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

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.

每当遭遇极端高温或低温天气时，人们总会不禁发问：此次极端最低或最高气温是否创下了国家、省份、特定地点或当月的气温纪录？
基于此，本研究从Schulze与Maharaj（2004）构建的1950-2000年共51年逐日气温数据库中，提取了气温区间两端的极端值，并以表格与地图形式开展分析。
尽管上述图表与地图具备一定的参考价值与趣味性，但其精度仍存在一定局限，相关局限性的成因将在包含本分析科学背景的灰色标注区块中展开讨论。
针对南非气温极端值制图所存在的局限性：覆盖南非全境的429700个空间分辨率为1弧分（arc minute）的网格点上，逐日气温时间序列的生成依赖于“最优”控制站点的选取、对特定区域内高于该区域最高海拔站点的区域进行气温外推，以及针对逐日气温初值与终值的计算流程（Schulze与Maharaj，2004）。
针对极端最低气温，本研究未考虑冷空气沿坡地向山谷汇聚的效应，该效应可能会加剧极端最低气温的极值幅度。
本研究依托Schulze与Maharaj（2004）提出的区域/季节气温递减率及插值补全技术，基于覆盖南非全境的429700个1弧分（即1.7×1.7公里）栅格点（raster point）上生成的经过质量控制的逐日最高、最低气温时间序列（1950-2000年，共51年），并结合超过970个合格气象站点的观测记录，推导出气温极端值。
为避免对因观测记录错误导致的异常气温极端值开展分析与制图，本研究将每个网格点气温时间序列中筛选得到的前两个最高值或最低值的平均值作为最终极端值。