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Weather Conditions What Makes up Earth’s Atmosphere? The layer of air surrounds our planet is called the atmosphere. Layers of the Atmosphere Troposphere Stratosphere Mesosphere Thermosphere Troposphere Layer closes to the earth Weather happens in this layer Live and breathe air in this layer Air temperature decreases as you go higher Stratosphere Airplanes travel in this layer to avoid bad weather Contains most of the atmosphere’s ozone Ozone protects living things from harmful rays of the sun Temperature increase with height Mesosphere Temperature decrease with height Coldest layer of the atmosphere Thermosphere Hot, outermost layer Temperature increase quickly with height How Do Air Masses Affect the Weather Greenhouse Effect Air Masses What happens when to air masses meet? When two air masses meet, they form a border called a front A front is the area where two air masses meet and weather happens Cold Front A cold air mass catches up with a warm air mass The cold air mass forces the warm air up in the atmosphere As warm air Cold Front As warm air pushes upward, it cool and forms cloud. Rain develops. Thunderstorm often occur along a cold front. Cold Front Generally move from northwest to southeast Air behind a cold front is colder and drier than the air ahead of it. When a cold front passes through, temperatures can drop more than 15 degrees within the first hour. Represented by a solid lines with triangles along the front pointing towards the warmer air and in the direction of movement Warm Front Forms when a warm air mass catches up with a cold air mass Warm air slides up over the colder, denser air Generally move from southwest to northeast Air behind a warm front is warmer and more moist than the air ahead of it Represented by a solid line with semicircles pointing towards the colder air and in the direction of the movement Steady rain or snow may fall as the front approaches and passes Common Characteristics of Warm Fronts While Passing Before Passing Winds Temperatures Pressure Clouds Precipitation Visibility Dew Point South-southeast After Passing Clouds and Weather Weather scientists classify a cloud based on its shape, its color, and where it forms in the atmosphere Cirrus A wispy white cloud Fair weather Cumulus Puffy cotton-ball clouds Begins to form when water droplets condense at middle altitudes Cumulonimbus Dense cumulus cloud with a hazy outline Usually producing heavy rain, thunderstorms, or hailstorms Stratus Dark gray clouds that form a low layer Sometimes bring rain or snow showers What is a Cycle? A sequence of events that repeat themselves Evaporation The sun heats up water in rivers, lakes, or ocean The water changes from a liquid into a gas, vapor, or steam. The water vapor leaves the rivers, oceans, or lakes and goes into the atmosphere. Condensation Water vapor in the air gets cold and changes back into liquid forming clouds Transpiration Is the process by which plants return water to the atmosphere. After absorbing water from the ground, plant release water through their leaves. This helps plants stay cool. Precipitation Occurs when so much water has condensed that the air cannot hold it anymore. Clouds get heavy and water falls back to earth in the form of rain, sleet, hail, or snow What instruments do meteorologist use to forecast weather? Anemometer Measures wind speed The cups catch the wind, turning a dial attached to the instrument. The dial shows the wind speed. Barometer Measures air pressure Psychrometer Measures relative humidity, using the cooling effect of evaporation Hygrometer Measures the amount of humidity in the air.