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M. WOLK, F. VAN CLEEF, and G. YAMAMOTO

Abstract

The vertical downward spectral radiances for eight spectral intervals in the 15-µ CO2 band were measured with a spectrometer having a resolution of 5 cm.−1 This experiment was designed to be similar to the proposed experiment in which a satellite-borne spectrometer will measure the vertical upward spectral radiance of the atmosphere. The purpose of each experiment is to determine the temperature distribution in the earth's atmosphere as a function of pressure.

The observations were obtained with an IR–7 spectrometer. The mathematical problem of inverting an integral equation for the case of measurements made from the ground is the same as that for satellite and balloon observations. The data and resulting temperature distributions are shown. The agreement between actual and deduced soundings is reasonably good near the ground, but deteriorates with height, as expected.

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H. Luce, G. Hassenpflug, M. Yamamoto, S. Fukao, and K. Sato

Abstract

Kelvin–Helmholtz (KH) instability is likely one of the most important sources of clear-air turbulence in the lower atmosphere. It produces billows, which mix and transport heat and materials vertically in the stably stratified atmosphere. Billows can also dissipate energy; therefore they can affect the larger-scale dynamics. While only a few direct observations have been reported in the tropopause region, in this work the authors report very detailed observations of billow structures around 16-km altitude, in the upper part of the jet stream. Observations were made with very high frequency (VHF)-band mid- and upper-atmosphere (MU) radar (Shigaraki, Japan; 34.85°N, 136.10°E) whose height resolution was improved with a range-imaging technique. KH billow structures were observed for at least 2 h and were found to have horizontal wavelengths of about 5.3 km and vertical extents between 0.5 and 1.0 km. Analysis of wind and temperature profiles measured by radiosondes launched from nearby meteorological stations indicated the presence of nearly monochromatic disturbances, likely due to a dominant inertia–gravity wave (IGW) superimposed on the background wind field. The presence of the IGW was also confirmed by analysis of wind profiles measured by the MU radar just before the KH billows were detected by the observations in range-imaging mode. The IGW, with vertical and horizontal wavelengths of about 3.5 and 600 km, respectively, may have been a direct radiation from the jet stream, as suggested by recent works, and likely played a major role in the onset of the observed KH instability.

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H. Luce, T. Takai, T. Nakamura, M. Yamamoto, and S. Fukao

Abstract

Humidity is, among other things, a key parameter in the evolution of atmospheric dynamics and in the formation of clouds and precipitation through latent heat release. The continuous observation of its vertical distribution is thus important in meteorology. In the absence of convection, humidity in the lower troposphere is distributed into nearly horizontally stratified layers. The thin humidity gradients at the edges of these layers are known to be the main cause of very high-frequency (VHF) stratosphere–troposphere (ST) radar backscatter in the lower troposphere. This property has been experimentally demonstrated many times in the literature from comparisons between balloon measurements and low-resolution radar observations. In the present work, original results of comparisons between Raman lidar measurements of water vapor and middle- and upper-atmosphere (MU) radar measurements of echo power using a range-imaging technique are shown at high spatial and temporal resolutions (∼50 m, ∼20 s). Other tremendous advantages of such comparisons are the simultaneity, time continuity, and colocalization of the lidar and radar measurements. The results show that the radar can be used for continuously monitoring the thin positive and negative gradients of humidity when operated in range-imaging mode. With additional information from balloon measurements, it would be possible to retrieve humidity profiles in the lower troposphere at an unprecedented vertical and time resolution.

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H. Luce, S. Fukao, M. Yamamoto, C. Sidi, and F. Dalaudier

Abstract

For many years, mesosphere–stratosphere–troposphere (MST) radar techniques have been used for studying the structure and dynamics of the lower and middle atmosphere. In particular, these instruments are unique tools for continuously monitoring vertical and horizontal components of the atmospheric wind at high spatial and temporal resolutions. From the very beginning, many studies have been carried out analyzing the reliability of the MST radar wind measurements and their accuracy. However, until now, very few studies have been presented confirming the high performances of the VHF Middle and upper Atmospheric (MU) radar of Japan (35°N, 136°E) for measuring the wind field. The present paper thus gives original comparisons between horizontal velocities measured by MU radar and by instrumented balloons using global positioning system (GPS) radiosondes. Twelve radiosondes were successfully used during the French–Japanese MU Radar Temperature Sheets and Interferometry (MUTSI) campaign (10–26 May 2000, Japan). They were launched about 30 km westward from the radar site, hung below capesphere-type balloons. During the campaign, two sets of radar parameters with oblique beams directed 10° and 15° off zenith at 150-m and ∼2-min resolutions were used. For both configurations, a very good agreement between the two kinds of measurements was found, indicating that both wind profiles are not affected by systematic measurement biases. Moreover, the standard deviation of the differences is less than 2.6 m s−1 using all radar data within a range height of 2–20 km and less than 1.5 m s−1 for a radar signal-to-noise ratio larger than 0 dB in oblique directions and a horizontal radar-balloon distance smaller than 50 km. Two cases of significant differences (10–15 m s−1) around the jet-stream altitude could qualitatively be explained by spatial and temporal variability of the wind field during the passage of a warm front.

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T. Watai, T. Machida, K. Shimoyama, O. Krasnov, M. Yamamoto, and G. Inoue

Abstract

Observations of the atmospheric CO2 concentration from a 90-m tower in Berezorechka, western Siberia, that have taken place since October 2001 were used to characterize CO2 variations over a vast boreal forest area. A new CO2 standard gas saving system was developed that reduced the consumption of standard gases and kept the analysis precision to within 0.3 μmol mol−1. The CO2 day-to-day variation correlated well with atmospheric stability. The average amplitudes of the diurnal variation at 80 m were found to be about 17 and 1.5 μmol mol−1 in July and December 2003, respectively. Extremely high daytime CO2 concentrations of greater than 400 μmol mol−1 were occasionally observed during the winter, which were caused by anticyclonic atmospheric conditions lasting more than several days. Afternoon CO2 values observed at the 80-m height agreed to within 0.4 μmol mol−1 with aircraft CO2 measurements taken in the planetary boundary layer; disagreements were found for anticyclonic conditions in the winter. The afternoon CO2 values reached their maximum in mid-January and their minimum late in July, with the seasonal amplitude of 30.9 μmol mol−1. Compared to observations at background stations, this observation tower recorded a larger seasonal amplitude and earlier occurrence of the seasonal minimum.

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M. F. Larsen, R. D. Palmer, S. Fukao, R. F. Woodman, M. Yamamoto, T. Tsuda, and S. Kato

Abstract

We present a method for deriving horizontal velocities, vertical velocities, and in-beam incidence angles from radar interferometer data. All parameters are calculated from the slope and intercept of straight lines fitted in a least-squares sense to the variation of the signal phase as a function of radial velocity for each pair of receiving antennas. Advantages of the method are that the calculations are computationally fast and simple, and the analysis leads to relatively simple expressions for the uncertainty in the velocity measurements.

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