A synoptic decomposition of rainfall over the Cape south coast of South Africa

Engelbrecht, Christien J.; Landman, Willem A.; Engelbrecht, François; Malherbe, Johan

doi:10.1007/s00382-014-2230-5

Cited by 106 publications

(91 citation statements)

References 32 publications

(60 reference statements)

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“…Consistent spatial patterns across the data sets are confirmed by high (>0.82) PPC coefficients (below diagonal in Table 2), found to be statistically significant at the 99% level, despite the high autocorrelation [Wilks, 2011;Adams and Lawrence, 2014]. MAE values (above diagonal in Table 2) confirm the good agreement with values Figure 4), this is likely the result of the inclusion of different rainfall regimes and drier climates, especially across South Africa [Engelbrecht et al, 2015;Weldon and Reason, 2014].…”

Section: Evaluation Over a Range Of Data Setsmentioning

confidence: 63%

The onset and cessation of seasonal rainfall over Africa

2016

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Variation in the seasonal cycle of African rainfall is of key importance for agriculture. Here an objective method of determining the timing of onset and cessation is, for the first time, extended to the whole of Africa. The method is applied to five observational data sets and the ERA‐Interim reanalysis. Compatibility with known physical drivers of African rainfall, consistency with indigenous methods, and generally strong agreement between satellite‐based rainfall data sets confirm that the method is capturing the correct seasonal progression of African rainfall. The biannual rainfall regime is correctly identified over the coastal region of Ghana and the Ivory Coast. However, the ERA‐Interim reanalysis exhibits timing biases over areas with two rainy seasons, and both ERA‐Interim and the ARCv2 observational data set exhibit some inconsistent deviations over West Africa. The method can be used to analyze both seasonal‐interannual variability and long‐term change. Over East Africa, we find that failure of the rains and subsequent humanitarian disaster is associated with shorter as well as weaker rainy seasons, e.g., on average the long rains were 11 days shorter in 2011. Cessation of the short rains over this region is 7 days later in El Niño and 5 days earlier in La Niña years with only a small change in onset date. The methodology described in this paper is applicable to multiple data sets and to large regions, including those that experience multiple rainy seasons. As such, it provides a means for investigating variability and change in the seasonal cycle over the whole of Africa.

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Section: Evaluation Over a Range Of Data Setsmentioning

confidence: 63%

The onset and cessation of seasonal rainfall over Africa

2016

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“…4 The monthly mean of the number of days with CAPE at 12h00 UTC exceeding 1000 JKg −1 over the period 1979-2010. Values over the ocean have been masked out convective activity is likely due to a range of factors, such as cooler adjacent SSTs, lower instability in the atmosphere and is situated in a boundary region between the winter and summer rainfall regions, not a core convective region (Taljaard 1996;Weldon and Reason, 2014;Engelbrecht et al 2015). …”

Section: Bulk Wind Difference (Bwd) or Deep-layer Shearmentioning

confidence: 98%

A climatology of potential severe convective environments across South Africa

et al. 2016

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“…rainfall) is determined for the synoptic conditions expressed by each of the SOM nodes (e.g. Cassano and Cassano 2010;Engelbrecht et al 2015;Engelbrecht and Landman 2016;Hewitson and Crane 2002;Schuenemann et al 2008;Verdon-Kidd and Kiem 2009). In an alternative bottom-up approach, synoptic states corresponding to particular weather conditions, e.g.…”

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confidence: 99%

Interannual rainfall variability and SOM-based circulation classification

et al. 2017

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synoptic variables over a particular location; even though they are used in the development of the SOM their influence, however, diminishes with the size of the SOM spatial domain. The influence of the SOM domain size, the choice of SOM atmospheric variables and grid-point explanatory variables on the levels of explained variance, is consistent with the general understanding of the dominant processes and atmospheric variables that affect rainfall variability at a particular location. Keywords SOM · Synoptic circulation · Rainfall variability · Southern AfricaThe relationship between synoptic circulation and local expressions of climate is the foundation of synoptic climatology and traditionally underpins the process of interpretative weather forecasting. The basic premise of synoptic climatology is that the large-scale atmospheric circulation exerts some control over weather and related environmental phenomena at the Earth's surface, thereby providing a level of deterministic forcing which influences the local weather. This directly leads to the use of atmospheric circulation patterns as a means to express drivers of weather (and climate) variability. Self-Organizing Maps (SOM, Kohonen 2001) is a pattern clustering method that is used as one of the methods to derive synoptic circulation types in this and other contexts, including statistical downscaling (e.g. Hewitson and Crane 2006;Yin et al. 2011;Ohba et al. 2016) and process-based validation of GCMs (e.g. Brown et al. 2010;Finnis et al. 2009;Higgins and Cassano 2010).In the application of SOM to study climate variability, the evolution of synoptic drivers of weather is typically represented by progression through classes of daily synoptic states identified as SOM nodes. That progression Abstract Self-Organizing Maps (SOM) based classifications of synoptic circulation patterns are increasingly being used to interpret large-scale drivers of local climate variability, and as part of statistical downscaling methodologies. These applications rely on a basic premise of synoptic climatology, i.e. that local weather is conditioned by the large-scale circulation. While it is clear that this relationship holds in principle, the implications of its implementation through SOM-based classification, particularly at interannual and longer time scales, are not well recognized. Here we use a SOM to understand the interannual synoptic drivers of climate variability at two locations in the winter and summer rainfall regimes of South Africa. We quantify the portion of variance in seasonal rainfall totals that is explained by year to year differences in the synoptic circulation, as schematized by a SOM. We furthermore test how different spatial domain sizes and synoptic variables affect the ability of the SOM to capture the dominant synoptic drivers of interannual rainfall variability. Additionally, we identify systematic synoptic forcing that is not captured by the SOM classification. The results indicate that the frequency of synoptic states, as schematized by a relatively disa...

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A synoptic decomposition of rainfall over the Cape south coast of South Africa

Cited by 106 publications

References 32 publications

The onset and cessation of seasonal rainfall over Africa

The onset and cessation of seasonal rainfall over Africa

A climatology of potential severe convective environments across South Africa

Interannual rainfall variability and SOM-based circulation classification

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