Atmospheric Dynamics Flashcards
(L1)
What is the Earth’s Diameter and where does weather occur?
8000 miles- weather occurs in a band only 11km thick
What aspects of the system circulation are short term (years to decades)?
Atmospheric circulation, energy focused in the tropics, energy redistributed around the globe
What aspects of the system circulation are log term (around 1000years)?
Deep ocean circulation, movement of carbon through system
How far does the atmosphere extend from the surface of the Earth?
Around 480km
What is the average lapse cooling rate in the troposphere?
6.4C/km
What does the lapse rate vary with?
Water content in air
What happens to the cooling rate when air is saturated in water?
Cools less rapidly
STOP AND READ
SALR (Saturated Adiabatic Lapse Rate)
SALR (Saturated Adiabatic Lapse Rate)
-Dew forms when the temperature drops to the point where water is condensing out of the air.
-Condensation releases energy. As a parcel of air rises, the actual temperature drops and water is condensed/precipitates.
-SALR varies with temperature from 4C/km to 9C/km
Temperature decreases quicker when the air is unsaturated.
What happens to the atmospheres density as you gain elevation into the atmosphere?
Density decreases
What percentage of the atmospheres mass is within 15km of the surface of the Troposphere?
90%
What will happen to a partially inflated balloon when it increases in altitude?
it will expand and pressure in atmosphere will decrease.
What happens when we increase the temperature of our balloon?
The molecules move faster which will increase pressure and expands the balloon.
What happens if we increase the volume of the balloon?
The density decreases to less than the surrounding air, becomes positively buoyant and rises until the air surrounding matches it.
What is the ideal Gas Law?
PV=nRT
n- number of moles - mol–6.02x10^23 molecules R- real gas constant (8.314JK^-1mol^-1)
What has happend to the temperature of the column if it results in lower atmospheric pressure at the surface?
The column has warmed
What has happend to the temperature of the column if it results in higher atmospheric pressure at the surface?
The column has cooled
Does convection happen as air rises or falls and what does it create?
Rises + cyclone
Does subsidence happen as air rises or falls and what does it create?
Falls + anticyclone
(MATHS)
What is a milibar?
1/1000th of a bar
How do we convert milibars to pascales?
1mb = 100Pa
What is 1atm in kPa?
101.325 kPa
What happens to pressure at sea level at the eye of a hurricane?
It drops around 20%
What is wind?
The Horizontal movement of air from high to low pressure
What is the equation for pressure gradient?
Change in pressure/distance
What is the pressure gradient force?
A net force that is directed from high to low pressure perpendicular to wind
What happens to the PGF and winds when the isobars are close?
The PGF magnitude increases and ergo the wind will be stronger
(Reasons for pressure variation)
1
- uneven absorption of solar radiation
(warmer air-> less dense-> exerts less pressure, column of cold air will increase in pressure with height more rapidly than will a warm column of air) - Moisture content of air
(The more water, the less dense the air (because water has a lower atomic mass) and the less pressure it will exert)
(Reasons for pressure variation)
2
Wind develops as a result of spatial (horizontal) differences in atmospheric pressure. Wind speed tends to be at their greatest during the daytime (greatest extremes in temp and pressure)
What is the global energy budget determined by?
The balance between solar energy absorbed and infrared emmited
Are either equally distributed across Earth?
No
What does incoming solar radiation vary with?
Latitude and season
What does outgoing radiation depend on?
Temperature of the surface/atmosphere at a particular location
Why do the tropics have a heat surplus?
Because the rays are more concentrated over a smaller are (parallel)
What happens to a heat surplus?
It is transferred by atmosphere and oceans to places with deficit heat along the latitudinal energy gradient.
What is the Earth’s tilt angle?
23.5 degrees
What is convergence?
The replacement of warm tropical air that has risen via convection by air from high pressure regions
What is the name given to converging air masses that meet in the tropics?
The inter-tropical convergence zone
What is the ITCZ characterized by?
Extensive cloud cover and heavy rainfall.
What are doldroms?
Erratic weather patterns with calms and violent thunderstorms as winds come from northern and southern hemisphere mix.
Why is the stratosphere warmer?
The stratosphere acts as a cap to stop further rising (and hence cooling) of air.
How is the troposphere warmed?
By energy absorption, turbulence and convections
How is the stratosphere warmed?
Heat comes mainly from UV light interacting with ozone molecules.
At what height is the top of the troposphere?
10-15km
What effect does this barrier have on rising air?
Causes it to diverge outward away from convective zone
What happens to air at 30N and 30S?
It subsides to replace the surface air moving towards the equator.
What prevents condensation and cloud formation as air sinks?
Increased temperature
What type of weather characterizes the atmospheric subsidence of air?
Higher surface pressure, clear skies and low rainfall amounts
Hadley Cell
- Tro-Str barrier forces uplifting air to diverge outward away from convective zone
- At 30N and 30S the air subsides to replace the surface air moving towards the equator
- The air warms as it sinks preventing condensation/cloud formation
- These regions of atmospheric subsidence are characterized by higher surface pressure, clear skies and low rainfall
Why does the Hadley Circulation not go right to the poles (i.e. what happens at 30-90 degrees latitude)?
Low temp at poles -> increased D of air at surface -> Higher pressure than tropics -> divergence and general horizontal movement of cool air towards equator -> cool air meets warm air from tropics resulting in steep temp gradient ‘polar front’ -> masses do not mix well -> warm air rises above cool air from poles and polar front slopes poleward with elevation
What cell has subsidence at 30 degrees and uplift at 60 degrees?
Ferrel Cell
(L2)
What is the Coriolis Effect?
The tendency for a fluid (air or water) moving across the Earth’s surface to be deflected from its straight-line path due to the rotation of the Earth.
What are the two aspects to the Coriolis effect?
Coriolis force and centrifugal force
What direction do objects deflect in the northern hemisphere (Coriolis Force)?
West from North to equator (northern) and East from South to equator (southern)
What direction does the object move in when viewed from space?
Straight
What does the Coriolis Force not explain?
Deflection with West to East movement
What is the centrifugal force?
A force that pushes an object away from the centre of rotation e.g. if an air mass is moving eastwards faster than the Earth’s rotation at that latitude, air mass will be diverted away from the spin axis like an old record.
Why does air at the tropics not deflect?
The vertical component gets stronger towards the tropics by which time it dominates.
In what direction does the centrifugal force act?
Away from the axis of rotation.
How do we get northerly winds in the mid latitudes?
Air moves outwards from high pressure areas, air moves inwards towards low pressure areas, both aspects of the Coriolis Effect deflects the wind and causes circulation around these systems.
What is geostrophic wind?
When pressure gradient force is equal to the Coriolis force - geostrophic wind blows parallel to pressure contours.
What does surface friction do to wind direction?
Induces a drag creating an imbalance between PGF and CF. Wind crosses isobars diverging from high and converging into low pressure.
What are the 3 Meridonal circulations (North-South)?
Hadley cell, Polar cell and Ferrel cell.
What are the 3 Meridonal circulations (East-West)?
Trade winds, Walker circulation and jet streams
Describe Walker circulation.
Longitudinally the Earth is not homogenous, differences causes a variation in the circulation longitudinally, warm air rises over land. (check diagram)
What are the two cores of high speed winds at high altitudes in the westerlies?
Polar front jet stream and subtropical front jet stream
Where is the polar jet stream located?
Between the polar cell and ferrel cell
Where is the subtropical front jet stream located?
Between the ferrel cell and hadley cell
What part of the atmosphere can jet streams be located?
Upper Troposphere
How are jet streams formed?
Large pressure gradient from tropics towards poles, great wind speeds where pressure gradient is steepest.
What are jet streams influenced by?
Coriolis effect which deflects wind to right in northern hemisphere
why are jet stream winds geostrophic?
Because there is no friction in the upper troposphere
How do these upper level winds move?
In a wavelike trajectory around the globe known as Rossby waves
How fast do jet stream winds travel?
Over 200kph
Which is stronger-polar jet or subtropical jet?
Polar jet
What impact do Rossby waves have on Earth’s weather?
Coupled with the migratory pressure systems and storms associated with the westerlies, the motion of rossby waves give the middle latitudes more short term weather variability than any other place on earth.
Putting everything together, what are the general global pressures in January?
Cold winter land surfaces lead to subsidence and high pressure in the northen hemisphere. Northern Hemisphere. North Pacific and Atlantic dominated by low pressure systems due to steep pressure gradient.
Where is the ITCZ positioned in January?
Roughly straight across the equator.
Where is the ITCZ positioned in July?
To the north of the equator.
Putting everything together, what are the general global pressures in July?
Low-High latitude pressure gradient decreases. sub tropical high pressure systems expand. weaker low pressures displaced northwards, continents dominated more by low pressure systems. SH is much less complicated,
What are the seasonal implications on variability and strength of atmospheric circulation?
The hemisphere experiencing summer has less of a temperature gradient between the tropics and the poles. Basically larger difference between the ITCZ and poles, this weakens the strength of the atmospheric circulation. Opposite is true for the winter.
When are the wet months for Asian monsoon season?
June-July
Does atmospheric circulation account for all the energy that needs to be redistributed to maintain the golbal energy balance?
NO
Describe local wind circulations.
During the day, land and ocean heat up differently. By afternoon, land is warmer than the ocean as it has a lower thermal heat capacity. Warm air rises creating low pressure. A local pressure gradient sets up and air moves from H to L resulting in a sea breeze. At night, land cools down faster than ocean, reversing the pressure gradient. wind blows off shore, resulting in land breeze.
Describe valley winds or breezes during the day.
During the day the air close to the mountainsides becomes warmer than the surrounding air, thus lowering pressure relative to the cooler air at the same height over the valley. this warm air rises up the mountain sides. His process leads to clouds and rain in the mountains in the summer, particularly in the late afternoon.
Describe mountain winds or breezes during the night.
At night the sides of the mountain cool down and cool air is pulled down by gravity. In the morning, the coldest air is therefore often found within the valley-capped with valley cloud related to a temperature inversion.
What happens when air encounters a mountain range?
It rises, cools and drops moisture on the windward slopes resulting in a precipitation distribution called rain shadow where the leeward slopes are dry.
What symbol represents cold front?
Triangles
What symbol represents warm front?
semi circles
What is an occluded front?
When a cold front overtakes a warm front
What symbol represents an occluded front?
Triangles and semi circles
(L3)
What is ENSO?
A coupled interaction between ocean and atmosphere causing periodical variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean affecting much of the tropics and subtropics
Where is the heat engine of the world and how is heat distributed?
Heat is redistributed from the heat engine (the tropics) and atmospheric circulation redistributes the heat to valance surplus
What inspired Led Gilbert Walker to study pressure oscilations between Northern Australia and the Central Pacific?
1899 failure of Indian Monsoon
What did he call Pressure Osciliations in this region?
Southern Oscilation
What are the two phases of ENSO?
Warm: El Nino
Cold: La Nino
How long do each last?
El-Nino- 12-18months
La-Nino - last from 1-3 years
Explain the La Nino Cool phase.
Strong easternly winds induce upwelling of cool water in the East Pacific (due to upwelling). Warm currents pushed westwards and a deep thermocline creates Low pressure and convection in west and high pressure and subsidence (clear air) in east.
Explain El Nino warm phase.
Weak Easterly winds result in less upwelling of cold water. Warm currents spread to east Pacific and increase of the East Thermocline. Low pressure and convection shifts to the east and High pressure and subsidence shift to the west.
Which parts of the US become warmer because of El Nino?
The Northern States.
Which parts of the US become drier because of El Nino?
The Eastern States.
Which parts of the US becomes wetter because of El Nino?
West and South.
What is SST?
Sea Surface Temperature
What are El Nino Instrumental Observations based on?
Observed SST anomalies in the equatorial Pacific in four regions and surface pressure differences between Tahiti and Darwin called the Southern Osciliation Index.
What is Nini 1 + 2 associated with?
Region that often warms during the onset of El Nino.
What is Nino 3 associated with?
Largest variability in sea surface temperatures over an average ENSO.
What is Nino 3.4 associated with?
Most highly correlated with eastern shift of convection.
What is Nino 4 associated with?
Most highly correlated with global weather patterns.
Which number is SIO most highly correlated with?
3.4
Describe the different ways to measure central tendancy.
Normal distribution -> mean= median= mode
Skewed Data -> Negative skew- mode>median>mean
How can we measure dispersion?
Standard deviation, interquartile range and range.
What value is r when there is a strong correlation between x and y?
Near -1 or 1
