Weather Exam 2

Coriolis Force

- Apparent deflection due to rotation of the earth - Right in northern hemisphere and left in southern hemisphere - Stronger wind = greater deflection - No Coriolis effect at the equator, greatest at poles - Only influence direction, not speed - Only has significant impact over long distances -To an observer on the Earth, objects moving in any direction are deflected to the right of their intended path in the Northern Hemisphere

geostrophic winds

- Earth turning winds - Travel parallel to isobars - Spacing of isobars indicates speed; close =fast, spread out = slow Above friction air initially accelerates until it flows parallel to the isobars at a steady speed which is equal to the PGF

floods

- Flood waters that rise rapidly with little or no warning are called flash floods; results when thunderstorms stall or move very slowly, causing heavy rainfall over a relatively small area- Flooding occurs primarily in the spring when heavy rain and melting snow cause rivers to overflow their banks

gradient winds aloft

- Gradient wind parallel to curved isobars - Cyclonic: counterclockwise - Anticyclonic: clockwise - Cyclostrophic near Equator

clear air turbulence

- Near Jet Stream in a zone of wind shear- Swirling eddies usually form in the upper troposphere near theJet Stream

mountain breeze circulation

- On mountain slopes, warm air rises during the day creating a valley breeze; during night nocturnal drainage of cool air creating a mountain breeze; gravity winds - Associated with cumulus clouds in the afternoon

coriolis effect depends on

- Rotation of the Earth - Latitude - The object's speed

winds on upper level charts

- Winds parallel to contour lines and flow west to east - Heights decrease from north to south

surface winds

-Friction reduces the wind speed which in turn decrease the Coriolis effect. - Winds cross the isobars at about 30° into low pressure and out of high pressure

rain drizzle - where does most come from virga

.5 mm less than .5 mm - rain falling through stratified clouds evaporated rain drops

Hadley Cell

0 to 30 degrees. Heat rises at equator, carried away and sinks at 30 degrees. Northeast trade winds

In a cloud with sufficient water, other significant factors are:

1. the range of droplet sizes 2. the cloud thickness 3. the updrafts of the cloud 4. the electric charge of the droplets and the electric field in the cloud

pressure increases by

10mb per 100m Or 1inch per 1000ft

Middle Cell

30-60 degrees. Not all the air moving towards poles sinks - some delflects east creating the prevailing westerlies.

what size will droplet be at bottom of cloud

5 mm; these raindrops fall fastest and reach the ground first. Begin at the start of rain showers in warm convective clouds.

polar cell

60 to 90 degrees. Air rises at 60 degrees and moves towards the poles. Air moves to the East.

sounds and snow snow with temp above freezing snow as an insulator

A blanket of snow will act like an acoustic tile and absorb sound wave Unsaturated wet bulb temperature 0°C, rain cooled by evaporation forms snow despite environmental temperature above freezing Protects the ground from harsh temperatures

single cell model

A simple conception of global atmospheric circulation calling for one circulation cell in each hemisphere; assumes: 1. Earths surface is uniformly covered with water 2. sun is always directly over equator 3. Earth does not rotate

what does the upper air portion of a low look like on a chart

A surface low pressure center is generally associated with trough on an upper-level isobaric chart.

windy afternoons

Afternoon convection- If the air begins to sink as part of a convective circulation, it may pull some of the stronger winds aloft downward with it- If this sinking air should reach the surface, it produces a momentary gust of strong wind- In addition, this exchange of air increases the average wind speed at the surface

subtropical highs/ horse latitudes

Air moving poleward from the tropics constantly cools and begins to converge - especially at the 30° latitude - The convergence(piling of air) aloft increases the mass of air thus the surface pressure rise

katabatic winds

Any downslope wind is Katabatic (fall) but usually the name is reserved for winds much stronger than a mountain breeze

what happens during different parts of the cloud during ice crystal process

Below the freezing level: liquid water only middle cloud: mixed ice and water, predominantly liquid upper cloud: ice only

permanent highs and lows

Bermuda High Pacific High Siberian High Icelandic Low Aleutian Low

mountains windward vs leeward

Disrupts the generalized pattern of global precipitation Mountains - Promote convection- Force air to rise along their windward slopes(orographic uplift) which are warmer than the surrounding air Windward side of mountains tend to be wet- Leeside tends to be a Rain shadow "Rainiest" places located on the windward side of mountains- Snowfalls heavier where cool, moist air rises along the windward slopes of mountains Driest regions of the world lie in the frigid polar region, the leeward side of mountains, and in the belt of subtropical high pressure

three cell model

Earth is allowed to spin and simple convection system breaks into a series of cells

What is the Polar Front Jet Stream

Established by steep temperature and pressure gradients between mid-latitude polar cell. 33k ft. Occasionally splits into two jet streams (northern and southern branches) Looping pattern helps cold air move towards equator and warm air towards poles; large portion of heat transfer. Important role in development of mid-latitude cyclones, storms Winds stronger and moves south in the winter when contrast in temp is greatest Winds weaker and higher in latitude in summer

Which of the following produces the strongest Coriolis force?

Fast winds, high latitudes.

what might be mistaken from hail?

Graupel.

ice crystal precipitation formation

Important for middle/high latitudes requires the presence of liquid and ice in cold clouds

cloud seeding

Inject cloud with small particles that act as condensation nuclei, triggering the precipitation process - NEED CLOUDS: seeding does not generate clouds - Cold clouds with a low seed ration best - Dry ice, silver iodide • Silver Iodide is best since it has a structure similarto an ice crystal

what is the ITCZ

Intertropical convergence zone - where air from the northeast trades and southeast trades converge in tropics. Air rises and develops huge thunderstorms that drop copious amounts of rain

what happens to rain drops as they fall?

Larger drops fall faster than smaller and grow even larger by colliding with smaller drops in their path. At 1 mm, a cloud with updraft will balance the pull of gravity

black ice

Light rain, drizzle, or supercooled fog droplets can come into contact with surfaces that have cooled to temperatures below freezing - Bridges and Overpasses - Tiny liquid droplets freeze on contact producing a sheet of ice that appears to be black

is it ever too cold to snow?

NO! ; While true, more water will condense in warmer air than colder it is never too cold to snow Ice crystals have been observed falling at temperature sof -53°F Snowflakes falling through air slightly above freezing melt a little and form a thin film on their edges that acts like glue- Attracts other snowflakes (fall as giant snowflakes)- Flakes up to 5.5 inches have been recorded

convergence affect on surface pressure

Net convergence of air would cause surface pressure to increase and net divergence would cause surface pressure to decrease.

what is the average wind flow for various latitudes (example: in middle latitudes it is West to East)

Northern Hemisphere: 0-30 = East to West North east trade winds 30-60 = West to East Prevailing westerlies 60-90: East to West polar easterlies

hail

Pieces of ice that are clear or opaque Sizes from a small peato a golf ball or larger

what is the sequence of precipitation during an advancing winter storm

Rain, freezing rain, sleet, snow

updraft effect on raindrops

Raindrops can also be stopped by an updraft If the draft weakens or becomes a down draft then the drops fall as a shower Continuous rain usually falls from layered clouds- Small vertical currents (slow updraft or none)

how is dry snow formed fluries squall

Snow falling through extremely cold air don't easily stick together- creates Dry snow or powder Snow falling from Cumulus clouds is often in flurries More intense snow showers are called a snow squall

drifting snow ground blizzard true blizzard snow grains snow pellet/graupel

Strong surface wind cause drifts is called drifting snow and is accompanied by blowing snow Combination of drifting and blowing snow after snowfall has ended is a ground blizzard A true Blizzard must have fine dry snow and winds in excess of 35mph Small grains of snow less than 1mm in dia. are called snow grains (solid drizzle) Grains that fall and don't bounce or shatter are called a snow pellet or graupel (size of a raindrop)

direct thermal circulation

The heating and cooling of air columns causes horizontal pressure variations aloft and at the surface. These pressure variations force the air to move from areas of higher pressure towards areas of lower pressure. In conjunction with these horizontal air motions, the air slowly sinks above the surface high and rises above the surface low.

what is a Santa Ana wind

Warm dry that blows from east or northeast into Southern California - Air descends from the elevated desert plateau and funnels through mountain canyons in the San Gabriel and San Bernadino mountains• Spreads over the LA Basin and San Fernando Valley (can blow 90mph) -Originates in the Santa Ana Canyon- Very fast, desiccates vegetation, providing fuel for fires -Santa Anna winds originate in the Canyon with an open side to the elevated desert

A typical raindrop is about ______ that of a typical cloud droplet.

a million times

what is a supercooled water droplet? how does it form

a water droplet that is still liquid below the freezing level. There is less pure water so the temperature at which the droplets will freeze is lowered

what is the visibility after a storm passes

after a storm passes, visibility improves because precipitation scavenges many of the suspended particles in the atmosphere. raindrops are rarely larger than 6 mm - collision breaks up

sleet freezing rain

air below freezing, then travels through a layer of air above freezing, begins to melt and then falls through a layer of air below freezing just above the ground surface ground surface is freezing as rain hits the surface it freezes

Radar gathers information about precipitation in clouds by measuring the:

amount of energy reflected back to a transmitter

precipitation

any formof water that falls from acloud and reaches theground

how does the ice crystal process produce precipiation?

around ice crystals and liquid droplets there are many supercooled water droplets. However, around the liquid droplet, there are more molecules escaping the surface of water in comparison to ice. More molecules escape the water surface = more vapor molecules must try and maintain saturation it takes MORE vapor molecules to saturate air around water than it does ice. More vapor molecules = higher vapor pressure.

The net force on air moving in a circle at constant speed is:

centripetal force.

The inward directed PGF is greater than the outward directed CF - the difference between these forces (net force) is the inward-directed

centripital force

collision coalescence process

coalescence is the merging of droplets through falling droplets collecting more as they move downwards.

precip happens in what kinds of clouds

collision/coalition: cold convective ice crystal: cold convective(mostly accretion), cold layered, nimbostratus, altostratus (not enough liquid for collision, thick and cold enough Warm layered clouds such as stratus then usually don't precipitate

preferred chart of weather above the surface warm air aloft vs cold air aloft

constant pressure chart When air aloft is warm then constant pressure surfaces are found at higher elevations than normal When air aloft is cold then the surfaces are found much lower than normal

two columns of air: both initially with same pressure and temperature what happens when one cools/warms

cooling - the molecules move slowly and crowd closer together - more dense - column shrinks warmer - the molecules move faster and farther apart - less dense - column gets taller Surface pressure remains the same because there is the same number of molecules.

The effect of friction is to slow down the wind so that near the ground the wind ______ the isobars and blows toward ______ pressure

crosses, lower

In the U.S. Isobars and Contours usually _______ South to North

decrease; They bend with Ridges (elongated highs) and Troughs (elongated lows) Upper-level charts are important because they show wind patterns (forecasting)

pressure change with height always

decreases; rapidly at first, then slowly at higher altitudes

In the winter you read in the newspaper that a large section of the Midwest is without power due to downed power lines. Which form of precipitation would most likely produce this situation?

freezing rain

Which type of precipitation would most likely form when the surface air temperature is slightly below freezing and the air temperature increases as you move upward away from the ground?

freezing rain

Low ______ on a constant height chart corresponds to low ______ on a constant pressure chart.

height, pressure

warm air aloft is associated with cold air aloft is associated with

high atmospheric pressure low atmospheric pressure

On an upper-level chart, normally we find warm air associated with ______ pressure, and cold air associated with ______ pressure.

high, low

diffusion process

higher vapor pressure over water vapor causes molecules to diffuse towards ice crystal. Water droplet evaporates - continues source for ice crystal

Warm air aloft is associated with constant pressure surfaces that are found at ______ altitudes than normal and ______ than normal atmospheric pressure aloft.

higher, higher

accretion

ice crystals grow larger colliding with supercooled water droplets

where is the collision coalescence top significant in regards to the production of precipitation

in clouds with tops warmer than 5 C

what would cause clouds to form over water at night

land breeze; the warmer water has a higher pressure than the colder land. Air moves from the sea aloft towards the land and then with an increase in pressure at the surface of the land, the air begins to move towards the sea from the land. Upward movement over sea creates clouds.

what produces larger drops of water in clouds?

larger condensation nuclei, turbulent mixing, spending lots of time in the cloud (updraft - tropical regions)

Stand with your back to the wind aloft, the center of lowest pressure will be to your ____ Stand with your back to the surface wind and then turn clockwise about 30°, the center of lowest pressure will be to your ____

left

countour lines

lines of equal elevation warm air = high countours cold air = low contours (one line can represent 1000 ft in florida vs ohio - florida will ave much higher)

the most important factor in the production of raindrops is the cloud's

liquid water content

Suppose you are a pilot who is flying from warm air into colder air. In the cold air, even though your altimeter is still indicating the same altitude as it did in the warm air, you would be flying

lower than indictaed

The largest snowflakes would probably be observed in ______ air whose temperature is ______ freezing.

moist, near

doldrums

over equatorial waters where warm air and weak pressure gradients create a frequently windless area near the Equator. Warm air rises - large cumulus clouds and thunderstorms

On an upper-level chart wind tends to blow:

parallel to the contour lines.

ice nuclei

particles that ice forms on - small number in the atmosphere at high altitudes. Clay, decaying plant leaf matter, and ice crystals are excellent ice nuclei (if their geometry resembles ice crystal)

what direction to isobars is pressure gradient force

perpendicular to isobars

what force causes wind to blow

pressure gradient force; air moves from high pressure to low pressure

hail formation

rain freezes and falls to a warmer part of air, condenses and refreezes to ice balls

A raindrop or partially melted snowflake that freezes into a pellet of ice in a deep subfreezing layer of air near the surface is called:

sleet

in the summer, much of the rain falling in middle and north latitudes begins as

snow

graupel

soft, white balls of ice: snowflakes covered in rime (accretion process). graupel splinters as it falls

snow summer vs winter ft droppage dry air

summer - freezing level is usually high - snowflakes melt as they fall winter - freezing level is much lower and falling snowflakes have a better chance of reaching the ground Snowflakes can generally fall about 1000ft below the freezing level before melting Winter air below the cloud is warmer but drier and it partially melts the flake Evaporation chills the flake and slows down the melting In dry air snowflakes may reach the ground in tempswell above freezing

In order for falling snowflakes to survive in air with temperatures much above freezing,

the air must be unsaturated and the wet-bulb temperature must be at or below freezing.

two columns of air: one cold and one warm how is pressure affected with height?

the atmospheric pressure decreases more rapidly in the colder column of air; rapid change in pressure the atmospheric pressure decreases not as rapidly with the warm column of air. This creates a horizontal difference in pressure.

Large cloud droplets fall faster than small cloud droplets because:

the ratio of the drop's surface area to weight is smaller.

why are there so few ice crystals in the middle of the cloud?

the smaller the amount of pure water, the lower the temperature at which water freezes. Cloud droplets are extremely small so it takes very low temperatures to turn to ice.

during the ice crystal (bergeron process), ice crystals grow larger at the expense of

the surrounding water droplets

Saturation vapor pressure increases as temperature increases.

true

what is a sea breeze circulation and how does it work

type of thermal circulation due to uneven heating of land and water. - Day: land hot (high pressure), water cold (low pressure), air aloft land moves and then surface air over water begins to move towards land = sea breeze - Night: water hot (high pressure), land cold (low pressure) air aloft from water moves to land. Air then at surface moves from the land towards the sea = land breeze- Sea breeze front, sea breeze convergence

cloudbursts

unusually heavy rainfalls originating from cumulonimbus clouds

warm clouds vs cold clouds

warm clouds = clouds that have above freezing temps (collision) cold clouds = clouds that have air temperatures below freezing (ice crystal)

billow clouds

wave clouds- looks like lines. it indicates wind shear

at what point will the droplet of water begin to descent during an updraft?

when the fall velocity of the droplet is greater than the updraft velocity

polar front

where polar easterlies meet the westerlies and produce a stormy belt - low pressure (subpolar low)

FLYING ALONG A CONSTANT PRESSURE SURFACE

you can fly along 29.92 but that can range in height - denser cold air will be lower and warmer air will be higher; must adjust

The net force acting on air, which is blowing parallel to straight contours at constant speed is:

zero