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Spectrum width and intensity of ozone (O3) observed in the MLT region behaves quite differently than in the stratosphere for submillimeter-wave limb emission spectroscopic observation. For example, O3 spectra in the stratosphere are stronger during the day than at night. Conversely, spectra in the MLT region at night are stronger than those occurring during the day due to diurnal variations in O3 behavior. These opposing behaviors cause problems, including oscillations and inaccuracies particularly for O3 vertical profiles in the MLT region retrieved with an application of one retrieval procedure for the entire vertical range (stratosphere to thermosphere). Recently, we developed an optimal retrieval method for O3 in the MLT region for spectra, observed by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) instrument on the International Space Station. Optimizations were performed for frequency window range, retrieval vertical range, vertical grids, and a priori information for O3 and temperature. Precision and accuracy were evaluated by error analysis and comparisons with previous products. The random error was estimated to be about 5% and 35% in the mesosphere and lower thermosphere, respectively, for nighttime O3 profiles in the MLT region. The total systematic error was about 6% in the MLT region. Certain improvements for both random noise (from 50% to 35%) and systematic error (from 10% to 6%) were obtained. We succeeded in revealing the positive correlation between O3 and ClO at nighttime in the upper mesosphere using the optimized O3 profiles; furthermore, its chemical mechanism was explained quantitatively.

Carbon dioxide ( CO 2 ) induced pressure broadening coefficients of water vapor ( H 2 O ) lines have been determined using a terahertz time-domain spectrometer (TDS). Thirty-two rotational transitions of H 2 O were observed in the spectral range of 18– 102 cm - 1 (550–3050 GHz) for the first time. Using TDS allows one to measure absorption spectra with one order of magnitude better precision than Fourier transform spectrometer in this frequency region. The precision of our broadening coefficient measurements was 2.4% in average. The measured CO 2 induced pressure broadening coefficients are compared to those calculated by the complex Robert–Bonamy formalism. The difference between the measurement and the theoretical estimation was in the range of - 10.7 % to + 19.0 % confirming the credibility of the theoretical approach. The impact on retrieval of water vapor abundance was examined by performing inversion analysis on H 2 O spectra of Venus atmosphere obtained with the Submillimeter Wave Astronomy Satellite. In this example case, the retrieved water vapor mixing ratio reduces by half at the altitude region of 70–85 km when applying the newly measured broadening coefficient compared to the air-broadening coefficient, and changes by 5% compared to that estimated by the complex Robert–Bonamy formalism.

The pressure broadening parameters g N2 and g O2 of pure rotational transitions of water vapor with nitrogen and oxygen as foreign gases, respectively, were measured with a terahertz time-domain spectrometer (THz-TDS) in the frequency region from 0.5 to 3.5 THz. A White-type multi-pass cell was introduced in the THz-TDS system to precisely measure the absorption spectra of water vapor. The parameters of 36 lines were determined for both N2 and O2, of which 25 parameters for gN2 and 28 parameters for gO2 were the first laboratory experimental data. The quantum number dependence of the parameters was experimentally observed for the first time due to the good signal-to-noise ratio of this system compared with the conventional Fourier transform infrared spectrometer (FT-IR) experiments. r 2008 Elsevier Ltd. All rights reserved.

The air induced broadening coefficients of the pure rotational transitions of H 2 O at 556.936 GHz ( 1 10 ← 1 01 ) , and 752.033 GHz ( 2 11 ← 2 02 ) were measured by terahertz time-domain spectroscopy. The air broadening coefficient was determined to be 4.012 ( 30 ) MHz Torr - 1 for the 556.936 GHz line and 3.964 ( 40 ) MHz Torr - 1 for the 752.033 GHz line, respectively. The present broadening coefficients for the 556.936 GHz water line are significantly smaller than those of Markov and Krupnov [Measurements of the pressure shift of the 1(10)–1(01) water line at 556.936 GHz produced by mixtures of gases. J Mol Spect 1995:172;211–4] but relatively close to the values of the HITRAN database. The measured data may improve the accuracy of the abundance of water vapor retrieved from spectra obtained by the Odin/SMR satellite instrument. The effect on the satellite retrieval processing is discussed.