Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Fires > Module 2: Fire Weather > Flashcards

Module 2: Fire Weather Flashcards

1
Q

What is the atmosphere?

A

a thin envelope of invisible gases, which surrounds the earth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the composition of the atmosphere?

A

21% oxygen 78% nitrogen 1% other gases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What else does the atmosphere contain? (3 things)

A
  1. suspended solids 2. liquid particles 3. water vapour
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

______________ are important as condensation nuclei.

A

suspended solids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Water vapour concentrations vary throughout the atmosphere from nearly __% over desert and arctic areas to as much as ___% by volume over tropical latitudes

A

0 & 4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

________ is an important atmospheric gas as it can change state under certain conditions of temperature & pressure

A

water vapour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What happens when water vapour is cooled?

A

it condenses into water droplets forming clouds, fog, dew or precipitation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

This process releases heat and its energy contribution is important in weather building processes such as storm clouds & winds leading to atmospheric instability. What is this called?

A

latent heat of condesation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The atmosphere is divided into a number of significant layers on the basis of temperature and density. T or F

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the bottom layer, adjacent to the earth’s surface called and what happens here?

A

troposphere is heated from below and temp generally decreases with height *mostly interested in the troposphere as this is where surface weather & wildfire interact*

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

The upper limit of the troposphere layer is defined by ____ which is an ______ of -56C

A

tropopause & isotherm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Approximately __% of the total weight of the atmosphere occurs below __km; most weather occurs here

A

50% & 5.5km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the general rules in the troposphere? (2 things)

A
  1. both temperature and pressure decrease with increasing elevation 2. subsiding air warms as it descends. as it warms it will expand & take up more space. this air is subject to increasing pressure as it descends & will be compressed against the earth’s surface. this heating, expansions & compression may result in strong surface winds- much like Chinooks
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What has a direct relationship with temperature?

A

relative humidity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

As temperature increases: RH _______ As temperature_______ : RH increases

A

decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is relative humidity?

A

the ratio between the amount of water vapour present in a given parcel of air compared to the maximum amount of water vapour that parcel can hold at a given temperature & pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the most important element of fire weather?

A

Relative Humidity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe the diurnal relationship: Temp, RH & moisture content of cured fine fuels.

A
  • RH < 20% results in aggressive burning conditions
  • Temp (r) : RH (d), RH goes down and the moisture content of cured fine fuels also decreases
  • peak buring time is between 2 pm & 4 pm
  • as RH (d) fire behaviour (i)
  • watch for temp : RH crossover
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is dew point?

A

the temperature to which air must be cooled in order to reach saturation (RH=100%)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is atmospheric pressure?

A

the force per unit area exerted by the weight of the atmosphere at a specific level

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

the most common measure of atmospheric pressure is?

A

millibars

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is an isobar and what intervals are they drawn at on surface weather maps?

A

a line of equal surface pressure shown in increments of 4 hecto- Pascal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what do isobars on a surface weather map indicate?

A

relative high and low pressure areas

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

high and low pressure areas can be distinguished on the map by?

A

the pressure values contained within them

25
Q

what exists between high and low pressure areas as the atmosphere works to balance diffences in pressure?

A

gradient force

26
Q

___ connect like valleys btween low-pressure areas while a ___ of high pressure occurs where the isobars connect or come close to connecting between high-pressure centrers

A

troughs

ridge

27
Q

a low pressure area is often referred to as?

What are some examples of cyclones?

as air ascends in a low pressure area, what happens?

if sufficient moisture is present, what occurs?

A

a cyclone or depression

hurricanes, typhoons & tornados

it is cooled

clouds and precipitation

28
Q

what are low pressure areas characterized by?

A

cyclone

vary in size

counter-clockwise rotation

ascending air increases in velocity

divergent aloft & convergent at surface

29
Q

a high pressure system is referred to as?

as air descends, what happens?

A

anti-cyclone

it is warmed & capable of holding more water vapour resulting in fewer clouds and fair weather

30
Q

what are high pressure areas characterized by?

A

anti-cyclone

generally much larger than L pressure areas

clockwise rotation

descending air slows in velocity with surface friction

convergent aloft & divergent at surface

31
Q

what is a jet stream?

A

a river of strong upper atmospheric wind (tropopause) situated between the cold polar easterlies & the mild westerlies

32
Q

how fast can jet streams blow at and what do they do to high and low pressure systems?

A

100 to 200 kph

steer direction from NW to SE across Canada

33
Q

pressure patterns at the surface are _________ and occure on ________scales

A

asymmetrical

very large

34
Q

Frontal Passage

A

Extremely important to understanding fire behaviour.

As cold front passed over a fire the winds become very gusty and erratic.

Caused by the dneser cold air undercutting the warmer air causing lift and turbulence.

35
Q

a parcel of air is considered to be stable if?

unstable if?

A

air is resistanct to vertical motion

air is not resistanct to vertical motion

36
Q

indicators of stable atmosphere?

A

stratiform clouds

limited vertical motion of air

cooler temps

light winds

low ground fog

reduced visibility

37
Q

Frontal Passage Effect on Fire Behaviour (6)

A
  1. Strong gusty winds, atmosphere instability
  2. Variable Wind Direction
  3. Strong dy cold front worst scenerio
  4. Increase in fir activity
  5. Rapid cold front may lead to thunder storms
  6. Cold front passage most common in fatalities
38
Q

what is lapse rate?

A

the rate of temperature change with an increase in elevation

39
Q

what is adiabatic lapse rate?

A

the lapse rate of rising or sinking air

40
Q

Air Mass descriptors

and

Temperature Characteristics

A

Dry continental - (c)

Moist Maritime - (m)

Arctic (cold) - (A)

Polar (temperate) - (P)

Tropical (warm) - (T)

41
Q

what is moist adiabtaic lapse rate (MALR)?

A

shows a considerable variation because the amount of heating is dependant upon how much water vapour condeses out

more condensations means more heat released

1.5C/ 1000 ft

42
Q

Common air mass descriptors

A

cA - only forms over frozen arctic, does not exist in summer slides south bringing cold temps

mA - this is a cA air mass that moves over open oceans

cP - forms over dry central North America

mP - a cA air mass moved over a warmer ocean

cT - forms over arid south-western US regions, summer time only and is rare

mT - forms over tropical ocean latitudes near equator and moves north

43
Q

is a type of lift, which results from differential heating of the earth’s surface. Air, which has been heated, becomes less dense than the surrounding air and rises.

A

Convection

44
Q

lifting occurs when air is lifted up and over a prominent topographic feature such as a range of mountains.

A

orographic

45
Q

lifing of the air may be caused by turbulence as airflows over a mountain or hill causing eddies on the lee side which may disrupt the flow of air near the surface

A

mechanical lifing

46
Q

lifing occurs when warmer air is forced upward by advaning cooler air

A

frontal

47
Q

where air at the surface is forced into a narrow pass, excess air is forced to rise

A

convergence lifing

48
Q

is a function of pressure difference in the horizontal from high surface pressure areas to low surface pressure areas

A

wind speed

49
Q

initiates the movement of air from areaas of high pressure to areas of low pressure

A

gradient force

50
Q

affects the direction of wind by causing it to flow parallel with the isobars at heights that are above the influence of surface friction

A

coriolis force

51
Q

upper atmospheric winds occure a few kilometres above the surface and flow parallel to the isobars

A

geostrophic winds

52
Q

the force of friction partially counteracts the coriolis force which causes the air to slow and to flow out of high pressure areas and into low pressure area, crossing the isobars at an angle

A

surface winds

53
Q

winds are always described in terms of

A

the direction the are coming from

54
Q

only lasts a few seconds

A

wind gust

55
Q

often associated with erratic shifts in wind direction, which may create difficulties in fire control

A

gustiness

56
Q

a gust may be caused by

(2 things)

A

mechanical turbulence, convergence or eddying effects

fairly intense unequal heating of the earth’s surface

57
Q

what is a squall

A

a sudden increase in wind speed which is sustained for several minutes

58
Q

what is a squall caused by

(2 things)

A

sustained down drafts from thunderstorms

rapidly moving cold front

Fires (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions