Hazardous earth Flashcards
solar insolation
the sun’s energy
what are the two ways in which heat is redistributed
by air movements caused by pressure differences and by ocean currents
one of the two ways in which heat is redistributed globally is by air movements caused by pressure differences.
Talk about pressure differences
Land and sea heat up differently.
On land, dark surfaces eg soil and forest absorb sunlight which is converted to heat. Land heats quickly in the summer, but only at the surface, so it cools quickly in winter. When it heats, it also heats the air above, so air expands, becomes lighter and rises. This forms areas of LOW PRESSURE over large landmasses in summer.
The sea behaves differently. Some sunlight is reflected from the surface while some is absorbed to 30m depth. It therefore takes the sea longer to heat but also longer to cool. in summer, air over the sea remains cooler and denser, forming areas of HIGH PRESSURE.
Differences in pressure causes air to move- from high to low pressure, creating wind. It moves in a circular way because of the Earth’s rotation.
one of the two ways in which heat is redistributed globally is by ocean currents.
Talk about these
Welcome to the Isles of Scilly. They are Britain’s most southernly location .
Winters are much warmer than the rest of the UK. Daffodils and new potatoes are picked three months earlier than elsewhere in the UK.
These differences are caused by the Gulf Stream, a warm ocean current. Driven by westerly winds, the Gulf Stream begins in the Gulf of Mexico, blowing bortheast where a branch of it heads towards Europe to become the North Atlantic Drift. So although the Scillies are 49.5 degres north of the Equator, the North Atlantic Drift keeps jnauary sea temperatures warm at 11 degrees celcuis.
The differences are caused by the Gulf Stream
What is the Gulf Stream
One of several ocean currents.
In the north Atlantic, cold, salty water is heavy sinks. This sets up a convection current, which drags surface water down. The current draws warmer salty water over the ocean surface from areas near the Equator sich as the Gulf of Mexico. This cools and sinks in the Labrador and Greenland Seas, and flows south toward the Equator where it is warmed again.
What causes the ITCS
ITCZ forms within the tropics, whe two masses of air meet - or converge. it is part of a movement of the atmosphere known as the global circulation model.
This consists of three huge ‘cells’ of air , the largest of which is the Hadley Cell. The cells are caused by heating and cooling, and between them create the world’s high and low pressure systems.
What causes the ITCS
ITCZ forms within the tropics, whe two masses of air meet - or converge. it is part of a movement of the atmosphere known as the global circulation model.
This consists of three huge ‘cells’ of air , the largest of which is the Hadley Cell. The cells are caused by heating and cooling, and between them create the world’s high and low pressure systems.
In July, the sun is overhead at the Tropic of Cancer, creating summer in the northern hemisphere. At this time, the Hadley Cell works as follows :
In North and West Africa, land is warmer than the surrounding seas because it is summer. Here, the air warms, exoands, becomes lighter and rises.
Further south, over the Gulf of Guinea, an area of cooler, denser, high pressure air fors because the sea is cooler than the land.
Winds blow from high to low pressure, towards West Africa and the southern Sahara away from the Gulf of Guinena. These winds, and moisture that they contain, are the cause of Mali’s rainy season.
However, the hadley cell actually consists of two parts, one either side of the Equator. Both of these move together as thesun moves overhead with the seasons. The second lies further noth over the Sahara , the Atlantic Ocean and the Mediterranean sea.
At the same time as the cell brings rain to Mali, high pressure also forms over the Mediterranean Sea and Atlantic Ocean. This is because the sea is cooler than surrounding lands int he northern hemisphere summer.
Drawn by the low pressure area at the ITCZ, Trad Winds blow south towards West Africa. These Trade Winds converge with those from the Glof of Guinea at the ITCZ. Forced to rise as they meet, they coolm and water vapour condenses to cause heavy rain.
The Hadley Cell is the driving force behing mali’s rainy seaspm on the northern hemisphere’s summer. It si also responsible for thedry winter season. In fact, the Hadle Cell is part of a global circulation model that afects rainfall everywhere, not just Mali. How does this happen?
Having brought rain to Mali in June, the Hadley cell moves south with the changing position of the overhead sun. By January, the pattern has reversed completely
The northern hemisphere winter createsa cool, dense high pressure area over North Africa
The sun is now overhea at the Tropic of Cappricorn, warming the southern hemisphere, and formbg a new low pressure area
Trade winds blow from high to low pressure drawing dry air from the Sahars scross Mali and causing its dry seasonn
These trade winds meet others from the southern hemisphere to create the ITCS which has shiftd southwardds. It brings rain to southern Africa at this time. To complete the hadley Cell, rising air from the iTCZ cools high in the atmosphere and becomes denser. Fed by air from below, it spreads out until it subsides as high presure air.
The Hadley Cell is just one part of the global atmosphere. In factm there are two hadley Cells. The ITCZ forms when the trade Winds from each one meet.
What is global circulation model
a theory that explains how the atmosphere operates in a series of three cells each side of the Equator.
Like the Hadley cell the other cells - ferrel cell and polar cell can be found in each hemisphere.
What is the ferrel cell caused by
by high pressure over North Africa. As well as blowing south as part of the Hadley Cell, some air also blows towards the poles. It’s these winds that drive the Gulf stream.
These winds collect moisture over the oceans and meet cold, dense air from the Polar Cell between 50-60 degrees N and S. Just like at the iTCZ, this creates a front bringing high rainfall. It’s this front that brings much of the UK’s rainfall.
The global circulation model affects climates around the world. One impact is that it leaves some tropical areas with little rain . The world’s tropical deserts all originate in this way.
Similarly , areas of highest rainfall also lie between 20N and 20 S and are caused by the iTCZ. Meanwhile the cooler Ferrel Cell (which contains less moisture because it is cooler ) takes mild subtropical winds as far as 50-60 degrees N and S, where they meet the colder winds from the Polar Cell. This forms a front, bringing rain. The dry dense air at the Poles creates the polar desert of Antarctica and the Arctric ice sheet.
