Hong Gao

Using TIMED/SABER nightglow observations to investigate hydroxyl emission mechanisms in the mesopause region

Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED)/Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) observations of vertical profiles of the OH nightglow emission rates, temperature, and ozone are used along with a theoretical model of the OH nightglow to distinguish the dominant mechanism for the nightglow. From the comparison between the model fit and the observations we conclude that the chemical reaction O-3 + H -> OH(v OH(v = 4. The analysis also determines the best fits for quenching of OH(v) by O-2 and O. The results show that the quenching rate of OH(v) by O-2 is smaller and that the removal by O is larger than currently used for the analysis of SABER data. The rate constant for OH(v) quenching by O-2 decreases with temperature in the mesopause region. The vertical profiles of atomic oxygen and hydrogen retrieved using both 2.0 and 1.6 mu m channels of Meinel band emission of the OH nightglow and the new quenching rates are slightly smaller than the profiles retrieved using only the 2.0 mu m channel and the quenching rate coefficients currently used for the analysis of SABER data. The fits of the model to the observations were also used to evaluate two other assumptions. The assumption of sudden death quenching of OH by O-2 and N-2 (i.e., quenching to the ground state rather than to intermediate vibrational levels) leads to poorer agreement with the SABER observations. The question of whether the reaction with or quenching by atomic oxygen depends on the OH vibrational level could not be resolved; assumptions of vibrational level dependence and independence both gave good fits to the observed emissions.

Strong longitudinal variations in the OH nightglow

[1]xa0Airglow from the hydroxyl Meinel bands, originating from about 87 km, gives a signature of the atmosphere that can be observed remotely. Analysis of long term global observations of the 2.0 μm OH Meinel brightness observed by the TIMED/SABER satellite instrument presents some striking patterns that appear in the Meinel airglow. The analysis shows that migrating and non-migrating tides have large effects on the nighttime OH airglow emission in the upper mesosphere. The OH airglow emission rate is positively correlated with temperature below 94 km and negatively correlated above. Variations with longitudinal wavenumbers 1 and 4 are shown to result from the impacts of the stationary (D0), westward wavenumber 2 (DW2), and eastward wavenumber 3 (DE3) nonmigrating diurnal tides.

Seasonal and QBO variations in the OH nightglow emission observed by TIMED/SABER

[1] Using TIMED/SABER observations, we present global distribution of the semiannual oscillation (SAO), annual oscillation (AO), and quasi‐biennial oscillation (QBO) in the OH nightglow peak emission rate and height as well as the intensity. The latitudinal variations of the SAO, AO, and QBO in the peak emission rate are similar to those in the intensity. For the peak emission rate and the intensity, the SAO and QBO amplitudes have three peaks (one at the equator and others at about 35°S and 35°N). The AO amplitude peaks at about 20°S and 20°N, respectively. The SAO phase is delayed poleward from the equinoxes at the equator to the solstices at 50°S/N; in addition, the phases of the AO are delayed poleward from 30°S. For the peak height, the SAO and QBO amplitudes have three peaks (around the equator, 40°S, and 40°N). Its AO amplitudes at 50°S and 50°N are larger than those at other latitudes; the phase of the SAO shifts from the solstice at the equator to near the equinoxes at 50°S/N. The airglow QBO is stronger in tropics than midlatitude and is likely the real QBO oscillation at the equator. In addition, the emission in the Southern Hemisphere is weaker than that in the Northern Hemisphere. The SAO and QBO are hemispherically symmetrical, and the AO is hemispherically antisymmetrical at some latitudes. The peak emission rate and peak height SAOs are generally in antiphase. The peak emission rate and intensity SAOs are generally in phase.

The longitudinal variation of the daily mean thermospheric mass density

[1]xa0This study uses the GRACE (Gravity Recovery And Climate Experiment) and CHAMP (CHAllenging Minisatellite Payload) accelerometer measurements from 2003 to 2008. These measurements gave thermospheric mass densities at ~480u2009km (GRACE) and ~380u2009km (CHAMP), respectively. We found that there are strong longitude variations in the daily mean thermospheric mass density. These variations are global and have the similar characteristics at the two heights under geomagnetically quiet conditions (Apu2009<u200910). The largest relative longitudinal changes of the daily mean thermospheric mass density occur at high latitudes from October to February in the Northern Hemisphere and from March to September in the Southern Hemisphere. The positive density peaks locate always near the magnetic poles. The high density regions extend toward lower latitudes and even into the opposite hemisphere. This extension appears to be tilted westward, but mostly is confined to the longitudes where the magnetic poles are located. Thus, the relative longitudinal changes of the daily mean thermospheric mass density have strong seasonal variations and show an annual oscillation at high and middle latitudes but a semiannual oscillation around the equator. Our results suggest that heating of the magnetospheric origin in the auroral region is most likely the cause of these observed longitudinal structures. Our results also show that the relative longitude variation of the daily mean thermospheric mass density is hemispherically asymmetric and more pronounced in the Southern Hemisphere.

Evidence for nonmigrating tides produced by the interaction between tides and stationary planetary waves in the stratosphere and lower mesosphere

In this work, 11years (2002-2012) of Thermosphere, Ionosphere, Mesosphere Energetics, and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) global temperature data are used to study the nonlinear interaction between stationary planetary waves (SPWs) and tides in the stratosphere and mesosphere. The holistic behavior of the nonlinear interactions between all SPWs and tides is analyzed from the point of view of energetics. The results indicate that the intensities of nonmigrating diurnal, semidiurnal, terdiurnal, and 6h tides are strongest during winter and almost vanish during summer, synchronous with SPW activity. Temporal correlations between the SPWs and nonmigrating tides for these four tidal components are strong in the region poleward of 20 degrees and below about 80km. In the tropics, where the SPWs are very weak in all seasons, the correlations are small. Bispectral analysis between triads of waves and tides shows which particular interactions are likely to be responsible for the generation of the nonmigrating tides that are largest in the midlatitude stratosphere. Based on the more limited SABER observations at high latitudes, the correlations there are similar to those in midlatitudes during spring, summer, and autumn; there are no high-latitude observations by SABER in winter. These results show that nonlinear interactions between SPWs and tides in the stratosphere and the lower mesosphere may be an important source of the nonmigrating tides that then propagate into the upper mesosphere and lower thermosphere. Key Points Investigation of relation of nonmigrating tides and stationary planetary waves Amplitudes of these tides and waves in midlatitude stratosphere vary in synch Seasonal variations of migrating tides are not controlled by the interaction

An observational and theoretical study of the longitudinal variation in neutral temperature induced by aurora heating in the lower thermosphere

In this paper, observations by thermosphere, ionosphere, mesosphere energetics and dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry from 2002 to 2012 and by Envisat/Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) from 2008 to 2009 are used to study the longitudinal structure of temperature in the lower thermosphere. In order to remove the longitudinal structure induced by tides, diurnally averaged SABER temperatures are used. For MIPAS data, we use averaged temperatures between day and night. The satellite observations show that there are strong longitudinal variations in temperature in the high-latitude lower thermosphere that persist over all seasons. The peak of the diurnally averaged temperature in the lower thermosphere always occurs around the auroral zone. A clear asymmetry between the two hemispheres in the longitudinal temperature structure is observed, being more pronounced in the Southern than in the Northern Hemisphere. In both hemispheres, the longitudinal variation is dominated by the first harmonic in longitude. The total radiative cooling observed by SABER has a structure in longitude that is similar to that of temperature. Modeling simulations using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model reproduce similar features of the longitudinal variations of temperature in the lower thermosphere. Comparison of two model runs with and without auroral heating confirms that auroral heating causes the observed longitudinal variations. The multiyear averaged vertical structures of temperature observed by the two satellite instruments indicate that the impact of auroral heating on the thermodynamics of the neutral atmosphere can penetrate down to about 105 km.

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. Citation: Gao, H., J. Xu, W. Ward, and A. K. Smith (2011), Temporal evolution of nightglow emission responses to SSW events observed by TIMED/SABER, J. Geophys. Res., 116, D19110, doi:10.1029/2011JD015936.

The responses of the nightglow emissions observed by the TIMED/SABER satellite to solar radiation

The responses of four nightglow emissions, NO emission at 5.3 mu m, O-2 infrared atmospheric band at 1.27 mu m, and OH emissions at 2.0 mu m and 1.6 mu m (referred to as OH2 and OH1 in this study), to solar radiation are studied and compared based on the data observed by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument over 13years. The quantitative relationships between the nightglow emissions and solar radiation are obtained by a linear regression fit using the F-10.7 index. The intensities and the peak heights of the 13year average global mean NO, O-2, OH2, and OH1 nightglows are 270.042.8kR, 106.92.2kR, 133.21.6kR, 217.52.4kR, 123.6 +/- 0.2km, 89.8 +/- 0.05km, 88.1 +/- 0.02km, and 86.6 +/- 0.02km, respectively. Among the four nightglow emissions, the influence of solar radiation on the ones at lower heights is weaker than the ones higher above. The responses of the global mean NO, O-2, OH2, and OH1 nightglow intensities to solar radiation are 176.3 +/- 4.8%/100solar flux units (sfu), 22.2 +/- 1.4%/100sfu, 12.9 +/- 1.1%/100sfu, and 11.4 +/- 1.3%/100sfu, respectively. The intensities and peak emission rates of the four global mean nightglow emissions are highly correlated to solar radiation. The response of the height of the global mean O-2 nightglow peak emission rate to solar radiation is 0.51 +/- 0.08km/100sfu. The responses of NO, OH2, and OH1 nightglow peak heights to solar radiation are not obvious. In addition, the responses of nightglow emissions to solar radiation change with latitude.

Double-layer structure of OH dayglow in the mesosphere

Observations by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics satellite from January 2002 to June 2014 are used to study the vertical structure of OH dayglow. The results indicate for the first time that there is a double-layer structure in the distributions of 12year averaged OH airglow emission, [O-3], and [H] during the daytime. The upper layer of OH dayglow is located in the mesopause region (similar to 88km) at a similar altitude to that of the OH nightglow. The lower layer is situated in the range of 70-85km. Both the peak emission and height of the lower layer increase with local time. The distance between the two layers decreases with local time. At the equator, the lower layer forms at similar to 09:00 LT and lasts for about 8h; during this time the interlayer distance decreases from 13km to 5km. The double-layer structure is more obvious and longer-lived during the equinoxes and at lower latitudes. The double-layer structure of OH dayglow emission is a long-term stable structure and is mainly caused by photochemical processes involving [O-3]. It is also modulated by background atmospheric temperature and [H].

The estimate of the peak density of atomic oxygen between 2000 and 2004 at 52°N

On the basis of the photochemical model for atomic oxygen [OI] 558 nm nightglow emission and an approximate expression for the altitude distribution of the atomic oxygen density in the MLT region at night, we develop a method for deriving the peak density of atomic oxygen in the MLT region from atomic oxygen [OI] 558 nm nightglow intensity. By using this method, the peak density of atomic oxygen is derived from the 558 nm airglow data received at the ISTP SB RAS Geophysical observatory in 2000-2004. The nocturnal variations and the seasonal variations of 558 nm airglow intensity and the derived peak density of atomic oxygen are considered. The results show that nocturnal variation of the 558 nm airglow intensity changes with season and that the monthly mean 558 nm airglow intensity changes with month, showing peaks in March, June and October, and larger values in the winter months The nocturnal and the seasonal variations of the peak density of atomic oxygen are generally similar to those of 558 nm airglow intensity.