u12 Flashcards
weather occurs as a result of..
heat exchange
relative humidity
amount of water vapour present in the atmosphere compared to the amount that the air can hold when saturated
dry adiabatic lapse rate
3º per 1000 ft
saturated adiabatic lapse rate
1.5º per 1000 ft
rain droplet size depends on
updraft strength
what is convergent rainfall
two air masses converge
warm front rainfall is steady
cold front rainfall is showery
what is orographic rainfall
when the mountains are _______ to the coastline, rain is more intense
what happens when air sinks on the leeward side of the moutanin
warm moist air rises over mountain = cools = condense into clouds and precipitation
parallel because warm ocean air is forced to rise
as air descends on leeward side, it’s compressed and warmed, rain stops and creates a rain shadow
what is conventional rainfall
what causes the storm to end
ground heated, air rises, expands and cools -> rainfall
as the rain falls, some of the rain evaporates into the (drier) air = takes latent heat away = downdraft air is very cold and strong = downdraft overpowers the warm vertical updraft = storm killed
how does lightning occur
discharge of electricity between the negative ground and positive ice crystals in upper cloud
would there be more snowfall when the temperature is -2ºC or -14ºC?
-2ºC because warm air holds more moisture than cold air so snowfalls are heaviest when air temperature is just below freezing
how are ice pellets made? how big are they
snow falls from top layer, melts into rain in a winter warm front, passes through thick cold layer and re-freezes as ice pellets
smaller than 5mm
how is freezing rain made
snow falls from top layer, enters winter warm front and melts into rain, when it enters a shallow cold layer it doesn’t have time to re-freeze so the droplets are supercooled and will freeze when it comes into contact with the cold ground/plane
how does hail form? how big is it
in cloud, small ice pellets thrown around by updrafts and downdrafts and come into contact with supercooled water droplets. the water freezes onto the pellet, and layer after layer it grows until it’s too heavy that gravity brings it down
larger 5mm
deposition is what
gas to solid
(cold water vapour in cloud condenses directly into snow)
what is sublimation
solid to gas
does dry or saturated parcel of air rise faster
saturated
because larger temperature difference between the parcel cooling and environment cooling every 1000 ft. so it rises faster
when the environment lapse rate is _______ than the DALR or SALT, the atmosphere is UNSTABLE
GREATER
**when the environment cools faster than the parcel of air, the parcel of air will always rise
stable air
- smooth or rough flying
- visibility
- precipitation
- what type of clouds/weather
- shallow or steep ELR
- occurs when a parcel of _____ air moves over _____ air
smooth
poor
steady
stratus clouds, fog
shallow ELR
warm air moves over cold air
how do stable conditions occur - examples both on surface and aloft
surface cooling
- radiation cooling at night
- cold air moves under warm air
warm air at higher altitudes
- radiation cooling - cool air near surface and aloft air re-absorbs outgoing radiation
- warm advection aloft
- large sinking of air due to high pressure system or moving over leeward side of mountain
unstable air
- smooth or rough flying
- visibility
- precipitation
- what type of clouds/weather
- shallow or steep ELR
- ____ temp/dew point spread
rough
good
showery
CB
steep ELR
high
how does unstable conditions occur during the day - give examples
radiation during the day
warm surface advection
cold parcel of air moves over a warm surface and heats up the bottom layers = mixing within itself
large scale rising of air
conditions that favour stable air
inversion
isothermal layer
ELR less than DALR/SALR (environment warm and parcel cold)
lifting processes that cause instability
convection from unequal surface heating
convergence of two pressure systems
mechanical turbulence
orographic lift over moutanin
frontal lift of a front
the _______ determines if the atmosphere is stable or not
ELR
**DALR and SALR always the same, only the ELR changes
what is absolute stability in terms of ELR, DALR, SALR
parcel of air tries to rise but will always be colder than the air around it
DALR/SALR are steeper (colder) than ELR
what is conditional stability in terms of ELR, DALR, SALR
stability depends on whether or not the air is saturated or dry when it tries to rise
the DALR is steeper (colder) than the ELR = parcel cannot rise
the SALR is shallower (warmer) than the ELR = parcel CAN rise
*parcel can only rise when saturated
what is absolute instability in terms of ELR, DALR, SALR
the parcel of air is always warmer than the outside temp so it will always rise
the DALR and SALR are shallower (warmer) than the ELR
what is potential instability in terms of DALR, SALR and ELR
initially stable but needs a trigger (lifting agent) for instability to occur
what is subsidence
- how does temperature and relative humidity change
- how does weather change
subsidence = dissipation of clouds
- sinking air = increase temperature and decreases relative humidity = visible moisture evaporates so clouds disappear
the sun has an ____ year cycle and it’s light takes ____ mins to reach earth
11y cycle
8 mins
what is solar wind and how does it affect us
outermost particles of sun escape suns gravity and interact with magnetic field
this gives northern lights
what are sunspots and how does it affect us
dark spots of high intensity energy on sun and can influence earths temperature
what is a solar flare and how does it affect us
dark spots of high intensity energy on sun and can influence earths temperature
earth tilted at _____, and the earths tilt is responsible for what
23.5º
changing seasons
seasonal temperatures are due to what two things
light spread phenomena (angle of light hitting surface)
atmospheric scattering (more light scattering at poles so less light reaches surface)
clouds need _______ in the air so that water droplets have a surface to condense onto
condensation nuclei
how many oktas is SCT, BKN, FEW
FEW 1-2/8
SCT 3-4/8
BKN 5-7/8
alto- clouds occupy what range of altitudes
6500 to 20 000 ft
tell me about cirrus clouds
high
whispy
occur in high pressure systems and fair weather
ice crystals
tell me about cirrostratus (CS) clouds
high and sheet like
thicken as warm front approaches
ice crystals
halo
tel me about cirrocumulus (CC) clouds
high and pebbly
sheet
ice crystals
tell me about altostratus clouds (AS)
layer
NO halo
light drizzle
tell me about altocumulus clouds (AC)
shows instability in atmosphere
warm humid summer morning can lead to afternoon thunderstorms
icing near top of cloud
tell me about altocumulus castellanus (ACC)
vertical development that can transition into CB
tell me about stratus (ST) clouds
low layer, flat sheet
smooth air
little turbulence
drizzle
tell me about nimbostratus (NS) clouds
low flat layer with steady precipitation
warm front
tell me about stratocumulus (SC) clouds
low lumpy layer of clouds
moderate turbulence
what are stratus fractus (SF) clouds
stratus clouds torn to pieces by strong wind
what are cumulus fractus (CF) clouds
torn by strong wind
what are mammatus clouds and what do they tell us
protrude from base of CU clouds
indicate unstable atmosphere and thunderstorms will come soon
what are orographic clouds
clouds that develop because air forced to rise over mountain
what are lenticular clouds
mountain wave cloud that appears at the top of a wave crest
what are rotor clouds
from mountain waves at level of top of mountain and severe turbulence
what are cap clouds
top of mountain and down leeward slope = indicates strong downdraft
what are contrails
plane produces hot exhaust with water vapour and when water vapour touches cold air at high altitude it turns to ice crystals
what are roll clouds and where are they located
base of thunderstorm in area with strong downdrafts
what is the coriolis force
which way is it deflected in the northern hemisphere
it’s strongest closest to the _______
apparent deflection of airflow due to earths rotation as if seen from observer on the ground
deflected right
strongest at poles
the coriolis force + pressure gradient causes wind ALOFT to flow _______ to the isobars
at what height are these geostropic winds ** to isobars
parallel
3000 AGL
the Buys ballot law states that if you stand with your back to the wind, the low pressure side is on your
left
what are doldrums
area near equator with gentle winds
30ºN is a permanent ______ pressure zone
what is the weather like here
HIGH
stable
clear skies
constant sun
60ºN is a permanent ______ pressure zone
what is the weather like here
LOW
unstable
in a climb, what do the winds do
increase in speed = less friction
veer = more coriolis force so flows more parallel to isobars
in a descent, what do the winds do
back and decrease in speed (friction)
why are winds stronger in afternoon compared to morning
morning = atmophere is stable due to radiation cooling overnight. surface is separate from strong aloft winds.
afternoon = mixing between surface and upper atmosphere so there aloft winds are carried down to surface but they back (less coriolis effect) and slightly decrease in speed due to friction.
i’m flying at 2000 AGL from the city to the ocean. what will happen to the winds?
less friction
increase in speed
veer by 30º (now blowing at an angle closer to the isobars)
gust vs squall
gust = sudden change of wind direction or speed
squall = prolonged change of wind direction or speed (longer than 1 min)
surface winds ______ and ______ at night
surface winds ______ and ______ during the day
back and decrease at night
veer and increase during the day
do you get a land breeze or sea breeze during the day? night?
sea breeze = daytime (high P ocean -> low P land)
land breeze = night time (high P land -> low P ocean)
where and when do katabatic winds form on a snowy mountain
snowy section in shaded area (cold air) during the day
at night katabaatic wind forms because of radiation cooling so overall flow of a mountain is downwards at night
when and where do anabatic winds form on a mountain
in sunny side of mountain, air rises and blows upwards during the daytime
what are the two types of wind shear and what do they create
changes in wind speed or direction can cause turbulent eddies
what is a rossby wave
how is it formed from a jet stream and what can it create
a rossby wave is a wave in a jet stream
formed due to earths rotation (coriolis) and horizontal temperature gradient (equator to poles)
pockets of warm/cold air can form and these H/L pressure systems can detach from the jet stream and move around the world - circulate differences in global temperature
polar front jet stream
- location
- what happens to the jet stream as winter approaches, what are it’s characteristics and what weather does it bring to a city below
- as summer approaches?
- between polar and ferrell cell (40-60º)
- winter: PFJS moves south, stronger/faster due to large temp difference between polar/ferrel cell, brings dry and stable conditions with high pressure
- summer: PFJS warms up and moves north, speed of jet stream slows down because not a big temp difference between polar/ferrel cell, brings heavy rain, warm air and strong wind to city below
subtropical jet stream
- location
- compare it to the polar front jet stream (PFJS)
between ferrel and hadley cell (20-30º)
slower winds and moves less than PFJS because the temp difference between ferrel and hadley cells is much less than the ferrel and polar
easterly equatorial jet stream (EEJS)
- location
- when does it appear
- what weather phenomena does it bring in india
- compare it to the PFJS
aloft the ITCZ
seasonal
summer monsoons in india
very gentle jet stream compared to PFJS because there’s barely any temp difference between two hadley cells
jet streams:
- what are they
- how are they formed
- why does the wind in the jet stream flow to the right
- what clouds are formed at the jet stream
high speed current of air along the tropopause
abrupt change in tropopause height = tropopause rips = circulating air creates a jet stream
coriolis force
cirrus clouds
jet stream characteristics
altitude
width
depth
speed
10 - 30 000 ft (but higher in summer)
few hundred miles
2-6 miles
over 60 KT
are jet streams stronger in the summer or winter
winter because larger temp difference between poles (extra cold) and equator (hot) in winter
whereas summer has warm pole and hot equator so not as big of a tropopause height difference
between two fronts (cold and warm), which front is the jet stream located in
jet stream located within the WARM front
for a polar jet stream in WINTER:
why is the altitude LOW,
why does it move SOUTH
why is the speed of the core FASTER
compared to a summer jet stream?
low altitude = bc of lower pressure heights
move south = cold polar air migrates south to warm equator
faster = greater temperature difference between pole and equator in winter than summer (warmer pole)
you can expect clear air turbulence when 30 KT isotachs are spaced closer than ______ on the _____ MB chart
90 NM
250 MB chart
where is turbulence strongest around a jet stream? why
x3 locations
- on the side of the jet stream that faces the cold front - slower wind on cold side = larger wind speed difference between core and slow cold side = stronger turbulence
- above the core - between core and tropopause
- upper trough (pole side)
you’re flying through a jet stream (tailwind) and you encounter turbulence, which direction should i turn to get out of the turbulence in the northern hemisphere
RIGHT
i want to cross a jet stream perpendicularly. should i climb, descend or stay at the same altitude to avoid prolonged turbulence? the OAT is increasing
OAT increasing = climb
i want to cross a jet stream perpendicularly. should i climb, descend or stay at the same altitude to avoid prolonged turbulence? the OAT is decreasing
descend
i want to cross a jet stream perpendicularly. should i climb, descend or stay at the same altitude to avoid prolonged turbulence? the OAT is constant
OAT constant = either climb or descend
t/f: the subtropical jet stream is a frontal jet stream
false
hot equator air rises and turns towards poles + coriolis turns winds right
**not because of two diff temperature fronts because both cells are warm
the subtropical jet stream is _____ and ______ than the polar
speed and altitude
slower and higher
t/f: the low level nocturnal jet is a nocturnal jet stream
FALSE it’s not a jet stream
inversion at night results in wind shear (diff speed/direction between ground and aloft), but with the morning sun the nocturnal jet disappears
