12-Weather_Systems 1

12-Weather_Systems 1 - Wind Generation Represents the...

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Unformatted text preview: Wind Generation Represents the Sun’s energy Due to pressure gradients Differential heating by the sun Direct Rays Sun Global Atmospheric Circulation • Horse Latitudes (convection cells) Sun’s rays (radiation) preferentially heats Equatorial region • Heat air rises and is replaced by air flow toward the Equator from north and south • The hot rising at the Equator cools as it rises and eventually flows away from the Equator the north & south • The cool air descends back toward the Earth’s surface at 30 degrees Climatic Effects Precipitation Deserts Wind Generation Represents the Sun’s energy Due to pressure gradients Differential heating by the sun Direct Rays Sun C o r io lis E ffe ct Causes all moving objects to be deflected to the right in the Northern Hemisphere. In the Southern Hemisphere moving objects are deflected to the left. Coriolis Effect Causes all moving objects in the Northern Hemisphere to be deflected to the right Global Wind Patterns Control: 1. Tropical Storm Tracks 1. 2. Easterly movement of Northeasters 2. 3. Migration of major sand dunes 3. 4. Prevailing wind direction R e c o r d e r s o f p a le o - w in d d ir e c tio n s Hurricane Tracks Note that storms curve in opposite directions on either side of the equator 1851-2004 North Atlantic P r o v in c e la n d s o f C a p e C o d P a r a b o lic D u n e s Parabolic Dune Field Northwest winds Dunes migrate southeast… Why? Movement of Weather System including Northeast storms Our weather approaches from the west Storm Dynamics Storm Tropical Storms- Hurricanes Extratropical- Northeasters Cyclonic weather patterns Counter clockwise circulation Isobars are lines of equal pressure Isobar spacing determines wind velocity (gradient) Easterlies Southerlies Westerlies Hurricanes Hurricanes Tropical Cyclone: Hurricane in Atlantic Typhoon in Western Pacific Typhoon Cyclone in Indian Ocean Cyclone Baguio in China Baguio Willy-Willy in Australia Tropical Cyclones have different names Depending where the storms Where is this tropical cyclone? Hurricane Formation Hurricane Late Summer through Mid-Fall (officially 1st June - 1st Nov Generated off the West Coast of Africa in Tropics Tropics: above Tropic of Cancer H u r r ic a n e I n t e n s it y S c a le Saffir Simpson Scale Saffir Number (category) 1 2 3 4 5 Wind Velocity(mph) 74-95 96-110 111-130 131-155 > 155 Amount sea level rises above normal Surge (ft) 4-5 6-8 9-12 13-18 > 18 Examples Name Katrina Hugo Camillle Year 2005 1989 1969 Category 3 4 5 Landfall LA-MS SC MS-AL Cost (Billion$) 125 7 5 Hurricane Hugo Storm Surge Storm Hurricanes kill due to the Storm Surge Definition: super-elevation of the water surface Caused by: 1 . W in d S tr e ss 2 . A n ti-b a r o m e te r e ffe c t For every inch of mercury the barometric pressure drops, the storm surge rises 13 inches H u r r ic a n e L a n d fa ll Here comes a Category #5 Hurricane!! How to save your family? Which way East or West? How Mainland Stayin' alive! winds blow offshore Death Winds blow onshore Hurricane Landfall: remember counter-clockwise circulation T h u s , th e s u r g e p ile s u p a n d is d r iv e n o n s h o r e e a s t o f th e la n d f a ll s ite C o n v e r s e ly , w e s t o f th e la n d f a ll w in d s a r e b lo w in g o f f s h o r e d im in is h in g th e s u r g e E x tr a tr o p ic a l S to r m s Name based on direction from which the wind blows In New England -> Northeaster most common Storm forms above the tropics Generation Sites: US E x tr a tr o p ic a l S to r m T r a c k s Weather Map illustrating: 1. Movement of storm from Gulf of Mexico northward 2. Isobars (lines of equal pressure) 3. Wind patterns approximately parallel to contour Legend for Weather Map 6 F eb 1978 Blizzard of 1978 • • • • Storm of Record 1.2 m storm surge 28 inches of snow Eastern New England state of emergency for seven days (no driving) • Boston University closed for a week 7 F eb 1978 Note the following: • Northward storm track • Tightly spaced isobars • Northeast wind in NE 8 Feb 1978 Blizzard of 1978 • Third Day • Persistent strong winds from the NE • Still tight isobars Hurricane Bob (August 19, 1991) 1 0 0 m p h w in d s P e a k g u s ts in C a p e C o d 1 2 5 m p h 1 2 to 1 5 f t s to r m s u r g e 29 Oct 1991 Perfect Storm T1- Extratropical storm combines with Hurricane Grace, note beginning of cyclogenesis T2- Counterclockwise circulation well developed T3 - System eventually reaches Category status 1 Nov 1991 30 Oct 1991 Perfect Storm (Halloween Eve Storm) • F o r m a tio n a n d S tr e n g th o f t h e s to r m d u e to c o m b in a tio n o f a n e x tr a tr o p ic a l s to r m a n d H u r r ic a n e G r a c e . • T h a t u n io n p r o v id e d a d e e p lo w pressure system 972 millibars. • A ls o , im p o r ta n t w a s th e s tr o n g h ig h p r e s s u r e s y s te m in C anada. • S to r m p r o d u c e d 4 0 f o o t s e a s . M o n d a y 2 M a r ch 2 0 0 9 T y p e s o f E x t r a t r o p ic a l S t o r m s Controlled by wind direction: Northeaster (winds from the NE) Southwester (SW) Southeaster (SE) N or th e as te r s L o w -p re ssu re sy ste m s th a t p a ss e a st o f C a p e C o d E x a c t w in d d ir e c tio n is d e te r m in e d b y th e s to r m tr a c k Northeasters occur during late fall, winter & early spring (15 - 20/yr) A ffe c ts e a ste r ly fa c in g sh o r e lin e : North Shore of Boston, South Shore, Outer Cape Cod Southwesters Southwesters L o w p r e ssu r e sy ste m s m o v in g u p th e H u d so n V a lle y o r a c r o ss C o n n e c tic u t S o u th w e ste r s m u c h le ss c o m m o n t h a n N o r th e a ste r s Southwesters affect southerly facing coasts including:southern coast of Martha’s Vineyard Nantucket, Cape Cod coast along Nantucket Sound Hudson Valley CT E x t r a - T r o p ic a l v e r s u s T r o p ic a l S t o r m s Storm Type Tropical Cyclone Common Name Hurricane Cyclone Typhoon NE’er SW’er SE’er Pressure LP Generation Site Tropics Max. Winds 100150mph Storm Surge 8-15’ States Impacted Gulf Coast Extra Tropical Cyclone LP SW SE Midwest 3040 mph 1/2-4’ Eastern Seaboard Factors affecting storm impact: Factors 1. Magnitude -> size, duration, wind velocity 2. Speed of storm -> slow vs. fast, duration 2. 3. Track of storm -> impact areas, wind direction 4. Hide Tide versus Low Tide -> what part of beach affected 5. Neap Tide versus Spring Tide -> height of storm surge 6. Interval between storms -> Does beach have time to recover? Other Storm Considerations Other Hurricane wind velocities vary according to storm track Maximum wind velocities occur at right quadrant Lowest velocities coincide with left side of hurricanes Fast moving storms have the greatest difference in wind speed between the right versus left quadrant S t o r m E ffe c t s o n C oas ts • Beach erosion • Scarping of fore dune ridge • Waves overtop barrier producing Washovers • Barrier are breached creating Tidal Inlets • Increased longshore sediment transport rates (Mary Ann Gerlach) • Coastal flooding • Marshes receive sediment Hazy-Hot Hazy-Hot Humid Days Humid of Summer Bermuda High High pressure system (HP) High Pressure system have clockwise circulation Hot moist air from Gulf of Mexico is delivered to New England Develops in mid-summer HP over Bermuda ...
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This note was uploaded on 04/14/2011 for the course GEO 142 taught by Professor Fitzgereld during the Spring '11 term at BU.

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