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Hurricanes and Tropical Storms

Hurricanes and Tropical Storms. Naming Convention. Hurricanes: extreme tropical storms over Atlantic and Eastern Pacific Oceans Typhoons: extreme tropical storms over western Pacific Ocean Cyclones: extreme tropical storms over Indian Ocean and Australia.

dorinda-urbina
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Hurricanes and Tropical Storms

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  1. Hurricanes and Tropical Storms

  2. Naming Convention • Hurricanes: extreme tropical storms over Atlantic and Eastern Pacific Oceans • Typhoons: extreme tropical storms over western Pacific Ocean • Cyclones: extreme tropical storms over Indian Ocean and Australia

  3. Ocean Temperatures and Hurricanes Hurricanes depend on large pools of warm water

  4. Annual Hurricane Frequency • There are no hurricanes in the southern Atlantic Ocean! • The strongest hurricanes occur in the western Pacific Ocean (often referred to as “super-typhoons.”)

  5. Hurricane Characteristics • Definition: Hurricanes have sustained winds of 120 km/hr (74 mph) or greater. • Size: Average diameters are approx. 600 km (350 mi). This is 1/3 the size of a mid-latitude cyclone (synoptic storm system). • Duration: Days to a week or more. • Strength: Central pressure averages 950 mb but may be as low as 870 mb (lower the pressure – stronger the storm). • Power: The power released by a single hurricane can exceed the annual electricity consumption by the US and Canada combined.

  6. Hurricane Seasons • Hurricanes obtain their energy from latent heat release in cloud formation processes. • Hurricanes occur where a deep layer of warm water exists during the time of the highest SSTs (sea surface temps). • Northern Hemisphere: August through September are most active months. • Southern Hemisphere: January through March are the most active months

  7. Latent Heat: Release Me! • Hurricanes draw their power from warm, extremely humid air found only over warm oceans. • The key energy source is the latent heat that's released when water vapor condenses into cloud droplets and rain. Tropical storms and hurricanes grow best in a deep layer of humid air that supplies plenty of moisture. • When a substance changes phase, energy must be supplied in order to overcome the molecular attractions between the constituent particles. This energy must be supplied externally, normally as heat, and does not bring about a change in temperature. When water is in the vapor state, as a gas, the water molecules are not bonded to each other. They float around as single molecules. When water is in the liquid state, some of the molecules bond to each other with hydrogen bonds.  The bonds break and re-form continually.

  8. Latent Heat • We call the energy needed to change phases latent heat (the word "latent" means "invisible"). The latent heat is the energy released or absorbed during a change of state. • To get the molecule of water vapor to become liquid again, we have to take the energy away, that is, we have to cool it down so that it condenses (condensation is the change from the vapor state to the liquid state).  When water condenses, it releases latent heat.

  9. Latent Heat Values • The amount of latent heat involved depends to some extent on the temperature at which the process is occurring. The figures below are those normally found in meteorology texts and are for temperatures found in the atmosphere, such as 0 Celsius (32 F). • Latent heat of condensation (Lc): Refers to the heat gained by the air when water vapor changes into a liquid. Lc=2500 Joules per gram (J/g) of water or 600 calories per gram (cal/g) of water. • Latent heat of fusion(Lf): Refers to the heat lost or gained by the air when liquid water changes to ice or vice versa. Lf=333 Joules per gram (J/g) of water or 80 calories per gram (cal/g) of water. • Latent heat of sublimation(Ls): Refers to the heat lost or gained by the air when ice changes to vapor or vice versa. Ls=2833 Joules per gram (J/g) of water or 680 calories per gram (cal/g) of water. • Latent heat of vaporization(Lv): Refers to the heat lost by the air when liquid water changes into vapor. This is also commonly known as the latent heat of evaporation. Lv= -2500 Joules per gram (J/g) of water or -600 calories per gram (cal/g) of water.

  10. Latent Heat • As water vapor evaporates from the warm ocean surface, it is forced upward in the convective clouds that surround the eyewall and rainband regions of a storm. As the water vapor cools and condenses from a gas back to a liquid state, it releases latent heat. The release of latent heat warms the surrounding air, making it lighter and thus promoting more vigorous cloud development. • The release of latent heat warms the surrounding air, making it lighter and thus promoting more vigorous cloud development. • Animation: http://svs.gsfc.nasa.gov/vis/a000000/a001600/a001605/cloud.mov

  11. Energy of Latent Heat • Condensation releases latent heat. This causes the temperature of a cloud to be warmer than it otherwise would have been if it did not release latent heat. Anytime a cloud is warmer than the surrounding environmental air, it will continue to rise and develop. • The more moisture a cloud contains, the more potential it has to release latent heat. • Temperatures in the middle of the rising air in cumulonimbi there may be as much as 15-20C (28-38F) warmer than air outside the storm. For Hurricane Rita, observations showed that, at 700 mb (approximately 10000 feet), the interior temperature of Rita was 31C and about 20C warmer than the outside of the storm at the same elevation.

  12. Hurricane Structure • A central eye is surrounded by large cumulonimbus thunderstorms occupying the adjacent eyewall. • Weak uplift and low precipitation areas are separated by individual cloud bands.

  13. Temperature Structure • Hurricanes characterized by a strong thermally direct circulation with rising of warm air near center of storm and sinking of cooler air outside. • The “warm core” of the hurricane serves as a reservoir of potential energy which is continually being converted to kinetic energy by thermally direct circulation

  14. Pressure Structureof Hurricanes • The horizontal pressure gradient with altitude decreases slowly • From surface to 400 mb: cyclonic circulation. • At about 400 mb, the pressure inside the storm is approx. that of outside of the storm. • From 400 mb to tropopause: anticylonic circulation. • The upper portions of the storm are blanketed by a cirrus cloud cap due to overall low temperatures.

  15. Hurricanes and Tropical Storms

  16. Naming Convention • Hurricanes: extreme tropical storms over Atlantic and Eastern Pacific Oceans • Typhoons: extreme tropical storms over western Pacific Ocean • Cyclones: extreme tropical storms over Indian Ocean and Australia

  17. Ocean Temperatures and Hurricanes Hurricanes depend on large pools of warm water

  18. Annual Hurricane Frequency • There are no hurricanes in the southern Atlantic Ocean! • The strongest hurricanes occur in the western Pacific Ocean (often referred to as “super-typhoons.”

  19. Hurricane Characteristics • Definition: Hurricanes have sustained winds of 120 km/hr (74 mph) or greater. • Size: Average diameters are approx. 600 km (350 mi). This is 1/3 the size of a mid-latitude cyclone (synoptic storm system). • Duration: Days to a week or more. • Strength: Central pressure averages 950 mb but may be as low as 870 mb (lower the pressure – stronger the storm). • Power: The power released by a single hurricane can exceed the annual electricity consumption by the US and Canada combined.

  20. Hurricane Seasons • Hurricanes obtain their energy from latent heat release in cloud formation processes. • Hurricanes occur where a deep layer of warm water exists during the time of the highest SSTs (sea surface temps). • Northern Hemisphere: August through September are most active months. • Southern Hemisphere: January through March are the most active months

  21. Latent Heat: Release Me! • Hurricanes draw their power from warm, extremely humid air found only over warm oceans. • The key energy source is the latent heat that's released when water vapor condenses into cloud droplets and rain. Tropical storms and hurricanes grow best in a deep layer of humid air that supplies plenty of moisture. • When a solid substance changes phase, energy must be supplied in order to overcome the molecular attractions between the constituent particles. This energy must be supplied externally, normally as heat, and does not bring about a change in temperature. When water is in the vapor state, as a gas, the water molecules are not bonded to each other. They float around as single molecules. When water is in the liquid state, some of the molecules bond to each other with hydrogen bonds.  The bonds break and re-form continually.

  22. Latent Heat • We call the energy needed to change phases latent heat (the word "latent" means "invisible"). The latent heat is the energy released or absorbed during a change of state. • To get the molecule of water vapor to become liquid again, we have to take the energy away, that is, we have to cool it down so that it condenses (condensation is the change from the vapor state to the liquid state).  When water condenses, it releases latent heat.

  23. Latent Heat Values • The amount of latent heat involved depends to some extent on the temperature at which the process is occurring. The figures below are those normally found in meteorology texts and are for temperatures found in the atmosphere, such as 0 Celsius (32 F). • Latent heat of condensation (Lc): Refers to the heat gained by the air when water vapor changes into a liquid. Lc=2500 Joules per gram (J/g) of water or 600 calories per gram (cal/g) of water. • Latent heat of fusion(Lf): Refers to the heat lost or gained by the air when liquid water changes to ice or vice versa. Lf=333 Joules per gram (J/g) of water or 80 calories per gram (cal/g) of water. • Latent heat of sublimation(Ls): Refers to the heat lost or gained by the air when ice changes to vapor or vice versa. Ls=2833 Joules per gram (J/g) of water or 680 calories per gram (cal/g) of water. • Latent heat of vaporization(Lv): Refers to the heat lost by the air when liquid water changes into vapor. This is also commonly known as the latent heat of evaporation. Lv= -2500 Joules per gram (J/g) of water or -600 calories per gram (cal/g) of water.

  24. Latent Heat • As water vapor evaporates from the warm ocean surface, it is forced upward in the convective clouds that surround the eyewall and rainband regions of a storm. As the water vapor cools and condenses from a gas back to a liquid state, it releases latent heat. The release of latent heat warms the surrounding air, making it lighter and thus promoting more vigorous cloud development. • The release of latent heat warms the surrounding air, making it lighter and thus promoting more vigorous cloud development. • Animation: http://svs.gsfc.nasa.gov/vis/a000000/a001600/a001605/cloud.mov

  25. Energy of Latent Heat • Condensation releases latent heat. This causes the temperature of a cloud to be warmer than it otherwise would have been if it did not release latent heat. Anytime a cloud is warmer than the surrounding environmental air, it will continue to rise and develop. • The more moisture a cloud contains, the more potential it has to release latent heat. • Temperatures in the middle of the rising air in cumulonimbi there may be as much as 15-20C (28-38F) warmer than air outside the storm. For Hurricane Rita, observations showed that, at 700 mb (approximately 10000 feet), the interior temperature of Rita was 31C and about 20C warmer than the outside of the storm at the same elevation.

  26. Hurricane Structure • A central eye is surrounded by large cumulonimbus thunderstorms occupying the adjacent eyewall. • Weak uplift and low precipitation areas are separated by individual cloud bands.

  27. Temperature Structure • Hurricanes characterized by a strong thermally direct circulation with rising of warm air near center of storm and sinking of cooler air outside. • The “warm core” of the hurricane serves as a reservoir of potential energy which is continually being converted to kinetic energy by thermally direct circulation

  28. Pressure Structureof Hurricanes • The horizontal pressure gradient with altitude decreases slowly • From surface to 400 mb: cyclonic circulation. • At about 400 mb, the pressure inside the storm is approx. that of outside of the storm. • From 400 mb to tropopause: anticylonic circulation. • The upper portions of the storm are blanketed by a cirrus cloud cap due to overall low temperatures.

  29. Hurricane Eye and Eyewall • A shrinking eye indicates storm intensification • The eyewall is moves at a speed of 20 km/hour and the calm weather associated with the eye will last less than 1 hour • The hurricane eye is an area of descending air, relatively clear sky and light winds: 25 km (15 mi) diameter on average. • The eyewall is comprised of the strongest winds, the largest clouds and the heaviest precipitation with rainfall rates as high as 2500 mm/day (100 inches/day).

  30. Hurricane Formation • Tropical Disturbance: Clusters of small thunderstorms. • Tropical Depression: When at least 1 closed isobar is present (organized center of low pressure). • Tropical Storm: Further intensification to wind speeds of 60 km/hr (37 mph). • Hurricane: Hurricane status is gained when the winds reach a sustained 120 km/hr (74 mph).

  31. Tropical Disturbances and Easterly Waves • Some tropical disturbances form from mid-latitude troughs migrating towards lower latitudes, some form from ITCZ convection, but most develop from “easterly waves.” • Easterly Waves, or undulations in the trade wind patterns, spawn hurricanes in the Atlantic. • Only 10% of tropical disturbance become more organized, rotating storms.

  32. Conditions necessary for Hurricane Formation • Hurricanes only form over deep (several 10s of meters) water layers with temperatures in excess of 27 degrees C. • Poleward to about 20 degrees, water temperatures are usually below this threshold. • Coriolis effect is an important contributor, hurricanes do not form from equator to 5 degrees. • Need unstable atmosphere: available in western parts of oceans but not in eastern parts of ocean. • Strong vertical shear must be absent. (both magnitude and direction). • Vertical shear: changing of wind speed and/or direction with height of the atmosphere.

  33. Hurricane Movement • Tropical depressions and disturbances are largely regulated by trade wind flow – move westward. • Tropical storms & hurricanes: upper-level winds and ocean temperatures gain importance. • Fully developed hurricanes will move poleward (stronger upper winds will steer the hurricanes northward).

  34. Hurricane Dissipation • After making landfall, a hurricane may die completely within a couple of days (no longer has moisture to feed into storm). • Even as storm weakens, it can still have large effects on land (especially flooding). • Hurricanes will also dissipate over cooler waters or if they encounter strong vertical shear. • Animation: http://svs.gsfc.nasa.gov/vis/a000000/a001600/a001605/coldwater.mov

  35. Hurricane Damage • Heavy rainfall • Strong winds • Tornadoes (generally F0-F2) • Storm surge – rise in water level induced by the hurricane.

  36. Tornado formation in hurricanes • Most hurricanes contain clusters of tornadoes. • Most tornadoes occur in right front quadrant of the storm. • It appears that slowing of wind by friction at landfall contributes to the formation of these tornadoes.

  37. Storm Surges • Process 1: Hurricane winds drag surface waters forward and pile water near coasts. • Process 2: Lower atmospheric pressure raises sea level (for every 1mb pressure decrease, sea level raises 1 cm) • Storm surges raise sea level by a 1-2 m for most hurricanes, as much as 7 m (a real problem when coastal locations are at or below sea-level)

  38. Hurricane Wind Structure • Winds and surge are typically strongest at right front quadrant of storm where wind speeds combine with speed of storm’s movement to create the highest area of potential impact.

  39. Trends for Atlantic • Mid 1990s-now: A significant increase in the numbers of hurricanes and intense hurricanes making landfall in US. • 1970s-mid 1990s: Lower than normal incidence of Atlantic Hurricanes. • Debate: Is the recent increase in hurricanes part of a natural cycle, global climate change or a combination?

  40. Forecasting • National Hurricane Center responsible for Atlantic and eastern/central Pacific. • Data gathered through satellite, surface observations and aircraft using dropsondes (dropping of instruments through hurricane) • Computer models assist in predictions.

  41. Hurricane Watch and Warning • Hurricane Watch: if an approaching hurricane is expected to make landfall within 24 hours. • Hurricane Warning: if the time frame is less, then it’s a warning.

  42. Naming of Hurricanes • When a tropical disturbance reaches a tropical depression, the storm will be given a name. • The name comes from an “A-W” list given by World Meteorological Organization (WMO). • The names of hurricanes with devastating effects are retired.

  43. Hurricane Intensity Scale • Saffir-Simpson Scale • Five Categories: the larger numbers indicate lower central pressures, greater winds and stronger storm surges

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