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Fundamentals of Physical Geography 1e Chapter 5: Humidity, Condensation, and Precipitation Petersen Sack Gabler Humidity, Condensation, and Precipitation Humidity, Condensation, and Precipitation • Water – Universal solvent – Acid rain • Capillary action If the floating ice melts completely before you can drink from the glass, will the liquid level rise, fall, or remain the same as before? Why? Humidity, Condensation, and Precipitation • Hydrosphere – Earth’s water – 73% of Earth’s surface covered by water – Can you distinguish between the Greenland and Antarctic ice sheets and the seasonal (pack ice) that has formed on the oceans’ surface? Humidity, Condensation, and Precipitation • Earth’s Water Resources – Vast majority salt oceans • How might global warming or cooling alter this figure? Freshwater lakes, 0.009% Saline lakes, 0.0008% Stream channels, 0.0001% Soil root zone, 0.00018% Deep groundwater 0.306% Shallow groundwater 0.306% Oceans 97.1% Hydrosphere Glaciers 2.24% Nonocean Component (% of total hydrosphere) Stepped Art Fig. 5-3, p. 101 The Hydrologic Cycle • Hydrologic cycle – Circulation of water over earth. A closed system. – Continuous cycle of evaporation, condensation, precipitation, and movement of water over land, in ground, and in water bodies. Moist air Condensation Condensation Precipitation Soil moisture Precipitation Evaporation from rivers, soils, vegetation, lakes, and falling precipitation Evaporation from ocean Seepage Ground water (fresh) Interface Salt water Stepped Art Fig. 5-4, p. 102 Water in the Atmosphere • The Water Budget – Troposphere contains 99% of the water vapor in the atmosphere – Through changes in the state of water, water plays a very important role in regulating Earth’s temperature •Latent heat •Heat transfer involved with evaporation and condensation is huge! •The energy stored and transferred in phase changes provides the power for Earth’s storms! Water in the Atmosphere • Saturation and Dew Point temperature – Saturation: air at a certain temperature holds all of the water vapor possible. It has reached capacity. – Dew Point: the temperature at which the air becomes saturated. The dew point is changes. Water in the Atmosphere • Humidity – The amount of water vapor in the air • Three different ways to measure Humidity: – Absolute Humidity – Specific Humidity – Relative Humidity (R.H.) Water in the Atmosphere • What do you notice about the relationship between temperature and relative humidity? Sources of Atmospheric Moisture • Evaporation • Transpiration • Evapotranspiration Sources of Atmospheric Moisture • Rates of Evaporation – Amount and temperature of water – Air’s relative humidity – Wind Sources of Atmospheric Moisture • Potential evapotranspiration – Annual potential evapotranspiration – Why is it so high in the southwest desert? Sources of Atmospheric Moisture • Water Budget System – When would irrigation at this site be necessary? Sources of Atmospheric Moisture • Condensation nuclei – Required for condensation to occur – Surface upon which condensation can occur •Sea salt •Dust, pollen, volcanic material – Air must be saturated and air temperature must be at the dew point. • Fog and clouds form when water vapor condenses and a large number of these droplets form a mass. Sources of Atmospheric Moisture • Fog – Radiation Fog •Develops during clear, cold, and calm weather – Advection Fog •Occurs when warm, moist air moves over a colder land or water surface •West Coast – Upslope Fog •Windward slopes Sources of Atmospheric Moisture • Dew – Tiny water droplets, formed by the condensation of water vapor on cool surfaces • Frost – Same process as dew but temperature is below the freezing point. – Is this sublimation or deposition? Sources of Atmospheric Moisture • Clouds – Source of all precipitation – Precipitation – Cloud forms: •Strato (low) •Alto (middle) •Cirro (high) Sources of Atmospheric Moisture • Major cloud types – – – – – – – Cirrus Stratus Cumulus Stratocumulus Nimbus: rain falling Nimbostratus Cumulonimbus Adiabatic Heating and Cooling • Adiabatic cooling – Rising parcel of air cools as with decreasing pressure – Cools at 5.6oF/1000 feet (10oC/1000 meters) • Adiabatic heating – Descending air is compressed by increasing pressure – Warms at 5.6oF/1000 feet (10oC/1000 meters) Adiabatic Heating and Cooling • Dry adiabatic lapse rate – Cooling of a parcel before condensing – 5.6oF/1000 feet (10oC/1000 meters) • Wet adiabatic lapse rate – Cooling of a parcel after condensing – 3.2oF/1000 feet (5oC/1000 meters • Environmental Lapse rate Adiabatic Heating and Cooling • The wet and dry adiabatic rate is not the same as the normal lapse rate (environmental lapse rate). • In the example below, using the environmental lapse rate, what is the air temperature at 2000m? Adiabatic Heating and Cooling • Instability and Stability – Stability: environment lapse rate< dry adiabatic – Instability (unstable): environment lapse rate> dry adiabatic • In these examples, what would the air temperature be at 2000m if the air at the surface rose to this level? Precipitation Processes • Relative sizes of: – Raindrops – Cloud droplets – Condensation nuclei If the diameter of a raindrop is 100 times larger than a cloud droplet, why does it take a million droplets to produce one raindrop? Precipitation Processes • Cloud droplet formation process – Collision-coalescence (warm clouds) – Bergeron (ice crystal) process •Cold cloud •Supercooled water Precipitation Processes • What is the difference between water and supercooled water? Precipitation Processes • Forms of Precipitation – Rain – Drizzle – Snow – Sleet – Hail – Freezing rain (glaze) What gives hailstones their spherical appearance? Precipitation Processes • Freezing rain (glaze) Why are power failures a common occurrence with ice storms? Precipitation Processes • Factors necessary for precipitation – Moist air – Condensation nuclei – Uplift mechanism (rising air) Precipitation Processes • Uplift mechanisms – Convectional – Frontal – Cyclonic (convergence) – Orographic What kind of air movement is common to the depictions in all four diagrams? Warm air Convectional Cyclonic (Convergence) Rain shadow Warm air Cold air Front Frontal Orographic Stepped Art Fig. 5-19, p. 114 Precipitation Processes • Convectional – Hot air rises – Cooler air sinks – Most common humid equatorial and tropics – In which case, will clouds appear due to convectional lifting? Precipitation Processes • Frontal Precipitation – Front •Boundary zone between relatively warm and cold air • Cyclonic Precipitation – Also known as convergence (cyclonic uplift) – Air moves counterclockwise toward the center of a low pressure Precipitation Processes • Orographic Precipitation – Air forces upward due to land barriers (ex: mountains) – Rain shadow occurs on the leeward side – Windward slope is wetter Distribution of Precipitation • Distribution over Time – Average annual precipitation – Rain days (0.01 inches of rain or more) – Average monthly precipitation Q: How would this rainfall pattern affect agriculture? Distribution of Precipitation • Latitudinal Distribution – General decrease from equator to poles – Equatorial zone •High precipitation •ITCZ – Trade Wind belt •East coasts wetter than west •Mount Waialeale, Kauai In general, where on Earth’s surface does the heaviest rain fall? Distribution of Precipitation • Latitudinal Distribution – Subtropical High •Subsiding air •Great deserts of the world – Northern and southern Africa – Arabia – North America – Australia •Exceptions – Wet along east coast – Monsoonal regions Distribution of Precipitation • Latitudinal Distribution – Westerlies •Polar front precipitation •Inland areas drier •Mountains – Windward wetter – Leeward drier •Precipitation increases toward the eastern coasts Distribution of Precipitation • Latitudinal Distribution – Polar regions have low precipitation •Low temps lead to low evaporation rates •Subsidence •High pressure Distribution of Precipitation • Latitudinal Distribution • Compare these graphs. What is the relationship between world rainfall patterns and world pressure distribution? Precipitation Variability • Seasonal changes • Annual changes – Mediterranean – West Africa’s Sahel – Russian Steppe – American Great Plains Fundamentals of Physical Geography 1e End of Chapter 5: Humidity, Condensation, and Precipitation Petersen Sack Gabler
