Monthly mean of diurnal (daily) temperature ranges for the 50 year (1950 - 1999) period (C) - January

The diurnal temperature range is the difference between the maximum and minimum temperatures on a given day. Some plants respond to the rhythmic variations brought about by shifts from high temperatures during the day to low temperatures during the night. The main long term factors affecting diurnal temperature ranges over South Africa are continentality and altitude (Schulze, 1997). It nevertheless needs emphasising here that short term, irregular diurnal conditions are often controlled by the passage of cold fronts or other air masses which may be associated with strongly contrasting temperature regimes. "Monthly means of diurnal (daily) temperature ranges were derived from the 50 year (1950 - 1999) time series of quality controlled daily maximum and minimum temperature 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). From theoretical considerations, experience and analyses of high quality daily temperature datasets, the diurnal temperature range is very seldom < 2 degree Celsius. When, therefore, on a given day the temperature range value was computed to be < 1.5 degree Celsius, this value was `forced` to be 1.5 degree Celsius, with equal compensatory adjustments being made to that day's maximum and minimum temperature values."

昼夜温差（diurnal temperature range）指某一日最高气温与最低气温的差值。部分植物会响应由日间高温向夜间低温转变所带来的节律性温度变化。影响南非地区昼夜温差的主要长期因素为大陆度与海拔（Schulze, 1997）。但在此需强调：短期、无规律的昼夜温度状况往往受冷锋过境或其他气团影响，此类气团通常伴随温差悬殊的温度环境。本数据集的昼夜（日）温差月均值，源自覆盖南非全境的429700个1弧分（即1.7×1.7 km）栅格点的50年（1950-1999）日最高、最低气温时序序列，数据处理采用了Schulze与Maharaj（2004）提出的区域/季节气温递减率及插值填充技术。基于理论推导、实践经验以及对高质量日气温数据集的分析可知，昼夜温差极少低于2摄氏度。因此，当某日计算得到的温差值低于1.5摄氏度时，将该值强制修正为1.5摄氏度，并对当日的最高、最低气温进行等量的补偿性调整。