Flashcards in Week 1 through Week 4 Deck (112):
what is the atmosphere?
mixture of gas molecules, small suspended particles of solid and liquid, and falling precipitation
what is the difference between climate and weather?
Weather refers to the short-term phenomena.
Meanwhile, climate refers to the long-term pattern.
Which way does air pressure go?
From high pressure centers to low pressure centers
In low pressure areas, what are there?
rising air and clouds
In high pressure areas, what are there?
sinking air and clear skies
what is density?
mass (kg) per unit volume (m3)
As altitude increases, what occurs to density.
As altitude increases, density decreases. This may be expressed in terms of the mean free path, or average distance a molecule travels before colliding with another molecule. Due to compressibility, atmospheric mass gradually “thins out” with height.
what occurs when molecules bounce around?
they have a velocity and kinetic energy associated with it.
KE= 1/2 * m * v^2
As kinetic energy increases, what does temperature do?
As kinetic energy increases, temperature increases. When the temperature is high, it just means that air molecules are moving slightly faster than usual!
What relationship do kinetic energy and temperature have?
what is pressure?
pressure is force divided by unit area
Which direction does pressure go in?
Molecules move in all directions, so pressure is exerted in all directions.
how is force produced?
the collision of molecules
What relationship do density and pressure have?
Suppose that instead we keep the density constant and increase the temperature of the gas. What happens to the pressure of the gas?
Pressure increases as we increase temperature
What happens if we increase the temperature of the gas?
Higher temperatures increase kinetic energy, and pressure results from the force cause by collisions of molecules with the surface. If we increase the temperature, there will be stronger collisions and higher pressure.
What relationship do pressure and temperature have?
What is the ideal gas law?
pressure= density* gas constant * temperature
If density decreases with height, what occurs w/ pressure at low elevations and higher elevations?
pressure decreases most rapidly at low elevations and gradually tapers off at greater altitudes
What is in the troposphere?
Layer of virtually all weather processes.
• Warmed at the surface by solar radiation.
• Steady temperature decrease with height.
• The top of the troposphere is called tropopause.
What is in the stratosphere?
What is in the mesosphere?
What is in the thermosphere?
low density, almost no mass
Name three ways in which energy/heat transfer can be transferred from one place to another.
Radiation, conduction, convection
•The transfer of energy by electromagnetic waves.
•Continually emitted by all substances.
•requires no physical medium (can occur through empty space).
example: the sun heats the ground
The transfer of energy between objects that are in physical contact.
Example: the ground heats the air
the transfer of energy between an object and its environment due to fluid motion
example: the warm air rises
PGF is related to:
Newton's second law which states acceleration implies action of a net force
What relationship to PGF have to distance between isobars?
PGF goes from high to low pressure
What is hydrostatic balance?
The balance between the vertical pressure gradient force and the gravitational force
What do local imbalances do (in relation to hydrostatic balance)?
Local imbalances create vertical motion
(updrafts and downdrafts)
In zones of sinking air, PGF is less than gravitational force. In zones of rising air, PGF is greater than gravitational force.
If you heat a column of air, what will occur?
the density will decrease because heating decreases density. the column contains the same amount of air, but has a lower density to compensate for its greater height.
"warmer atmosphere is deeper"
What can the height of isobaric surfaces show?
Constant pressure surfaces of cooler air will be lower in altitude than those of warmer air.
High heights of isobaric surfaces (e.g., 500-mb surface) correspond to ______ pressure on a nearby constant- height surface.
Is PGF the only force affecting the winds?
No, there are additional forces affecting winds.
How are winds initiated?
Once air is in motion, two additional forces come into play which are:
1. Coriolis force–Not a “real” force, but rather an effect due to observations made in a rotating reference frame
2. Frictional force-A force of opposition which slows air in motion
Explain the Coriolis force
1. The Coriolis force produces an apparent deflection of moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere
2. The Coriolis force is zero at the equator and increases with increasing latitude
3. The Coriolis force acting on any object increases with object’s speed
4. The Coriolis force changes only the direction of the object, not its speed
Explain frictional force
A force of opposition which 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.
Does friction only reduce wind speed or does it reduce wind speed and the coriolis force?
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 is PGF caused by?
PGF caused by differential heating of equator and poles
What is geostrophic balance?
PGF and Coriolis Force are in balance, so the wind does not change anymore!
Hydrostatic balance (in the vertical)
Geostrophic balance (in the horizontal)
Coriolis Force = PGF (also, there is wind pointing to the right and the wind is proportional to the coriolis force)
If wind is faster than geostrophic balance, what is it called?
If wind is slower than geostrophic balance, what is it called?
Upper level winds (no friction)
PGF=Coriolis (with wind going to the right)
Near-surface winds (with friction)
PGF > Coriolis
Friction goes to left, wind goes to right
What occurs to winds near the surface?
•Winds near the surface slow due to friction and therefore are not parallel to the isobars
• Coriolis deflection still occurs but it is reduced
• Winds cross the isobars directed into low pressure regions
What are cyclones?
•Low pressure centers (cyclones), have counterclockwise airflow in the Northern Hemisphere
•This occurs as air converges to the low pressure areas at the surface and is deflected by Coriolis force
What are anti-cyclones?
•High pressure centers (anticyclones), have clockwise airflow in the Northern Hemisphere
•This occurs as air diverges from the high pressure areas at the surface and is deflected by Coriolis force
What are troughs and ridges?
-In the upper atmosphere, low and high pressure systems occur as elongated areas called troughs (low pressure) and ridges (high pressure)
-Pressure is distributed as cyclones and anticyclones at the surface and gradually give way to ridges and troughs in the upper atmosphere
What is evaporation?
Molecules escape from liquid into the overlying volume as water vapor
Evaporation rate is proportional to the temperature of the liquid
What is the relationship between evaporation and the temperature of the liquid?
What is condensation?
Water vapor molecules randomly collide with the water surface and bond with adjacent molecules
What is the relationship between condensation and the amount of vapor?
When evaporation rate = condensation rate, the system is..
in a state of equilibrium called saturation
What is "amount of water vapor"?
What are several ways to quantify humidity?
vapor pressure, specific humidity, mixing ratio
What is vapor pressure?
pressure exerted on the atmopshere by water vapor molecules (mb)
what is specific humidity?
mass of water vapor in a unit mass of air (g/kg)
what is mixing ratio?
Mixing ratio: mass of water vapor in a unit mass of dry air (g/kg)
We know that evaporation rate increases with temperature. How does temperature affect vapor pressure at saturation?
Vapor pressure at saturation increases with increasing temperature
Considering that the rate of evaporation depends on temperature and the rate of condensation depends mostly on how many water vapor molecules are in the air, what occurs if we raise the temperature?
-Evaporation rate increases
-Need higher "humidity" for condensation rate to match evaporation rate – saturation vapor pressure increases!
“Water-holding capacity” of the atmosphere increases by about 7% for every 1 °C rise in temperature
Shows the equilibrium curve. At the curve, it is clouds. To the left of the curve is liquid, and to the right of the curve is all vapor.
What is relative humidity?
amount of water vapor in relation to saturation point
RH = (vapor pressure/saturation vapor pressure) * 100%
Can the term be used to compare moisture content at different locations having different temperatures?
Because of temperature dependency, the term cannot be used to compare moisture content at different locations having different temperatures
When does the highest RH occur?
occurs in the morning, during the coolest time of the day
When does the lowest RH occur?
occurs in late afternoon, during the warmest time of the day
What is dew point temperature?
temperature to which air must be cooled to reach saturation (without changing vapor pressure)
What do infrared satellites cover?
• High clouds are white
• Low clouds are grey
• Dry areas are hard to identify
What do water vapor satellites occur?
• Uses infrared band
affected by water vapor
• Dry air stands out as dark regions
What are processes that cause saturation?
Three possible mechanisms:
1. The addition of water vapor
2. Cooling the air to dew point (most clouds)
3. Mixing cold air with warm moist air
Suppose we do our “saturation” experiment. Assume the air, the container, and the liquid water are all at the same temperature. Where is the condensation going to occur?
At the liquid surface and at the walls of the container
What are the two ways of nucleating water from vapor?
Homogeneous nucleation & Heterogeneous nucleation
What is homogeneous nucleation?
only water vapor molecules coming together to form water (effect of curvature, requires supersaturation with RH=400%, so it never happens in practice)
What is heterogeneous nucleation?
water vapor molecules adhere to a solid surface (hygroscopic aerosols) on a condensation nucleus (cloud condensation nuclei, CCN)
How do you nucleate ice from liquid water?
Pure water must be supercooled to T < -20oC in order to get it to freeze
• Ice crystal formation requires ice nuclei, a rare temperature-dependent substance similar in shape to ice (six-sided).
• Examples: clay, ice fragments, bacteria, etc.
• Ice nuclei become active at temperatures below -4°C
What are two processes that can cool air to reach saturation?
Adiabatic and diabatic processes
What is a diabatic process?
Changes in temperature caused by heat transfer into or out of the air parcel
What is an adiabatic process?
Changes in temperature caused by expansion or contraction due to changes in pressure
(no heat transfer)
What is the adiabatic lapse rate?
Rate at which temperature decreases with increasing altitude
LR= (final temp - initial temp/final height - initial height)
What is the DALR?
"Dry” adiabatic lapse rate (Dry = air + water vapor)
What is the SALR?
SALR - “Saturated” adiabatic lapse rate
(Saturated = air + water vapor + liquid water droplets)
What causes Santa Ana winds?
Synoptic pattern: high pressure system (anticyclone with clockwise rotation) over the Great Basin
-Adiabatic heating is the key for the high temperature and the low relative humidity
-Air descending from the high deserts:
• warms by adiabatic compression
• temperature increases reduces RH (by increasing saturation vapor pressure)
What is dew?
liquid condensation on surface often occurring during the early morning hours
• Surface air becomes saturated and condensation forms on objects acting as condensation nuclei
What is frost?
similar to dew except that it forms when surface temperatures are below freezing.
• Deposition (vapor to solid) occurs instead of condensation.
What is frozen dew?
Frozen dew occurs when normal dew formation processes occur, followed by a drop in temperature to below freezing.
• Causes “black ice” on roadways
What is fog?
surface cloud when air either cools to the dew point, has moisture added, or when cooler air is mixed with warmer moister air.
what types of fogs are there?
radiation fog, advection fog, and upslope fog
what type of fog occurs in SF and Santa Monica?
How can we calculate
the height of cloud formation?
LCL = (Tsfc- DPsfc)/ 8
What are mechanisms that lift air?
What causes convection?
vertical motions caused by buoyancy
what is buoyancy
An air parcel that is more dense than its environment sinks, while an air parcel that is less dense rises
What are the three stabilities?
stable, indifferent, unstable
How do we find out the stability?
In the atmosphere we characterize stability by comparing lapse rates.
If the air parcel is “dry”, what do we compare the DALR with?
If the air parcel is “dry”, we compare the DALR with the ELR
at new position Tp < Te, the air parcel will...
the air parcel sinks back to original position and equilibrium is STABLE
If DARL Te, the air parcel will...
the parcel rises away from original position and equilibrium is UNSTABLE
at new position Tp = Te, the air parcel will,
the air parcel stays at new position and equilibrium is NEUTRAL
If the air parcel is saturated, how do you calculate its stability?
What Determines the ELR?
1. Heating or cooling of the lower
2. Advection of cold and warm air at different levels
3. Advection of an air mass with a
What type of clouds are there?
stratus, cumulus, nimbus
Wide flat layer of clouds (stable ELR, no vertical motion)
Puffs/piles of clouds (unstable ELR, vertical motion)
Precipitating cloud (i.e. rain)
High clouds: cirrus
Bases above 19,000 ft
• Mostly ice crystals
• Wispy appearance (low water content)
Middle clouds (Alto)
• Bases between 6,000 and 19000 ft
• Mostly liquid droplets
• Bases below 6,000 ft
• Mostly liquid droplets