UGA Geography 1111 Exam 2, GEOG 1111 Hopkins Test 2

Clouds Fog, and Dew all have this is common:

1. They must form from saturated or nearly saturated air.

2. They must have a surface (solid or liquid) upon which the water vapor can condense

Dew

the condensation event (water vapor changing to liquid water) wherein liquid water droplets form on the ground, vegetation, a car, or similar surface near the ground

Cloud & fog

are condensation events wherein the droplets form suspended in the air. They form on solid particles known as condensation nuclei

A condensation nuclei

a microscopic particle which is necessary as a surface on which water vapor condenses to form moisture droplets. These can be particles of dust, sea salts, soot, ash, sulfate & nitrate crystals, etc.

Cloud

a form of condensation best described as a dense, visible aggregation of minute moisture droplets and/or tiny ice crystals

Two basic criteria are used for classifying clouds

Altitude and Shape

Four altitudinal classes

low, middle, high, vertically developed through the troposphere

Low clouds

those which lie from near the surface up to 2000 m (6500 ft.). These clouds Typically consist of liquid water droplets.

Examples of Low clouds

stratus, stratocumulus, nimbostratus

Middle clouds

those which lie between 2000 m & 6000 m (20,000 ft.). These typically consist of a mixture of liquid water and ice crystals, dependent on the season

Examples of Middle Clouds

altostratus, altocumulus

High clouds

those which lie between 6000 m & 13,000 m (43,000 ft.). These typically consist primarily of ice crystals

Examples of High clouds

cirrus, cirrostratus, cirrocumulus

"Vertically developed thru the troposphere" clouds

those cloud masses which may stretch from near the surface to over 13,000 m. These typically consist primarily of liquid water at lower levels and ice crystals at higher levels.

Examples of "vertically developed through the troposphere" clouds

cumulus, cumulonimbus

Three basic shape forms

flat, puffy, and wispy

Flat

those which show primarily horizontal development and are often layered. These are stratiform clouds

Puffy

clouds are those which show more vertical development. These are cumuliform clouds

Wispy

are those which form at high altitude and consist of ice crystals. These are cirroform clouds

Stratus clouds

layered, horizontally developed and usually low altitude

Cumulus clouds

puffy like cotton balls and vertically developed

Cirrus clouds

wispy shaped "curls of hair". They form high in the atmosphere and are composed of ice crystals

Nimbus clouds

refers to those which are producing precipitation (rain,

snow, etc.)

Two types of nimbus clouds

Cumulonimbus and Nimbostratus

Cumulonimbus

or more commonly called Thunderstorms (T-storms) are cumulus clouds which are producing precipitation.

Nimbostratus

are stratus clouds which are producing precipitation

Fog

basically a cloud in contact with the ground, but the air parcel does not reach saturation by rising and cooling. It either cools to the d.p.t or has water vapor added to reach saturation at the ground

Four main categories of fog:

Radiation, Advection, Upslope, Evaporation

Radiation fog

produced over land as the ground emits LW radiation, thus losing heat energy and cooling.

Advection fog

occurs when warm, moist air moves over a colder surface & the air cools to its d.p.T. This is most common as warm air from off a large water surface (ocean, gulf) moves over the colder, coastal land. (Remember that advection means the horizontal movement of air.)

Upslope fog

forms as warm, moist air flows up along an elevated plain, or mountain range. The air temperature reaches d.p.t by adiabatic cooling as it rises.

Evaporation fog

forms when the air reaches saturation by having water vapor added to it and not by lowering of the air temperature.

Steam fog

Forms when cold air moves over warmer water and the warmer water evaporates into the unsaturated cold air causing saturation, condensation and fog formation.

Frontal fog

forms as warm raindrops evaporate in a cool air mass as they fall. This is the type fog associated with frontal systems and dreary, drizzly days

Dew

water that has condensed onto objects near the ground when their Tº's have fallen below the d.p.Tº of the surface air. In winter, however, this may form solid forms of dew.

Frozen Dew

refers to dew which has formed and then has frozen

Frost or Hoarfrost

covering of ice produced by deposition because the d.p.t is below freezing

Rain

Water vapor condenses into liquid water droplets forming clouds

Snow

Water vapor condenses into liquid water droplets forming clouds

Two basic mechanisms to explain precipitation formation:

Bergeron Process and the Collision-Coalescence Process

Bergeron Process

(Ice-Crystal Process) is the primary process for forming precipitation in the middle and high latitudes and the only process to form snow.

Collision-Coalescence Process

is the primary process in tropical areas for raindrop formation and in mid-latitudes during the summer. The basic process is water vapor changing to liquid water droplets (cloud droplets) by condensation, and these droplets coalescing with other droplets to form raindrops

nimbostratus; cumulonimbus

Remember that all precipitation comes from either _________________ or _________________

Conversion of snow to rain

10 inches of snow is equivalent to 1 inch of rain

Sleet

essentially a frozen raindrop. If it starts as a snowflake (Bergeron Process), then it melts to form a raindrop that then freezes (re-freezes) before it hits the ground

Freezing rain

similar to sleet except it freezes (re-freezes) after making contact with the ground. This usually involves supercooled raindrops which allows them to freeze on contact with solid objects/surfaces. Commonly referred to as Ice storms.

Hail

another form of solid precipitation consisting of hard, rounded pellets or lumps of ice. They are only produced in large cumulonimbus clouds, thunderstorms

Air Pressure systems

greatly affect precipitation patterns with areas of Low Pressure typically being unstable (ITCZ) and areas of High Pressure consisting of subsidence and being stable (STH).

Wind

Wind directions affect precipitation patterns by whether it is flowing onshore or offshore, diverging or converging, encounters mountain ranges, etc

Seasonality

shifting of pressure belts (ITCZ & STH) during the year which shifts wind directions.

Landmass & Ocean

locations which can affect wind flow, differential heating, rain shadows, etc.

Sub-Tropical High pressure cells (STH's)

which sit over oceans, don't have the same characteristics on both the east & west side

East side of STH

shows the typical subsidence, temperature inversion, and stable, dry conditions. They are also affected by upwelling of cold ocean currents

West Side of STH

shows little subsidence, more uplifting, convergence, and warm ocean currents which leads to greater instability, and wetter conditions.

Rain shadow deserts

are formed by mountain barriers and orographic effects such that the leeward side is often much drier than the windward side

Monsoon

an annual cycle of dryness & wetness, with seasonally shifting winds produced by shifting atmospheric pressure patterns.

Air Mass

an immense body of air, some 1600+ km across and 1-3 km thick, with relatively homogeneous physical properties (density, Tº & moisture) at a given altitude.

Classification Scheme

based on the basic T° and moisture (water vapor content or humidity) conditions of the air. A two-letter abbreviation system is used to indicate the various types of air masses

First letter

a reference to the surface over which the air mass develops & thus the level of moisture (dry vs humid).

"c"

Continental for those air masses which form over a landmass and thus typically have a low water vapor content, dry air.

"m"

Maritime for those air masses which form over an ocean and thus typically have a high water vapor content, humid air.

Second letter

a reference to the latitude of origin & thus the Tº (cold vs warm).

A=Arctic

bitterly cold

T=Tropical

warm

P=Polar

cold to very cold

E=Equatorial

very warm

Source Region

determines the initial characteristics of the air mass.

Fronts

refer to a boundary separating air masses of different characteristics, primarily temperature, warm versus cold

Polar Front

refers to the zone separating air masses of polar origin from air masses of tropical origin.

Wave Cyclones

refers to a weather pattern which may develop in conjunction with or along the polar front

Cold Front

the boundary at the forward edge of an advancing cold air mass that is displacing warmer air

Cumulus and cumulonimbus clouds

typically associated with cold fronts and thus quite often more violent weather is associated with cold fronts

Warm Front

the boundary at the forward edge of an advancing warm air mass that is displacing cooler air. Usually stratus and nimbostratus clouds associated with warm fronts and thus less severe weather is associated with warm fronts.

Stationary Front

represents a situation when air movement is almost parallel to the boundary & the surface position of the front doesn't move very quickly

Occluded Front

refers to a situation when a cold front has over taken a warm front

Mid-Latitude Wave Cyclone

low pressure cell that forms & moves along a frontal boundary. It exhibits counter-clockwise circulation (NH) around the low center and produces a wavelike deformation of the front.

Warm sector

The area between the warm front and the cold front; the winds are primarily southwesterly to southerly

Cool sector

The area ahead of the warm front; the winds are primarily southeasterly to easterly and then northeasterly as you move counter-clockwise around the low pressure center

Cold Sector

The area behind the cold front; the winds in this sector are primarily

Warm sector

Has humid to very humid conditions, often with clear skies to Here in the U.S. this is primarily mT air off the Gulf of Mexico. Precipitation may be associated with the advancing cold front.

Cool sector

Has humid to very humid conditions with a large area of stratus & nimbostratus clouds. Light to moderate precipitation along and ahead of the warm front. It exhibits cool Tºs.

Cold sector

This sector exhibits dry, clear air back from the cold front, but often has intense precipitation (T-storms) along the cold front. It has cold Tºs.

Thunderstorm (T-storm)

is a cumulus cloud which has developed sufficiently to produce precipitation and thus be classified as a cumulonimbus (Cn) cloud. It also is producing the characteristic events of lightning and thunder; an indication of great instability in the atmosphere and show a great deal of vertical development.

Requirements for Formation of a T-storm

1. Warm, moist air

2. High surface temperatures

warm, moist air

which releases Latent energy when lifted and condensation occurs. This provides buoyancy, and maintains lift to develop updrafts

High surface temperatures

which enhances instability, air parcel warming and uplift

Stages of Formation:

Cumulus, mature, and dissipating

Cumulus Stage

the initial build-up of cumulus clouds fueled by updrafts (up to 160 kph) of warm, moist air cooling adiabatically. Droplet formation is by the Bergeron & Collision-Coalescence processes. Updrafts dominate during this stage

Mature Stage

which raindrops start to fall initiating downdrafts. The process of entrainment (the influx of cool, dry surrounding air) helps to fuel the downdrafts. Heavy rains, lightning, & thunder are most intense during this stage. It is also during this stage that hail or a tornado may occur.

Dissipating Stage

occurs as the rate and amount of rain lessens with the loss of warm, moist air & latent heat energy. The storm breaks up & the cloud mass evaporates. Downdrafts dominate during this stage.

Locations of occurrence

* Thunder storms occur in many parts of the world. They are a daily occurrence along the ITCZ. In the U.S. they form primarily east of the Rocky Mountains, with Florida being the state with the greatest number of days per year of thunder storm occurrence. The Great Plains is the region with the greatest number per year.

Lightning

flashes of light generated by the flow of tens of millions of volts of electrons (electrical charge) between oppositely charged parts of a cloud or between the cloud and the ground.

What causes lightning?

Charges are separated within the cloud as the thunder storm develops with positive charges primarily near the top and negative charges at the base.

Tornado

a violently rotating column of air or vortex which can be seen when filled by a funnel-shaped or tubular mass of cloud & debris. It extends downward from a cumulonimbus cloud in response to extremely low air pressure.

The Enhanced Fujita Scale

ranges from an EF0 (winds 65-85 mph) up to an EF5 (winds > 200 mph).

Weaker tornadoes

form as winds drawn into the T-storm converge and form a vortex that is already in a vertical orientation, and is pulled upward into the cloud base.

Stronger tornadoes

start out in a horizontal position. As wind is drawn into the T-storm from tens of miles away, the air closest to the ground moves slower than the air above it, causing the air to tumble like a barrel rolling on the ground. This mesocyclone is then drawn upward by the updrafts and becomes a vertically orientated column of spinning air or tornado.

Tornado Watch

means conditions are favorable for the occurrence of a severe thunderstorm or tornado in your area, within the time period stated in the watch announcement, but is not occurring as yet.

Tornado Warning

means that this type of weather has been spotted by a trained observer, OR has been indicated by Doppler radar in your area.

Hurricanes

intense tropical cyclonic storm consisting of a warm-core low pressure cell at its center, inward-spiraling rain bands, and having sustained winds in excess of 119 kph (74 mph).