Arctic Sea Ice

The U.S. National Ice Center (NIC) is an inter-agency sea ice analysis and forecasting center comprised of Dept. of Commerce/NOAA, Dept. of Defense/U.S. Navy, and Dept. 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 (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组分构成。自1972年起，NIC便持续制作北极与南极海冰图。本数据集是基于NIC每周或每两周一期的业务化海冰图时间序列生成的北极海冰密集度气候态。用于构建该气候态的海冰图时间跨度为1972年至2004年，其月度气候态产品包含中位数、最大值、最小值、第一四分位数与第三四分位数的密集度数据，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EASE格网（EASE-Grid，网格化二进制）格式存储。可通过对等面积EASE格网单元的数量求和，从密集度数据中推导海冰范围。此外还提供了GIF格式的预览文件。该气候态数据同时提供兼容地理信息系统（Geographical Information System, GIS）的格式。NIC海冰图基于现有原位观测、遥感及模式数据源进行分析制作，主要用于任务规划与航行安全保障。总体而言，NIC海冰图所呈现的海冰覆盖范围大于被动微波反演得到的海冰密集度数据，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。学界普遍认为，NIC序列的海冰密集度记录要优于被动微波传感器的反演结果，尤其是1990年代中期之后的序列（详见文档中的参考文献），但该序列缺乏部分被动微波时间序列所具备的一致性。