Some melting layer characteristics at two tropical locations in Indian region

Observation of bright-band height data from TRMM-PR for satellite communication in South Africa

Abstract: The deleterious effects of rain on a satellite link operating at a frequency above 10 GHz can be estimated using various parameters such as rain rate, drop size distribution, and rain height. In order to accurately account for rain fade along satellite link, real-time measurement of rain height data are needed. In this paper, Bright-Band Height (BBH) and 0 °C isotherm height (ZDIH) over some selected stations in South Africa were processed and used to determine rain height based on the precipitation data of 5-year (2011–2015) collected by the Tropical Rainfall Measuring Mission-Precipitation Radar (TRMM-PR) satellite. These results are then compared with the previous ITU-R P.839-2 and the recent ITU-R P.839-4. The results show that the BBH vary over the years and locations, and will mostly lie between 3.4557 and 4.2244 km. The average rain height observed also lies between 4.085 and 4.457 km across the studied locations. Comparison between the two versions of Recommendation P.839 showed that the ITU-R P.839-2 performs better with respect to three chosen locations such as Durban, Johannesburg, and Kimberley. However, the most recent version (ITU-R P.839-4) appears to be better in the case of a location like Cape Town. The overall results suggest the use of locally derived rain height values for rain attenuation prediction.

Radar-Observed Characteristics of Precipitation in the Tropical High Andes of Southern Peru and Bolivia

Abstract: This study investigates precipitation delivery using the first detailed radar measurements of the vertical structure of precipitation obtained in the tropical Andes of southern Peru and Bolivia. A vertically pointing 24.1 GHz Micro Rain Radar in Cusco, Peru (3,350 m asl, August 2014-February 2015) and La Paz, Bolivia (3,440 m asl, October 2015-February 2017) provided continuous 1-min profiles of reflectivity and Doppler velocity during the respective time periods. Additional datasets collected include thermodynamic profiles from rawinsonde releases, hourly observations of various meteorological variables, and backward air trajectories from the NOAA HYSPLIT model. The vertically-pointing radar time-height data reveal a bimodal diurnal cycle in precipitation with cellular convection predominant in the afternoon and stratiform precipitation predominant overnight. Backward air trajectories for two stratiform case studies indicate that low-level flow originated in the Amazon basin three days prior to the events. Median melting layer heights were above the altitude of nearby glacier termini (~5,000 m) approximately 17% of the time in Cusco and 30% of the time in La Paz, indicating that some precipitation is falling as rain rather than snow on nearby glacier surfaces. Melting layer heights were highest in La Paz during the 2015-16 El Nino (47% above 5,000 m).

Analysis of bright-band height data from TRMM-PR for satellite communication in Durban, South Africa

Abstract: In this paper, 4-year precipitation data obtained from Tropical Rain Measuring Mission-Precipitation Radar (TRMM-PR) satellite were processed and used to determine the distribution of rain height based on 00C isotherm height over Durban in South Africa. The results show that there is a strong variation of bright-band height over the years of observation and will mostly lie between 3639 m and 4197 m above mean sea level. The observed rain height lies between 4517 m and 4803 m. Comparison of the observed results show that the International Telecommunication Union — Recommendation (ITU-R) P.839 recommended values were underestimated. Thus, the specific attenuation values are determined using ITU-R P.618 by incorporating the determined rain height for the location of Durban. It is noticed that the differences between the estimated attenuation based on the measured rain height and the established ITU-R rain height can be as high as 8 dB at Ka band. Thus, recommending using the physical information about rain height derived from the local databases to improve in the rain attenuation prediction accuracy for this region.

Comparative analysis of bright band data from TRMM and ground radar data in Malaysia

Abstract: Good knowledge of the formation and recognition of the bright band is necessary to determine the location of the melting layer. This is partly because the melting layer is one of the major hydrometeors (others include as rain, hail, and cloud) responsible for signal degradations along the slant-path, in the tropical regions of the world. These may result in signal fading, amongst others, which may lead to errors in slant-path attenuation predictions. This paper involves the comparative analysis of radar data sourced from both ground 3D RAPIC bistatic radar and space-borne precipitation radar above the Malaysian air space. For this research work, the terrestrial meteorological radar data were sourced from the Meteorological Department of Malaysia, while the satellite radar data were obtained from the near-real-time TRMM Multi-Satellite Precipitation Analysis (TMPA-RT) version 7 products. Frozen hydrometeors are observed to exhibit peculiar characteristics in terms of increased radar reflectivity as they fall from the sky, transiting from solid to liquid, and manifesting in the popular bright band signature. The melting layer is the region where melting occur, just below the 0℃ isotherm height. It is a major factor responsible for the problems being encountered in characterization and modelling of microwave signal propagation along the earth-space link.

Characterization of Maximum Radar Reflectivity Height During Stratiform Rain Events

Abstract: The effects of rain on terrestrial and satellite communication systems, especially at frequencies above 10 GHz, have been statistically dealt with at length. It is also well known that rain height plays an important role in signal fading and co-channel interference due to scattering. The rain height is directly related to the 0°C isotherm. At this height hydrometeors change from solid to liquid state in the melting layer, increasing their reflectivity and causing the bright band effect in radar measurements. The bright band is defined by the top, bottom and maximum reflectivity heights. The peak reflectivity height can be obtained from radar volume scans. This paper presents a statistical characterization of the time and space variability of the maximum reflectivity height during stratiform rain events. This paper also focuses on the dependence between simultaneous meteorological parameters derived from weather radar and from surface automatic weather observation stations at local scale in a temperate climate region. The data used in this study was obtained from 2006 to 2011.

Doppler radar characteristics of precipitation at vertical incidence

Abstract: A comprehensive review and extension of the theoretical bases for the measurement of the characteristics of rain and snow with vertically pointing Doppler radar are presented. The drop size distribution in rain can be computed from the Doppler spectrum, provided that the updraft can be estimated, but difficulties are involved in the case of snow. Doppler spectra and their moments are computed for rain by using various power law relations of fall speed υ versus particle diameter D and an exponential fit to the actual fall speed data. In the former case, there is no sharp upper bound to the spectra and all the spectral moments increase with rainfall rate R without limit; in the latter case, there is a sharp upper bound of the spectra corresponding to the limiting terminal velocity of raindrops, and the spectral moments approach an asymptote. Accordingly, the power laws are useful approximations over only limited ranges of precipitation rate. A comparison of theoretical and experimental mean Doppler velocity 〈υ〉 as a function of radar reflectivity factor Z shows that the empirical relation 〈υ〉 = 2.6Z0.107 of J. Joss and A. Waldvogel seems to be the only practical relation; even so, the scatter in 〈υ〉 is about ±1 m sec−1. This is also the kind of error to be expected in measuring updraft speeds by present methods. Such updraft errors result in unacceptably large errors in the drop number concentration estimated from Doppler spectra. In the absence of updrafts the mean Doppler velocity 〈υ〉 is uniquely related to Λ, the slope of the exponential drop size distribution. Simultaneous measurements of Z and 〈υ〉 can then be used to estimate N0, Λ, D0, M, and R, where N0 is the intercept of the exponential drop size distribution at D = 0, D0 is the median volume diameter, and M is the liquid-water content.

Electromagnetic Wave Propagation Through Rain

Abstract: Effects of Rain. Rain Structure and Rain--Rate Statistics. Rain--Rate Climate Models. Modeling Attenuation by Rain. Attenuation Mitigation via Diversity. Worst--Month Statistics. Estimating Risk. References. Appendix. Index.

Rain observations with a vertically looking Micro Rain Radar (MRR)

Abstract: Measurements of rain were obtained with a vertically pointing micro radar (MRR) with 1 min time resolution and 50(100) m height resolution at the German Baltic coast on the Zingst peninsula (54.43°N, 12.67°E). The comparison with a conventional rain gauge (30 min integration time) for a five months summer period show a correlation coefficient of p = 0.87 for the rainrate and agreement within 5% for the total rainfall integrated over the whole period. Single measurements with 30 min integration time showed deviations up to a factor of 2 between MRR and rain gauge. Classification of the measurements into rainrate intervals shows that rainrates around 0.2 mm h -1 provide the highest contribution per rainrate interval to the total rainfall. Typical distributions of number-concentration, liquid-water- concentration and rainrate versus drop size, retrieved with the MRR, are presented. Simultaneous estimates of rainrate and reflectivity factor with data of a C-band (frequency 6 GHz) weather radar suggest that the MRR may be used to support quantitative rainrate estimates with weather radars. The weather radar used for comparison is operated by the German Weather Service and is situated 51 km from the MRR.

Radar Observations and Simulation of the Melting Layer of Precipitation

Abstract: The melting layer in precipitation is physically modeled and compared with high resolution Doppler radar data. The model includes a new formulation of the dielectric properties and can handle all ice particles with densities ranging from pure snow to hail. The air temperature is calculated from the vertical air velocity. The model can simulate the aggregation and breakup of the melting particles. The melting layer is often observed as a bright band; the prominence of the bright band is related to the density of particles before melting. The width of the band increases with the rain intensity; according to the model this is mainly caused by an increase in the almost isothermal layer at the upper part of the melting layer. The results of the model are in good agreement with Doppler radar observations. According to the model, the reflectivity is very sensitive to the dielectric properties and density of the melting particles and the influence of aggregation is restricted. Because of the assumption o...

Propagation impairment on Ka-band satcom links in tropical and equatorial regions

Abstract: Due to pressures in the commercial sphere for increased information transfer rates or from the military to further miniaturize equipment to improve its portability, there has been a steady move toward higher carrier frequencies. For more than a decade now, increasing numbers of satellite communications systems have been in operation at millimeter wavelengths. Even where there is a clear view of the satellite from the ground station, a range of meteorological phenomena still combine to make propagation impairment a serious problem. Because of their complexity, difficulties in modeling them, and deficiencies in basic physical understanding, progress in engineering such systems has involved a large dose of empiricism. Ideally, this means a solid database of propagation measurements, made as nearly as possible in the intended geographical area of operations. Because of the time and cost of their accumulation, attempts have been made to use classification into climate zones on a worldwide basis to extend existing data to a wider range of situations. However, most of the measurements in the databases have been made in northern hemisphere temperate zones. Much evidence suggests that in tropical and equatorial zones, the factors that make important contributions to propagation impairment are different, putting a strong question mark over the use of existing design methods. This review looks at those deficiencies and their likely impact on system performance. At this time, rather than providing definitive answers - which must wait on further work - the best that can be done is to highlight difficulties and encourage realistic expectations. In a final section, the review examines the question of whether costly, application-specific measurement programs might now be avoided by mining increasingly sophisticated national meteorological records.