Class #32: Friday, November 13

1. Class #32: Friday, November 13 Weather Forecasting (conclusion) Climate types of the present Class #32: Friday, November 13

2. The Comeback of Analog Forecasts • ENSO has characteristic weather patterns that are statistically more common in El Niño, La Niño, and neutral conditions. • Some of the uncertainty of numerical weather forecasts (the 6th type of forecasts) can be assessed using a type of analog forecast. Class #32: Friday, November 13

3. A New Method of Forecasting • Spectral models view the atmosphere as having a number of waves of different wavelengths and amplitudes (wave heights). • Spectral models are faster than grid point models. • Spectral models are used for mid and long range forecasts. Class #32: Friday, November 13

4. Another New Forecasting Method: Ensemble Forecasting • Involves running the same forecasting model many times, using very slightly different conditions. • Is a research tool, because it is too slow to show in real time • Slight changes in initial conditions can produce very different forecasts • 50 in test ensemble that follows • Resembles the old analog method Class #32: Friday, November 13

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8. Climate • Is to weather what a friend’s personality is to his/her mood • Sums up the weather’s long-term behavior • Is the collective state of the atmosphere for a given place over a specified interval of time Class #32: Friday, November 13

9. Climate is defined by • Location • Globe, continent, region, city • Chapter 14: regional and global scale • Time: a specified interval • 30 year average is normal • 100 years or longer for history of climate • Averages and extremes of variables • Chapter 14: temperature and precipitation Class #32: Friday, November 13

10. Controls on climate • Similar to controls on temperature in Chapter 3 • Latitude: solar energy input • Elevation: air temperature, snow vs. rain • Topography: moist vs. dry, temperature, distribution of cloud patterns, solar energy reaching the surface Class #32: Friday, November 13

11. Controls on Climate (continued) • Proximity to large bodies of water • Thermal properties of water (absorption, heat capacity, transparency, mixing) moderate temperature downwind • Prevailing atmospheric circulation • Intertropical Convergence Zone (ITCZ) • Subtropical Highs Class #32: Friday, November 13

12. Classifying Climate • Hard to do • No clear boundaries • Complex natural systems • How it is done • Important to life: hot or cold; moist or dry • Most common system: based on vegetation • Köppen climate classification scheme based on vegetation and temperature Class #32: Friday, November 13

13. Köppen (KEPP-in) Scheme • Modified by Trewartha and Horn • Related to geography and global circulation • Uses letters (1, 2 or 3) in Chapter 14 • Has many other subdivisions within the categories shown in our book • Has 6 major groups: A, B, C, D, E, H Class #32: Friday, November 13

14. The 6 major climate groups • A: Tropical moist • B: Dry (can be subtropical or mid latitude) • C: Moist with mild winters (mid latitude) • D: Moist with severe winters (mid latitude) • E: Polar (high latitude) • H: Highland (rapid climate change with elevation) • 2nd letter: usually latitude (except B) • 3rd letter: differences in temperature Class #32: Friday, November 13

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18. Tropical Humid Climates: Af, Aw, Am • All tropical (A) climates are humid • Letter “f” means no dry season, rain year round, usually closest to the equator • Letter “m” means “monsoonal”, with a short dry season and a very rainy season • Letter “w” means “winter dry season” except no real winter in tropics, just cool Class #32: Friday, November 13

19. Tropical humid climates (continued) • Af • Closest to the equator • Smallest annual range of temperature • 6.9-10 inches of rain per month • Most thunderstorms in afternoon • Linked to ITCZ • Tropical rain forests • Am • Seasonal onshore winds during summer monsoon • Climates with most yearly precipitation • Jungle vegetation Class #32: Friday, November 13

20. Tropical moist climates (continued) • Aw • Farthest A climate from the equator • Often border Af • Tropical wet and dry • Wet summers, dry, cooler winters • Linked to the seasonal migration of the ITCZ • Vegetation is savannah or tropical grasslands with scattered deciduous trees, as in the grasslands of Africa. Class #32: Friday, November 13

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22. Dry (B) climates • Potential evaporation minus precipitation is greater than 0. • More land of this climate type than any other • Lubbock has a B climate • Descending branch of the Hadley circulation near the subtropical highs or • Rain shadow of a mountain range Class #32: Friday, November 13

23. Dry climate subtypes • 2nd letter • “S” for steppe or semi-arid (like Lubbock) • “W” for true desert (extremely dry) • 3rd letter • “h” for low-latitude, hot (yearly average temperature >= 64ºF) • “k” for mid latitude, cool (yearly average temperature <64ºF) Class #32: Friday, November 13

24. Dry climate subtypes (continued) • BWh Extremely dry and hot; can have large sand dunes; Sahara, Arabian peninsula, central Australia, most extreme B climate • BSk Least extreme B climate; midlatitude steppe, often high plateau, Lubbock, Denver, San Diego; often rain shadow • BSh Much of Mexico, lower latitude, subtropical steppe • BWk Central Asia, very dry, midlatitude rain shadow, continental interior Class #32: Friday, November 13

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