Thermosphere Ionosphere Mesosphere Energetics And Dynamics Research Articles

Nighttime secondary ozone layer during major stratospheric sudden warmings in specified‐dynamics WACCM

A major stratospheric sudden warming (SSW) strongly impacts the entire middle atmosphere up to the thermosphere. Currently, the role of atmospheric dynamics on polar ozone in the mesosphere‐lower thermosphere (MLT) during SSWs is not well understood. Here we investigate the SSW‐induced changes in the nighttime “secondary” (90–105 km) ozone maximum by examining the dynamics and distribution of key species (like H and O) important to ozone. We use output from the National Center for Atmospheric Research Whole Atmosphere Community Climate Model with “Specified Dynamics” (SD‐WACCM), in which the simulation is constrained by meteorological reanalyses below 1 hPa. Composites are made based on six major SSW events with elevated stratopause episodes. Individual SSW cases of temperature and MLT nighttime ozone from the model are compared against the Sounding of the Atmosphere using Broadband Emission Radiometry observations aboard the NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. The evolution of ozone and major chemical trace species is associated with the anomalous vertical residual motion during SSWs and consistent with photochemical equilibrium governing the MLT nighttime ozone. Just after SSW onset, enhanced upwelling adiabatically cools the polar region from 80 to 100 km and transports low H from below. These conditions promote a concentration increase in the secondary ozone layer. Subsequent downwelling from the lower thermosphere warms the MLT and enhances the descent of H from the thermospheric reservoir, thereby limiting the secondary ozone concentration increase. Negative correlation of secondary ozone with respect to temperature and H is more pronounced during winters with SSWs than during non‐SSW winters.

Technique to produce daily estimates of the migrating diurnal tide using TIMED/SABER and EOS Aura/MLS

A technique to explicitly compute the day-to-day variability of the migrating diurnal tide (DW1) between 20km and 80km on a global scale is presented and analyzed. Our method employs temperature data from two satellite instruments: the MLS (Microwave Limb Sounder) instrument on the EOS (Earth Observing System) Aura spacecraft and the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on the TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) spacecraft. By taking advantage of the four daily solar local time measurements from the two instruments, a least squares fit representing the DW1 is constructed. Consequently, the daily zonal mean, DW1 amplitude and phase are all estimated on a daily basis. Before the implementation of our technique, a comparative analysis between the instrument data sets is conducted. The analysis reveals temperature biases of up to 10K, which are removed to improve our estimates. To evaluate performance, our method is applied to a model atmosphere constructed from tidal fields obtained from the Global Scale Wave Model (GSWM). Performance results indicate that the DW1 is most effectively extracted from the background atmosphere and other tidal components when each latitude circle is well sampled and the local time sampling is evenly spaced. A comparison of our results to the GSWM and past observations support the conclusion that our method produces daily estimates of the DW1 that can be utilized for scientifically useful investigations of short term tidal variability.

Is Space Weather Different Over Africa, and If So, Why? An AGU Chapman Conference Report

Key Points Chapman Conference Meeting Report

Atomic oxygen in the mesosphere and lower thermosphere derived from SABER: Algorithm theoretical basis and measurement uncertainty

Atomic oxygen (O) is a fundamental component in chemical aeronomy of Earth's mesosphere and lower thermosphere region extending from approximately 50 km to over 100 km in altitude. Atomic oxygen is notoriously difficult to measure, especially with remote sensing techniques from orbiting satellite sensors. It is typically inferred from measurements of the ozone concentration in the day or from measurements of the Meinel band emission of the hydroxyl radical (OH) at night. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite measures OH emission and ozone for the purpose of determining the O‐atom concentration. In this paper, we present the algorithms used in the derivation of day and night atomic oxygen from these measurements. We find excellent consistency between the day and night O‐atom concentrations from daily to annual time scales. We also examine in detail the collisional relaxation of the highly vibrationally excited OH molecule at night measured by SABER. Large rate coefficients for collisional removal of vibrationally excited OH molecules by atomic oxygen are consistent with the SABER observations if the deactivation of OH(9) proceeds solely by collisional quenching. An uncertainty analysis of the derived atomic oxygen is also given. Uncertainty in the rate coefficient for recombination of O and molecular oxygen is shown to be the largest source of uncertainty in the derivation of atomic oxygen day or night.

Global distribution of pauses observed with satellite measurements

Several studies have been carried out on the tropopause, stratopause, and mesopause (collectively termed as ‘pauses’) independently; however, all the pauses have not been studied together. We present global distribution of altitudes and temperatures of these pauses observed with long-term space borne highresolution measurements of Global Positioning System (GPS) Radio Occultation (RO) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) aboard Thermosphere-IonosphereMesosphere Energetics and Dynamics (TIMED) satellite. Here we study the commonality and differences observed in the variability of all the pauses. We also examined how good other datasets will represent these features among (and in between) different satellite measurements, re-analysis, and model data. Hemispheric differences observed in all the pauses are also reported. In addition, we show that asymmetries between northern and southern hemispheres continue up to the mesopause. We analyze inter and intra-seasonal variations and long-term trends of these pauses at different latitudes. Finally, a new reference temperature profile is shown from the ground to 110 km for tropical, mid-latitudes, and polar latitudes for both northern and southern hemispheres.

The effect of the 135.6 nm emission originated from the ionosphere on the TIMED/GUVI O/N2 ratio

The column number density ratio of atomic oxygen to molecular nitrogen (O/N2 ratio) provided by the Global Ultraviolet Imager (GUVI) onboard the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite has been used as a diagnostic of the thermospheric neutral composition. However, a recent study claimed that the GUVI O/N2 ratio is not a pure thermospheric parameter in low latitudes during periods of low geomagnetic activity. This study quantifies the O/N2 ratio contamination by the ionosphere using the GUVI observations and model ionosphere acquired from 31 August to 2 September 2002. During this period, the local time of the GUVI observation was near 1500 and the average Kp index was 2°. The 135.6 nm emission originated from the ionosphere is estimated using the electron density profiles provided by the Utah State University‐Global Assimilation of Ionospheric Measurements model. Our results show that the 135.6 nm emission originated from the equatorial ionization anomaly (EIA) contributes 5 ~ 10% to the total 135.6 nm intensity and O/N2 ratio. The EIA feature and longitudinal wave patterns in the GUVI 135.6 nm intensity maps are identified above an altitude of 300 km and show a good agreement with those in the F region plasma density. However, the EIA feature and longitudinal wave patterns do not appear in the GUVI 135.6 nm intensity maps below an altitude of 300 km and in the GUVI N2 Lyman‐Birge‐Hopfield band intensity maps in any altitude. These observations indicate that the longitudinal wave patterns in the GUVI O/N2 ratio represent the ionospheric phenomenon.

Ion-neutral coupling during deep solar minimum

The equatorial ionosphere under conditions of deep solar minimum exhibits structuring due to tidal forces. Data from instruments carried by the Communication/Navigation Outage Forecasting System (C/NOFS) which was launched in April 2008 have been analyzed for the first 2 years following launch. The Planar Langmuir Probe (PLP), Ion Velocity Meter (IVM) and Vector Electric Field Investigation (VEFI) all detect periodic structures during the 2008–2010 period which appear to be tides. However when the tidal features detected by these instruments are compared, there are distinctive and significant differences between the observations. Tides in neutral densities measured by the Gravity Recovery and Climate Experiment (GRACE) satellite were also observed during June 2008. In addition, Broad Plasma Decreases (BPDs) appear as a deep absolute minimum in the plasma and neutral density tidal pattern. These are co-located with regions of large downward-directed ion meridional velocities and minima in the zonal drifts, all on the nightside. The region in which BPDs occur coincides with a peak in occurrence rate of dawn depletions in plasma density observed on the Defense Meterological Satellite Program (DMSP) spacecraft, as well as a minimum in radiance detected by UV imagers on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) and IMAGE satellites.

Empirical STORM-E model: II. Geomagnetic corrections to nighttime ionospheric E-region electron densities

Auroral nighttime infrared emission observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) satellite is used to develop an empirical model of geomagnetic storm enhancements to E-region electron densities. The empirical model is called STORM-E and will be incorporated into the 2012 release of the International Reference Ionosphere (IRI). The proxy for characterizing the E-region response to geomagnetic forcing is NO+(v) Volume Emission Rates (VER) derived from the TIMED/SABER 4.3μm channel limb radiance measurements. The storm-time response of the NO+(v) 4.3μm VER is most sensitive to auroral particle precipitation. A statistical database of storm-time to climatological quiet-time ratios of SABER-observed NO+(v) 4.3μm VER are fit to widely available geomagnetic indices using the theoretical framework of linear impulse-response theory. The STORM-E model provides a dynamic storm-time correction factor to adjust a known nighttime quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. Part I of this series gives a detailed description of the algorithms and methodologies used to derive NO+(v) VER from SABER 4.3μm limb emission measurements. In this paper, Part II of the series, the development of the E-region electron density storm-time correction factor is described. The STORM-E storm-time correction factor is fit to a single geomagnetic index. There are four versions of the STORM-E model, which are currently independent of magnetic local time. Each version is fit to one of the following indices: HP, AE, Ap, or Dst. High-latitude Incoherent Scatter Radar (ISR) E-region electron density measurements are compared to STORM-E predictions for various geomagnetic storm periods during solar cycle 23. These comparisons show that STORM-E significantly improves the prediction of E-region electron density enhancements due to auroral particle precipitation, in comparison to the nominal IRI model or to the quiet-time baseline electron density concentrations measured by ISR. The STORM-E/ISR comparisons indicate that the STORM-E fits to the Ap-, AE-, and HP-indices are comparable in both absolute accuracy and relative dynamical response. Contrarily, the Dst-index does not appear to be a suitable input driver to parameterize the E-region electron density response to geomagnetic activity.

Empirical STORM-E model: I. Theoretical and observational basis

Auroral nighttime infrared emission observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) satellite is used to develop an empirical model of geomagnetic storm enhancements to E-region peak electron densities. The empirical model is called STORM-E and will be incorporated into the 2012 release of the International Reference Ionosphere (IRI). The proxy for characterizing the E-region response to geomagnetic forcing is NO+(v) volume emission rates (VER) derived from the TIMED/SABER 4.3μm channel limb radiance measurements. The storm-time response of the NO+(v) 4.3μm VER is sensitive to auroral particle precipitation. A statistical database of storm-time to climatological quiet-time ratios of SABER-observed NO+(v) 4.3μm VER are fit to widely available geomagnetic indices using the theoretical framework of linear impulse-response theory. The STORM-E model provides a dynamic storm-time correction factor to adjust a known quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. Part II of this series describes the explicit development of the empirical storm-time correction factor for E-region peak electron densities, and shows comparisons of E-region electron densities between STORM-E predictions and incoherent scatter radar measurements. In this paper, Part I of the series, the efficacy of using SABER-derived NO+(v) VER as a proxy for the E-region response to solar-geomagnetic disturbances is presented. Furthermore, a detailed description of the algorithms and methodologies used to derive NO+(v) VER from SABER 4.3μm limb emission measurements is given. Finally, an assessment of key uncertainties in retrieving NO+(v) VER is presented.

A discussion on the assumption of ambipolar diffusion of meteor trails in the Earth's upper atmosphere

Abstract For the first time, height profiles of meteor trail decay time due to the ambipolar diffusion process are estimated using temperature and pressure measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on-board Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. The comparison of the meteor trail decay time measured by a meteor radar over Thumba (8°.5 N, 77°E) and SABER offered very valuable insights into the meteor trail decay processes and also provided much needed validation for assumption of ambipolar diffusion of meteor trails. It is observed that the assumption of ambipolar diffusion is valid in the height region of 90–96 km only where both SABER and radar measurements show excellent agreement in meteor trail decay time. The present analysis also shows that there are other processes which govern the meteor trail decay in the 80–90 km region, where large deviations are found between radar and SABER measurements. The differences between the SABER- and radar-observed decay times are quantified, and the processes responsible for the observed differences are also discussed extensively in the light of present understanding. The important outcome of the present study is the validation of assumption on ambipolar diffusivity of the meteor trails, which has significant implications in estimating the temperature using meteor trail decay time.

The emission of oxygen green line and density of O atom determined by using ISUAL and SABER measurements

Abstract. Emissions of the 557.7 nm green line airglow observed by the ISUAL (Imager of Sprites and Upper Atmospheric Lightning) instrument on board the FORMOSAT-2 satellite in May and November 2008 are studied here to derive the density distributions of the atomic oxygen by using atmospheric parameters from MSISE-00 model and TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics)/SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) measurements. The May observations were made in 10 days from a fixed orbit of longitude (100° E) with the results showing emission rate and O atom density both peaked at heights of about 90 km over 10° to 20° latitudes in the Northern Hemisphere (NH). In the Southern Hemisphere (SH), the emission rate and density of O atom are both low compared with those in NH. In November, the observations were made as the satellite traveled over all 14 orbits around the earth, covering all longitudes and latitudes of 25° S–45° N. Strong peaks of emission rates and O atoms are found at heights of about 95 km in the mid-latitudes in both hemispheres. In the equator, the airglow layer has a weaker emission rate but with higher altitude compared with those of mid-latitudes. In the lower and upper mesosphere at heights below 85 km and above 105 km, there are more O atoms in the equatorial regions than in the mid-latitudes. And there is a good correlation between the O atom and the temperature structure. A comparison with O atom distribution derived from OH airglow observed by TIMED/SABER at about the same time shows similar results.

Global structure and variation of mesospheric and lower thermospheric zonal wind in 120 °E meridian

Multiyear (2002-2011) wind observations from TIMED Doppler Interferometer (TIDI) onboard the thermosphere ionosphere mesosphere energetics and dynamics (TIMED) satellite are used for studying the typical structures and variations of mesospheric and lower thermospheric (MLT) mean zonal wind from 80 to 105 km in 120 °E meridian. Comparisons between TIDI measurements and empirical models indicate that TIDI is in good agreement with models in the extratropic regions especially in the middle and high latitudes, but significant differences occur mainly in the tropic regions. In the altitudes of TIDI's coverage from 80 to 105 km, monthly zonal winds are always westward over the tropical regions, forming an easterly band centered at the equator. Results from multiyear observations show complicated variations in the MLT tropical easterlies. The averaged width of easterlies is 37.5 degrees and corresponding variation is about 14 degrees.

A study of space shuttle plumes in the lower thermosphere

[1] During the space shuttle main engine burn, some 350 t of water vapor are deposited at between 100 and 115 km. Subsequent photodissociation of water produces large plumes of atomic hydrogen that can expand rapidly and extend for thousands of kilometers. From 2002 to 2007, the Global Ultraviolet Imager (GUVI) on NASA's Thermosphere Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite imaged many of these hydrogen plumes at Lyman α (121.567 nm) while viewing in the nadir. The images reveal rapid plume expansion and occasional very fast transport to both north and south polar regions. Some plumes persist for up to 6 d. Near-simultaneous direct detections of water vapor were made with the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) instrument, also on TIMED. We compare the spreading of the hydrogen plume with a two-dimensional model that includes photodissociation as well as both vertical and horizontal diffusion. Molecular diffusion appears to be sufficient to account for the horizontal expansion, although wind shears and turbulent mixing may also contribute. We compare the bulk motion of the observed plumes with wind climatologies derived from satellite observations. The plumes can move much faster than predictions of wind climatologies. But dynamical processes not contained in wind climatologies, such as the quasi-two-day wave, can account for at least some of the high speed observations. The plume phenomena raise a number of important questions about lower thermospheric and mesospheric processes, ranging from dynamics and chemistry to polar mesospheric cloud formation and climatology.

Search for indications of stellar mass ejections using FUV spectra

Aims. We search for highly energetic activity phenomena in a small sample of late-type main-sequence stars in the far ultraviolet (FUV) using data from the Far Ultraviolet Spectroscopic Explorer (FUSE). Methods. Because FUSE allows a simultaneous photometric and spectroscopic analysis, we are able to analyze variations in the light curves (flares) and possible, activity-related signatures (line asymmetries, enhancements, and shifts) in the spectra. Furthermore, the computation of the well-known density-sensitive line ratio C iii(λ1176 A)/C iii(λ977 A) is also possible, and allows the investigation of its dependence on stellar activity. Results. Three late-type main-sequence stars found in the FUSE archive (HD 36705, HD 197481, and Gl 388) show flares in their light curves. We find no obvious Doppler shifts in the brightest lines of these stars, but the O vi(λ1032 A) transition region line of AD Leo shows a blue wing enhancement one spectrum after a flare event. This emission feature is shifted by ∼–84 km s −1 from the line core. We can exclude that the spectral feature was caused by a gas cloud co-rotating with the star and favor an interpretation of a mass ejection. In addition we find an increase of the C iii(λ1176 A)/C iii(λ977 A) line ratio during all detected flares. We compare this finding to the Sun using solar full-disk spectra from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) and SOlar Radiation and Climate Experiment (SORCE) missions, and find that powerful flare events also show an increased C iii(λ1176 A)/C iii(λ977 A) line ratio but this result is of low statistical significance. Owing to a lack of perfectly temporally coinciding TIMED/SORCE spectra and a low temporal resolution (∼15 spectra per day) it is not possible to distinguish clearly if this increase is caused by the flares or by the related mass ejections.

Origin of a tidal structure in the thermospheric O/N2 ratio

One recently recognized way of studying the ionospheric and thermospheric structure is through measurements of the column number density ratio of atomic oxygen to molecular nitrogen (O/N2). Data from the Global Ultraviolet Imager on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite show that this ratio exhibits a tidal structure. Kil and Paxton found that the 135.6‐nanometer emission produced by the radiative recombination of the oxygen ion contributes to the retrieved O/N2 ratio, and therefore the tidal structure in the O/N2 ratio originates in the ionosphere, not the thermosphere. (Geophysical Research Letters, doi:10.1029/2011GL049432, 2011)

Temporal evolution of nightglow emission responses to SSW events observed by TIMED/SABER

[1] Using the SSW (Stratospheric Sudden Warming) event in 2009 as a representative case, the temporal evolution of the responses of OH and O2 infrared atmospheric (0–0) nightglow emissions to SSW events is analyzed using the TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics)/SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) data. The results show that during the mesospheric cooling that occurs during the stratospheric warming stage of SSW events, the brightness of OH and O2 nightglow emissions and the thicknesses of OH and O2 emission layers decrease noticeably and the peak heights of the emissions ascend. During the recovery stage in the mesosphere, the brightness of both nightglow emissions and the thicknesses of the emission layers increase dramatically and the peak heights of the emissions descend. These emission variations are mainly caused by perturbations in temperature and the transport of O in the MLT (Mesosphere Lower Thermosphere) region. For the SSW event that started in January 2009, the onset times of the cooling stage and recovery stage in the mesosphere are ∼2 days ahead of the onset times of the warming stage and recovery stage of the SSW event, respectively. For this event, the influence of the SSW on the OH and O2 nightglow emissions increases with latitude between 50°N and 80°N.

Seasonal variability of the diurnal tide in the mesosphere and lower thermosphere over Maui, Hawaii (20.7°N, 156.3°W)

[1] The seasonal variability of the diurnal tide in the mesosphere and lower thermosphere over Maui, Hawaii (20.7°N, 156.3°W), is investigated using meteor radar horizontal wind measurements from the years 2002 to 2007. The semiannual oscillation (SAO) of tidal amplitudes is dominant above ∼88 km, with amplitudes at equinoxes 2–3 times larger than at solstices. Below 88 km, the annual oscillation (AO) dominates, and its magnitude is smaller than the SAO. The AO dominates in the phase variation of the diurnal tide, which advances in winter and lags in summer as compared with equinoxes. The vertical wavelength also has a noticeable seasonal variation with shorter vertical wavelengths found at equinoxes. The reconstructed diurnal tide from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) Doppler interferometer (TIDI) and Sounding the Atmosphere using Broadband Emission Radiometry (SABER) measurements is compared with the meteor radar observation, and a consistency is found in the seasonal variation of the tidal amplitude. On the basis of the TIDI and SABER measurements, the migrating diurnal tide (DW1) is the dominant tidal component, while three other nonmigrating tides, DW2, DS0, and DE3, are nonnegligible. The seasonal variation of the diurnal tide is well captured by the global scale wave model and the Whole Atmosphere Community Climate Model, although important discrepancies still exist.

TIMED/GUVI observation of solar illumination effect on auroral energy deposition

[1] It has been established that the local nighttime aurora is more intense in winter or darkness than in summer or sunlight. Here we expand previous work to confirm empirical relationships between energy flux and average energy of aurora and solar zenith angle (SZA) and ionospheric photoconductance by analyzing ∼6 years (2002–2007) of FUV auroral images acquired from the Global Ultraviolet Imager (GUVI) on board NASA's Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite. The total number of auroral images, north and south combined, is 55,675. The B3C auroral transport code is used to extract auroral parameters, assuming pure electron precipitation. It is found that the mean energy and energy flux carried by precipitating electrons (>0.25 erg/cm2 s) increase monotonically with SZA for SZA less than ∼108° (corresponding to an EUV shadow height of ∼430 km). The rate of increase is most pronounced in the premidnight sector, where the energy flux rate is ∼0.04 erg/cm2 s/deg and the mean energy rate is ∼0.02 keV/deg. The auroral power is anticorrelated with the ionospheric Pedersen photoconductance for all local times, with the steepest drop (−0.2 gw/mho) in the midnight sector. These results are stronger than those for the simple cases of “sunlight” versus “darkness” and/or “summer” versus “winter” used in previous work for the solar illumination effect. While the present result cannot distinguish known mechanisms, we suggest that more than one mechanism is responsible for the observed sunlight effect.

The temperature structure of the mesosphere over Taiwan and comparison with other latitudes

[1] We present here a detailed investigation of the mesospheric temperature structure over Taiwan, a subtropical location, using 9 years of observations (March 2002 to October 2010) by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite. The mesopause (MP) is always found to be located at a higher level with a mean altitude of 98.2 ± 1.8 km and mean temperature of 165.0 ± 5.8 K. The climatological study shows that MP is lower and warmer during summer and higher and cooler during winter, which is different from the midlatitudes and high latitudes as well as from low latitudes. The temperatures of the mesospheric temperature inversions (MTI) and secondary minimum (SM), on the other hand, are lower during summer and higher during winter, and their altitudes do not show any annual variation. It is found that the thermal structure over Taiwan undergoes a phase shift between 89 and 95 km, and above this region it is in phase with the solar flux. Since MP is always above these altitudes, it shows a seasonal variation that is in phase with the solar energy inputs, and the temperatures below (that of MTI and SM) show the opposite seasonal variation caused by mesospheric adiabatic cooling and warming processes.

The O I 135.6 nm airglow observations of the midlatitude summer nighttime anomaly by TIMED/GUVI

[1] This study presents the O I 135.6 nm airglow observation of the middle-latitude electron density enhancement during local summer nighttime by Global Ultraviolet Imager (GUVI) on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft. The nighttime density enhancement at magnetic middle latitudes in the Southern Hemisphere, known as the Weddell Sea Anomaly (WSA), had been studied by using multipoint observations, and a similar anomalous nighttime enhancement was also found in the Northern Hemisphere recently. The resemblance of both anomalies at magnetic middle latitudes in the Northern and Southern Hemispheres suggests that they should be categorized as the midlatitude summer nighttime anomaly (MSNA). To further explore the three-dimensional structure of the MSNA and its day-to-day variation, the two-dimensional global radiance maps and the vertical electron density profiles derived from disk and limb scans of the TIMED/GUVI 135.6 nm airglow observations are utilized in this study. These global observations show that the northern MSNA mainly occurs in Asia, Europe, and the North Atlantic Ocean regions, while the southern MSNA occurs in the South America-Antarctica region, near the WSA region. The GUVI day-to-day observations in 2006 further illustrate that the southern MSNA appears nightly in January-February and November-December, while the northern MSNA appears in 36 out of 41 total observation nights in May-June.