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We present the results of theoretically simulating, by variational methods, rotation-vibration spectra of NH and PH. The simulations carried out for NH are based solely on calculations, i.e., they are purely theoretical and involve no fitting to experiment. The PH simulations are made from a potential energy function refined to reproduce experimental data and from an dipole moment function. We show that our simulations reproduce observed rotation-vibration intensities with an accuracy approaching that obtained in fittings to these intensities in terms of models involving an effective dipole moment operator. Our results suggest that theoretical simulations of spectra are now close to attaining a level of accuracy where they can successfully compete with quantitative-spectroscopy measurements of intensities and thus assist in the interpretation of remote-sensing spectra.

Infrared instruments designed to monitor atmospheric pollutants from space use observed radiances in specific spectral regions for retrievals of global distributions and atmospheric concentration profiles of the gases of interest, including CO, CH, O, HCN, NO and HO. However, particularly for the troposphere, errors in the spectral line broadening and shift parameters and in the line shape models used in the “forward calculation” can contribute significantly to the total errors in retrievals of atmospheric gas concentration profiles. Line parameters in the HITRAN database for many of the gases mentioned above were significantly updated in the 2000 and 2004 editions. Nevertheless, uncertainties remain in some spectral regions, particularly in the understanding of line shapes, line mixing, and the temperature dependences of line broadening and shift parameters. The recent updates of broadening and shift parameters in the spectroscopic databases are reviewed, and new laboratory results are discussed.

Pressure-broadened half-widths are the principal source of error in the retrieval of concentration profiles for the Earth’s atmosphere. The importance of the pressure-induced line shift is now becoming understood. In this work the current state of knowledge of the line shape parameters for water vapor transitions is discussed with respect to the experimental record and the theory. The measurement databases that have been compiled and the intercomparisons of measurements are discussed. The theoretical determination of the line shape parameters via the Complex Robert- Bonamy (CRB) formalism is presented. The dependence of the line shape parameters on rotational state, vibrational state, imaginary terms, temperature, intermolecular potential, collision dynamics, and method of calculation are discussed. Finally a comparison of the CRB line shape parameters with the measurement database is made and compared with the intercomparisons of the measurements.

The paper presents some recent advances in rotational spectroscopy linked to atmospheric studies. The preparation of the recent space missions such as Odin or EOS-MLS has induced strong spectroscopic efforts to provide accurate line shape parameters that minimize the errors in the retrieval procedures. A critical evaluation of these parameters is needed. The main points related to line positions, line intensities, line broadenings and line shifts are discussed.

For atmospheric purposes, the self- and N-broadening parameters of the = 6 ← 5 (22.2 GHz) rotational transition of water has been investigated in the temperature range 296–338 K. This investigation should be considered of particular interest in monitoring the Earth’s atmosphere because water is a fundamental component and it is well established that the accuracy of collisional broadening parameters has a crucial influence on reduction of remote sensing data. Therefore, a particular effort has been made in order to reduce instrumental as well as systematic errors. Experimental determinations have also been supported by theoretical calculations.

Environmental monitoring, atmospheric remote sensing and astrophysical studies promoted by NASA require a strong basis of spectroscopic information. The rotational spectroscopy capabilities at NASAs Jet Propulsion Laboratory (JPL) are currently maintained for the measurement of key mission priorities that enable modeling and retrieval of geophysical data from the atmosphere as well as validation of the spaceborne instruments in the Earth Observing System, particularly the Microwave Limb Sounder. Rotational spectra are measured using a variety of spectroscopic techniques including pulsed-beam Fourier transform microwave spectroscopy (at CalTech); millimeter wavelength Stark spectroscopy; millimeter, submillimeter and THz FM spectroscopy; laser sideband spectroscopy and Fourier Transform far-infrared spectroscopy. Remote measurements of atmospheric rotational spectra are made using two limb-sounder instruments in the submillimeter and THz. Recent advances in the direct synthesis of THz radiation enables efficient laboratory science. Software for comprehensive and systematic study of different molecular systems is maintained at JPL, the software is freely available via http://spec.jpl.nasa.gov and is used by our group to create and sustain the JPL spectral line catalog also available online.

We present the approach to remote sensing of water vapor based on the Global Positioning System (GPS). Signals propagating from GPS satellites to ground-based GPS receivers are delayed by atmospheric water vapor. Given surface meteorological measurements, this delay can be transformed into an estimate of the precipitable water overlying that receiver. We validate GPS precipitable water at rabt station with National Center for Environmental Prediction (NCEP) measurements. We show short-term correlation between GPS and rainfall during two different seasons, and we describe GPS tropospheric water vapor tomography, which could be utilized in operational weather forecasting and in fundamental research into atmospheric storm systems, the hydrologic cycle, atmospheric chemistry, and global climate change (severe events particularly).

Because they scatter and absorb solar and terrestrial radiation, aerosol plumes can easily be detected on satellite images. Thus, the time-dependent spatial extension of the aerosol clouds can be derived from space-borne observations. However, using remote observations for estimating particle concentrations, let alone for apportioning aerosol loads between all the potential sources of particulate matter, is less straightforward. Indeed, this apportionment would require perfect knowledge of the scattering and absorbing potential of particles of different origins as well as the spectral dependence of these potentials. Contrary to what can be done with most atmospheric gases, it is usually impossible to reproduce in the laboratory the complexity of natural atmospheric aerosols. As a consequence, measuring their wavelength-dependent optical properties can only be done during specially designed experiments performed in natural conditions. This is the case of the Cairo Aerosol CHaracterization Experiment (CACHE) that was performed in the Egyptian capital from the end of October 2004 to mid April 2005. During this period a wide variety of aerosol conditions have been sampled, but this work is focused on the spring intensive observation period during which several occurrences of mineral dust transport to Cairo were observed. We detail the modifications of optical properties resulting from these inputs of mineral particles into the background ‘urban aerosol’ and show that scattering and absorption, as well as their spectral dependence are extremely sensitive to the proportions of the “urban pollution/mineral dust” mixtures that form over Cairo during the dust events. Unfortunately, this precludes the use of predefined aerosol models supposed to represent particularly simple aerosol types (e.g., urban pollution, mineral dust,...) for inverting satellite observations over areas where aerosol mixing is known to be the rule rather than the exception (e.g., over the eastern Mediterranean in spring, over or downwind of continental China during the dust season, over west Africa during the biomass burning period, ...). In these cases, sophisticated parameterizations of the optical properties must be used for assessing the impact of aerosol mixtures on radiative transfer.

This work compares approaches both of mathematical and physical modelling of pollutant dispersion in simulated atmospheric boundary layer (ABL) with results of remote sensing of atmospheric pollutants. Measurements were performed over a highway outside a city and in an urban street canyon with extensive traffic under different meteorological conditions (autumn versus summer period). Time-resolved spatial distributions of pollutants (NO and O) were measured by the combined DIAL (differential absorption light detection and ranging)/SODAR (sound detection and ranging) method and using spot analyzers appropriately located on the leeward and windward sides near the urban street canyon bottom. Qualitative agreement was found between the results obtained by remote sensing in the real atmosphere and those obtained by physical modelling in the simulated atmosphere of a wind tunnel for the autumn period. On the other hand, the analysis of the monitoring results and outputs of the physical modelling shows disagreement for the summer period. Besides neglecting the thermal effect during the sunny period, chemical reactions or photochemical processes taking place in the street canyon can affect the dispersion and distribution of pollutants very significantly. To improve the description of the system investigated, the Computational Fluid Dynamics (CFD) environment was tested for a basic implementation of photochemical reactions into the commonly used mathematical models of turbulence and dispersion processes as well.

The Ether system has been developed in France in order to support scientific studies based on atmospheric chemistry. Ether is the focal point for French and foreign scientists for studying processes from the local to the global scales via the mesoscale, from the troposphere to the stratosphere, within a wide temporal range (from the minute to the decade). A huge variety of products is stored from ground-based, balloon-, air-, and space-borne measurements, to modelled and assimilated constituent fields, together with spectroscopic and kinetic rates data sets. In addition, the development of added-value services such as interactive graphic tools, extraction software, scientific ground-segments as for the Odin/SMR experiment and ancillary data production like potential vorticity fields, helps the efficient use of these heterogeneous products. Finally, information relative to the ongoing activities within the scientific community is presented on the Web site ().