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Raindrop size distribution （RSD） is fundamental in understanding the precipitation microphysics and quantitative precipitation estimation， especially in complex terrain with complicated rainfall mechanism and high spatial and temporal variability.In this paper， the RSD characteristics of different rainfall rates and rain types in the mountainous and plain areas of the Ili River Valley during the summer of 2020 -2022 are investigated using Parsivel2 disdrometer.The results show that the precipitation in the mountainous and plain areas is mainly composed of small raindrops， and medium raindrops are the largest contribution to the rainfall rate R.Precipitation in the mountainous and plain areas mainly occurs during the late afternoon and early evening， and the concentration of large and medium-sized raindrops is higher in the mountainous areas in all time periods.The spectral width and the concentration of drops with diameters increase with increasing rainfall rate.The number concentration of medium and large particles in the mountainous areas is obviously higher than that in the plain areas during light rain and heavy rain.For the same rainfall rate and rain type， precipitation in the mountainous areas has higher mass-weighted mean diameter （Dm） and lower normalized intercept parameter （log10Nw）.In addition， the convective rain spectrum in the mountainous and plain areas of the Ili River Valley tend to be “continental-like convective cluster”.It is found that there are also significant differences in the μ-Λ relationship and Z-R relationship of precipitation between the two areas， and the empirical relationship of Z =300R1.40 clearly overestimates precipitation.The results reveal the microphysical characteristics of precipitation under different terrain conditions in the Ili River Valley， and provide a reliable factual basis for the subsequent retrieval of precipitation using radar data.

This paper examines five globally recognized rain attenuation models for slant path communication to compute the attenuation and identify the models required for optimal rain-induced attenuation prediction over Nigeria's North-Central region. The models considered are Garcia-Lopez, Svjatogor, Bryant, ITU-R P.618-9, and Simple Attenuation. These models have been evaluated for circularly polarized signals in the centimeter wave bands. The Lavergnat-Gole rain rate model was employed to transform the original 5-minute integration time rainfall data to a 1-minute integration time. Attenuation estimates for rain varied widely between 9 and 14 dB for the Ku-band and between 20 and 32 dB for the Ka-band at 0.01% of the time over a typical year. Furthermore, the calculations of the Garcia-Lopez, Bryant, and ITU-R P.618-9 models generally agreed, while the Simple Attenuation and Svjatogor models consistently underestimated the rain-induced attenuation across the selected region and all time percentages. [ABSTRACT FROM AUTHOR]

The study introduces the Ant Lion Recurrent Climate Estimation (ALRCE) model for precise climate forecasting, emphasizing critical parameters like rainfall, humidity, temperature, wind speed, and dew point. Its primary goal is to mitigate natural hazard risks stemming from sudden climate shifts. Data from Surat city, Gujarat, including these features, is meticulously processed to train the ALRCE model. It employs an ant lion fitness function for analysis, particularly predicting rainfall and drought rates. Implemented in MATLAB, it demonstrates superior precision, accuracy, and risk reduction, validated for future climatic predictions from 2025 to 2050. Comparative analysis with existing techniques shows ALRCE outperforms, achieving 96.5% accuracy, 98% precision, 0.18838 RMSE, and 0.63 correlation coefficient. The study enhances accuracy by 2% post-optimization, highlighting ALRCE's potential to significantly improve climate prediction and mitigate risks associated with abrupt climate changes. [ABSTRACT FROM AUTHOR]

Using the sequential intensity filtering technique (abbreviation is the SIFT method), two parameters (rainfall rate R and median diameter Dm) were selected to analyze the drop spectrum data of rainfall in Shenyang from 2020-2021, the results show that: 1. The SIFT method reduces distribution fluctuations and sampling errors by comparing standard deviations SD, mean relative error AFE, standard deviation SDFE of the rainfall rate R, mean diameter Dm, raindrops concentration Nt, radar reflectance factor Z of the measured spectrum with the mean spectrum obtained by the SIFT method. 2. By analyzing the difference between the average spectrum and the SIFT method, the SIFT method has the smallest error of fitting, which shows that the SIFT method can reduce the influence of the sampling error caused by natural rainfall changes on the droplet spectrum fitting, improve the accuracy of the inversion droplet spectrum distribution characteristics. [ABSTRACT FROM AUTHOR]

Summary: Since 2009, ONERA has been running Ka band propagation experiments in Toulouse (France, latitude 43.57°N, longitude 1.47°E). A rain gauge was also deployed on site to collect rainfall rate measurements concurrently to beacon data. Since April 2011, the beacon receiver has been recording the 20.2 GHz (vertical polarisation) Astra 3B beacon signal along a slant path of 35.1° of elevation angle. All years of the experiment had excellent data availability, hence giving 12 years of data at Ka band. First, the propagation experiment and the data processing methodology are described. Second, a statistical analysis of rain attenuation and rainfall rate is conducted. Comparisons are then performed with the prediction methods of Recommendations ITU‐R P.837‐7 (rainfall rate), P.618‐13 (rain attenuation) and P.678‐3 (variability of propagation phenomena). [ABSTRACT FROM AUTHOR]

Free Space Optical (FSO) communication systems are gaining popularity due to its tremendous speed, advanced capacity, cost effectiveness, secure and easy to deploy wireless networks. This technology has proven an effective choice for last mile applications and hard to reach areas where deployment of optical fibre links is not feasible. But FSO link is highly weather dependent and as signal passes through the atmospheric channel, the main impairments are the atmospheric turbulence, which induce fading and deteriorate the system performance. Delhi has a great potential for FSO communication because of its clear skies. Since there is no analysis for weather condition found in Delhi, this work provides analysis of typical Delhi weather condition ranging from heavy to light rain, fog and clear sky. The performance of FSO link is analysed in terms of attenuation and link length margin under different weather condition. The results are concluded to identify which atmospheric condition influences more on FSO link performance. [ABSTRACT FROM AUTHOR]

Many design principles for rain gauges that have the capacity to record rainfall intensity have been proposed or developed. These are here grouped into 15 categories, and the abilities and limitations of each are discussed. No standard or optimum method has emerged, despite more than 80 years of effort in the last two centuries, together with prior work from the 17th C onwards. Indeed, new methods continue to be explored for both point-based and area-wide collections of intensity data. Examples include the use of signal attenuation by rain along the tower-to-tower links of cellular phone networks, monitoring the speed of vehicle windscreen wipers, and exploiting the sound or vision from security and traffic-monitoring cameras. Many of these approaches have the potential to provide vastly more observation sites than conventional meteorological stations equipped with rain gauges. Some of these contemporary approaches seek to harness the potential of crowdsourced or citizen-science data. It is hoped that the present overview of methods will provide a guide for those wishing to collect or analyses rainfall intensity data for application in areas such as soil erosion processes, ecohydrology, agrochemical washoff, or urban flash flooding. Because rainfall intensity is one of the key aspects of the hydrologic cycle likely to respond as climate change and variability proceed, the choice of appropriate data collection methods has additional contemporary importance for the monitoring of regional and global precipitation changes. [ABSTRACT FROM AUTHOR]

Event-based rainfall-runoff models are practical tools commonly used to predict catchments' response to a rainfall event. However, one of the main concerns is that the characteristics of rain events are neglected in the model development. This paper develops a novel event-based rainfall-runoff equation to incorporate rainfall characteristics into account. The performance of the new equation is evaluated based on the root mean square error, Nash–Sutcliffe efficiency coefficient, and per cent bias for 13,339 rainfall-runoff events between 2005 and 2020 over 23 catchments across New Zealand and Australia with oceanic, mediterranean, tropical, subtropical, and semiarid climates. Compared to the previous event-based models, the new equation shows an improvement in runoff estimation in almost all case studies. Furthermore, considering the new equation is simple, efficient, and takes the rain event duration into account, the new equation has the potential to become a robust alternative method to the conventional curve number method in hydrological engineering projects. [ABSTRACT FROM AUTHOR]

The prediction of rain rate and corresponding attenuation is a vital parameter to be considered while analyzing a terrestrial free space optical (FSO) communication link. Actual tropical rainfall occurs for 15 % of the year, therefore hourly data of rain rate must be accurately estimated for higher rainfall sites. This paper is concerned with the empirical determination of the power-law coefficients that allow for the development of a rain model. The measured attenuation for tropical rainy weather significantly varies from defined International Telecom Union (ITU-R) standard. The experimental work is examined using optimized laser wavelength, launched power and link range. The purpose of the study is to obtain the regression parameters (k and α ) for rain specific attenuation (RSA) applicable to tropical weather conditions. The test rain channel is imitated in the laboratory, where a 10 Mb/s, 1550 nm on-off keying (OOK) signal is propagated through the rain closet chamber of 0.5 × 0.5 × 5 m3. The effective optical link of 15 m is made using round-trip reflection by plane mirrors, and a concave mirror is used to gather irradiance onto the receiver aperture. The average RSA is measured from collected data for maximum rain intensity of 210 mm/h for the Indian monsoon. The testbed analyses FSO link in terms of received optical power, bit error rate (BER) and Q-factor. Using the least square mean equation approach, k and α are estimated to be 0.63 and 0.91, respectively. The finding contributes to reporting power margin and improving the system performance for deploying an optical link in areas of higher rain intensity. [ABSTRACT FROM AUTHOR]

From January 2017 to December 2021, Office National d’Etudes et de Recherches Aérospatiales (ONERA) and Centre National d’Etudes Spatiales (CNES) operated a beacon receiver able to record the 20.1995 GHz beacon signal of the Amazonas-3 satellite at the Guiana Space Centre in Kourou, French Guiana. A rain gauge was also deployed on site to collect rainfall rate measurements concurrently to beacon data. All years of the experiment, except 2019, had excellent data availability, hence giving four full years of data (2017, 2018, 2020, and 2021). First, the climatic characteristics of French Guiana are shown. Second, the propagation experiment and the data processing methodology are described. Third, the results of the statistical analysis are highlighted and commented. Comparisons are performed with the prediction methods of Recommendation ITU-R P.837-7 (rainfall rate), Recommendation ITU-R P.618-13 (rain attenuation), Recommendation ITU-R P.678-3 (variability of propagation phenomena), and Recommendation ITU-R P.1623-1 (fade dynamics). [ABSTRACT FROM AUTHOR]

The characteristics of the raindrop size distribution (DSD) in summer in the western (Nilek) and central (Urumqi) regions in the Tianshan Mountains of China were studied based on three years of second-generation Particle Size Velocity (Parsivel2) disdrometer data. The FengYun-2G satellite remote sensing data and the ERA5 reanalysis product were used to reveal the possible thermo-dynamical and microphysical processes that caused the dissimilarities in DSD between Urumqi and Nilek. The DSD in Nilek is significantly different from that in Urumqi. The concentration of mid- and large-size drops is higher in Nilek than in Urumqi. The DSD characteristics for six rain rate classes and two rain types (convective and stratiform) are studied. It is found that the raindrops in Nilek have overall higher mass-weighted mean diameters (Dm) and lower logarithm of normalized intercept parameters (log10 Nw) than those in Urumqi, which is true for different rain rates and rain types. Convective clusters in Urumqi are similar to maritime clusters, whereas those in Nilek are more similar to continental clusters, according to a classification standard of convective clusters. The radar reflectivity, rain rate relations, and the shape and slope relations for rainfall in Urumqi and Nilek are also different. The DSD variability in the two regions may be attributed to differences in convective intensity that are closely related to the specific terrain of the Tianshan Mountains. [ABSTRACT FROM AUTHOR]

In this paper, the effect of heavy rainfall on the propagation of a 38-GHz in a tropical region was studied and analyzed. Real measurement was collected, with a path length of 300 meters, for a (5G) radio linkage in Malaysia, installed at the Universiti Teknologi Malaysia (UTM) Johor Bahru campus. The employed system entails an Ericsson MINI-Link 38 E-0.6 mm, with a horizontal polarization (HP) antenna at the top integrated with a rain gauge and a data logger. Daily registered samples with a single minute span, for a full study period of 1 month, were collected and evaluated. The obtained rain rate was found as 56 mm/hr with a specific rain attenuation of 18.4 dB/km for 0.01% of the time. In addition to that, a calculated average rain attenuation of 5.5 dB for the transmission path of 300 meters length, was calculated. Based on these findings, a recommendation to update the International Telecommunication Union (ITU) specification of the rain attenuation for Malaysia is proposed. Based on the results, we suggest shifting the zone classification of Malaysia from zone P to zone N-P. Therefore, accurate design for future 5G systems would rely on more precise estimated attenuation levels leading to enhanced performance. [ABSTRACT FROM AUTHOR]

This research aims to calculate the rate of rainfall for two consecutive years, 2018 and 2019, to study and analyze the drought periods during these years. The research was conducted in Kirkuk province north of Iraq, by dividing the study area into five regions based on five stations of rainfall records. Two types of data used in investigations; remotely sensed daily precipitations from integrated multi-satellite retrievals and monthly precipitations average rate from NASA power application. The methodology involved the calculation of rainfall rats by three methods; Mean, Thiessen’s polygons, and the Isohyetal technique. Data were analyzed, and final maps were produced using Geographic Information Systems. For the year 2018 the average annual rainfall rate produced by Mean, Thiessen’s polygons, and Isohyetal technique were; 1.376, 1.341, and 1.343 respectively. But, for the year 2019 the average annual rainfall rate produced by Mean, Thiessen’s polygons, and Isohyetal technique were; 0.966, 0.932, and 0.882 respectively. The results showed the scarcity of water and the lack of rainfall during the study years, which has a great impact on the region's exposure to drought, represented by the drying up of rivers.

The classical sub-6 GHz spectrum currently being used by wireless networks cannot support the requirement of 5G and higher upcoming mobile communication networks due to its limited bandwidth. Millimeter Wave (MMW) radio systems operating at 30 to 300GHz band provides higher bandwidth, frequency reuse and communications security but suffers greatly from atmospheric, environmental and rain attenuation. The attenuation of millimeter wave radio signal at worst hour rainfall rate was therefore investigated. The data was collected from the Tropospheric Data Acquisition network (TRODAN), the International Institute for Tropical Agriculture (IITA) and the Federal University of Technology, Akure. The rainfall rates were measured at 5 and 1-minutes integration time and the Lavergnat and Gole model was used for the conversion of the measured 5 minute to equivalent 1-minute values. The results revealed that throughout the study period, about 66.67% of the sites recorded the worst rainfall events at the 15 hours Local Time (LT). The range of rainfall rate at 0.01% exceedance was 1.18 to 62 mm/hr while at 0.001% it ranged from 51.50 to 116 mm/hr. The specific attenuation at the threshold frequency of 200 GHz at the 0.01% exceedance ranged from 1.638 to 6.175 dB/km. The clear signal band frequency threshold was 60 GHz and the path attenuation ranged from 15.34 dB to 20.43 dB. These results suggest the inclusion of the estimated attenuation values by radio propagation engineers in designs for this region.

The foundations and criteria for the definition of aridity and the identification of dry regions varied from one researcher to another, the objective of this study is to measure the degree of aridity in the Eastern Region of the Kingdom of Saudi Arabia and climatically classified. The methods followed by the study are the regional, historical, descriptive analytical and inductive approaches. The study relied on climatic data that were obtained from Meteorological Service and Environmental Protection for five meteorology stations, Qaisumah, Dhahran, Al-Ahsa, Hafr Al-Batin, and Dammam, during the period from 2000 to 2012. Six aridity indices: Lange, de Martin, Cousin, Thornthwaite, Koppen and Wilmey were applied to monthly, seasonal and annual rainfall and temperature rates. The results revealed that all months in the Eastern Region and all stations are classified as dry months according to the Kossin and Thornthwaite. The results also show that the seasons were characterized by varying degrees of aridity. With regards to seasons, the summer was the driest, followed by the autumn, while the aridity decreased during the winter and spring seasons. The study area was also characterized by the annual aridity according to the application of the Lang, de Marton, Koppen and Wilmy. The study recommended that the necessity of activating water-harvesting projects to make the most of varying rainfall rates, rationalize water consumption, and conduct studies concerned with the applied climate

The knowledge of raindrop size distribution (DSD) is crucial for understanding the microphysical processes involved with the precipitation. Different empirical relationships established with DSD parameters, like radar reflectivity– rainfall rate (Z – R) relationships and shape–slope (μ – Ʌ) relationships, can progress the rainfall estimation algorithms and cloud modeling simulations. In the present study, long-term (2018–2021) measurements of a Laser Precipitation Monitor (LPM) disdrometer installed at the National Institute of Technology, Rourkela, India is used to investigate the DSD characteristics of pre-monsoon (March–May) rainfall. Along with the disdrometer data, auxiliary parameters like convective available potential energy (CAPE), total column water vapor (TCWV), vertical profiles of temperature and relative humidity from reanalysis data sets of ECMWF (European Centre for Medium-Range Weather Forecasts) fifth-generation reanalysis (ERA5) are also used in this study. Based on standardized rainfall anomaly, the pre-monsoon precipitation days are classified into strong, moderate, and weak rainy days, and they contributed to 58.69%, 32.7%, and 8.61% of total rainfall, respectively. The average DSD indicated noteworthy variations among strong, moderate, and weak rainy days with maximum (minimum) concentration of raindrops in strong (weak) rainy days. The mean value of rain rate (R), normalized intercept parameter (N w), and mass-weighted mean diameter (D m) is maximum during days of strong rainfall. Strong rainy days showed high-value CAPE, TCWV and vertical profile of relative humidity. The majority of R is contributed by moderate-sized raindrops with a significant difference in the Z–R and μ–Λ relationships among three types of rainy days. • The strong and weak rainy days has same occurrence time of precipitation. • The strong rainy days contribution in the total precipitation is ∼58.69%. • Empirical relations of microphysical parameters differ for strong, moderate and weak rainy days. • The moderate-sized drops have highest contribution to rain rate. [ABSTRACT FROM AUTHOR]

The microphysical processes of cloud and precipitation in the Tianshan Mountains still remain unclear due to the complex terrain and the lack of ground-based observational data. In this study, the characteristics of summer raindrop size distribution (RSD) in the western and central Tianshan Mountains of China were investigated in 2020 and 2021. According to the average raindrop spectra, the RSD characteristics exhibit significant differences that the concentration of medium and large particles is relatively higher at Zhaosu than that at Tianchi. Weak precipitation prevails in the Tianshan Mountains most of the time, yet moderate rainfall and heavy rainfall have a great impact on the accumulated rainfall amount. For each rainfall rate class, raindrops of diameter less than 0.75mm have a lower concentration and raindrops of diameter greater than 3 mm have a higher concentration at Zhaosu as compared to those at Tianchi. Compared with Tianchi, Zhaosu has a larger mass-weighted mean diameter (Dm) and a lower normalized intercept parameter (log10Nw). Compared with the classical convective spectrum, the RSDs at both Zhaosu and Tianchi are similar to the continental convective cluster. The relationships between the shape and slope (μ–Λ), and radar reflectivity and rainfall rate (Z– R) exhibit a significant difference in the western and central Tianshan Mountains of China. [ABSTRACT FROM AUTHOR]

A new algorithm is proposed, which estimates two parameters of the particle size distribution (PSD) at each range bin from the global precipitation measurement’s (GPM’s) dual-frequency precipitation radar (DPR) data. The equation that expresses the relationship of the PSD parameters between adjacent range bins is derived. By including the attenuation effect within the bin in the discretized equation, the new algorithm alleviates the double-solution problem when attenuation within the bin is sufficiently large. The stability of the solutions to the equation depends on the value of the mean diameter $D_{m}$ and its gradient with respect to the range in the case of liquid precipitation. There is a critical diameter above which the backward processing of the equation provides a stable or moderately diverging solution, unlike the forward processing that often gives unstable solutions. To provide a set of initial conditions without using the surface reference technique (SRT) in the backward processing, an initialization method using the Hitschfeld–Bordan (HB) attenuation correction method is proposed and tested. The proposed algorithm may provide a tool for investigating the assumptions used in various algorithms. [ABSTRACT FROM AUTHOR]

A new comprehensive space-time model for the characterization of point rainfall rate is presented. A detailed assessment of four key rain characteristics (probability of rain/no rain condition, first and second order lognormal statistics and, space and time correlation functions) with consideration of the impact of varying spatial-temporal integration lengths are discussed. A set of empirical equations have been developed and the results show that they provide estimates of probability of rain/no rain with root mean square errors of less than 1.3 in space and 0.04 in time. They provide good estimates of the parameters at any space-time scales, particularly at higher resolutions that are of great importance to the design and planning of networks operating at frequencies above 10 GHz. In particular, the authors have created databases of rain characteristic parameters spanning North West Europe from which rain rate at any location of interest at different space-time scales can be conveniently obtained. These have been validated by comparing the rain rate exceedance distribution, $R _{0.01}$ , from the model estimates at different space-time scales across the British Isles with values calculated from measured data. It has been found that the proposed model gives highly accurate estimates of $R _{0.01}$ for the continental area with error percentages (E) generally less than 2.5 but the error percentage increases at the edges of the radar scans and in the oceanic area due to low data availability.

Due to the severe threat of tropical cyclones to human life, recent years have witnessed an increase in the investigations on raindrop size distributions of tropical cyclones to improve their quantitative precipitation estimation algorithms and modeling simulations. So far, the raindrop size distributions of tropical cyclones using disdrometer measurements have been conducted at coastal and inland stations, but such studies are still missing for oceanic locations. To the authors’ knowledge, the current study examines—for the first time—the raindrop size distributions of fourteen tropical cyclones observed (during 2003–2007) at an oceanic station, Aimeliik, located in the Palau islands in the Western Pacific. The raindrop size distributions of Western Pacific tropical cyclones measured in the Palau islands showed unlike characteristics between stratiform and convective clusters, with a larger mass-weighted mean diameter and smaller normalized intercept parameter in the convective type. The contribution of the drop diameters to the total number concentration showed a gradual decrease with the increase in drop diameter size. Raindrop size distributions of Western Pacific tropical cyclones measured in the Palau islands differed slightly from Taiwan and Japan. The helpfulness of empirical relations in raindrop size distribution in rainfall estimation algorithms of ground-based (Z–R, μ–Λ, Dm–R, and Nw–R) and remote-sensing (σm–Dm, μo–Dm, Dm–Zku, and Dm–Zka) radars are evaluated. Furthermore, the present study also related the rainfall kinetic energy of fourteen tropical cyclones with rainfall rate and mass-weighted mean diameter (KEtime–R, KEmm–R, and KEmm–Dm). The raindrop size distribution empirical relations appraised in this study offer a chance to: (1) enhance the rain retrieval algorithms of ground-based, remote sensing radars; and (2) improve rainfall kinetic energy estimations using disdrometers and GPM DPR in rainfall erosivity studies.

Seasonal and diurnal variations of lightning activity over West Sumatra have been investigated using observations of Tropical Rainfall Measuring Mission–Lightning Imaging Sensor (TRMM–LIS) over a 16-year period. This study also used TRMM 3B43 and 2A25 data to observe the correlation between lightning activity with rainfall and precipitation type. Results show that lightning occurs more frequently over land than over ocean and coastal areas, in contrast to total rainfall, which is higher over ocean and coastal areas. The lightning pattern is similar to the convective rainfall (particularly deep convective) pattern, which indicates that the majority of lightning in West Sumatra is associated with deep convective rain. The lightning intensity in Indonesia during the convection period, namely, December–January–February and September–October–November, is higher than that during other periods. The diurnal cycle of lightning coincides with the diurnal cycle of cloud migration from the ocean to inland Sumatra, as reported in previous research. Lightning and deep convective precipitation are dominant during the day and evening (16.00–20.00 Local Standard Time [LST]), particularly over land. Stratiform precipitation occurs more frequently from afternoon to early morning (16.00–04.00 LST) over land and at 00.00–12.00 LST over the ocean.

In this paper, a new image-based disdrometer is developed to survey the movement of free falling raindrops. The proposed high-speed image velocimetry (HSIV) system comprises a high-speed camera mounted on a lens with long depth of field, a backlight source using an array of blue LEDs, and a computation/control unit for image acquisition and analysis. Further image processing algorithms are produced for raindrop detection and raindrop tracking. The performance of the HSIV system is compared with that of a commercial PARSIVEL2 disdrometer during a local rainfall event within 12 h, while a tippingbucket rain gauge is also used to estimate the amount rainfall rate during that period. The data obtained from the proposed HSIV system are in good agreement with those of PARSIVEL2. Furthermore, the results of the HSIV system are closer than those of PARSIVEL2 to the actual rainfall, which is determined by the rain gauge. To validate the raindrop tracking algorithm, another experiment is conducted to compare the tracking results with the frame-by-frame visual observation from 2880 consecutive frames within 5 min. Experimental results suggest that the proposed HSIV system facilitates the measurement of the precipitation properties, fall velocity, equivolume diameter, raindrop concentration, and rainfall rate, to real-time monitoring of the rainfall with stable and reliable analysis.

This work evaluated the performance of International Telecommunication Union-Radiocommunication Sector (ITU-R) P.837-6 and P.837-7 models (Annex 1) to estimate one-minute rainfall rates in Indonesia. In addition to the default ITU-R P.837-6, the input of ITU-R P.837-6 is also modified using data which has better spatial resolution, i.e. a combination of Tropical Rainfall Measuring Mission (TRMM) 3A25 and 3B43 (ITU-R+3A25+3B43), 3B42 and 3B43 (ITU-R+3B42+3B43), Global Satellite Mapping of Precipitation (ITU-R+GSMaP), and Global Precipitation Measurement (ITU-R+GPM). Among the five test sites, the default ITU-R P.837-6 and ITU-R+3A25+3B43 could predict one-minute rainfall rates at two locations accurately. The ITU-R P.837-7 exhibited a marginally better performance for sites that had a high percentage of very heavy rain, particularly at large (1%) and small (0.001%) percentages of time exceeded. The spatial distribution of rainfall rate produced by ITU-R P.837-7 and ITU-R+3A25+3B43 was closer to the pattern demonstrated by recent satellite precipitation measurements. [ABSTRACT FROM AUTHOR]

The rainfall rate is a crucial variable in modeling runoff and water erosion. Rainfall rates present a very large spatial and temporal variability. Radars are used to estimate the spatial and temporal changes in rainfall rates during storms. The radar reflectivity is strongly affected by the drop size distribution (DSD) that results from the relative intensity of the microphysical processes involved in rainfall formation. One of the mathematical models applied to quantify the DSD is the Weibull function. Rainfall rate and kinetic energy, and radar reflectivity, are all related to different moments of the DSD. An analytical expression for these moments is proposed in the case of the Weibull distribution. The resulting relationships between radar reflectivity, rainfall rate, and kinetic energy are presented. The use of a scaled DSD that is independent of rainfall rate and characterizes a specific location allows an a priori estimate of relationships between radar reflectivity, rainfall rate, and kinetic energy that will be also characteristics of that location. Radar reflectivity can be used to estimate the kinetic energy of rainfall events. This extends the application of radar to agriculture and environmental purposes such as potential rainfall damages estimates in terms of soil loss, erosion, and sediment transport. Key Points: An analytical expression of the moments of the drop size distribution corresponding to R and Z are presented for the Weibull distributionThe use of a scaled DSD characterizing a specific location allows to estimate of relationships between Z, R, and dE/dt for that locationZ can be used to estimate dE/dt; the Z (dE/dt) relationship is of a power type, but could be approximated by a linear one [ABSTRACT FROM AUTHOR]

The relationship ( Z = AR b ) between radar reflectivity factor, Z and rainfall rate, R is studied using the micro rain radar (MRR) observation located over Darjeeling (27.05° N, 88.26° E, 2194 m above the msl) in the foothills of the eastern Himalayan Mountains during Indian summer monsoon and post monsoon seasons (June–October) 2013. Observations from MRR are classified mainly into two types, stratiform and convective, based on the bright band and non-bright band signatures in the radar reflectivity, respectively. We have observed 12 and 7 cases for the stratiform convective rain events, respectively. In the present study MRR is operated mostly during low intensity rainfall rate (0.02–20 mm/h). During southwest monsoon season Z - R relation for the stratiform and convective rainfall types are found to be Z = 272 R 1.78 and Z = 192 R 1.54 respectively. Z - R relation for both stratiform and convective rain shows high temporal variation during different months of monsoon and post monsoon seasons. The coefficient A varies between 225 and 289 for stratiform rain and between 153 and 235 for convective rain. The exponent b varies between 1.4 and 2.1 for stratiform rain while between 1.2 and 1.8 for convective rain. Interestingly, we observed a distinct relation with smaller values of A and b for convective rain than stratiform rain over Darjeeling. The height dependence of A and b are also studied which is found to be very small up to ~ 1.5 km above the surface for both types of the precipitating systems. [ABSTRACT FROM AUTHOR]

Communication at higher frequency bands has numerous benefits but susceptible to rain impairments. Rain-induced attenuation becomes more prominent as the carrier frequency and rain rate increase. Hence, precise knowledge of rain rate can help in predicting the level of rain-induced attenuation. The paper determines point cumulative rainfall rate at 0.1% of time exceedance and converts integration time from 5 min to 1 min. The specific and the total rain-induced attenuation were predicted at 0.1% of time exceedance from 12 GHz to 18 GHz for both horizontal and vertical polarizations. Lavergnat-Gole rain rate conversion model and ITU-R P.838-3 model were employed using four-year rainfall data obtained from Port Harcourt, Nigeria. The results revealed that the peak activities of rainfall rates were recorded at lower integration times, and the total rain-induced attenuation increases with increasing operating frequencies, which is greater for horizontally polarized waves compared to vertically polarized waves. [ABSTRACT FROM AUTHOR]

Rainfall has an attenuation of backscatter coefficient of the sea surface and a change in the sea surface roughness, and these effects give rise to some errors in retrieving the sea surface wind speed, the significant wave height, and wave slope. It is meaningful to make considerable efforts to study the attenuation of radio waves caused by rainfall. In this article, a new model of analyzing the attenuation characteristics of satellite radar altimeter pulse signals because of rainfall is presented. First, the model of the equivalent permittivity of rainfall is calculated and presented. The imaginary part of the equivalent permittivity is studied when radio frequency and rainfall rate vary, respectively. Second, a new theoretical model and method of analyzing the effect of rainfall on satellite radar altimeter pulses is presented based on a multilayer‐medium model with the equivalent permittivity of rainfall. On the other hand, some existing models of computing rainfall attenuation characteristics of radar signals are studied and improved to some extent. Finally, some attenuation characteristics of radar signals due to rainfall are calculated by those models. The calculated results show that the attenuation characteristics of radar altimeter pulse signals are all in good agreement with those by other models. The results computed by the multilayer‐medium model can provide a good theoretical explanation and understanding for these attenuation characteristics of radar pulse signals and can also give some data support and corrections for the measured oceanic parameters by the satellite radar altimeter. Key Points: The permittivity of rainfall is analyzed, and a linear relationship between rainfall rate and attenuation for Ku/C band is presentedA new model of wave attenuation due to rainfall is presented and can help us to understand the wave attenuation from electromagnetic theoryThe Ku/C wave attenuation due to rainfall is calculated by the new model, and results are in good agreement with those by other models [ABSTRACT FROM AUTHOR]

We made an effort to inspect the raindrop size distribution (RSD) characteristics of Indian Ocean and Pacific Ocean tropical cyclones (TCs) using ground-based disdrometer measurements from observational sites in India and Taiwan. Five TCs (2010 - 2013) from the Indian Ocean and six TCs (2014 - 2016) from the Pacific Ocean were measured using particle size and velocity disdrometers installed in south India and south Taiwan, respectively. Significant differences between the RSDs of Indian Ocean and Pacific Ocean TCs are noticed. For example, a higher number of small drops is observed in Indian Ocean TCs, whereas Pacific Ocean TCs have more mid-size and large drops. RSDs of Pacific Ocean TCs have higher mass-weighted mean diameter and lower normalized intercept parameter than Indian Ocean TCs. RSD values quantified based on rainfall rate and precipitation types also showed similar characteristics between Indian Ocean and Pacific Ocean TCs. The radar reflectivity and rainfall rate (Z-R) relations and shape and slope (μ-Λ) relations of both oceanic (Indian and Pacific) TCs are found to be distinctly different. Possible causes for the dissimilarities in RSD features between Indian Ocean and Pacific Ocean TCs are due to relative differences in water vapor availability and convective activity between TCs in these two oceanic basins. [ABSTRACT FROM AUTHOR]

The current study summarizes the raindrop size distributions (RSDs) characteristic of the North Indian Ocean (NIO) tropical cyclones (TCs) measured with ground-based disdrometers installed at the coastal (Thiruvananthapuram, 8.5335°N, 76.9047°E) and inland (Kadapa, 14.4742°N, 78.7098°E) stations in south India. The NIO TCs observed at the coastal station showed more mid- and large-size drops (>1 mm) than the inland station. On the other hand, for both inland and coastal stations, small and mid-size drops (

Recent years have witnessed a growing interest in techniques and systems for rainfall surveillance on regional scale, with increasingly stringent requirements in terms of the following: (i) accuracy of rainfall rate measurements, (ii) adequate density of sensors over the territory, (iii) space-time continuity and completeness of data and (iv) capability to elaborate rainfall maps in near real time. The devices deployed to monitor the precipitation fields are traditionally networks of rain gauges distributed throughout the territory, along with weather radars and satellite remote sensors operating in the optical or infrared band, none of which, however, are suitable for full compliance to all of the requirements cited above. More recently, a different approach to rain rate estimation techniques has been proposed and investigated, based on the measurement of the attenuation induced by rain on signals of pre-existing radio networks either in terrestrial links, e.g., the backhaul connections in cellular networks, or in satellite-to-earth links and, among the latter, notably those between geostationary broadcast satellites and domestic subscriber terminals in the Ku and Ka bands. Knowledge of the above rain-induced attenuation permits the retrieval of the corresponding rain intensity provided that a number of meteorological and geometric parameters are known and ultimately permits estimating the rain rate locally at the receiver site. In this survey paper, we specifically focus on such a type of “opportunistic” systems for rain field monitoring, which appear very promising in view of the wide diffusion over the territory of low-cost domestic terminals for the reception of satellite signals, prospectively allowing for a considerable geographical capillarity in the distribution of sensors, at least in more densely populated areas. The purpose of the paper is to present a broad albeit synthetic overview of the numerous issues inherent in the above rain monitoring approach, along with a number of solutions and algorithms proposed in the literature in recent years, and ultimately to provide an exhaustive account of the current state of the art. Initially, the main relevant aspects of the satellite link are reviewed, including those related to satellite dynamics, frequency bands, signal formats, propagation channel and radio link geometry, all of which have a role in rainfall rate estimation algorithms. We discuss the impact of all these factors on rain estimation accuracy while also highlighting the substantial differences inherent in this approach in comparison with traditional rain monitoring techniques. We also review the basic formulas relating rain rate intensity to a variation of the received signal level or of the signal-to-noise ratio. Furthermore, we present a comprehensive literature survey of the main research issues for the aforementioned scenario and provide a brief outline of the algorithms proposed for their solution, highlighting their points of strength and weakness. The paper includes an extensive list of bibliographic references from which the material presented herein was taken.

Knowledge of the spatial–temporal variation of rain fields is required for the planning and optimization of wide-area high-frequency terrestrial and satellite communication networks. This article presents data and a method for characterizing multi-resolution statistical/dynamic parameters describing the spatial–temporal variation of rain fields across ocean climate in North-Western Europe. The data are derived from the NIMROD network of rain radars. The characterizing parameters include 1) statistical distribution of point 1 min rainfall rates, 2) spatial and temporal correlation functions of rainfall rate, and 3) the probability of rain/no rain. The main contributions of this article are the assessment of the impact of varying spatial and temporal integration lengths on these parameters, their dependencies on the integration volumes and area sizes, and the model for both temporal and spatial correlation parameters. [ABSTRACT FROM AUTHOR]