National Ice Center Arctic sea ice charts and climatologies in gridded format, 1972-2004

The U.S. National Ice Center (NIC) is an inter-agency sea ice analysis and forecasting center comprised of Department of Commerce/National Oceanic and Atmospheric Administration (NOAA), Department of Defense/U.S. Navy, and Department of Homeland Security/U.S. Coast Guard components. Since 1972, NIC has produced Arctic and Antarctic sea ice charts. This data set is an Arctic sea ice concentration climatology derived from the NIC weekly or biweekly operational ice chart time series. The charts used in the climatology are from 1972 through 2004, and the monthly climatology products are median, maximum, minimum, first quartile, and third quartile concentrations, as well as frequency of occurrence of ice at any concentration for 33 year, 10 year, and 5 year periods. These climatologies and the charts from which they are derived are provided in 25 km EASE-Grid (the NSIDC Equal-Area Scalable Earth Grid/gridded binary). Ice extent can be derived from concentration by summing the number of equal area EASE-Grid cells. GIF browse files are also provided. The climatologies are also made available in a Geographical Information System (GIS) compatible format. NIC charts are produced through the analyses of available in situ, remote sensing, and model data sources. They are generated primarily for mission planning and safety of navigation. NIC charts generally show more ice than do passive microwave derived sea ice concentrations, particularly in the summer when passive microwave algorithms tend to underestimate ice concentration. The record of sea ice concentration from the NIC series is believed to be more accurate than that from passive microwave sensors, especially from the mid-1990s on (see references in the documentation), but it lacks the consistency of some passive microwave time series.

美国国家冰情中心（U.S. National Ice Center, NIC）是跨部门海冰分析与预报机构，由美国商务部/国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）、美国国防部/美国海军以及美国国土安全部/美国海岸警卫队的相关部门组成。自1972年起，NIC便开始编制北极与南极海冰图。本数据集源自NIC每周或每两周发布的业务化海冰图时间序列，为北极海冰密集度气候态数据集。本气候态所用的海冰图取自1972年至2004年，其月度气候态产品包含中位数、最大值、最小值、第一四分位数和第三四分位数的密集度值，以及33年、10年和5年时段内任意密集度海冰的出现频率。上述气候态数据及其源海冰图均采用25千米分辨率的EASE格网（NSIDC等面积可缩放地球格网/栅格二进制格式）存储。可通过累加等面积EASE格网单元的数量，从密集度数据中推导出海冰覆盖范围。此外还提供了GIF格式的预览文件，同时气候态数据也支持以地理信息系统（Geographical Information System, GIS）兼容格式分发。NIC海冰图基于原位观测、遥感与模式模拟多源资料分析生成，主要服务于任务规划与航行安全保障。总体而言，NIC海冰图所显示的海冰范围通常大于被动微波反演得到的海冰密集度，尤其在夏季，此时被动微波反演算法往往会低估海冰密集度。现有研究认为，NIC序列的海冰密集度记录相较于被动微波传感器的反演结果更为准确，尤其是在1990年代中期之后（详见文档参考文献），但该序列缺乏部分被动微波时间序列所具备的一致性。