Raindrop size distribution and rainfall attenuation modeling in equatorial and subtropical Africa: the critical diameters

Adetan, Oluwumi; Afullo, Thomas J.

doi:10.1007/s12243-013-0418-z

Cited by 11 publications

(6 citation statements)

References 24 publications

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“…1(a)-1(f), modeled drop size distribution for two different DSD models with rain rates 5, 10.5, 25, 50, 65, and 110 mm/h, respectively, have been shown. As demonstrated by Adetan and Afullo [35], an intrinsic change in the shapes of the DSD is observed as the rain rate increases.…”

Section: Variability Of Dsd Models In Doualamentioning

confidence: 71%

Raindrop size distribution and rainfall attenuation modeling in central Africa

Ntanguen

2022

Preprint

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Raindrop sizes were measured in Douala, Cameroon ( 4o03'N, 9o42'E) using a Parsivel disdrometer. The data obtained are used for the analysis of the drop size distribution (DSD) and specific rain attenuation modeling in the 5-150 GHz frequency range. The Lognormal and gamma distribution models are employed using the method of moments estimation, considering the third, fourth, and sixth-order moments. The parameter fits for the two DSD models proposed here for different values of rain rates are investigated. The specific rainfall attenuation using the Douala DSD models is compared to the ITU-R models in vertical and horizontal polarisation and models for some countries with different climates such as semi-arid, tropical, and subtropical in Africa. The comparison with the ITU-R model shows significant differences occurring at high frequency with both high and low rainfall rates. The comparison with other regions of Africa also shows that Douala is characterized by equatorial climate, and Durban characterized by subtropical climate show similar rainfall attenuation characteristics at operating frequency range 10≤ f ≤150 GHz, especially at a lower rain rate. At a higher rain rate, specific rain attenuation at Douala is always higher than in other African locations. The proposed models are very important for the determination of rainfall attenuation for terrestrial and satellite systems.

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Section: Variability Of Dsd Models In Doualamentioning

confidence: 71%

Raindrop size distribution and rainfall attenuation modeling in central Africa

Ntanguen

2022

Preprint

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“…This empirical equation was originally developed for the United States. We evaluated the representativeness of this equation for the LKR by analyzing published raindrop size distribution data from Butare, Rwanda (Adetan and Afullo, 2014). For six rainfall events with intensities ranging between 1 and 79 mm h −1 , we obtained a relative difference of only 13% between the observed rainfall energy and equation (2).…”

Section: Methodsmentioning

confidence: 99%

Spatial and seasonal patterns of rainfall erosivity in the Lake Kivu region: Insights from a meteorological observatory network

Bagalwa

Chartin

Baumgartner

et al. 2021

Progress in Physical Geography: Earth and Environment

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In the Lake Kivu region, water erosion is the main driver for soil degradation, but observational data to quantify the extent and to assess the spatial-temporal dynamics of the controlling factors are hardly available. In particular, high spatial and temporal resolution rainfall data are essential as precipitation is the driving force of soil erosion. In this study, we evaluated to what extent high temporal resolution data from the TAHMO network (with poor spatial and long-term coverage) can be combined with low temporal resolution data (with a high spatial density covering long periods of time) to improve rainfall erosivity assessments. To this end, 5 minute rainfall data from TAHMO stations in the Lake Kivu region, representing ca. 37 observation-years, were analyzed. The analysis of the TAHMO data showed that rainfall erosivity was mainly controlled by rainfall amount and elevation and that this relation was different for the dry and wet season. By combining high and low temporal resolution databases and a set of spatial covariates, an environmental regression approach (GAM) was used to assess the spatiotemporal patterns of rainfall erosivity for the whole region. A validation procedure showed relatively good predictions for most months (R2 between 0.50 and 0.80), while the model was less performant for the wettest (April) and two driest months (July and August) (R2 between 0.24 and 0.38). The predicted annual erosivity was highly variable with a range between 2000 and 9000 MJ mm ha−1 h−1 yr−1 and showed a pronounced east–west gradient which is strongly influenced by local topography. This study showed that the combination of high and low temporal resolution rainfall data and spatial prediction models can be used to improve the assessments of monthly and annual rainfall erosivity patterns that are grounded in locally calibrated and validated data.

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“…We have earlier noted at this site, the dearth of smaller rain droplets, which ultimately plays an important role in the DSD and reflectivity profile. Recently, Adetan and Afullo [29] suggested a maximum diameter bound of ≤ 3.5 mm in the percentage of critical diameters responsible for specific attenuation at Butare. Furthermore, their studies reported a decline in the role(s) of these range of critical diameters in Butare compared to their observation at Durban.…”

Section: Implications Of Microphysical Variations On Rain Attenuationmentioning

confidence: 99%

Rainfall Microstructural Analysis for Microwave Link Networks: Comparison at Equatorial and Subtropical Africa

Alonge¹,

Afullo²

2014

PIER B

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Abstract-The quest to understand the variation of rainfall microstructures at subtropical and equatorial regions is vital to rain attenuation studies. In this study, point rainfall datasets obtained at Butare (2 • 36 S, 29 • 44 E) and Durban (29 • 52 S, 30 • 58 E), are compared at the reflectivity threshold of 38 dBZ. Joss-Walvogel (JW) distrometer measurements collected from these two locations represent physical rainfall data from equatorial and subtropical climates respectively. The reflectivity threshold enables the classification of rainfall datasets into stratiform and convective (S-C) precipitation regimes. These thresholds, R th , at Durban and Butare are analysed based on three known rainfall microphysical parameters: rain rate, rainfall Drop Size Distribution (DSD) and radar reflectivity. The results from rain rate distributions at the both regions are similar for both stratiform and convective classes. However, the sampled DSDs indicate the dominance of larger rain droplets at Butare compared to observations at Durban, irrespective of the rain classes. In addition, it is found that the reflectivity distributions at both regions, under stratiform and convective conditions, are distinct in their probability profiles. The overall S-C analysis implied that the reflectivity and DSD profiles at both regions -result in significant variation of predicted specific attenuation -at microwave and millimeter band. In comparison with other global locations, it is affirmed that the S-C transition occurs globally at rain rates between 6 mm/h and 13 mm/h.

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Raindrop size distribution and rainfall attenuation modeling in equatorial and subtropical Africa: the critical diameters

Cited by 11 publications

References 24 publications

Raindrop size distribution and rainfall attenuation modeling in central Africa

Raindrop size distribution and rainfall attenuation modeling in central Africa

Spatial and seasonal patterns of rainfall erosivity in the Lake Kivu region: Insights from a meteorological observatory network

Rainfall Microstructural Analysis for Microwave Link Networks: Comparison at Equatorial and Subtropical Africa

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