Internal Kelvin Wave (KW) propagation is studied about variations in the sea surface temperature anomaly (SSTA) over the tropical Pacific. Temperature and Salinity (TS) observations have been used to define the vertical structure of the ocean about the propagation properties of KWs. Changes in the vertical structure of the water column determine consistent zonal variations in the wave velocity, with values varying, roughly, from 1.8 to 2.6 m/s. The authors document that KWs are formed regularly at the western boundary of the tropical Pacific, but, in these cases, never overcome the dateline. Occasionally, KWs are generated in the region comprised between 170o E and 170o W, and, on all these occasions, a positive phase of the El Niño Southern Oscillation (El Niño) event is recorded. A model, named Sloping Interface Model (SIM), is proposed to relate changes in the pycnocline depth, associated with transiting KWs, and SST anomaly variations. In the SIM, whose equations are consistent with the Recharge/Discharge paradigm, the ocean is described as a two-layer system and the climatological state, represented by a sloping pycnocline, is maintained by a constant easterly wind stress. Using the SIM and coherently with the Recharge/Discharge paradigm, the authors show that changes in the averaged SSTA over El Niño 3, 3.4 and 4 regions are nearly perfectly correlated to pycnocline displacements due to transiting KWs.
{"title":"Kelvin Wave Propagation over a Sloping Interface and Relationships with El Niño Southern Oscillation","authors":"G. Borzelli, Arnold Sullivan","doi":"10.30564/jasr.v7i2.6228","DOIUrl":"https://doi.org/10.30564/jasr.v7i2.6228","url":null,"abstract":"Internal Kelvin Wave (KW) propagation is studied about variations in the sea surface temperature anomaly (SSTA) over the tropical Pacific. Temperature and Salinity (TS) observations have been used to define the vertical structure of the ocean about the propagation properties of KWs. Changes in the vertical structure of the water column determine consistent zonal variations in the wave velocity, with values varying, roughly, from 1.8 to 2.6 m/s. The authors document that KWs are formed regularly at the western boundary of the tropical Pacific, but, in these cases, never overcome the dateline. Occasionally, KWs are generated in the region comprised between 170o E and 170o W, and, on all these occasions, a positive phase of the El Niño Southern Oscillation (El Niño) event is recorded. A model, named Sloping Interface Model (SIM), is proposed to relate changes in the pycnocline depth, associated with transiting KWs, and SST anomaly variations. In the SIM, whose equations are consistent with the Recharge/Discharge paradigm, the ocean is described as a two-layer system and the climatological state, represented by a sloping pycnocline, is maintained by a constant easterly wind stress. Using the SIM and coherently with the Recharge/Discharge paradigm, the authors show that changes in the averaged SSTA over El Niño 3, 3.4 and 4 regions are nearly perfectly correlated to pycnocline displacements due to transiting KWs.","PeriodicalId":508222,"journal":{"name":"Journal of Atmospheric Science Research","volume":"118 41","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140379013","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Precipitation on the Tibetan Plateau (TP) has an important effect on the water supply and demand of the downstream population. Involving recent climate change, the multi-decadal variations of the impact of El Niño-Southern Oscillation (ENSO) events on regional climate were observed. In this work, the authors investigated the changes in summer precipitation over TP during 1950–2019. At the multi-decadal scale, the authors found that the inhabiting impact of El Niño events on the TP summer precipitation has strengthened since the late 1970s. The main factor contributing to this phenomenon is the significant amplification in the decadal amplitude of El Niño during 1978–2019 accompanied by a discernible escalation in the frequency of El Niño events. This phenomenon induces anomalous perturbations in sea surface temperatures (SST) within the tropical Indo-Pacific region, consequently weakening the atmospheric vapor transport from the western Pacific to the TP. Additionally, conspicuous anomalies in subsidence motion are observed longitudinally and latitudinally across the TP which significantly contributes to a curtailed supply of atmospheric moisture. These results bear profound implications for the multi-decadal prediction of the TP climate.
{"title":"Multi-decadal Changes of the Impact of El Niño Events on Tibetan Plateau Summer Precipitation","authors":"Weinan Jiang, Ning Cao, Aze Riga, Jianjun Xu","doi":"10.30564/jasr.v7i1.6180","DOIUrl":"https://doi.org/10.30564/jasr.v7i1.6180","url":null,"abstract":"Precipitation on the Tibetan Plateau (TP) has an important effect on the water supply and demand of the downstream population. Involving recent climate change, the multi-decadal variations of the impact of El Niño-Southern Oscillation (ENSO) events on regional climate were observed. In this work, the authors investigated the changes in summer precipitation over TP during 1950–2019. At the multi-decadal scale, the authors found that the inhabiting impact of El Niño events on the TP summer precipitation has strengthened since the late 1970s. The main factor contributing to this phenomenon is the significant amplification in the decadal amplitude of El Niño during 1978–2019 accompanied by a discernible escalation in the frequency of El Niño events. This phenomenon induces anomalous perturbations in sea surface temperatures (SST) within the tropical Indo-Pacific region, consequently weakening the atmospheric vapor transport from the western Pacific to the TP. Additionally, conspicuous anomalies in subsidence motion are observed longitudinally and latitudinally across the TP which significantly contributes to a curtailed supply of atmospheric moisture. These results bear profound implications for the multi-decadal prediction of the TP climate.","PeriodicalId":508222,"journal":{"name":"Journal of Atmospheric Science Research","volume":"26 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140477255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents an analysis of spatial and temporal variation of rainfall and thunderstorm occurrence over Kenya from January 1987 to December 2017. The meteorological data used were obtained from the Kenya Meteorological Department (KMD) for the same period. This included the monthly thunderstorm occurrences and rainfall amounts of 26 synoptic stations across the country. The characteristics of monthly, seasonal and annual frequency results were presented on spatial maps while Time series graphs were used to display the pattern for annual cycle, seasonal variations and the inter-annual variability of rainfall amounts and thunderstorm occurrences. A well-known non-parametric statistical method Mann Kendall (MK) trend test was used to determine and compare the statistical significance of the trends. Thunderstorm frequencies over the Eastern, Central and Coast regions of the country showed a bimodal pattern with high frequencies coinciding with March-April-May (MAM) and October-November-December (OND) rainy seasons. Very few thunderstorm days were detected over June-July-August (JJA) season. The areas to the western part of the country, near Lake Victoria, had the highest thunderstorm frequencies in the country over the three seasons: MAM, JJAS and OND. The annual frequency showed a quasi-unimodal pattern. These places near Lake Victoria showed significantly increasing thunderstorm trends during the MAM and OND seasons irrespective of the rainfall trends. This shows the effects of Lake Victoria over these areas, and it acts as a continuous source of moisture for thunderstorm formation. However, most stations across the country showed a reducing trend of thunderstorm frequency during MAM and JJA seasons. The importance of these findings is that they could support various policy makers, and users of climate information, especially in the agriculture and aviation industries.
{"title":"Seasonal Variability of Rainfall and Thunderstorm Patterns in Kenya","authors":"Mary Kurgat, W. Gitau","doi":"10.30564/jasr.v7i1.6144","DOIUrl":"https://doi.org/10.30564/jasr.v7i1.6144","url":null,"abstract":"This paper presents an analysis of spatial and temporal variation of rainfall and thunderstorm occurrence over Kenya from January 1987 to December 2017. The meteorological data used were obtained from the Kenya Meteorological Department (KMD) for the same period. This included the monthly thunderstorm occurrences and rainfall amounts of 26 synoptic stations across the country. The characteristics of monthly, seasonal and annual frequency results were presented on spatial maps while Time series graphs were used to display the pattern for annual cycle, seasonal variations and the inter-annual variability of rainfall amounts and thunderstorm occurrences. A well-known non-parametric statistical method Mann Kendall (MK) trend test was used to determine and compare the statistical significance of the trends. Thunderstorm frequencies over the Eastern, Central and Coast regions of the country showed a bimodal pattern with high frequencies coinciding with March-April-May (MAM) and October-November-December (OND) rainy seasons. Very few thunderstorm days were detected over June-July-August (JJA) season. The areas to the western part of the country, near Lake Victoria, had the highest thunderstorm frequencies in the country over the three seasons: MAM, JJAS and OND. The annual frequency showed a quasi-unimodal pattern. These places near Lake Victoria showed significantly increasing thunderstorm trends during the MAM and OND seasons irrespective of the rainfall trends. This shows the effects of Lake Victoria over these areas, and it acts as a continuous source of moisture for thunderstorm formation. However, most stations across the country showed a reducing trend of thunderstorm frequency during MAM and JJA seasons. The importance of these findings is that they could support various policy makers, and users of climate information, especially in the agriculture and aviation industries.","PeriodicalId":508222,"journal":{"name":"Journal of Atmospheric Science Research","volume":"32 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140489445","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The temperature is one of the most important factors in weather and climate forecasting. Studying its behaviour is crucial to understanding climate variability, which could vary spatially and temporally at local, regional, and global scales. Several recent studies on air temperature findings show that the Earth' s near surface air temperature increased between 0.6 °C and 0.8 °C throughout the twentieth century. Using temperature records from ten meteorological stations, this study examined climate variability in Rwanda from the 1930s to 2014. The air temperature data were collected from Meteo Rwanda. Before making the analysis, the authors used software, such as Excel 2007 and INSTAT to control the quality of the raw data. The analysis of maxima and minima indicated that the trends of maximum air temperature were positive and significant at height meteorological stations, whereas the trends for minimum air temperature were found to be at 10 meteorological stations. For all parameters analysed, Kigali Airport meteorological station indicated the higher significance of the trends. The majority of meteorological stations showed an increase in both hot days and nights, confirming Rwanda' s warming over time. The analysis of average seasonal air temperature showed almost similar trends even though not all were significant. This similarity in trends could be attributed to the fact that Rwanda' s short and long dry seasons coincide with rainy seasons.
{"title":"Analysis of Extreme Temperature Variability in Rwanda","authors":"Portais Seshaba, Edouard Singirankabo, Donat Nsabimana","doi":"10.30564/jasr.v7i1.6107","DOIUrl":"https://doi.org/10.30564/jasr.v7i1.6107","url":null,"abstract":"The temperature is one of the most important factors in weather and climate forecasting. Studying its behaviour is crucial to understanding climate variability, which could vary spatially and temporally at local, regional, and global scales. Several recent studies on air temperature findings show that the Earth' s near surface air temperature increased between 0.6 °C and 0.8 °C throughout the twentieth century. Using temperature records from ten meteorological stations, this study examined climate variability in Rwanda from the 1930s to 2014. The air temperature data were collected from Meteo Rwanda. Before making the analysis, the authors used software, such as Excel 2007 and INSTAT to control the quality of the raw data. The analysis of maxima and minima indicated that the trends of maximum air temperature were positive and significant at height meteorological stations, whereas the trends for minimum air temperature were found to be at 10 meteorological stations. For all parameters analysed, Kigali Airport meteorological station indicated the higher significance of the trends. The majority of meteorological stations showed an increase in both hot days and nights, confirming Rwanda' s warming over time. The analysis of average seasonal air temperature showed almost similar trends even though not all were significant. This similarity in trends could be attributed to the fact that Rwanda' s short and long dry seasons coincide with rainy seasons.","PeriodicalId":508222,"journal":{"name":"Journal of Atmospheric Science Research","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140490614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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