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《Module 2 Environmental problems Unit 4 Natural disaters More practice The ice storm》名校名师PPT课件（沪教版九年级下册）
Module 2 Environmental problems
Period 6
More practice
Project
Natural disasters
What is an ice storm?
a type of winter storm characterized by freezing rain,
also known as a glaze event or, in some parts of
the United States, as a silver thaw.
The U.S. National Weather Service defines an ice
storm as a storm which results in the accumulation of
at least 0.25-inch (6.4?mm) of ice on exposed surfaces
Branches and whole trees fell down.
How does an ice storm form?
ice storm 冰暴
当两股冷空气相遇(一股接近地球表面，一股高
高在上)，且中间还夹有一层暖空气，就会形成冰
暴。从上层冷空气会形成雪花，但当雪花降落至中
间暖层时，会融化成雨水，当雨水再降落并穿过最
下层的冷空气层时，会发生知之甚少的所谓“过冷”
现象，使雨水快速变冷至冰点以下，却依然保持液
态——当这些非正常冷却水到达地面时，会马上冻
结成半透明的冰凌，并包裹在所附着物的表层，形
成复杂的美丽花纹。
Brainstorm ideas with your classmates.