Ramesh D. Sharma

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 ...

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.

Production of vibrationally and rotationally excited NO in the night time terrestrial thermosphere

A quantitative interpretation is given of the observed quiescent nighttime radiance of nitric oxide in the fundamental vibration-rotation band near 5.3 μm. The radiance measured in the space shuttle experiment Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS-1A) is known to have two components, one characterized by a thermal population of rotational levels and the other by a highly excited rotational population. The analysis presented here confirms that the thermal population is due to impact excitation of NO by atomic oxygen and attributes the highly excited distribution to the reaction of N(4S) atoms with O2. The measured nighttime emission profile is compared with predictions for several model atmospheres. Both sources of excited NO depend upon the latitude, longitude, local time, and geomagnetic indices. The fraction of vibrationally excited NO produced by the reaction of N(4S) with O2 increases rapidly with altitude from 130 to 200 km and its contribution to cooling, though much less than that from inelastic excitation of NO(v=0) is, at higher altitudes, comparable to cooling produced by the atomic oxygen fine-structure line at 63 μm.

Model of the 5.3 μm radiance from NO during the sunlit terrestrial thermosphere

This paper models the fundamental vibration-rotation band emission from NO around 5.3 μm observed by the interferometer aboard the cryogenic infrared radiance instrumentation for shuttle (CIRRIS 1A) during the sunlit terrestrial thermosphere. The four dominant contributions to the 5.3 μm emission are solar pumping, the inelastic collisions with O of NO(v=0), the reactions of N(2D) with O2, and the reactions of N(4S) with O2. The contribution to the chemiluminescence due to the reaction of N(4S) with O2 is calculated using the energy distribution function (EDF) of these atoms obtained by solving the time dependent Boltzmann equation. The calculated radiance is derived using two model atmospheres: (1) the model atmosphere obtained from the atmospheric ultraviolet radiance integrated code (AURIC) [Strickland et al., 1998] and (2) the model atmosphere obtained from the thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) [Roble and Ridley, 1994]. The calculated results reproduce gross features of the CIRRIS 1A observations, and disagreement by a factor of ∼2 in the total band radiance calls for a fine tuning of the model atmospheres and/or the underlying phenomenology. The cooling of the atmosphere at high altitudes due to chemiluminescence from the reaction of N(4S) with O2 is found to be comparable to that due to collisions of NO with O.

Interpretation of infrared measurements of the high-latitude thermosphere from a rocket-borne interferometer

Abstract A preliminary analysis of high-resolution infrared spectra of the aurorally dosed lower thermosphere above Poker Flat Research Range (PFRR), Alaska, obtained by an uplooking cryogenic field-widened interferometer (FWI) is presented. Both models and spectral-fitting/resolution-enhancement methods are used to discuss the behavior of NO, CO, NO + , and CO 2 v 3 vibrational bands in the high-latitude thermosphere.

Quasiclassical Trajectory Study of NO Vibrational Relaxation by Collisions with Atomic Oxygen

Room-temperature and temperature-dependent thermal rate constants are calculated for the state-to-state vibrational relaxation of NO(v ⩽ 9) by atomic oxygen using the quasiclassical trajectory method and limited ab initio information on the two lowest O + NO potential-energy surfaces which are responsible for efficient vibrational relaxation. Comparisons of the theoretical results with the available experimental measurements indicate reasonable agreement for the deactivation of NO(v = 2, 3) at 300 K and NO(v = 1) at 2700 K, although the calculated relaxation rate constant for NO(v = 1) at 300 K is approximately a factor of two below the measured value. The state-to-state relaxation rate coefficients involve the formation of long-lived collision complexes and indicate the importance of multiquantum vibrational relaxation consistent with statistical behaviour in O + NO collisions. The present results, combined with recent measurements of vibrational relaxation for NO(v = 2, 3), suggest that the current atmospheric models of NO cooling rates require higher atmospheric temperatures and/or an increase in the NO/O number densities.

Cooling Mechanisms of the Planetary Thermospheres: The Key Role of O Atom Vibrational Excitation of CO2 and NO

Cooling due to infrared emissions from O atom excited CO2 and NO is a critically important process in the thermal budget of the terrestrial thermosphere. Increasing CO2 density due to human activity makes the role of its emission particularly worthy of quantitative evaluation. Furthermore, the O atom excited 15 microns CO2 emission has a unique role in the lower thermosphere of Venus where it is the only significant cooling mechanism; it is also an important process in the Martian thermosphere. The experimental and theoretical status of these rate coefficients is reviewed and the unsatisfactory current state of knowledge is pointed out.

On the rotational distribution of the 5.3-μm “thermal” emission from nitric oxide in the nighttime terrestrial thermosphere

The rotational distribution of the “thermal” emission from the v = 1 vibrational level of NO, resulting from impacts of NO in the ground vibrational level (v=0) with oxygen atoms, is examined using the cryogenic infrared radiance for shuttle (CIRRIS-1A) database. A block of NO quiescent (nonauroral) nighttime limb radiances observed by the CIRRIS -1A interferometer and radiometer around 5.3 μm are inverted to obtain the local rotational envelopes of the 1→0 vibrational transition as functions of altitude for both spin components. It is found possible to describe these local rotational envelopes by Maxwell-Boltzmann distributions and to obtain rotational temperatures for each spin component of the vibrationally excited NO. The two spin components, within the accuracy of the measurements, are described by the same rotational temperature, which differs, however, from the mass spectrometer incoherent scatter (MSIS) model temperature at most altitudes. At low altitudes (≤110 km), the rotational temperature and the temperature describing the relative population of the spin states of the vibrationally excited NO approach each other, indicating the onset of thermodynamic equilibrium for the spin and the rotational degrees of freedom.

Radiative transfer effects on aurora enhanced 4.3 micron emission

Large enhancements in the 4.3 micron infrared radiance have been observed since the early 1970s. Auroral photochemical models predict large enhancements in the populations of NO+(ν) and CO2 v3 that radiate in the 4.3 micron region. The strong 4.26 micron band of 12C16O2 is largely self-absorbed in the 90–110 km region with limb-viewing line-of-sight (LOS) optical depths at line center approaching 1000. Line-by-line calculations of the 626 isotope (001-000) transition and weak bands (636, 627, 628, and the 626 011-010 hot band) are necessary in order to calculate accurate limb spectra. The large effect of radiative transfer of the CO2 lines means that their contribution to the limb spectra compared to that of the optically thin NO+(Δν=1) lines is a sensitive function of the geometry of the auroral arc along the LOS.

Impact of the new rate coefficients for the O atom vibrational deactivation and photodissociation of NO on the temperature and density structure of the terrestrial atmosphere

Recent laboratory work has arrived at a value of the rate coefficient for the room temperature O atom vibrational relaxation of NO(ν=1) which is nearly one third the previously accepted value [Fernando and Smith, 1979]. Laboratory measurements have also established a new value for the rate coefficient for the photodissociation of NO which is ∼1.6 times the previously accepted value. Since the NO(ν=1→ν=0) emission, around 5.3 μm, is a very important cooling process in the lower terrestrial thermosphere, the new values of the two rate coefficients lead to a decrease in the amount of NO as well as the rate at which it cools. Using the global mean model [Roble, 1995] of the mesosphere, thermosphere, and ionosphere, we find that the new rate coefficients introduce large changes in the thermal and density structure of the atmosphere. The resulting model atmosphere appears unrealistic. We find that these large changes are moderated and the resulting neutral temperatures agree better with the Mass Spectrometer Incoherent Scatter (MSIS) model when the value of the CO 2 +O rate coefficient for excitation of the bending vibration is increased two fold to the value arrived at by modeling the 15 μm emission from CO 2 from the lower terrestrial thermosphere. Finally, we describe the results of a number of runs with the thermosphere/ionosphere/mesosphere electrodynamics general circulation model (TIME-GCM) to examine the global temperature, composition, and circulation changes that result from using the new rates for both NO and CO 2 .