Meteorology Exam #3

Chapters 8-11

Atmospheric Pressure

mass of air above a given level

Equation of State or Ideal Gas Law

p=TpC

true or false

warm air aloft is associated with high pressure

true

True or false

air flows from low pressure to high pressure

false. air flows from high pressure to low pressure

warm air at surface results in

low pressure

cold air at surface results in

high pressure

1 bar =

1,000 millibar (mb)

1 hectopascal (hPa) =

1 millibar

standard of atmosphere

1013.25 mb = 1012.25 hPa = 29.92 Hg

Mercury Barometer

a tube of mercury rises and falls with pressure changes

aneroid barometer

small box compresses and expands with changing pressure

Altimeter

measures pressure and altitude

barograph

records a trace of atmospheric pressure

Station Pressure

pressure reading after correcting for temp, gravity, and instrument error.

true or false

small changes in elevation produce large pressure changes so pressure readings from different elevations must be reduced to sea level to compare

true

Isobar

lines of equal pressure on a weather map

sea level pressure chart

all station pressures are reduced to sea-level and plotted. smoothed to provide easier view

Constant height chart

each map shows isobars at a constant height level. isobars represent variations in horizontal pressure at that altitude. most used in meteorology

On a weather map, blue H represents high pressure

anti-cyclone, weather generally fair, clockwise flow of air

on a weather map red L represents low pressure

cyclone, weather generally unsettled, counter-clockwise flow of air

wind direction

direction FROM which the wind is blowing

prevailing wind direction

most frequently observed wind direction during a given time

Newton’s 1st Law of Motion

body at rest stays at rest, body in motion stays in motion unless acted upon by an outside force

2nd Law of Motion

total force exerted on an object equals its mass x the acceleration produced

F=ma

Pressure Gradient Force (PGF)

PG is change in air pressure over a given area.

closer isobars = large pressure change over short distance with faster winds

oriented from high pressure toward low pressure

Corilois Force

apparent force created by rotation of earth and deflects objects from straight path (deflects to the right in northern hemisphere)

varies with rotation, latitude, speed of object (strongest at the poles, weakest at equator)

its only significant for fast moving objects or objects that travel long distances

Geostrophic Winds

“winds aloft”

PGF acts upon parcel (north towards lower pressure)

CF takes over (deflects right, path now curved)

Speed takes over (PGF and CF balence out)

air parcel at constant speed (unless another acts force upon parcel)

Winds and forces in low air pressures

cooler air, stronger winds

winds and forces in high air pressures

warmer air, weaker winds

Zonal Wind Patterns

East to West flow

Meridional wind patterns

north to south flow

surface level winds

much slower than at high altitudes because of friction

reduces wind speed at surface (reduces Coriolis force)

Vertical Winds

Winds blow out and away from center of high pressure (outward flowing air diverge)

winds blow in and towards center of low pressure (inwards flowing air converge)

low pressure = rising air

high pressure = sinking air

Planetary scale

weeks or more, entire planet

includes long waves in the westerlies

10,000 km and higher

ex el nino and la nina

Synoptic scale

includes high and low pressure systems and hurricanes

500-2,000 km

Mesoscale

fronts and thunderstorms

from a few km - 500

lasts hours - few days

microscale

tornadoes and smaller winds (eddies)

less than 1 km

few minutes - 1 hour

Planetary Boundary Layer (PBL)

aka atmospheric boundary layer or friction layer

lowest 1,000 meters (3,000 ft)

very important for surface friction

Viscosity

friction of fluid flow

irregular, random turbulent whirls called eddies form in viscous flow

eddies

form from irregular random turbulent whirls called eddies form in viscous flow

within each eddie, wind speed and direction change rapidly. creates internal friction and slows flow

wind blowing over a smooth surface produces few eddies and vise versa

surface heating

steep lapse rate cause deep thermal turbulence (rising thermals)

what causes strong mechanical turbulance

strong wind speeds and rough and hilly landscapes

wind shear

when wind changes speed or direction abruptly

if strong wind shear occurs with no visible cloud or dust, it is called clear air turbulence (cat)

wind vane

spins on a post until arrows point into wind (direction only)

anemometer

cups on a pole spin around in the wind (speed only)

aerovane/skyvane

combo of wind vane and anemometer

wind profiler

vertical pointing radar that can tell how wind changes with height

emits pulses of microwaves into atmosphere

irregularities in moisture and temp and will backscatter energy

observations are plotted on a map at different locations (mainly midwest)

Radioshonde

instrument package on a weather balloon

measures temp, humidity, pressure, wind

Skew-T Diagram

vertical profile that displays weather info/observations from weather balloons

shows temp, dewpoint, wind, pressure, and lapse rates

Upper air maps

maps that display weather info and observations from weather balloons

thermal circulations

rising and falling pockets of air all at different temps

driven by unequal heating of surfaces

land and sea breezes

uneven heating rates of land vs water create mesoscale coastal winds

Sea Breeze

During day: begin mid-late morning once land has chance to warm

land heats faster than water

lower pressure over land, high over water

wind blows from the high to low pressure (sea to land)

causing cooling breeze from the sea. often produce afternoon thunderstorms

Land Breeze

during night

land cools faster than water

forms low pressure over water

wind blows from land to water

causes cooling breeze from the land

Moisture Advection

Lake effects snow

wind picks up water from a large lake (ie michigan)

moist air moves over land and precip falls over last east of the water source

Monsoon

seasonally driven change in wind direction

Winter monsoon

dec-feb

dry season

winds blow from land to sea

Summer monsoon

wet season

june-sept

large scale low pressure over land causes wind to blow from water to land

true or false

there is monsoonal circulation over the SW of the USA

true

Chinook Wind

warm dry wind that descends the eastern slope of rocky mts.

strong westerly winds aloft flow over north/south oriented range

wind moves over mts and moisture in the air condenses and turns into precip

warms air by releasing latent heat

Santa Anna Wind

warm, dry downslope wind in CA that enhances wildfire risks

persistant (blocking) high pressure over rockies produces strong winds over SOCAL

dry wind = dry atmosphere

Dust Devils

spinning vortices commonly seen on hot days in dry areas (deserts) aka whirlwinds

sunlight heats earth → lack of surface water → surface and atmosphere very hot → convection begins → no water = no clouds → barriers rotate “wind tubes” → spinning whirls of dust/dirt

rotate anti-cyclonically and cyclonically

NOT tornadoes

very weak and not long lived

Atmospheric Circulation

general circulation is long term average of wind over the globe. Provides insight into large scale conditions over different parts of the globe and underlying causes

3 Cell Model

Idealized triple cell model that transports heat and energy dispersion across different parts of hemisphere.

Hadley Cell

0 degrees to 30 degrees. convection cell

Intertropical Convergence Zone (ITCZ)

Area of lower pressure with convergence of air and rising motion. Lots of thunderstorms and rain, found along equator. result of trade winds converging in one location

Ferrel Cell

30-60 degrees. Mid latitudes

area of large temperature contrasts. air travels to pole at the surface. Air rises as it meets the polar cell and then returns towards the equator aloft

Polar Cell

60-90 degrees

coldest cell due to outgoing radiation. air sinks at polar high because it is cold and dense. air moves towards equator at surface

true or false

areas of high and low pressure are stationary and do not weaken/strengthen as seasons change

false

areas of high and low pressure move around and weaken/strengthen as seasons change

jet streams

fast flowing narrow air currents found in atmosphere somewhere between 30,000 and 40,000 ft. (just under tropopause) form at boundaries of adjacent air masses with significant differences

Subtropical jet stream

southern jet stream. warmer air, moisture, spring and summer

Polar front jet stream

northern jet stream. colder air, fall and winter

what happens when jet streams merge?

severe weather. fight each other for control of the atmosphere

low level jet stream

forms over central plains

close to surface (few 100 meters up)

½ of the speed of upper level jet streams

advects moisture to overnight thunderstorm complexes

strongest at night and weakest in mid morning

most common in spring and summer

El Nino

warm current of water in south pacific. occurs around christmas time

typically lasts from a few weeks to a couple months

Conditions of El Nino

low pressure over east pacific

high pressure over west pacific

pressure differences and change cause trade winds to weaken and reverse their direction

effects counter ocean currents and brings warmer air, warmer sea surface temps and stormier weather

Conditions of La Nina

low pressure over west pacific

high pressure over east pacific

provides easterly trade winds along equator (cooler water upwelling is enhanced)

high pressure over east pacific is “stubborn” and won’t move much, backing up the weather traffic out over west pacific (ie low pressure)

Air masses

large body of air whose properties of temp and humidity are similar in any given direction and altitude. cover 1000s of miles. form in source regions

source regions

where air masses form

usually flat with light winds (can be land or water)

dominated by high pressure

mid latitudes are not good

How are air masses characterized

Moisture: Dry (c for continental) Wet (m for maritime)

Temp: warm (T for tropical) Cold (P for polar) Frigid (A for arctic)

5 Main types of air masses

cT: Continental tropical (deserts)

cP: Continental polar (Canada)

cA: Continental arctic (arctic circle)

mT: Maritime tropical (south pacific, gulf of mexico, south atlantic)

mP: maritime polar (north atlantic, north pacific)

cP and cA Air Masses

forms over ice and snow covered regions of Alaska and Canada

brings very cold air south into central US

outbreaks of below 0 temps for MO and freezing weather in FL

Air mass slowly warms as it heads south

dry cP air moving over gulf warms rapidly and gains moisture

Dry cP quickly becomes maritime

mP Air Masses

forms over cold water like the north pacific and atlantic

moves inland over pacific northwest (Washington state) and Northeast (Maine)

Causes major winter time snowstorms

maritime polar air provides shows and precip to CA and other places on west coast

“modified” mP provides showers and precip weather in plains states when mixed with warm, moist air (hits the rockies)

lots of moisture for major new england snowstorms

mT Air masses

warm moist air from subtropical pacific, gulf, and/or atlantic moves inland

in winter in California, “pineapple express” brings heavy rain and mudslides

humid air is a fuel source for summer and winter storms in midwest

cT air masses

hot and dry air masses originate over deserts of mexico

air may be unstable but lack of moisture ensures dry weather

provides long, dry, hot days to central plains and midwest

if a “blocking pattern” sets up, extreme drought conditions and hot temps can be realized and high pressure wont budge

Frontogenisis

strengthen the front and increase the temp differences across a front

Frontolysis

to weaken, decrease temp difference across front

Cold Front

drawn on a map with blue

triangles in the direction the cold air is moving toward

usually active weather along the front

Warm Front

drawn on a map with red

red ovals point in the direction the warm air is advancing

light rain along the front

Stationary Front

Drawn in alternating colors (blue and red)

essentially no movement

least active type of front system

big difference in air masses (north and south of front)

Occluded Front

drawn in alternating pips

where cold and warm fronts run into each other

attached to strong low pressure systems

what are weather fronts typically associated with

changes in temp

changes in humidity

changes in wind direction (always)

cloud cover

precip