Meteorology Keynotes

where does most of the weather occur and most of our flying occur in the atmosphere

where does most of the weather occur and most of our flying occur in the atmosphere

the troposphere

how does the height of the troposphere change and what are the alt

varies drastically with latitude and with the seasons. In the polar region its between 25 000 - 35 000ft while in the equatorial regions its from 50 000 - 60 000ft

what are the four layers of the atmosphere

1. how does the earth absorb the suns heat

2. is the heat short wave or long wave

1. through the surface of the earth

2. short wave

this heats the earth which in turn re-radiates the heat at a much longer wave length which is absorbed by the atmoshphere

what are the four factors the cause uneven heating of the surface

1. seasonal variations

2. latitude variations

3. diurnal (day/night) variations

4. Different surfaces of the earth, such as rock collects heat more than trees

What are the 3 benefits of the sun reaching high alt

1. travels through more atmosphere

2. spreads out over larger area and is therefore less intense than at the equator

3. strikes the surface at a more oblique angle

all this results in less heating at high alt

how does water play a key role in the weather

it provides a mechanism for transporting thermal energy to different parts of the globe. water is able to do this because it absorbs significant energy when it is heated and especially when it changes phase

what is the environmental lapse rate

1.98 degrees C per 1000ft

what is the term when the environmental lapse rate turns negative

temperature inversion

dry adiabatic lapse rate

3 degrees C per 1000ft

wet adiabatic lapse rate

1.5 degrees C per 1000ft

what is a stable atmosphere

what is an unstable atmosphere

what’s a conditionally (or potentially) unstable atmosphere

what is the ISA (international Standard Atmosphere) for temp

15 degrees C

what is the height of the tropopause

36 090ft

atmospheric pressure drops by approx (blank) of mercury for every 1000ft that you climb in the lower atmosphere

1 inch

the higher the temperature of the air, the (blank) the quantity of water it can hold

greater

relative humidity

the amount of water in the air relative to the max which it can hold at that temp and pressure

dewpoint

if air is cooled at a constant pressure the temp at which condensation begins is known as the dewpoint. The closer the dewpoint temp is to the outside air temp, the more likely it is that clouds will form

water vapor is less dense than air, which means the higher the humidity the (blank) dense the air will be

less

poorer airplane performance will be

convection

vertical movement of air

advection

horizontal movement of air

sublimation

when a solid changes phase directly to a gas without going through the liquid phase

deposition

when a gas changes directly to a solid without going through the liquid phase

isobars

these are line of constant pressure

isotachs

lines of constant wind velocity

contour lines

line joining points where the alt at which a specifies pressure occurs is constant

origins of pressure differences and air movement in the atmosphere

what are the fundamental forces which arise from the pressure differences (3)

1. coriolis force which causes moving air to be deflected to the right in the northern hemisphere and to the left in the southern hemisphere

2. friction with the surface of the earth. Friction forces are greatest below aprox 3 000 AGL

3. acceleration or centrifugal forces when the air is following a curved path

what’s a coriolis force and how do they behave:

what are the two factors that affect coriolis (2)

what direction does it deflect to on the northern and southern hemisphere?

are felt by moving air as a result of the rotation of the earth about its axis. It depends on:

1. wind speed: the higher the wind speed, the higher the coriolis force

2. latitude: the higher the latitude, the higher the coriolis force. At equator, the coriolis forces are zero. at the poles they are max

what are the three wind pattern cells

1. polar cell

2. hadley cell

3. ferrel cell

whats the pattern of the wind in the northern winter and northern summer

sounterwards in the northern winter and vice versa in the northern summer

how are winds different from the surface then higher up

surface winds are more complex and influenced by the surface over which they are blowing (land, water, mountains, valleys etc)

low pressure systems:

1. what direction does it circulate

2. trough or ridge?

3. associated with (blank) air and the arrival of (blank) weather and precip

1. air circulates counter-clowckwise in the northern hemisphere

2. known as troughs, especially when they have an elongated shape

3. surface lows are usually associated with rising (or ascending) air and the arrival of cloudy weather and precip

high pressure systems:

1. air circulates what direction

2. ridge or trough

3. associated with (blank) air, with what type of weather

1. air circulates clockwise

2. if high pressure system is elongated is shape then it is referred to as a ridge of high pressure

3. associated with descending (or subsiding) air, clear weather and gentle wind

the closer the isobars the (blank) the wind

stronger

in the northern hemisphere, if you stand with your back to the wind then the low pressure will be on your (blank) side

left

as we climb, the wind will usually (blank) and as we descend, the wind will (blank) during the day. At night air close to the earth is (blank blank) to the air higher up by the convective air currents.

1. veer

2. back

3. not connected

gust

a rapid increase in wind speed for a short period of time before returning to the average speed

squall

a rapid increase in wind speed lasting for a minute or longer before returning to the average speed

may also be caused by a line of thunderstorms which often occur along a front in which case they are known as line squalls

veering

when the direction from which the wind blows increases, for example when the wind changes from a southerly from an easterly to a north easterly direction

backing

when the direction from which the wind blows decreases, ex wind changes from an easterly to a north easterly direction

downburst

very strong localized downdraft from a thunderstorm

microburst

a downburst which is less than 2 NM in horizontal extent and persist for less than 5min

macroburst

a downburat which is greater than 2NM in horizontal extent and persist for between 5-20min

the wind direction is the direction the wind is blowing (blank)

from

how are clouds formed

when air containing moisture (gaseous water vapor) is cooled to saturation resulting in the water condensing as liquid droplets or as crystals

what are the 3 types of cooling (for clouds)

1. adiabatic expansion resulting from lifting air

2. advection (horizontal movement) of air over a colder surface

3. evaporative cooling

what are the 5 lifting types of adiabatic cooling

1. the primary cause of the cooling is adiabatic expansion resulting from lifting of the air. Lifting can occur because of:

a. atmosphere convergence - where air masses clash horizontally and the air is left with no place to go other than up

b. orographic features - where air travels over orograpihc features such as mountains and is forced to rise

c. frontal action - where one air mass undercuts forcing the second air mass to rise or one mass rides over the top of another air mass

d. mechanical turbulence - similar in nature to lifting cause by orographic features

e. convection - where adjacent bodies of air are warmed (or cooled) differently usually by different ground surfaces. The body of air which is warmed more rises while the other body sinks

clouds are classified to their physical appearance and according to the height of their base, what are the four classifications:

1. high cloud

2. middle cloud

3. low cloud

4. clouds of vertical development

high cloud

base above 20,000 ft.

normally contain the word “cirro” or cirrus

cirrus = clouds with a fibrous or streaky appearance

cirrostratus = usually a thin layer

cirrocumulus = small puffy clouds which give the appearance of being flattened

middle cloud

base between 6 500 - 20 000 ft (alto)

altostratus = uniform layered cloud

altocumulus = puffy clouds usually patchy in their coverage

altocumulus castellanus = puffy clouds which grow to a significant height

low cloud

base below 6 500ft. normally described by their appearance and do not have a preffix

stratus = uniform layered cloud

nimbostratus = a dark layer cloud which usually produces continuous precip, be it rain, sleet, snow, freezing rain

fractostratus = (sometimes called stratus fractus)/ this is a stratus cloud with gaps in the layer which gives the appearance of the layered cloud having been torn apart or fractured

cumulus = puffy clouds often grouped together. If they form a continuous layer then they are referred to as stratocumulus

clouds with vertical development

are cumulus clouds which as their name suggest, grow vertically into towering cumulus or cumulonimbus thunderstorm clouds. the bases of these clouds can be in the lower (below 6 500ft) or middle (6 500 - 20 000ft) level and the tops can extend into the stratosphere in the extreme cases

cloud coverage description for clear

sky is clear below 10 000ft as interpreted by an autostation

cloud coverage description for SKC

no clouds

cloud coverage description for FEW

clouds cover greater than zero and up to 2/8 of the sky

Scattered

3/8 - 4/8

broken

5/8 - just less than 8/8

Overcast

8/8

mist =

fog =

mist = vis 5/8sm or greater

fog = vis is less than 5/8

ceiling

height of the base of the lowest broken or overcast layer of cloud

calc of cloud base:

surf temp. 20 degrees C/ Dew point 5 C. what’s the height of the base of the convective cloud?

difference between 20-5=15

divide 15/3=5

height of the base of the convective cloud will be 5 000ft AGL

(3 degrees C per 1000ft) calculation for cloud base for TC exam

anabatic winds

created when a mountain or hillside is exposed to direct sunlight. The surface warms faster than the valley. The heated slope warms air in contact with it causing it to expand and rise. This draws in more cool air from the valley floor or in a circulation pattern

Katabatic winds

occurs as a result of a rapid radiation of heat from exposed mountain or hill slopes at night. particularly true of surfaces which are not covered with vegetation. Once the slopes have cooled they cool the air in contact with the slope causing it to increase in density and sink. This process draws in more air from above and displaces warmer air in the valley

sea and land breezes

sea breezes:

arise during the day because land masses warm up and much more rapidly than adjoining water masses. as land warms, it warms the air in contact causing the air density to drop. the lower density air is more buoyont than the surrounding air and thus rises. As the warmed air rises, its place is taken by the cooler air from over the eater setting up a circulation pattern.

land breezes:

at night land will cool off more rapidly than water. This cools the air in contact with it, increasing its density and causing it to sink. these are known as land breezes and are usually more gentle than sea breezes

chinooks

occur when air containing a significant amount of moisture blows towards a mountain range and is forced to rise. in the process, the air cools adiabatically first at the dry adiabatic rate (3 per 1000) and if the mountain range is high enough, the moisture will condense reducing the rate of cooling to 1.5 per 1000. In this situation, clouds will form and precip will occur on the windward side, reducing the moisture content of the air. On the leeward side the air will sink and warm adiabatically. Only now the air no longer contains the moisture so all the warming will be at the dry adiabatic lapse rat (3 per 1000). As a result, the air will warm substantially more when it descends than it did when it was forced to rise and cool

mountain waves

when stable air is blowing towards a mountain range it is forced to rise. On the downwind or lee side of the mountains, the descends and bc of the terrain eddies and vortices are formed in the descent. The air compresses as it descends and then springs back. This creates an oscillating flow with its associated up and down drafts and often sever turbulence. If the air contains sufficient moisture, distinctive clouds will form in the regions where the pressure and temp drop providing warning signs. Lenticular clouds will form at the crests of the waves, while rotor clouds will form in the extreme turbulence of the eddies downwind. clouds may be hidden by other clouds

what flying hazards are there associated with mountain waves

1. (blank) can reach speeds of up to (blank) ft pre min

downdrafts, severe or extreme turbulence and the windshear. Downdrafts can reach speeds of up to 5000 ft per min and the most severe are usually found at the same height as the mountain ridge

altimeter may read incorrectly due to the pressure increasing and decreasing as the air oscillates like a spring

radiation fog

forms on clear nights with gentle wind (-5kts). on clear nights the surface of the earth loses heat through radiation into space. as the temp of the surface drops, it cools the air in contact. If the air contains sufficient moisture and the temp drop of the air is enough for the air to reach its dew point then condensation will occur and a cloud will form at ground level.

forms usually a few hours before dawn cause thats when the radiation cooling of the surface has been sufficient to cause condensation. a little wind is necessary to mix the air up as it flows over the surface so as to enable to surface to cool a layer of air for some thickness. if no wind only dew, no cloud. too much wind then there will be insufficient temp drop for the DP to be reached and for condensation to occur

advection fog

Type of fog formed when warm, moist air moves over a cold surface, causing the air to cool and condense into fog.

ex. air flows from where it is located over a warm water current to a cool one, or where air flows from over a warm land mass to over a colder one

may form when the wind is blowing at greater speeds , up to 15kts depending on the temp difference between the air and the cool surface and the moisture content of the air

frontal fog

Type of fog that occurs when a warm front moves over a colder surface, causing condensation. It reduces visibility and forms a low-lying cloud near the ground. rain falling from the warm air mass into the cold air mass evaporates. the process of evaporation will cool the cold air further. this cooling in combo with the evaporation saturates the cold air which causes some re-condensation to occur into small suspended droplets forming a cloud. if it occurs at the surface then fog will form

arctic sea smoke

forms through a process of evaporation and re-condensation. when cold air flows over relatively warm water, the water warms the layers of air closest to it and evaporation of the water occurs. The warmed air rises and then cools as it mixes with the colder air above and condensation occurs. As the warmed air rises further and mixes with more cold, dry air, the relative humidity drops and the moisture re-evaporates

upslope fog

forms when air which is forced to rise cools adiabatically. If the upslope and moisture content is sufficient then the dewpoint will be reached and condensation will occur

what is an air mass

a body of air with horizontally uniform temperature, humidity, pressure and tropopause height

how are air masses categorized and what are the 4 categories

categorized by nature of the surface over which they were formed

1. continental arctic -cA

2. maritime arctic - mA

3. maritime polar - mP

4. Maritime tropical - mT

describe each

1. continental arctic -cA

2. Maritime Arctic - mA

3. Maritime polar - mP

4. Maritime tropical - mT

1. generally dry, very cold and stable with the tropopause at low alt

2. moist, cold, unstable in the lower layers with the tropopause at low alt

3. moist, unstable throughout with the tropopause somewhat higher

4. generally moist, hot, very unstable with a high tropopause

what is a front

boundary zone between 2 air masses where a large change of temp occurs within a relatively short distance

the name and type of front is derived from where

the name is derived from the colder air mass involved in the front, while the type of front is derived from the advancing airmass.

ex. if a maritime polar and a maritime tropical airmass were to meet, with the warmer airmass (mT) advancing, then the front formed would be a mP warm front

the weather associated with a cold front largely depends on

the stability of the air in the warm sector

in a cold front if the air is warm, moist and stable then (blank) clouds will form

stratiform

in a cold front if the air is moist and unstable then (blank) clouds will form

cumuloform

in a cold front if the warm air is dry then how many clouds will from

very few clouds

the slower the front is moving, the (blank) the band of cloud and precip will be

wider

what is the general behavior of weather phenomena with the approach and passage of a cold front

warm fronts tend to be more (blank) than cold fronts

gradual

what are the two factors that determine the weather in a warm or cold front

dependent on moisture content of the warm air mass and the slope of the frontal surface. which in turn depends speed of the front and the relative temperature of the air masses

what is the general behavior of weather phenomena with the approach and passage of a warm front

estimating the position of a frontal surface:

ex. you are planning a flight at 9,000 ft. The surface analysis chart shows a warm front along your route which you will be approaching from the warm sector. How far from the surface position of the front will you intercept the frontal surface if the frontal surface has a slope of 1:130

195 NM

when does an occlusion occur

when a cold front catches up with a warm front, this happens bc the wind speed behind a cold front increases more than anywhere else in deepening low pressure system

warm front occlusion (less common)

what happens when a cold front catches up with a warm front

it undercuts the warm air and forces it aloft forming a trough of warm air aloft, known as (trowal)

what are the 3 elements you need to create a thunderstorm

1. source of lifting agent or trigger

2. an adequate supply of moisture (to fuel the growth)

3. instability reaching the upper parts of the tropospher

what are the 3 stages of a thunderstorm

1. developing or cumulus stage

2. mature stage

3. dissipating stage

developing (cumulus) stage of a thunderstorm

primarily composed of updrafts (can reach speeds of 2 500 - 3 000ft per min:

-as the air rises and the temp drop, condensation occurs and small drops become large raindrops

above the freezing level, ice will begin to form

once the raindrops reach a size where the updrafts are not capable of supporting them, they start to fall dragging some of the air with them

mature stage of a thunderstorm

begins when rain first reaches the surface:

cloud contains both up and downdrafts: updrafts can reach speeds up to 6000ft per min/ downdrafts up to 2500ft per min

-lightning and turbulence

-as the rain falls, evaporation will slow the compression heating

-updrafts can cause tops of clouds to reach 5000-6000ft into the stratosphere

-when downdraft first hits the surface it will spread out creating a gust front sometimes known as a plow wind

dissipating stage of thunderstorm

-entire area of the cloud becomes an area of downdraft which removes the source of the turbulence, hail, and lightning

how are thunderstorms classified

based on the trigger which starts them growing

what are the 2 different classifications of thunderstorms and explain them

1. air mass: form within a warm, moist airmass which is not associated with a front. are generally isolated and scattered over a wide area

2. frontal: the initial source of lifting is cold air undercutting warm air at a cold front or warm air riding up over cold air at a warm front

what are the 4 types of air mass thunderstorm

1. form within a warm, moist airmass which is not associated with a front. are generally isolated and scattered over a wide area

2. orographic: where the initial source of lifting is provided by an orographic feature such as a mountain range

3. Convective: The initial source of lifting is convective heating associated with uneven heating of the surface of the earth

4. Nocturnal: form at night and where the initial source of lifting is convective heating of air by a warm body of water, land breeze action or cooling or a moist layer of air aloft at night