Isotherm Height Research Articles

Performance of advanced-deep learning algorithm for modeling and prediction of rain height over some selected locations in the tropics and sub-tropics zone for radio propagation applications

As demand for high-frequency broadband communication services keeps rising, rain-induced attenuation remains the predominant threat to radiowave propagation. Accurate prediction of attenuation requires continuous measurement and monitoring of rain-induced meteorological parameters, specifically rain rate and rain height, due to their spatio-temporal variations. Rain height is an upper dataset mostly computed from Zero- degree Isotherm Heights (ZDIH) measured by radar. This research proposes a novel approach for predicting rain height from earth surface data such as surface temperature, pressure, total cloud cover, dew point temperature, surface solar radiation, water vapor amount in the air, and humidity. This research investigates the relationship between meteorological surface data and rain height. Subsequently, six machine learning models were employed for predicting rain height using the ten years surface data as input variables. The models were applied to six sub-tropical (Polokwane, Pretoria. and Cape Town) and tropical (Sokoto, Akure, and Port Harcourt (PH)) stations in South Africa and Nigeria, respectively. Analysis of the results shows that the Gradient Boosting Algorithm (GBA) performed best with determination coefficients greater than 0.80 and RMSE less than 350 in all three stations in South Africa. However, all the models failed to produce good result for the Nigeria stations. The Random Forest model has the fairest performance metrics with r2 of 0.40, 0.46 and 0.46 in Sokoto, Akure and PH. respectively. GBA is recommended for predicting rain height in South Africa. The research outcome would assist radio engineers in improving the prediction of rain-induced attenuation and determining appropriate fade mitigation techniques.

Detection of Bright Band Heights from Vertical Profile of Radar Reflectivity in Akure, South Western Nigeria

Bright band is an important phenomenon that occurs in radar observations of precipitation. It is a layer of intense reflectivity caused by the melting of the snowflakes in the atmosphere. Accurate detection of bright band and its associated properties are essential for the estimation of precipitation rates and characterization of precipitation types as required in Agriculture, Aviation, Navigation, Telecommunication sectors etc. Bright Band Height (BBH) is a vital parameter in the determination of rain height, rain-induced radio signal attenuation and mitigation techniques. This paper presents an empirical study on the measurement of BBH and Zero Degree Isotherm Height (ZDIH) from Micro Rain Radar (MRR) data obtained in Akure, Nigeria. Vertical profile of radar obtained during stratiform rainy events were examined to detect bright bands and its features. Analysis of the result showed that the ZDIH varies between 4.48 and 4.60 km while the BBH also vary from 4.16 to 4.48 km during intense rainy events in September and October 2010. The derived propagation data would be needed for the optimization and improvement of quality of service (QoS) offered by earth-space links during rainy events in Akure and its environs.

Thunderstorm environments in Europe

Abstract. Meteorological environments favorable for thunderstorms are studied across Europe, including rare thunderstorm conditions from seasons with climatologically few thunderstorms. Using cluster analysis on ERA5 reanalysis data and EUCLID (European Cooperation for Lightning Detection) lightning data, two major thunderstorm environments are found: wind-field thunderstorms, characterized by increased wind speeds, high shear, strong large-scale vertical velocities, and low CAPE values compared to other thunderstorms in the same region, and mass-field thunderstorms, characterized by large CAPE values, high dew point temperatures, and elevated isotherm heights. Wind-field thunderstorms occur mainly in winter and more over the seas, while mass-field thunderstorms occur more frequently in summer and over the European mainland. Several sub-environments of these two major thunderstorm environments exist. Principal component analysis is used to identify four topographically distinct regions in Europe that share similar thunderstorm characteristics: the Mediterranean, Alpine–central, continental, and coastal regions, respectively. Based on these results it is possible to differentiate lightning conditions in different seasons from coarse reanalysis data without a static threshold or a seasonal criterion.

Study of melting layer features related to atmospheric parameters over a tropical location

The present study deals with the variation in height and width of the melting layer (ML) in relation to atmospheric parameters such as near-surface temperature (2 m), zero-degree isotherm height, cloud liquid water content (CLWC), and prevailing instability expressed in terms of convective available potential energy (CAPE) during the pre-monsoon (March-May) and monsoon (June-September) seasons over a tropical location Kolkata (22.57° N, 88.37° E), India. Stratiform rains which are characterized by the presence of ML, are prevalent over Kolkata during both pre-monsoon and monsoon seasons. The ML height is observed to be dependent on the near-surface temperature, zero-degree isotherm height, and atmospheric instability. Again, CLWC controls the melting layer width. Also, the diurnal and seasonal variations of ML height and width have been investigated over the present location. In addition, a long-term change in ML height, zero-degree isotherm altitude, and atmospheric instability (CAPE) have been observed over this location. The decreasing CAPE has been found to be responsible for increasing (decreasing) stratiform (convective) precipitation over the years.

Polarimetric radar observation of the melting layer during the pre-summer rainy season over South China

ABSTRACT The geometric and polarimetric characteristics of the melting layer (ML) during the pre-summer rainy season over South China (PRSC) are investigated from 389 S-band polarimetric radar volume scans. The existing ML detection algorithm is slightly improved, in which the ML is automatically detected by using vertical gradients of radar reflectivity factor for horizontal polarizations (Z H), and co-polar cross-correlation coefficient (ρ HV) from quasi-vertical profiles. And these profiles are obtained by azimuthal averaging of polarimetric radar variables at antenna elevation 19.5°. The comparison between the detected ML top and the 0°C isotherm heights from ERA5 demonstrates that the detection algorithm has high accuracy with an offset of 158 m. Due to larger snowflakes, the average ML thickness in PRSC is thicker (i.e. 150 m) than that in other climatic regions. The ML is characterized by large Z H, large differential reflectivity (Z DR) and small ρ HV, with average values of 32 dBZ, 0.91 dB and 0.94. Furthermore, the peak values of Z H and Z DR in the ML are obviously larger than that from rain regions and snow regions, while the opposite is true for ρ HV distribution.

Influence of Reduced Anthropogenic Activities on Rain Microphysical Properties and Related Atmospheric Parameters Over an Urban Tropical Location

This letter reveals the prevailing scenario of raindrop size distribution (DSD) in terms of mass-weighted mean drop diameter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D_{m}$ </tex-math></inline-formula> ) over a tropical metropolis, Kolkata (22.57°N, 88.37°E), India, in a contrasting aerosol environment that occurred during the COVID-19 pandemic in the absence of usual human activities. In the premonsoon months (March–May), the probability of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D_{m}$ </tex-math></inline-formula> values exceeding 2 mm has increased in 2020, indicating the dominance of large raindrops, compared to the years 2017–2019. Increased number densities of larger drops have influenced the drop fall velocity spectrum as measured by a laser precipitation monitor in terms of the percentage occurrence of high-velocity small drops (superterminal) and low-velocity large drops (subterminal) for both convective and stratiform precipitations. As measured from a Ka-band microrain Doppler radar, the mean melting layer altitude during stratiform rain has decreased by ~800 m during the premonsoon of 2020 compared to 2017–2019. According to the ERA-5 reanalysis data, changing rain microphysical characteristics are related to decreasing zero-degree isotherm height and reduced wind shear.

Calculation and analysis of cloud attenuation and other cloud parameters in India for earth-space links

• The cloud attenuation is higher during the SW monsoon season followed by NE monsoon, pre-monsoon and winter seasons at the places considered. • The maximum cloud attenuation of 1.67 dB/km is measured in Hyderabad by WVP-NTU cloud detection model at 24 GHz. • The WVP-NTU cloud detection model is more suitable for the five places considered as compared to the SU model. An effort is made to examine the cloud parameters over few stations in India for one year from October 2016 to September 2017. This study includes the investigation of cloud base height, cloud top height, zero degree isotherm height, number of cloud layers, cloud thickness, number of days cloud detected, cloud liquid water content and cloud attenuation at 6 GHz, 12.5 GHz and 24 GHz. Salonen Uppala (SU) model and Water Vapor Pressure-Nanyang Technological University (WVP-NTU) model are used for cloud detection using the radiosonde data at Bangalore, Hyderabad, Mumbai, Thiruvananthapuram and Chennai. The cloud parameters found using both the models are compared. WVP-NTU model shows enhanced values for most of the cloud parameters over SU model. Cloud base height calculated using these models are compared with METAR data and found that Cloud base height from WVP-NTU model matches well with METAR data. Cloud liquid water content and cloud attenuation values are calculated using the ITU-R model. The cumulative distributions (CDF) of cloud attenuation for one year are compared for the places considered. The seasonal CDFs of cloud attenuation using the WVP model are compared with the rain statistics. In this study, the maximum cloud attenuation of 1.67 dB/km is measured in Hyderabad by WVP-NTU combined ITU-R model at 24 GHz.

Geoclimatic characterization and latitudinal dependence of rain heights over Nigeria

Attenuation due to rain remains the most severe threat to terrestrial and satellite communication links in the tropics. Rain height is a precipitation parameter that plays important role in the determination of rain-induced attenuation. In this paper, a statistical study was carried out to establish the relationship between rain height and earth station latitude using rain heights derived from Zero Degree Isotherm Height (ZDIH) data retrieved from Global Precipitation Measurement (GPM). A strong positive correlation of 0.83 propelled the attempt to model equations for the estimation of rain height based on latitude. The research recommends a polynomial function of order 3 which has the best coefficient of determination (0.8). The annual mean values of rain heights were also computed and recommended for each of the four geo-climatic zones in Nigeria.

Numerical modeling of freezing of structural objects in transition zones of railways

The structure of the transition zone of the railway formation is composed of layered materials built into it, which must be resistant to adverse winter climatic conditions characteristic for the region. Among the most dangerous factors is the freezing of these materials and therefore the increased resistance to freezing in winter period is required. By this damage, change of their internal structures and material-technical characteristics can occur. For example, as a consequence of freezing, the structure may be affected by the consequent reduction of resistance of these layers to traffic load (axle loads, deformation modules of the individual layers, etc.). Special construction structures are also designed in the track and the paper is dedicated to transition zone, i.e. reinforced concrete tub as an intermediate element in changing the types of railway formation (the area between the slab track and the continuous track bed). In the experiments using the numerical models, the depth of freezing of the structural objects in the transition zones of the tracks is analyzed, i.e. the zero isotherm height position for 0 °C in the railway structure is determined and compared with respect to the bottom surface of the concrete tub as well as the FPL (frost protection layer) in the continuous track bed, subsequently the design of the objects may be modified.

Temporal evolution of atmospheric parameter-profiling on rain height over two geoclimatic regions in Nigeria

This work studies the temporal variation of rain heights in the Sub-Sahelian and Coastal regions of Nigeria using six (6) years Tropical Rain Measuring Mission Precipitation Radar (TRMM-PR) reprocessed data retrieved from the Global Precipitation Measurement (GPM) constellation Satellites and Era-Interim Field of the European Centre for Medium-Range Weather Forecast (ECMWF). The research reveals seasonal, temporal as well as spatial dependence of rain height over the regions. The average annual Zero Degree Isotherm Heights (ZDIH) and rain height in the Sub-Sahelian regions are 4.796 km and 5.11 km respectively while the corresponding values in the Coastal regions are 4.845 km and 4.91 km. The results show that the values recommended by the International Telecommunication Union Radio section (ITU-R) underestimate both ZDIH and rain height. Atmospheric parameters at rain height levels were also compared with rain height. Among all the atmospheric parameters considered, the result shows that variation of rain height in both regions depends strongly on temperature with a determination coefficient (r2) of 0.73 and 0.85 in the Sub-Sahelian and Coastal regions respectively. The recommended rain heights will aid better prediction and mitigation of rain-induced attenuation to optimize the performance of earth-space satellite links in Nigeria.

Daily and seasonal variation of the surface temperature lapse rate and 0°C isotherm height in the western subtropical Andes

AbstractThe spatial distribution of surface air temperatures is essential for understanding and modelling high‐relief environments. Good estimations of the surface temperature lapse rate (STLR) and the 0°C isotherm height (H0) are fundamental for hydrological modelling in mountainous basins. Although STLR changes in space and time, it is typically assumed to be constant leading to errors in the estimation of direct‐runoff volumes and flash‐floods risk assessment. This paper characterizes daily and seasonal temporal variations of the in‐situ STLR and H0 over the western slope of the subtropical Andes (central Chile). We use temperature data collected during 2 years every 10 min by a 16 sensors network in a small catchment with elevations ranging between 700 and 3,250 m. The catchment drains directly into Santiago, the Chilean capital with more than seven million inhabitants. Resulting values are compared against those obtained using off‐site, operational data sets. Significant intra‐ and inter‐day variations of the in‐situ STLR were found, likely reflecting changes in the low‐level temperature inversion during dry conditions. The annual average in‐situ STLR is −5.9°C/km during wet‐weather conditions. Furthermore, STLR and H0 estimations using off‐site gauges are extremely sensitive to the existence of gauging stations at high elevations.

Radar characteristics of summer thunderstorms in the Kanto Plain of Japan with and without cloud-to-ground lightning

The elucidation of characteristics of cumulonimbus clouds that cause lightning is important for predicting thunderstorm development. These characteristics, with and without lightning, were observed during a day (in 2010) of severe thunderstorms and lightning in Japan and statistically analyzed using radar observations with cell tracking. Observed cells were categorized into a cell including cloud-to-ground lightning (CG) and intra-cloud lightning (CGIC), a cell containing only intra-cloud lightning (IC), and a cell without lightning (NoL). These cells were compared to the average and temporal evolution of radar observations. Out of the 265 cells generated, 103 were CGIC cells, 30 were IC cells, and 132 were NoL cells. Significant differences were detected between the averaged values of lifetime, size, echo top, vertically integrated liquid (VIL), maximum radar reflectivity, and radar reflectivity of each cell category, when the − 10 °C isotherm height was considered. The temporal evolution of CGIC cell characteristics revealed changes in radar reflectivity at 0 °C and − 10 °C that were synchronized with lightning activity. The VIL value was elevated only for CGIC cells and had the tendency to decrease with time as lightning activity. CGIC cells produced the highest echo top and maintained their height during their lifetime. To predict CG within 20 min using 35 dBZ radar reflectivity at − 30 °C as the criterion, a critical success index (CSI) of 0.82 and false alarm rate (FAR) of 0.64 were found to have the best prediction scores.

Seasonal variations on the conditions required for the lightning production

Given the growing concern on lightning threats outside the main warm-season, the objective of this study is to get further insight on the seasonal variations of the necessary conditions required for the production of lightning. In this regard, the study aims to find a basic indicator of cloud electrification that could be useful as an all-year-round robust predictor to warn about lightning threats. To this end, a large dataset of weather radar data products, total lightning observations and radiosounding isotherm heights have been used.According to previous studies, the radar storm height is tightly correlated with the total lightning flash rate. A fifth order relationship fits from spring to autumn and a third order power law in winter. In spite of the good correlation between the radar storm height and the total lightning flash rate, the vertical development alone may be insufficient as a basic indicator for thunderstorm conditions. Alternatively, two different predictors for the lightning onset have been analysed: 12 dBZ radar reflectivity echoes reaching the −40 °C isotherm height and 35 dBZ reflectivity echoes reaching the −10 °C. Results show that the most suitable all-year-round predictor is the TOP-35 above −10 °C.

Rainfall Estimation from Tropospheric Attenuation Affecting Satellite Links

A novel methodology for estimating rainfall rate from satellite signals is presented. The proposed inversion algorithm yields rain rate estimates by making opportunistic use of the downlink signal and exploiting local ancillary meteorological information (0 °C isotherm height and monthly convectivity index), which can be extracted on a Global basis from Numerical Weather Prediction (NWP) products. The methodology includes different expressions to take the different impact of stratiform and convective rain events on the link into due account. The model accuracy in predicting the rain rate is assessed (and compared to the one of other models), both on a statistical and on an instantaneous basis, by exploiting a full year of data collected in Milan, in the framework of the Alphasat Aldo Paraboni propagation experiment.

Characterization of rain heights due to 0° isotherm in tropical and subtropical climates: implication on rain-induced attenuation prediction

In this paper, the dynamics of the structure of the rain profile as related to the zero-degree isotherm height and the implications for attenuation prediction along the Earth-space propagation links at locations in Nigeria, a tropical region, and South Africa, a subtropical region, are presented. Five-year (January 2010–December 2014) precipitation data on board the Tropical Rainfall Measuring Mission (TRMM) satellite have been analyzed over some selected locations in the two regions. The influences of the zero-degree isotherm height on some observed weather parameters are also discussed. The result on the influence of air temperature on rain height hr shows a significant increase in the tropical environment as compared with those in the subtropics. However, when hr results are compared with those obtained using rain height as recommended by the International Telecommunication Union (ITU), there is a significant difference at the 0.01% unavailability of the signal in a year particularly at higher frequencies. Further comparison with the slant path attenuation at 0.01% unavailability of the signal in a year shows a slight deviation (between 1.04 and 2.13 dB) in rain height than those acquired using the measured rain height in the tropical locations. Nevertheless, the result is slightly less than those obtained using the measured rain height in the subtropical locations with the differences in dB between − 0.49 and − 1.18. The overall results will be useful for estimating the link budgeting for digital radio satellite broadcasting. It will also be applicable for radar propagation systems at higher-frequency bands in Nigeria and South Africa.

Characteristic and Correlation Between Surface Temperature and 0℃ Isotherm Height Derived from ERA-Interim Reanalysis and Radiosonde Data

Characteristic and Correlation Between Surface Temperature and 0℃ Isotherm Height Derived from ERA-Interim Reanalysis and Radiosonde Data

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

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.

The Consistent Behavior of Tropical Rain: Average Reflectivity Vertical Profiles Determined by Rain Top Height

AbstractSixteen years of Tropical Rain Measuring Mission (TRMM) reflectivity profile data are collected for oceanic, continental, and island tropical regions within the boreal winter intertropical convergence zone (ITCZ). When sorted by the rain top height (RTH), a consistent behavior emerges where the average reflectivity profiles originating at different RTHs form non-overlapping manifolds in the height–reflectivity space, excluding the brightband regions for stratiform type profiles. Based on reflectivity slope (dBZ km−1) profile characteristics and physical considerations, the profiles are divided into three classes: 1) cold profiles, which originate above the −20°C isotherm height and display convergence to a single reflectivity slope profile independent of RTH; 2) warm profiles, which originate below the 0°C isotherm height and display strong reflectivity slope dependence on RTH, with slope values per RTH linearly decreasing with decreased height; and 3) mixed profiles, which originate at the layer located in between the lowest cold rain and highest warm rain profiles and show a gradual transition from cold profile to warm profile reflectivity slope behavior. Stratiform type profiles show similarity for all regions. It is shown that the typical tropical stratiform cold rain profile can be simply parameterized given the temperature profile. Convective type profiles present larger interregional differences. Their deviation from the typical stratiform cold rain profile is used as a measure for convective intensity, where continental and island regions show larger deviations compared to oceanic ones.

Statistical analysis of rain height over Malaysia

Rain height is one of the key parameters in rain attenuation prediction. However, few studies on it had been carried out due to unavailability of data especially over tropics. Presented here is the result of eleven years zero degree isotherm height for eight locations over Malaysia. The studies had been carried out over two main seasons in the country (Northeast and Southwest Monsoon). The result shows that rain height is grossly under estimated by ITU-R P. 839-3.

Characteristics of cloud-to-ground lightning activity in hailstorms over Yunnan province

The characteristics of cloud-to-ground (CG) lightning for nine hailstorms in Yunnan province of China are analyzed statistically. It is determined that the hailstorms were found to present dominant negative CG lightning flashes at any given stage. One specific hailstorm occurring on July 16, 2006, is analyzed in detail by using the data from a CG lightning location network and Doppler radar. This severe hailstorm, which exhibited strong vertical development with cloud tops reaching 15.9km, produced hailstones as large as 15mm and had a lifespan of 3h and 12min. The total CG lightning within the hailstorm showed high levels of activity with flash rates of up to 79fl/5min. The analysis of the storm cell’s lifecycle shows similar trends between the CG lightning flash rates and radar-derived parameters. Cloud-to-ground flashes tended to initiate within the cloud region with reflectivity of more than 30 dBZ at the −10°C isotherm height. A distinct increase in CG flash rate is shown during the rapid development stages of hailstorms. The CG lightning jump pattern appears to be an effective tool for short-term forecasting of possible occurrences of severe weather.