Katrina worst natural disaster insurance industry has ever
Katrina worst natural disaster insurance industry has ever handled property/casualty insurance will pay out estimated $40.6 billion on some 1.7 million claims in six states over 1000 deaths What is a HURRICANE / TYPHOON / TROPICAL CYCLONE ? Mass of thunderstorms (collective diam. typically about 600 km) driven by energy available in very warm, moist tropical surface air and organised in cyclonically spiraling bands (pinwheel formation) around a low pressure centre
Sustained wind speed >= 120 kph and up to 350 kph; lifetime of days to a week or more Fig. 12-3 cirrus aloft may obscure the pinwheel formation (see CD animation in textbook) What is a HURRICANE / TYPHOON / TROPICAL CYCLONE ? Typical central pressure about 950 mb, extreme cases <900 mb, eg. Gilbert, 14 Sept.1988, atlantic storm of century, 888 mb
Wilma, 18 Oct. 2005, 882 mb Katrina, 902 mb Wind drag piles up water on a coast (storm surge) & the low central pressure also contributes to sealevel rise/swell, typically 1-2 m but up to 7 m Fig. 12-3
Where/under what conditions do they form ? Requires ocean surface layer temperature > 27oC (in layer tens of metres deep favouring the tropics and late summer/early fall). Vital role of Coriolis force (prevents filling of central Low) prohibits formation below about 5 o latitude, and formation is suppressed in regions of strong wind shear. energy supply? latent heat evaporated off ocean thus... peak season in late summer/early fall, when ocean temps highest Fig. 12-4
bands of heavy convection separated by areas of weaker uplift & precip Joseph Conrad: Typhoon (published 1904) Captain McWhirr: The wisdom of his country had pronounced by an Act of Parliament that before he could be considered fit to take charge of a ship he should be able to answer certain simple questions on the subject of circular storms and apparently he had answered them, since he was now in command of the Nan-Shan in the China seas during the season of typhoons. The Nan-shan was ploughing a vanishing furrow upon the circle of the sea that had the surface and the shimmer of an undulating piece of grey silk. Its the heat, said Jukes. It would make a saint swear.
Where/under what conditions do they form ? Fig. 12-2 Increasing ocean temp cold upwelling results in a stable atmos. I wonder where that beastly swell comes from, said Jukes aloud, recovering himself from a stagger.
Development... Small cluster of thunderstorms known as tropical disturbance forms in convergence zone of an easterly wave at low latitude Fig. 12-9 Tropical disturbance migrates slowly westward < 10% Tropical depression (at least one closed surface isobar)
Tropical storm (sustained winds > 60 kph) Hurricance (sustained winds > 120 kph) Sprawling over the table with arrested pen, he glanced out the door, and in that frame of his vision he saw all the stars flying upwards between the teak-wood jambs on a black sky. Ship rolling heavily in a high cross swell. Heat very oppressive, he stuck the end of the pen-holder in his teeth, pipe fashion, and mopped his face carefully. paths can be wildly erratic precursor disturbances move westward in trade winds tendency to move to (or develop towards) warmer water
often turn poleward dissipate when move over land or cooler water preferred path varies across Aug/Sep/Oct Fig. 12-12b A gale is a gale, Mr. Jukes, resumed the captain, and a fullpowered steamer has got to face it. Ive been reading the chapter on the storms there you would think an old woman had been writing this. It passes me. If that
thing means anything useful, then it means that I should at once alter the course away, and come booming down on Fu-chau from the northward at the tail of this dirty weather thats supposed to be knocking about in our way. From the north. Do you understand, Mr. Jukes? Three hundred extra miles to the distance, and a pretty coal bill to show Suppose I went swinging off my course and came in two days late and they asked me Where have you been all that time Captain? What could I say to that? Went round to dodge the bad weather, I would say. It mustve been damn bad, they would say. Dont know, I would have to say; Ive dodged clear of it. See that, Jukes?
A whistling could be heard now upon the deep vibrating noise outside its increase filled his ears while he was getting ready to go out and confront what it might mean. It was tumultuous and very loud - made up of the rush of the wind, the crashes of the sea A faint burst of lightning quivered all around, as if flashed into a cavern - into a black and secret cavern of the sea, with a floor of foaming crests. It unveiled, for a sinister, fluttering moment a ragged mass of clouds hanging low, the lurch of the long outlines of the ship, the black figures of men caught on the bridge, heads forward, as if petrified in the act of butting. The darkness palpitated down upon all this, and then the real thing came at last.
In the eyewall intense Cb up to 25 cm/hour rain rate It was something formidable and swift. It seemed to explode all round the ship with an overpowering concussion Jukes was driven away from his commander The rain poured on him, flowed, drove in sheets Structure/mechanism?
Intense cyclonic lowlevel winds result from the strong radial pressure gradient winds whip up the ocean surface, resulting in huge sea-air fluxes of vapour and sensible heat Fig. 12-4 adiabatic expansion as parcels spiral to centre,
so relatively weak temperature gradient at low levels but max at 10-20 km Structure/mechanism? ... warm central core aloft, from release of latent heat Fig. 12-5
air descending in the core warms adiabatically Structure/mechanism? hot towers embedded in the eyewall recently discovered Fig. 12-8 Our boats - I say boats - the boats, sir! Two gone! Nobody - not even Captain McWhirr, who alone
on deck had caught sight of a white line of foam coming on at such a height that he couldnt believe his eyes - nobody was to know the steepness of that sea and the awful depth of hollow the hurricane had scooped out behind the running wall of water Structure/mechanism? Warm core results in weaker dp/dz than environment thus central pressure aloft is a High result is diverging anticyclonic winds aloft. In the eye of the storm (diam 20-50 km) air is sinking less cloud. Wind is light. There was no wind, not a breath, except the
faint currents created by the lurches of the ship. The smoke tossed out of the funnel was settling down upon her deck. We have done it, sir, he gasped. On a bright, sunshiny day, with the breeze chasing her smoke far ahead, the Nan-Shan came into Fu-chau. Summary: Feedback:
Feedback warm, moist surface air, gaining latent heat and converging due to cross-isobar flow (friction of rough, wind-driven ocean) lift release latent heat aloft warming air aloft (warm core of air aloft) slow p/z so that upper region of hurricane has HIGH p relative to same level outside storm anticyclonic winds & divergence aloft reduce central surface pressure ( L ) increase surface winds increase surface QH + QE and increase surface convergence Hurricane Bonnie after it crossed the Atlantic, leaving a cooler trail of water in its wake. Hurricane Danielle, following behind, crossed Bonnie's path and was affected by the loss of ocean thermal energy available to fuel it. (National Science Digital Library)
Modelling the HURRICANE at high resolution need for data to initialize dynamical model; satellite, aircraft, powerful computers 1992-2001 average error in 24 hr forecast of hurricane landfall position was 150 km ARCTIC HURRICANE evolves from a Polar Low when the extremely cold (eg. -30oC) & dry continental air moves off the icepack onto open water (0oC). Then, huge sea-air heat &
moisture flux QH + QE vigorous cumulonimbus deepening Low travels parallel to ice edge spiral cloud bands, about cloud-free eye strong surface winds close to centre rough ocean surface Marine Icing Gallery Dr. E. Lozowski EAS, U. Alberta HURRICANE versus MID-LATITUDE STORM
Hurricane Mid-latitude storm Energy Source QH+QE off very warm ocean Grav. potl energy due to horiz temp gradient Low level Rotation
cyclonic cyclonic Vertical motion in core downdraft updraft Frontal structure no
yes Surface isobar pattern tightly- packed, circular contours weaker contour packing, not so symmetric Core warm
cold Strongest winds surface aloft Joseph Conrad was captain of this vessel, the barque Otago seen here moored at Port Chalmers (Dunedin, New Zealand). Photo from N.Z. Geographic No.78, 2006.
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