Monsoon Climate Flashcards
What is a major influence in tropical climates?
Convergence zone itcz and role of associated subtropical anticyclones (the band of high pressure from Hadley cells)
What is the inter tropical convergence zone?
Occurs along a line where northeast trade winds blowing away from subtropical high pressure cell in northern hemisphere meets south east trade winds blowing in similar fashion from sub tropical high in Southern Hemisphere.
Two Hadley cells meet
Maximum heating
What happens at the Itcz ?
Intense heating in low lattitudes due to sun being directly overhead, causes air to rise.
Where is there an increase frequency of storms?
On western side of the ocean.
What happens in northern summer? (About the itcz)
Zone of maximum hearing moves north and as a result so does Hadley cells towards North Pole as does sub tropical high belt.
This move northward of itcz from equator is further than might be expected in summer months, in particular over great continental land mass of Asia- the land is heated intensely.
Itcz is associated with an area of precipitation as a result of its low pressure pressure and therefore precipitation moves north and south of equator through out year following the sun.
What is the word monsoon derived from?
Arabic for season.
But in meteorology associated with the seasonal reversal in wind direction seen in Indian sub continent and other parts.
What happens in the wet season?
Winds blow from sea to land bringing main annual rainfall to most of India, Bangladesh, Pakistan and Burma
Some areas remain dry - Thor desert in Pakistan.
Why doe those regions have little rain in dry season?
Offshore winds
What happens in June (summer in northern hemisphere)
Land mass of Asia much hotter than adjoining seas- particuarly hot over Sind desert in north west India and gobi desert in China.
Air in these regions very warm and air pressure is low and this is where the itcz is located.
At same time, it is winter in Southern Hemisphere and landmass is cooler than surrounding seas.
Air in central Australia is cool and heavy and air air pressure is high (air sinking)
Air moves from high to low pressure and so wind blows from north Australia to east Asia.
As wind crosses equator, it is deflected according to coriolis force.
In summer in India, the warm low density air in interior rises and is replaced by inflowing sea. Breezes from Australia (cold and dense)
As the cold air moves over the Indian Ocean, becomes unstable as warmed from below and gains a lot of moisture from Indian Ocean - heavy rain (downpours and drop in temp)
Rainfall totals are further increased by uplift of air over foothills of Himalayas mountains ranges and by intense convection.
Low pressure, especially moist air from ocean will ride Conde and form clouds and cause precipitation.
What happens just before monsoon bursts in May?
Mean temp rises to its annual maximum just before monsoon burst ( in May, sometimes later in parts of Southeast Asia)
- at this time of year clear skies associated with high pressure and sinking air allows more intense heating Than in wet season when low pressure generates clouds and absorb and reflect some incoming radiation.
What happens in December?
The whole patterns of temperatures, pressures and winds had been completely reversed.
Air pressure is now high over Indian land mass and low over central Australia.
Bitterly cold winds from gobi area now spill over south east Asia where winters are now cold and dry for most of Indian subcontinent. High pressure.
At same time onshore winds bring heavy rainfall to places such as Darwin on north Australian coast.
Itcz moves south towards Capricorn.
When do cyclones occur?
During rainy season, when upto 2,500 mm of rainfall.
These intense low pressure systems bring violent winds, torrential rainfall and thunderstorms ( June to September)
Is the timing of monsoon reliable?
Not always.
Why is timing of monsoon not always reliable?
Because upper atmospheric conditions have to be correct to allow winds to come from south.
Failure of monsoon, result in prolonged drought, while excessive rains cause serious flooding in some years.
Summarise the three seasons in monsoon climate ?
Rainy season June to September
Cold dry system October to January
Hot dry season February to May.
