Processes

Question 1

Why is it warmer at the equator than at the poles?

Answer 1

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.

Question 2

Explain the difference between cold and hot air.

Answer 2

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

Question 3

Explain convection

Answer 3

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.

Question 4

Explain the Coriolis Effect

Answer 4

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.

Question 5

Name the three cells of atmospheric circulation.

Answer 5

Hadley, Ferrel and polar cell (three north and three south of the equator.

Question 6

Explain air circulation in the Hadley cell.

Answer 6

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).

Question 7

What is the Intertropical Convergence Zone?

Answer 7

Is the belt of rising air close to the equator, it’s called ICZ due to the convergence of air along the surface.

Question 8

Why is the Ferrel cell different than the Hadley and Polar cell?

Answer 8

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.

Question 9

How does the Hadley cell influence precipitation patterns?

Answer 9

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.

Question 10

From which direction blows the wind at the surface in the tropics, from which direction does it blow at mid-latitudes.

Answer 10

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.

Question 11

How does the Coriolis force impact the jet stream, trade winds and westerly winds at mid-latitudes?

Answer 11

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.

Question 12

What is latent heat of vaporization/condensation?

Answer 12

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.

Question 13

What is the lapse rate?

Answer 13

The lapse rate is the rate of temperature decrease with height in the atmosphere.

Question 14

How does vertical water vapor transport impact the lapse rate?

Answer 14

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.

Question 15

When does evaporation occur?

Answer 15

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.

Question 16

When does condensation occur?

Answer 16

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.

Question 17

How does the difference in heat capacities of air and water impact climate variations?

Answer 17

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.

Question 18

Which component of the climate system absorbs most of the energy (heat content) that currently accumulates on Earth?

Answer 18

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.

Question 19

In which direction do surface waters flow in the tropics, and what about mid-latitudes?

Answer 19

The easterly trade winds push water towards the west near the tropics, while the westerly winds push toward the east at mid-latitudes.

Question 20

What are the subtropical gyres and what forces them?

Answer 20

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.

Question 21

What is the strongest ocean current in the world?

Answer 21

The Antarctic Circumpolar Current: it transports more than 100 million cubic meters of water per second around Antarctica flowing from west to east.

Question 22

Explain convergence and divergence.

Answer 22

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.

Question 23

How is the ocean stratified?

Answer 23

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.

Question 24

What is the Thermohaline circulation?

Answer 24

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).

Question 25

Where do surface waters sink into the ocean’s interior?

Answer 25

Surface waters only sink in a few regions where the density of surface waters is large enough. In the current ocean there is deep water formation (sinking water) in the North Atlantic and near Antarctica.

Question 26

Why is the Atlantic saltier than the Pacific?

Answer 26

Surface waters of the Atlantic are saltier because of water vapor transport within the atmosphere. Whereas mountain ranges at mid-latitudes block water vapor transport from Pacific to Atlantic with westerly winds there, in the tropics gaps in the mountains allow water vapor transport with the east trade winds from Atlantic to Pacific. This causes fresher, more buoyant surface waters in the Pacific.

Question 27

Where is the ocean warming the most?

Answer 27

Most of the increase in temperature is concentrated near the surface consistent with a warming atmosphere as its cause. A prominent maximum of heat uptake is in the North Atlantic. The reason is the sinking of southward penetration of North Atlantic Deep Waters, which transports both anthropogenic carbon and heat from the surface to the deep ocean.

Question 28

How are changes in salinity related to changes in the atmospheric hydrological cycle?

Answer 28

Acceleration of the atmospheric hydrological cycle affects ocean surface salinities. Regions that are already salty such as subtropics and the Atlantic get even saltier, while regions that are already fresh like the north pacific and the southern ocean get even fresher.

Warming and freshening of surface waters at high latitudes decreases their density and increases their buoyancy. This reduces deep water formation and the meridional overturning circulation.

Question 29

Explain potential temperature.

Answer 29

The potential temperature of a parcel of fluid at pressure P is the temperature that the parcel would attain if adiabatically brought to a standard reference pressure P0, usually 1,000 hPa (1,000 mb).

Potential temperature is a more dynamically important quantity than the actual temperature. This is because it is not affected by the physical lifting or sinking associated with flow over obstacles or large-scale atmospheric turbulence. A parcel of air moving over a small mountain will expand and cool as it ascends the slope, then compress and warm as it descends on the other side- but the potential temperature will not change in the absence of heating, cooling, evaporation, or condensation (processes that exclude these effects are referred to as dry adiabatic). Since parcels with the same potential temperature can be exchanged without work or heating being required, lines of constant potential temperature are natural flow pathways.

Potential temperature is a useful measure of the static stability of the unsaturated atmosphere. Under normal, stably stratified conditions, the potential temperature increases with height, and vertical motions are suppressed. If the potential temperature decreases with height, the atmosphere is unstable to vertical motions, and convection is likely. Since convection acts to quickly mix the atmosphere and return to a stably stratified state, observations of decreasing potential temperature with height are uncommon, except while vigorous convection is underway or during periods of strong insolation. Situations in which the equivalent potential temperature decreases with height, indicating instability in saturated air, are much more common.

Question 30

What is the difference between diabatic and adiabatic processes?

Answer 30

They are 2 ways in which the temperature of an air parcel can be changed.

• Diabatic involves direct energy exchanges. Like the heating or cooling of the air as it moves through a hot or cold surface.
• Adiabatic does not involve net energy exchange. Heating or cooling is achieved by compression or expansion of the air.

Question 31

How is air compressed or expanded in nature?

Answer 31

Air pressure decreases with altitude. So if an air parcel rises, it gets into a region of lower pressure, therefore expand and cool. If we force an air parcel to sink, it will contract and warm.

As long as there is no condensation involved, the temperature of a rising parcel decreases at a fix rate: the dry adiabatic lapse rate - 10° C/1km.

If an air parcel is lifted up high enough, it will eventually get so cold that it cannot hold the water vapor any longer. This is the height at witch saturation occurs, also called Lifting Condensation level, because further lifting will cause condensation (water vapor gets from a gas to a liquid state - clouds form).

The process of condensation releases energy, therefore the rate at which the air temperature decreases from the lifting condensation level upward, will be less. The air parcel still expands and cools, but not as much due to the fact that energy is released. The rate of this cooling, si called moist adiabatic lapse rate and equals to 5°C/1km.

Question 32

What is the environmental lapse rate?

Answer 32

Also called Ambient lapse rate, is the temperature difference per 1km altitude difference. It’s about 6.5C/km.

Example: how temperature decreases with altitude in the atmosphere (not referring to air parcel).

Question 33

Explain the differences between stable and unstable air.

Answer 33

Stable air - is air that is colder and denser than the surrounding air. It’s non-buoyant, remains immobile unless forced to rise. If clouds develop, tend to be stratiform or cirriform. If precipitation occurs, tends to be drizzly.

Unstable air - is air that is warmer and less dense than its surrounding air. It’s buoyant, rises without outside force. if clouds develop, tend to be cumuliform. If precipitation occurs, tends to be showery.

Question 34

What is conditionally unstable air?

Answer 34

It occurs when an air parcel cools faster than the atmosphere but then cools slowly after condensation. After condensation latent heat is released which offsets the cooling of the air parcel. The air is unstable because it has risen to condensation level in the first place.

The dry adiabatic lapse rate is greater than the environmental lapse rate but lower than the ELR after condensation.

Weather conditions are fine at lower levels but can be unstable after condensation.

Question 35

What is latent heat?

Answer 35

Latent heat is energy absorbed or released by a substance during a change in its physical state (phase) that occurs without changing its temperature. The latent heat associated with melting a solid or freezing a liquid is called the heat of fusion; that associated with vaporizing a liquid or a solid or condensing a vapor is called the heat of vaporization. The latent heat is normally expressed as the amount of heat (in units of joules or calories) per mole or unit mass of the substance undergoing a change of state.

Question 36

Explain Meridional energy transfers.

Answer 36

The difference between the absorbed solar radiation and emitted terrestrial radiation gives the net heat gain from these fluxes. In the tropics the gain is positive. That is, there is more energy gain than energy loss. At the poles, on the other hand, there is more energy loss than energy gain. Therefore, if no other processes were involved, the equator would warm up and the poles would cool down. But this is not the case, which implies a heat transport from the tropics towards the poles.

Taking the difference ASR – ETR and integrating it from one pole to the other gives the total
meridional heat flux. In the southern hemisphere values are negative indicating southward
heat transport. Positive values in the northern hemisphere represent northward transport. Poleward heat fluxes are peak at mid-latitudes with values of between 5 and 6 PW.

Most of the meridional heat transport is carried by the atmosphere (4-5 PW) whereas the ocean is responsible for a smaller portion (1-2 PW).

Question 37

How are deep waters formed?

Answer 37

Deep waters are “formed” where the air temperatures are cold and where the salinity of the surface waters are relatively high. The combinations of salinity and cold temperatures make the water denser and cause it to sink to the bottom.

The Gulf Stream carries salt into the high latitude North Atlantic where the water cools. The cooling and the added salt cause the waters to sink in the Norwegian Sea. This is the formation of Atlantic Deep Water

Question 38

How is the cryosphere important for climate?

Answer 38

Acting like a highly reflective blanket, the cryosphere protects Earth from getting too warm. Snow and ice reflect more sunlight than open water or bare ground. The presence or absence of snow and ice affects heating and cooling over the Earth’s surface, influencing the entire planet’s energy balance. Changes in snow and ice cover affect air temperatures, sea levels, ocean currents, and storm patterns all over the world.

Question 39

How does the lithosphere affect the climate?

Answer 39

Lithosphere (solid earth): Absorbs solar energy, radiates heat and stores carbon; continents and landforms help direct ocean and wind currents.

The presence or absence of vegetation affects albedo and therefore the warming of cooling of the Earth’s climate.

Question 40

What is biome?

Answer 40

A biome is a large collection of flora and fauna occupying a major habitat.

The Earth’s biomes are categorized into two major groups: terrestrial and aquatic. Terrestrial biomes are based on land, while aquatic biomes include both ocean and freshwater biomes. The eight major terrestrial biomes on Earth are each distinguished by characteristic temperatures and amount of precipitation. Comparing the annual totals of precipitation and fluctuations in precipitation from one biome to another provides clues as to the importance of abiotic factors in the distribution of biomes. Temperature variation on a daily and seasonal basis is also important for predicting the geographic distribution of the biome and the vegetation type in the biome. The distribution of these biomes shows that the same biome can occur in geographically distinct areas with similar climates.

Type of biomes are:

Tundra
Taiga
Deciduous forest
Grasslands
Desert
High plateaus
Tropical forest
Minor terrestrial biomes