Lecture 9-Precipitation and Violent Weather(1)

Lecture 9-Precipitation and Violent Weather(1) - Lecture...

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Lecture 9-Precipitation and Violent Weather
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What is precipitation? We need moisture to form clouds- what about rainfall? Precipitation is water (solid/liquid forms) It is heavy enough to fall to earth Types Rain Snow Sleet Hail Virga
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Precipitation Formation Cloud droplets grow larger by merging with each other, as we saw in cloud formation. These droplets bump into each other and merge together until they are heavy enough to fall (too heavy to stay aloft!). This process is known as collision-
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Rain and Snow Both created by same processes.. With snow/ice Where ice crystals grow at the expense of water droplets, as droplets encounter ice crystals, they freeze onto them and increase the size of the crystals-as with raindrops, when it becomes too heavy to stay aloft it falls as snow or ice.
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Types of precipitation-Freezing Rain (always check notes for process/details!)
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2. Sleet
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3. Hail Particles of ice held aloft by thunderstorm updrafts (so these can form very high up!)-these ice particles are circulated long enough to grow quite large as they encounter droplets in clouds.
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4. Virga Type of precipitation when rain doesn’t quite make it to the ground.
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Getting into weather now-Air Masses and Weather Systems (see notes for introduction)
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Air Mass Is an extremely large body of air with consistent temperature and moisture characteristics Characteristics based on source region (where we find the air mass) Moisture and temperature used in classifying air masses….
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Air Mass Classification 1. Moisture -Continental ( c ): dry Formed over large land mass -Maritime ( m ): moist Formed over ocean Temperature (determined by latitude) - Polar ( P ): cold formed poleward of 60° N or S - Tropical ( T ): warm Formed within ~30° of the equator - Arctic ( A ): very cold Formed over the Arctic We use these moisture and temperature characters to classify different air masses-so we will see combinations of these characters (such as a continental polar air mass, or a cP, for example. The letters are used to indicate the characteristics of the air mass, so it is a convenient shorthand to use.
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We Have Principal Air Masses (in the N Hemisphere) cP – continental polar mP – maritime polar mT – maritime tropical This figure shows the air masses that influence America and its weather in winter-in summer, the location of these air masses will change and produce different characteristics.
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North American Air Masses This makes sense, right? As summer occurs in the N Hemisphere (where we live), the polar air masses shift northwards-and the tropical air masses also shift northwards, making it warmer (and in our case in Florida/East Coast) and wetter in the summer.
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Continental polar (cP) air masses form only in the N Hemisphere…..why? (see notes!) These produce cold, stable air, clear skies, high pressure ; anticyclonic wind flow (because it is a high pressure system-remember lectures 6 and 7?) Maritime polar (mP) air masses in N hemisphere are found NW and NE of our continent Cool, moist, unstable conditions through the year ( low pressure )
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