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.

当遭遇极端高低温天气时，人们总会询问该次‘极端’（extreme）最低或最高气温是否创下了该国、该省份、特定地点或对应月份的气温纪录。
正因如此，研究团队从Schulze与Maharaj（2004）构建的1950—2000年共51年逐日气温数据库中，提取了气温两端的‘极端’（extremes）值，并以表格与制图形式开展分析。
尽管这些图表与地图兼具信息价值与学术趣味性，但其准确性仍存在一定局限，相关原因将在包含本分析科学背景的阴影区块中详细讨论。
南非极端气温制图面临的局限性：覆盖南非的429700个1弧分空间分辨率栅格点的逐日气温时间序列生成，依赖于"最优"控制站点的选取、针对特定区域内高于最高站点海拔区域的气温外推方法，以及针对逐日气温初末值的计算流程（Schulze与Maharaj，2004）。
针对极端最低气温，本研究未考虑冷空气向山谷汇集的效应，该效应可能会加剧极端最低气温的异常偏差。
本研究利用Schulze与Maharaj（2004）提出的区域/季节气温递减率与空间插值技术，基于覆盖南非的429700个1弧分（即1.7×1.7千米）栅格点的51年（1950—2000年）经过质量控制的逐日最高、最低气温时间序列，从970余个合格气象站点的观测记录中反演得到极端气温值。
为避免分析与制图中出现因观测记录错误导致的异常极端气温，本研究将每个栅格点气温时间序列中筛选出的两个最高或最低值的平均值，作为该栅格点的最终极端气温值。