Midterm Flashcards
Hurricane Florence
category 4 hurricane
2018 - august 31 to september 19
winds up to 140mph
lowest pressure 939 mb
What is the difference between weather and climate?
Weather refers to the short-term phenomena.
Climate refers to the long-term patterns.
What is the atmosphere composed of?
mixture of gas molecules, small suspended particles of solid and liquid, and falling precipitation
What did we learn from dropping the two paper balls in class?
If gravity were the only force, large and small drops would fall at the same speed.
But in reality we also have a frictional force acting due to air resistance, which causes mass (and shape) to affect the outcome.
What falls faster: larger water drops or smaller? Why?
Larger because of air resistance
Early inventions to measure weather (4)
Anemometer (wind speed) in 1450 by Leone Alberti
Hygrometer (air humidity) ~ 1450 by Nicholas of Cusa
Thermometer (air temperature) in 1593 by Galileo Galilei
Barometer (air pressure) in 1643 by Evangelista Torricelli
What invention marks the start of meteorology for modern times?
1847 - First “network” of surface weather stations with the goal of studying spatial patterns in weather phenomena more or less simultaneously to the establishment of the telegraph allowing rapid transmission of data
What are radiosondes?
unmanned air balloons in 1920
used to take measurements in the upper atmosphere
What did Lewis Richardson do?
in 1922 had the idea of solving the equations for meteorology using numerical methods
several months to produce a wildly inaccurate six-hour forecast for an area near Munich, Germany.
estimated that 64,000 human calculators were needed to keep pace with weather developments
Who is Charlie Howler?
Meteorologist during WWII
Very few data points– quote about elephant standing behind the barn and you can only see its tail and you’ve never seen an elephant before
3 modern meteorology inventions
First electronic computer developed by von Neumann in the 1940’s
First successful “Numerical weather predictions” lead by Jules Charney in 1950
First weather satellite in 1960
Development of climate predication
1950-1960: numerical techniques were applied to the problem of predicting atmospheric motion (i.e., weather prediction).
1960-1970: weather prediction models were adapted for climate purposes, but they still only contained atmospheric components.
1970’s: numerical techniques applied to oceanic motion.
1970-1980: modules were built to exchange information between atmosphere and ocean models.
These “coupled” models were the first true global climate models (GCMs), because they allowed for simulation of essential climate phenomena such as ENSO.
2000’s: biogeochemical components were embedded within GCMs, enabling simulations of the carbon cycle.
Equation for density
Density (r) = mass (kg)/ volume (m^3)
Another name for the average distance a molecule travels before colliding with another molecule is
Density
The density of near surface air is approximately ____
1kg/m^3
Temperature is directly proportional to
Kinetic energy
How many molecules in the food container and how fast ar they moving?
10,000 billion billion, moving 1000 mph
equation for pressure
p = F/A
pressure = force / area
pressure is typically measured in
pascals
what does pressure result from?
the force caused by colliding molecules
what happens to the pressure of a gas if we increase the density?
causes more collisions
pressure increases
pressure is proportional to density
Suppose that instead we keep the density constant and increase the temperature of the gas. What happens to the pressure of the gas?
causes stronger collisions because molecules are moving faster
pressure increases as we increase the temperature
pressure is proportional to temperature
Use the ideal gas law to explain how hot air rises
If we are keeping the pressure constant, having a higher temp means that the density must be lower and therefore will rise
How much does pressure decrease by altitude?
about 50% every 5km
Suppose you are at a location where the sea-level pressure is lower than the surface pressure. Where are you?
Possibly in the Death Valley, because it is located below the sea level
4 thermal layers of the atmosphere
troposphere
stratosphere
mesosphere
thermosphere
which is the layer where virtually all weather takes place?
troposphere
which is the coldest layer of the atmosphere?
the mesosphere
the top of the troposphere is called the _______
tropopause
which layer of the atmosphere contains the ozone layer?
stratosphere
Which layer has a very low density, almost no mass
Thermosphere
Three processes of heat transfer and examples
Conduction (ground heats the air)
Convection (warm air rises)
Radiation (sun heats the ground)
Definition and characteristics of radiation
Definition: transfer of energy by electromagnetic waves
- continually emitted by all substances
- requires no physical medium (can occur through empty space)
Definition of conduction
transfer of energy between objects that are in physical contact
convection
transfer of energy between an object and its environment, due to fluid motion
why are clouds patchy?
zones of rising air next to zones of sinking air
what is the relationship between PGF and isobar spacing?
inversely proportional
the greater the isobar spacing, the lower the PGF
PGF equation
pressure difference/ distance
The pressure gradient force forms an angle of _____ with the isobars, pointing in the direction of ______ pressure
90 degrees, lower
What is hydrostatic balance?
vertical PGF in balance with gravitational force
describe the relationship between PGF and gravity that results in downdrafts
pressure gradient force is weaker than the force of gravity, when PGF is greater, this causes updrafts
what effect does heating an air column have on density and pressure?
pressure stays the same, density diminishes because the air has to expand
why would a hot air column next to a colder one cause PGF?
due to the fact that the warmer air column expands from higher temp, there is a point of higher pressure along side colder pressure on the shorter column
constant pressure surfaces of cooler air will be ____ in altitude than those of warmer air
lower
Height contours run ____ to the pressure gradient
perpendicular
two other forces that effect winds besides PGF
Coriolis
Frictional force
Coriolis deflects objects to the _____ in the northern hemisphere and the _____ in the southern
Right, left
How does conservation of angular momentum explain Coriolis?
When mass moves closer to the axis of rotation, the angular velocity increase to conserve angular momentum
because of this, the Coriolis force is stronger near the poles and 0 at the equator
Coriolis force increases with an increase in speed
Coriolis only changes direction of a object, not its speed
Definition of friction
Until what altitude is it relevant?
force of opposition that slows air in motion
- Initiated at the surface.
- Important for air within 1.5 km (1 mi) of the surface (the planetary boundary layer), and negligible aloft (the free atmosphere).
- Friction reduces wind
speed, so it also
reduces Coriolis force.
An airplane is flying forward at constant speed. At a given moment the forces acting on the airplane are such that Thrust is balanced by Air Friction, but Lift is smaller than the Weight. How is the airplane motion going to respond?
Airplane will continue moving forward at the same speed, but will accelerate downward
what causes PGF
differential heating at the poles
True or False: Warmer atmosphere is deeper
True
How does friction affect wind direction?
What about when there is no friction in the upper atmosphere?
Friction decreases the Coriolis force so that it is no longer in balance with PGF and so winds cross the isobars.
When there is no friction, winds are in geostrophic balance in the upper atmosphere. (gradient flow)
evaporation rate is proportional to
the temperature of the liquid
condensation rate is proportional to
the “amount of water vapor”
does evaporation rate change over time?
no it depends only on temperature
does condensation rate change over time?
condensation rate increases as number of molecules in the vapor form increase
what is saturation?
when evaporation rate = condensation rate
another word for amount of water vapor in the air
humidity
two ways to meaure humidity
vapor pressure & mixing ratio
vapor pressure
the portion of atmospheric pressure exerted by water vapor molecules
mixing ratio
mass of water vapor in a unit mass of dry air (g/kg)
If we raise the temperature, what happens to the saturation vapor pressure?
- Evaporation rate increases
- Need higher “humidity” for condensation rate to match evaporation rate
Therefore, saturation vapor pressure increases!
why cant relative humidity be used to compare humidity of two different locations?
it is temperature dependent, somewhere with a higher temp seems to have much less humidity just because its saturation vapor pressure is higher
(RH= Vapor pressure/saturation vapor pressure)
highest relative humidity occurs during what part of the day?
morning, coolest times of the day
dew point temp definition
temp at which air must be cooled to reach saturation (without changing pressure)
Processes that cause saturation (3)
- The addition of water vapor
- Cooling the air to dew point (most clouds)
- Mixing cold air with warm moist air
what conditions are necessary in order for homogeneous nucleation to occur? Why?
requires supersaturation, relative humidity of 400%
The curvature of the molecule
What happens during heterogeneous nucleation?
water vapor molecules adhere to a solid surface (hygroscopic aerosols) on a condensation nucleus (cloud condensation nuclei AKA CCN)
what makes ice molecules so rare in the atmosphere? Examples of nuclei?
They have to have a six sided structure for the molecules to bond to
examples: Clay, ice fragments, bacteria
at what temperature do ice nuclei become active?
below -4 degrees
Definition of diabetic processes
changes in temp caused by heat transfer into or out of parcel
Adiabatic processes
changes in temp caused by expansion or contraction due to changes in pressure (no heat transfer)
Explain adiabatic change in temp with the ideal gas law
we suppose that pressure is constant, so if air parcel expands it means that density decreases and that means temp must increase even if no heat is added
keep in mind the case is different when warm air rises, expands and cools because in that case the pressure is changing too
DALR vs SALR
10 degrees celsius/km vs 5 degrees celsius/km
why? Condensation releases latent heat
explain how the santa ana winds form
high pressure system over the great basin, air that flows down is warmed by adiabatic compression
temp increases reduce RH (by increasing saturation vapor pressure)
Mechanisms that lift air (4)
- Orographic lifting
- Frontal lifting
- Surface convergence
- Convection
How does dew form?
surface air becomes saturated and condensation forms on objects acting as condensation muclei
How does frost form?
surface-air saturated when surface temps are below freezing (deposition occurs)
What is another name for frozen dew?
Black ice
What is fog and how does it form?
Surface cloud, 3 ways it happens: when air cools to the dew point, has moisture added, or when cooler air is mixed with warmer moist air
What type of fog occurs in san Francisco?
Advection fog, which occurs when warm humid air from the ocean runs over cooler sea and ground surface air
why does warm air rise?
because it is less dense than the surrounding air
how do we explain the fact that warm air rises with the idea gas law?
if pressure in an air parcel is equal to its environment, that means if it has a higher temperature, the density must be lower
What are the three states of equilibrium for buoyancy?
stable “it goes back”
indifferent or neutral “it stays”
unstable equilibrium “it moves away”
what is an inversion? how do they correct unstable equilibrium?
When air becomes warmer as you go up in altitude. In the stratosphere, the temp rises with altitude, so even warm parcels whose temp exceepds the ELR are met with higher temps in the stratosphere.
which changes when you go to the moon, kilograms or pounds?
Pounds because Weight is affected by gravity whereas kilograms are just a measure of mass
due to the __________ of air, there is MORE or LESS atmospheric mass at lower altitudes?
compressibility, more
At sea level, air density is about
1.2kg/m3
in the US, pressure is measured in ______
millibars
At sea level, air pressure is about
Sea level pressure is 1013 mb
At higher altitudes, you have to travel farther or less far to experience the same pressure change ?
Pressure falls rapidly near the surface and more slowly up higher
Pressure falls by ___ for every ___ of altitude
50%, 5kg
The troposphere contains ____% of the mass of the atmosphere
85%
Where does the troposphere end?
Depends on the average temp
Warming a pot of water is an example of which type of heat transfer?
Convection
True or false: The atmosphere can undergo forced convection in the absence of buoyancy
true, thanks to the wind
Major changes in temp over short distance is often due to the presence of ____
fronts, represented by blue and red banners on map
What are atmospheric rivers?
Atmospheric rivers are relatively narrow regions in the atmosphere that are responsible for transporting large amounts of water vapor over long distances
In class we looked at satellite measurements of atmospheric humidity (water vapor)
Rising or falling air and clouds in the low-pressure regions (associated with weather in general)
High-pressure areas correlate to rising or falling and clear skies
rising in low pressure, falling in high pressure
Vertical vs horizontal pressure gradients
Pressure gradients are generally small, about 5% difference in pressure for inside of a hurricane vs outside the storm
Vertical pressure gradients:
On average 600 times greater than the extreme horizontal pressure gradient associated with a hurricane
difference in pressure between isobars
4mb
What has a greater effect on vapor pressure: density change or temp change?
Temp influences are smaller than density changes, vapor pressure follows changes in density or abundance of molecules rather than temp
PGF equation
PGF = difference in pressure /(divided by) distance (between isobars)
vertical velocities much smaller than the horizontal velocities. How is this so?
Vertical PGF is in balance with gravity
Balance between the vertical PGF and the gravitational force: hydrostatic balance
Clouds are formed by ________ processes while fog is formed by ________
adiabatic, diabatic
lifting condensation level
Altitude at which condensation happens because air parcel rises high enough and cools sufficiently (because expansion lowers its temp to the dew or frost point)
Radiation fog vs Advection fog
Radiation Fog: when the nighttime loss of longwave radiation causes cooling to the dew point
Advection fog: when warm, moist air moves horizontally over a cooler surface (warmer air flows from a region of warmer water over a cold ocean current like in San Francisco)
true or false: For curved water surfaces, the evaporation rate is lower?
false, the evaporation rate is greater
Highly curved droplets of pure water require relative humidities in excess of 100% to keep them from being evaporated away
What are 4 mechanisms that lift air to create clouds?
- orographic lifting
- frontal lifting
- convergence
- localized convective lifting due to buoyancy
Explain orographic uplift
forcing air above a mountain barrier
Upward displacement of air leads to adiabatic cooling and possible cloud formation
On the other side of the mountain, air descends the slope and warms by compression to create a rainshadow (area of lower precipitation)
explain frontal lifting
displacement of one air mass over another
Usually temperature changes are gradual
However, there are also fronts– transitional zones where great temperature differences occur across relatively short distances
Not like vertical walls, instead, slope gently
Airflow along fronts causes clouds to form in two ways:
Cold front: Cold air advances toward warmer air and the denser air displaces the lighter warm air ahead of it
Warm front: warm air is forces upward in the same way that the orographic effet causes air to rise above a mountain barrier
explain convergence
low level winds flow toward a location from multiple directions
Has to due with pressure differences
Horizontal convergence: Low pressure cell near the surface, winds in lower atmosphere converge on the center of the low from all directions, air rises and creates clouds through adiabatic cooling
explain localized convection
lifting due to buoyancy
Lifting that results from heating air near the surface
Creates updrafts strong enough to form clouds and precipitation
Effect of buoyancy: can speed or slow the uplift begun by the orographic effect, frontal lifting and convergence
