Weather Factors and Instruments

What is weather?

Chapter 2: Section 1

Weather Defined

• Weather refers to the state of the atmosphere at a specific time and place.

• Weather describes conditions such as air pressure, wind, temperature, and the amount of moisture in the air.

Air Temperature

• Temperature is the measure of the average amount of motion of molecules.

• When the temperature is high, the molecules in air move rapidly.

• When the temperature is low, the molecules in air move less rapidly.

• Air temperature is measured by a thermometer in Fahrenheit or Celsius.

Wind

• Air moving in a specific direction is called wind.

• Wind results because air moves from areas of high pressure to areas of low pressure.

• Wind direction can be measured using a wind vane.

• Wind speed can be measured using an anemometer in miles or kilometers per hour.

Wind Instruments

Wind Vane Anemometer

Humidity

• The amount of water vapor present in the air is called humidity.

• More water vapor can be present when the air is warm than when it is cool.

• When enough water vapor is present in air for condensation to take place, the air is saturated.

• 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.

Measuring Humidity

• Humidity is measured using a psychrometer and is represented by a percentage.

Dew Point

• The temperature at which air is saturated and condensation forms is the dew point.

• The dew point changes with the amount of water in the air.

• Frost may form when temperatures are near 0°C.

Pressure

• Atmospheric pressure is an indication of weather systems.

• Low pressure areas are windy and can be associated with stormy weather.

• High pressure areas are associated with fair weather.

• A barometer measures atmospheric pressure in Millibars.