Weather

Atmosphere and Air Temperature insolation – the amount of the Sun’s energy that reaches Earth at a given time and place When the sun is directly overhead its shadow is shortest. As the angle decreases, the shadow lengthens. The angle of insolation affects temperature.

It takes more heat to raise the temperature of water than it takes to raise the temperature of land. In winter, warm water warms the air and in the summer, the cooler water cools the air.

atmosphere – the blanket of gases that surround the earth Troposphere – the layer of the atmosphere that is closest to the Earth’s surface The higher the altitude, the colder the air temperature!

air pressure – the force put on a given area by the weight of the air above it Air has weight. As altitude increases, air pressure decreases.

Weather includes a number of conditions at any one time weather – what the lower atmosphere is like at any given place and time Weather includes a number of conditions at any one time barometer – a device for measuring air pressure Barometers help to predict the weather Example: When air pressure falls, rain is likely

Water in the Air water vapor – water in the form of gas humidity – the amount of water vapor in the air evaporation – the changing of a liquid into a gas Evaporation requires heat and in places where evaporation takes place become cooler as a result.

relative humidity – a comparison between the actual amount of water vapor in the air and the amount the air an hold at a given temperature. condensation – the changing of a gas into a liquid Molecules in water vapor move more quickly than molecules in cold water. Heat causes water to change to water vapor.

How can warm air become cool? Warm air can be pushed upward by winds Warm air can be pushed up by cool air Warm air can cool by rising and expanding

Clouds of Water and Ice Stratus Clouds stratus clouds – a cloud that forms in a blanket like layer

Cumulus Clouds cumulus cloud – a puffy cloud that appears to rise up from a flat bottom

Cirrus Clouds cirrus cloud – a high altitude cloud with a featherlike shape, made of ice crystals

Fog fog – a cloud that forms at ground level

Precipitation precipitation – any form of water particles that falls from the atmosphere and reaches the ground The larger the cloud the more water it holds, so it may produce more precipitation.

The Water Cycle water cycle – the continuous movement of water between Earth’s surface and the air, changing from liquid to gas to liquid.

Air Pressure and Wind Warming molecules speed up and spread out. This lowers air pressure. Molecules of water vapor weigh less than oxygen and nitrogen in the air, and thus exert less pressure. The direction a barometer is changing can be a clue to future weather. A falling barometer may be a sign that a storm is on its way A rising barometer may be a sign that fair weather is approaching

wind – air that moves horizontally updraft – air that rises Air that is warmed rises downdraft – air that sinks Air moves down when air pressure above is higher and the moves down to an area of lower pressure convection cell – part of the atmosphere where air moves in a circular pattern because of unequal heating and cooling.

sea breeze – wind that blows from sea to land Air moves from an area with higher pressure to an area of lower pressure sea breeze – wind that blows from sea to land When the air over the land gets hotter than the air over the water land breeze – wind that blows from land to sea When the air pressure over the sea is higher than the air pressure over the land.

Coriolis effect – the curving of the path of a moving object caused by Earth’s rotating. If the Earth did not rotate, air would travel away from the equator towards the poles. At the poles, the air would move back towards the equator.

air mass – a large region of the atmosphere where the air has similar properties throughout front – a boundary between air masses with different temperatures

Cold Front cold front - cold air moves in under a warm air mass What kind of weather would you expect a cold front to produce? Cold fronts can produce short, heavy rains, often thunderstorms with heavy winds, followed by clear skies and cooler, drier weather.

Warm Front warm front – warm air moves in over a cold air mass What kind of weather does a warm front produce? A warm front can cause steady rain or snow that may last for days and light winds, followed by warmer and more humid weather.

Occluded Front occluded front – a front formed where a warm front and cold front meet

Stationary Front stationary front – an unmoving front where a cold air mass and a warm air mass meet

What Do Fronts Look Like from Space? Satellites show large weather patterns, such as fronts and storms which help weather scientists.

Thunderstorm thunderstorm – the most common severe storm, formed in cumulonimbus clouds What causes lightning? Air from updrafts rubs against air from downdrafts, creating static electricity. The static electricity builds up, until lightning sparks.

Tornado tornado – a violent whirling wind that moves across the ground in a narrow path

Hurricane hurricane – a very large, swirling storm with very low pressure at the center Hurricane Fran

Storm Surge storm surge – a great rise of the sea along a shore caused by low pressure A steeper continental shelf (below) will not see as much of a storm surge. A shallow slope off the coast (above) will allow a greater storm surge.

Doppler Radar Doppler radar bounces sound waves off the storm clouds. Doppler radar can tell if raindrops are moving toward or away from observers, and it can spot spinning movements in clouds. This helps scientists predict which way storms will travel.

Climate climate – the average weather pattern of a region

Factors That Affect Temperature Distance from the equator Air pressure and winds Altitude Distribution of water

radiative balance – a balance between energy lost and energy gained The Earth is constantly radiating energy into the atmosphere, which lowers temperature.

Greenhouse Effect greenhouse effect – the ability of the atmosphere to let in sunlight but to not let heat escape

What causes climate change? The Sun (sunspots) Ocean Currents Volcanoes

isobar – a line on a weather map connecting places with equal air pressure Show patterns better than numbers

wind vane – a device that indicates wind direction anemometer – a device that measures wind speed

Exploring Weather – The Atmosphere In Motion