Climatology of the Mascarene High and Its Influence on Weather and Climate over Southern Africa

Xulu, Nkosinathi G.; Chikoore, Hector; Bopape, Mary-Jane M.; Nethengwe, Nthaduleni Samuel

doi:10.3390/cli8070086

Cited by 41 publications

(23 citation statements)

References 51 publications

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“…The austral winter season (May to October) records the lowest amount of precipitation. The semi-permanent anticyclones, the St. Helena High and the Mascarene High, also significantly influence the region's precipitation [19,20]. Further, some studies [8,21] argue that Rossby waves potentially affect precipitation changes over the SA region through the eastward shift of the South Indian Convergence Zone (SICZ).…”

Section: Introductionmentioning

confidence: 99%

Multi-Decadal Variability and Future Changes in Precipitation over Southern Africa

et al. 2021

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The future planning and management of water resources ought to be based on climate change projections at relevant temporal and spatial scales. This work uses the new regional demarcation for Southern Africa (SA) to investigate the spatio-temporal precipitation variability and trends of centennial-scale observation and modeled data, based on datasets from the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The study employs several statistical methods to rank the models according to their precipitation simulation ability. The Theil–Sen slope estimator is used to assess precipitation trends, with a Student’s t-test for the significance test. The comparison of observation and model historical data enables identification of the best-performing global climate models (GCMs), which are then employed in the projection analysis under two Shared Socioeconomic Pathways (SSPs): SSP2-4.5 and SSP5-8.5. The GCMs adequately capture the annual precipitation variation but with a general overestimation, especially over high-elevation areas. Most of the models fail to capture precipitation over the Lesotho-Eswatini area. The three best-performing GCMs over SA are FGOALS-g3, MPI-ESM1-2-HR and NorESM2-LM. The sub-regions demonstrate that precipitation trends cannot be generalized and that localized studies can provide more accurate findings. Overall, precipitation in the wet and dry seasons shows an initial increase during the near future over western and eastern SA, followed by a reduction in precipitation during the mid- and far future under both projection scenarios. Madagascar is expected to experience a decrease in precipitation amount throughout the twenty-first century.

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Section: Introductionmentioning

confidence: 99%

Multi-Decadal Variability and Future Changes in Precipitation over Southern Africa

et al. 2021

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“…The heterogenous distribution of these increases in the incidence and duration of cold events across the country would suggest that there is no singular distinct causal mechanism. Changes in the dynamics of the Mascarene High over recent decades, and resultant atmospheric blocking, have been associated with anomalous temperatures, and in particular extreme cold events associated with the enhanced cut off lows (Xulu et al ., 2020). While there is a considerable geographical distribution of cut‐off lows along the South African coastline (Singleton and Reason, 2007), these systems are unlikely to have induced an increase in cold events in regions of the Northern Cape and North West Province.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, there is the potential for cold air outbreaks in the polar masses to increase in regions such as South Africa, due to internal variability and external forcings (Smith and Sheridan, 2020). Where the Mascarene High induces atmospheric blocking, slow‐propagating cut‐off lows can develop from the westerly wave, resulting in enhanced rainfall and even colder temperatures (Xulu et al ., 2020).…”

Section: Discussionmentioning

confidence: 99%

Trend analysis of cold extremes in South Africa: 1960–2016

Walt

Fitchett

2020

Intl Journal of Climatology

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Extreme cold events (“cold waves”) have disastrous impacts on ecosystem and human health. Evidence shows that these events will still occur under current increasing mean temperatures. Little research has been done on extreme cold events, especially in developing countries such as South Africa. These events pose a significant threat due to the low adaptive capacity, urgent development needs and relatively inadequate infrastructure in South Africa. This study presents annual and seasonal, spatial and temporal trend analyses of extreme cold temperature events for the period 1960–2016. We apply the World Meteorological Organisation Commission for Climatology and Indices Expert Team on Sector‐Specific Climate Indices (ET‐SCI) to South Africa for the first time, with comparison to the World Meteorological Organisation Expert Team on Climate Change Detection (ETCCDI) indices previously used in South Africa. The extreme cold indices are calculated using the RClimDex and ClimPACT, respectively. Trends were calculated using the non‐parametric Mann‐Kendall test, Spearman Rank Correlation Coefficient and Sen's slope estimates. A decreasing trend is found for annual cold spell duration and cold wave frequency, at rates of 0.10 days.day−1 and 0.02 events.day−1, respectively. Seasonally, coldest day temperatures increased in autumn, with increases of 0.02°C.day−1 for the period 1960–2016. Regionally, increasing trends in annual cold spell duration days were evident in stations located in the Western Cape, Eastern Cape, North‐West Province, at a rate of 0.03 days.day−1. Increasing trends in cold waves were observed for stations in Northern Cape, Gauteng, KwaZulu‐Natal and the Eastern Cape Province, at a rate of 0.01 events.day−1. These results contribute to the awareness and recognition of the incidence and duration of cold extreme events in South Africa, seeing that studies suggest that anomalously cold events may persist in a warming world.

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“…It can influence the formation of the Indian Ocean subtropical dipole (IOSD) through the surface heat flux and wind speed anomalies (Behera and Yamagata, 2001; Morioka et al ., 2010; 2012). During austral summer, the trade winds out of the MH plays an important role in importing moisture transported from the warm Southwest Indian Ocean and the Agulhas Current toward the Angola Low, affecting rainfall over southern Africa (Harrison, 1984; Cook, 2000; Tyson and Preston‐Whyte, 2000; Manatsa et al ., 2014; Xulu et al ., 2020). The variation of MH also largely determine the movement of tropical cyclones developed over the Southwest Indian Ocean (Miyamoto et al ., 2018; Xulu et al ., 2020).…”

Section: Introductionmentioning

confidence: 99%

Structure and maintenance mechanisms of the Mascarene High in austral winter

Zhao

Wen

et al. 2021

Intl Journal of Climatology

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The Mascarene High (MH), is a key component of the Asian-Africa-Australia monsoon system in austral winter (JJA). Its three-dimensional structures and maintenance mechanisms are examined in this study. It is a low-level subtropical high dominating the southern Africa and South Indian Ocean, characterized by a northwestward tilt with height, which is attributed to its spatially inhomogeneous thermal structure. Large-scale subsidence characterizes the main body of the MH, with the stronger subsidence to the east than to the west. Diagnosis using the complete form of the vertical vorticity tendency equationshows that the anticyclonic structure of the MH, which can be described by the distribution of meridional wind, is maintained mainly by the vertical gradient of diabatic heating, change in static stability, and friction dissipation. In particular, a combination of sensible heating and longwave radiative cooling results in a vertical decreasing gradient of diabatic heating in the lower troposphere. It generates the stronger southerlies over the subtropical South Indian Ocean than over the southern Africa. Meanwhile, over the South Indian Ocean, the increasing static stability as a result of the downward transport of a more stable atmosphere partly offsets the effect of the vertical gradient of diabatic heating, and southerlies still prevail there. Over the southern Africa, topographic friction dissipation induces northerlies, balancing the effect of the vertical gradient of diabatic heating with a stronger magnitude, and northerlies prevail.

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Climatology of the Mascarene High and Its Influence on Weather and Climate over Southern Africa

Cited by 41 publications

References 51 publications

Multi-Decadal Variability and Future Changes in Precipitation over Southern Africa

Multi-Decadal Variability and Future Changes in Precipitation over Southern Africa

Trend analysis of cold extremes in South Africa: 1960–2016

Structure and maintenance mechanisms of the Mascarene High in austral winter

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