Tropical Revolving Storms

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A tropical storm

-An intense low pressure weather system that develops in the tropics

-Brings heavy rain

-300 miles in diameter

-Winds of over 74mph

-Center is known as the eye (15 miles)

-Can create a storm surge

Direction of storm in northern hemisphere

Anticlockwise

Direction of storm in southern hemisphere

Clockwise

Morphology of a tropical storm

-Central eye (when system reaches maturity)

-Eye wall with large grey cumulonimbus clouds (associated with thunderstorms)

The eye of a tropical storm

-Central part

-15 miles in diameter

-Light winds

-Clear sky

The eye wall of a tropical storm

-Surrounds the eye

-Strongest winds (up to 186mph)

-Largest cumulonimbus clouds with heaviest precipitation (high as 2500mm/day)

Cumulonimbus clouds

-Dense clouds producing heavy rainfall and thunderstorms

-They are grey due to the dense water droplets in the sun’s shadow

How a tropical storm forms

-Start with an area of low pressure, caused by surface heating where warm air is drawn in a spiraling manner

-Enlarges into a tropical depression with rotating wind systems

-Continues to grow into a much more intense and rapidly rotating system (tropical revolving storm)

Conditions needed for formation of a tropical revolving storm

-Oceanic location with sea temps over 27 degrees

-Ocean depth of at least 70m with supply of latent heat

-Location of 5 - 30 degrees north or south of the equator

-Low level convergence of air in the lower atmospheric circulation system

-Rapid outflow of air in the upper atmospheric circulation system

Why is an oceanic location with sea temps over 27 degrees needed for formation

-Provides a continuous source of heat to encourage high rates of evaporation

-Maintains rising air currents and moisture for the development of cumulonimbus clouds

Why is an ocean depth of at least 70m with supply of latent heat needed for formation

-Water vapour is needed for condensation to create the cumulonimbus clouds

-High amounts of condensation releases a large amount of latent heat, meaning the air cools at a slow rate, which helps to continue to drive the system

Why is a location of at least 5 degrees north or south of the equator needed for formation

-The tropics location receives high levels of insolation, meaning ocean temperatures can reach 27 degrees

-These latitudes mean the coriolis force can bring about the maximum rotation of air, causing the whole storm to spiral around a central calm point (the eye has high pressure)

What lines of latitude can tropical revolving storms occur at

5-30 degrees north and south

Why is a low level convergence of air in the lower atmospheric circulation system needed for formation

Wind needs to be coming together near the center of the low pressure to drive the uplift of air

Why is a rapid outflow of air in the upper atmospheric circulation system needed for formation

-Helps push away the warm air which has risen close to the center of the storm (it drags water vapour outwards)

-The cloud cover then extends for a long distance, either side of the eye

Why does a tropical revolving storm end

-Friction with the land slows it down

-As it reaches land, there is less latent heat to drive the uplift of air, since it’s not on the ocean anymore, so the magnitude is smaller

-If the storm heads polewards, ocean temperatures cool so there’s less evaporation and formation of cumulonimbus clouds

Forms of storm hazard

-High winds

-Storm surges

-Coastal flooding

-River flooding

-Landslides

High winds as a form of storm hazard

-Exceed 150km/hr and up to 300km/hr

-Can cause structural damage and collapse of buildings, bridges and road infrastructure

-Can uproot trees, bring down electricity transmission lines and ruin agricultural land

-Able to pick up large amounts of debris and fling it, a serious threat to people’s lives

Storm surges as a form of storm hazard

-A large rise in sea level/tide caused by strong winds pushing warm water towards the coast and the low pressure of the storm

-Can cause significant coastal flooding and large amounts of damage to property, especially areas close to sea level

-Cause the majority of deaths

-Agricultural areas take a very long time to recover from this (the soil becomes contaminated with salt)

Coastal flooding as a form of storm hazard

-Storm surges can cause significant coastal flooding

-High relief at coastal areas can lead to rainfall exceeding 700mm in a single day

-High rainfall in combination with storm surge exacerbates the flooding

River flooding as a form of storm hazard

-Heavy rainfall leads to rapid increase of river discharge and higher risk of flooding

-Heavy rain can persist as storm moves inland and cause more extensive damage inland

Landslides as a form of storm hazard

-Heavy rainfall infiltrates soil and rock, making it less stable

-Risk of landslides and mudslides increase massively

What force does not happen at the equator

Coriolis

Tropical revolving storms in East Asia/Western Pacific ocean

Typhoons

Tropical revolving storms in central America and Gulf of Mexico/Carribean sea

Hurricanes

Tropical revolving storms in India/Bay of Bengal

Cyclones

Saffir Simpson scale

-Classifies tropical revolving storms

-5 levels based on wind speed, pressure, storm surge and damage potential

-5 is the strongest with catastrophic damage

Spatial distribution of storm hazards

-Form in the tropics between 5 and 30 degrees north and south the equator

Magnitude of storm hazards

-On the Saffir Simpson scale, 5 is the strongest with wind speeds of 155mph and storm surges over 18 feet

-Higher frequency of lower magnitude storms, but number of higher magnitude storms is increasing

Frequency of storm hazards

-Tropical storms are quite frequent (100 occur each year)

-8% of these turn into tropical revolving storms (however some never reach land so never develop into a major hazard)

-More frequent in the Northern hemisphere between June and October

-More frequent in the Southern hemisphere between November and April

When are TRS usually in the Northern hemisphere

June to October

When are TRS usually in the Southern hemisphere

November to April

Difference between tropical storms and tropical revolving storms

-Tropical storms have wind speeds less than 74mph

-Tropical revolving storms have wind speeds more than 74 mph

Regularity of storm hazards

-Hazards are irregular because there are lots of factors affecting where and when a storm will form

-No clear spatial or temporal pattern

Predictability of storm hazards

-Certain cloud formation in tropical areas can be identified by satellite imagery and used to tell when a tropical storm is forming

-Storm can be tracked and modeled, helping scientists work out when/where it’s likely to hit land (they predict the probable track using a 5 day track forecast cone)

-Not possible to predict the number or intensity of storms (they can only say there is a 5% chance of a major hurricane hitting the coast from April to November)

Primary impacts of storm hazards

Physical: high winds, storm surges, flooding, landslides

Human: death, injury, infrastructure damage, loss of crops

Secondary impacts of storm hazards

Human: homelessness, increased food prices

Social effects of seismic hazards

-People can drown and die by debris that’s blown around or carried in flood water

-Houses are destroyed, so people are homeless

-Electricity cables are damaged, so supplies are cut off

-Flooding = sewage overflows = contaminated water = spread of disease

-Agricultural land damaged so possible food shortages

Environmental effects of seismic hazards

-Erosion of beaches and damage to coastal habitats

-Sediment deposited in aquatic ecosystems = damaged fish breeding grounds

-Salt water pollutes environments

-Landslides can block watercourses, so they change course

Economic effects of seismic hazards

-Building and infrastructure cost huge amount to rebuild

-Businesses damaged/destroyed = no trade

-Agricultural land damaged = less commercial farming = less income

Political effects of seismic hazards

-People may blame the authorities for food, water and energy shortages = conflict and political unrest

-Expensive repairs limit amount of money spent on development, possibly hindering it

Physical factors effecting level of impact of storms

-Wind speed

-Location it reaches

-If storm surge occurs

-Original tide level (effects height of storm surge)

-Distance it forms from sea

-Speed of movement

-Magnitude

Human factors effecting level of impact of storms

-Level of development

-Infrastructure

-Preparation

-Predictions

-Coastal population density

-Human response

Mitigation of storm risks

-Hazard resistant design (protection against storm surge and wind, sea walls and levees can be built)

-Building design (raise buildings on stilts using concrete/brick)

-Land use planning (past storm data can be used to identify areas at high risk, and limit development in these areas to those more compatible with flooding such as beaches and parks)

Adaption to storm risks

-Community preparedness (public must be aware of specific actions to carry out for warnings to be effective)

-Prediction and warning systems (scientists monitor storm development and forecast their intensity and track so the population can prepare themselves by evacuating)

-Storm drills practiced (so the public are more prepared for when the storm occurs)

-Education and awareness programmes

-Insurance (especially in HICs)

-Emergency aid (food and water is essential to survivors)

Park model for tropical revolving storms

-Stage 1: hurricane drills, build emergency shelters, prepare evacuation plans, educate public, monitor atmospheric conditions, build sea walls and houses on stilts

-Stage 2: continue to monitor, issue alerts and warnings, evacuate people

-Stage 3: search and rescue survivors, treat injured

-Stage 4: emergency aid provided, temporary infrastructure built

-Stage 5: rebuild permanent infrastructure, enhance planning and preparedness for next time

Hazard management cycle for tropical revolving storms

-Prevention/mitigation: land use planning, build houses on stilts and sea walls for storm surge

-Preparation: educate people, take out insurance, hurricane drills and kits made, create emergency plan, monitor atmospheric conditions and track

-Response: order evacuations, give emergency aid, shelter built, treat injured, search and rescue for survivors

-Recovery: infrastructure rebuilt, long term aid given