Extremes (1950 - 2000) Of Minimum Temperatures (C) September

When days with very low or very high temperatures are experienced, the question is invariably asked as to whether that `extreme` minimum or maximum temperature was a record, either for the country or province, or for a specific location or month of the year. It is for that reason that `extremes` of temperatures, at both ends of the spectrum, were extracted from the daily temperature database generated by Schulze and Maharaj (2004) for the 51 year period (in this case) from 1950 to 2000, and analysed in tabular and mapped form. While these maps/tables are informative and interesting, there are nevertheless some limitations as to their accuracy, for reasons which are discussed in the shaded blocks containing some scientific background to the analyses.Limitations over South Africa to mapping extremes of temperatures, the generation of daily temperature time series at one arc minute spatial resolution at the 429 700 grid points covering South Africa depends on the selection of "best" control stations, extrapolating to altitudes above that of the highest-lying station in a particular region, as well as computational procedures regarding initial and final daily temperature values (Schulze and Maharaj, 2004). With respect to extreme minimum temperatures, no account has been taken of cold air drainage into valleys, which may aggravate minimum extremes.

Extremes of temperatures were derived from over 970 qualifying stations` records for the 51 year (1950 - 2000) time series of quality controlled daily maximum and minimum values generated at each of the 429 700 one arc minute (i.e. 1.7 x 1.7 km) raster points covering South Africa, using the regional/seasonal lapse rate and infilling techniques developed by Schulze and Maharaj (2004). In order to avoid analysing and mapping anomalous temperature extremes resulting from incorrect recordings, the extremes which were derived are therefore taken as the means of the two highest or lowest values found in the temperature time series at each grid point.

当遭遇气温极低或极高的日子时，人们总会问这样一个问题——这种“极端”最低或最高气温是否创下了全国、全省、特定地点或一年中某月份的纪录？正因如此，研究人员从Schulze与Maharaj（2004）生成的日气温数据库中提取了1950年至2000年这51年间的气温极值（涵盖高低两端），并以表格和地图形式进行分析。尽管这些地图/表格兼具信息量与趣味性，但由于分析的科学背景部分（见阴影区块）所讨论的原因，其准确性仍存在若干局限。

在南非进行气温极值制图时存在若干局限，例如在覆盖南非的429700个1角分空间分辨率网格点上生成日气温时间序列，依赖于“最佳”控制站的选择、向特定区域内最高站点海拔以上区域的外推，以及与日气温初始值和终值相关的计算流程（Schulze与Maharaj，2004）。关于极端最低气温，研究未考虑冷空气向山谷的下沉现象，而这一现象可能加剧最低气温的极端程度。

气温极值是利用Schulze与Maharaj（2004）开发的区域/季节气温直减率（lapse rate）及填充技术，从覆盖南非的429700个1角分（即1.7×1.7千米）栅格点（raster points）上生成的51年（1950-2000）质量控制日最高与最低气温时间序列中提取而来，这些时间序列的数据来源于970余个符合条件的站点记录。为避免分析和绘制由错误记录导致的异常气温极值，最终提取的极值为每个网格点气温时间序列中最高或最低的两个值的平均值。