Ch 17 - Air Masses

Question 1

Air Mass

Answer 1

A large volume of air that is several hundred km across

Properties it has it have;

• Same temp
• Same humidity levels

Can stay over their source region for days/weeks at a time before moving

Question 2

Source Regions

Answer 2

Maritime Equatorial mE
Maritime Tropical mT
Maritime Polar mP
Continental Polar cP
Continental Arctic cA

Equatorial masses are the only not to hit the UK

Air masses are stable at their source (high pressure systems)

Artic mass only reaches the UK in winter

Question 3

Air Mass Sources Latitudes

Answer 3

Arctic 60-90’N/S
Polar 40-60’N/S
Tropical 20-30’N/S
Equatorial 0-20’N/S

Question 4

Air Mass Journey

Answer 4

Either goes from a cool surface area to a warmer surface area, warming, rising creating unstable conditions - CB, TCU, TS, Rain showers or reverse; from warm to cold areas, cooling, condenses and creating stable conditions; less clouds, stratus, drizzle, fog/haze

Question 5

MT

Answer 5

Example Azores to the UK

Cools on journey, becomes stable, increasing moisture content (RH increases), leads to ovc stratus, winter-coastal fog, low visibility

Question 6

CT

Answer 6

Africa - EU/S. UK

UK in summer (Jun-Aug) sometimes at other times

Goes from hot and dry, cooling and becoming stable on its journey and either bringing cool stable humid air mass with stratus clouds in winter, or v. Warm/hot dry stable air in summer with poor vis (Haze/Dust/Sand) and CB-TS in the afternoon

Question 7

MP

Answer 7

Canada, Greenland towards UK - the most common air mass to effect the UK

At its source it is cool, cold and very humid, it heats on its way across, becomes unstable, picks up more moisture on route and brings wet, unstable, convective air with good vis away from showers in summer. In winter, it brings much greater instability due to the huge temp differences between Canada and uk. Storms, CB, TS but vis good away from bad wx

Question 8

MPR

Answer 8

Can effect the UK all year - again from Canada or Greenland and has layers within it

Moves down towards Azores round a L pressure system, becoming unstable, lower levels are stable in the uk, brining stratus clouds, fog and drizzle. At high alt., it is very unstable leading to CU or SC

Question 9

MA

Answer 9

In the winter it is the most common mass to reach the UK - can still reach in summer though

Comes from the arctic (pole) moving south over the sea towards Scotland

Journey becomes very unstable, RH decreases, temp increases, vis good in summer away from showers. In winter, there is greater instability

Question 10

Most unstable conditions for UK

Answer 10

mP and mA

Question 11

CP

Answer 11

2 different journeys;
Short Sea Track (channel)
Long Sea Track (North sea)

Source Siberia stable, comes across in winter generally, low RH and very dry.

Short sea track produces stable conditions. Frost, fog and moderate vis. Long sea track brings increased humidity, slightly unstable, SHSN, SHRA and good vis away from showers

Question 12

Frontogenisis

Answer 12

The creation of a front (formation)

Question 13

Frontolysis

Answer 13

Dissipation of a front

Question 14

Front

Answer 14

A narrow section, just a few miles across

Question 15

Transitional Zone

Answer 15

100’s of miles across

ITCZ is an example