Processes Flashcards
(40 cards)
Why is it warmer at the equator than at the poles?
There is more sunlight at the tropics. Due to the curvature of the Earth’s surface the equator receives more incident solar radiation per area than the poles. The more tilted the Earth’s surface with respect to the sun’s rays, the less energy it receives.
Explain the difference between cold and hot air.
Colder air is denser than warm air. Cold air has higher pressure than warm air. Warm, less dens air rises, while colder and more dense air sinks
Explain convection
The most important atmospheric processes for climate include upward motions, which are called convection.
When the Sun heats up the Earth’s surface, the air in contact with this surface also heats up and becomes less dense (lighter). This happens because an increase in temperature causes the air to expand, so that the same air mass will occupy a greater volume, it will be less dense. As a consequence it becomes unstable, since it now has denser (heavier) air on top of it. It then tends to rise, recalling denser air to occupy the position it left.
Explain the Coriolis Effect
The power of Earth’s spin to turn flowing air is known as the Coriolis Effect. Earth’s rotation causes a deflection of air and water masses towards the right in the northern hemisphere and towards the left in the southern hemisphere.
If the Earth didn’t spin, there would be just one large convection cell between the equator and the North Pole and one large convection cell between the equator and the South Pole. But because the Earth does spin, convection is divided into three cells north of the equator and three south of the equator.
Name the three cells of atmospheric circulation.
Hadley, Ferrel and polar cell (three north and three south of the equator.
Explain air circulation in the Hadley cell.
Rising warm moist air at the equator causes water vapor condensation due to cooling of the air during the ascent. Clouds form and precipitation occurs. Some of the deepest cumulonimbus clouds on Earth form in the tropics. They can reach the top of the troposphere or higher. The cool relatively dry air then moves poleward. Now the Coriolis effect kicks in, deflects the air towards the right (left) in the northern (southern) hemisphere, which creates the jet stream. The air cools by emitting longwave radiation to space. This increases the density and the air descends back to the surface in the subtropics (~30°N/S). During the descent the air warms and its relative humidity decreases. This leads to dry conditions in the subtropics indicated by the major deserts at those latitudes.
Subsequently the dry air moves back towards the equator. The Coriolis force deflects it towards the right (left) in the northern (southern) hemisphere, creating the easterly trade winds in the tropics. During this movement along the sea surface the air picks up water vapor from evaporation. Once the air returns to the equator it is saturated with water vapor (close to 100% relative humidity).
What is the Intertropical Convergence Zone?
Is the belt of rising air close to the equator, it’s called ICZ due to the convergence of air along the surface.
Why is the Ferrel cell different than the Hadley and Polar cell?
The Hadley and Polar cells are both thermally drive, while the Ferrel cell is not. The Ferrel cell is actually driven by eddies coming from surrounding fast jet streams (subtropical jet from the Hadley cell, and polar jet from polar cell). Eddies are swirls of air that produce turbulence because they work in the opposite direction than the regular flows.
How does the Hadley cell influence precipitation patterns?
When the sun heats air at the equator, it also encourages evaporation. When a humid mass of air cools down, as it does when it rises, moisture in the air will condense into clouds, which then precipitate large amounts of rain over the equator. This forms what’s known as the Intertropical Convergence Zone (ITCZ), doldrums, or horse latitudes. The large volume of rain that these 10 degrees of latitude around the equator receive supports numerous tropical rainforests, including the Amazon rainforest, Congo rainforest, and Indonesian rainforest.
Further north at the edge of these cells, the Hadley circulation is having the complete opposite effect. After depositing huge amounts of rain over the equator, air continues to rise until it reaches the tropopause. From there, it is diverted towards the subtropics.
At about 30 degrees North or South of the equator, the air masses begin to sink. This air is very dry, as it has already been depleted of moisture at the equator. As the air sinks, an increase in pressure causes it to warm in a process called adiabatic heating. This, in turn, further decreases the air’s relative humidity.
This low relative humidity coupled with an already dry mass of air results in extremely dry conditions at the edge of Hadley cells. This leads to very little precipitation to these regions and, consequently, atmospheric conditions that provide us with most of the world’s hot deserts (as opposed to cold deserts, like Antarctica). If you look at a satellite image of Earth and note the locations of the planet’s hot deserts, such as the Saharan desert, Arabian desert, Australian deserts, and Kalahari desert, you’ll see that many of them are located at similar latitudes.
From which direction blows the wind at the surface in the tropics, from which direction does it blow at mid-latitudes.
The trade winds (also called trades) are the prevailing pattern of easterly surface winds found in the tropics near the Earth’s equator, equator-ward of the subtropical ridge. These winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere.
The westerlies or the prevailing westerlies are the prevailing winds in the middle latitudes (Ferrel Cell), which blow in areas poleward of the high pressure area known as the subtropical ridge in the horse latitudes. These prevailing winds blow from the west to the east, and steer extra-tropical cyclones in this general direction. The winds are predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere.
How does the Coriolis force impact the jet stream, trade winds and westerly winds at mid-latitudes?
From the equator, warm air rises, reaches the troposphere and starts to move poleward. During this poleward movement, the Coriolis effect kicks in and deflects the air towards the right in the northern hemisphere and towards the left in the southern hemisphere, creating jet streams.
From the poles, air moves back towards the equator and during this movement the Coriolis force deflects air towards the right in the northern hemisphere and the south in southern hemisphere, creating easterly trade winds.
In the Northern Hemisphere, above the subtropical highs, and in the Southern Hemisphere, below the subtropical highs, winds blow from the west towards the east. These winds are called westerly winds, after the direction from where they come. In the Northern Hemisphere, these winds deflect to the right and in the Southern Hemisphere to the left. Thus the westerly winds move from the subtropical areas to the poles.
What is latent heat of vaporization/condensation?
The latent heat of vaporization is the thermal energy required for a liquid to vaporize to a gas or the amount that is released when a gas condenses to a liquid. The latent heat of vaporization is also referred to as the enthalpy of vaporization. Water has a high latent heat of vaporization, which is why steam burns are so dangerous. When steam burns a person’s arm for example, this energy transfer causes the steam to condense.
Latent heat of vaporization is about 2.300 joules per gram of water, the same amount of energy is released during condensation.
What is the lapse rate?
The lapse rate is the rate of temperature decrease with height in the atmosphere.
How does vertical water vapor transport impact the lapse rate?
The observed lapse rate in the atmosphere is on average -6.5°C/km, which is close to the moist adiabatic lapse rate (adiabatic means that no heat is added or removed from the air parcel). This, in contrast to the dry adiabatic lapse rate, which is approximately -10°C/km. Thus, given a surface air temperature of 30°c, the air at 10km altitude at the equator would be -70° in a dry atmosphere compared with -35°c in the real moist atmosphere.
When does evaporation occur?
It occurs when the relative humidity of the air above a water surface is less then 100%. The lower the relative humidity, the higher the rate of evaporation.
Stronger winds also cause more evaporation. Evaporation leads to cooling of the remaining liquid water since it removes the fastest molecules and the slower ones stay behind. Evaporative cooling is important in keeping the Earth and oceans cool.
When does condensation occur?
it occurs when the air is at 100% relative humidity and when cloud condensation nuclei are available. Cloud condensation nuclei are small particles in the air. In the atmosphere condensation typically occurs when air is cooled - during ascending motions in convection or when air is lifted over mountains.
The latent heat released during condensation in clouds leads to warming and thus more intense upward motions. This is an important driver of convection and storms.
How does the difference in heat capacities of air and water impact climate variations?
Heat capacity of water is much larger than that of air. On a per volume basis the heat capacity of water is 4.200 times that of air. This means that the tops 2m of ocean have the same heat capacity of the whole atmosphere. Basically: it takes more heat to warm a gram of water. This is why, throughout the course of a warm summer day, the water in the ocean does not experience a significant change. Land, on the other hand, has a much lower heat capacity.
Since air travels around, air temperature is also regulated by these principles. Air that is in contact with the ocean will be much cooler from energy transfer between water and air, while air that sits above land will heat up much more quickly.
Therefore, coastal climates are much more temperate because a body of water is nearby to regulate the temperature and keep it more constant. In the hot days of summer, landlocked places such as the Midwestern United States are much warmer than coastal cities at the same latitude because the land gets heated quickly and can’t disperse the heat. Temperate coastal areas are regulated by the ocean through land and sea breezes, which fluctuate depending on the temperature differences.
Which component of the climate system absorbs most of the energy (heat content) that currently accumulates on Earth?
About 90% of the observed increase in Earth’s heat content goes into the ocean, and most of the remaining 10% goes into ice and land. Heat gain of the atmosphere is very small in comparison.
In which direction do surface waters flow in the tropics, and what about mid-latitudes?
The easterly trade winds push water towards the west near the tropics, while the westerly winds push toward the east at mid-latitudes.
What are the subtropical gyres and what forces them?
A gyre is any large system of circulating ocean currents, particularly those involved with large wind movements. Concerning the surface circulation of the subtropics, 5 large gyres are its main features.
The easterly trade winds move surface water from east to west near the tropics. This water hits land, where it piles up, then moves poleward. Here, the westerly winds move surface water back towards the east. Water here hits land and either continues south towards the equator, to close the circle, or goes north towards the poles. This water moving poleward generates warm currents like the Gulf Stream, the Kuroshio or the Humboldt currents.
Within the subtropical gyres, water flows in a spiral-like pattern towards the center of the gyre. This convergenze causes sinking at the center, but since it is warm it sinks only a few hundred meters.
What is the strongest ocean current in the world?
The Antarctic Circumpolar Current: it transports more than 100 million cubic meters of water per second around Antarctica flowing from west to east.
Explain convergence and divergence.
Divergence of currents will create an upwelling phase (interior waters reach the surface) and convergence a downwelling phase (surface waters sink in the interior ocean), linking surface and interior waters.
Convergence happens at the center of subtropical gyres.
The Southern Ocean is an important region for upwelling of deep waters caused by a wind-driven divergence of surface waters.
How is the ocean stratified?
In contrast to the atmosphere the ocean is stably stratified. Denser water is layered below lighter water. The density of sea water is determined by temperature and salinity. The colder and saltier, the heavier it is. Typically warmer more buoyant water is on top of colder water, especially at low latitudes.
First layer, where winds causes lots of turbulence, is called the surface mixed layer. Below, between 200 - 1000m deep is a region where temperature decreases faster with depth called the thermocline. Further down is the deep and abyssal ocean, where vertical temperature gradients are small.
What is the Thermohaline circulation?
The sinking and transport of cold, salty water at depth combined with the wind-driven flow of warm water at the surface creates a complex pattern of ocean circulation called the global conveyor belt or Thermohaline circulation (thermo = temperature, haline = salinity).
