using measurements from the ICON EUV instrument. The retrieval results throughout 2020 are summarized and compared to measurements from ICON FUV, GOLD, and SWARM.

Investigation of Different ΣO/N2 Variations Observed by GOLD During a Minor Geomagnetic Storm From 2 to 4 August 2021

AbstractDuring 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.

Ionospheric Response to Solar EUV Radiation Variations Using GOLD Observations and the CTIPe Model

AbstractTo understand the global response of thermospheric‐ionospheric (TI) parameters to variations in solar irradiance measurements from the Global‐Scale Observations of the Limb and Disk (GOLD) ultraviolet imaging spectrograph, solar radio flux F10.7, predictions from the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model, and International Global Navigation Satellite System Service total electron content maps (TEC) have been used. Various parameters such as GOLD O/N2, O2, and the nighttime peak electron density (Nmax) have been compared with the CTIPe model simulations. The GOLD observed Nmax shows a number of significant features including a winter anomaly and an equatorial ionization anomaly. The comparison with solar proxies showed that the GOLD QEUV correlates very well with the EUV observations compared to the F10.7 index. The study also examined the relationship between the solar proxies and Nmax on different time scales and found that Nmax responded significantly to QEUV at both medium‐ and long‐term timescales. Furthermore, a low correlation between Nmax in the equatorial region and solar proxies was found. A delayed ionospheric TEC response against solar flux variations within the 27‐day solar rotation was investigated. This ionospheric delay of TEC with respect to solar flux was observed to be less than 1 day, which was reproduced in model simulations. The current study has shown that the GOLD observations can be used to investigate the delayed ionospheric response and to gain a better understanding of the influence of solar activity on the TI system.

Thermospheric Responses to the 3 and 4 November 2021 Geomagnetic Storm During the Main and Recovery Phases as Observed by NASA's GOLD and ICON Missions

AbstractLeveraging 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.

Inferring the Ionospheric State With the Far Ultraviolet Imager on the Fengyun‐4C Geostationary Satellite: Retrieval Algorithm and Verification

AbstractThe Multiband Ultraviolet Spectrum Imager (MUSI) is an optical remote sensing instrument scheduled to launch on the Fengyun‐4C meteorological satellite in 2024. MUSI is designed to measure the airglow emissions between ∼120 and 160 nm above the East Asia and Pacific region from a geostationary orbit to infer ionospheric parameters. Here we develop a lookup‐table algorithm for retrieving the peak electron density (nmF2) and the Total Electron Content (TEC) from nighttime observations of the OI 135.6 nm emission. The algorithm takes into account the north‐south asymmetry of the equatorial ionization anomaly and the atmospheric variations with solar activity and local time. Analysis of synthetic observations shows that the assumptions made in the algorithm only lead to ∼2%–4% uncertainties in the retrievals under the modeled ionospheric conditions. The algorithm is verified by retrieving nmF2 and TEC from the Global‐Scale Observations of the Limb and Disk (GOLD) mission and comparing with coincided radio measurements. The comparison indicates almost negligible systematic differences (typically less than ∼3%) between the GOLD and the ionosonde nmF2, which are within the error limit of the GOLD retrievals. The accuracy of the GOLD TEC retrievals is shown to be comparable to (or in some sense even better than) that of the measurements from the Global Navigation Satellite System. Several simplified yet robust retrieval methods are also developed, which can be readily implemented for both existing and upcoming missions. Our results promote far ultraviolet (FUV) remote sensing to be a key technology for accurate determination of the ionospheric state.

Investigation of the Physical Mechanisms of the Formation and Evolution of Equatorial Plasma Bubbles During a Moderate Storm on 17 September 2021

AbstractWe investigate in detail the occurrence and evolution of ionospheric equatorial plasma bubbles (EPBs) during a moderate storm on 17 September 2021, using Global‐scale Observations of the Limb and Disk (GOLD) observations and Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X) simulations. GOLD observations show that there were no EPBs on 16 September before the storm but EPBs occurred after the storm commencement on 17 September. The EPBs extended to ∼30° magnetic latitude. A diagnostic analysis of WACCM‐X simulations reveals that the rapid enhancement of prompt penetration electric fields (PPEFs) after the sudden storm commencement is the main reason that triggered the occurrence of the EPBs. Further quantitative analysis shows that vertical plasma drifts, which are enhanced by the PPEF, played a dominant role in strengthening the Rayleigh‐Taylor instability, leading to the occurrence of the EPBs and the large latitudinal extension of the EPBs to ∼30° magnetic latitude during the night of 17 September.

Unveiling the combined effects of neutral dynamics and electrodynamic forcing on dayside ionosphere during the 3–4 February 2022 “SpaceX” geomagnetic storms

Geomagnetic storms of G1-class were observed on 3 and 4 February 2022, which caused the loss of 38 out of 49 SpaceX satellites during their launch due to enhanced neutral density. The effects of storm-time neutral dynamics and electrodynamics over the American sector during this minor storm have been investigated using Global Positioning System—total electron content (TEC) and Global‐scale Observations of the Limb and Disk (GOLD) mission measured thermospheric composition and temperature. Results revealed an unexpected feature in terms of increase in O/N2 and depletion in TEC over the American low-latitudes. This feature is in addition to the classic storm time ionospheric variations of enhancement in ionospheric electron density in presence of enhanced O/N2 and an intense equatorial electrojet (EEJ). Further, significant morning-noon electron density reductions were observed over the southern mid-high latitudes along the American longitudes. Results from Multiscale Atmosphere-Geospace Environment (MAGE) model simulations elucidated storm-induced equatorward thermospheric wind which caused the strong morning counter electrojet by generating the disturbance dynamo electric field. This further explains the morning TEC depletion at low-latitudes despite an increase in O/N2. Sub-storm related magnetospheric convection resulted in significant noon-time peak in EEJ on 4 February. Observation and modelling approaches together suggested that combined effects of storm-time neutral dynamic and electrodynamic forcing resulted in significant ionospheric variations over the American sector during minor geomagnetic storms.

Unique Combinations of Differently Shaped Equatorial Plasma Bubbles Occurring Within a Small Longitude Range

AbstractOn 12 October 2020 and 26 December 2021, NASA's Global‐scale Observations of the Limb and Disk (GOLD) mission observed differently shaped equatorial plasma bubbles (EPBs) simultaneously within ∼10° longitude, near the subsatellite point and over the Atlantic, respectively which is unusual. On 12 October 2020, three EPBs with differing curvatures were observed in a ∼12° longitude sector. The westside EPB was curved toward the east, in a C‐shape. The middle was straight. The eastside EPB was curved westward, in a reversed C‐shape. In the second case, 26 December 2021, in a smaller longitude range of ∼6° adjacent C‐shaped and reversed C‐shaped EPBs were observed. EPBs' zonal drift velocities at the magnetic equator and both equatorial ionization anomaly crests were compared. These occurrences of oppositely shaped EPBs simultaneously in a narrow longitude may indicate that small‐scale longitudinal variations in the E‐region density, electric field, neutral wind variations, or a combination of them were present.

Automated Detection and Tracking of Equatorial Plasma Bubbles Utilizing Global‐Scale Observations of the Limb and Disk (GOLD) 135.6 nm Data

AbstractEquatorial plasma bubbles (EPBs) are regions of depleted plasma within the ionosphere that form during post‐sunset hours near the magnetic equator. EPBs tend to align with local geomagnetic field lines, extend hundreds of kilometers along geomagnetic longitudes, and thousands of kilometers along geomagnetic latitudes. EPBs can attenuate lower frequency radio waves, such as HF radar. Smaller features, usually 10s of meters, along the EPB's wall can interfere with centimeter scale wavelengths, such as GPS, via Bragg scattering. Statistical analysis of EPBs can further understanding of their occurrence and behavior. The current study utilizes Global‐Scale Observations of the Limb and Disk (GOLD) 135.6 nm nightglow data from 5 October 2018 to 30 September 2022. GOLD has a unique perspective from geostationary orbit, allowing consistent viewing of nightglow and structures over the Americas and Atlantic. An EPB detection method is developed and used to generate a database of occurrences. Occurrences are used to calculate EPB drift speeds and separations. All data is looked at as a whole, including any possible solar or geomagnetic disturbance periods. Seasonality in occurrence rate is evident. Occurrences peak during December solstice and minimize during June solstice for longitudes seen by GOLD. Within GOLD's view, higher occurrences are seen to the west during December solstice and to the east during June solstice. EPB drift speeds and separations show consistent distributions regardless of magnetic latitude region, geographic region, or season. This suggests EPBs behave consistently and regularly once formed, at least on spatial scales observed by GOLD.

Investigation of Interhemispheric Asymmetry of the Thermospheric Composition Observed by GOLD During the First Strong Geomagnetic Storm in Solar‐Cycle 25, 1: IMF By Effects

AbstractAn interhemispheric asymmetry of thermospheric Oxygen (O) to Nitrogen (N2) column density ratio (∑O/N2) variations was observed by the Global‐scale Observations of the Limb and Disk (GOLD) during the 3–5 November 2021 geomagnetic storm. ∑O/N2 depletion is more equatorward in the local morning than in the local afternoon in the northern hemisphere (NH), while more equatorward in the local afternoon than the local morning in the southern hemisphere (SH). The Thermosphere Ionosphere Electrodynamics General Circulation Model simulations reproduced the observed ∑O/N2 asymmetry. The impacts of interplanetary magnetic field (IMF) east‐west component (By) on the interhemispheric asymmetry of ∑O/N2 depletion was investigated. Comparisons of simulation results with and without real By show that the dominant positive IMF By results in the Joule heating maximum occurring in the local afternoon of NH and local morning in the SH during the storm initial phase, which generates the corresponding ∑O/N2 changes. Additionally, the IMF By during this storm are more crucial in the SH than in the NH. Without By, equatorward penetration of the ∑O/N2 depletion in GOLD Field of View are almost same in the SH. However, in the NH, there is still more equatorward depletion in the local morning than the local afternoon without By.

Hemispheric Asymmetries in Thermospheric Composition and Temperature: GOLD Observations

AbstractWith the launch of the Global‐scale Observations of the Limb and Disk (GOLD) mission, spatial variations of the thermospheric composition (ΣO/N2) and temperature can be investigated. In this work, we defined the hemispheric asymmetry indexes of thermospheric composition and temperature and investigated their local time (LT), latitude, and seasonal variations. For the first time, it is found that the hemispheric asymmetry of the thermosphere is weaker toward the duskside statistically. In addition, the hemispheric asymmetry of the thermosphere is found to be weaker toward lower latitudes, and the northern hemisphere has a longer duration with lower ΣO/N2 and higher temperature.