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Wind Lecture3.doc

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Environmental Science
Tanzina Mohsin

Wind – Lecture 3: HURRICANES Terms for Tropical Cyclones: - Hurricane: North American term (Atlantic hurricanes, Eastern pacific hurricanes) o Taino language of Caribbean meaning “god of evil” - Typhoon: term used in Western Pacific o “Taifung” – Chinese word for “big wind” - Cyclone: term used in Australia and in the Indian Ocean (southeastAsian storms) - *** Define in terms of hurricane ORIGIN (hurricane, typhoon, cyclone) Definitions: - Tropical storm: storm (tropical region) with sustained wind of 18 to 33 ms^-1 - Hurricane: tropical storm with sustained winds ranging from 33 to 50 ms^-1 - Major Hurricane: tropical storm with sustained winds exceeding 50 ms^-1 - **defined by the wind speed** - Saffir-Simpson Scale: Herbert Saffir (consulting Engineer), Robert Simpson (Director of National Hurricane Centre (USA)) Tropical Storm Classification: - Saffir-Simpson Scale  1-5 rating scale o 1  119-153km/h (33-42.5m/s), > 980 mb o 5  greater than 249 km/h (>69m/s), < 920 mb  most crucial o Wind speed and pressure is used to differentiate the categories o The lower the pressure, the stronger the tropical storm!!! o **note down all 5 category classifications!** Dynamics: - How do hurricanes form?  intense low pressure-system o Tropical storms fueled by sea surface temperatures (source of latent heat) and latent heat release (**26.5degC threshold** is necessary but not sufficient)  Below 26.5deg. C, there is hardly any possibility of formation of hurricanes o What is latent heat?  heat that is released or absorbed due to change in phase o Convergence at the surface  another main thing you need for low pressure system to occur  Convergence at the surface, divergence aloft  Warm air expands, causing divergence aloft  Wind generated waves, increasing spray, increasing evaporation and latent heat formation  fuel for the storm - Tropical Storm Development – Atlantic Basin: o Begins as a tropical wave (originates in EastAfrica) in the Intertropical convergence zone (ITCZ) o June through November o Latitudes 5-20deg North o Group of thunderstorms that become organized and self-sustaining and if the conditions are favourable, they can turn into hurricanes - Requirements for the formation of tropical cyclone: o Threshold of 26.5deg. C o Convergence at the surface o Divergence aloft o Rising air released latent heat, warms upper atmosphere, causes air to diverge o Eye forms in the middle where air is sinking  only storm that has this is hurricanes! - What affects the length and strength of a tropical cyclone? o SSTs  the warmer the surface, the stronger and longer the storms are  If the SSTs is not favourable to hurricanes, then that will affect the length and strength of the storm  When 26.5deg. C, hurricanes are average, normal – but is this SSTs sustains over the next several weeks, the hurricane gets the chance to get stronger and longer  stronger hurricane  increase in category o Upper wind structure  strong upper level winds inhibit tropical cyclone longevity  QBO – quasi-biennial oscillation of the winds in the stratosphere • If at westerly phase  stronger • Easterly face  weaker  El-Nino – affects winds in Eastern Pacific (EP) andAtlantic (ATL) hurricanes (Enhances EP, suppressesATL) • Kind of the opposite of QBO o i.e., Toronto, El Nino year  we will see much less hurricane  Toronto, non- El Nino year  much more hurricanes occurring  Landfall  cuts off cyclone from both sources of energy (SSTs and water vapour), increases surface roughness (friction)  Examples: Atlantic Hurricanes and ENSO: • 1997  El Nino year  hardly any hurricanes • 1998  Non-El Nino year  almost double the hurricanes o Sea surface temperatures has opposite phases for el nino and non el nino years  The mixing of the east and west ocean water – during el nino year, most of the eastern oceanic water where you have up or down oiling of deep ocean water, the east and west water mixes so east ocean water is warmer, so when it mixes with west water, and therefore, the west water is hotter than usual  During non-elnino year, the water does not mix, therefore, we feel cold Tropical Storm Distribution: - Why do tropical storms not occur in the SouthAtlantic and the southern Eastern pacific? o Where is the hurricane originating and what is the threshold, where is it 26.5deg. C threshold?  Note temperature distribution of the world ocean  all regions of hurricane development exceed 26.5deg C o ***However in 2004…there was an exception:  CYCLONE Katrina: March 26-27, 2004 • First hurricane-strength storm observed in the SouthAtlantic (category 2) (somewhere you never see storms – SouthAtlantic) • Why now?  combination of SSTs and atmospheric flow o o Canadian Hurricanes:  Eastern provinces occasionally are hit by tropical storms – as far west as the Great Lakes  Not an issue in the Western provinces  Canadian Hurricane Centre in Halifax  Eastern provinces  starts in mid-June and ends in October • In terms of the time frame (1900-2000), avg. number of hurricane activity is increasing o What is happening that is different in the recent year(s) that is causing the hurricanes to be more frequent and stronger?   Hurricane Damage in Canada: emergency preparedness Canada • 8 costliest natural disaster in Canada • 19 from 1990 to 1999 • 136 fatalities, 1868 evacuated • 1.15 billion dollars of damage o 2010  hurricane hit Newfoundland  hurricane IGOR Forecasting Hurricanes: - (William) Gray Index – forecasting Atlantic Basic Hurricanes o The only reliable forecast measure in NorthAmerica o Statistical Methods employed o Factors Affecting Hurricanes:  ENSO (El Nino Southern Oscillation)  QBO (quasi-biennial Oscillation)  SSTs (sea surface temperatures)  Sahel rainfall (related to larger scale air flow which affect hurricane development) o Gray forecasted in 2004  there will be 15 named storm (observed 14), Cyclones 9  observed 8  2005: 15 (27), 8(15) • 2005 – poorest forecast on record forAtlantic tropical storms • First time number of storms exceeded available names (Alpha to Zeta used) • Year when New Orleans was swept off by Hurricane Katrina  2006: 11(9), 6(5)  2007 Summary: 14 (17) • Hurricane Dean (5) hit Mexico • Hurricane Felix (5) hit Nicaragua and Honduras • Hurricane Humberto (1) hit Texas • **notice how the intensity (category 4,5) of hurricanes have been increasing by the year (mainly after year 2000)**  2008 Hurricanes: • 9 named hurricanes • 5 of them are category 5 hurricanes • Bertha (5) hit Bermuda and is the longest-lived JulyAtlantic tropical cyclone that died after 17 days • Hurricane Dolly (5) made landfall two times at Texas and also near Cancun • Hurricane Gustav (5) made landfall at Haiti • Hurricane Hanna (5) hit South Carolina and Haiti • Hurricane Ike – third deadliest, affected part of Eastern Canada o Comparisons of the hurricane seasons of 2005 and 2009:  2005 had the busiest season on record  Alot of activity in 2005, not so much in 2009 o 2009 Hurricanes: El Nino Year  Forecasters expected 12 tropical storms  Six of these were expected to become hurricanes  Two of which are expected to be major hurricanes  Where are all the storms/hurricanes??? • El-Nino  #1 cause (b/c it affected SSTs) – the pacific warm-water pattern that tends to limit the formation of tropical storms and hurricanes in the Atlantic • Wind shear  marked by criss-crossing winds at different layers of the atmosphere, can kneecap the rotation of brewing storms • Dry air high in the atmosphere that sinks down and tends to sap the thunderstorms which fuel the hurricane dynamo  *Only exception was Hurricane Bill* • Global temperature  temperature increased more than 26.5deg. C
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