BRNC Met CH1-3

Question 1

What is an inversion layer

Answer 1

An inversion is a layer in which temperature increases with height

Question 2

What is an isothermal layer

Answer 2

An isothermal layer is a layer in which temperature remains the same with height

Question 3

The source of the earths heat is the sun. What type of radiation does it emit?

Answer 3

Short wave radiation

Question 4

How much of the suns radiation enters the earths atmosphere

Answer 4

45%, the rest is either reflected (by clouds or the earths surface), scattered (by particles in the atmosphere) or absorbed (by earths surface)

Question 5

How is the atmosphere heated

Answer 5

From below, by conduction, convection and absorption of long wave radiation

Question 6

What factors influence global surface temperature variation

Answer 6

• Time of day
• effect of cloud cover on surface temp
• effect of wind on surface temp
• Seasons
• Latitude
• Nature of the surface

Question 7

What is the temperature variation between land and sea

Answer 7

The temperature variation between day and night over the open sea is only about 1 degree C, whilst over the land it is often 15 degrees C.

This is due to;
•Specific heat, transparency, reflection, convection

Question 8

Is the solar energy that reaches the earths surface at the poles, greater or less than that at the equator?

Answer 8

Less, which is why there is such a large temperature difference between the 2 regions

Question 9

What is the underlying cause of global air movement in the atmosphere?

Answer 9

The temp difference between the poles and equator

Question 10

In equatorial regions what happens to the heated air?

Answer 10

It becomes less dense, rises, and creates a low pressure zone at the surface called the Inter Tropical Convergence Zone (ITCZ).

The air cannot rise indefinitely, and so spills over in the upper troposphere and diverges to the poles

Question 11

What happens to the cooled air in polar regions?

Answer 11

It becomes more dense and sinks, creating an area of high pressure called the Polar High

At the surface the air then diverges away from this high pressure region (our cold northerlies), while at altitude air converges to replace the subsided air

Question 12

What are the Polar Easterlies

Answer 12

The name given to the resultant winds that are always easterly due to the coriolis effect being greatest at the polar regions in both the northern and Southern Hemisphere

Question 13

What are the Westerlies (roaring forties)

Answer 13

The resultant winds that flow westerly in temperate latitudes in the Southern And northern hemisphere.

*next band from the polar easterlies

Question 14

In low latitudes where the coriolis effect is least, what directions are the winds

Answer 14

Northern hemisphere = Winds coming from NE (NE Trade winds)

Southern Hemisphere = Winds coming from SE ( SE trade winds)

Question 15

What is the axis of low pressure around the equatorial regions called

Answer 15

Inter Tropical convergence zone (ITCZ).

It is the zone in which 2 equatorial airflows (north east & south East trade winds) from northern & Southern Hemispheres converge

Question 16

What happens when the NE & SE trade winds converge in the ITCZ?

Answer 16

As both winds are unstable, when they converge the air may be forced to rise to the Tropopause (at equator hgt =55,000ft) which results in heavy and possibly thundery showers

Question 17

What are the sub-tropical high pressure belts

Answer 17

They are the belts located between the trade winds and westerlies in both hemispheres.

This area of subsidence or sinking air is where large semi-permanent anticyclones occur over the oceans.

There is little cloud or precipitation, large land areas at these latitudes are where the major arid areas of the world are (Sahara, kalahari, Australian deserts)

Question 18

What is a polar front

Answer 18

It is the bands between the polar easterlies and westerlies (roaring forties) in both hemispheres. Where air with a polar origin meets air with a tropical origin, in temperate latitudes

Question 19

What is a jet stream

Answer 19

It is a strong, narrow stream of air concentrated at or near the tropopause.

There are 2 separate jet streams
•Polar jet
•Subtropical jet

The 2 jet streams are rarely continuous, speed and position vary day to days. Wind speeds are generally greater than 100knots and are marked on upper air charts when speeds exceed 50 knots

Question 20

What weather would you find in a;
1- High pressure zone
2- Low pressure zone

Answer 20

1- fine weather

2- poor weather

Question 21

What is pressure gradient force

Answer 21

The amount of change of pressure over a given distance

Question 22

What is geostrophic wind

Answer 22

As air starts to move under the influence of Pressure Gradient Force, it is soon acted upon by the Coriolis forces that acts at right angles to the direction of motion (of the air).

Eventually an equilibrium will be reached, when the two forces balance each other out. The resulting flow of air moves along the isobars, aka geostrophic wind.

Question 23

In what direction does air circulate in the northern hemisphere (in low / high pressure flows)

Answer 23

Air circulates in a clockwise direction around a high pressure isobar (anticyclone) and anti-clockwise for a low pressure isobar (depression) “”remember L for left and low””

Question 24

What is Buys Ballot law

Answer 24

Buys Ballot law states that if you stand with your back to the wind in the northern hemisphere, low pressure will always be to your left.

The converse is true in the Southern Hemisphere.

However within 5 degrees of the equator, Coriolis force is negligible and buys ballot laws does not apply.

Question 25

What is meant when wind backs

Answer 25

When the wind changes in an anti-clockwise direction

Question 26

What is meant when wind veers

Answer 26

The wind has changed direction in a clockwise sense

Question 27

What other force affects wind close to the ground

Answer 27

Friction

Above 2000ft friction is negligible, and geostrophic wind can be taken as the wind that is blowing. There on a plotted chart geostrophic wind is that at about 2000ft

Below 2000ft friction slows wind down and causes it to back

Question 28

Friction varies, particularly over land. What two rules form a basis to work off?

Answer 28

1) over the sea, where friction is small, the surface wind is backed 15 degrees (approx 1 point of a 16 point compass) from the geostrophic wind and is 2/3 of its speed.
2) over land, where friction is greater, surface wind is backed 30 degrees (approx 2 points of a 16 point compass) from geostrophic wind and is 1/2 of its speed.

Question 29

What is a gust

Answer 29

A sudden increase in wind speed that lasts for just a few seconds

Question 30

What is a squall

Answer 30

An increase in wind speed that can last for several minutes

Question 31

What is the name of the scale used to specify wind speed?

Answer 31

Beaufort wind scale

Question 32

What is centripetal force

Answer 32

Above the friction layer, if the isobars are straight the only forces acting are the PGF and the coriolis force and are in balance.

However if the isobars are curved, another force is involved. Centripetal force.

Question 33

What is gradient wind

Answer 33

Gradient wind is the resultant wind when PGF, Coriolis force and centripetal force are all in balance.

Gradient wind is either greater or lesser than geostrophic wind depending on whether the curvature of the isobars are cyclonic (around a low pressure system) or anticyclonic (around a high pressure system)

Question 34

With a cyclonic (low pressure system) curvature, is the actual wind speed greater or less than geostrophic wind?

Answer 34

LESS.

Because, to produce circular motion in cyclonic sense, the PGF must over balance the geostrophic or Coriolis force (acting to the left), to provide centripetal acceleration. (Remember low pressure, wind goes left (anti-clockwise), PGF acts/pulls to the left, left is less, so actual wind is less than geostrophic wind.

Question 35

With an anticyclonic curvature (clockwise - around a high px system) is the actual wind greater or less than geostrophic wind and why?

Answer 35

Greater.

To produce circular motion in an anticyclonic sense (around a high px system) the geostrophic or coriolis force must overcome the PGF, (acting to the right) to provide centripetal force.

Anticyclonic actual winds speeds are greater than geostrophic winds