Three things necessary for weather are Heat, Air, Moisture (HAM) Weather takes place in the Troposphere (The lower part of the atmosphere).

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1 Grade 5 SCIENCE WEATHER WATCH Name: STUDY NOTES Weather - The condition of the atmosphere with respect to heat/cold, wetness/dryness, clearness/ cloudiness for a period of time. Weather changes over time and from place to place. Three things necessary for weather are Heat, Air, Moisture (HAM) Weather takes place in the Troposphere (The lower part of the atmosphere). Climate the long-term weather pattern of an area, including temperature, precipitation, and wind. Meteorology The study of weather. Meteorologists use lots of instruments to study weather and make predictions. Temperature The amount of heat in a substance and is measured by a thermometer. Measured in degrees of Centigrade (Celsius). An example is 10 C or -15 C. Convection current the movement of air or water due to heating and cooling. Warm air rises (lighter) and falls when it cool down (heavier). The ceiling is usually warmer. (That s why smoke rises and, in a fire, you should crawl on the floor to get away from it) The floor is usually cooler. Air moves to take the shape of whatever container it is in. Air can stretch out (expand) or squeeze in (compress) Air can have different pressures. Nature doesn t like to leave empty spaces (no air). HP LP Air moves from areas of high pressure (thick, heavy, gas molecules squeezed together) to low pressure (thin, light, gas molecules spread out) (The arrow is wind)

2 A barometer measures air pressure. When air pressure is high there is not much room between molecules for water so weather is usually fair High pressure = fair weather When air pressure is low there is room between molecules for water so weather is usually rainy Low pressure = rainy When air pressure drops it means weather is getting worse. Some animals can feel the pressure dropping and act different. That fact causes lot of old weather sayings: Air pressures are often shown on weather maps as H and L. These make warm and cool fronts. A front is a moving mass of air. When a warm front and a cool front run in to each other, the warm, moist front usually gets pushed up on top of the heavier cool front. This rises the warm moist air up into the sky where it cools down and forms clouds. When warm air rises it leaves a low pressure and other air moves in to replace it. Solids heat faster than liquids. Land heats faster than the ocean. Sea Breeze cool air blowing from the sea on to the shore During a hot summer day, the air over the land is warmer than the air over the ocean. The warm 'land air' rises and cooler 'ocean air' moves to the shore

3 Solids lose heat faster the liquids. Land cools down faster than the ocean (Water keeps heat longer than land). Land Breeze - cool air blowing from the land out to sea In the evening after a hot summer day the land cools quickly. As the ocean slowly releases its warmth the air over the ocean warms and rises. Cooler land air moves out to sea to fill in the space Water cycle - The evaporation of water from a body of water into the air (as water vapour gas), the condensation of this moisture into precipitation and its collection back to a large body of water. Evaporate When a liquid turns into a gas. Condense When a gas turns into a liquid by cooling. Example: 1. tiny drops of water on outside of glass of cold water. 2. Dew drops on grass in the morning. Humidity - The measure of the amount of moisture in the air. Can be measured with a psychrometer or with a hygrometer. It is measured in % which means out of 100. A day with 5 % humidity would be hot and dry. A day with 100 % humidity would be foggy or rainy. Human hair reacts to the humidity in the air (flat or frizzy).

4 Dew Point - The temperature at which the water vapor in air condenses out into droplets of water forming precipitation. Warmer air can hold more moisture. For instance: a day that is 28ºC would be more humid than a day that is 1ºC if there is water nearby (a desert is hot but dry because there is no water nearby). Warm air soaks up water vapour like a sponge. Clouds - A mass of minute water droplets or ice crystal. Clouds form when a mass of warm moist air moves into an area with lower air pressure. The air expands and cools and the water vapour condenses. Four main types Cirrus Found high in the sky. Thin, wispy, feathery looking. Made of tiny ice crystals in the sky. A change in the weather will often follow. Often a sun halo. Stratus Form near the Earth s surface. Means relative humidity near the ground is high. Usually flat clouds that cover large parts of the sky. Means stormy weather coming. Fog is a very low form. Cumulus Most often seen in summer. Thick, fluffy, white and have flat bases. (bunches of white cotton). Sign of fair weather. Nimbus Dark, dense and low, Sky usually all dark colour due to large amount of moisture. They almost always mean rain or thunder showers.

5 Notice how different clouds are at different heights. Cumulonimbus causes big storms and lightning. Precipitation - The name for moisture that falls out of clouds. Temperature changes what it is. Rain liquid water. Sleet (freezing rain)- falls as rain and freezes near ground. Hail ice built up as layers (like an onion). Snow water frozen as crystals. Wind is measured by strength and direction. anemometer an instrument for measuring the speed of the wind in km/h Wind vane measures the direction wind is coming from. (points on a compass: N, NE, E, SE, S, SW, W, NW) Wind occurs when air naturally tries to balance high pressure areas and low pressure areas. HP always moves to LP. There are many types of storms and severe weather: Thunderstorms, Blizzards, Tornado, Hurricanes, Drought (long time with no water), Flood, Heat Wave Specific events must happen for storms to occur.