Humidity and Clouds WATER is the most important GAS for understanding weather! Changes of state of Water Heat absorbed Heat released Moisture: Change of State What happens to molecules and heat during a change of state? Heat absorbed = molecules move apart (density decreases) Heat released = molecules move closer (density increases) What are humidity and saturation? Humidity = amount of water vapor in air Saturation = when air holds the most water vapor possible depends on temperature and pressure How do warm and cold air compare? Warm air holds MORE water than cold air! This helps explain why you feel the humidity more on a hot day Warm air holds more moisture than cold air. What is relative humidity? Relative Humidity (RH) = ratio of the amount of water in the air versus the amount of water air can hold when saturated Changes with temperature/pressure RH = actual content X 100 potential What is Dew Point? Dew point = the temperature at which water vapor turns to liquid High dew points means moist air Low dew points mean dry air Dew on a spider web What is a cloud? A group of tiny water drops or ice formed around a bit of dust or salt Clouds form when the dew point is reached! 4 ways that clouds form Convection How do clouds form from convection? Warm moist air flows upward in convection currents to form clouds Orographic lifting Explain Orographic lifting Mountains act as barriers to the flow of air, forcing the air to move upward, forming a cloud Frontal lifting/wedging Explain What is a front ? a boundary or edge where two air masses meet Warmer, less dense air rises above the cooler air, causing clouds, condensation, and storms Frontal lifting/wedging Convergence Explain Convergence Air masses with the same temperatures crash into each other and both rise Temperature Inversion When air found at lower levels is actually cooler than the air above it it is more dense so it stays below This can happen on a cool night - land cools quickly, causing the air above it to cool as well Temperature inversions can create smog in cities with high pollution (polluted air stays low and blankets city) Clouds are classified by. Shape Height Shapes of Clouds Stratus Cumulus Cirrus Nimbus Describe each type! Height is determined by where the base of the cloud is High (cirro-) Middle (alto-) Low (strato-) Cloud names come from combining the shape and height descriptions e.g., cirrostratus, altocumulous Base Heights of Clouds Cirrus Clouds High clouds = ice crystals Cirrostratus Cirrocumulus Altocumulus Middle clouds = ice crystals & water droplets Altostratus Cumulus Low clouds = water droplets Stratus Stratocumulus Nimbostratus Very tall clouds, extending to the tropopause (top often shaped like an anvil) Intense weather: lightning & thunder hail tornadoes heavy rain Cumulonimbus Clouds (thunder clouds) Fog is a cloud with its base on the ground Fog Your summary box Take a few minutes to summarize your notes on humidity and cloud formation You may discuss with your table partner