Radio Acoustic Sounding System Data Research Articles

Combination of the Equatorial Atmosphere Radar – Radio Acoustic Sounding System (EAR-RASS) in Determining a Fine Structure of Total Precipitable Water (TPW) over Kototabang, West Sumatera, Indonesia

This study is mainly concerned an application the combined of the Equatorial Atmosphere Radar (EAR) and Radio Acoustic Sounding System (RASS) in determining a fine structure of Total Precipitable Water (TPW) in the lower troposphere at Kototabang, West Sumatera (0.20°S; 100.32°E) during the CPEA I Campaign started from April 10 to May 9, 2004. It looks possible, since EAR-RASS is designed specially to detect the wind at three dimensional direction and virtual temperature with good time and spatial height resolution. By applying the Weisner technique (1970), we found a fine structure of TPW vertically during the above period. While, by applying the Cross-Correlation Function (CCF), we found an a goog agreement between TPW and Optical Rain Gauge (ORG). In the same time, we analyzed the Boundary Layer Radar (BLR) to investigate the updraft and downdraft air mass activities from surface up to 5 km. We found the consistency of BLR, RASS and radiometer data when we investigated the vertical profile of TPW. Futhermore, we found the time variation of TPW, especially on April 24 and May 5, 2005 are about 0.43 and 0.35, respectively. Detailed results of this study are discussed in this paper.

Evaluation of the Interpretation of Ceilometer Data with RASS and Radiosonde Data

Since 2006 different remote monitoring methods for determining mixing-layer height have been operated in parallel in Augsburg (Germany). One method is based on the operation of eye-safe commercial mini-lidar systems (ceilometers). The optical backscatter intensities recorded with ceilometers provide information about the range-dependent aerosol concentration; gradient minima within this profile mark the tops of mixed layers. Special software for these ceilometers provides routine retrievals of lower atmospheric layering. A second method, based on sodar observations, detects the height of a turbulent layer characterized by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component. This information is extended by measurements with a radio-acoustic sounding system (RASS) that directly provides the vertical temperature profile from the detection of acoustic signal propagation and thus temperature inversions that mark atmospheric layers. Ceilometer backscatter information is evaluated by comparison with parallel measurements. Data are presented from 2 years of combined ceilometer and RASS measurements at the same site and from comparison with a nearby (60 km) radiosonde for larger-scale humidity information. This evaluation is designed to ensure mixing-layer height monitoring from ceilometer data more reliable.

Observation of the structure of the urban boundary layer with different ceilometers and validation by RASS data

U rban air quality assessment requires the knowledge of the temporal and spatial structure of the mixing layer, because this structure controls the vertical dilution of near-surface pollutants. The behaviour of the mixing layer is a consequence of vertical temperature and moisture profiles in the lower atmosphere so that remote sensing can be a suitable tool to monitor it. Three ceilometers, a Vaisala LD40 and two Vaisala CL31, have been operated for many months in the German city of Augsburg in order to observe the vertical aerosol distribution. Wind and temperature profile information have been obtained for a part of the period from radioacoustic sounding system (RASS) observations. This paper investigates the abilities of the instruments and compares the information received by the ceilometers among each other and with temperature profiles from the RASS data. Zusammenfassung

Measurements of vertical eddy diffusivity across the tropopause using radio acoustic sounding system (RASS)

[1] A four day high temporal resolution MU radar RASS data set was obtained under light wind conditions in August 1995, enabling retrieval of virtual temperatures up to 20 km. This provided a unique opportunity to study the vertical eddy diffusivity K across the tropopause using RASS Brunt-Vaisala frequency N and radar spectral width. Co-located six hourly radiosondes enabled calculation of K using radiosonde N and radar spectral width. RASS K decreased across the WMO tropopause, from (0.39 ± 0.05) m2s−1 in the uppermost kilometre of the troposphere to (0.27 ± 0.03) m2s−1 in the lowermost kilometre of the stratosphere. The equivalent radiosonde K were (0.43 ± 0.06) m2s−1 and (0.31 ± 0.07) m2s−1 respectively. The WMO tropopause seems to provide a better definition than the cold-point tropopause in separating the stratosphere from the troposphere when considering the mixing of minor constituents.

RASS time series parametric modeling: A way to overcome the classical Fourier Transform

RASS (Radio Acoustic Sounding System) is designed in order to remotely measure atmospheric temperature profiles by combining acoustic and radar techniques. Usually, RASS data are processed with the same signal processing algorithms as for wind profiling: using the classical Fourier analysis. In order to improve the accuracy of the temperature estimates, this paper proposes to take into account RASS time series characteristics. A parametric approach is studied and AutoRegressive modeling is shown to give better temperature estimation than the usual Fourier Transform based algorithm.

Evolution of the atmospheric convective boundary layer monitored by the metric RASS

The automatic metric RASS (Radio Acoustic Sounding System), operating at an acoustic wavelength ∼1 m, proved to be able to measure continuously the thermal vertical profiles as far as about 1 km in 50% of soundings with an accuracy generally within a few tenths ofK degrees and with an altitude resolution of (30÷40) m. A set of triennal data of the diurnal evolution of the convective boundary layer (CBL) during Summer, as monitored by a metric RASS operating in the Po Valley (Italy) is presented and discussed. Although atmospheric turbulence, pertinent to the considered unstable conditions, is one of the main factors limiting the radio-acoustic sounding range, by means of the metric RASS it is possible to follow the growth of the mixing layer and to estimate the multilayered structure of the CBL. In addition to the RASS data, the measurements of wind speed, temperature, radiation, humidity and so on, performed by conventional equipments near ground level, are considered.