Chapter 2: Weather and Climate Victoria Alapo, Instructor Geog 1010

1. Introduction to GeographyPeople, Places, and Environment, 4eEdward F. BergmanWilliam H. Renwick Chapter 2: Weather and Climate Victoria Alapo, Instructor Geog 1010

2. Weather and Climate • Weather • Day-to-day variations in temperature and precipitation. Examples: temporary storms, temperature changes. • Climate • Statistical summary of weather conditions over several decades or more, but usually 30 yrs. • Thirty years was chosen as a period long enough to eliminate year-to-year variations. • Source: http://www.metoffice.gov.uk/climate/uk/averages/

3. Intensity of Solar Radiation (Insolation) • Affected by: • Angle of incidence – more vertical at the equator. Oblique towards the poles. • Also, axial tilt = 23.5 degrees.

4. Latitude • Summer Solstice – June 20 or 21 Longer days In the northern hemisphere • Winter Solstice – December 20 or 21 Longer nights in the northern hemisphere • But in the southern hemisphere, the opposite is occurring on both days! (June & Dec) • Equinoxes • (equal day/night) – see next slide. • Vernal/Spring Equinox – March 20 or 21 • Autumnal Equinox – Sept. 20 or 21

6. Greenhouse Effect • Explain the “Greenhouse Effect” • Greenhouse gases • Water vapor, carbon dioxide, ozone, methane • Increased greenhouse gases = increased global warming

7. Relative Humidity Water content of air; it measures the “wetness of air”. It’s also the percent (%) of water air could hold at a given temperature (as seen on TV).

8. Precipitation: 3 Types (ways it forms) • (1) Convectional precipitation • Warm, humid air rises, and cools • Saturation point is reached • Clouds form • Leads to convectional storms

10. (2) Orographic Precipitation • Wind forces air up and over mountains • Rain on windward side • Desert on leeward side: Rain shadow • Examples • The Rockies and Sierra Nevada. Also, see picture on pg 55, and caption.

12. (3) Frontal Precipitation • This happens when air is forced up the boundary between cold and warm air masses (called a front). • Cold front • When cold air mass moves towards warm air mass • Warm front • When warm air mass moves towards cooler air mass • See animation

14. Circulation Patterns • Air mass = 14.7 lbs per square inch. Air has weight! Think of a cylinder of propane/oxygen. • Atmospheric pressure • Varies with altitude • Higher altitude = less atmospheric pressure • That’s why your ear ‘pops’ as the pressure increases on descent in an airplane. • Barometer – instrument for measuring pressure.

15. Pressure and Winds • Coriolis Effect • An apparent deflection of any freely moving object from its expected (straight) path, caused by the Earth’s rotation. The earth rotates from west to east. • Causes winds to move in an indirect, curving path, including hurricanes, and ocean currents, see next slide. If the earth did not move (rotate), winds would just move in a straight line from high pressure to low pressure. • Happens to planes too, esp. when traveling in a straight line from the north pole to the equator. That’s why pilots fly in a curve. Otherwise, they’ll land to the west of their intended destination. See animation.

16. Ocean Circulation Patterns Gyres is the special name ocean currents are called. • These are wind-driven circular flows.

17. Coriolis Effect

18. Global Circulation

19. Global Circulation • Only 3 of these zones will be discussed: A) Inter-tropical convergence zone (ITCZ) • This is where the N/E & S/E winds converge. See previous slide. These converging winds are also called “Trade Winds”, because they were important to sailing ships. B) Subtropical high-pressure zones • These are areas of dry, bright sunshine, and little precipitation. They cause deserts. It is an area of warm dry air found about 30 degrees N & S latitudes. See next slide.

20. Subtropical Highs Responsible for the world’s greatest deserts. Dry conditions caused by no uplift of air due to high pressure.

21. Global Circulation C) Polar high-pressure zones • The intense cold causes dense air because coldness causes contraction, and so there is little molecular space, therefore air can’t lift. This causes high pressure. • As a result, the air stays close to the ground and there is little precipitation, leading to “polar deserts”. Polar deserts are typically drier than hot deserts – see climograph of McMurdo, Antarctica.

22. Storms • Cyclones • These are low-pressure systems • There are 2 types: A) Hurricanes (N/America) and Typhoons (Pacific) • Also known as tropical cyclones B) Midlatitude cyclones – tornadoes, Box on pg 66.

23. Storms Hurricanes/ Typhoons: • Need warm, moist air • Most powerful over oceans (occur more during summer). • Once the winds reach 74 miles/hr they are called hurricanes/typhoons. • They cause storm surges • This is when there is an elevated sea level in the center of the storm. i.e. high waves crashing inland (e.g. Katrina). 90% of people die from this.

24. World Precipitation 2 primary measures of climate are: Temperature & Precipitation

25. Classifying Climate • The Köppen System • It is the most widely used system and was developed by Wladimir Köppen in 1918. • He used the distribution of plants to help draw boundaries btw climate regions (because vegetation types tend to closely follow precipitation and hence temperature in area). So these 3 are interrelated. • Köppen identified 5 basic climate types, and subdivided them further to reveal important distinctions. See page 74 & 75 of text and next slide. An American Professor added the H Climate (Mountains) • These classifications allows analysis and planning by geographers, govts, etc.

27. Climate Regions • As the map shows, these regions are horizontal bands based on latitude. Read about each climatic region (A to E) on your own. Pages 76 to 86. • Sometimes climatologists use climographs to show temp and precipitation for every month of the year. Every climatic region and every city in the world has one. Draw a simple one for the test. • The one on next slide is for Lanzhou, China (pg 79). • Also see website for Omaha climograph: • http://www.hprcc.unl.edu/stations/index.php?action=metadata&network_station_id=256255

28. Omaha – Eppley Station Data: http://www.hprcc.unl.edu/stations/index.php?action=metadata&network_station_id=256255

29. Climate Change • The earth has alternated btw warm & cold periods over time. 3 hypotheses – reasons given for climate change: • Astronomical • Sunspots – relatively cool regions on the surface of the sun, which varies in #, in a cycle lasting 11 yrs. • Geologic • Volcanic eruptions – large amts of dust & gases can be ejected to reduce solar radiation, and cool the earth. E.g. Krakatau, Indonesia. • Human • Atmosphere – increase in CO2 in the atmosphere since the start of the industrial revolution in the 18th century. CO2 is a greenhouse gas. • Vegetation – clearing