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Weather and Climate > Study Guide > Flashcards

Study Guide Flashcards

1
Q

Pressure

A

The force per unit area (Force / Area)

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2
Q

Density

A

mass per unit volume (mass / volume)

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3
Q

Hydrostatic balance

A

The change in pressure with height is equal to the weight of the fluid

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4
Q

How do liquid barometers work?

A

As the atmospheric pressure increases, more force is placed on the reservoir of mercury, which in turn forces the mercury to a higher level of the tube.

Along the length of the barometer tube are millimeter markings, allowing for an easy reading of the pressure at any given time

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5
Q

Geostrophic balance

A

The most fundamental horizontal force-balance arises when the PGF is counterbalanced by the Coriolis force

Balance exists because the Earth turns and causes the Coriolis force

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6
Q

PGF always pushes from ______________________

A

higher toward lower pressure

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7
Q

Gradient balance

A

The three-way balance of horizontal pressure gradient, Coriolis force, and centrifugal force

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8
Q

Guldberg-Mohn balance

A

The ability of friction to slow the wind and therefore weaken the Coriolis force

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9
Q

Divergence

A

Surface pressure drops when there is divergence of the wind in the column aof air above the low

the horizontal spreading out of air

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10
Q

Convergence

A

Occurs when air near the surface flows together from different directions.

When the air near the round converges, or is squeezed together, it causes upward motion

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11
Q

Lifted index

A

A stability index

Index starts with an air parcel from the surface, lifting and cooling it dry adiabatically to saturation and then lifting and cooling it moist adiabiatically to 500 millibars.

The temperature of the parcel at 500 =mb is subtracted from the environment’s temperature at 500mb. If the observed 500-mb temperature is colder than the lifted air parcel, then the parcel is unstable and will be able to keep on rising and form a tall cumulonimmbus cloud => negative

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12
Q

Negative values of the LI can be related to the potential for thunderstorm severity

A

0 => -3 air is marginally unstable and unlikely to lead to severe thunderstorms

  • 3 => -6 moderately unstable conditions
  • 6 => -9 very unstable regions

LI values less than -9 reflect extreme instability

* >0 => thunderstorms unlikely without strong lifting mechnamism

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13
Q

Eveolution of a single cell thunderstorm

A

Cumulus stage - initial stage of a thunderstorm; warm air near the ground rises and cools initially at the dry adiabatic lapse rate. The rising air parcel approaches saturation as the relative humidity increases, until condensation occurs

Mature stage - begins when precipitation starts to fall from the cloud. The thunderstorm produces the most lightning, rain, and even small hail. The updrafts in the cumulonimbus become organized and strong, providing the vertical motion needed for coud-droplet growth

Dissipating stage - Occurs when the updraft, which provides the required moisture for cloud development, beings to weaken and collapse. Downdraft dominates the updraft and the cumuonimbus begins to disappear

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14
Q

Multicell Thunderstorms

A

Composed of several individual single-cell storms, each one at a different stage of development: cumulus, mature, and dissipating

Key difference: prescence of moderate amounts of vertical wind shear

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15
Q

Supercell Thunerstorms

A

A large single-cell storm

Produce one or more of the following: strong wind gusts, large hail, dangerous lightning, and tornadoes

Development of a supercell requires a very unstable atompshere and strong vertical wind shear

Often, wind direction at the surface is southerly, whereas the winds aloft are much stronger and from the west

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16
Q

Vertical wind shear in multicell thunderstorms

A

Multicell storm has a moderate amount of vertical wind shear

This shear tilts the thunderstorm and prevents the precipitation from falling into the updraft and quenching it, as happens in the single-cell thunderstorm. This allows the updraft and downdraft to co-exist.

The dense, cold air of the downdraft forms the gust front, which helps to lift the warm, moist air flowing toward the storm and then form new cells

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17
Q

Vetical wind shear in Supercell thunderstorms

A

Supercell requires a strong vertical wind shear

Vertical wind shear causes supercell thunderstorms to rotate around a vertical axis

The vertical updraft inside the thunderstorm then tilts this spinning air so that it spins in the vertical

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18
Q

Types of Severe Weather

A

Tornadoes, lightning, flooding, hail, and high winds

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19
Q

Conditions necessary for tornado formation

A

Develop underneath supercell thunderstorms

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20
Q

Sea Breeze

A

Steady wind blowing in from the water that is a result of the uneven heating during the daytime between the land and the adjacent water.

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21
Q

Stability

A

A measure of the liklihood that a physical system will remain unchanged after it is perturbed

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22
Q

Stability of the Atmosphere

A

Refers to the liklihood that a parcel will:

  • return to its origin (stable)
  • accelerate away from its origin (unstable)
  • be at equilibrium with its environment (neutral)
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23
Q

Stability of the Atmosphere key:

A

Compare a parcel’s temperature with the temperature of the environment into which it’s lifted

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24
Q

If the parcel is unsaturated, then as it is lifted, it will be _______________

A

colder than its surroundings

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25
Q

Absolutely stable

A

Environmental lapse rate is less than 6 degrees C/1000m

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26
Q

Absolutely Unstable

A

Environmental Lapse Rate is greater than 10 degrees Celsius / 1000m

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27
Q

Conditionally Unstable

A

Enviornmental Lapse Rate is less than 10 degrees C/1000m but greater than 6 degrees C/1000m

Stabilty depends on where the parcel is

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28
Q

Condionally Unstable

If the parcel is unsaturated, then as it is lifted it will be __________ than its surroundings

A

colder

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29
Q

Conditionally unstable

If the parcel is saturated, then as it is lifted it will be _____________ than its surroundings

A

warmers

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30
Q

Stable

A

Few clouds, light cumulus humilus, clear skies

Often no level of free convection (LFC)

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31
Q

Shallow to moderately deep layer of conditional unstability

A

Cumulus congestus, patchy clouds, and sometimes breezy

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32
Q

Deep layer of conditional instability

A

Cumulonimbus, thunderstorms possible, possible severe weather

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33
Q

Single-cell thunderstorm has 3 stages

A
  1. Cumulus - parcels ascend in the updraft and get saturated at the lifting condensation level, LCL, which marks cloud base
  2. Mature - begins when precipitation starts to fall
    - time of most lightning, rain, small hail
    - a downdraft develops with cooling due to evaporation precipitation
  3. Dissipating - updraft weakens, downdraft dominates
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34
Q

Lifting Condensation Level

A

As a parcel of air rises, it cools.

The LCL, or cloud base, occurs where the actual and dewpoint temperatures of that parcel are equal

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35
Q

Level of free convection

A

When parcel’s temperature becomes warmer than the enviornment, it freely convects: rises on its own

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36
Q

Level of Free Convection

A

level at which parcel’s temperature first becomes warmer than its enviornment

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37
Q

Above 6km, the moist adiabatic lapse rate is closer to ___________

A

8 degrees/km,

Parcel continues to cool as it rises, and eventually becomes colder than the environment

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38
Q

Cloud Top

A

Level at which parcel becomes cooler than its surroundings

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39
Q

LI =

A

T(enviornment) - T(air parcel) at 500mb

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40
Q

Lifted Index

A

A way to describe stability with one number

Is a difference in temperature at 500 mb

Negative values are unstable

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41
Q

3 stages of a single-cell thunderstorm

A
  1. cumulus stage
  2. mature stage
  3. dissipating stage
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42
Q

How can a thunderstorm grow in intensity?

A

Need to cancel the “shutoff” mechanism for a single-cell thunderstorm

Get rid of evaporation (saturated enviornment)

  • This sometimes occurs in hurricane genesis

Move the precipitation away from the updraft

  • vertical wind shear
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43
Q

Vertical Wind Shear

A

More severe thunderstorms can develop when there is vertical shear of the horizontal wind

  • The westerly (west to east) part of the wind increasing as height increases
  • Clockwise turning of the direction from which the wind blows as height increases
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44
Q

Air-mass/ordinary single-cell

A

“Popcorn” in visible satellite image

Small vertical wind shear

Chance of severe weather: unlikely

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45
Q

Multicell

A

MCC: state-sized circular cloud in infared sattellite image

Squall line: line of thunderstorms in radar or satellite images

Vertical Wind Shear: Small, moderate

Chance of Severe Weather: Likely,

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46
Q

Supercell

A

Hook echo in radar reflectivity image

Vertical Wind Shear: Large

Chance of Severe Weather: very large

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47
Q

Multicell Thunderstorms

A

Composed of several individual single-cell storms, each one at a different stage of development

  • can last several hours
  • can produce severe weather

Moderate amount of vertical wind shear

  • Wind shear moves downdraft away from updraft
  • new cells originate along gust front
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48
Q

Supercell Thunderstorm Characteristics

A

Strong wind gusts, large hail, dangerous lightning and tornado

Require a very unstable atmosphere

Requires strong wind shear

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49
Q

Microbursts

A

Develop when rain falling from a thunderstorm evaporates underneath the cloud, cooling the air beneath

– Cold heavy air plunges to the surface and splashes
against the ground
– Air then rushes sideways and swirls upward as a
result of the pressure gradient between the cold
air and the warm surroundings

*can do as much damage as a tornado

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50
Q

Characteristics of a tornado

A

Around very narow regions of low pressure beneath a thunderstorm

Visible because of condensation, dust, and debris

If the circulation does not hit the ground, called a funnel cloud

Usualy < 1.6km across

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51
Q

Velocity

A

magnitude and direction of motion

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52
Q

Speed

A

magnitude of velocity

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53
Q

Acceleration

A

Chance in velocity

*can be a change in speed and/or direction

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54
Q

Net Force

A

= Mass x Acceleration

Sum of all forces acting on an object

55
Q

Gravity

A

Mass x gravitational acceleration

*always directed downward

**equals mass times 9.8 m/s^2

56
Q

Friction

A

Acts opposite to direction of motion

Strength is proportional to speed

57
Q

Pressure Gradient Force

A

Change in pressure over a distance

  • always directed toward lower pressure
58
Q

Why doesnt air fall down?

A

Net force must be zero or air would accelerate upwards or downwars

59
Q

Hydrostatic balance

A

Gravitational force balances Pressure Gradient Force

60
Q

Pressure Gradient Force

A

Equals change in pressure over a given distance (height)

Always pushes toward lower pressure

61
Q

Hydrostatic equation:

A

= -p x g x ∆z

62
Q

Pressure changes _______________ in the vertical than in the horizontal direction

A

much more

63
Q

Trough

A

Elongated region of low height

64
Q

Ridge

A

Elongated region of high heights

65
Q

Winds:

A

Tend to blow parallel to the lines of constant height

66
Q

Pressure Gradient Force

A

The force that results from pressure differences over distances in a fluid

PGF always directed from high to low pressure

= pressure change / distance

67
Q

The PGF:

A

Points (locally) towards lower pressure (from high toward low pressure)

Is larger where isobars (contour lines) are closely spaced

Is perpendicular to contours of constant pressure / height

68
Q

Friction

A
69
Q

Coriolis Force

A

Apparent force that exists because we live on a rotating reference frame

  • Deflects wind to the right in the NH, to the left in the SH
  • is the strongest at the poles, and zero at the equator
  • is stronger for stronger winds, and weaker for weaker winds
  • is 0 for calm, it cannot start wind
70
Q

Winds aloft (above about 1km)

A

Pressure Gradient Force

Coriolis Force

No friction

71
Q

Winds near the surface

A

Pressure Gradient Force

Coriolis force

friction

72
Q

Air spirals ____________ around a low in the northern hemisphere

A

Counter-clockwise

73
Q

Cyclonic

A

counter clockwise movement

74
Q

Anticyclonic

A

Clockwise motion

75
Q

Divergence

A

The spreading out of air / fluid

76
Q

Convergence

A

The piling up of air / fluid

77
Q

Trough

A

Cyclonic (PGF > CF)

78
Q

Ridge:

A

Anticyclonic (CF > PGF)

79
Q

Jet Streams

A

Thin “Rivers” of air with winds exceeding 100kt
(sometimes 200kt) found at ~ 10-15km elevation

80
Q

Thermal Wind

A

A horizontal change in temperature causes
wind speed to increase with height.

81
Q

Thermal Wind

A

Relates temperature and winds to each other

The winds are more westerly as you go up wherever
it’s colder toward the poles

82
Q

Sea Breeze

A

Daytime circulation

Depends on differenAal heaAng at the surface
between land and water

Has the warmer, rising air column over the land,
which absorbs more incoming solar radiaAon

•  Has the cooler, sinking air column over the water,
which absorbs less radiaAon

83
Q

Monsoons

A

Monsoons are weather features driven by
seasonal differences in the heating of land
and ocean

– Indian summer monsoon has cooler air over
water, heated air over land, upslope onshore
wind and generation of clouds and
precipitation—wet season
– Indian summer monsoon has return flow aloft
from land to water and sinking air over the
Arabian Sea and the Bay of Bengal

84
Q

General circulation

A 
what conditions (e.g. winds, pressure,
 precipitation, temperature) look like if we average over long
 periods of time, and over large areas
85
Q

Air mass

A

A large body of air whose properties of temperature and moisture content (humidity) are similar in any horizontal direction

86
Q

Source regions have similar characteristics

A

Light winds

A uniform surface over a large region

Not coastline

87
Q

Air mases can:

A

move away from their source regions

88
Q

Polar (P)

A

Formed poleward of 60 degrees

Cold or cool

89
Q

Arctic (A)

A

Formed over the arctic

very cold

90
Q

Tropical (T)

A

Formed within about 30 degrees of the equator

hot or warm

91
Q

Continental (C)

A

Formed over large land masses

Dry

92
Q

Maritime (m)

A

Formed over the oceans

moist

93
Q

Continental polar (Cp)

A

Winter: very cold and dry

Summer: Cool and dry

94
Q

Maritime tropical

A

Winter: warm and humid

Summer: warn and humid

95
Q

cP

A

Cold, dry days

“Polar front” (sits over us during winter)

Cold surges

Lake effect snows

96
Q

Lake Effect Snow

A

• cP air (cold, dry) blows over relatively warm water
• Air gains moisture / heat => more buoyant near
surface => unstable
• Downstream, clouds and snow (hills and
convergence on leeward side help with lifting)

97
Q

mT: Maritime Tropical

A

mT: Warm, moist air from tropical regions. Pacific (Hawaii), Gulf of Mexico

Midwest: low pressure stalls over central / western US =>
warm moist flow from Gulf => warm, humid conditions

98
Q

Front

A

Transition zone between two air masses of different
densities (usually due to temperature differences)

99
Q

Cold Fronts

A

Denoted by blue line with triangles pointing in direction of
movement

Cold, dry air is replacing (relatively) warm, moist air

100
Q

Cold Fronts

A

Sharp temperature gradient across front

Changes in moisture content (dewpoint)

Wind shift / pressure minimum

Clouds andPrecipitation

101
Q

Warn fronts

A

Denoted by red lines with semi-circles pointing in
direction of movement.

Warm, moist air is overriding more stationary, cold, dry air

102
Q

Occluded fronts

A

Denoted by purple linewith alternating triangles and semicircles pointing in direction of movement
Cold front “catches up” with a warm front

103
Q

Extra-tropical (Mid-latitude) Cyclones:

A

Weather phenomenon characterized by surface low,
~1000-2000 km horizontal scale, warm / cold fronts, and
associated weather.

104
Q

Extra-tropical (Mid-latitude) Cyclones:

A

(i)  Begin as a disturbance, some times on a
stationary front
(ii)  Develop into “open wave”
(iii)  Intensify, begin to occlude (maximum intensity)
(iv)  Dissipates (dies off) after occlusion

105
Q

Key ingredients for cyclogenesis

A

– Surface temperature gradients, a front

– A strong jet stream, helps the low deepen and the
fronts intensify

– Presence of mountains or other surface
boundaries like a coastline near a warm ocean
current

– Winds blowing across temperature gradients

106
Q

Alberta Clipper

A

–  Develop over western Canada, move southeastward to
Great Lakes

107
Q

Nor-easter

A

Develop over Gulf Stream – pummel N.E. U.S

108
Q

If a system tilts westward with height =>

A

it will strengten

109
Q

Temperature advection

A

–  Cold advection under an upper level trough causes the
trough to intensify.
–  Warm advection under an upper level ridge causes the
ridge to intensify.

110
Q

Upper level divergence / convergence

A

–  Divergence above a surface low causes the low to deepen
–  Convergence above a surface high causes the high to
strengthen

111
Q

Total Effect

A

Cold advection beneath trough => trough intensifies
Warm advection downstream of trough => ridge develops
NET EFFECT: TROUGH CURVATURE INCREASES

112
Q

Vertically stacked cyclone

A

low pressure aloft is directly above low pressure at the surface

113
Q

Divergence aloft (above a low)

A

Loss of mass (above a low)

Low pressure deepens

114
Q

Air tends to __________ upstream of a trough

A

converge

115
Q

Air tends to ___________ downstream of a trough

A

diverge

116
Q

Cold advection beneath trough =>

A

trough intensifies

117
Q

Warm advection downstream of trough =>

A

ridge develops

118
Q

If divergence aloft > surface convergence

A

Loss of mass

Low intensifies

119
Q

If convergence aloft > surface divergence

A

Accumulation of mass

High intensifies

120
Q

Vorticity

A

‘spin’ of air around its vertical axies

121
Q

Stretching:

A

increases relative vorticity

122
Q

Squashing

A

Decreases relative vorticity

123
Q

Absolute vorticity =

A

Relative + Planetary

124
Q

Cold advection under an upper level trough causes:

A

trough to intensify

125
Q

Warm advection under an upper level ridge causes:

A

the ridge to intensify

126
Q

Sea Level Pressure

A

The atmospheric pressure at mean sea level

All surface barometric pressure readings are adjusted to sea level to remove the effect of altitude on pressure

127
Q

Geostrophic balance

A

An equilibrium achieved when the horizontal pressure gradient and Coriolis forces push equallly in opposite directions

128
Q

westerly wind

A

A wind that is coming from the west

129
Q

Eastward ocean current

A

A current that moves toward the east

130
Q

Cp

A

Winter: very cold and dry

Summer: cool and dry

131
Q

mT

A

Winter: warm and humid

Summer: warn amd humid

132
Q

Lake-effect snow is more common in the __________

A

fall

*as cold cP air mas moves over a warm body of water, there is a rapid exchange of heat and moisture. The lowest layer of the air mass warms and moistens, increasing the instability of the air mass. If the temperature difference between the air and water is large, rapid evaporation occurs

133
Q
A

Weather and Climate (10 decks)

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