TOPIC 7

What is weather? Weather is the state or condition of the variables of the atmosphere at any given location for a short period of time.

What are some weather variables? Variables include: – Temperature – Air Pressure – Wind – Moisture conditions – Cloud cover – Precipitation – Storms

Where do most weather changes occur? Most weather changes occur in the troposphere (lower layer of the atmosphere)

What creates the atmospheric changes? Atmospheric changes are created by the uneven heating of the Earth’s surface (land vs. water)

What is air temperature and how is it measured? Air temperature is the measure of average kinetic energy (Topic 5) It is measured with a thermometer. The units or scales can be °C (degrees Celsius), °F (degrees Fahrenheit) or K (Kelvin). ESRT pg. 13. They are modeled on maps as isotherms (line connecting equal temperatures)

How is the atmosphere heated? The atmosphere is heated by: – Direct absorption of insolation – Direct absorption of long wave radiation (what the Earth gives out) – Condensation – change of water vapor to liquid, releasing energy to form clouds, dew, fog and frost. – Convection Currents (Cells) – air pressure differences causes air to move. – Expansion and Cooling of air – Air expands, its temperature decreases Air condenses, its temperature increases

What is atmospheric pressure? How is it measured? Atmospheric pressure is also called air pressure. It is the pressure due to the weight of overlying atmosphere pushing down on any given area. It is measured with an instrument called a barometer. Units can be millibars (mb), inches of mercury (inches) or atmospheres (atm).

What is the standard air pressure at sea level? The standard air pressure at sea level is 1 atm (atmosphere), inches or mb (millibars)

How does temperature effect air pressure? As the temperature of air increases, the air pressure will decrease. This occurs because warm air will expand and decrease its density. Air pressure is shown on maps by the use of isobars (lines connecting equal pressure values) This is an indirect relationship

How does water vapor affect air pressure? The greater the amount of water vapor (moisture content or absolute humidity), the lower the air density and pressure. This is an indirect relationship. Each water molecule in the atmosphere replaces another molecule of air (usually oxygen or nitrogen). A water molecule has a mass of 18g. Oxygen (o 2 ) has a mass of 32g (16g x 2 molecules). Nitrogen (N 2 ) has a mass of 28g (14g x 2 molecules). When the mass gets smaller, the density will change.

How does altitude (elevation) affect air pressure? As the altitude increases, the pressure decreases (ESRT pg. 14) This is an indirect relationship.