4.3 Atmospheric Disturbances

Question 1

What are tropical storms?

Answer 1

• Hurricanes in Atlantic, Typhoons in NW Pacific, Tropical cyclones in Indian Ocean and South Pacific.
• Bring intense rainfall, high winds, storm surges, coastal flooding, inland flooding and mudslides
• Relate to enormous amounts of water due to origin over tropical seas, causing high intensity rainfall and flooding.

-Paths often erratic and so hard to give notice or predict pathing for proper evacuation

Question 2

What conditions are needed for tropical storms to form?

Answer 2

Position: far from equator so coriolis force creates rotation - between 5 and 20 degrees

• Seas/season - ocean over 27 degrees, 60-100m deep as warm water gives off large quantities of heat when condensed through latent heat, releasing heat. Driven by seasons due to temperature differences and continentality
• Fronts and latent heat - atmospheric disturbances occur at fronts when warm and cold air masses meet, creating undercutting of cooler mass making uplift - condensation and latent heat drives further uplift - pressure lower than 900mb
• No wind shear - lack of wind shear at different heights needed or else they tear up and rotate rising air patterns - friction slows down the winds and so storms would not form.

Question 3

What are the general movements of tropical storms?

Answer 3

In NH track westwards due to westward flowing air streams from convergence of north and southeast trade winds

Steer polewards before dying out, usually hitting air masses due to lack of warm water driving uplift.

Question 4

How do tropical storms develop?

Answer 4

• Start as intense low pressure systems over tropical oceans which spiral around calm eye - diameter as much as 800km
• Pressure falls as low as 800mb so strong contrast with eye leads to strong winds.
• Often move excess heat from low latitude to high latitude - develop in westward flowing air in NH.
• Begin as small scale depressions - a localise area of low pressure causing warm air to rise, thunderstorms which may develop into tropical storms
• 10% disturbances become storms
• Warm water causes massive evaporation from sea surface - air rises, cools, condenses, latent release - thunderclouds
• Heat from below drives more vertical growth and intense low pressure
• To be classified as storm, wind speeds exceed 119km/h
• All tropical storms begin with coalesing of several storms on eastern side of oceans
• Major cell of low pressure develops and as winds are drawn in, system spins anticlockwise and westwards around central eye
• in the eye cold air descneds in an area of calm

Question 5

What is the global distribution of tropical storms?

Answer 5

5-20 degrees north and south of the equator

• Not on equator due to lack of Coriolis force
• Oceans exceed 27 degrees
• Depth of roughly 100m
• Do not develop off Africa and S America due to cold offshore currents
• Original disturbance occurs at a front where warm and cool air masses meet causing the cooler mass to uplift, creating condensation and latent heat driving further uplift
• Most storms form in region in NW Pacific known as typhoon alley, where most powerful cyclones develop. West of Japan and Korea experience during El Nino.

Question 6

What is the general pathing of a typhoon?

Answer 6

Straight westward path, parabolic recurving track around East Asia or northward track

Question 7

What are the 6 stages of the formation of a typhoon?

Answer 7

1. Ocean water above 27 degrees needed 60-100m deep so storms can stir up the ocean and bring cold water from below.
2. Hot, moist air rises from the ocean creates low pressure at the surface and more warm, moist air moves in over the ocean to replace the air that has risen
3. Winds need to be converging together near the surface, causing further uplift and unstable air rising.
4. The rising air spirals and rises rapidly. It needs to be humid as it is pulled into the storm, as the excess water vapour supplies latent heat
5. Thick cumulonimbus clouds and heavy rain is produced. There must also be pre-existing winds coming from same direction at all altitudes to avoid ripping the storm apart.
6. At the highest levels, there is a high pressure area which helps pump air away rising in the storm. This air cools at high levels and sinks in the centre, forming the eye of the storm.

Question 8

What are the different pressures in the tropical storm?

Answer 8

-At the approach high pressures of 1012mb, clouds and showers

As you get closer increasing winds, thunderstorms and pressures of 1006mb. In the eye it is calm with pressures of 960mb

Question 9

What is the Saffir Simpson scale?

Answer 9

1. Very dangerous 119-153km/h - damage to roofs, gutters, trees, power lines and poles
2. Extremely dangerous 154-177km/h - well constructed homes sustain major damage, shallow rooted trees snapped or uprooted and block roads, power loss outages
3. Devastating 178-208km/h - well built framed homes major damage, trees snapped, blocked roads, electricity and water unavailable for weeks
4. Catastrophic 209-251km/h - well built homes, loss os fstructure, trees uprooted, power poles, communication loss, area unhabitatble
5. Catastrophic 252+ - most of framed homes destroyed, roofs destroyed, walls collapse, power outages, fallen power poles and trees

Question 10

What factors affect the impact of tropical storms?

Answer 10

• Unpredictable paths so hard to effectively manage threat
• Strongest storsm do not cause the most damage and depends on other factors such as distribution of population, human response (planning laws, relife operations, flood aid an water)
• LICs lose more lives due to inadequate planning and preparation

Question 11

What are the hazards of tropical storms?

Answer 11

High winds over 119km/h and gusts over 200km/h destroys homes, flatten crops and trees, damage power and telephone lines, rescue problematic due to debris, devastate businesses, markets and economies

Question 12

What are storm surges?

Answer 12

Abnormal increase in ocean level, oven several metres high and miles wide. Come ashore five hours before the storm, causing severe flooding and damage in low lying coastal areas. Low pressure produces temporary rise in sea level - a fall in 1mb of pressure rises the sea by 1cm.

• This is coupled with large onshore waves associated with fast winds which pile against the coast, generating surface current and waves.
• Little coastal defences or natural ones such as dunes, mangroves and levees can cause severe damages
• Strong winds drive the surge, rises in shallow water and pushes inland causing flooding - the highest part of the surge is where the strongest winds are - the lower the pressure the higher the surge.

Question 13

What is the effect of storm surges?

Answer 13

• Depends on the coast - wide, shallow coasts experience large surges due to shoaling. Bays funnel storm surges, adding to the height
• Surges also be damaging when they coincide with high or spring tides.
• Strong onshore winds, approaching the coast at right angles, the sea floor is gently sloping, few obstructions to slow the water
• Intense rainfall from the clouds can also cause severe river flooding and mass movements due to the saturation of slopes causing unstable slopes and collapse mass movements.

Question 14

What are tornados?

Answer 14

Small, short lived but destructive storms
Hard to measure and observe - elongated funnels of clouds which descend from the base of a well developed cumulonimbus cloud, eventually contacting the ground beneath. For a vortex to be classified as a tornado it must be in contact with the ground and the cloud base.

80% of tornados occur at tornado alley in the US as warm air from the Gulf of Mexico meets cold air in the rockies

Question 15

What is necessary for a tornado to form?

Answer 15

• Moisture
• Instability
• Lift and wind shear
• Most rotate cyclonically
• Warm humid air meets cold air along a front
• Convectional rainfall occurs due to heating from sun and updrafts

Question 16

How do tornados form?

Answer 16

1. Front becomes steepened due to large temperature difference, creating instability and turbulence and a series of fronts between them where cold air meets warm air. The warm air rises, and cold air undercuts it.
2. Creates strong updrafts by front and convection, forms clouds as moisture condenses, creating towering cumulonimbus clouds from cooling and condensing latent heat warms further and strengthening the updrafts.
   - This creates a supercell storm as there is intense low pressure from rapidly rising air. Air is drawn from the sides due to increasing pressure gradient. They form in warm moist air above 18 degrees.
3. Different levels of wind shear - stronger at higher heights due to less friction, causing the top of the cloud to be ‘pushed over’ and spin around as a horizontal vortex.
4. Physical drag of the cold rear flank and precipitation drags the last part of the tornado to the ground. When it touches the ground it is a tornado. As it lowers, it pulls warm moist air from around it and humid air from the base as there is low pressure inside the core.
5. The moist air causes it to grow in intensity and the air expands and cools, causing heat release and a rotational wall cloud. The updraft grows in intensity, creating low pressure at the surface and pulling the mesocyclone down as a funnel cloud. The cold sinking air wraps around the vortex and since its cold it is sinking, has hail and precipitation and so is pulled down at the rear, hence called the rear flank downdraft. At this point to mesocyclone is fully vertical. When the vertical funnel is widest, the tornado is most mature
6. The rear flank vortex is pulled down to the ground. The cloud wall is fully flat. Cold air from the downdraft spreads at the ground surface and cuts off the supply of moist warm air refuelling the tornado, weakening the funnel which becomes wavy and rope like before disappearing.

Question 17

What are the hazards of tornados?

Answer 17

• Intense precipitation, rainfall and hail, infrastructural damage, broke glass, localised flooding, damage to roofs, wildlife and livestock killed, hail
• Winds: debris, objects fly around, roofs ripped off, buildings damaged and collapsed, infrastructure destroyed, environmental destruction
• Pressure imbalances - windows break, damage to does as they explode - tornados centres of low pressure so external pressure around buildings reduced rapidly but internal does not change so windows, walls and roofs explode due to pressure differences.

Question 18

What are the differences between tropical storms and tornados?

Answer 18

Often smaller scale, harder to predict - higher proportion in HICs - stronger but more damaging at local scale. Mainly in US - 1000 year, killing 60 a year mainly from debris.

• Intense precipitation, high wind sped, gust, pressure imbalance.
• Strong winds remove objects, rotational movements twist objects from fixings
• Low atmospheric pressure causes imbalances
• Most damage due to multiple vortex tornados or intense single vortex tornados

Tropical storms tend to do much more damage over bigger areas, long flooding periods, high winds, collapsing buildings and infrastructure, larger scale - tend to hit LICs more. However they are lower frequency and intensity at a local scale and can be predicted better

Question 19

How does hail form?

Answer 19

Condensation occurs when the dew point is reached turning into water vapour. Strong updrafts lead to droplets moving up in the cloud to the freezing point, causing water to hit the frozen condensation and freeze. The hail falls as the updraft cannot hold the ice and it partially melts, making it less heavy and so can be pushed back up.

• Collision may also lead to connecting hailstones
• Process repeats 10-20 times, creating larger hailstones as it repeats
• When the weight exceeds the updraft the hailstone falls.

Question 20

How are tornados classified?

Answer 20

Enhaned Fujita scale categorises it in F0-F5 categories using description and 28 damage indicators.

EF0 - minor damage 65-68mph - light damage to chimneys trees

EF1 - moderate damage 86-110 - roofs and mobile homes

EF2 - considerable 111-135mph - roofs and mobile homes, large trees, objects lifted

EF3 - severe damage 136-165mph - roofs and walls, trains, cars

EF4 - devastating 166-200mph - well constructed housings, foundations uprooted, large obstacles in air

EF5 - incredible -200+mph - strong houses, reinforced structures damaged, cars flung, trees rooted

Question 21

How are hurricanesm onitored?

Answer 21

• National Hurricane Centre and Nasa use satellites, computer modelling, instruments, aircraft, field missions to contribute and gain information to predict paths.
• NASA have 8 satellites and spacecraft with this purpose
• Analyse rainfall, wind speed, cloud height, ocean heat, temperature and humidity
• Identify where storms are potentially going to form and how strong there will be
• Computer modelling uses models and instruments to give closer look at models of the storm. Airborne missions also use radiometers reading moisture levels, as well as lidars which measure aerosols, moisture and winds
• Dropsonde measures temperature, pressure, moisture and winds

Question 22

What does the NHC do?

Answer 22

• Tracks intensity, size and structure of cyclones, storm surges, rainfall and tornados
• Satelittles, reconnaissance, ships, buoys, radar track and predict hurricanes using remote measurements of the intensity and estimates of the location of the eye, its motion and intensity.
• Once it becomes a threat to the land it is monitored by US Air Force and NOAA hurricane aircraft, dropsondes and land stations - data is transmitted to NHC forecasters and public.
• As the hurricane approaches the coast land based radars provide accurate precipitation and velocity data.
• After collected, the data is controlled and examined using models to predict track and intensity. The models are used as guidance for forecasts and warnings. Models are compared and used to ensemble best possible forecast, coordinated between national centres and offices to provide consistent weather forecasts.

Question 23

What do buoys, satelittes, flights and doppler radar do?

Answer 23

Buoys - 1250 in NA ocean measures winds, waves, pressure, temperatures, humidity and air temperatures which can determine the formation, extent of wind circulation and eye location

Satellites: detects formation with remote sensing, using microwave images produced every house. Remain stationary in orbit to measure the changes. Older sensors may lack quality and failed launches are expensive and set back research

Hurricane Hunter manned flights - large areas scanned in seconds with characteristics of the storm, sends out EM radiation and measured reflections, surface winds over oceans, radiation and dropsonde balloons deployed to gather profiles - can fly for 26 hours however 53 people have died

Doppler - scans entire storms in less than a minute, 3D image of storm made, beamed off precipitation in the cloud, reveals density of cloud - collected every 5 mins. Further you are from storm worse the view and beam spreads out. birds may interfere and images can only be created 400-500km of the territory.

Question 24

Who monitors and predicts tropical storms?

Answer 24

The WMO monitor cyclone programmes and individual bodies take over, such as the NHC run by the NOAA.

Monitoring, prediction and warning systems are composed of detecting and monitoring the hazard, analysing the risk posed and spreading the warnings at the right time through authorities and response plans?

Question 25

How are hurricanes predictable?

Answer 25

• Formed in tropics over 27 degrees due to energy from sea, releasing latent heat and fuels storm - can predict where
• Only occur in summer so hurricane seasons developed
• Also be tracked and courses predicted as follow curved paths westwards due to trade winds
• Computer tracking programmes forecast paths, satellite and radar systems maintain a careful watch on hurricane’s progress.
• Coastal communities at risk are informed about potential dangers and so know what to do - move to high ground and shelters or away from coast
• Technology forecasts and predict at risk areas and reduces potential death tolls

Question 26

How do people prepare for hurricanes?

Answer 26

• Fixing storm shutters
• Storm straps
• Building on stilts
• Risk assessment - evaluate risks on map to estimate probability of damage using records, history of wind speeds and frequencies
• Land use zoning put in place to control development in least vulnerable areas
• Floodplain management also developed to protect assets.
• New buildings wind and water resistant
• New design standards incorporated into building code
• Communication and utility lines away from coast
• Raised ground level
• Protect river embankments, levees and coastal dikes - managed and inspected
• Vegetation cover increased helps reduce soil erosion and landslides

Question 27

What is done to prepare before, during and after a storm?

Answer 27

Before: shelters, supplies, protect windows, insurance, arrangements for animals and evacuation, emergency communication

During: radio, supplies, car has fuel, bring in outdoor objects, secure buildings

AFter: assist in help, seek medical attention, clean debris, report damage, watch for secondary hazards

Question 28

How are tornados managed?

Answer 28

SPC issue forecastss and outlooks for organized thunderstorms over US based on observations and models. Monitor areas at risk for tornados based on mapping.
-Doppler radar used to send out EM pulses which reflect off precipitation in the cloud and tell which direction and map out the rain.

Question 29

What features indicate a storm?

Answer 29

Hook echoes - hook shaped weather features found in lower portions of a storm when air flows into a mesocyclone, forming a curved feature

Inflow bands - low cumulus clouds suggest air gathering

Beavers tail - flat cloud band

Wall clouds - lowering clouds attached to base of storm to rear of precipitation indicate tornado forming as they rotate

Rear flank downdraft - downdraft of air on back of storms descending to rear of wall cloud creating surface winds and hook echo

Rain free base - low level air drawn into updraft which is cooled, removing moisture as air quickly condenses and so the base of the cloud has little rain

Question 30

What are watches and warnings?

Answer 30

Watches - issued by NOAA SPC, meaning people stay in view of alerts

Warning issuedby NOAA Weather Service Forecast who watch weather 24/7 in an area - means tornado specifically reported by spotters or indicated there is serious threat.

Benefits - 85% of EF3 tornados predicted, warning time up to 15 minutes - 6 in 1994. Network of 148 DRs across the US giving wider coverage

Birds and dust may interfere with old systems, people must be on the ground to confirm , tornados may occur without usual observed patterns.

Question 31

How are tornados prepared for?

Answer 31

Warnings - watch/warning, drills and awareness days especially in tornado alley to avoid panic in schools and workplaces, advised to move to outer edges of buildings and get down

Personal - check warnings, sign up for notifications (FEMA warning app), communication plans, meeting places, safe buildings, emergency kit - practice plans

Mapping - extensive tracking and mapping in US identifies locations experiencing the greatest number and highest intensity storms. In Bangladesh there is mapping based on some radar but is poor and patchy. Using locations of past tornados cannot help as they occur literally anywhere

Question 32

How do buildings codes and proofing help prevent effects?

Answer 32

-Large facilities withstand speeds up to 250mph but homes do not need this in Tornado alley
US building regulations stand little chance against tornados - need concrete and steel reinforced doors, many houses wooden and not reinforced, need thicker windows
-Cost $5,000 but could save house but many do not pay
-Emergency shelters also built fitting 6 people for $3,000 and 12 or more for up to $30,000. There are 10,000 shelters in Oklahoma
-In Bangladesh there are shelters but there are few and for settlements and not individuals so often overcrowded.