Jeng-Hwa Yee

Global simulations and observations of O(1S), O2(1Σ) and OH mesospheric nightglow emissions

Despite a large number of observations of mesospheric nightglow emissions in the past, the quantitative comparison between theoretical and experimental brightnesses is rather poor, owing primarily to the short duration of the observations, the strong variability of the tides, and the influence of short-timescale gravity waves. The high-resolution Doppler imager (HRDI) instrument onboard the upper atmosphere research satellite (UARS) provides nearly simultaneous, near-global observations of O( 1 S) green line, O 2 (0-1) atmospheric band, and OH Meinel band nightglow emissions. Three days of these observations near the September equinox of 1993 are presented to show the general characteristics of the three emissions, including the emission brightness, peak emission altitude, and their temporal and spatial variabilities. The global distribution of these emissions is simulated on the basis of atmospheric parameters from the recently developed National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM). The most striking features revealed by the global simulation are the structuring of the mesospheric nightglow by the diurnal tides and enhancements of the airglow at high latitudes. The model reproduces the inverse relationship observed by HRDI between the nightglow brightness and peak emission altitude. Analysis of our model results shows that the large-scale latitudinal/tidal nightglow brightness variations are a direct result of a complex interplay between mesospheric and lower thermospheric diffusive and advective processes, acting mainly on the atomic oxygen concentrations. The inclination of the UARS spacecraft precluded observations of high latitude nightglow emissions by HRDI. However, our predicted high-latitude brightness enhancements confirm previous limited groundbased observations in the polar region. This work provides an initial validation of the NCAR-TIMEGCM using airglow data.

Observations of the 6.5‐day wave in the mesosphere and lower thermosphere

Previous observations of atmospheric oscillations with zonal wave number 1 have consistently located waves of periods between 5 and 7 days. This study presents a global and seasonal analysis of the 6.5-day wave in High Resolution Doppler Imager daytime mesosphere and lower thermosphere horizontal winds, temperatures, and nighttime atomic oxygen at 95 km. The horizontal structures of all these atmospheric variables are similar to the gravest symmetric wave number 1 Rossby wave, i.e., the (1,1) mode. The seasonal and spatial analysis displays possible modification by the zonal mean wind. Finally, the observed vertical structures of the 6.5-day wave indicate that it is an internal Rossby wave, not an external or Lamb wave.

Remote sensing of mesospheric temperature and O2(1Σ) band volume emission rates with the high-resolution Doppler imager

An algorithm for obtaining temperatures and volume emission rate profiles in the mesosphere and lower thermosphere from HRDI measurements is described. Temperature and volume emission rates are derived via perturbation theory by comparing measured brightness to brightness computed from the forward model described here. Error analysis shows that the method recovers the temperatures with an error of 7° K and volume emission rates with an error of 3% from 80 to 100 km, providing global measurements of these fields in this altitude range for the first time. Results show the structure of the cold summer mesopause near the poles, the semiannual oscillation, and the diurnal tidal oscillations at the equator.

Simultaneous measurements of the O2(¹Δ) and O2(¹Σ) Airglows and ozone in the daytime mesosphere

We report simultaneous measurements of the O2(¹Δ) and O2(¹Σ) airglow volume emission rate profiles in the daytime mesosphere. We use these measurements to derive ozone concentrations separately from each airglow. The measurements were made as part of the Mesosphere-Thermosphere Emissions for Ozone Remote Sensing (METEORS) sounding rocket project launched from White Sands Missile Range, New Mexico. These data offer the opportunity to assess the consistency of ozone profiles derived from measurements of the oxygen airglows and thus provide a fundamental test of our understanding of dayglow physics and solar energy deposition. In both airglow-derived profiles the ozone decreases with altitude throughout the middle mesosphere and a pronounced secondary maximum exists near 90 km. The derived ozone profiles are in agreement to within measurement uncertainty. This agreement confirms that the major processes responsible for the generation of mesospheric oxygen dayglow are well understood via measurement.

A Spectral Parameterization of Drag, Eddy Diffusion, and Wave Heating for a Three-Dimensional Flow Induced by Breaking Gravity Waves

Abstract There are three distinct processes by which upward-propagating gravity waves influence the large-scale dynamics and energetics of the middle atmosphere: (i) nonlocalized transport of momentum through wave propagation in three dimensions that remotely redistributes atmospheric momentum in both zonal and meridional directions from wave generation to wave dissipation regions; (ii) localized diffusive transport of momentum, heat, and tracers due to mixing induced by wave breaking; and (iii) localized transport of heat by perturbing wave structures due to dissipation that redistributes the thermal energy within a finite domain. These effects become most significant for breaking waves when momentum drag, eddy diffusion, and wave heating— the “breaking trinity”—are all imposed on the background state. This paper develops a 3D parameterization scheme that self-consistently includes the breaking trinity in large-scale numerical models. The 3D parameterization scheme is developed based on the general relat...

Variations, with peak emission altitude, in auroral O2 atmospheric (1, 1)/(0, 1) ratio and its relation to other auroral emissions

Spectral distributions of auroral optical emissions, peaked at distinctly different heights in the thermosphere, show significant variations, with altitude, in the O2 atmospheric (1, 1)/(0, 1) band ratio. The latter increases with height in auroras peaked between 110 and 150 km and then gradually decreases at higher altitudes. To minimize ambiguities associated with auroral height determination needed for investigating this effect, four independent height-assessment methods are employed. The first one is based on the incoherent scatter radar (ISR) soundings of the auroral ionization profile from which the height, where precipitating particles dissipate most of their energy, can be determined. Concurrent spectroscopic observations of the thermalized rotational distributions of auroral band emissions yield the ambient air temperature, and hence an independent assessment of the height, of the thermospheric region where these emissions peak. Changes in O/O2 and O/N2 ratios with height lead to changes in the ratios of auroral emissions, from these species, peaked at different heights. Finally, changes in collision frequency with height lead to changes in the brightness of the auroral emissions, resulting from radiatively allowed transitions relative to those produced from radiatively forbidden transitions. The four methods yield comparable values for the height of the thermospheric region where emissions, from each auroral event, peak. The observed variations in O2 atmospheric (1, 1)/(0, 1) with auroral height is compared with that expected from O (1D) + O2 excitation source and quenching by O2 and O. The effects of electron impact excitation of O2(b1∑g+, v′) and high rotational levels of the P branch of O2 atmospheric (0, 0) band on O2 atmospheric (1, 1)/(0, 1) ratio are discussed. Quantitative ratios of various auroral emissions, from O, N2, and N+2, peaked at different heights, that can provide an assessment of auroral heights where these emissions peak, are listed.

NO2 air afterglow and O and NO densities from Odin‐OSIRIS night and ACE‐FTS sunset observations in the Antarctic MLT region

[1] The continuum spectrum produced by the NO + O(+M) → NO 2 (+M) + hv chemiluminescent reaction has been detected in the upper mesospheric dark polar regions by Optical Spectrograph and Infra-Red Imager System (OSIRIS) on the Odin spacecraft. For the sample period of 8-9 May 2005, Southern Hemisphere, limb radiance profiles of continuum spectra, resolved from OH airglow and auroral contamination, are inverted to obtain volume emission rate altitude profiles. The maximum observed differential brightness referred to zenith viewing is 1.2 × 10 7 photons cm -2 s -1 nm -1 at 580 nm with a measurement uncertainty 5 × 10 5 photons cm - s -1 nm -1 , for an analysis range 80-101 km. Atomic oxygen densities [O] required by the analysis to derive NO densities [NO] are determined from OSIRIS O 2 (b 1 Σ + g - X 3 Σ - g ) 0-0 band night airglow observations and from Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) sunset ozone observations. The derived Southern Hemisphere [O] map that shows pronounced longitudinal variation, maximum of 7 × 10 11 cm -3 , considerably exceeding MSIS model values, and suggests significant dynamical influence. Combining the continuum observations and the derived [O], a hemispheric map of derived [NO] is assembled that also shows considerable spatial variation, maximum of 1.1 × 10 9 cm 3 measurement uncertainty of 3 × 10 7 cm -3 . Comparing the two maps, the geographical distribution of [NO] differs considerably from that of [O]. From a qualitative comparison, the distribution of derived [NO] is similar to that in coordinated GUVI LBH1 auroral precipitation images. The OSIRIS-derived [NO] agrees with the measured ACE-FTS [NO] to within 1 × 10 8 cm -3 . The estimated systematic uncertainty of the NO densities derived from OSIRIS observations is approximately 30%.

Leonid meteor spectrum from 110 to 860 nm

During the Leonid meteor shower on 18 November 1999, the five spectrographic imagers onboard the Midcourse Space Experiment (MSX) satellite recorded the first complete meteor spectra from 110 to 860 nm. The observation occurred at 00:23:36.2 UT, at which time the satellite was pointed at a tangent altitude of 100 km over 37.2°N and 78.2°E. The spectrograph slits were oriented approximately parallel to the horizon at a tangent altitude of 100 km, and the meteor passed approximately perpendicular through the slits’ fields of view. All five spectrographic imagers observed the passage of a bright object (mv < −2.8 at 100 km) and each recorded several frames of data. In the visible, common meteor emissions were observed from iron, sodium, and oxygen. However, the ultraviolet spectrum displayed a wealth of more intense features, some of which actually caused saturation in the spectrographs. The most intense features appeared between 220 and 300 nm and are attributed to neutral and singly ionized iron and ionized magnesium. Some unknown emissions, possibly from an unidentified molecular species such as iron oxide, appear between 180 and 220 nm. In the far ultraviolet from 110 to 130 nm, oxygen and nitrogen features appear in the spectrum, with some features from ionized iron and magnesium. In particular, the FUV spectrum showed an intense emission from hydrogen Lyman alpha and a much weaker emission from what appeared to be neutral carbon. The atmospheric emissions can be associated with the heating within the meteor shock, while the metallic emissions originate from the fireball of the meteor proper. The ultraviolet emissions were much stronger than those in the visible and near-infrared parts of the spectrum. The energy of emissions in the ultraviolet (110 < λ < 337 nm) exceeded the energy of the visible (337 < λ < 650 nm) by a factor of at least 5.

Effect of short-term solar ultraviolet flux variability in a coupled model of photochemistry and dynamics

Abstract Variability in the solar ultraviolet radiative flux is known to cause changes in the chemistry and dynamics of the middle and upper atmosphere. Specifically, the 27-day solar rotation signal in irradiance has been correlated with responses in temperature and ozone. This study investigates the ozone and temperature responses in the upper stratosphere and mesosphere through analytic formulations and the Johns Hopkins University Applied Physics Laboratory (JHU/APL) 2D chemical–dynamical coupled model. From a simple ozone–temperature coupled analytical model, conditions are derived that would yield the greater sensitivities and negative phase lags in the ozone response as observed in the upper stratosphere. Using the JHU/APL photochemical model, both the diurnal and 27-day solar ultraviolet flux forcings are coupled to examine the effects of localized photochemistry on ozone response. A strong local-time dependence of the ozone response is then systematically explored. The JHU/APL 2D model is integra...

Diagnosis of Dynamics and Energy Balance in the Mesosphere and Lower Thermosphere

Abstract A diagnostic technique has been developed to consistently derive all the dynamical and chemical tracer fields based on one or a few well-measured fields such as temperature and ozone distributions. The technique is based on the new Johns Hopkins University/Applied Physics Laboratory (JHU/APL) globally balanced 2D diagnostic model that couples the dynamics with photochemistry. This model is especially useful for studying the mesosphere and lower thermosphere where dynamics, radiation, and photochemistry strongly interact. The novelty of the diagnostic model is to derive the wave drag and eddy diffusion coefficient directly from the better-defined thermal forcing with its major contributions derived from the zonal mean components. The latter is also affected by the advective and diffusive transports. The derived tracer distributions together with input field(s) provide the necessary radiative and chemical heating rates for the calculation of the thermal forcing. Two numerical experiments with diffe...