last info of midterm (after quiz 2) Flashcards
At what altitude do clouds form?
- three concepts related to stability/instability
- Three more concepts related to stability/instability
- Convective Condensation Level
- Level of Free Convection
- Equilibrium Level
convection condensation level (ccl)
The convective condensation level (CCL) is the height to which a parcel of air rises
until it is just saturated.
Usually, it is the height of the base of cumuliform clouds produced by thermal
convection caused solely by surface heating
Level of Free Convection
(LFC)
The level of free convection (LFC) is the height at which a
parcel of air, when lifted, becomes warmer than its surroundings and thus convectively buoyant.
The parcel is lifted dry-adiabatically until saturated (at the LCL) and then moist-adiabatically thereafter
Equilibrium Level (EL)
The equilibrium level (EL) is the height where the temperature of a
buoyantly rising parcel again equals the temperature of the environment.
Top of clouds
What moves, stops and deflects air?
- Pressure gradient force - generated by differential heating
→ horizontal
→ vertical - Friction
- Coriolis effect
what makes stuff move?
forces
force
In physics, a force is an influence that
can cause an object to change its velocity, i.e., to accelerate, meaning a change in speed or direction, unless counterbalanced by other forces. The concept of force makes the everyday notion of pushing or pulling mathematically precise
pressure
(symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that
force is distributed
Our present
day
understanding
of forces was
developed by
Isaac Newton
- They work!
- They represent mankind’s first great success at
describing diverse aspects of nature with simple
mathematical formulas. - They form the most intuitively appealing physical
theory. - They lay the groundwork for later physics developments.
- They tie into almost everything we see in everyday life. These laws tell us exactly how things move or sit still,
like why you don’t float out of bed or fall through the
floor of your house
Newton’s Laws
Three physical laws that describe the relationship between the motion of an object and the forces acting on it
1. A body remains at rest, or in motion at a constant speed in a straight line, except insofar as it is acted upon by a force
2. At any instant of time, the net force on a body is equal to the body’s acceleration multiplied by its mass or, equivalently, the rate at which the body’s momentum is changing with time.
3. If two bodies exert forces on each other, these forces have the same magnitude but opposite directions
Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy)
- The Principia is considered one of the most important works in the history of science
- The French mathematical physicist Alexis Clairaut assessed it in 1747: “The famous book of Mathematical Principles of Natural Philosophy marked the epoch of a great revolution in physics. The method followed by its illustrious author Sir Newton … spread the light of mathematics on a science which up to then had remained in the darkness of conjectures and hypotheses”
- The french scientist Joseph-Louis Lagrange described it as “the greatest production of the human mind”
- French polymath Pierre-Simon Laplace stated that “The Principia is pre-eminent above any other production of human genius”
- Newton’s work has also been called the “the greatest scientific work in history”, and “the supreme expression in human thought of the mind’s ability to hold the universe fixed as an object of contemplation”.
when were newtons laws first stated
The three laws of motion were first stated by Isaac Newton in his Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), originally published in 1687
Pressure-gradient force
The force that results when there is a difference in pressure between two locations
Two columns of air. Both have the same amount of mass above them at the surface. Both have the same surface pressure. Which column will be taller, the hotter or the colder?
Hotter because it is lower density (fills a bigger volume with same mass)
At some high altitude, say 10 km, which column will have higher pressure?
The hotter, taller one, because there is more mass above 10 km
Which direction does air pressure push air at 10 km?
From hotter (higher pressure at 10km) towards cooler (lower pressure at 10km)
How does this forcing and movement affect pressure at the surface?
It adds mass toward the location without heating and raises pressure. This raises surface pressure in cold column and creates a surface pressure gradient force
Atmospheric Convection Cell
Warm air rises at the equator. As it rises, it cools and generates large amounts of precipitation. Air cools as it moves away from the equator. At about 30 degrees north or south the dense air falls toward Earth’s surface. As it does, it warms and tends to reduce precipitation. Once this air reaches the surface, pressure differences cause air to move along the surface toward the equator.
Isobar
*an imaginary line or a line on a map or chart connecting or
marking places of equal
barometric pressure
- Pressure gradient force always perpendicular to isobars
heat transfer
Conduction: transfer of energy between adjacent molecules
Convection: movement of hot fluid
Radiation: emission of electromagnetic rays
ASIDE: Conduction and Convection in Atmosphere
Air in the lower atmosphere is heated from the ground upward
Coriolis Effect
- The Coriolis effect describes the pattern
of deflection taken by objects not firmly
connected to the ground as they travel long
distances around Earth. - The Coriolis effect is responsible for many
large-scale weather patterns.
Coriolis Force (CF)
Key points about the Coriolis Effect (aka Force; aka Acceleration) Magic Rules
- Apparent deflection due to rotation of the Earth.
- Right in northern hemisphere and left in southern
hemisphere. - It would not exist if the wind were not already
blowing - Only influences direction, not speed.
- Only has significant impact over long distances.
is there a coriolis effect at the equator
no
→ the horizontal coriolis effect is biggest at the north pole and south but it decreases with magnitude so that at the equator there is no coriolis effect
Can you explain why the Coriolis Effect is strongest at the poles and zero at the equator?
The Coriolis Effect is strongest at the poles and zero at the equator because, like on a carousel, the rotational speed is much greater near the outer edge (equator) compared to the center (poles), meaning any object moving on the Earth’s surface will experience a greater apparent deflection as it moves closer to the poles where the rotational speed is significantly slower; essentially, the object “appears” to curve more due to the difference in rotational speed between its starting point and its destination
Wind: a balance between pressure gradient force and Coriolis Effect
- where does wind tend to blow
- what is this called
- the result is that wind tends to blow along isobars (lines of constant pressure)
–> this is called the the Geostrophic Balance
Coriolis Effect on Weather Patterns
- Meteorology and oceanography
- Storms develop into cyclones: the Coriolis force deflects air parcels moving toward a center of lower pressure and causes them to swirl around the center of low pressure
- Induced rotation is clockwise in southern hemisphere and counterclockwise in northern hemisphere
How to find high and low pressure center outdoors
- Face into the wind.
- Hold your arms out from the side of your body.
- Your left hand points to the
center of High pressure. - Your right hand points to the center
of Low pressure.
* Not so much for the Seattle area
Forces that Affect Atmospheric Motion
- Newton’s second law of motion states that the rate of change of momentum (i.e, the acceleration) of an object, as measured relative to coordinates fixed in space, equals the sum of all the forces acting.
- For atmospheric motions of meteorological interest, the forces that are of primary concern are the pressure gradient force, the gravitational force, and friction. These are the FUNDAMENTAL forces.
- For a coordinate system rotating with the Earth, Newton’s second law may still be applied provided that an apparent force, the Coriolis force, is included among the forces acting
Pressure Gradient Force
- PG = (pressure difference) / distance
- Pressure gradient force goes from high pressure to low pressure
- Closely spaced isobars on a weather map indicate steep pressure gradient
Examples of pressure gradient
Hurricane Andrew 1992
Extratopical cyclone
Pressure Gradients
- pressure gradients
- horizontal pressure gradient
- vertical pressure gradient
- Pressure Gradients
– The pressure gradient force initiates movement of atmospheric
mass, wind, from areas of higher to areas of lower pressure - Horizontal Pressure Gradients
– Typically only small gradients exist across large spatial scales
(1mb/100km)
– Smaller scale weather features, such as hurricanes and tornadoes,
display larger pressure gradients across small areas (1mb/6km) - Vertical Pressure Gradients
– Average vertical pressure gradients are usually greater than
extreme examples of horizontal pressure gradients as pressure
always decreases with altitude (1mb/10m)
Gravitational force
Newton’s law of universal gravitation states that any two elements of mass in the universe attract each other with a force proportional to their masses and inversely proportional to the square of the distance separating them
Frictional Force (what slows air)
- Frictional force (drag) is strongest near the Earth’s surface and decreases rapidly with height
- The atmospheric layer in which frictional force is important is called the boundary layer, whose depth can vary from a few hundred meters to a few thousand meters
- There are three sources to generate turbulence eddies to give rise to the frictional force: (1) mechanical turbulence (airs encounter surface roughness), (2) thermal turbulence (air near Earth’s surface get heated) and (3) wind-shear induced turbulence
→ most turbulence near Earth’s surface
What is the driving force for atmospheric motion?
The sun
→ and the uneven distribution of solar radiation across the earth
how is solar energy distributed over Earth?
- Solar energy is not
distributed evenly over
the earth - Each beam transfers
the same amount
of energy from the
sun. The northern
beam is spread out
over a larger area
Why don’t the poles get colder and the tropics hotter and hotter?
The circulation of the atmosphere and ocean. The atmosphere brings warm air to the poles, circulation of the atmosphere which is driven by the uneven heating keeps us in balance.
what are atmospheric and ocean circulation examples
Atmospheric and ocean circulation are examples of
convection that transport heat from low to high latitudes
convection cell plus Coriolis effect: How will air flowing back towards the equator in the Hadley Cell be deflected?
→ in the northern hemisphere (NH) to the right which is west
→ in the southern hemisphere (SH) to the left which is also west
Hadley Cell: connective cell driven by temperature
- Sinking air in subtropics
- Rising air near the equator
Hadley Cell: thermally driven convection cell
- Sinking air in subtropics
→ dry air - Over equator: warm humid air rises, condense into cumulus clouds, lots of thunderstorms and large release of latent heat that provides the energy to drive the Hadley Cell
- NOTE: Winds are described based on direct from which they flow
- Because the earth is rotating, the Coriolis force deflects the equatorward winds: wind blows from northeast NH and from southwest SH - these are the tradewinds.
trade winds
- The trade winds or easterlies are permanent east-to-west prevailing winds that flow in the Earth’s equatorial region.
- The trade winds blow mainly from the northeast in the Northern Hemisphere (north-easterly) and from the southeast (south-easterly)
in the Southern Hemisphere, strengthening during the winter
Word Origin: Trade Winds
- The term originally derives from the early fourteenth century sense of trade (in late
Middle English) still often meaning “path” or “track”. - The Portuguese recognized the importance of the trade winds (then the volta do
mar, meaning in Portuguese “turn of the sea” but also “return from the sea”) in
navigation in both the north and south Atlantic Ocean as early as the 15th century. - The captain of a sailing ship seeks a course along which the winds can be expected
to blow in the direction of travel. - By the 18th century, the importance of the trade winds to England’s merchant fleet
for crossing the Atlantic Ocean had led both the general public and etymologists to
identify the name with a later meaning of “trade”: “(foreign) commerce”.
ITCZ
- area where ___
- encircles where
- appears as
- location of ITCZ
*The Intertropical Convergence Zone (ITCZ) known by sailors as the doldrums or the calms because of its
monotonous windless weather,
*Area where the northeast and the southeast trade winds converge.
*Encircles Earth near the thermal equator though its specific position varies seasonally.
*The ITCZ appears as a band of clouds, usually thunderstorms, that encircle the globe near the Equator.
*The location of the ITCZ gradually varies with the seasons, roughly corresponding with the location of the thermal equator
Polar Cell
- The polar cell is a simple system with strong convection drivers.
- Though cool and dry relative to equatorial air, the air masses at the 60th parallel are still sufficiently
warm and moist to undergo convection and drive a thermal loop.
Ferrel cell - Mid-latitudes
- existence depends on
- thought of as
- why is the ferrel cell weak?
- weather in mid-latitudes is …
- A secondary circulation feature, whose existence depends upon the Hadley and polar cells on either side of it
- Thought of as an eddy created by the Hadley and polar cells
- The ferrel cell is weak, because it has neither a strong source of heat nor a strong sink
- The airflow and temperatures within it are much more variable than in the Hadley and polar cells
→ For this reason, the mid-latitudes are sometimes known as the “zone of mixing” - Weather in mid-latitudes is variable and dominated by moving low and high pressure systems
Mid-latitude air flow and heat transport is dominated by what
storms
Why do we care about highs and lows?
- Low-pressure areas are commonly associated with inclement weather,
extratropical storms (such as cloudy, windy, with possible rain or storms) - High- pressure areas are associated with lighter winds and clear skies
- Winds circle anti-clockwise around lows in the northern hemisphere
- Clockwise in southern hemisphere
Recall what is and what causes high and low pressure systems
- convergence zone
- divergence zone
- Convergence Zone: region where flows meet
- Divergence Zone: a region in the atmosphere where flows cause mass to decrease
Main Points to Learn
- extratropical cyclones develop as a direct result of
- force imbalances are associated with (3)
- what ultimately destroys extratropical cyclones
Extratropical cyclones (i.e., low-pressure systems) develop as a direct result of acceleration created by force imbalances
These force imbalances are associated with:
1. Curved flow in jet stream
2. Jet Streaks
3. Heating and Cooling
* Frictional force in the boundary layer ultimately
destroys extratropical cyclones
Jetstream
- describe
- band of strongest winds is typically how many km wide and can extend where
- jetstreams typically follow what kind of pattern
- the fastest jetstreams
- The jetstream is a narrow band of strong winds that encircles the Earth in the mid-latitude
- The band of strongest winds is typically 300 to 500 km wide and can extend from near the tropopause to about 500mb
- The jetstream typically follows a wavelike pattern
- The fastest jet streams are the Polar Front Jet, commonly known as the Polar and the Subtropical Jet (STJ), which flow from west to east
Jet streak - Region of locally strong pressure gradient
Notice how isobars get closer together
Wind Barb
Wind barbs are symbols on the map that show wind direction and speed at some specified location
→ more barbs mean higher wind speed
→ each barb represents a certain number of knots so the more barbs there are, the stronger the wind is blowing
Newton’s First and Second Laws (paraphrased)
- A body remains at rest, or in motion at a constant speed in a straight line, unless acted upon by a force
- The net force on a body causes a body’s velocity (speed and/or direction) to change
What Newton was like
- Newton wasn’t initially a good student and apparently was a bit problematic to his family
- Newton had written in his college notebooks about himself, “Making pies on Sunday night… punching my sister… threatening my Father and Mother Smith to burn them and the house over them.”
Recall Geostrophic Wind
- define
- from newtons laws the wind would flow along….
- real winds
- The theoretical wind that would result from an exact balance between the Coriolis force and the pressure gradient force
- From Newton this wind would flow along straight parallel isobars
- Real wind tends to deviate from geostrophy
Gradient Wind
- gradient wind accounts for
- it is an extension of ___
- do geostrophic wind or gradient wind better represent the actual wind better
- Gradient wind, wind accounts for air flow along a
curved trajectory. - It is an extension of the concept of geostrophic wind—
i.e., the wind assumed to move along straight and
parallel isobars (lines of equal pressure). - The gradient wind represents the actual wind better than does the geostrophic wind, especially when the wind speed and trajectory curvature are large, as they are in hurricanes and jet streams
Why would trade winds flow east to west?
Coriolis effect in the southern hemisphere will move things to the left, trade winds that is coupling the circulation with the coriolis effect
atmospheric pressure
weight of air above a unit area
weather front
A weather front is a transition zone between two different air masses at the Earth’s surface. Each air mass has unique temperature and humidity characteristics
Weather Fronts Between Air Masses
- Cold Front: cold air moves in displacing warm moist air upward (tunderheads)
- Warm Front: warm moist air rides over denser cold air (grey skies)
warm fronts
- how it forms
- associated weather
How it forms
- A warm front is the leading edge of a warm air mass that is replacing a cool air mass. Moisture in the warm air mass condenses as it moves up and over the denser cool air mass
Associated Weather
- Cloudy skies and light rain with warmer temperatures
cold front
- When a cold air mass pushes into and under a warm air mass
- Heavy downpours, gusty winds, and cooler temperatures
- On hot summer days causes thunderstorms, followed by lower temperatures and humidity
question on the midterm: What direction is the pressure gradient force
always high to low, and always at right angle to isobar
- coriolis in northern hemisphere is already to the right of the wind
fronts
Fronts are the boundaries between
different air masses, usually air
masses of different temperatures
geostrophic wind pt 2
- gradient wind around a low in nh
- gradient wind around a high in nh
- A gradient wind, around a low in the Northern hemisphere, has a lower speed than a geostrophic wind. It is sub-geostrophic
- A gradient wind, around a high in the Northern hemisphere, has a higher speed than a geostrophic wind. It is super-geostrophic.
gradient wind balance
- what happens near trough and ridge
- Near a trough, wind slows as as centrifugal force adds to coriolis
- Near a ridge, wind speeds up as centrifugal force opposed coriolis
fronts military definiton
- In a military context, the term front can have several meanings
- According to official US Department of Defense and NATO definitions, a front can be “the line of contact of two opposing forces”
weather front
A weather front is a transition zone between two different air masses at the Earth’s surface. Each air mass has unique temperature and humidity characteristics
weather fronts between air masses
- Cold Front: cold air moves in displacing warm moist air upward (tunderheads)
- Warm Front: warm moist air rides over denser cold air (grey skies)
weather front history
- In 1919, Jacon Bjerknes, son of a noted Norwegian meteorologist, Vilhelm Bjerknes, announced his discovery of air masses and fronts
- Prior to that, it was thought that if today happened to be colder, it was simply yesterday’s air with some heat that was lost to space
- Or if today turned out to be warmer, then it was assumed that it was yesterday’s air with some heat added in
- But Bjerknes realized that there were masses of colder and warmer air that swept across the globe and bumped into each other and in the process produced zones of unsettled weather near and along their respective boundaries
many fronts cause
Many fronts cause weather events such as rain, thunderstorms, gusty winds, and tornados
air mass
- volume of air defined as
- adapt to
- classified according to
- Volume of air defined by its temperature and humidity. Air masses cover many hundreds or thousands of square miles
- Adapt to the characteristics of the surface below them
-Classified according to latitude and their continental or maritime source regions
mT: maritime tropical
mP: maritime polar
cT: continental tropical
cP: continental polar → dry
cA: continental arctic
warm fronts
- how it forms
- associated weather
- How it forms
A warm front is the leading edge of a warm air mass that is replacing a cool air mass. Moisture in the warm air mass condenses as it moves up and over the denser cool air mass - Associated Weather
Cloudy skies and light rain with warmer temperatures
cold front
- When a cold air mass pushes into and under a warm air mass
- Heavy downpours, gusty winds, and cooler temperatures
- On hot summer days - causes thunderstorms, followed by lower temperatures and humidity
main points to learn
- extratropical cyclones develop as a direct result of
- frictional force does what
- Because extratropical cyclones are the parent storms for many hazardous weather, it is essential to understand how they are created and demised
- Extratropical cyclones (i.e. low pressure systems) develop as a direct result of acceleration created by the imbalance between the pressure gradient force and the coriolis effect
- Frictional force in the boundary layer ultimately destroys extratropical cyclones
what is a trough?
- An elongated region of relatively low atmospheric pressure (without a closed isobaric contour that would define it as a low pressure area)
- Low pressure implies a low height on a pressure surface
what is a ridge?
- An elongated area of relatively high atmospheric pressure compared to the surrounding environment, without being a closed circulation
- High pressure implies a high height on a pressure surface
- Troughs and ridges refer to features in an identical sense as those on a topographic map
Upper tropospheric flow pattern
- upper tropospheric flows are characterized by…
- winds
- convergence and divergence
- Upper tropospheric flows are characterized by trough (low pressure; isobars dip southward) and ridge (high pressure; isobars bulge northward)
- The winds are in gradient wind balance at the bases of the trough and ridge and are slower and faster, respectively, than the geostrophic winds
- Therefore, convergence and divergence are created at different parts of the flow patterns, which contribute to the development of the low and high systems
jet streaks
- entrance (exit) region of jet streak
- A portion of the overall jet stream where winds along the jet core flow are stronger than in other areas along the jet stream
- The entrance (exit) region of a jet streak is where winds are accelerating into the back/upstream (decelerating out of the front/downstream) side of the streak
convergence/divergence in jet streak
- PGF increases what
- PGF chances leads to
- the CF leads to
- The pressure gradient force (PGF) increases in the jet streak (isobars closer together)
- The PGF change leads to Coriolis Force (CF) in the entrance to the jet streak. This causes flow to the north and convergence (divergence) to the north (south) of the jet streak at the entrance
- The CF leads the PGF at the exit of the jet streak. This causes flow to the south and divergence (convergence) to the north (south) of the jet streak exit
