L2 The Motion of the Atmosphere

Flashcards about the motion of the atmosphere.

What force drives the movement of air in the atmosphere?

The Sun's energy.

How does the atmosphere acquire heat energy from the sun?

The atmosphere acquires virtually no heat energy directly from the sun.

What are the factors that result in a higher concentration of insolation in tropical areas?

The virtual spherical shape of the earth and the oblique depth of the atmosphere at different latitudes.

What are the processes by which energy is transferred from the Earth's surface to the troposphere?

Conduction, terrestrial radiation, and convection.

What causes the northern and southern hemispheres to receive varying concentrations of solar energy?

The tilt of the Earth on its axis.

How do the heating properties of land and water differ?

Land heats and cools quickly while water changes temperature slowly.

What creates areas of high and low pressure?

The uneven heating of the Earth's surface.

What is wind?

The flow of air from high pressure to low pressure.

Give an example of locations with different elevations.

RAF Valley is 37 ft AMSL, whereas Biggin Hill is about 600 ft AMSL.

Why is observed pressure adjusted to sea level?

To give a uniform datum.

What is the sea level pressure datum called?

QFF.

What are isobars?

Lines joining points of equal sea-level pressure.

What does 'isobar' mean?

Equal weight of atmosphere

What do closely spaced isobars indicate?

Isobars close together indicate a steep pressure gradient and stronger winds.

What do widely spaced isobars indicate?

A slack pressure gradient.

How do pressure patterns at the surface and tropopause relate?

Surface low leads to rising air and divergence in an upper high, surface high leads to divergence and subsidence in an upper low.

What is the Coriolis force a consequence of?

A consequence of the rotation of the Earth on its axis.

How does the Coriolis force act on a moving particle?

90 degrees to the right in the northern hemisphere and 90 degrees to the left in the southern hemisphere.

Where is Coriolis force strongest?

The poles.

Where Coriolis force is zero?

The equator.

Who is the Coriolis effect named after?

Gustave-Gaspard Coriolis.

When does geostrophic wind occur?

When the pressure gradient force is equal to the Coriolis force.

What is the resulting wind referred to in curved isobars?

The gradient wind.

What two components are always quoted together when measuring wind?

Wind direction and wind speed.

What is wind direction?

The direction from which the wind is blowing.

How is wind direction usually referred to in weather forecasts and reports?

degrees 'true', although wind direction given by radio from an ATSU is usually in degrees 'magnetic'.

What measures wind speed?

An anemometer.

What is wind speed normally reported in?

Knots (KT).

What can we use the alignment of the isobars to do?

To estimate wind direction and estimate wind strength.

How can you get the speed in knots?

Double the metres per second figure.

What does 'EGNH 190550Z 31010KT CAVOK 15/10 Q1021' describe?

The reporting of surface wind velocity.

When is it said that the wind has veered?

When the wind direction increases clockwise.

When is it said that the wind has backed?

When the direction decreases anti-clockwise.

What is the wind velocity at 2000 ft often referred to as?

The 'free wind'.

What are the effects of contact with the surface?

Friction reduces its speed and the Coriolis force is reduced and the wind direction backs.

What reduces wind speeds the most over land?

The irregular surface and obstructions.

Over the sea, the difference between the surface wind and the 2000 ft wind.

About 20% and a backing of about 10 degrees.

What is wind reduction and backing over the land?

The reduction in speed is much greater - nearer 50% - and therefore the backing in direction is more marked at about 30 degrees.

What is the layer of atmosphere through which change occurs?

The friction layer.

What affects the thickness of the friction layer?

The type of surface and wind speed.

How does the sea affect heating?

There is little change in surface heating over the sea, and little change in the friction layer by day or night.

What happens within the friction layer?

The wind velocity decreases and the direction backs with decreasing altitude from 5000 ft.

What happens by day?

Surface heating causes convection which increases mixing in the atmosphere.

How do surface winds change at night?

Winds tend to back, decrease and become more steady.

What is a wind blowing down the mountain side during the night referred to as?

A katabatic wind.

What is the result of an up-slope wind?

Anabatic wind.

What is the daily variation of temperature known as?

Diurnal variation.

When will the highest temperature occur?

3pm.

When is the lowest temperature at the surface?

The lowest temperature at the surface occurs just after sunrise.

What causes sea breezes?

Sea breezes are caused by the diurnal variation of temperature and the different heating properties of land and sea.

What is a sea breeze?

A cool breeze blowing towards the land from the sea.

What force may veer the wind flow?

The Coriolis force.

What is an off-shore breeze blowing from the land to the sea known as?

A land breeze.

What happens during a clear night?

Katabatic wind.

What causes a more general daily variation of wind?

Diurnal temperature cycle.

Where is turbulent air often found?

Downwind of an obstruction or high terrain.

Where does a change in wind velocity, wind speed or both occur?

Over a relatively short vertical or horizontal distance.

What is known as the change in wind velocity, wind speed or both?

Windshear or sometimes wind gradient.

What is a ridge?

An elongated area of high pressure.

What is a depression?

An area of low pressure is called a depression.

What is an anticyclone?

clockwise wind flowing around it in the northern hemisphere.

What is a col?

An area of little or no pressure-gradient between anticyclones and depressions.

How does the air follow Isobards?

Air follows isobars anti-clockwise around a low-pressure area and clockwise around a high-pressure area, in the northern hemisphere.

What law states, that in the northern hemisphere, if you stand with your back to the wind, the low-pressure area is on your left?

Buys Ballot's Law.

Describe the Bora wind.

A northern to north-eastern katabatic wind flows from Balkans into the Adriatic.

Describe the Mistral wind.

A strong, cold, northwesterly wind that blows from southern France into the Gulf of Lyon in the northern Mediterranean.

Describe the Sirocco wind.

A Mediterranean wind that comes from the Sahara and can reach hurricane speeds in North Africa and Southern Europe.

What is Meteorology?

The study of the atmosphere and its phenomena

What results in the everyday phenomenon of wind?

The horizontal movement of air in the atmosphere.

The atmosphere is _ to solar radiation.

Transparent.

Radiation from the sun heats up what?

The Earth's surface.

In the tropics, does the Earth's surface absorb more or less of the sun's energy than in the polar regions?

More.

In effect, the atmosphere is heated from _.

From below.

What would be the net result at the Earth's surface if there were an uncomplicated circulation of air over the planet?

High pressure at the poles, low pressure in the tropics.

Land tends to heat and cool _.

Rapidly.

Water changes temperature _.

Slowly.

When assessing current and forecasting future weather conditions, a knowledge of _ is of prime importance.

Pressure distribution.

Observing points are all at _.

Different elevations.

To give a uniform datum, the observed pressure is increased using _.

A standard formula.

Isobars can be likened to the _ of a map.

Contour lines.

Air flows down a pressure gradient - from _.

High pressure to low pressure.

The Coriolis 'force' is often referred to as _.

The Coriolis effect.

The flow of air may be sufficiently deflected so that it travels _ to straight isobars.

Parallel.

The deflection 'curves' the path of the air particles with respect to _.

The earth beneath.

On meteorological surface pressure charts, surface friction will change both speed and direction.

Surface friction.

When a wind direction changes clockwise, it is said to have _.

Veered.

When the direction decreases anti-clockwise, it is said to have _.

Backed.

Where air flows over _, friction reduces its speed.

The surface.

Sometimes it is necessary to climb surprisingly high to find _ on a blustery day.

Smooth air.

Within the friction layer the direction of the local winds will be affected by _.

Terrain, buildings.

The lowest temperature at the surface occurs _.

Just after sunrise.

The highest temperature occurs around _.

3 p.m.

Over the sea, cooler air is more dense and tends to be _.

Subsiding.

Initially the sea breeze blows at _.

90 degrees to the coast.

In time the Coriolis force may veer the wind flow cause it to blow at _.

An angle to the coastline.

At night, an _ breeze blows from the land to the sea.

Off-shore.

During a clear night the land cools _.

Rapidly.

Layer of cool, dense air flows down the slope _.

Draw by gravity.

Wind blowing down the mountain side during the night is referred to as _.

Mountain wind.

Anabatic wind is also known as _.

Up-slope wind.