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130 Cards in this Set

  • Front
  • Back
Hydrologic Cycle
The continuous movement of water from the earth's surface to the atmosphere and back to the surface, then to the atmosphere.

Basic Process: Evaporation and Transpiration
Transpiration
the water absorbed by vegetaion and then released to the atmosphere.
Evaportranspiration
The combined amount of water lost by evaporation and transpiration
States of water (Matter)
Solid

Liquid

Gas
Melting
Solid to liquid
Evaporation
Liquid to a Vapor
Condensation
Vapor to a Liquid
Sublimation
Solid to Gas
Deposition
Gas to a Solid

Releases energy
Humidity
the amount of water vapor in the air
Specific Humidity
Grams of water vapor per kilogram of air
Absolute Humidity
Grams of water vapor per cubic meter of air
Relative Humidity
Ratio of a parcel of air's actual amount of water vapor to the parcel's water vapor capacity, expressed as a percentage.
Partial Pressure
Each component of the atmosphere makes up a part of the total air pressure.
Water Vapor Pressure
That portion of the air pressure which is made up of water vapor
Saturation
When the air is holding all the water vapor it can

The capacity of water vapor the air can hold is a function of temperature.
Warmer air can hold more water vapor
.
Saturation vapor pressure increases with increasing temperature
.
Specific Humidity
The mass of water vapor per unit mass of air
Relative Humidity (RH)
Actual water vapor content/water vapor capacity X 100
RH = 100%
The air is saturated
Dew Point
The temperature at which saturation will occur, given sufficient cooling.

It is an indication of the moisture level in the air

Controlled by Vapor pressure, not by air T
What controls Relative Humidity?
This is controlled by the water vapor content and the air's capacity, which is controlled by T
Dew Point
The Temperature at which saturation will occu, given sufficient cooling.

It is an indication of the moisture level in the air.
How to change the RH?
by adding or subtracting water vapor

lowering or raising the T
When the R.H. varies during the day it's because of a change in air temperature or a change in the amount of moisture (water vapor) in the air
.
Examples of how to bring air to the point of saturation:
By adding water vapor to air (Temperature is held constant)

By cooling the air ( vapor content constant)
Adiabatic
The term for processes in which no heat is added or removed.
Adiabatic Temperature Change
Expanding Air = Temperature Decreases

Compressing Air = Temperature Increases
Adiabatic Temperature Change
The temperature changes without heat being added or taken away.

This is caused by changes in pressure of a gas.
Adiabatic Heating
When a parcel of air decends, the pressure of the parcel increases. Due to this increase in pressure, the parcel's volume decreases and its temperature increases, thus increasing the internal energy.
Adiabatic Cooling
When the pressure applied on a parcel of air decreases, the air in the parcel is allowed to explan as the volume increases, the temperature falls and internal energy decreases.
Rising Air
In the atmosphere rising air expands and cools
Sinking Air
In the atmosphere sinking air is compressed and warmed.
Rate of Adiabatic Change
The Rate at which the temperature changes as it rises or falss through the atmosphere.

This varies based on the humidity of the air

Dry = unsaturated

Wet = Saturated
Gas Law
At the surface as temperature decreases, density and pressure increases as temperature increases, air density and pressure decreases.
Dry Adiabatic Rate (DAR)
When air is unsaturated air temperature is greater than the dew point temperature.

Rising Air = Cools at 1C/100m

Fallin Air = Warms at 1C/100m
Wet or Saturated Adiabatic Rate (SAR or SALR)
When the air is saturated

Air Temperature = Dew Point Temperature; RH = 100%.

Not at a constant rate, 5-9 degrees celsius per 1000 meters.

It is dependent on the moisture content of the air. The more water vapor condensing to liquid there is in the air, the slower the rate of decline.
SAR Con't
So as air rises by convection it cools and the air temperature may reach the dew point temperature (saturation) and thus condesation may begin. If there is enough water vapor in the air parcel, then a cloud may form. The level of the atmosphere where this occurs is known as the condesation level.
Condesation Level
Height at which condesation occurs, where cloud formation begins (Usually seen as the bottom of a cloud mass).

RH=100%, Air Temperature = Dew Point Temperature
The rate of Temperature change is slower for saturated air than for unsaturated air.
.
Stability
Refers to the tendecy of an air parcel with its water vapor either to remain in place or to change vertical position by ascending or descending

Stable Air resists displacement

Unstable Air continues to rise until it reaches air with density and a temperature similar to its own
Rules of Stability
1) When an air parcel is warmer than the surrounding air, the parcel will rise

2) When an air parcel is colder than the surrounding air, it will tend to stay at the same level or sink

3) The Envrionmental Lapse Rate (ELR) is the temperature profile of the atmosphere (surrounding air). The ELR determines air stability. The acutal temperature lapse rate in the lower atmosphere at any particular time under local weather conditions is the ELR
Unstable Air
When an air parcel is warmer than the surrounding air, the parcel will rise
Stable Air
When an air parcel is colder than the surrounding air, it will tend to stay at the same level or sink
Envrionmental Lapse Rate (ELR)
is the temperature profile of the atmosphere (surrounding air). The ELR determines air stability.

The actual temperature lapse rate in the lower atmosphere at any particualr time under local weather conditions is the ELR.
Types of Stability
Absoulte Stability

Absolute Instability

Conditional Instability
Absolute Stability
The condition of air when the ELR < DAR

Usually results in no uplift of air, but subsidence or sinking air.

Often associated with high pressure cells.

Clear Skies, maybe a few stratus clouds.
Temperature Inversion
More severe example of absolute stability.

When the air temperature is increasing with increasing altitude in the troposphere.
Absolute Instability
The Condition of air when ELR>DAR

Often occurs during the warmest months and on clear days; often leads to cloud formation, cumulus clouds and precipitation.

Often associated with low pressure cells.
Conditional Instability
The condition of the air when the ELR is between the DAR and the SAR

SAR<ELR<DAR

Air can vary between stable and unstable

Usually if air is saturated the upper portion is unstable

If the air is unsaturated then the lower portion is stable
Importance of Stability
For daily weather patterns

Controls whether clouds form or not and the type

partially controls precipitation type and amounts
Lifting Mechanisms
Convective Lifting

Orographic Lifting

Frontal Wedging

Convergence
Convective Lifting
The process by which a parcel of air at the suface by convection, then the whole parcel rising into the atmospher since it is warmer than the surrounding air

The heating helps produce unstable conditions

Common in summertime as afternoon thundershowers

Part of the process that occurs in low pressure cells in conjunction with convergence
Orographic Lifting
The process by which air is forced to rise over a mountain range or other elevated land barrier and thus cool adiabatically

Little or no precipitation occurs on the leeward side, it occurs on the windward side.
Rain Shadow Desert
Orographic lifting creates this on the leeward side
Frontal Wedging
The process by which cold, dense air acts similarly to a mountain barrier forcing warmer, less dense air to rise over it.

The leading edge of a mass of cold air is know as a cold front and similarly the leading edge of a mass of warm air is known as a warm front. So this mechanism is associated with warm and cold fronts and mid latitude wave cyclones (frontal systems)

Usually produces clouds and precipitation; often severe storms or thunderstorms.
Convergence
The process by which winds come together from opposite direction and are forced to rise due to compression or squeezing

Part of the process that occurs in low pressure cells

Both convection and convergence are at work to form the ITCZ
Clouds, Fog, and Dew all have 2 propertices in common:
Must form from Saturated Air (RH=100%, dew pint temperature=air temperature)

Must have a surface on which the water capr can condense
Condensation Nuclei
Microsopic particles of dust, salt, smoke, etc
Hygroscopic Nuclei
Are very water absorbent condesation nuclei usually of sulfate and nitrate crystals.
Clouds
A form of condesation best descrived as a dense, visible aggreagation of minute droplets of water and tiny crystals of ice
How do clouds form?
A parcel of moist air reaches the point of saturation where the water vapor is changed to liquid water droplets. Either by coolin the air temperature to the dew point temperature or by adding more water vapor.

Cooling the air temperature is the most common method
Cloud Classification
Two Criteria for Classifying Clouds:

1) Height of cloud base above the surface.

2) Degree of vertical development.
Height of Cloud Base
3 Categories

< 2000m =Strato Clouds

2000m-6000m alto

< 6000m = cirro
Degree of Vertical development
is an indication of the degree of stability/instability

2 Main Categories:

Startus = Layer, horizontal development

Cumulus= heap or cotton balls, vertical development

Cirrus=curl of hair, clouds found the highest up in the atmosphere, composed of ice crystals

Nimbus= Violent rain, cumluonibus and nimbostratus
Fog
Basically a cloud on ground level

Condensation can occur in some instances where the RH is as low as 75% - 80%

As water droplets get bigger they become visible, this decreases visibility (being able to look through the droplets)

If visibility is reduced to 1km, the haze or cloud is categorized as FOG.
4 Main Categories of Fog
1) Radiation Fog (Ground Fog)

2) Advection Fog

3)Upslope Fog

4) Evaporation Fog
Radiation Fog (Ground Fog)
Produced over land when radiational cooling decreased air temperature to the dew point temperature

Valley Fog is of this type, it forms in low lying areas from cold, heavy air draining down hill and collecting in the valley bottom.

forms best on calm clear nights in late fall and winter.
Advection Fog
Occurs when warm moist air moves over a cold surface and the air cools to below its dew point.

Advection= Horizontal movement of air

This type of fog is usually associated with winds of 10-30 kph and is often 300-600m thick.
Upslpoe Fog
Created when warm moist air flows up along an elevated plane, hill, or mountain.

Air temperature reached dew point temperature by adiabatic cooling as it rises.
Evaporation Fog
When air reaches saturation by adding water vapor not lowering temperature

Water evaporates into the parcel of air
2 Main types of Evaporation Fog
1)Steam Fog

2)Frontal Fog
Steam Fog
Forms when cold air moves over warm water; the warmer water evaporates into the unsaturated cold air causing saturation, condesation, and fog formation.
Frontal Fog
Forms as warm raindrops evaporate in cool air mass as they fall

This is the type of fog associated with systems and dreary, drizzly days.
Dew
Water that has condensed onto objects near the ground when their temperatures have fallen below the dew point temperature of the surface air.
Frozen Dew
Dew which has formed (liquid) and then frozen (solid)
Frost or Hoarfrost
Covering of ice produced by deposition when the dew point temperature is below freezing.
1 Raindrop =
1 million cloud droplets
Bergeron Process or Ice-Crystal Process
Discovered by Tor Bergeron

Primary process for forming rain in the middle and high latitudes

Requires untilizing 2 properties of water:

1) pure water in the air doesn't freeze until -40C.

2) Saturation vapor pressure over ice crystals is much lower that over supercooled liquid water.

Water < 0C is called supercooled

Need temperatures below -10C; at temperatures b/w -10C & -20C will have both liquid drops and ice crystals.

Difference in vapor pressure allows for supersaturation to exist

Under supersaturated conditions, ice crystals collect more water vapor than they lose and thus grow.

As they grow, may break up and these pieces act as freezing nuclei to make more crystals.
Collision-Coalescence Process
Primary process in tropics for raindrop formation.

need larger cloud droplets from large condesation nuclei or hygroscopic nuclei

Small droplets don't coalesce and collide by themselves cery well

Max size of a raindrop is 5mm if it gets bigger, then it gets pulled apart bu friction and drag

The collison-coalescence process is the idea behind cloud seeding.
Precipitation Types
1) Rain

2) Snow

3) Sleet

4) Freezing Rain

5) Hail
Rain
At least .5mm to 5mm in size

From nimbostratus and cumulonimbus clouds

Can start frozen or liquid --> liquid (before ground)
Snow
1-2mm in size

Water vapor deposited as ice crystals that stay frozen

Frozen (cloud) --> frozen (as it hits the ground)

Ration of snow to rain is 10in = 1in
Sleet
.5-5mm in size

freezes as it falls and is a frozen raindrop which freezes on contact with solid objects/surfaces

Frozen (cloud) --> Liquid (in atmosphere as it falls) --> liquid/frozen (liquid as it hits ground then freezes)
Hail
5mm-10cm+

Hard, rounded pellets or lumps of ice; only produced in large cumulonimbus clouds/thunderstorms

Needs a series/networks of updrafts and down drafts

largest reported hailstone =1.67lbs and over 5.5" in diameter
Pressure Systems
The areas of uplift (ITCZ) and subsidence (STH) affect precipitation patterns
Winds
Don't blow in nice straight paths and where they meet, like the polar front, are turbulent
Seasonality
These pressure belts and winds shift from season to season
Landmasses and Oceans
Mountains get in the way of winds and moisture differential heating
STH
Don't have the same characteritics on both the east and west side
Eastside of STH
Subsidence, temperature inversion, and upwellin of cold ocean currents = stable dry conditions
Westside of STH
little subsidence, more uplifting, convergence, and warm ocean currents = greater instability and wet conditions.
Rainshadow Deserts
Due to mountain barriers and ornographic effect leeward side often much drier than windward side.
Monsoon
A wind system that exhibts a pronounced seasonal reversal in direction.
Air Mass
An immense body of air, some 1600+ km acroos and 1-3km thick, with relatively homogeneous physical properties (density, temperature, and moistiure) at a give altitude
Classification Scheme for Air Masses
2-Letter abbreviations are used to indicate source region, characteristics, and types of Air Masses
Source Regions
Area in which air mass orginates

Source region determines inital characteristics of the air mass

2 Criteria:

1) Large and physically uniform area

2) characterized by a general stagnation of atmospheric circulation
Types of Air Masses
Continental Arctic (cA)

Continental Polar (cP)

Continental Tropical (ct)

Maritime Polar (mP)

Maritime Tropical (mT)
Continental Arctic (cA)
Arctic Basin and Greenland

Bittery cold and very dry

Stable
Continental Polar (cP)
Interior Canada and Alaska

Very Cold to cool and dry, stable
Continental Tropical (cT)
Northern interior Mexico and SW U.S. ( Summer only)

Hot and dry

Unstable
Maritime Polar (mP)
1) North Pacific; cool and humid; unstable in winter and stable in summer

2) NW Atlantic; cold (winter) to cool (summer) and humid; unstable in winter, stable in summer
Maritime Tropical (mT)
1) Gulf of Mexico, Caribbean and Western Atlantic; warm and humid and unstable on the western side of the STH

2) Subtropical, eastern Pacific; warm and humid but stable on the eastern side of a STH
Fronts
A boundary separating air masses of different densities

One air mass is usually warmer and more moist
Size varies from 15 to 200km wide
Polar Front
Wave Cyclones; develop in conjunction or along the polar front

Low pressure cells and front are the primary structure of mid-latitude wave cyclones
Types of Fronts
1) Cold

2) Warm

3) Stationary

4) Occluded
Cold Front
Boundary at the forward edge of an advancing cold air mass that is displacing warm air

Moves at approx 35kpm and has a slope of 1:100

Cumulus and cumulonimbus clouds associated with cold fronts

Symbolized on weather maps as a line with triangles on it.
Warm Front
Boundary at the forward edge of an advancing warm air mass that is displacing cooler air

Moves at approz 25 kph with a slope of 1:200

May see evidence of the approaching front up to 1000km ahead of it

Usually stratus clouds associated with warm fronts

Symbolized on weather maps as a line with semi circles on it
Stationary Front
When air movement is almost parallel to the boundary (front) and the surface position of the front moves at less that 5mph foward speed

Symbolized by oppostie facing circles and triangles
Occluded Front
A front formed when a cold front takes over and replaces a warm front at the surface (semi circles and triangles on the same side of the line.
Mid-Latitude Wave Cyclone
A low pressure cell that forms and moves along a front.

Counter-Clockwise circulation (NH) around the cyclone tends to produce the wavelike deformation of the front.

Last 3 to 5 days
Stages of the Wave Cyclone Life Cycle:
Stage 1: 2 air masses, a cold and a warm are set up alon a front and are moving parallel to it.

Stage 2: A wave forms and warm air starts to move poleward while cold air moves equatorward

Stage 3: Cyclonic (counter-clockwise) circulation develops, with general convergence at the surface and uplifting; warm air overrides the cold air (frontal wedging)

Cold Front and warm front clearly established

Stage 4: Cold front moving faster than the warm front and begins to overtake it; occulsion begin, beginning formation of an occulded front

Stage 5: Full development of an occluded front and maximum intensity of the wave cyclone; steep pressure gradient and strong winds.

Stage 6: Sloping discontinuity (front) begins to disappear, pressure gradient weakends, energy exhausted and system dissipates.
Winds of a Wave Cyclone
Warm Sector: Primarily Southwesterly to southerly

Cool Sector: Southeasterly to easterly and then northeasterly

Cold Sector: Northerly, to northwesterly to westerly
Moisture, Sky, and Weather Conditions
Warm Sector: Humid to very humid; clear skies to scattered cumulus clouds; warm temperatures

Cool Sector: Humid, large area of stratus clouds with light to moderate precipitation ahead of the warm front; clouds thinner further from the front (cirrus type clouds) cool temperature .

Cold Sector: dry, clear air back from the cold front; intense precipitation along and just behind the cold front; cold temperatures
Cyclogenesis
The process that creates or develops a new wave cyclone, or strengthens an existing wave cyclone.
Criteria for a wave cyclone to form:
Cyclonic flow must be established.
Vorticity
rotation of the air
Relative Vorticity
The Vorticity (spin) relative to Earth's Surface
Earth Vorticity
Which is due to Earth's daily rotation about it axis
If the flows are both in the same direction (counterclockwise in NH) then they complement each other increasing absoulte vorticity
.
Low pressure cells in the NH basically show positive vorticity, while high pressure cells in the NH basically show negative vorticity.
.
Rossby Waves and Vorticity
The Vorticity changes as you move along a wave which is caused by convergence (coming together) of air in one portion and divergence (pullin apart) in another.
On the down slope of a trough there is more convergence and thus increased vorticity or spin, while on the upslope there is divergence and decreased vorticity.
.
Upper-Level Divergence
Helps draw air upward from the surface and acting as a lifting mechanism above the surface low pressure cell.
Speed Divergence
In a Rossby Wave speed divergence occurs basically on the downslope of a trough
Speed Convergence
In a Rossby Wave occurs on the upslope of a trough.
Difflunence
Moving air is being spread apart on the trough upslope
Confluence
Moving ait is being forced closer together on the trough on the downslope.
The role of geostrophic winds (Rossby WAves and the Jet Stream) is not only the development of a mid-latitude cyclone system, but also to move the wave cyclone along
.