Elements of Weather

Weather is defined as the condition of the Earth’s atmosphere at a certain time and place. What is weather?

Temperature refers to how hot or cold something is. In the case of weather, temperature refers to the temperature of the air in the Earth’s Troposphere. Temperature is measured with a thermometer. What is temperature and how is it measured?

The amount of water vapor in the air is called humidity. The humidity level in the air depends on the temperature of the air. Warm air is less dense. –Has more room to hold water vapor. Cold air is more dense –Has less space to hold water vapor What is humidity and how is it measured?

The Relative Humidity is the amount of water vapor in a given volume of air compared to the maximum amount of water vapor that could be present in the air at that temperature. RH = Absolute Humidity Saturation Value Relative Humidity maximum amount of water vapor that can be present at that temperature amount of water vapor present

Measuring Relative Humidity Sling Psychrometer An instrument used to measure relative humidity, consisting of a wet-bulb thermometer, and a dry- bulb thermometer. Psychrometric Chart A Psychometric Chart is used along with a Sling Psychrometer to determine relative humidity. Sling Psychrometer

Determining Relative Humidity If the dry-bulb thermometer reads 24°C and the wet-bulb thermometer reads 20°C, what’s the relative humidity? 24°C20°C Called the “Depression”

Saturated Air When the relative humidity of the air is 100%, the air is described as saturated. Saturated air “is holding” the “maximum amount of moisture it can hold” at a given temperature. Air can become saturated when evaporation adds water vapor to the air. Air can also become saturated when it cools to its dew point. (rising air masses forming clouds) Dew Point: The temperature at which condensation begins.

Precipitation is any form of water that falls to the Earth’s surface from clouds. Rain is the most common type of precipitation. The amount of rainfall is measured by a rain gauge. What is precipitation and how is it measured?

Rain: Water droplets in clouds get so big they fall to Earth. Sleet: Small ice pellets fall as sleet when rain falls through cold air on the way down. Hail: Hailstones are layered lumps of ice that fall from cumulonimbus clouds. Snow: Snow is made of hexagonal shaped ice crystals that fall from clouds. They fall as single crystals or crystals can join forming snow flakes. Types of Precipitation

Air pressure is the force of air molecules pushing on an area. »Air pressure is measured by an instrument called a barometer. High pressure weather systems are associated with fair weather since cool, dense air is sinking. Low pressure weather systems are associated with poor weather since warm, less dense air is rising. What is air pressure and how is it measured?

FALLING RISING What is air pressure and how is it measured?

Unequal heating of the Earth’s surface causes pressure differences from place to place. Wind is air that moves horizontally, or parallel to the ground, from an area of high pressure to an area of low pressure. Wind speed is measured by an instrument called an anemometer. Wind direction is measured by an instrument called a wind vane. What is wind and how is it measured?

Visibility is a measure of the transparency of the atmosphere. Visibility is the way we describe how far we can see. Poor visibility can be the result of air pollution or fog. What is visibility and how is it measured?

Technological instruments provide measurements from both stationary and moving locations. »Ground Stations »Anchored Weather Buoys »Ships »Airplanes »Satellites Ways to Collect Weather Data