Climate: Tropical Region
Basic climate characteristics: Monsoon
Role of the Inter Tropical Convergence Zone: The ITCZ is an area of low pressure and marks the point of trade wind convergence.
Difference in heat capacity of land and ocean: The oceans warm up and cool down much more slowly than the land resulting in subtle ITCZ seasonal movement.
Summer:
Difference in heat capacity of land and ocean: The oceans warm up and cool down much more slowly than the land resulting in subtle ITCZ seasonal movement.
Summer:
- In June the ITCZ moves polewards towards the Tropic of Cancer.
- The ITCZ can reach 30 degrees N over India due to the intense heating of the land mass.
- This intense heating and the movement of the ITCZ create low pressure over Northern India.
- Meanwhile, the sea surrounding India heats up slowly, creating a zone of relatively high pressure off India’s Southern Coastline.
- Because winds blow from High to Low pressure air moves south westerly from the sea over to India. (The winds are defected by the Coriolis force.
- This low pressure draws in the warm unstable air from the Indian Ocean which is laden with water vapour.
- Rainfall totals are further increased by the uplift of this air over the foot hills of theHimalaya and by intense convection of the landmass.
- In January the ITCZ and the subtropical jet stream move southwards over the Equator and towards the Tropic of Capricorn.
- At the same time, the continental landmass at the centre of Asia around Mongolia and the Himalaya experiences intense cooling
- The intense cooling creates an area of high pressure in Northern India and the low pressure of the ITCZ is found to the south of India.
- The winds blow from the Northeast, away from the high pressure cell over northern India and this brings dry conditions to most of the Indian subcontinent as the winds travel over land.
Tropical revolving storms
Hurricane Katrina, Usa (August 2005)
- Embryonic storm developed over the Bahamas – 23rd August
- Monitored and given Tropical storm status (Named Katrina) – 24th August
- Moved westward and just before landing at Florida it became a hurricane – 25th August
- Once over land is lost ocean heat source but regained force from Gulf of Mexico – Category 3 upgraded to 5
- Warm waters of Loop Current (Offshoot of Gulf) reduced the pressure and increased wind speeds – 280km/hr (902mb) fourth most intense Atlantic storm 28th August
- Lost heat source and became a tropical depression – 30th August
Intensifying factors:
- Most densely populated areas of the Gulf coast
- Vast areas surrounding the Mississippi river was reclaimed floodplain which was below sea level – 6th Ward, 12 ft below sea level
- Inadequate Levees system channelled water into poorest areas of New Orleans
- Unnecessary evacuation for Hurricane Ivan left many sceptical
Impacts of the storm event:
- $80 billion in damage
- 1830 deaths as a result of hurricane and subsequent flooding
- Storm surge inundated 10-20km inside Mississippi
- 233,000km² area damaged
- 3 million people had no electricity
- 5,300km² of trees lost costing $5bn to forestry industry
- Economic impact in Mississippi and Louisiana estimated at $150bn
- Insurance premiums increased – now unaffordable
Responses to the hurricane (Management):
- No management to remove the floodwater (take 1 month)
- Mayor of New Orleans ordered an evacuation
- National response plan states response is down to local government until its resources are exhausted
- FEMA (Federal Emergency Management Agency) – Supplies and refrigerated trucks for the dead
- Volunteers helped evacuees and aided them for 6 months
- Coast Guard rescued 35,000 from New Orleans
- 58,000 National guard from 50 states
- September Congress supplied $62.3bn in aid and Secretary of Homeland security took over logistical control
- FEMA failed to provide targeted housing due to lack of trailers, funded 12,000 hotel stays and by July 2006 still 100,000 living in the trailers
- 70 countries pledged aid – Kuwait pledged $500m
- Raise ground above sea level and restore coastal wetland