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AFWA/XOGM

Initial Tropical Training for Satellite Analysts. AFWA/XOGM. Tropical Section. Originally produced by: TSgt Nast. Revisions by: Paul McCrone. Sources. AWS/TR-95/001 AWS TR240 NAVEDTRA 40970/40971 JTWC Forecasters Handbook NEPRF TR-85-01 Tropical Weather Course (Keesler)

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AFWA/XOGM

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  1. Initial Tropical Training for Satellite Analysts AFWA/XOGM Tropical Section Originally produced by:TSgt Nast Revisions by: Paul McCrone

  2. Sources • AWS/TR-95/001 • AWS TR240 • NAVEDTRA 40970/40971 • JTWC Forecasters Handbook • NEPRF TR-85-01 • Tropical Weather Course (Keesler) • Tropical TIPS

  3. Overview • Primary Physical Controls of the Tropics • Planetary-Scale Circulation in the Tropics • Non-Severe Weather Systems and Tertiary Circulation's • Basic Analysis and Circulation Models • Monsoons • Climate Anomalies • Tropical Cyclones • Severe Weather in the Tropics • Tropical Forecasting

  4. Primary Physical Controls of the tropics • Earth’s Energy Budget • Effects of Land-SeaDistribution • Terrain Effects • Diurnal Effects

  5. Primary Physical Controls of the tropics

  6. AWS/TR-95/001 Page 11 Figure 2-1

  7. Earth’s Energy Budget

  8. Earth’s Energy Budget • Vertical heat transfer mechanisms • Radiation - not very significant • Sensible heat transfer • Latent heat transfer - Most important vertical mechanism in tropics • Conduction - molecular boundary layer • Convection - air warmed by conduction • Condensation (latent heat becomes sensible heat) • Evaporation (Sensible heat becomes latent heat)

  9. Earth’s Energy Budget

  10. Earth’s Energy Budget • Horizontal Heat Transfer • Horizontal heat transfer mechanisms • Sensible heat transfer through warm- or cold-air advection • About 40% of earth's total horizontal heat exchange occurs through ocean currents. • Latent heat transfer. • Moisture advection. • Latent heat release aloft, carried poleward by the Hadley cell.

  11. Earth’s Energy Budget

  12. Effects of Land-Sea Distribution • Determines climate type (monsoon, maritime, Continental.). • Max seasonal variations occurs over land. • Most convection and latent heat-sensible heat conversion takes place over land. • Land-sea breeze circulation's are a direct result.

  13. Terrain Effects • High altitude more typical of mid-latitude weather. • Rainfall: • Leeside or windward location usually most important factor. • In trade winds, heaviest rain usually on slopes just below trade-wind inversion.

  14. Terrain Effects • Whether a location is on the leeside or windward side is a very important factor Rainfall

  15. Diurnal Effects • Temperature Range • Clouds • Rainfall

  16. Diurnal Effects • Temperature Range • On small islands and coastlines 3-5°C with prevailing onshore flow. • On inland locations or coasts 5-10°C with prevailing land breeze. • In the interior in the dry season > 10°C.

  17. Diurnal Effects • Clouds • Oceans • Maximum (0400-0700L), minimum (1400L-1900L) • Land • Daytime maximum, nocturnal minimum

  18. Diurnal Effects • Rainfall • Nocturnal max over oceans, and small islands. • Shower maximum over land in afternoon. • Monsoon areas and areas in disturbances have night to early morning maximum.

  19. Planetary-Scale Circulation in the Tropics Definitions and General Characteristics Primary Weather Zone Tropical Wind Profiles Upper Tropospheric Features

  20. Definitions and General Characteristics • Classical Definitions. • Ancient Greeks - Tropics of Cancer to Capricorn (23.5N to 23.5S) • Alexander Supan - Average Annual Temp > 68 F (20°C) • Early 1900s - W.P. Koppen • World is divided into climatic Zones A to F. • A= tropical rainy, Af = rain forest, Aw = savanna, Am = monsoon.

  21. Definitions and General Characteristics • Dynamic Definitions - allow for seasonal, longitudinal variations. • Dividing line between mid-Tropospheric easterlies and westerlies (axes of STRs). H H H H H H

  22. Definitions and General Characteristics • Tropical weather characteristics • Cumulus clouds predominate. • Conditionally unstable. • Air temperatures comparable to ocean surface temperatures. • Predominately easterly low-level flow.

  23. Definitions and General Characteristics • Climatology is more important in the tropics than it is in the mid-latitudes • Weather dominated by semi-permanent, slowly migrating systems • Subtropical Ridge (STR) • Equatorial Trough (ET)

  24. Primary Weather Zones and Systems • Subtropical Ridge (STR) • Surface • Centered on five oceanic anticyclones. • Over the oceans: • shrinks and retreats equatorward in winter, grows and builds poleward in summer. (inducing TUTT formation)

  25. Primary Weather Zones and Systems • Subtropical Ridge (STR) • Surface • Axis tilts ENE-WSW in Northern Hemisphere, ESE-WNW in Southern Hemisphere. • Ridge axis normally 23-35 degrees latitude North and South

  26. Primary Weather Zones and Systems

  27. Primary Weather Zones and Systems • Subtropical Ridge (STR) • Aloft H H • Slopes to equator with height. • Position of axis at 200 mb is 15-20° latitude. H L H H H • More elongated east-west than the surface ridge.

  28. Primary Weather Zones and Systems • Trade-wind region • Region of low-level prevailing easterlies between STR and ET. • NE trades in Northern Hemisphere, SE trades in Southern Hemisphere. • General subsidence with capping trade-wind inversion.

  29. Equatorial Trough (ET) • Other terms • Near equatorial trough (NET). • ITCZ or ITC. • Doldrums. • Meteorological or thermal equator. • Near-equatorial Tradewind Convergence (NETWC).

  30. Equatorial Trough (ET) • Location, strength, circulations vary • Generally found where trade winds from each hemisphere converge • Low pressure from heating and upward motion • May be axis of convergence or series of cyclones

  31. Equatorial Trough (ET) • Several streamline configurations: • Near Equatorial Convergence Zone (or trade-wind trough). • Monsoon trough • Confluent westerlies. • Equatorial Buffer Zone

  32. (ET) Streamline Configurations • Near Equatorial Convergence Zone (or trade-wind trough). • Confluent zone between trade winds of each hemisphere. • Usually over oceans, but can extend over adjacent land areas.

  33. Trade Wind Trough

  34. (ET) Streamline Configurations • Monsoon trough • Often a series of cyclonic centers: • Heat lows (over land primarily). • Thunderstorm clusters, non developing. • Monsoon depressions. • Tropical disturbances.

  35. (ET) Streamline Configurations • Monsoon trough • Locations • Africa - Sub-Sahara in July and Kalahari-Madagascar in January. • Central America - East Pacific: south of Central America all year and occasionally crosses into Caribbean.

  36. Africa - Sub-Sahara in July

  37. (ET) Streamline Configurations • Monsoon trough • Locations • South Asia - West Pacific: Iraq to northern India through SE Asia to Guam. • Australia - along the northern coast from December through February.

  38. (ET) Streamline Configurations • Confluent westerlies. • Locations: • West of Central America in fall. • NW of Australia in Southern Hemisphere summer. • Winds generally light, speed convergence increasing downstream.

  39. H H (ET) Streamline Configurations H H Monsoon Trough C C Confluent Westerlies Tradewind Trough H

  40. (ET) Streamline Configurations • Equatorial Buffer Zone • July: • Southern Hemisphere SE winds become SW entering monsoon trough. • Equatorial Buffer Zone • January: • Northern Hemisphere NE winds become NW entering Southern Hemisphere monsoon trough.

  41. B (ET) Streamline Configurations • Equatorial Buffer Zone • Buffer Cells • Weak, closed circulations near equator where curving winds "cut off". • No net inflow or outflow. • Labeled with a "B" on streamline analysis.

  42. Tropical Vertical Wind Profiles: Deep Easterlies • Low-level east winds remain easterly with height • Found within 15° of equator • May extend to 30° in summer hemisphere • Not in all seasons or regions • Narrowest north-south extent at 200 mb

  43. Tropical Vertical Wind Profiles: Shallow Easterlies • Shallow Easterlies • Low-level easterlies become westerly with height • Average 15-30° latitude, closer to equator in winter hemisphere • Example - Hawaiian islands (20°N) in shallow easterlies all year

  44. Tropical Vertical Wind Profiles: Shallow Westerlies • Low-level westerlies become easterly with height. • Found in monsoon regions in summer. • Examples: western Pacific, Indian Ocean, western Africa (shallower in Africa).

  45. Upper-Tropospheric Features • Subtropical Jet (STJ) • Found 20-35°N and 25-32°S (average). • Causes • Upward branch of Hadley cell circulation. • Conservation of angular momentum accelerates air to east as it moves north.

  46. Sub Tropical Jet

  47. Upper-Tropospheric Features • Tropical Easterly Jet (TEJ) • Feature of northern hemisphere (NH) summer monsoon in Asia • Very persistent in NH summer months • Location: central Africa to SE Asia (from 5 degrees to 20 degrees North latitude) • Strongest winds (80-100 kts) over Arabian Sea between 40,000-55,000 ft (200-100 mb). Highest observed winds: 152 kts

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