Climatological Data For Clouds Over the Globe From Surface Observations, 1982-1991: The Total Cloud Edition (1994) (NDP-026a)

Routine, synoptic surface weather reports from ships and land stations over the entire globe, for the 10-year period December 1981 through November 1991, were processed for total cloud cover and the frequencies of occurrence of clear sky, sky-obscured due to precipitation, and sky-obscured due to fog. Archived data, consisting of various annual, seasonal and monthly averages, are provided in grid boxes that are typically 2.5° — 2.5° for land and 5° — 5° for ocean. Day and nighttime averages are also given separately for each season. Several derived quantities, such as interannual variations and annual and diurnal harmonics, are provided as well. This data set incorporates an improved representation of nighttime cloudiness by utilizing only those nighttime observations for which the illuminance due to moonlight exceeds a specified threshold. This reduction in the night-detection bias increases the computed global average total cloud cover by about 2%. The impact on computed diurnal cycles is even greater, particularly over the oceans where it is found (in contrast to previous surface-based climatologies), that cloudiness is often greater at night than during the day. For access to the data files, click this link to the CDIAC data transition website: http://cdiac.ess-dive.lbl.gov/ndps/ndp026a.html1981年12月至1991年11月的10年间，全球范围内船舶与陆基气象站的常规天气图式地面气象报告，被用于分析总云量（total cloud cover）、晴空（clear sky）出现频率、因降水引发的天空遮蔽（sky-obscured due to precipitation）频次以及因雾引发的天空遮蔽（sky-obscured due to fog）频次。 存档数据包含多类年、季、月平均值，以网格单元形式存储：陆地区域网格尺寸通常为2.5°×2.5°，海洋区域为5°×5°。此外，数据集还按季节分别提供日间与夜间的平均统计结果。 本数据集同时提供多项衍生统计量，包括年际变化（interannual variations）、年谐波与日谐波（diurnal harmonics）等。 本数据集仅选取月光照度超过指定阈值的夜间观测数据，以此优化夜间云量的表征方式。该修正措施降低了夜间探测偏差（night-detection bias），使计算得到的全球总云量平均值提升约2%；对昼夜循环（diurnal cycles）的计算结果影响更为显著，尤其在海洋区域——与以往基于地面观测的气候数据集（surface-based climatologies）不同，本研究发现海洋区域的夜间云量通常高于日间。 如需获取数据文件，请点击此链接跳转至CDIAC数据转换网站：http://cdiac.ess-dive.lbl.gov/ndps/ndp026a.html