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Meteorology: Atmosphere and Environement > thunderstorm > Flashcards

thunderstorm Flashcards

1
Q

what are associated with thunderstorms

A
  • lightning and thunder
  • gusty surface wind
  • heavy rain/hail
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2
Q

thunderstorms are separated into which three storms

A
  • ordinary storms
  • multicell storms
  • supercell storms
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3
Q

What meteorological conditions are necessary for the occurrence of a thunderstorm

A
  • A conditionally unstable atmosphere
  • Substantial boundary layer moisture
  • A trigger to release the instability (e.g., low-level lifting) + parcel has to reach LFC
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4
Q

why is an absolutely unstable atmosphere unfavourable in the development of thunderstorm?

A
  • bc the ELR is greater than the D/MALR, so convection is found from the start –> no CIN –> no accumulation of energy as energy is immediately released.
  • no CIN –> no energy to form thunderstorm
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5
Q

discuss the energy of CIN in thunderstorm formation

A

larger CIN- more energy accumulation - stronger thunderstorm. however if CIN is bigger than the CAPE, thunderstorms do not form

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6
Q

why is it hard to form a thunderstorm

A
  • atmosphere has to be conditionally unstable (stable at first unstable later) to prevent initial convection.
  • however, without initial unstable condition parcels cannot rise. therefore other conditions are needed to rise the parcel
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7
Q

what are the factors that cause air parcel to rise without an unstable condition?

A
  • Extra-tropical cyclone (low-pressure) convergence force
  • Warm air rising along a frontal zone
  • Large-scale uplift along mountain barriers
  • Effect of small hills, sea-breeze front, localized convergence
  • turbulent eddies
  • unequal surface heating
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8
Q

what is the convective cloud growth when CAPE < CIN

A

cumulus

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9
Q

what is the convective cloud growth when CAPE > CIN

A

towering cumulus

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10
Q

what is the convective cloud growth when CAPE > CIN greatly

A

cumulonimbus

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11
Q

ordinary cell/single cell thunderstorm

A
  • relatively small thunderstorms, rarely become severe
  • isolated cumulonimbus cloud, short lived
  • have a predicted life cycle
  • single heavy rain
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12
Q

what are the conditions for developing ordinary cell thunderstorms

A
  • very little vertical wind shear
  • turbulence overturning
  • localised surface wind convergence
  • in warm humid air, far from fronts
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13
Q

what are the three stages of life cycle

A
  1. cumulus
  2. mature
  3. dissipating
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14
Q

discuss the cumulus stage

A
  • Warm buoyant plume rising
  • Inside cloud, transformation of water vapour to liquid or solid cloud particles releasing great amount of latent heat, the parcel is warmer than the surrounding hence continues to rise
  • At edges of the cloud, entrainment happens, bringing drier air into the parcel. Evaporation happens to add water to the drier air – this cools the parcel down slowing the growth but this is necessary in order to moisten the air
  • air moistens, RH increases, more condensation can take place –> more successive updrafts to sustain clouds to higher and higher levels –> towering cloud
  • no rainfall or lightning at this stage
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15
Q

discuss the mature stage

A
  • Growth of drops & ice continues until they become large and heavy –> updraft can no longer support – fall
  • At the same time, entrainment happens. Raindrops evaporate, the air cools. The parcel is now heavy and cool– sinks
  • Both these processes lead to development of a downdraft
  • Most intense stage – heavy rain, thunder, lightning (occas. small hail)
  • Maximum updraft and downdraft at middle levs– severe turbulence detrainment above that level
  • Anvil starts to form at top as result of horizontal spread
  • Raindrops are called supercooled drops above freezing level in the updraft, snow/ice are called snowflakes/pellets below frez. level in the downdraft
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16
Q

discuss the dissipating stage

A
  • downdraft grows until it is greater than the updraft and totally cut it off –> no fuel supply for cloud development
  • Without supply, droplets no longer form (no condensation), light precipitation
  • The rain formed, dragging air down, cause downdraft. this upsets the warm air rising as they are at the same place. Self limiting itself.
  • Rainfall stops; all that is left is the anvil
17
Q

why does the rainfall declines in dissipating stage and how does this differ in different places/conditions

A
  • Only about 20% of the water vapour condensed in the updraft actually reaches the ground as precipitation (rest evaporates in downdraft or left behind as cloud patches (then evaporates))
  • In places with dry air, the raindrops evaporates before reaching the ground.
18
Q

define multi-cell thunderstorm

A

Contain a number of cells, each at a different stage of development: once one cell subsides, another grows adjacent to the last cell

19
Q

what promotes multi-cell thunderstorms

A
  • Moderate-strong vertical wind shear: helps thunderstorm development and lifetime by separating the updraft from the downdraft
  • The cool downdraft from an existing TS causes a “gust front” when it meets the surface. This may push up surrounding warm moist air(like cold front) –> uplifts, and trigger a new cell to develop, sustaining the multicell storm and its propagation
  • high severity
20
Q

windshear

A
  • wind speed and direction change throughout the vertical profile.
  • a type of turbulence
21
Q

gust front

A
  • the leadings edge of the cold downdraft of an existing TS.
  • great temp drop, strong gust winds, turbulence (change in wind speed and air flow)
  • aka mesohigh
  • small scale front
  • promotes the uplift of an adjacent TS, pushing up surrounding warm air
22
Q

what clouds can gust front form

A

roll clouds. when the surface air is pushed up along the front.

23
Q

squall lines

A
  • Multicell thunderstorms organized in a line, favoured by the arrival of a cold front
  • Frequent over midlatitudes
  • much stronger than normal TS
  • warm air forced up the cold front
24
Q

Mesoscale convective systems

A
  • Multicell thunderstorms organized in a large circular convective system
  • Individual TSs work together to generate a long-lasting (> 6hrs) system moving slowly
25
Q

Supercell thunderstorms

A
  • Rotating updraft: rotation causes the storm to bring in more air, hence stronger.
  • longer-lived (hours), dangerous
  • low pressure formed by at centre of rotation, called a mesolow
  • Rotation can lead to formation of a tornado
  • No downdraft of air happen with the updraft of air at the same place, no limitation
26
Q

formation of a horizontal shear/rotation

A
  • strong and deep change in wind speed and direction with height.
  • air is accumulated at both sides of the wind direction. air at the bottom rises to replace the air that are dragged on the other side.
  • rotation is created.
27
Q

how does a horizontal shear acquire vorticity about a vertical axis

A
  • updraft of warm air

- more surface heating –> more updraft –> vertical motion with rotation

28
Q

true or false:

mesocyclone induces more convergence and updraft

A

true

29
Q

true or false

Precipitation falls ahead advected by strong wind

A

true

Meteorology: Atmosphere and Environement (15 decks)

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