The need to investigate diurnal weather cycles in West Africa originates from the fact that complex interactions often result between mesoscale and synoptic weather processes. This study investigates diurnal cycles of...The need to investigate diurnal weather cycles in West Africa originates from the fact that complex interactions often result between mesoscale and synoptic weather processes. This study investigates diurnal cycles of rainfall and convective properties using six (6) hour interval data from the ERA-Interim and derived products from the Tropical Rainfall Measurement Mission (TRMM). Results showed that the land<span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">ocean warming contrast is more strongly sensitive to </span><span style="font-family:Verdana;">the seasonal cycle, being very weak during March</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">May (MAM) but clearly spelled out during June</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">September (JJAS). Dipoles of wind convergence/divergence</span><span style="font-family:Verdana;"> and wet/dry precipitation, between CASS and Nigeria Savannah zones, were identified in the morning and evening hours of MAM, whereas distinct night and day anomalies, same location in CASS, were found to be consistent during the JJAS season. The locations of flash count and system sizes agree with the climatology of convective properties, that morning and day-time hours are dominated by stratiform precipitation and small system sizes. Most results clearly showed that the eastern locations of Sudano and Sahel are consistently dry because rainfall and precipitation features are predominantly few. Very unique results about the dipole of wind and precipitation between two zones and the unusual dry zones of Sudan and Sahel have been found. Results presented had shown the importance of diurnal variation in understanding precipitation, flash count, system sizes patterns at diurnal scales, and understanding land-ocean contrast, precipitation and wind field anomaly at diurnal scales.</span>展开更多
An evaluation of Radar Precipitation Feature (RPF) characteristics and distribution of convective intensity is performed across 12 regions in West Africa. Results presented in this study have shown that these characte...An evaluation of Radar Precipitation Feature (RPF) characteristics and distribution of convective intensity is performed across 12 regions in West Africa. Results presented in this study have shown that these characteristics over West Africa revealed interesting results which were not observed on a larger spatial scale. The ice scattering characteristics and heights attained by the 15, 20, 30, and 40 dBZ echoes show patterns that agree with the season and movement of the Inter-Tropical Discontinuity (ITD). Some locations in the Western-coast rainforest, Nigeria/Cameroon rainforest and South Sudan savannah had strong potential for convective intensity during MAM, JJA, and SON as shown by their 37-GHz and 85-GHz PCT which fell below 250 K and 225 K respectively while the maximum height attained by their 20 dBZ, 30 dBZ and 40 dBZ are well above the freezing level in those locations. One result revealed a location on the eastern part of south-central Sahel (SC Sahel) where the maximum height attained by the 30 dBZ reflectivity is above 12 km and the maximum height attained by the 40 dBZ reflectivity is above 10 km during SON. The 37-GHz and 85-GHz PCT for this particular location are below 215 K and 150 K respectively indicating a very strong potential for intense convection and hence destructive storms. The distribution of convective intensity, considering only the 85-GHz PCT ice scattering signature, revealed that the percentage of convective intensity increases, especially in the rainforest and savannah, as the ITD shifts northwards during MAM, JJA and during its retreat in SON.展开更多
A 5-year mean seasonal analysis of mean storm height data and histograms from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) have been used to study the storm structure of the major climatic r...A 5-year mean seasonal analysis of mean storm height data and histograms from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) have been used to study the storm structure of the major climatic regions in Africa and over the adjacent Atlantic ocean. The analysis was carried out in two ways. First, the mean storm height and histogram were analyzed for the entire continent bounded by 40?N to 40?S and 20?W to 60?E. Secondly, the analysis was carried out on sub-regional basis, on which Africa was structured into ten regions: Desert (North), Semi-desert (north), Deciduous forest (North), Brush Grass Savanna (North), Tropical Rainforest, Deciduous forest (South), Brush Grass-Savanna (South), Temperate Grassland/Montane Forest, Steppe (East) and Atlantic Ocean. As observed over Africa, and some parts of the Atlantic Ocean and the Indian Ocean, the storm height over the land is higher than that over the sea because ground surfaces tend to be heated more and convections are more easily developed over the land than over the Ocean. There are high storm counts over the land at 250 mb whereas the storm counts are high over the Ocean at 700 mb. Over the regions, the vertical structure of the histograms reveals a distinct bi-modal distribution in the northern hemisphere and the southern hemisphere, but a unimodal distribution is close to the equator both in the northern and southern hemisphere.展开更多
Lightning(LTG)and thunderstorms(TS)are a significant weather phenome-non in Nigeria,with crucial impacts on local climates,agriculture,energy,and transportation.This study investigates the spatial and temporal variabi...Lightning(LTG)and thunderstorms(TS)are a significant weather phenome-non in Nigeria,with crucial impacts on local climates,agriculture,energy,and transportation.This study investigates the spatial and temporal variability of lightning and thunderstorm activities in Nigeria by assessing the performance of Worldwide Lightning Location Network(WWLLN)data and the data from the Nigerian Meteorological Agency(NIMET)over time and spatial scales.The study spans four years,from 2020 to 2023.A comprehensive analysis of 37 stations across Nigeria,representing different climatic zones,was con-ducted for the study.Monthly totals were aggregated to form seasonal datasets for each station,enabling the examination of seasonal variability.The coeffi-cient of correlation was computed,and the use of GIS technology and heat maps provided a visual representation of spatial variations in thunderstorm activities,facilitating the identification of areas with high thunderstorm fre-quencies.TS activity is more frequent in areas between Lat 4˚N and Lat 8˚N than areas between Lat 8˚N and 14˚N,including a strong correlation between WWLLN and NIMET data.The findings further substantiate that 2022 was a significant flood year in Nigeria,with the Yenagoa station experiencing the most severe impact.This study contributes to the existing body of knowledge on thunderstorm activities in Nigeria,providing insights into the spatial and temporal variability of lightning and thunderstorms.The findings have signif-icant implications for climate resilience strategies,early warning systems,and public awareness in Nigeria,highlighting the need for continued research and monitoring of lightning and thunderstorm activities in the context of climate change.展开更多
文摘The need to investigate diurnal weather cycles in West Africa originates from the fact that complex interactions often result between mesoscale and synoptic weather processes. This study investigates diurnal cycles of rainfall and convective properties using six (6) hour interval data from the ERA-Interim and derived products from the Tropical Rainfall Measurement Mission (TRMM). Results showed that the land<span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">ocean warming contrast is more strongly sensitive to </span><span style="font-family:Verdana;">the seasonal cycle, being very weak during March</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">May (MAM) but clearly spelled out during June</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">September (JJAS). Dipoles of wind convergence/divergence</span><span style="font-family:Verdana;"> and wet/dry precipitation, between CASS and Nigeria Savannah zones, were identified in the morning and evening hours of MAM, whereas distinct night and day anomalies, same location in CASS, were found to be consistent during the JJAS season. The locations of flash count and system sizes agree with the climatology of convective properties, that morning and day-time hours are dominated by stratiform precipitation and small system sizes. Most results clearly showed that the eastern locations of Sudano and Sahel are consistently dry because rainfall and precipitation features are predominantly few. Very unique results about the dipole of wind and precipitation between two zones and the unusual dry zones of Sudan and Sahel have been found. Results presented had shown the importance of diurnal variation in understanding precipitation, flash count, system sizes patterns at diurnal scales, and understanding land-ocean contrast, precipitation and wind field anomaly at diurnal scales.</span>
文摘An evaluation of Radar Precipitation Feature (RPF) characteristics and distribution of convective intensity is performed across 12 regions in West Africa. Results presented in this study have shown that these characteristics over West Africa revealed interesting results which were not observed on a larger spatial scale. The ice scattering characteristics and heights attained by the 15, 20, 30, and 40 dBZ echoes show patterns that agree with the season and movement of the Inter-Tropical Discontinuity (ITD). Some locations in the Western-coast rainforest, Nigeria/Cameroon rainforest and South Sudan savannah had strong potential for convective intensity during MAM, JJA, and SON as shown by their 37-GHz and 85-GHz PCT which fell below 250 K and 225 K respectively while the maximum height attained by their 20 dBZ, 30 dBZ and 40 dBZ are well above the freezing level in those locations. One result revealed a location on the eastern part of south-central Sahel (SC Sahel) where the maximum height attained by the 30 dBZ reflectivity is above 12 km and the maximum height attained by the 40 dBZ reflectivity is above 10 km during SON. The 37-GHz and 85-GHz PCT for this particular location are below 215 K and 150 K respectively indicating a very strong potential for intense convection and hence destructive storms. The distribution of convective intensity, considering only the 85-GHz PCT ice scattering signature, revealed that the percentage of convective intensity increases, especially in the rainforest and savannah, as the ITD shifts northwards during MAM, JJA and during its retreat in SON.
文摘A 5-year mean seasonal analysis of mean storm height data and histograms from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) have been used to study the storm structure of the major climatic regions in Africa and over the adjacent Atlantic ocean. The analysis was carried out in two ways. First, the mean storm height and histogram were analyzed for the entire continent bounded by 40?N to 40?S and 20?W to 60?E. Secondly, the analysis was carried out on sub-regional basis, on which Africa was structured into ten regions: Desert (North), Semi-desert (north), Deciduous forest (North), Brush Grass Savanna (North), Tropical Rainforest, Deciduous forest (South), Brush Grass-Savanna (South), Temperate Grassland/Montane Forest, Steppe (East) and Atlantic Ocean. As observed over Africa, and some parts of the Atlantic Ocean and the Indian Ocean, the storm height over the land is higher than that over the sea because ground surfaces tend to be heated more and convections are more easily developed over the land than over the Ocean. There are high storm counts over the land at 250 mb whereas the storm counts are high over the Ocean at 700 mb. Over the regions, the vertical structure of the histograms reveals a distinct bi-modal distribution in the northern hemisphere and the southern hemisphere, but a unimodal distribution is close to the equator both in the northern and southern hemisphere.
文摘Lightning(LTG)and thunderstorms(TS)are a significant weather phenome-non in Nigeria,with crucial impacts on local climates,agriculture,energy,and transportation.This study investigates the spatial and temporal variability of lightning and thunderstorm activities in Nigeria by assessing the performance of Worldwide Lightning Location Network(WWLLN)data and the data from the Nigerian Meteorological Agency(NIMET)over time and spatial scales.The study spans four years,from 2020 to 2023.A comprehensive analysis of 37 stations across Nigeria,representing different climatic zones,was con-ducted for the study.Monthly totals were aggregated to form seasonal datasets for each station,enabling the examination of seasonal variability.The coeffi-cient of correlation was computed,and the use of GIS technology and heat maps provided a visual representation of spatial variations in thunderstorm activities,facilitating the identification of areas with high thunderstorm fre-quencies.TS activity is more frequent in areas between Lat 4˚N and Lat 8˚N than areas between Lat 8˚N and 14˚N,including a strong correlation between WWLLN and NIMET data.The findings further substantiate that 2022 was a significant flood year in Nigeria,with the Yenagoa station experiencing the most severe impact.This study contributes to the existing body of knowledge on thunderstorm activities in Nigeria,providing insights into the spatial and temporal variability of lightning and thunderstorms.The findings have signif-icant implications for climate resilience strategies,early warning systems,and public awareness in Nigeria,highlighting the need for continued research and monitoring of lightning and thunderstorm activities in the context of climate change.
