fronts and airmasses

Question 1

what is an air mass?

Answer 1

an air mass is a large parcel of air with fairly uniform properties throughout.

Question 2

airmasses are usually defined how?

Answer 2

defined depending on its source, hot or cold normally.

Question 3

airmasses moving from the poles towards the equator are usually what type?

Answer 3

cold

Question 4

airmasses moving from the equator towards the poles are usually what type?

Answer 4

warm

Question 5

what are the 4 types of air masses?

Answer 5

tropical air mass consists of air flowing from the tropics (WARM)
polar air mass consists of air flowing from polar regions (COLD)
maritime air masses are ones flowing over a large sea area (MOIST)
continental air masses are ones flowing over a large land area (DRY)

Question 6

tropical maritime air brings air from where?

Answer 6

it brings warm moist air from pacific areas

Question 7

polar maritime air originates from where, and bring normally what to NZ?

Answer 7

originates from the antarctic bringing cold moist air to NZ. typically spreading from up south to north.

Question 8

what happens when polar maritime air masses move across warmer land?

Answer 8

instability increases, leading to severe turbulence and thunderstorms with severe icing, in winter, snow showers are common.

Question 9

what happens when an air mass moves over a warmer surface?

Answer 9

the surface temperature increases and lapse rate in lower levels produce on instability which may lead to severe convection currents and towering cumulus

Question 10

what happens when an air mass moves to a colder surface?

Answer 10

some change in stability is inevitable with a change in landmass temperature.

if an air mass moves over a colder surface area, it’ll be cooled from below - decreasing lapse rate to a stable value.

Question 11

what will mechanical turbulence do to the lower layer of an air mass?

Answer 11

it will mix the lower layer of the air mass. lowe stratus cloud may form and advection fog may occur.

Question 12

why does pressure distribution play a big part in determining the properties of an air mass?

Answer 12

air flowing out of a higher pressure system will have different properties of an air mass and from that flowing into a low pressure system.

Air descending slowly into an area of high pressure will warm and become dry and stable, normally associated with fine weather

Question 13

what is a front?

Answer 13

when two air masses of different temperatures meet they don’t mix together but stay bound together. the area between the two masses is called a front.

Question 14

how is a front formed?

Answer 14

Initially, a small wave of warm air intrudes into colder air.

This wave ripples its way along the front with the air stream. the pressure at the tip of the wae decreases and the front is made.

leading part of the wave becomes a warm front and the rear the cold front.

Question 15

what is the air between the fronts and the air surrounding the tip called?

Answer 15

the air between is the warm sector and the air surrounding is the cold sector.

Question 16

what is the frontal surface?

Answer 16

when the contrasting air masses meet, the warm light air tends to rise above the cold dense air.

the cold air forms a flat wedge underneath the warmer air and the tilted boundary between the two masses is the frontal surface.

Question 17

what is a cold front? And how are they characterised?

Answer 17

It’s where cold air forces its way underneath warm air.

cold fronts are characterised by extreme temperature changes and can produce sudden and severe weather for a short period of time.

Question 18

how is a cold front depicted on weather charts usually?

Answer 18

a blue line with barbs pointing in direction of movement.

Question 19

what is a warm front?

Answer 19

a warm front is one in which warm air moves and overrides cold air. the change in temperature is very gradual, so a warm front may extend over a very large area.

Question 20

how is a warm front depicted on a weather chart?

Answer 20

depicted by a red line with semicircles pointing in direction of movement.

Question 21

what is an occluded front?

Answer 21

An occlusion occurs as a result of warm and cold fronts merging. resulting weather tends to be a mix of warm and cold fronts.

Question 22

how is an occluded front depicted on weather charts?

Answer 22

depicted by alternate spikes and half circles coloured purple

Question 23

what is a stationary front? and what causes it

Answer 23

a front that’s air mass is not strong enough to overpower the other. caused by a pair of air masses, neither of which is strong enough to replace each other.

Question 24

how is a stationary front depicted on weather charts?

Answer 24

depicted by an inter-playing series of blue spikes pointing one direction and red domes pointing the other.

Question 25

what happens when warm air moves up the frontal surface?

Answer 25

it cools at the dry adiabatic rate, as it rises the air becomes saturated and clouds form.

Question 26

the extend and severity of cloud and precipitation associated with fronts is usually dependent on what factors?

Answer 26

mainly on the slope of the frontal surface, and the stability and moisture content of the warm air being lifted by the front.

the steeper the frontal surface the more severe the weather.

Question 27

what type of slope do cold fronts usually have and how does this affect weather?

Answer 27

typically a steep slope resulting in severe weather over a short distance

Question 28

what type of slope do warm fronts usually have and how does this affect weather?

Answer 28

warm fronts have a more gentle slope, producing moderate weather over a much greater distance.

Question 29

how can isobar patterns detect potential frontal formation?

Answer 29

if there’s a large contrast in pressure between two air masses, it follows that the isobars will show a marked change and an active front develops.

Question 30

how does an inactive front occur?

Answer 30

it occurs when there’s less contact contrast in pressure.

Question 31

what are the characteristics of an inactive front?

Answer 31

active front forms a sharp V shape while an inactive front is a shallow U shape.

the more severe this shape the more severe the weather change during the passage of a front.

Question 32

what type of clouds are expected of an approaching warm front?

Answer 32

due to the gentle slope of a warm front, the cirrus cloud may be seen in advance of the front surface position - sometimes up to 600NM, gradually thickens to become cirrostratus.

Cloud base will gradually lower and clouds will thicken further to become alto stratus. from which precipitation my fall. up to 300 NM from the front itself nimbostratus and continuous precipitation can be seen

Question 33

what are conditions like during a warm front in flight?

Answer 33

conditions deteriorate, ceiling lowers and visibility is reduced. as well as the characteristic cloud development, another notable feature ahead a warm front.

Question 34

what happens to atmospheric pressure during an approaching warm front?

Answer 34

atmospheric pressure falls for an appreciable length.

Question 35

What happens to air temperature and wind with approaching warm front?

Answer 35

air temperature rises as the warm air moves in, the wind veers ahead of the front to become nearly parallel to the surface front.

Increase in pressure gradient ahead of warm front = increase in wind speed.

Question 36

what happens at the passage of a front?

Answer 36

the winds backs and its speed eventually decreases.

Question 37

what happens behind the warm front?

Answer 37

cloud and visibility conditions are the same as those normally occurring in warm air.

May have scattered cloud and good visibility. may be low stratus cloud with drizzle and fog or poor visibility.

Question 38

what happens during an approaching cold front and how does it occur?

Answer 38

cold fronts have a steeper slope than a warm front, it also moves faster than a warm front.

Along the upper part of the frontal slope, warm air is descending resulting in a narrow band of weather along the forward edge.

There is no average Cold Front weather. You may experience a minor wind shift or a severe thunderstorm. What occurs is determined by the nature of the warm air preceding the Front, the angle of the slope and the speed of the Front

Question 39

since cold fronts span a very short distance what happens to the weather conditions associated with it

Answer 39

they will be short-lived

Question 40

what happens in a cold front if air is relatively dry?

Answer 40

cloud formation is limited and precipitation won’t form.

Question 41

how is the approach of a cold front typically marked?

Answer 41

by a fall of pressure and the wind veering until it’s nearly parallel to surface front.

Question 42

what happens to wind speed in a cold front?

Answer 42

With a change in pressure, some change in wind speed Is inevitable. The wind speed will steadily increase to a peak at the time of the frontal passage

Question 43

what type of wind is expected at the cold front itself?

Answer 43

very gusty winds & squalls may be experienced.

Question 44

what happens to wind at the passage of a front?

Answer 44

the wind Backs and its speed eventually decreases, brief but sometimes violent.

Question 45

what happens to the weather after the cold front has passed? And what happens if conditions are unstable ?

Answer 45

wind may decrease rapidly or may continue for a time as a strong gusty wind. pressure rises rapidly, temperature and dew point drop.

weather conditions behind are usually the same as those of cold air. If air is unstable, showers may be encountered and secondary fronts may occur.

Question 46

what can a cold front usually bring at ground level?

Answer 46

may often bring a warming influence at ground level, especially in mountainous areas in winter. In winter - shallow layer of cold air will reach the upper air.

With the increasing wind near the front, the very cold air at the surface will disperse and be replaced by cold air of the front.

Question 47

what is an occlusion?

Answer 47

Warm and Cold Fronts are usually parts of depressions forming along the Polar Front.

They move in such a manner that the Cold Front section moves faster than the Warm Front section, eventually overtaking it, this is the occluded front

Question 48

depending on the temperature within each part of the mass, an occlusion may bring warming, or a cooling effect, or no temperature change at all? True or False?

Answer 48

True

Question 49

what is the weather associated within occlusions?

Answer 49

a combination of warm and cold front conditions. The dominating character is determined by the temperature difference between the two cold air masses.

Question 50

when flying in an occlusion what should you expect?

Answer 50

When flying in such an area, you should expect complex weather with great cloud development.

Question 51

what is the warm sector?

Answer 51

The area that forms between the Warm and Cold Fronts.

Warm air is transported in from the North, cloud cover in a warm sector can vary from clear to overcast, but mostly of the Stratus type - there is no typical weather associated with a warm
sector.

Question 52

what is a stationary front? What are conditions like in one? And how is it viewed on a chart?

Answer 52

A Stationary Front is one that has become stationary. A Stationary Front’s symbols are shown as back to back red and blue barbs.

The wind flow is parallel to the frontal zone and on the Synoptic chart the Stationary Front is Parallel to the isobars.

Because the Front is stationary, there is normally not a great deal of wind or cloud development associated with this type of front.

Question 53

what are the operational considerations when flying through fronts?

Answer 53

passing through cold air - prepare for diversion. Potential thunderstorms, violent wind, heavy showers and severe turbulence. flight visibility will be good away from showers

a warm front and moist northerly flows from tropics, often involving low cloud, poor visibility, and light winds.