North Temperate Lakes LTER: Ice Duration - Madison Lakes Area 1853 - current

Data include dates of freeze-up and thaw and ice duration of three primary lakes in the Madison area (Lake Mendota, Lake Monona, and Lake Wingra). Data are obtained from the State Climatologist. For Monona and Wingra, the freeze date (ice on) is defined as the first date on which the water body is observed to be completely ice covered, and the breakup date (ice off) is the date of the last breakup observed before the open water phase. Ice duration is the number of days that a water body is completely covered with ice and excludes any period during which the lake thawed in mid-winter before freezing again. For Mendota, duration is calculated in the same manner, but ice on and ice off dates are assigned as follows: The lake is deemed frozen if it has solid ice from Picnic Point to Maple Bluff and total ice cover is greater than 50 %. The lake is deemed open if it is ice-free from Picnic Point to Maple Bluff and total ice cover is less than 50%. Sampling Frequency: annually Number of sites: 3

本数据集涵盖麦迪逊地区三座核心湖泊——门多塔湖（Lake Mendota）、莫诺纳湖（Lake Monona）与温格拉湖（Lake Wingra）——的封冻日期、解冻日期及冰期时长数据。数据由州气候学家（State Climatologist）提供。针对莫诺纳湖与温格拉湖，封冻日期（冰面覆盖）指首次观测到水体完全被冰体覆盖的日期，解冻日期（冰面消退）则为开放水体阶段来临前最后一次观测到冰面消融的日期。冰期时长为水体完全被冰体覆盖的累计天数，需排除冬季中期出现解冻后再次封冻的时段。对于门多塔湖，冰期时长的计算规则与上述一致，但冰面覆盖与消退日期的判定标准不同：若从野餐角（Picnic Point）至枫树崖（Maple Bluff）区域存在坚固冰层，且总冰盖占比超过50%，则判定该湖泊已封冻；若该区域无冰，且总冰盖占比低于50%，则判定该湖泊已解冻。本数据集的采样频率为年度采样，共设置3个监测站点。