lecture 18: hurricanes and tornadoes

Question 1

tropical cyclones

Answer 1

most destructive of weather disasters, affecting huge areas (thousands of km2) with 3 types of hazard:

• high winds (up to 240km)
• storm surges (raising sea level up to 6m)
• heavy rains and subsequent flooding (landsliding)

Question 2

typhoon mangkut

Answer 2

2018- southern coast of china

120km/h winds

Question 3

hurricane michael

Answer 3

oct 2018, florida

Question 4

hurricane formation

Answer 4

tropical cyclones are storms with 1 minute sustained winds >120km/h, form between 5-20 degrees N/S

Question 5

subdivision of tropical cyclones geographically

Answer 5

hurricanes: south atlantic and mexico
typhoons: southeast asia
cyclones: southwest indian and australia

Question 6

why arent tropical cyclones formed

Answer 6

S atlantic: high winds
SE Pacific: insufficient water temperature
red sea/persian gulf: insufficient surface area
equator: insufficient coriolis effect

Question 7

hurricane formation

Answer 7

start by summer heating of tropical oceans with a) warm shallow water >27-50 degrees to enhance evaporation b) unstable air for thunderclouds to form c) weak vertical wind shear to stop storm from breaking up

Question 8

4 stages of hurricane formation

Answer 8

1. tropical disturbance low pressure draws in surrounding thunderstorms with weak winds
2. storms coalesce into tropical depression and winds strenghten (37-63km)
3. tropical storm has stronger winds that start to form cyclonic pattern, can now be named
4. tropical cyclone has winds >120km/h that cannot reach the core due to rotation, forms eye of storm

Question 9

path of hurricane

Answer 9

follows a curve due to coriolis effect (earths rotation)

- deflected to the right in northern hemisphere and left in southern hemisphere

Question 10

hurricane decline

Answer 10

winds decline when warm water energy source is cut off as they go over land or reach colder waters
- can interact with other weather systems in mid-latitude and gain strength again

Question 11

typhoon freda

Answer 11

Oct 1962, killed 46 people in US and 7 in canada

• came up west coast mass of water vapour blew up
• took 2 weeks to travel 8000km across the pacific

Question 12

3 steps of hurricane

Answer 12

1. air moves towards low pressure eye over warm sea, evaporating water
2. humid air spirals up the eyewall. Rising water vapor cools and condenses, forming clouds which releases latent heat of condensation intensifying the updrawft
3. cold air is sucked down the eye

Question 13

rotation of hurricanes in hemispheres

Answer 13

anticlockwise in northern

clockwise in southern

Question 14

eye and eyewall

Answer 14

eye: circular region of calm clear weather at hurricane centre
eyewall: surrounding cyclinder of upward spiralling winds that are the strongest in the entire hurricane

Question 15

hurricane energy

Answer 15

storm motion speed along its track is added or subtracted from storm wind speed to give the actual wind speed experienced on the ground
storm motion is 30km/h: storm winds 160km/h safe semicircle is 130, unsafe is 190km/h, might be 200km/h in eye

Question 16

what happens when eyewall passes overhead

Answer 16

intense winds as eyewall passes overhead followed by winds dying away as the eye itslef passes overhead
after eye passes, sudden intense eyewall winds in opposite direction

Question 17

how is storms energy calculated

Answer 17

terajoules (1TJ = 1,000,000,000,000J)

based on wind speed and size of wind field

Question 18

hurricane scale

Answer 18

strength measured on Saffir- simpson scale
C1: minimal, winds damage trees & mobile homes
C2: moderate, trees blown down and major damage to roofs and mobile homes
C3: extensive, large trees down, mobile homes destroyed and structural damage to small buildings
C4: extreme, all signs blown down, damage to windows, doors, roofs, coastal builidngs and flooding
C5: catastrophic: damage to windows, doors and roof, small buildings turned overhead and blown away

Question 19

north atlantic hurricane season

Answer 19

1 jun - 30 nov (peak in mid aug to late oct)

lifespan: 1-30 days
diameter: 200-1300km
eye: 16-70km

Question 20

north atlantic hurricanes

Answer 20

start at 10-20N, move westward by easterly trade winds than northwards by coriolis effect and eastwards at midlatitudes by westerly winds
- depending on size it will take different paths

Question 21

subtropical ridge or bermuda/azores high

Answer 21

high pressure zones that can furthur influence path of north atlantic hurricanes

Question 22

hurricane mitigation

Answer 22

land use planning: avoid population centres in low lying coastal lands
securing roof, eliminate eaves from roof, strap roof to walls in attic, no thin ashfalt roofs, building codes for mobile homes

Question 23

tornadoes

Answer 23

most intense of all atmospheric phenomenon with winds up to 500km/h
can damage buildings, blow off roofs, blow buildings off foundations and demolish buildings , can batter people and buildings up with projectiles

Question 24

tornado formation: single cell thunderstorm

Answer 24

warm moist air rises vertically in single updraft
moisture condenses from coolign air
falling rain causes cool downdraft surpassing updraft
limits thunder-storm intensity and reduces chances of tornado

Question 25

tornado formation: supercell thunderstorm

Answer 25

wind shear shifts updraft, tilting the thundercloud into anvil
seperates warm up and cool down
allows for more intense thunderstorms and higher chance of tornado forming
- responsible for tornado outbreak in may 2013 oklahoma

Question 26

where are the most tornadoes int he world

Answer 26

US with 1200 per year
- mostly in Texas and midwest (tornado alley)
canada is at the end of the alley and experiences 100 per year

Question 27

why do many tornadoes form at mid west

Answer 27

1. high altitude, high speed jet stream winds from west
2. mid altitude cool dry air from northwest
3. low altitude warm moist air from gulf of mexico to south
   - converging air masses cause atmospheric instabilities and intense rotation/thunderstorms

Question 28

tornado fujita scale

Answer 28

6 level ratin based on: wind speed,path length, path width, storm damage
F0: light, >half all tornados, short length/width
F1: moderate, 1/4 of tornados, damage to roofs sheds and garages, push cars of roads
F2: considerable, 1/6, roof and chimneys torn off, vehicles lifted off ground and large trees snapped
F3: severe, <5%, uproot forests, roofs blown off, metal building collapse, heavy vehicles lifted
F4: devastating, <1%, steel/concerete buildings lose walls, cars tossed 100m, bark stripped from trees
F5: incredible, rare, few seconds but incredible strength, carries vehicles and homes great distances