DO NOW Pick up notes and Review #20. Turn in any completed work.
REVIEW On a clear summer day, which surface heats up the fastest – land or water? Why? LAND Absorbs energy – stays at surface (doesn’t mix with deeper layers). Heat is not lost from evaporation. Land retains heat during day.
WEATHER PATTERNS AND TOPOGRAPHY SES5c. Relate weather patterns to interactions among ocean currents, air masses, and topography.
HAWAII Prevailing winds: Northeast Trade Winds
WINDWARD SIDE: WEST SIDE What do you notice?
LEEWARD SIDE: EAST SIDE What do you notice?
WEATHER PATTERNS There is more rain on the Windward side of the islands.
OROGRAPHIC LIFTING: RAIN SHADOW EFFECT
OROGRAPHIC LIFTING: RAIN SHADOW EFFECT Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude, it quickly cools down adiabatically, which can raise the relative humidity to 100% and create clouds and, under the right conditions, precipitation.
WINDWARD SIDE: AIR RISES On the WINDWARD side of the island are mountains for air to rise up on. Air that rises is cooled. Clouds form. Lots of precipitation.
LEEWARD SIDE: AIR FALLS On the LEEWARD side of the island, air sinks down the back of the mountains. Air warms as it sinks. Air is dry. Air is clear.
OROGRAPHIC LIFTING: RAIN SHADOW EFFECT
WEATHER DIFFERENCES
WEATHER DIFFERENCES As air rises, it cools. Before clouds form, cooling rate is 10°C per 1 km. DRY ADIABATIC Cooling rate = 10°C per km.
WEATHER DIFFERENCES When clouds form, energy is released in the form of LATENT HEAT. After clouds form cooling rate is 5°C per km. WET ADIABATIC Cooling rate = 5°C per km. Cooling rate of rising air slows once clouds form.
LATENT HEAT Latent heat is the energy of phase changes. It took energy to evaporate water on surface. When water condenses to form clouds, energy is released as LATENT HEAT.
WEATHER DIFFERENCES Air that descends down the mountain is dry. Heats at Dry Adiabatic Lapse rate of 10°C per km. End result – air mass warmer than when it started.
OTHER PLACES?
CHINOOK: RAIN SHADOW WINDS These are on the Eastern slopes of the Rocky Mountains. Warm winds. Dramatic weather changes. Temperature can change by as much as 28°C (50°F) in a few hours.
REVIEW B A Compare the weather at City A to the weather at City B: Which city is warmer? Which city is wetter? WHY? B A
LAB: ADIABATIC TEMPERATURE CHANGES How does topography affect weather?
LAB: ADIABATIC TEMPERATURE CHANGES Purpose: Understand how clouds can form in rising air and calculate the temperature of air as it goes over a mountain.
LAB: ADIABATIC TEMPERATURE CHANGES The usual way of cooling things is to remove heat. However, when gases are compressed into smaller volumes or when they are allowed to spread out, their temperature changes. This type of temperature change is called adiabatic. compressed = higher pressure = higher temperature allowed to expand = lowered pressure = lowered temperature
LAB: ADIABATIC TEMPERATURE CHANGES When air goes up a mountain (see A, below), the pressure gets lower, the air can expand, and the temperature goes down. When air is rising, it cools at the rate of 10oC every 1000 meters. This is called the dry adiabatic lapse rate. However, the level of humidity in the air increases as the temperature cools (the air cannot hold as much moisture as it could when it was warmer).
LAB: ADIABATIC TEMPERATURE CHANGES Once the air rises above the elevation at which clouds begin to form and rain falls, it cools more slowly (see B, below). This rate varies as the level of humidity changes, but a general guideline is 5oC every 1000 meters. This is called the wet adiabatic lapse rate. When air comes down the other side of the mountain (see C, below), the pressure gets higher, the air is compressed, and the temperature increases at the dry adiabatic lapse rate
LAB: ADIABATIC TEMPERATURE CHANGES
LAB: ADIABATIC TEMPERATURE CHANGES
LAB: ADIABATIC TEMPERATURE CHANGES
TO DO Work on Adiabatic Temperature Changes. Turn in when finished. Then Review #20.