Atmosphere Flashcards
Lectures 4, 5 and 6
What happens to air density when two columns have different temperatures but the same pressure at a certain altitude?
The cold column has higher density than the warm column because air density is inversely proportional to temperature.
How does pressure change with altitude in warm and cold air columns?
Above the altitude π§β : Pressure drops faster in the cold column due to higher density.
Below π§β : Pressure increases faster in the cold column.
What is the significance of the altitude π§β in two adjacent air columns?
zβis the altitude where pressure is equal in both columns despite the temperature difference. Above π§β, pressure is lower in the cold column; below π§β, it is higher in the cold column.
What do horizontal temperature differences lead to in the atmosphere?
Horizontal temperature differences create horizontal pressure differences, driving atmospheric motion.
What does the pressure gradient force (PGF) do?
The PGF initiates wind by causing air to move from areas of higher pressure to areas of lower pressure.
How is the pressure gradient force calculated?
PGF = -dP/dX
pressure difference over distance change, minus is high to low pressure
What happens to air in a high-pressure system?
In a high-pressure system, air descends and warms dry adiabatically, leading to clear skies and sunny, dry conditions.
What happens to air in a low-pressure system?
In a low-pressure system, air ascends, cools dry adiabatically at first, and once saturation occurs, it cools moist adiabatically, leading to clouds and often rain.
Why does land heat faster than adjacent ocean during the day?
Land heats faster than the adjacent ocean because solar radiation is absorbed to a greater depth in water compared to land, and water has a higher heat capacity, heating a much thicker layer of water.
What happens to air temperature over land and water during the day?
Over land, the air is warmer, and over water, the air is cooler due to the differing heating rates of land and ocean surfaces.
What does the horizontal pressure gradient between land and water cause at the surface?
At the surface, the horizontal pressure gradient between land and water causes a sea breeze from the water to the land, where there is lower pressure over the land and higher pressure over the ocean.
What happens in the atmosphere due to the horizontal pressure gradient during the day?
At higher altitudes, typically a few hundred meters, the pressure gradient reverses, with higher pressure over land and lower pressure over the ocean, leading to convergence and rising warm air over land, and descending cooler air over the ocean.
How does the sea breeze help reduce temperature and pressure differences?
The sea breeze transports warm air from the land to the ocean, helping to reduce temperature and pressure differences between the land and the ocean.
What forces affect atmospheric motion when air moves over long distances?
The rotation of Earth around its axis leads to forces affecting atmospheric motion in addition to the pressure gradient force.
What does the Coriolis force depend on?
The Coriolis force depends on air density (Ο), wind velocity (v), and the Earthβs rotation (Ο).
How does the Coriolis force relate to the direction of motion?
The Coriolis force is perpendicular to both the direction of motion and the direction of Earthβs rotational axis.
How does the Coriolis force change with latitude?
The Coriolis force is zero at the equator and increases towards the poles. It is strongest at the poles where the horizontal plane is perpendicular to the rotational axis.
What equation describes the magnitude of the Coriolis force?
The magnitude of the Coriolis force scales with the sine of the latitude angle between the equator and the pole. It is also influenced by Earthβs angular speed (Ξ©), which is equal to 2Ο divided by the Earthβs rotation time.
What is the Coriolis parameter (f)?
The Coriolis parameter (f) simplifies the Coriolis force equation, making it the product of the Coriolis parameter, air density, and velocity.
What is the geostrophic wind?
The geostrophic wind is the wind that results when the pressure gradient force and Coriolis force are balanced, leading to a wind direction and speed that does not change over time.
What is the pressure gradient force?
The pressure gradient force is the force that causes air to move from high to low-pressure areas. It is illustrated by equally spaced isobars, with the force pointing from higher to lower pressure.
How does the Coriolis force affect wind direction?
The Coriolis force deflects moving air to the right (in the Northern Hemisphere) as it begins to move, modifying the windβs direction.
What happens as air moves under the influence of the pressure gradient force?
As air moves, the Coriolis force begins to deflect the wind, and the wind will continue to accelerate until the Coriolis force and pressure gradient force are balanced, making the wind flow parallel to the isobars.
What is geostrophic balance?
Geostrophic balance occurs when the pressure gradient force and the Coriolis force are equal in magnitude but opposite in direction, resulting in a wind that moves parallel to the isobars without changing direction or speed.
What is the energy source for tropical cyclones?
The energy source for tropical cyclones is the evaporation of water from warm ocean waters. When this water vapor condenses to form clouds, the latent heat released fuels the storm.
What are hurricanes and typhoons?
urricanes are tropical cyclones in the North Atlantic and East North Pacific. Typhoons are tropical cyclones in the West North Pacific.
Why do tropical cyclones form a near-symmetric structure?
Tropical cyclones form near-symmetric structures due to the combined action of the pressure gradient force, Coriolis force, and frictional force, with friction being relatively low over the ocean.
What happens when a tropical cyclone makes landfall?
When a tropical cyclone makes landfall, it is cut off from its energy source and experiences increased friction. This causes the storm to decay quickly, but it can still produce heavy rainfall and cause significant damage to infrastructure.
How do warming ocean temperatures affect tropical cyclones?
In a warming world, ocean surface temperatures above 26.5ΒΊC will provide conditions for more frequent tropical cyclones. However, limiting factors may prevent an increase in the number of cyclones, though those that form will be stronger and more destructive.
What is an example of a rapidly intensifying hurricane?
Hurricane Ida in August/September 2021 rapidly intensified just before landfall in Louisiana, becoming one of the strongest hurricanes to make landfall in the US. Despite weakening over land, it caused severe flooding due to unprecedented rainfall in New Jersey and New York City.
What is the core type in hurricanes and mid-latitude cyclones?
Hurricanes have a warm core with sinking air in the eye, while mid-latitude cyclones have a cold core with rising air at the center.
How do pressure gradients differ in hurricanes and mid-latitude cyclones with height?
In hurricanes, pressure gradients decrease with height, meaning the strongest winds are near the surface. In mid-latitude cyclones, pressure gradients intensify with height, and the strongest winds are found at higher altitudes.
Where is most of the excess heat in the tropics stored?
Most excess heat in the tropics is stored in the upper layer of the tropical oceans, not in the atmosphere.
George Hadleyβs proposal regarding heat transport from the Equator to the poles?
Hadley proposed a single hemispheric convection cell that transports heat from the Equator to the poles, with warm air over the Equator creating low pressure and cold air over the poles creating high pressure.
Why doesnβt the single Hadley cell work on Earth?
The single Hadley cell doesnβt work due to the conservation of angular momentum. As air moves poleward, its speed must increase, and at about 30Β° North or South, air would become supersonic, making the flow unstable.
What is the subtropical jet and where does it form?
he subtropical jet is a band of strong westerly winds that forms near 30Β° South, caused by the conservation of angular momentum.
How does the Coriolis force affect winds in the Hadley cell?
n the Hadley cell, as air returns to the Equator near the surface, the Coriolis force deflects the wind to the left, producing easterly winds that become south-easterly near the surface due to friction.
What is the Polar cell and how is it driven?
The Polar cell is driven by the polar high, where cold, sinking air moves toward the mid-latitudes and is deflected by the Coriolis force, creating easterly winds.
What is the Ferrel cell and how is it driven?
The Ferrel cell is passively driven by the descending branch of the Hadley cell and the rising branch of the Polar cell, characterized by westerly winds.
What is the polar front, and how does it affect weather?
The polar front separates cold polar air from warm subtropical air, and the temperature difference produces mid-latitude cyclones, influencing weather patterns like those in the UK.
What is the polar front jet?
The polar front jet, or jet stream, is a strong westerly wind that forms above the polar front, where pressure differences between cold and warm air increase with altitude.
How does the three-cell model compare to real atmospheric conditions?
The three-cell model represents an average condition, but real atmospheric features, such as the two jets, are often not as clearly separated as the model suggests.
What is the Intertropical Convergence Zone (ITCZ)?
The ITCZ is the rising branch of the Hadley cells near the Equator, characterized by lower atmospheric pressure and low wind speeds.
What kind of weather is associated with the ITCZ?
The ITCZ is typically a narrow band of thunderstorms and high precipitation due to converging surface flow bringing warm, moist air that triggers convection.
How does the ITCZ behave in the maritime continent around Indonesia?
In the maritime continent around Indonesia, convection covers a broader area than in other regions of the ITCZ, making it an exception.
What happens in the subtropics when air sinks dry adiabatically?
In the subtropics, sinking air creates a belt of high-pressure systems, leading to clear skies and reducing the temperature gradient due to the cloud albedo effect in the Hadley cell.
What is the difference in pressure systems between the Southern and Northern Hemispheres in mid-latitudes?
In the Southern Hemisphere, mid-latitudes do not have significant semi-permanent pressure systems due to the smaller continents, while in the Northern Hemisphere, there are high-pressure systems over cold continents (Canadian and Siberian High) and low-pressure systems over warmer oceans (Aleutian and Icelandic Low).
How does the difference in temperature between continents and oceans affect wind and precipitation during summer?
Air moves from the ocean to the continent near the surface, where it rises, leading to adiabatic cooling and cloud formation. This results in precipitation, making the summer wet. The monsoon circulation is completed by descending air over the ocean and a return flow aloft.
What are the two primary forces that drive motion in the ocean?
The two main forces driving ocean motion are wind stress, caused by atmospheric winds dragging the ocean surface, and density differences, caused by variations in temperature (thermo) or salinity (haline).
What is the Ekman spiral and how does it form?
The Ekman spiral forms when wind blows across the ocean surface, creating friction that moves surface water. Due to the Coriolis force, the water is deflected to the right in the Northern Hemisphere, and deeper layers of water are dragged along, becoming increasingly deflected and moving more slowly with depth.
ow does wind stress cause upwelling near the coast?
When wind blows parallel to the coastline, Ekman transport moves surface water away from the coast. This causes the sea surface to slope, and as water is displaced, deeper water rises to replace it, leading to upwelling.
How does the direction of wind affect coastal upwelling in the Northern Hemisphere?
In the Northern Hemisphere, when wind blows parallel to the coastline with the coast on the left, Ekman transport moves water away from the coast, causing upwelling of deeper water to replace the displaced surface water.
What is the temperature profile like below one kilometre in the ocean?
Below one kilometre, the ocean temperature is nearly constant and unaffected by the seasons. Temperature gradually decreases with depth, and density increases with depth.
What is the transition zone between the deep ocean and the surface layer called?
The transition zone is called the pycnocline, where density increases more rapidly with depth. If the density change is primarily due to temperature, it is known as the thermocline. If it is due to salinity, it is known as the halocline.
What are the primary factors that increase the density of surface water in the ocean?
cooling (from evaporation, longwave radiation, or contact with colder air) and increasing salinity (from evaporation leaving salt behind).
How does the thermohaline circulation work to maintain ocean flow?
As surface water sinks at high latitudes, it is replaced by surface water from lower latitudes. This sinking water mass creates a return flow at greater depths, completing the thermohaline circulation between low and high latitudes.
What is the main driver of the thermohaline conveyor belt circulation?
Bottom water formation, where near-surface water sinks all the way to the bottom of the ocean, is the main driver of the conveyor belt.
In which regions does bottom water formation primarily occur?
Bottom water formation occurs in three distinct regions: the Labrador Sea and Greenland Sea in the North Atlantic, and the Weddell Sea in the South Atlantic.
How does sea ice formation contribute to bottom water formation?
Sea ice formation leads to brine rejection, making the seawater more salty and denser, which contributes to bottom water formation, particularly in the Weddell Sea.
Where does the Gulf Stream originate, and where does it flow?
The Gulf Stream originates in the Gulf of Mexico near Cuba and flows along the US East coast until Cape Hatteras, North Carolina, where it detaches and flows across the North Atlantic.
What happens to the Gulf Stream after it detaches from the coast at Cape Hatteras?
After detaching from the coast, the Gulf Stream broadens, slows down, and becomes the North Atlantic Drift, which splits into northward and southward branches.
What do the trade winds in the equatorial Pacific do to the ocean water?
The trade winds drag the water from the East to the West Pacific, causing water to pile up in the West Pacific and creating differences in sea surface height.
What causes coastal upwelling in the equatorial Pacific?
The meridional wind component of the trade winds (southeasterlies in the Southern Hemisphere and northeasterlies in the Northern Hemisphere) produces coastal upwelling due to Ekman transport.
What is the thermocline depth, and how does it differ across the equatorial Pacific?
The thermocline is the upper ocean layer where density increases with depth. It is much deeper in the West Pacific than in the East Pacific, with a difference of about 200 meters.
Geoengineering
Deliberate large scale intervention in the earthβs climate system in order to moderate global warming.
Issues
Methods of intervention
Feasibility
Uncertainties (effectiveness, costs, environmental impacts)
Political controversy and public opinion
Strategies -
CDR (CO2 removal) - addresses root cause by removing GHG from atmosphere, ocean and land based methods
Solar radiation management - mirrors in space, cloud brightening, offsets GHG concentration increases by increasing albedo
Carbon capture and storage
can be applied to large, singular sources, power plants. Ocean storage, acidification, partial release into the atmosphere over time. Geological storage, tectonic stability
CO2 removal technique
Enhance biological uptake
Terrestrial and oceanic sequestration
Using engineered systems
Aerosols
particles suspended in air, primary aerosols - sea salt, mineral dust, biogenic aerosol, organic and black carbon. Secondary - formed by gas-to-particle conversion - sulphate, nitrate.
Required for cloud formation, many are anthropogenic origin.
Climate effects of aerosols -
Net cooling, scatter and absorb radiation (direct effect)
Aerosols increase concentration of cloud droplets and ice particles, cooling (indirect)
Decrease precipitation efficiency (cooling)
(robock, 2008)
Sulphate aerosols - reduce precipitation over wide regions, hundreds of millions exposed to droughts
Geoengineering with no restrictions to GHG emissions, ocean would continue to acidify.
Aerosols allow ozone depletion.
Geopolitical instability, production could be halted at any time, would allow rapid warming
