Richard H. Picard

Retrieval of mesospheric and lower thermospheric kinetic temperature from measurements of CO2 15 µm Earth Limb Emission under non‐LTE conditions

We present a new algorithm for the retrieval of kinetic temperature in the terrestrial mesosphere and lower thermosphere from measurements of CO2 15 µm earth limb emission. Non-local-thermodynamic-equilibrium (non-LTE) processes are rigorously included in the new algorithm, necessitated by the prospect of satellite-based limb radiance measurements to be made from the TIMED/SABER platform in the near future between 15 km and 120 km tangent altitude. The algorithm requires 20 seconds to retrieve temperature to better than 3 K accuracy on a desktop computer, easily enabling its use in operational processing of satellite data. We conclude this letter with a study of the sensitivity of the retrieved temperatures to parameters used in the non-LTE models, including sensitivity to the rate constant for physical quenching of CO2 bending mode vibrations by atomic oxygen.

MSX satellite observations of thunderstorm-generated gravity waves in mid-wave infrared images of the upper stratosphere

Data from the Midcourse Space Experiment (MSX) has provided the first observations of thunderstorm-generated gravity waves imaged from space. Gravity wave theory predicts that isolated, sufficiently convective thunderstorms can launch waves and create a unique intensity pattern of concentric circles on a radiating surface of constant altitude above such a storm. Among the MSX constant-nadir-angle mid-wave infrared (MWIR) observations, two instances of such patterns have been identified. It was confirmed from meteorological satellite images that highly convective isolated thunderstorms occurred at the locations and times expected.

Simultaneous observations of mesospheric gravity waves and sprites generated by a midwestern thunderstorm

from a central excitation region directly above the storm. During the initial stages of the storm outwardly expanding waves possessed a period of � ≈10 min and wavelength � ≈50 km. Over a 1 h interval the waves gradually changed to longer period � ≈11 min and shorter wavelength � ≈40 km. Over the full 2 h observation time, about two dozen bright sprites generated by the underlying thunderstorm were recorded near the center of the outwardly radiating gravity wave pattern. No distinctive OH brightness signatures uniquely associated with the sprites were detected at the level of 2% of the ambient background brightness, establishing an associated upper limit of approximately A T . 0:5 K for a neutral temperature perturbation over the volume of the sprites. The corresponding total thermal energy deposited by the sprite is bounded by these measurements to be less than ∼1 GJ. This value is well above the total energy deposited into the medium by the sprite, estimated by several independent methods to be on the order of ∼1–10 MJ. c

Energy transport in the thermosphere during the solar storms of April 2002

The dramatic solar storm events of April 2002 deposited a large amount of energy into the Earths upper atmosphere, substantially altering the thermal structure, the chemical composition, the dynam ...

Observations of infrared radiative cooling in the thermosphere on daily to multiyear timescales from the TIMED/SABER instrument

16 17 Abstract. We present observations of the infrared radiative cooling by carbon dioxide (CO2) and 18 nitric oxide (NO) in Earths thermosphere. These data have been taken over a period of 7 years 19 by the SABER instrument on the NASA TIMED satellite and are the dominant radiative cooling 20 mechanisms for the thermosphere. From the SABER observations we derive vertical profiles of 21 radiative cooling rates (W m -3 ), radiative fluxes (W m -2 ), and radiated power (W). In the period 22 from January 2002 through January 2009 we observe a large decrease in the cooling rates, 23 fluxes, and power consistent with the declining phase of solar cycle 23. The power radiated by 24 NO during 2008 when the Sun exhibited few sunspots was nearly one order of magnitude 25 smaller than the peak power observed shortly after the mission began. Substantial short-term 26 variability in the infrared emissions is also observed throughout the entire mission duration. 27 Radiative cooling rates and radiative fluxes from NO exhibit fundamentally different latitude 28 dependence than do those from CO2, with the NO fluxes and cooling rates being largest at high 29 latitudes and polar regions. The cooling rates are shown to be derived relatively independent of 30 the collisional and radiative processes that drive the departure from local thermodynamic 31 equilibrium (LTE) in the CO2 15 μm and the NO 5.3 μm vibration-rotation bands. The observed 32

Photochemical‐dynamical modeling of the measured response of airglow to gravity waves: 1. Basic model for OH airglow

A photochemical-dynamical model for the OH Meinel airglow is developed and used to study the fluctuations in OH emission due to atmospheric gravity waves propagating through the mesosphere. The linear response of the OH Meinel emission to gravity wave perturbations is calculated assuming realistic photochemistry and gravity wave dynamics satisfying Hines (1960) isothermal windless model. The current model differs from prior models in that it considers fluctuations in vibrationally excited hydroxyl populations [OH(ν)] instead of fluctuations in the production rate of OH(ν). Two types of correction terms to the latter class of models are found, one involving advection of excited-state populations by the gravity wave and one involving quenching of OH(ν) by collisions with perturber molecules. Effects of these additional terms are expressed in terms of the so-called Krassovsky ratio η, which relates relative fluctuations in the column intensity measured by a passive optical instrument to relative fluctuations in the ambient temperature. The extra wave advection term is found to be unimportant under typical conditions, but quenching is important and has two major effects: (1) It makes η a vibrational-level-dependent quantity, and (2) it can lower η by more than 50% depending on the wave period. A typical range for η over a reasonably chosen range of wave parameters was found to be from less than 1 up to 9. The measuring instrument was also explicitly considered in the model formulation. Instead of simply assuming that the instrument measured the brightness-weighted temperature, as is commonly done in gravity wave response models, two common instruments for determining temperature from passive column-integrated measurements were explicitly modeled. The instruments modeled consisted of (1) a moderate-resolution instrument, such as a Michelson interferometer, which infers the temperature from the ratio of two rotational lines in a vibrational band (the rotational temperature) and (2) a high-resolution instrument, such as a Fabry-Perot interferometer, which uses the Doppler width of a single line to infer the temperature (the Doppler temperature). For gravity waves with large phase velocity (large-scale waves), calculations by both of these methods are found to be generally in agreement with each other and with the brightness-weighted temperature. However, for gravity waves with small phase velocity (small-scale waves) the two realistic simulations can differ from simulations using the brightness-weighted temperature by as much as 35%. The effect of vertical standing waves is considered by modifying the Hines model to include a rigid ground boundary. It is found that the standing waves have a profound effect on the phase of the gravity wave response. Values of η generated from the model are compared with published ground-based OH Meinel measurements of a quasi-sinusoidal short-period gravity wave by Taylor et al. (1991) from Sacramento Peak, New Mexico, at 15° elevation, as well as with the Svalbard polar-night data of Viereck and Deehr (1989). The agreement was found to be reasonable in both amplitude and phase for standing waves.

CO2 non-local thermodynamic equilibrium radiative excitation and infrared dayglow at 4.3 μm: Application to Spectral Infrared Rocket Experiment data

Infrared radiative excitation in non-local thermodynamic equilibrium (non-LTE) regions of the Earths atmosphere for the v3-mode vibrationally excited states of CO2 under sunlit conditions and the resulting 4.3-μm limb radiance are calculated using a line-by-line (LBL) radiative transfer model. Excited-state population densities and the corresponding vibrational temperature profiles are calculated for the important emitting states using a model which includes radiative absorption and emission as well as various collisional processes. The quenching of O(1D) by N2 has a greater impact on these population densities than has been previously reported in the literature. Integrated radiance in a limb view for the 4.3-μm bands is calculated from the model and compared with sunlit earthlimb measurements obtained by the Spectral Infrared Rocket Experiment (SPIRE). Solar pumping is the dominant excitation process for the 4.3-μm emitting states in the daytime. The major contribution to the total limb radiance for tangent heights of 55–95 km is made by the fluorescent states at approximately 3600 cm−1 which absorb sunlight at 2.7 μm and then emit preferentially at 4.3 μm. The predicted radiance is in good agreement with the SPIRE measurements for all tangent heights in the 50- to 130-km range. This is the first detailed comparison of results of a full line-by-line non-LTE radiative transfer calculation with 4.3-μm earthlimb radiance data.

A model for the response of the atomic oxygen 557.7nm and the OH Meinel airglow to atmospheric gravity waves in a realistic atmosphere

We describe a model for the response of atomic oxygen and hydroxyl airglow to a gravity wave. The airglow models uses a realistic atmospheric-gravity-wave model, describing the wave velocity and pressure fluctuations in the presence of a nonisothermal background temperature profile and background winds. The gravity-wave model is coupled to the OH photochemical model of Makhlouf et al. [1995] and to a simple chemical model for the 557.7 nm airglow as described below. It is shown that the chemistry of the 557.7 nm airglow does not affect the phase of the Krassovsky η, due to the short chemical lifetime of the O(1S) and the O2(c ∑u−) precursor states, whereas for the OH airglow the chemistry and dynamics couple for wave periods of 10–25 min, and chemistry does affect the phase of η. The effect of standing waves and traveling waves on the phase of η is shown to be different, and this behavior can be used to differentiate between freely propagating waves and ducted waves. These effects are illustrated by applying the model to examples of Airborne Lidar and Observations of Hawaiian Airglow (ALOHA-93) campaign data. A combination of model prediction and ground-based measurements from the ALOHA-93 campaign are used to estimate the vertical eddy diffusivity Dzz due to nonlinear gravity waves following the formulation of Weinstock [1976]. The estimated values of Dzz vary between 1.0 × 102 and 5.0 × 103 m2/s, which is in the range of measured and inferred values.

Sudden narrow temperature‐inversion‐layer formation in ALOHA‐93 as a critical‐layer‐interaction phenomenon

A sudden and dramatic mesospheric heating event was observed over Haleakala, Maui, on October 21, 1993 (day 294), during the ALOHA-93 Campaign. It consisted of a persistent, narrow temperature-inversion layer about 3-4 km wide near 87 km altitude with a peak temperature rise approaching 40 k, lasting for about 3.5 hours. Owing to the large number of ground-based instruments recording the event, it is possible to attempt to seek out a physical explanation for this temperature rise. There is powerful evidence to suggest that the temperature-inversion layer is associated with energy deposition, direct and indirect, resulting from gravity wave/critical layer interaction. Indeed, lidar wind profiles and mesospheric wave structures simultaneously observed with CCD imagers reveal the presence of a critical layer at the appropriate altitude. The data also show a narrow unstable background wind profile over a 2-3 km thickness in the immediate vicinity of the critical layer. We will show quantitatively that there is sufficient energy available from the dissipation of the observed gravity wave and from the observed instability in the background winds to account for the heating. After the critical layer has disappeared, the temperature rise subsides, and the background wind again becomes stable at all height levels of interest.

Retrieval of kinetic temperature and carbon dioxide abundance from nonlocal thermodynamic equilibrium limb emission measurements made by the SABER experiment on the TIMED satellite

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment was launched onboard the TIMED satellite in December, 2001. SABER is designed to provide measurements of temperature, constituents, and the key radiative and chemical sources and sinks of energy in the mesosphere and lower thermosphere (MLT). SABER measures Earth limb emission in 10 broadband radiometer channels ranging from 1.27 μm to 17 μm. Measurements are made both day and night over the latitude range from 52°S to 83°N with alternating hemisphere coverage every 60 days. In this paper we concentrate on retrieved profiles of kinetic temperature (Tk) and CO2 volume mixing ratio (vmr), inferred from observed 15 μm and 4.3 μm limb emissions. SABER-measured limb radiances are in non-local thermodynamic equilibrium (non-LTE) in the MLT region. The complexity of non-LTE radiation transfer combined with the large volume of data measured by SABER requires new retrieval approaches and radiative transfer techniques to accurately and efficiently retrieve the data products. In this paper we present the salient features of the coupled non-LTE Tk/CO2 retrieval algorithm, along with preliminary results.