MET module 6-8

Barometers

are instruments that detect and measure pressure changes.

Air pressure

is simply the mass of air above a given level.

What is the unit of pressure most commonly found on surface weather maps?

Milibar

What is the standard atmospheric pressure at sea-level?

1013.25 mb=1013.25h Pa=29.92 in.Hg

What is the mercury barometer?

A barometer with a mercury column, and its height was used to measure atmospheric pressure, invented by Evan Torricelli in 1643.

What are aneroid barometers composed of?

No fluid, an aneroid cell, and its cells size represent different pressures, and changes in its size is amplified by levers and transmitted to an indicating arm that points to current atmospheric pressure.

Station pressure

is a barometer that reads at a location above sea level, and terms elevation.

What is sea-level pressure?

When station pressure adjusts to sea level/average surface height of the ocean.

Isobars

are lines at 4mb intervals with 1000mb as the base value, and these lines connect points of equal pressure.

What are centers of high pressure, and shown as blue H’s on maps?

Anticyclones.

Mid-latitude cyclonic storms

are shown as red L’s on maps that represent low pressure centers, and form outside of tropics in mid latitudes.

What are isobaric maps?

Upper air maps that construct height variations along a constant pressure surface.

What are contour lines?

Solid dark lines on a surface map that connect equal altitude points above sea level.

What are bent/turned contour lines called?

Ridges; places where the air is warmer indicating depressions, and winds around high pressure areas.

Troughs

are places where the air is colder, and are winds around low pressure areas.

What is the amount of pressure change that occurs over a given surface?

Pressure gradient.

Pressure gradient formula

difference in pressure/(divided by)/distance

Which force is apparent and is a result of Earth’s rotation?

Coriolis force

What is geostrophic wind?

Air that flows in a straight path, parallel to the isobars at constant speeds.

Which wind pattern flows in looping meanders, while following a more/less north-south trajectory?

Meridional zone

Where do winds blow west-to-east?

Zonal zone

What is the friction layer?

The atmospheric layer that is influenced by friction and extends upward around 1000m or 300 ft over the surface.

Hydrostatic equilibrium

is when the upward-directed pressure gradient force is balanced by gravity.

What is onshore wind?

Wind blowing from the water onto the land.

What is offshore wind?

Wind blowing from land to water.

What is prevailing wind?

The wind direction most often observed during a given time period/ where wind blows more than other directions.

What represents prevailing wind?

Wind rose, the % of time the wind blows from different directions.

What determines wind direction?

Wind vane.

What measures wind speed?

Anemometer.

What indicates wind speed/direction, and has bladed propeller that rotates at a proportional rate to wind speed?

Aerovane.

Which type of radar detects vertical profiles of wind speed/direction up to 16km or higher?

Wind profiler.

Why does atmospheric pressure always decrease with increasing altitude?

There are fewer air molecules as we increase in altitude which reduces atmospheric pressure.

What might cause the air pressure to change at the bottom of an air column?

Air of the same temperature being stuffed into a column causing surface air pressure to rise, or air being removed causing the surface air pressure to drop.

Why is the decrease of air pressure with increasing altitude more rapid when the air is cold?

Cold air has more densely packed molecules.

Why will Denver, Colorado always have a lower station pressure than Chicago, Illinois?

Atmospheric pressure decreases as altitude increases.

On an upper-level map, is cold/warm air aloft generally associated with low or high pressure?

Cold air aloft-low pressure, and warm air aloft-high pressure.

What does Newtons 1st law state?

Newtons first law states that an object at rest will remain at rest or in motion in a straight line unless a external force acts on it.

What does Newtons 2nd law state?

The force exerted on an object equals its mass times the acceleration produced:F=ma

What does a steep/strong pressure gradient mean? How does it look on a surface map?

A production of rapid change in pressure over a relatively short distance, and lower pressure is on the right and higher pressure is on the left on a surface map.

Why on maps do closely spaced isobars indicate strong winds and widely spaced isobars indicate weak winds?

Closely spaced isobars=greater pressure gradient and results in a stronger PGF.

What does the Coriolis force do to moving air in the Northern/Southern hemisphere?

In the Northern hemisphere, the Coriolis force causes the wind to deflect to the right of its intended path, and to the left in the Southern hemisphere.

How does wind speed and latitdue influence the Coriolis force?

Coriolis force increases as wind speed increases and increases for all wind speeds from zero at the equator to a maximum at the poles. Deviation is the highest toward the pole and nonexistent at the equator which strengthens the Coriolis force at high latitudes.

Why do upper-level winds in the middle latitudes of both hemispheres generally blow from west to east?

Upper level winds in middle latitudes blow from west to east due to the PGF/Coriolis force bending moving air to the right in the Northern hemisphere and to the left in the Southern hemisphere=horizontal differences in pressure.

How do geostrophic winds blow on upper level charts?

They flow parallel to isobars.

How does the wind blow around high/low pressure areas aloft and near the surface in the Northern/Southern hemispheres?

Winds blow counterclockwise around areas of low pressure and clockwise around areas of high pressure in the Northern hemisphere, and in the Southern hemisphere winds blow counterclockwise in high pressure areas and blow clockwise in low pressure areas.

If the clouds overhead are moving from north to south, would the upper-level center of low pressure be to the east or west of you?

East, with your back to the wind, with the low on the left and the high on the right.

On a surface map, why do surface winds tend to cross the isobars and flow from higher pressure toward lower pressure?

Friction

Since there is always an upward-directed pressure gradient force, why doesn't air rush off into space?

The vertical motion is not strong enough to exceed the escape velocity imposed by gravity: hydrostatic equilibrium.

What are some ways you can of determine wind direction and speed?

Trees, flags, wet finger, and wind instruments.

What is the function of a cup anemometer?

Measures speed, and its cups spin and speed is registered.

What is a radiosonde?

An instrument package that measures the vertical profile of temperature, pressure, and humidity located below a balloon.

What measures movements of clouds?

Satellites.

An upper wind direction is reported as 225o. From what compass direction is the wind blowing?

Southwest

What are scales of motion?

Heiarchy of motion from tiny gusts to giant storms.

What is the microscale?

The smallest scale of atmospheric motion constituted by eddies.

Define the mesoscale.

Mesoscale ranges from a few km’s to about 100km’s in diameter, they last longer than microscales and can last for minutes up toa day: thunderstorms, tornadoes, and small tropical cyclones.

Define the synaptic scale.

Circulations near high/low pressure areas, cyclones/anticyclones of the mid-latitudes, lower latitude tropical cyclones, they dominate regions of 100’s-1000’s of square km’s, and they last for days/weeks.

Global/planetary scale

is where we look at the entire Earth’s wind pattern.

Macroscale

is the largest atmospheric motion scale, and the combination of the synoptic and global scales.

What are rotors?

Violent vertical motions that produce extreme turbulence and hazardous flying conditions.

Wind shear

are the changes in wind speed/direction.

What’s the relationship between turbulence aloft and wind shear?

Turbulence aloft can occur unexpectedly especially where the wind changes its speed/directions, and the shearing creates force produced eddies along a mixing zone.

When eddies form in clear air they form?

Clear air turbulence/CAT

What is thermal circulation?

Circulations brought on by changes in air temperature in which warmer air rises and colder air sinks.

Sea breeze

is a type of thermal circulation that blows at the surface from the sea toward the land.

Land breeze

is a breeze that flows from the land toward the water.

What is valley breeze?

When heated air is less dense than the air of the same altitude above the valley, rises as a gentle upslope wind.

Mountain breeze

is where cooler and denser air glides downslope into the valley.

What are kabatic winds?

Downslope winds that are much stronger than mountain breezes can rush down elevate slopes at hurricane speeds, mostly at 10 knots or less.

The chinook wind

is a warm/dry downslope wind that descend down the eastern slope of the rocky mountains.

Santa Ana wind

is a warm dry wind blowing downhill from the east or northeast into Southern California.

What are haboobs?

Dust/sand composed storms that are cold downdrafts along the leading edge of a thunderstorm lifting dust/sand into a dark cloud that can extend horizontally over 100 km that rise vertically to the thunderstorms base.

Dust devils

are rising/spinning columns of air that collect dust/sand in dry areas on clear, and hot days.

What are monsoons?

Thermal circulations that are larger than sea/land breeze based circulations.

Monsoon wind systems

change direction seasonally and are well developed in eastern/southern Asia.

General circulation of the atmosphere

are when global winds are averaged over a long period of time causing the local winds to vanish.

Define the Hadley cell.

A cell driven by solar energy(created by George Hadley in the 18th century).

Doldrums

are where warm/humid air rise; often condensing into cumulus clouds and thunderstorms that liberate enormous amounts of latent heat.

What are subtropical highs(anticyclones)?

Belts of high pressure produced by air aloft convergence at latitudes near 30*.

What are trade winds?

Winds that provide sailing ships with a route to the New world.

The intertropical convergence zone (ITCZ)

is the boundary near the equator where the northeast trades converge with the southeast trades, and along the ITCZ its wet as rising air develops into thunderstorms that form from rainshowers.

Westerlies

is air that move towards the poles and deflect toward the east which creates more/less westerly airflow.

What is the polar front?

A boundary separating surface air traveling poleward from latitude 30* from cold air moving down from the pole.

What is the subpolar low?

A low pressure zone where surface air converges/rises, and clouds/storms develop.

Define polar easterlies.

When Cold air from the poles are deflected by the Coriolis force located behind the polar front in the Northern hemisphere so that the general air flow is from the northeast.

Define the Bermuda and Pacific high.

The Bermuda high is in the eastern Atlantic between 25-35 * N latitudes, and in the Pacific high is in the Pacific ocean, and both are subtropical anticyclones that develop due to air aloft convergence.

Icelandic low

is in the North-Atlantic and covers iceland and Southern greenland.

The Aleutian low

sits over the Gulf of Alaska and the Bering sea near the North Pacific.

Define the Siberian high.

Over Asia the thermal anticyclone that forms due to intense cooling land of the land.

Jet streams

are rivers of fast flowing air where level winds tend to concentrate into narrow bands.

Where is the subtropical jet stream located?

Near 30* latitude around 13 km (43000 ft) above the subtropical high.

Where is the polar fron jet stream located?

To the north situated at lower altitudes of about 10 km (33000 ft) near the polar front.

Define the Gulf stream.

A tremendous warm water current in the North Atlantic flowing northward along the east coast of the U.S, and carries aloft of tropical water into higher latitudes.

Upwelling

is the rising of cold water from below, and the cause for cold coastal water.

El nino

is prolonged warming that occurs at irregular intervals every 3-7 years.

Southern oscillation

is the seesaw pattern of reversing surface air pressure at opposite ends of the Pacific ocean.

La Nina

are cold water episodes where water temperature is colder in the eastern tropical Pacific (than average).

What are teleconnections?

Ocean atmospheric interactions where a warmer/colder ocean surface can influence weathern patterns in distant parts of the world.

Define the (PDO).

More influential in the North pacific’s mid latitudes while lasting longer than ENSO.

Define the North Atlantic Oscillation.

A periodic reversal of pressure has an effect on Europe’s and North Americans east coasts weather especially during winter.