What is weather?<br />Chapter 2: Section 1<br />
Weather Defined<br />Weather refers to the state of the atmosphere at a specific time and place.<br />Weather describes conditions such as air pressure, wind, temperature, and the amount of moisture in the air.<br />
Air Temperature<br />Temperature is the measure of the average amount of motion of molecules.<br />When the temperature is high, the molecules in air move rapidly.<br />When the temperature is low, the molecules in air move less rapidly.<br />Air temperature is measured by a thermometer in Fahrenheit or Celsius.<br />
Wind<br />Air moving in a specific direction is called wind.<br />Wind results because air moves from areas of high pressure to areas of low pressure.<br />Wind direction can be measured using a wind vane.<br />Wind speed can be measured using an anemometer in miles or kilometers per hour.<br />
Humidity<br />The amount of water vapor present in the air is called humidity.<br />More water vapor can be present when the air is warm than when it is cool.<br />When enough water vapor is present in air for condensation to take place, the air is saturated.<br />Relative humidity is the measure of the amount of water vapor present in the air compared the amount needed for saturation at a specific temperature.<br />
Measuring Humidity<br />Humidity is measured using a psychrometer and is represented by a percentage.<br />
Dew Point<br />The temperature at which air is saturated and condensation forms is the dew point.<br />The dew point changes with the amount of water in the air.<br />Frost may form when temperatures are near 0°C.<br />
Pressure<br />Atmospheric pressure is an indication of weather systems.<br />Low pressure areas are windy and can be associated with stormy weather.<br />High pressure areas are associated with fair weather.<br />A barometer measures atmospheric pressure in Millibars.<br />
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