连下了几天雨，这是天上的云。
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明早。
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好天气。
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casio protrek prg－250t的气压计功能还不错，基本上跟kestrel 4000读数一致。

层云（stratus，St）

定义：云底很低，呈灰色或灰黑色的均匀云层。

层云云体均勾成层，呈灰色，似雾，但不与地接，常笼罩山腰。层云又可分成2类：层云、碎层云；同名植物，仙人掌的一种；同名人物，霹雳布袋戏虚拟人物。

层云（stratus）

概述

云底离地面高度常在2000米以下，属低云族。云体均匀成层，呈灰色或灰白色，像雾，但不接地，经常笼罩山体和高层建筑。主要由小水滴构成，为水云。

在一定条件下层云几乎能够达到地面。层云完全没有结构，它由细小的水珠组成。层云中往往会落下细雨或者细雪，但是不会下大雨。一般在风比较静的气象条件下会形成层云。在气温非常低的状况下甚至可能出现光晕。
  
层云也有时降毛毛雨，冬季降小雪。云维持时间不长，约几小时。层云被风吹散或趋于消失时，常分裂成不规则的散片，称为碎层云（它呈灰色或灰白色，当碎层云出现时将是晴天）。

层云是由直径5-30微米的水滴或过冷水滴组成。层云厚度一般在400-500米之间。云底高度一般为50-100m。内云滴直径偏小，其平均体积直径约为13μm。含水量很小，平均约0．2g/m。寒冷季节时的层云也可能是冰晶和过冷水滴组成的混合云，其液态含水量更小，平均约O．1g/m。在个别情况下，层云由冰晶组成。

层云是在大气稳定的条件下，因夜间强辐射冷却或乱流混合作用，水汽凝结或由雾抬升而成。层云常在太阳升起之后气温逐渐升高，稳定层被破坏，层云也逐渐消散。

形成

由于夜间降温，或者潮湿气流流入，或者大雨后蒸发，大气的下层潮湿阴冷时能够形成层云。太阳升起后地面加热后雾也能成为层云。薄的层云一般在天亮后，或者在白天里逐渐消散。冬季在反气旋和逆温的情况下层云也可以维持数日。

分类

层云云体均勾成层，呈灰色，似雾，但不与地接，常笼罩山腰。层云又可分成2类：

1.层云：云体均勾成层，呈灰色，似雾，但不与地接，常笼罩山腰。

2.碎层云：由层云分裂或浓雾抬升而形成的支离破碎的层云小片。

积云（cumulus，Cu）
定义：轮廓分明

积云通常在湿润地区和热带地区出现，但有时也会在干燥地区出现。除非积云变成积雨云，否则不会出现阵雨，尤为正午后形成的云堆和积雨云表示阵雨很可能出现。

积云（Cumulus，Cu），分为淡积云、浓积云、碎积云三类，

是一种垂直向上发展的云块。积云为轮廓分明，顶部凸起，云底平坦，云块之间多不相连的直展云；它是由低层空气对流作用使水汽凝结或在冬季凝华而形成的云。积云云底基本为水平状，顶部为圆弧状，有孤立的，也有重叠圆拱状的或直线排列的，外型类似棉花堆。

积云云底高度在湿度大的地区一般在600-1200米，在干燥的地区为3000米，积云底部清晨接近地面，在午后就会上升。积云一般在上午出现，午后最多，傍晚渐渐消散。

成因

积云是由气块上升、水汽凝结而成。

一团空气上升，在开始时它的内部水汽含量和温度的水平分布基本上是均匀的，从而水汽产生凝结的高度是一致的，因此，一朵积云具有水平的底部。由于在形成阶段，云内为上升气流且云顶※※上升气流最强，四周较弱，云外为下沉气流，造成积云具有圆拱形向上凸起的顶部以及明显的轮廓。积云主要在白天形成，因为阳光使空气变热，另一方面，地面也使空气变热。积云也可在白天山顶上形成，因为山坡受热比谷底受热快。这种不稳定的受热形成运动中的对流。积云有时伴随或提前冷锋而形成。因为在锋区，空气被迫抬升。

积云主要在白天形成，因为在阳光照射下地面会迅速增温，使空气变热，热对流导至积云产生。 积云通常在湿润地区和热带地区出现，但有时也会在干燥地区出现。除非积云变成积雨云，否则一般不会出现降雨。

组成

积云（cumulus）是由水滴组成，但有时可伴有冰晶，它主要是由空气对流上升冷却使水汽发生凝结而形成的。因此，积云的外形特征与空气对流运动的特点紧密相联。

特征

积云（cumulus）垂直向上发展的顶部呈圆弧形或圆拱形重叠凸起，而底部几乎是水平的云块。云体边界分明。 如果积云和太阳处在相反的位置上，云的中部比隆起的边缘要明亮；反之，如果处在同一侧，云的中部显得黝黑但边缘带着鲜明的金黄色；如果光从旁边照映着积云，云体明暗就特别明显。

分类

个体明显，底部较平，顶部凸起，云块之间多不相连，云体受光部分洁白光亮，云底较暗。积云又可分成3类。

淡积云

空气对流运动不很强（一般垂直速度不超过5m/s）时形成的积云，对流所及高度高于凝结高度不多，云向上发展较弱， 因此形体扁平，顶部略有拱起，云的水平宽度大于垂直厚度。厚的淡积云中间有阴影。淡积云孤立分散在空中， 晴天常见。

浓积云

空气对流运动旺盛时（垂直速度强盛时可达15-20m/s）形成的积云。由于对流所及高度高于疑结高度很多， 故云体向上发展较强，在成熟阶段的浓积云，厚度可达4-5千米，显得庞大高耸， 其垂直厚度大于水平宽度云内每一股强盛的上升气流使云顶形成一个云泡，故浓积云云顶呈重选的圆拱形隆起， 状似花椰莱。由于浓积云比淡积云厚密庞大，不易透过阳光，故凹凸的云表面有明显阴影。被阳光照耀部份很白亮， 被遮阴部份则显得阴暗。浓积云在中、低纬度地区有时可降阵雨。在浓积云迅速发展过程中， 如其云顶上部有一层比较潮湿的空气层，受上升气流的影响，局部上抬，则若有水汽凝结，就可形成白色云纱般的云片， 状如覆盖在浓积云顶的头巾或帽子，如图2，此种云称为云幞。浓积云一般不产生降水，但有时也可降小雨。 如果清晨有浓积云发展，表明大气层结不稳定，常有积雨云发展，甚至有雷阵雨产生。

碎积云

在淡积云形成之前或积云被风吹散时，会形成边缘破碎、轮廓不完整、形状多变的碎积云。 碎积云多有1—15微米的水滴组成。如单独出现且无明显发展，一般表示天气稳定。

层积云，stratocumulus，Sc

定义：由众多白色或灰色云块组成的低云，常带有阴暗部分，云块单体具有不同形状，但视角宽度大于5°。

层积云(Stratocumulus Sc) 云块一般较大，在厚薄、形状上有很大差异，有的成条，有的成片，有的成团。常呈灰白色或灰色，松散，薄的云块可辨太阳的位置，厚的云块比较阴暗。云块常成群、成行或成波状排列。

基本信息

层积云（Stratocumulus Sc）

层积云和高积云
云底离地面高度常在2000米以下，属低云族。是由片状、团块或条形云组成的云层或散片。有时呈波状或滚轴状，犹如大海波涛。层积云个体肥大，结构松散，多由小水滴组成，为水云。呈灰白色或灰色。在云块较薄处，太阳的位置可辨认。层积云又可分为透光层积云、蔽光层积云、积云性层积云、堡状层积云、荚状层积云等。

基本特征

云块一般较大，其薄厚或形状有很大差异，常呈灰臼色或灰色，结构较松散。薄云块可辨出日、月位置；厚云块则较阴暗。有时零星散布，大多成群、成行、成波状沿一个或两个方向整齐排列。

形成过程

层积云的组成成分是直径为5-40微米的水滴。在冬季出现的层积云也可能由冰晶、雪花组成。层积云在多数情况下，是由于空气的波状运动和乱流混合作用使水汽凝结而形成。有时是由强烈的辐射冷却而形成的。薄的层积云一般表示天气较稳定，不过层积云逐渐加厚，甚至融合成层时则表示天气将有变化。低而厚的层积云往往产生降水，但不太可能形成大型降水，因为层积云的云层薄，向上运动很弱，可能出现的降水为毛毛雨和零星小雨。它的存在影响日气温变化，即白天降低日照，夜晚又阻碍冷空气的扩散，所以形成凉爽、潮湿的天气。

主要分类

层积云在海洋环境下，云层底部距地面达150-600米，在冷锋后和靠近湖区，云底高度约为600-1500米，在其它地区，尤其是积云扩散形成的层积云底部高度可达900-2000米。层积云的厚度一般从几百米到二千米。层积云全球皆会出现，尤其在凉爽的海洋和沿海地区，但在干燥地区较为少见。

透光层积云：云块较薄，呈灰白色，排列整齐，缝隙处可以看见蓝天，即使无缝隙，云块边缘也较明亮。
蔽光层积云：云块较厚；显暗灰色，云块间无缝隙，常密集成层，布满全天，底部有明显的波状起伏。
积云性层积云：云块大小不一，呈灰白或暗灰色条状，顶部有积云特征，由衰退的积云或积雨云展平而成。
荚状层积云：云体扁平，常由傍晚地面四散的受热空气上升而直接形成。
堡状层积云：云块顶部突起，云底连在一条水平线上，类似远处城堡。

这段时间在学习云的知识。

今早。
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谍中谍。
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爬沙丘。
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再摆一个。
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摆pose。
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昨天娃儿去了skytower，下面是玻璃地板，但娃儿一点儿也不害怕～～

没买。要想要数据线的话，那就干脆买蓝牙版的了。

自己翻出了旧的手机套挖了两个洞。
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有数据线？

雪暴（英语：Blizzard），又稱暴风雪、飞雪，-5℃以下大降水量天气的统称，且伴有强烈的冷空气气流。

雪暴的形成类似于与暴风雨相似。在冬天，当云中的温度变得很低时，使云中的小水滴结冻。当这些结冻的小水滴撞到其他的小水滴时，这些小水滴就变成了雪。当它们变成雪之后，它们会继续与其他小水滴或雪相撞。当这些雪变得太大时，它们就会往下落。大多数雪是无害的，但当风速达到每小时56千米，温度降到-5℃以下，并有大量的雪时，雪暴就會形成。

雪是水或冰在空中凝結再落下的自然現象，或指落下的雪花。雪是水在固态的一种形式。

雪只會在很冷的溫度及溫帶氣旋的影響下才會出現，因此亞熱帶地區和熱帶地區下雪的機會較微。以香港為例，現有的紀錄只有1893年1月才下過（1967年12月28日也有記錄[1]）。有些溫暖地區，如台灣或熱帶非洲的平地不下雪，但該地寒冷的高山會下雪。而某些主題公園會提供人工雪給人玩。

雪花是在雲內由微小的冰晶互撞黏在一起後形成豐富多樣的形狀。沒有兩個雪花是完全相同的，但雪花仍然謹守著最初的冰晶基本的六角形對稱標準結構。透過顯微鏡可以看見雪花錯綜複雜的構造大多都是六角形的，而雪花的中心一定呈現出對稱的六角形，它之所以有這樣的形狀，是因為它要在平面上以最有效率的方式佈置，它是結晶學的研究對象之一。

天氣非常寒冷時，冰晶不易黏在一起，雪呈細粉狀的小雪珠。雪珠是雲中溫度低於攝氏零度的許多小雲滴在冰晶上互相碰撞凝結而成，仔細觀察雪珠的形狀，可以看出小雪珠是由許多細白的冰粒聚集而成的。當冷空氣逐漸向前推移，上升氣流減弱，雲中水氣直接在冰晶上凝結成較大的形態，此即我們所見到的雪花。如果溫度接近冰點，則會落下溼雪，形成較大的雪花，特別是無風的時候。大型的星形雪花直徑可達5到7公分。多數的雪花在落下地面的途中會融化成雨，只有當接近地面的空氣夠冷，才能讓雪花落到地面成雪。

形成

大氣中的水蒸汽直接凝华或水滴直接凝固而成，就是雪。也可說是雲中的溫度過低，小水滴結成冰晶，落到地面仍然是雪花時，就是下雪了。冰融化時會吸熱，所以地面氣溫會比下雪時低。

條件
大氣中需含有較冷的冰晶核。
充分的水汽。
0℃（冰點）以下。如該冷空氣相當強烈，並帶著濕氣，1℃至10℃的氣溫同樣可以降雪。

能降雪的地方
氣候區屬中緯度至高緯度（即大約於南回歸線以南／北回歸線以北地區）的地方就會有降雪的機會，如果於低緯度地方中有些地勢高於海拔2000米的高山或高原也有同樣的機會。
海洋氣流也能間接影響該區下雪的機會率，如果在高緯度地區一帶有較多暖流支配，會減低該區下雪的機會（例如日本本州至九州一帶）。

雪的融化

当有能量输入的时候，积雪会由固态转变为其他形态。使积雪融化的能量可能来自下列途径：辐射（太阳发出的短波辐射或者长波热辐射）、热传导（当气温高于0℃时），或者通过落入积雪的，温度超过0℃的雨滴。积雪的融化速度，不仅取决于所输入的能量的多少，也取决于当时的气温和湿度。具体说来，空气越干燥，积雪融化的速度越慢，因为此时雪更容易升华——即固体不经由液体，直接转变为气体的过程——而升华需要较多的能量，这使得周围的积雪被冷却，从而减缓了融化的速度。

通过“湿球温度”和“露点温度”，我们可以界定积雪融化过程的三个状态。“湿球温度”指的是从干湿计的湿球温度计上读出的温度，该温度始终低于大气温度——即使大气相对湿度为100%的时候也不例外。而“露点温度”指的是，空气中所含的气态水达到饱和，从而凝结成液态水所需要的温度。露点温度又总是低于湿球温度。

当湿球温度低于0℃的时候，积雪升华。这个过程十分缓慢，而此时积雪也保持干燥。在相对湿度小于20%的时候，升华甚至可以在7℃的气温下进行。

当湿球温度高于0℃，而露点温度低于0℃的时候，积雪熔解。这时，固态的雪既转化为气态，同时又转化为液态。

当露点温度也高于0℃的时候，积雪会融解，也就是说，积雪只从固态转变为液态。这时积雪融化的速度最快。

举例来说，在相对湿度为50%的时候，当气温低于3.5℃时，积雪升华；当气温介于3.5－10℃之间时，积雪熔解；当气温高于10℃，则积雪融解。

濕球溫度.露點溫度,干球溫度,相對濕度的定義及區別:

濕球溫度：表示蒸發水的制冷效應，當水分被蒸發到飽和空氣時空氣將冷卻到的溫度。
露點溫度：水分將會從空氣中凝結出來的溫度點。
干球溫度：由普通的溫度計測得的空氣溫度。
相對濕度：在給定的空氣溫度下，水蒸氣壓（當前空氣中的水分量）和飽和水蒸汽壓（空氣中能夠維持的水分總量）之比。

酷热指数（Heat Index）是一种综合空气温度和相对湿度来确定体感温度的指数──即真正感受到的热度。人体通过排出汗液来达到降温的目的，在这个过程里汗液中的水分得以蒸发并且从人体带走热量。但是当相对湿度较高时，水分的蒸发率就会降低。这意味着从身体中带走热量的过程变得缓慢，相对处于干燥空气中的情况，人体内就保留了更多的热量。基于在已知温度和湿度时的主观描述定义的计量方法，得出的指数可以将一组温度和湿度的组合换算成干燥空气中的一个相对更高的温度值。

而在加拿大，采用类似的湿度指数来代替酷热指数。

在高温时，能够使酷热指数高于实际温度所需的相对湿度的大小要低于在低温条件下的情况。例如，在80°F（接近27°C）时，如果这个时候的相对湿度是45%的话，酷热指数等于实际温度。但在110°F（差不多43°C）时，任何高于17%的相对湿度将使得酷热指数高于110°F。 如果实际温度低于接近68°F（20°C）时──特别是相同的温度低于风寒指数的温度时，湿度就不被认为是升高体感温度的全部原因。应该要注意到湿度指数和风寒指数是基于在遮蔽处而不是暴露在阳光下的计量，因此当暴露在阳光下时需要额外注意。

有的时候酷热指数和风寒指数被合称为一个名词“体感温度”或是“相对室外温度”。

气象学上的考虑

在室外开放空间中，随着相对湿度的增加，首先出现阴霾最后形成浓密的云层覆盖，这导致阳光直射地面的总量减少；因此得到一个可能最大温度值和可能最大相对湿度值的倒转关系式。出于这个原因，人们曾经认为在地球上任何地方能够得到的最大酷热指数是接近于160°F（71°C）。然而，在2003年的7月8日，沙特※※※的达兰，露点达到95°F（35°C），当时实际温度是108°F（42°C），已知的相对湿度是67%。这个时候的酷热指数是176°F（80°C）。[1]整整16°F（9°C）高于地球上曾被认为能够得到的最高酷热指数。

一个比较酷热指数和真实温度不同之处的很好例子是通过比较美国路易斯安那州新奥尔良和加利福尼亚州贝克斯菲尔德的气候。新奥尔良在夏天由于靠近新墨西哥湾特别拥有较低的日间温度，然而这个城市的酷热指数却很高，因为当地的湿度通常很大。相对而言，贝克斯菲尔德的日间温度通常比新奥尔良高，但是它的湿度却低得多，因此感觉上就不如新奥尔良炎热。

要注意的是，这个指数只可作为参考，这是因为不同的人对热的适应程度不同。例如有些人在摄氏31度和相对湿度百分之70的情况下已感到很不舒服，有些人则不以为然；而且，风速、劳动强度、在高温环境下的暴露时间、体质强弱、水份供给和健康状况也会影响人对高温的反应。

酷热指数的影响 (遮蔽处取值)

华氏温度 摄氏温度 注意事项
80–90 °F 27–32 °C 警告 — 太长时间的暴晒和活动可能会导致疲劳
90–105 °F 32–41 °C 严重警告 — 可能引起中暑, 热痉挛和 热衰竭
105–130 °F 41–54 °C 危险 — 极有可能引起中暑, 热痉挛和热衰竭; 可能导致重度中暑
超过 130 °F 超过 54 °C 极度危险 — 持续暴晒极有可能引起中暑和重度中暑

有风的时候，感觉（wind chill）比气温要冷。
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合影，右上角是我的，左下角是lp的，右下是老大的，左下是老二的。

给lp买了个鸟牌的安全带，r280大号。选这个型号的主要原因是打折，又是推荐产品。我买的另外三个bd都是网兜装的，这个装在铁罐子里，鸟牌果然是派头十足。
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以后收集了些有用的文章会贴在这里。

What compasses are required by The Mountaineers for their Navigation Classes?

The Mountaineers was formed in 1906 to explore the wild areas and peaks surrounding the still-young city of Seattle. The club grew in leaps and bounds, eventually reaching a high point of 15,000 members in the 1990's. Today, the club is home to around 10,500 active members. Although the club has a small full-time staff, volunteers are responsible for running most of the programs. Volunteer leaders do everything from leading trips to teaching classes to promoting their programs.

The Mountaineers, the Mazamas, The Angeles Chapter of the Sierra Club and other outdoor clubs in the world offer classes to their members at a nominal cost because they are taught by qualified Volunteers.

Webmeister's Note: I was the Chairman of the Angeles Chapter Basic Mountaineering Training Committees for three years in the early 1980's. We trained about 1,000 Members each year in Basic and in Advanced Mountaineering covering Hiking, Rock Climbing, Navigation, Steep Snow Climbing, Light Weight Backpacking and the like. There is a lot to learn! "He who knows naught, knows not that he knows naught. Hiking the hills and summating peaks have Risks that are hidden to the uninformed, Risks that can, in part, be mitigated by the information and instruction (provided by major outdoor clubs and this Website)."

The Mountaineers offers a class in Navigation with map and Compass to Members, for about $35.00. The Class is Required for participation in certain Club Classes and Climbs. Participants must come to the first Class equipped with the proper compass.

Quoted below are, in part, the Navigation Class Requirements of The Mountaineers (and of TraditionalMountaineering):
Compass Requirements:
All compasses have a magnetized needle that points north, and have a way to indicate direction of travel. Mountaineering requires a compass with additional qualities. Compasses that hang from parka zippers or hook on watchbands are not suitable for this course or as part of your ten essentials. Good compasses are easily found, but many compasses on the market are not suitable for use in this course.

Caution - when buying a compass:
Every year, some students buy unsuitable compasses, usually the result of not following the guidelines below. Often, a sales person (who may or may not know the requirements of a good compass) was asked for advice. To complicate things further, our local outdoor stores sometimes run out of stock of the recommended compasses. Sales people will try to recommend alternatives (mostly unsuitable). They aren't malicious, but in fact are trying to be helpful. In reality, a good mountaineering compass has no substitute. Retailers will carry a variety of compasses, some suitable, some not.

Required Features:
1. Adjustable declination: A moveable orienting arrow, which provides a built-in declination adjustment. If there is one feature that simplifies map and compass work, this is it. Compasses with adjustable declination can often be identified by the presence of an adjustment screw on the back of the housing (on the underside of the compass, look at the bezel - the screw is usually brass or copper colored).
• All students MUST have a compass with adjustable declination. Be aware that compass descriptions in stores may not always be accurate. Be very sure to understand the requirements, not merely to read summary sheets. If you aren't sure, ask a salesperson to show you how to adjust the declination on a specific compass.
• If you already have a compass without adjustable declination, you may not use it in this course. Recent experience indicates that such compasses detract from the learning experience.

2. A transparent rectangular base plate with a direction of travel arrow (or a sighting mirror).
• Transparency allows map features to be seen underneath the compass.
• The rectangular shape provides straight edges and square angles for plotting and triangulating on the map.

3. A bezel (the rotating housing) marked clockwise from 0 to 360 degrees in increments of two degrees or less. (Some compasses are numbered backwards, in a counterclockwise direction. These are not suitable for use in this course.) In general, bezels should be large to allow use while wearing gloves - the larger size also improves accuracy. Black bezels with sloping sides are preferred.
4. Meridian lines: Marks on the bottom of the interior of the circular compass housing, marked with parallel 'meridian lines', which rotate with the bezel when it is turned. The meridian lines run parallel to the north-south axis of the bezel, however turned. Meridian lines are necessary for plotting and triangulating on the map.
5. A ruler and/or gradient scale engraved on one of the straight edges, used for measuring distances.
6. A 3 to 4-inch base plate. A longer straight edge makes map work easier.

Additional recommendations:
• A sighting mirror in the cover: This reduces errors introduced when moving the compass from eye-level after sighting to waist-level for reading the dial.
• A liquid-filled housing to reduce erratic needle movement (only needed on some compasses). In some cases, steadying the compass needle can be difficult.
• An inclinometer: a gravity driven arrow that allows you to measure slope angle.
• Note: Stay away from "quadrant-type" compasses marked from 0 to 90 degrees, 0 to 90, 0 to 90, 0 to 90, because they are difficult to use.

Recommended compasses:
Compasses must have the first 6 features listed, including a declination adjustment mechanism. Don’t buy a new compass without this declination adjustment feature. The declination adjustment can usually be identified by the presence of a small adjustment screw on the back of the bezel (on the underside of the compass).

The following list includes compasses that are equipped with appropriate features. This list is not all-inclusive, but is representative of good quality, fully equipped compasses suitable for this course and for other mountaineering activities. Prices for a good compass start at $20 without a mirror, more with a mirror.

Compasses SUITABLE for the course include:
SUUNTO model M2D Locator (around $20 - a best value for a compass without a mirror)
SUUNTO M3D (Note: This is my absolute favorite! Webmeister Speik)
SUUNTO MC-2G Navigator
SILVA 515 CL (in the past, this compass has been problematic, but the newer version has addressed previous problems)
Photographs of acceptable compasses - we suggest you look at this link before buying a compass.

Unacceptable compasses:
Compasses are unsuitable for mountaineering if they are too small for accurate bearings, do not have meridian lines, are numbered in 5 degree increments, have non-transparent housings, do not have degrees from 0 to 360, or cannot be used for measuring and plotting bearings on a map.

Features which make a compass undesirable or unsuitable:
Lack of a straight edge for plotting lines on a map
Lack of declination adjustment
Lack of meridian lines inside the bezel
Small size -- less than 3.5" x 2.2"
Small bezel - less than 2" in diameter

UNSUITABLE compasses for this course:
BRUNTON 26 DNL-CL
BRUNTON model 8020 GPS
SUUNTO KB20/360
SUUNTO MB-6 Matchbox
BRUNTON model 9020 G

Copyright © 2000-2001 The Mountaineers - all rights reserved

Hiking vs Trekking

Diffen › Recreation
We've often heard the terms hiking and trekking used interchangeably. We all know they're both outdoor recreational activities. But are they really the same?

Hiking is an outdoor activity of walking in beautiful natural environments on pre-charted paths called hiking trails. There are day hikes and overnight hikes.

Trekking is a long journey be undertaken on foot in areas where there are usually no means of transport available. Trekking is not necessarily mountaineering; it is walking for a number of days, usually on uncharted paths, in challenging environments which are likely to be hilly or mountainous.

Equipment

Depending on the weather and if the hike is for a day, a few hours or overnight, the equipment one carries varies. For a simple hike, good hiking shoes (preferably water proof), weather-appropriate clothing (hat, sunscreen, waterproof jacket), a trail map, compass, sunscreen, water, food and basic medical kit can be carried. The weight and bulk limit the amount of equipment that one can carry. The Leave No Trace policy also requires that equipment have multiple or alternative uses. Apart from what one would take on a day hike, overnight hikes and treks require a backpack, tent and sleeping bag for camping, fire lighting tools either flint or matches, food, water, survival kit, water purifying tablets, a compass, flashlight, map, insect repellent, A trekking pole or hiking pole which look like ski poles can be used in challenging treks can also be used. Equipment carried is to mitigate the dangers associated with hiking and trekking such as getting lost, dehydration or hypothermia, sunburn or frostbite, animal attacks, internal injuries like ankle sprains.

Trekking requires all of the above and a good supply of food.

Worldwide differences
Hiking is known by many names over the world. What is known as hiking in the U.S and Britain is called tramping in New Zealand, and bush-walking in Australia. Bushwhacking is a term used specifically for hiking through dense forest where vegetation needs to be whacked for slashed with a machete in order to advance. Thru-hiking is a term associated with long end-to-end hiking (hiking a trail completely in sequence in its entirety) on a trail specifically, the Appalachian Trail.

Locations
People usually go hiking in places of natural beauty. Hiking trails usually guide people through these areas which may be signposted so people do not lose their way. Whereas while trekking, the path is usually not marked and may not be previously charted. Trekking can take place in areas of great natural beauty but unlike hiking, not exclusively so. Trekking can also be a means of necessity in places where there is no vehicular transport. Hiking is a popular holiday experience especially in Europe, New Zealand, Chile, Costa Rica and Hawaii. Trekking is popular is the Himalayan foothills in Nepal, Bhutan and India and in the Andes in South America.

Environmental Impact
Hikers and trekkers follow a Leave No Trace policy to reduce the impact of their presence on the natural environment. A number of hikers over years on the same trail can cause unexpected damage on the environment such as wood depletion, wood fires. Fecal matter and non-biodegradable materials can contaminate the watershed. Some hikers have complained that pole use leaves a visible impact on the surrounding trail, poking visible holes in the ground and damaging adjacent vegetation. The most common complaint is that the carbide tips leave visible white scratches on rock, and make scraping sounds.

AVC Glossary of Atmospheric Terms

A

Absolute humidity:  It is the mass of water vapor in a given volume

Absolutely stable air:  It is an atmospheric condition that exists when the environmental lapse rate is less than the moist adiabatic lapse rate.

Absolutely unstable air:  It is an atmospheric condition that exists when the environmental lapse rate is greater than the dry adiabatic lapse rate.

Absorption:  Absorption is the process in which incident radiant energy is retained by a substance by conversion to some other form of energy.

Absorptivity: It is the efficiency of radiation absorption.

Accretion:  It is the growth of a precipitation particle by the collision of an ice crystal or snowflake with a super cooled liquid droplet that freezes upon impact.

Actual evapotranspiraton:  It is the rate of water lost from vegetation and soil, ordinarily at a slower rate than the potential rate.

Adiabat:  It is a line on a thermodynamic chart relating the pressure and temperature of a substance (such as air) that is undergoing a transformation in which no heat is exchanged with its environment.

Adiabatic process:  It is a process that takes place without a transfer of heat between the system (such as an air parcel) and its surroundings.  In an adiabatic process compression always results in warming, and expansion results in cooling

Adiabatic lapse rate:  It is the rate of decreased temperature experienced by a parcel of air when it is lifted in the atmosphere under the restriction that it cannot exchange heat with its environment.  For parcels that remain unsaturated during lifting, the (dry adiabatic) lapse rate is 9.8 degrees per kilometer.

Advection:  It is the horizontal transfer of any atmospheric property by wind.

Aerovane:  It is a device that resembles a wind vane with a propeller at one end.  It is used to indicate wind speed and direction.

Aerosol: Aerosol is a system of colloidal particles dispersed in a gas, such as smoke or fog.

Air density:  It is mass per unit volume of air; about 1.275 km per cubic meter at 0�C and 1000 millibars.

Air mass:  Air mass is a body of air covering a relatively wide area and exhibiting horizontally uniform properties.

Air pressure:  It is the cumulative force exerted on any surface by the molecules composing air.

Albedo:  Albedo is the reflectivity; the percent of radiation returning from a surface compared to that which strikes it.

Altimeter:  It is an instrument that indicates the altitude of an object above a fixed level. Pressure altimeters use an aneroid barometer with a scale graduated in altitude instead of pressure.

Altocumulus:  It�s a cloud belonging to a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus. These clouds are of medium altitude, about 8000-20,000 ft (2400-6100 m).  A middle cloud, usually white or gray, often occurs in layers or patches with wavy, rounded masses or rolls.

Altostratus:  It�s a cloud belonging to a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus. These clouds are of medium altitude, about 8000 to 20,000 ft (2400-6100 m).

Ambient air:  Ambient air is the air surrounding a cloud, or the air surrounding rising or sinking air parcels.

Anemometer: It is an instrument designed to measure wind speed.

Aneroid barometer:  It is an instrument for measuring atmospheric pressure in which a needle, attached to the top of an evacuated box, is deflected as changes in atmospheric pressure causes the top of the box to bend in or out.  It contains no liquid.

Anomalies: They are the departures of temperature, precipitation, or other weather elements from long-term averages.

Anticyclone:  It is a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere.

Arctic air:  Arctic air is a very cold and dry air mass that forms primarily in winter and the northern interior of North America.

Atmospheric pressure:  It is the pressure exerted by the earth's atmosphere at any given point, determined by taking the product of the gravitational acceleration at the point and the mass of the unit area column of air above the point.

Atmospheric window:  It is a region of the electromagnetic spectrum from 8 to 12 �m where the atmosphere is transparent to radiation.

Azimuth angle: 1. It is the direction or bearing toward which a sloping surface faces (e.g., a north-facing slope has an azimuth angle of 360�; a northeast-facing slope, an azimuth angle of 45�. 2. It is the arc of the horizon measured clockwise from north to the point where a vertical circle through a given heavenly body intersects the horizon (e.g., used for solar azimuth angle).

B

Barometer:  It is an instrument that measures atmospheric pressure. The two most common barometers are the mercury barometer and the aneroid barometer.

Barometric pressure: It is the pressure of the atmosphere as indicated by a barometer.

Beaufort scale:  It is a scale of wind strength based on visual assessment of the effects of wind on seas and vegetation.

Black body:  It is a hypothetical object that absorbs all of the radiation that strikes it. It also emits radiation at a maximum rate for its given temperature.

Blizzard:  It is a severe weather condition characterized by low temperatures and strong winds (greater than 32 mi/hr) bearing a great amount of snow. When these conditions continue after the falling snow has ended, it is termed a ground blizzard.

Bowen ratio:  A Bowen ratio is the ratio of energy available for sensible heating to energy available for latent heating.

Boyle's law:  It is when the temperature is held constant, the pressure and density of an ideal gas are directly proportional.

Boundary layer:  It is the layer of fluid in the immediate vicinity of a bounding surface; in the atmosphere, the air layer near the ground affected by diurnal heat, moisture or momentum transfer to or from the surface.

Brightness temperature:  See IR brightness temperature.

C

Capping inversion: It is an elevated inversion layer that caps a convective boundary layer, keeping the convective elements from rising higher into the atmosphere.

Ceilometer:  It is a device using a laser or other light source to determine the height of a cloud base. An optical ceilometer uses triangulation to determine the height of a spot of light projected onto the base of the cloud; a laser ceilometer determines the height by measuring the time required for a pulse of light to be scattered back from the cloud base.

Centrifugal force:  It is a force directed outward, away from the center of a rotating object; equal in magnitude to the centripetal force but in the opposite direction.

Centripetal force:  It is an inward-directed force that confines an object to a circular path; and is equal in magnitude to the centrifugal force but in the opposite direction.

Charles' law:  It says with constant pressure, the temperature of an ideal gas is inversely proportional to the density of the gas.

Chinook: It is a warm, dry wind on the eastern side of the Rocky Mountains. In the Alps, the wind is called a Foehn.

Cirrocumulus:  It is a cirriform cloud characterized by thin, white patches, each of which is composed of very small granules or ripples. These clouds are of high altitude (20,000-40,000 ft or 6000 -12,000 m).

Cirrostratus: It�s a cloud belonging to a class characterized by a composition of ice crystals and often by the production of halo phenomena. It appears as a whitish and usually somewhat fibrous veil, often covering the whole sky and sometimes so thin as to be hardly discernible. These clouds are of high altitude (20,000-40,000 ft or 6000 -12,000 m).

Cirrus:  It is a cloud belonging to a class characterized by thin white filaments or narrow bands and a composition of ice crystals. These clouds are of high altitude (20,000-40,000 ft or 6000 -12,000 m).

Climate:  It is the accumulation of daily and seasonal weather events over a long period of time.  It is a description of aggregate weather conditions; the sum of all statistical weather information that helps describe a place or region.

Climatology:  It is the science that deals with the phenomena of climates or climatic conditions.

Cloud base: It is the lowest portion of a cloud.

Cloud condensation nucleus: It is a particle, either liquid or solid, upon which water condenses to form cloud droplets.

Cloud cover:  It is the amount of the sky obscured by clouds when observed at a particular location.

Cloud deck:  It is the top of a cloud layer, usually viewed from an aircraft.

Coalescence:  It is the merging of cloud droplets into a single larger droplet.

Cold front:  It is a zone separating two air masses, of which the cooler, denser mass is advancing and replacing the warmer.

Collection efficiency:  It is the fraction of droplets approaching a surface that actually deposit on that surface.

Condensation: It is the process by which water changes phase from a vapor to a liquid.

Conditionally unstable air:  It is an atmospheric condition that exists when the environmental lapse rate is less than the dry adiabatic lapse rate but greater than the moist adiabatic lapse rate.

Conduction:  It is the transfer of heat by molecular activity from one substance to another, or through a substance. Transfer is always from warmer to colder regions.

Contrail (condensation trail): It is cloudlike streamer frequently seen forming behind aircraft flying in clear, cold, humid air.

Convection: 1. It is a vertical air circulation in which warm air rises and cool air sinks, resulting in vertical transport and mixing of atmospheric properties. 2. It is a flow of heat by this circulation.

Convective condensation level (CCL):  It is the level above the surface marking the base of a cumiliform cloud that is forming due to surface heating and rising thermals.

Convergence:  It is an atmospheric condition that exists when the winds cause a horizontal net inflow of air into a specified region.

Coriolis force: It is a fictitious force used to account for the apparent deflection of a body in motion with respect to the earth, as seen by an observer on the earth. The deflection (to the right in the Northern Hemisphere) is caused by the rotation of the earth.

Cumuliform:  It is having the appearance or character of cumulus clouds.

Cumulonimbus: It�s a cloud belonging to a class indicative of thunderstorm conditions characterized by large, dense towers that often reach altitudes of 30,000 ft (9000 m) or more, cumuliform except for their tops, which appear fibrous because of the presence of ice crystals.  The cloud is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail. It is also known as a thunderstorm cloud.

Cumulus: It�s a cloud belonging to a class characterized by dense individual elements in the form of puffs, mounds or towers, with flat bases and tops that often resemble cauliflower.  They are found at a lower altitude than altocumulus, usually below 8000 ft (2400 m).

Cup anemometer:  It is an instrument used to monitor wind-speed. Wind rotation of cups generates and electric current calibrated in wind speed.

Cyclone: A cyclone is a large-scale circulation of winds around a central region of low atmospheric pressure, counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere.

D

Density:  It is the ratio of the mass of a substance to the volume occupied by it.

Deposition: It is a process that occurs in subfreezing air when water vapor changes directly to ice without becoming a liquid first. (Also called sublimation in meteorology.)

Dew-point (dew point temperature):  It is the temperature to which air must be cooled (at constant pressure and constant water vapor content) for saturation to occur. When the dew point falls below freezing it is called the frost point.

Diffuse insolation: It is the solar radiation that is scattered or reflected by atmospheric components (clouds, for example) to the earth's surface.

Direct insolation:  It is the solar radiation that is transmitted directly through the atmosphere to the earth's surface without interacting with atmospheric components.

Diurnal: Diurnal means daily, especially pertaining to actions which are completed in 24 hours and are repeated every 24 hours.

Divergence: It is an atmospheric condition that exists when the winds cause a horizontal net outflow of air from a specific region.

Doppler velocity [m/s]:  When using doppler velocity, the positive is down (towards the radar). Particle and air motions contribute to the velocity.

Downdraft:  It�s downward moving air, usually within a thunderstorm cell.

Drizzle:  It is small drops between 0.2 and 0.5 mm in diameter that fall slowly and reduce visibility more than light rain.

Dry adiabatic lapse rate:  It is the rate at which the temperature of a parcel of dry air decreases as the parcel is lifted in the atmosphere. The dry adiabatic lapse rate (abbreviated DALR) is 5.5�F per 1000 ft or 9.8�C per km.

Dry line:  The dry line is roughly north-south boundary between moist air in the Mississippi Valley and dry air on the west side of the Great Plains descending from the Mexican Plateau and Southern Rockies. Thunderstorms often form along this line, which moves eastward during the morning and westward in the evening.

E

Eddy: Eddy is swirling currents of air at variance with the main current.

Effective emissivity:  It is a correction factor, dependent on the radiational characteristics of the earth-atmosphere system, that permits application of black body radiation laws to the earth-atmosphere system.

El Ni�o:  It means literally, the Christ child, a name given to an extensive ocean warming in the equatorial eastern Pacific along the coast of Peru and Ecuador that often begins around Christmas (hence, the name). The warming brings nutrient-poor tropical water southward along the west coast of South America in major events that recur at intervals of 3-7 years. El Ni�o is associated with atmospheric circulations that produce wide ranging effects on global weather and climate.

Emissivity:  It is the fractional amount of radiation emitted by a given object or substance in comparison to the amount emitted by a perfect emitter.

Emittance:  It is the rate at which a black body radiates energy across all wavelengths.

Entrainment:  It is the mixing of environmental air into a preexisting air current or cloud so that the environmental air becomes part of the current or cloud.

Environmental lapse rate: It is the rate of decrease of air temperature with height, usually measured with a radiosonde.

Equilibrium vapor pressure: It is the necessary vapor pressure around liquid water that allows the water to remain in equilibrium with its environment.  It is also called saturation vapor pressure.

Evaporation: Evaporation is the process by which a liquid changes into a gas.

Evapotranspiration:  It is the vaporization of water through direct evaporation from wet surfaces and the release of water vapor by vegetation.

F

Fall streaks:  It is the falling ice crystals that evaporate before reaching the ground.

Flux:  Flux is the rate of transfer of fluids, particles or energy per unit area across a given surface.

Fog:  Fog is a cloud with its base at the earth's surface. It reduces visibility to below 1 km.

Free atmosphere: It is the part of the atmosphere that lies above the frictional influence of the earth's surface.

Freezing level:  It is the altitude at which the air temperature first drops below freezing.

Front (or frontal zone):  It is an interface or zone of transition between two distinct air masses.

Frontal inversion: It is a temperature inversion that develops aloft when warm air overruns the cold air behind a front.

Frost (also called hoarfrost):  Frost is a covering of ice produced by deposition (sublimation) on exposed surfaces when the air temperature falls below the frost point (the dew point is below freezing).

Frost point: See Dew point

G

Geostrophic wind: It is a theoretical horizontal wind blowing in a straight path, parallel to the isobars or contours, at a constant speed. The geostrophic wind results when the Coriolis force exactly balances the horizontal pressure gradient force.

GMT:  This means Greenwich Mean Time, same as UTC.

GPS: It means Global Positioning System, a navigation system which uses a constellation of artificial earth satellites to make precise determinations of the latitude and longitude of locations on the earth's surface or in the atmosphere.

Gradient:  It is a rate of change with respect to distance of a variable quantity, as temperature or pressure, in the direction of maximum change.

Graupel: It is the same as snow pellets or small hail.

Greenhouse effect: It is atmospheric heating caused by solar radiation being readily transmitted inward through the earth's atmosphere but longwave radiation less readily transmitted outward, due to absorption by certain gases in the atmosphere.

H

Hail: Hail is solid precipitation in the form of chunks or balls of ice with diameters greater than 5 mm. The stones fall from cumulonimbus clouds.

Hailstones:  They are transparent or partially opaque particles of ice that range in size from that of a pea to that of golf balls.

Halo: Halos are rings or arcs that encircle the sun or moon when seen through an ice crystal cloud or a sky filled with falling ice crystals. Halos are produced by reflection of light by ice crystals suspended in the earth's atmosphere and exhibiting prismatic coloration ranging from red inside to blue outside.

Haze: It is the fine dry or wet dust or salt particles dispersed through a portion of the atmosphere. Individually these are not visible but cumulatively they will diminish visibility.

Heat: Heat is a form of energy transferred between systems by virtue of their temperature differences.

Heat capacity:  It is the ratio of the heat absorbed (or released) by a system to the corresponding temperature rise (or fall).

Heat index (HI):  It is an index that combines air temperature and relative humidity to determine an apparent temperature-how hot it actually feels.

Hertz:  It is an international unit of frequency equal to one cycle per second, and named after a German physicist.

Hurricane:  It is a severe tropical cyclone having winds in excess of 64 knots (74 mi/hr).

Hygrometer:  It is an instrument designed to measure the air's water vapor content. The sensing part of the instrument can be hair (hair hygrometer), a plate coated with carbon (electrical hygrometer), or an infrared sensor (infrared hygrometer).

I

Ice crystal:  It is precipitation consisting of small, slowly falling crystals of ice.

Ice nuclei:  They are particles that act as nuclei for the formation of ice crystals in the atmosphere.

Ideal gas laws: They are the thermodynamic laws applying to perfect gases.

Infrared radiation:  It is the electromagnetic radiation with wavelengths between about 0.7 and 1000 �m. This radiation is longer than visible radiation but shorter than microwave radiation.

Insolation:  It is the incoming solar radiation that reaches the earth and the atmosphere.

Inversion:  It is an increase in air temperature with height.

IR brightness temperature [�C]:  It is the down welling atmospheric emission in the 9.9-11.4 �m band; in general, relatively warmer temperatures imply "thicker" clouds.

Isobar:  It is a line of equal or constant pressure; an isopleth of pressure.

Isotach:  It is a line on a weather map or chart connecting points where winds of equal speeds have been recorded.

Isotherm:  It is a line of equal or constant temperature, an isopleth of temperature.

Isothermal: It is the temperature remaining constant with height or time.

Isotropic: It is a line of constant equal physical properties along all axes.

J

Jet: c a fast-moving wind current surrounded by slower moving air.

Jet stream: It is generally strong westerly winds concentrated in a narrow and shallow stream in the upper troposphere.

Jet stream cirrus:  It is a loose term for filamentous cirrus that appears to radiate from a point in the sky, and exhibits characteristics associated with strong vertical wind shear, such as twisted or curved filaments.

K

Kelvin-Helmholtz waves: (Stull's definition) It is vertical waves in the air associated with wind shear across statically-stable regions. Can appear as breaking waves and as braided patterns in radar images and cloud photos.

L

Lapse rate: It is the rate at which an atmospheric variable (usually temperature) decreases with elevation.

Latent heat: It is the heat that is either released or absorbed by a unit mass of a substance when it undergoes a change of state, such as during evaporation, condensation, or sublimation.

Latent heat flux: It is the flux of heat from the earth's surface to the atmosphere that is associated with evaporation or condensation of water vapor at the surface; a component of the surface energy budget.

LDT: This means Local Daylight Time.

Lightning: Lightning is a visible electrical discharge produced by a thunderstorm. The discharge may occur within or between clouds, between the cloud and air, between a cloud and the ground or between the ground and a cloud.

LOS: LOS stands for line-of-sight. For our work this usually refers to contributions of radiation from the atmosphere along the line-of-sight (path) that an instrument recieves.  

Liquid water path [gm/m^2]: It is a measure of the total amount of liquid water present in the column. A retrieved quantity from the microwave radiometer.

Longwave radiation: It is a term used to describe the infrared energy emitted by the earth and atmosphere at wavelengths between about 5 and 25 micrometers. Compare this to shortwave radiation.

Low-level jet: It is a regular, strong, nighttime, northward flow of maritime tropical air over the sloping Great Plains of the central United States. The wind increases to a peak in the lowest kilometer and then decreases above.

LST:  This means Local Standard Time.

LWP: See Liquid water path .

M

Macroscale:  This pertains to meteorological phenomena, such as wind circulations or cloud patterns, that are greater than 200 km in horizontal extent.

Melting layer:  The layer below the 0�C isotherm where snowflakes melt and turn into raindrops. When viewed by radar this layer appears as a band of enhanced reflectivity; thus it is commonly known as the 'radar bright band'. The microphysics of the melting layer of precipitation is an important feature for Stratiform precipitation.  The melting layer's degrading effect on satellite communication links makes understanding it important as well.

Mercury barometer:  It is an instrument for measuring atmospheric pressure. The instrument contains an evacuated and graduated glass tube in which mercury rises or falls as the pressure of the atmosphere increases or decreases.

Mesoscale:  This is a scale of meteorological phenomena that ranges in size from a few km to about 100 km. It includes local winds, thunderstorms, and tornadoes.

Meteorology:  It is the study of the atmosphere and atmospheric phenomena as well as the atmosphere's interaction with the earth's surface, oceans, and life in general.  A distinction can be drawn between meteorology and climatology, the latter being primarily concerned with average, not actual, weather conditions.

Microburst: It is an intense, localized downdraft of air that spreads on the ground, causing rapid changes in wind direction and speed; a localized downburst.

Microscale: It pertains to meteorological phenomena, such as wind circulations or cloud patterns, that are less than 2 km in horizontal extent.

Millibar: It is a unit of atmospheric pressure equal to 1/1000 bar, or 1000 dynes per square centimeter.  Sea level pressure is normally close to 1013 mb.

Mixed layer: It is an atmospheric layer, usually the layer immediately above the ground, in which pollutants are well mixed by convective or shear-produced turbulence.

Mixing ratio:  It is the ratio of the mass of water vapor in a given volume of air to the mass of dry air.

Moist adiabatic lapse rate:  It is the rate at which the temperature of a parcel of saturated air decreases as the parcel is lifted in the atmosphere. The moist adiabatic lapse rate (abbreviated MALR) is not a constant like the dry adiabatic lapse rate but is dependent on parcel temperature and pressure.

MSL: This means it is above mean sea level.

N

Neutral stability (neutrally stable air): It is an atmospheric condition that exists in unsaturated (saturated) air when the environmental lapse rate equals the dry (moist) adiabatic rate.

Nimbostratus: It is a cloud of the class characterized by a formless layer that is almost uniformly dark gray; a rain cloud of the layer type, of low altitude, usually below 8000 ft (2400 m).

O

Occluded front:  It is a composite of two fronts, formed as a cold front overtakes a warm or quasi-stationary front. Two types of occlusions can form depending on the relative coldness of the air behind the cold front to the air ahead of the warm or stationary front. A cold occlusion results when the coldest air is behind the cold front and a warm occlusion results when the coldest air is ahead of the warm front.

Ozone:  It is a form of oxygen, O3. It�s a powerful oxidizing agent that is considered a pollutant in the lower troposphere but an essential chemical in the stratosphere where it protects the earth from high-energy ultraviolet radiation from the sun.

P

Pilot balloon (pibal):  It is a small helium-filled meteorological balloon that is tracked as it rises through the atmosphere to determine how wind speed and direction change with altitude.

Potential energy: It is the energy that a body possesses by virtue of its position with respect to other bodies in the field of gravity.

Potential temperature:  It is the temperature that a parcel of dry air would have if it were brought dry adiabatic ally from its original position to a pressure of 1000 mb.

Precipitable water:  It is the depth of water that would result if all the vapor in the atmosphere above a location were condensed into liquid water.

Precipitation:  Precipitation is any form of water particles-liquid or solid-that falls from the atmosphere and reaches the ground.

Pressure:  Pressure is the exertion of force upon a surface by a fluid (e.g., the atmosphere) in contact with it.

Prevailing wind:  It is the wind direction most frequently observed during a given period.

Psychrometer:  This is an instrument used to measure the water vapor content of the air. It consists of two thermometers (dry bulb and wet bulb). After whirling the instrument, the dew point and relative humidity can be obtained with the aid of tables.

Pyranometer:   It is an instrument that measures the amount of radiation.

R

Radar:   Radar is an instrument useful for remote sensing of meteorological phenomena. It operates by sending radio waves and monitoring those returned by such reflecting objects as raindrops within clouds.

Radiation:  It is energy transported through electromagnetic waves. These waves do not need molecules to propagate them, and in a vacuum they travel at nearly 300,000 km per sec.  See shortwave radiation and longwave radiation

Radiosonde:  It is an instrument that is carried aloft by a balloon to send back information on atmospheric temperature, pressure and humidity by means of a small, expendable radio transmitter. Radiosondes can be tracked by radar, radio direction finding, or navigation systems (such as the satellite Global Positioning System) to obtain wind data. See also rawinsonde

Rain:   Rain is precipitation that falls to earth in drops more than 0.5 mm in diameter.

Rain gage:  This is a device-usually a cylindrical container-for measuring rain-fall.

Rawinsonde:   It is a radiosonde that is tracked to measure winds.  See Radiosonde

Reflection:  It is the process whereby a surface turns back a portion of the radiation that strikes it.

Reflectivity [dBZ]:  This is a measure of the returned power, which is sensitive to the size and number of hydrometeors (i.e. the particle size spectra).

Refraction:   It is the bending of light as it passes from one medium to another

Relative humidity:   It is the ratio of the amount of water vapor actually in the air compared to the amount of water vapor the air can hold at the particular temperature and pressure. The ratio of the air's actual vapor pressure to its saturation vapor pressure.

Residual layer:  It is the elevated portion of a convective boundary layer that remains after a stable boundary layer develops at the ground (usually in late afternoon or early evening) and cuts off convection.

Resonance:  It�s the state of a system in which an abnormally large vibration is produced in response to an external stimulus, occurring when the frequency of the stimulus is the same, or nearly the same, as the natural vibration frequency of the system.

Ridge:  On a weather chart, it�s a narrow elongated area of relatively high pressure.

Rossby waves:  These are a series of troughs and ridges on quasi-horizontal surfaces in the major belt of upper tropospheric westerlies. The waves are thousands of kilometers long and have significant latitudinal amplitude.

S

Sampling frequency:  It is the rate at which sensor data is read or sampled.

Saturation vapor pressure:  It�s the maximum amount of water vapor necessary to keep moist air in equilibrium with a surface of pure water or ice. It represents the maximum amount of water vapor that the air can hold at any given temperature and pressure. (See Equilibrium vapor pressure)

Scattering:  Scattering is the process in which a beam of light is diffused or deflected by collisions with particles suspended in the atmosphere.

Sea level pressure:  It is the atmospheric pressure at mean sea level.

Sensible heat flux:  It is the flux of heat from the earth's surface to the atmosphere that is not associated with phase changes of water. It is

Severe thunderstorm:  It is a thunderstorm that produces heavy precipitation, frequent lightning, strong, gusty surface winds or hail. A severe thunderstorm can cause flash flooding and wind and hail damage and may spawn tornadoes.  

SGP:  The Southern Great Plains site covers Oklahoma and part of Kansas.

Shortwave radiation:  It is a term used to describe the radiant energy emitted by the sun in the visible and near-ultraviolet wavelengths (between about 0.1 and 2 micrometers). Compare this to longwave radiation.

Short wave trough:  This is a relatively small-scale trough that is superimposed on and propagates through the longer wavelength Rossby waves.

Sling psychrometer:  It is an instrument used to measure the water vapor content of the atmosphere, which wet and dry bulb thermometers are mounted on a frame connected to a handle at one end by means of a bearing or a length of chain. The psychrometer is whirled by hand to provide the necessary ventilation to evaporate water from the wet bulb.

Snow:  Snow is precipitation in the form of ice crystals, mainly of intricately branched, hexagonal form and often agglomerated into snowflakes, formed directly from the freezing [deposition] of the water vapor in the air.

Snowflake:  A snowflake is an aggregate of ice crystals that falls from a cloud.

Sounding:  It is a set of data measuring the vertical structure of an atmospheric parameter (temperature, humidity, pressure, winds, etc.) at a given time.

Specific heat:  It is the ratio of the heat absorbed (or released) by the unit mass of the system to the corresponding temperature rise (or fall).

Specific humidity:  It is the ratio of the mass of water vapor in a given parcel to the total mass of air in the parcel.

Spectral width [m/s]:  It is a measure of the spread of the Doppler spectrum and consequently is sensitive to the spread in the particle size spectra. A larger spectral width is indicative of the presence of a broader range of sizes of hydrometeors.

Squall line:  A squall  line is any nonfrontal line or band of active thunderstorms.

Station pressure:  It is the actual air pressure measured at the observing station.

Stability:  It is the degree of resistance of a layer of air to vertical motion.

Stable air: see absolutely stable air

Standard atmosphere:  It is a hypothetical vertical distribution of temperature, pressure and density which, by international consent, is taken to be representative of the atmosphere for purposes of pressure altimeter calibrations, aircraft performance calculations, aircraft and missile design, ballistic tables, etc.

Stationary front:  It is a front between warm and cold air masses that is moving very slowly or not at all.

Stratiform:  A stratiform is (a cloud) having predominantly horizontal development.

Stratocumulus:  It is a cloud belonging to a class characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumulus and the whole being at a lower altitude, usually below 8000 ft (2400 m).

Stratosphere:  It is the layer of the atmosphere above the troposphere and below the mesosphere (between 10 km and 50 km), generally characterized by an increase in temperature with height.

Stratus:  It is a cloud belonging to a class characterized by a gray, horizontal layer with a uniform base, found at a lower altitude than altostratus, usually below 8000 ft (2400 m).

Sublimation:  It is the process whereby ice changes directly into water vapor without melting. In meteorology, sublimation can also mean the transformation of water vapor into ice. (See Deposition.)

Subsidence:  It is the slow sinking of air, usually associated wit high-pressure areas.

Sundog: A sundog is a colored luminous spot produced by refraction of light through ice crystals that appears on either side of the sun. Also called parhelion

Sun pillar:  It is a vertical streak of light extending above (or below) the sun. It is produced by the reflection of sunlight of ice crystals.

Supercool:  It means to cool a liquid below its freezing point without solidification or crystallization.

Supersaturated air:  It is a condition that occurs in the atmosphere when the relative humidity is greater that 100 percent.

Surface energy budget:  It is the energy or heat budget at the earth's surface, considered in terms of the fluxes through a plane at the earth-atmosphere interface. The energy budget includes radiative, sensible, latent and ground heat fluxes.

Surface weather chart:  It is an analyzed synoptic chart of surface weather observations. A surface chart shows the distribution of sea-level pressure (therefore, the position of highs, lows, ridges and troughs) and the location and nature of fronts and air masses. Often added to this are symbols for occurring weather phenomena. Although the pressure is referred to mean sea level, all other elements on this chart are presented as they occur at the surface point of observation.

Synoptic scale:  This is the typical weather map scale that shows features such as high- and low-pressure areas and fronts over a distance spanning a continent. Also called the cyclonic scale.  Typically ranging on the scale of 1000 to 2500km.

T

Temperature:  It is the degree of hotness or coldness of a substance as measured by a thermometer. It is also a measure of the average speed or kinetic energy of the atoms and molecules in a substance.

Temperature inversion:  It is an extremely stable air layer in which temperature increases with altitude, the inverse of the usual temperature profile in the troposphere.

Terminal velocity:  It is the constant speed obtained by a falling      object when the upward drag on the object balances the downward force of gravity.

Thermal:  It is a small, rising parcel of warm air produced when the earth's surface is heated unevenly.

Thermally driven circulation:  It is a diurnally reversing closed cellular wind current resulting from horizontal temperature contrasts caused by different rates of heating or cooling over adjacent surfaces; includes along-slope, cross-valley, along-valley, mountain-plain and sea breeze circulations.

Thermistor:   It is a resistor whose resistance changes with temperature. Because of the known dependence of resistance on temperature, the resistor can be used as a temperature sensor.

Thermograph:  It is a recording instrument that gives a continuous trace of temperature with time.

Thermometer:  It is an instrument used to measure temperature.

Thunder:  It is the sound caused by rapidly expanding gases in a lightning discharge.

Thunderstorm:  It is a local storm produced by a cumulonimbus cloud and accompanied by lightning and thunder.

Tornado:   It is an intense, rotating column of air that protrudes from a cumulonimbus cloud in the shape of a funnel or a rope and touches the ground.

Transpiration:  It is the passage of water vapor into the atmosphere through the vascular system of plants.

Tropopause:  It is the boundary between the troposphere and stratosphere, characterized by an abrupt change in temperature lapse rate (temperatures decrease with height in the troposphere, but it increases or remains constant with height in the stratosphere).

Troposphere:  It is the portion of the earth's atmosphere from the surface to the tropopause; that is, the lowest 10-20 km of the atmosphere. The troposphere is characterized by decreasing temperature with height, and is the layer of the atmosphere containing the most clouds and other common weather phenomena.

Trough: A trough is on a weather chart, a narrow, elongated area of relatively low pressure.

Turbulence:  It is an irregular motion of the atmosphere, as indicated by gusts and lulls in the wind.

U

Ultraviolet radiation:   It is an electromagnetic radiation with wave-lengths longer than X-rays but shorter than visible light.

Unstable air: see absolutely unstable air

Upper-air weather chart:  They are weather maps that are produced for the portion of the atmosphere above the lower troposphere, generally at and above 850 mb. Isolines on these maps usually represent the heights of a constant pressure surface, such as the 500 mb surface.

V

Vapor pressure:  It is the pressure exerted by the water vapor molecules in a given volume of air.

Virga:  It is precipitation that falls from a cloud but evaporates before reaching the ground. (See Fall streaks)

Virtual temperature:  It is an adjustment applied to the real air temperature to account for a reduction in air density due to the presence of water vapor.

Visibility:  It is the distance at which a given standard object can be seen and identified with the unaided eye.

Visible light:  It is the portion of the electromagnetic spectrum to which the eye is sensitive, i.e., light with wavelengths between 0.4 and 0.7 micrometers. Compare this to the shortwave radiation and longwave radiation.

Vortex:  A vortex is a whirling mass of air in the form of a column or spiral. It need not be oriented vertically but, for example, could be rotating around a horizontal axis.

Vorticity:   It is a measure of the spin of a fluid, usually small air parcels. Absolute vorticity is the combined vorticity due to the earth's rotation and the vorticity due to the air's circulation relative to the earth. Relative vorticity is due to the curving of the air flow and wind shear.

W

Wake:  A wake is the region of turbulence immediately to the rear of a solid body caused by the flow of air over or around the body.

Warm front:  It is a transition zone between a mass of warm air and the colder air it is replacing.

Water vapor path [cm]:  It is a measure of the total amount of water vapor present in the column. A retrieved quantity from the microwave radiometer.

Weather:  It is the state of the atmosphere with respect to wind, temperature, cloudiness, moisture, pressure, etc.

Westerlies:  It is the prevailing winds that blow from the west in the mid-latitudes.

Wet-bulb depression:  It is the difference in degrees between the air temperature (dry-bulb temperature) and the wet-bulb temperature.

Wet-bulb temperature:  It is the lowest temperature that can be obtained by evaporating water into the air.

Wind chill: see wind chill equivalent temperature.

Wind chill equivalent temperature:  It is the apparent temperature felt on the exposed human body owing to the combination of temperature and wind speed.

Wind-chill factor:  This factor is the cooling effect of any combination of temperature and wind, expressed as the loss of body heat.  It is also called a wind-chill index.

Wind field:  It is the three-dimensional spatial pattern of winds.

Wind shear:  It is a difference in wind speed or direction between two wind currents in the atmosphere.

Wind Vane:  It is an instrument used to determine wind direction.

Windsock:  It is a large, conical, open bag designed to indicate wind direction and relative speed; usually used at small airports.

Winter solstice:  It is approximately December 22 in the Northern Hemisphere when the sun is lowest in the sky and directly overhead at latitude 23.5�S, the Tropic of Capricorn.

What is the dewpoint temperature?
露点温度

The dewpoint temperature is the temperature at which the air can no longer "hold" all of the water vapor which is mixed with it, and some of the water vapor must condense into liquid water. The dew point is always lower than (or equal to) the air temperature. 露点温度永远低于或者等于气温。

If the air temperature cools to the dew point, or if the dew point rises to equal the air temperature, then dew, fog or clouds begin to form. At this point where the dew point temperature equals the air temperature, the relative humidity is 100%. 当气温降低到露点温度，或者露点温度升高到气温时，露水、雾、或者云就会形成。当露点温度等于气温时，相对湿度达到100%。

If there is then further cooling of the air, say because the air parcel is rising to higher (and thus colder) levels in the atmosphere, even more water vapor must condense out as additional dew, fog, or cloud, so that the dew point temperature then falls along with the air temperature. This is how precipitation forms...when water vapor is removed from the air so rapidly that the liquid water drops grow to a size where they fall out of the cloud. 如果水汽因为升高而变冷，凝结的水蒸气就会更多而成为露水、雾气或者云，这样，露点温度就会降低到气温。当水蒸气快速从空气中离开时，液态的水珠体积会增大而从云里边落下来，而形成降水。

While relative humidity is (as its name suggests) a relative measure of how humid the air is, the dewpoint temperature is an absolute measure of how much water vapor is in the air. In very warm, humid conditions, the dewpoint temperature often reaches 75 to 77 degrees F, and sometimes exceeds 80 degrees. No matter how hot the temperature gets, a dewpoint temperature of (say) 75 deg. F always represents the same amount of water vapor in the air in absolute terms (but different relative humidities). 顾名思义，相对湿度是空气湿度的相对指标；相比之下，露点温度标示的则是空气里水蒸气的绝对数量。在非常温暖湿润的情况下，露点温度经常可以达到23到25摄氏度，有时候甚至可以超过26摄氏度。无论气温有多高，相同的露点温度所代表的空气中的水蒸气的绝对数量是一样的，当然相对湿度是不一样的。

During the summer, the dewpoint temperature -- not the relative humidity -- is usually a better measure of how humid it feels outside. It is also a good measure of how much water vapor "fuel" is available to showers and thunderstorms, with a higher dewpoint representing more water vapor available for conversion to rain. 在夏季的户外，用露点温度来标示潮湿感觉通常比相对湿度更好。

Interesting facts:
SOUPY AIR: When the dewpoint approaches 75 degrees F, most people can "feel" the thickness of the air as they breathe, since the water vapor content is so high (about 20 grams of water vapor per kilogram of dry air, or 2% of the air's mass).

——摘自 http://www.weatherquestions.com/What_is_dewpoint_temperature.htm，中文是我随便翻的。 本帖最后由 14ii 于 2013-4-17 18:49 编辑

風寒指數是一種暴露於皮膚的表觀氣溫，是由氣溫與風速所對應的函數。

風寒指數是根據風寒效應所定立的指數。而風寒效應的出現是由於風也會影響我們對冷的感覺，引致溫度計的讀數有些時候可與人們對冷暖的感覺有明顯的分別。在冬季期間，持續的強風天氣會令我們對冷的感覺來得更強烈。這個風速與人體對外界溫度感覺的關係，稱為「風寒效應」。——摘自※※※※

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