Transcript Weather
Weather Section 1: Water in the Atmosphere Basics • The Water Cycle is the movement of water between the atmosphere and earth’s surface • Evaporation: Process where liquid water turns to a vapor • Condensation is when water vapor changes back to a liquid (#6) • Dew Point: Is the temp where condensation happens (#7) Humidity • The measure of the water vapor in the air – Air can hold various amounts at different temperatures • Relative Humidity: is a percentage…it tells how much is in the air in relation to what it can actually hold. • Psychrometers: are instruments used to measure relative humidity – Measures based on the temperature change in the wet bulb of the psychrometer. Clouds • Cirrus Clouds: – Soft, feathery – Form at high levels in low temperatures – Made of ice crystals • Cumulous Clouds: – Fluffy like cotton balls – Lower to the ground but can extend higher – Can be combined with the suffix –Nimbus to indicate a rain cloud • Stratus Clouds: – Form in flat layers and cover most of the sky – Can produce rain or snow (nimbostratus) Other Clouds • The Prefix “—Alto” may be added to a cloud if it is one of the three main types, but higher than usual – Examples: altocumulus, altostratus • Fog is formed when hot, humid days lead to cooler nights, causing vapor to condense lower to the ground. – Fog tends to form over areas with more water… Pg. 439 SECTION 2: PRECIPITATION Precipitation • Any form of water that leaves clouds and comes back to Earth’s surface • Does Precipitation always fall from clouds? • No • Remember: precipitation occurs when ice or liquid is heavy enough to fall • Types of Precipitation: Rain, Hail, Snow, Sleet, Freezing Rain Rain • Precipitation that falls as drops of water • Small drops are called Drizzle or mist – These usually come from stratus clouds Hail • Round pellets of ice (larger than 5mm---about the size of a pea) called hailstones • Updrafts of wind carry the ice pellet through the cloud many times, forming many layers of ice • Hail tends to have rings when cut in half (like an onion) Snow • Water in the clouds is changed strait to ice crystals—ie. Snowflakes • Powder happens when snow falls in cool, dry air • Clumpy snow happens in moist, humid areas. Sleet • Raindrops freeze after leaving the cloud • Sleet is usually smaller than 5mm (the size of a pea) Freezing Rain • Rain that freezes when it touches a cold surface • Causes ice to build up and coat things at the surface level Pg. 442 AIR MASSES & FRONTS Air Masses • A huge body of air that has it’s own temperature, humidity, and air pressure. • Can spread over millions of kilometers and be up to 10 kilometers deep • Characterized by temperature and humidity • 4 kinds(North America): Tropical, Polar, Maritime, and Continental. Tropical • Warm air masses that form in the tropics • Have low air pressure Polar • Cold air masses that form in polar regions • High air pressure Maritime • Form over oceans • Can become very humid Continental • Air masses that form over land • Drier than maritime because they don’t have the evaporation process. Combining Air Masses • Types of air mass can be combined to imply area of Earth and the part of the Earth it forms over • Example: – Maritime Tropical---Forms over tropical oceans – Maritime Polar---Form over polar ocean areas – Continental Tropical---Form over tropical Land – Continental Polar---form over polar land areas Air Mass Movement • Moving air masses interact with other masses causing the weather to change • Prevailing Westerlies: Major wind belts of US – Push Air masses west to east • Jet Streams: Bands of high speed winds 10 kilometers from the surface of Earth • Fronts: Huge masses of air that move across oceans and collide • Don’t’ mix well due to different densities • Area of the collision develops a “Front” • 4 types---type of front depends on the characteristics of the air masses and how they are moving. Fronts • Cold: – Cold air (dense) sinks…Warm air (less dense) rises – Cold air mass slides under warm air mass, pushing the warm air up – As it rises, it expands and cools, making vapor change rapidly to water or ice crystals…forming clouds – Can move quickly and cause thunderstorms…brings colder, drier air and lower temperatures. • Warm: – Fast air mass overtakes a colder air mass – Warm air moves over the cold air – Rain or snow forms if the air is humid…clouds if the air is dry – Warm fronts move slow, lasting several days…. – After---weather is warm and humid • Stationary: – Warm and cold meet, but neither move the other – Water vapor can condense along the front causing rain, snow, fog, or clouds for days. • Occluded: – Warm air mass trapped between two cold air masses – Cold is denser, so they go under the warm and push it upward – Temperature near the ground becomes cooler – As warm air cools, weather becomes rainy. • Read pg. 448… • Complete the double bubble map for cyclones and anticyclones • Complete 2c pg. 449 Pg. 450 SECTION 4: STORMS Storm • A violent disturbance in the atmosphere • 4 types: Thunderstorms, Tornadoes, Snow Storms, Hurricanes Thunderstorms • A small storm that often has heavy rain and frequent thunder/lightning • Form in Cumulonimbus clouds (thunderheads) • Thunderstorms form on hot, humid afternoons when warm air is forced upward along a cold front (warm air rises rapidly) • Lighting is a sudden spark, or electric discharge that happens when charges jump. Tornadoes • A rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to touch Earth’s surface • Over a lake or ocean, it is called a waterspout. • Formation: – Commonly—in thick cumulonimbus clouds – When thunderstorms are likely – Warm air mass and cold air mass meet going opposite directions Snow Storms • Occurs mostly in Northern US and at higher elevations • Large amount of precipitation is snow • Heavy snow can block roads • Can be extremely dangerous if wind picks up, blowing the snow and hindering visibility Hurricanes • A tropical cyclone that has winds of 119 kilometers per hour or higher • Begins over warm ocean water as a low pressure area or tropical disturbance. • Grows into a tropica storm, then a hurricane The hurricane gets its energy from the warm, humid water creating bands of wind and heavy rain.