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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
Absolutely stable
Environmental lapse rate is less than 6 degrees C/1000m
26
Absolutely Unstable
Environmental Lapse Rate is greater than 10 degrees Celsius / 1000m
27
Conditionally Unstable
Enviornmental Lapse Rate is less than 10 degrees C/1000m but greater than 6 degrees C/1000m Stabilty depends on where the parcel is
28
Condionally Unstable If the parcel is unsaturated, then as it is lifted it will be __________ than its surroundings
colder
29
Conditionally unstable If the parcel is saturated, then as it is lifted it will be _____________ than its surroundings
warmers
30
Stable
Few clouds, light cumulus humilus, clear skies Often no level of free convection (LFC)
31
Shallow to moderately deep layer of conditional unstability
Cumulus congestus, patchy clouds, and sometimes breezy
32
Deep layer of conditional instability
Cumulonimbus, thunderstorms possible, possible severe weather
33
Single-cell thunderstorm has 3 stages
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
34
Lifting Condensation Level
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
35
Level of free convection
When parcel's temperature becomes warmer than the enviornment, it freely convects: rises on its own
36
Level of Free Convection
level at which parcel's temperature first becomes warmer than its enviornment
37
Above 6km, the moist adiabatic lapse rate is closer to \_\_\_\_\_\_\_\_\_\_\_
8 degrees/km, Parcel continues to cool as it rises, and eventually becomes colder than the environment
38
Cloud Top
Level at which parcel becomes cooler than its surroundings
39
LI =
T(enviornment) - T(air parcel) at 500mb
40
Lifted Index
A way to describe stability with one number Is a difference in temperature at 500 mb Negative values are unstable
41
3 stages of a single-cell thunderstorm
1. cumulus stage 2. mature stage 3. dissipating stage
42
How can a thunderstorm grow in intensity?
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
43
Vertical Wind Shear
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
44
Air-mass/ordinary single-cell
"Popcorn" in visible satellite image Small vertical wind shear Chance of severe weather: unlikely
45
Multicell
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,
46
Supercell
Hook echo in radar reflectivity image Vertical Wind Shear: Large Chance of Severe Weather: very large
47
Multicell Thunderstorms
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
48
Supercell Thunderstorm Characteristics
Strong wind gusts, large hail, dangerous lightning and tornado Require a very unstable atmosphere Requires strong wind shear
49
Microbursts
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
50
Characteristics of a tornado
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
51
Velocity
magnitude and direction of motion
52
Speed
magnitude of velocity
53
Acceleration
Chance in velocity \*can be a change in speed and/or direction
54
Net Force
= Mass x Acceleration Sum of all forces acting on an object
55
Gravity
Mass x gravitational acceleration \*always directed downward \*\*equals mass times 9.8 m/s^2
56
Friction
Acts opposite to direction of motion Strength is proportional to speed
57
Pressure Gradient Force
Change in pressure over a distance - always directed toward lower pressure
58
Why doesnt air fall down?
Net force must be zero or air would accelerate upwards or downwars
59
Hydrostatic balance
Gravitational force balances Pressure Gradient Force
60
Pressure Gradient Force
Equals change in pressure over a given distance (height) Always pushes toward lower pressure
61
Hydrostatic equation:
= -p x g x ∆z
62
Pressure changes _______________ in the vertical than in the horizontal direction
much more
63
Trough
Elongated region of low height
64
Ridge
Elongated region of high heights
65
Winds:
Tend to blow parallel to the lines of constant height
66
Pressure Gradient Force
The force that results from pressure differences over distances in a fluid PGF always directed from high to low pressure = pressure change / distance
67
The PGF:
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
Friction
69
Coriolis Force
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
Winds aloft (above about 1km)
Pressure Gradient Force Coriolis Force No friction
71
Winds near the surface
Pressure Gradient Force Coriolis force friction
72
Air spirals ____________ around a low in the northern hemisphere
Counter-clockwise
73
Cyclonic
counter clockwise movement
74
Anticyclonic
Clockwise motion
75
Divergence
The spreading out of air / fluid
76
Convergence
The piling up of air / fluid
77
Trough
Cyclonic (PGF \> CF)
78
Ridge:
Anticyclonic (CF \> PGF)
79
Jet Streams
Thin “Rivers” of air with winds exceeding 100kt (sometimes 200kt) found at ~ 10-15km elevation
80
Thermal Wind
A horizontal change in temperature causes wind speed to increase with height.
81
Thermal Wind
Relates temperature and winds to each other The winds are more westerly as you go up wherever it’s colder toward the poles
82
Sea Breeze
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
Monsoons
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
General circulation
``` what conditions (e.g. winds, pressure, precipitation, temperature) look like if we average over long periods of time, and over large areas ```
85
Air mass
A large body of air whose properties of temperature and moisture content (humidity) are similar in any horizontal direction
86
Source regions have similar characteristics
Light winds A uniform surface over a large region Not coastline
87
Air mases can:
move away from their source regions
88
Polar (P)
Formed poleward of 60 degrees Cold or cool
89
Arctic (A)
Formed over the arctic very cold
90
Tropical (T)
Formed within about 30 degrees of the equator hot or warm
91
Continental (C)
Formed over large land masses Dry
92
Maritime (m)
Formed over the oceans moist
93
Continental polar (Cp)
Winter: very cold and dry Summer: Cool and dry
94
Maritime tropical
Winter: warm and humid Summer: warn and humid
95
cP
Cold, dry days "Polar front" (sits over us during winter) Cold surges Lake effect snows
96
Lake Effect Snow
• 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
mT: Maritime Tropical
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
Front
Transition zone between two air masses of different densities (usually due to temperature differences)
99
Cold Fronts
Denoted by blue line with triangles pointing in direction of movement Cold, dry air is replacing (relatively) warm, moist air
100
Cold Fronts
Sharp temperature gradient across front Changes in moisture content (dewpoint) Wind shift / pressure minimum Clouds andPrecipitation
101
Warn fronts
Denoted by red lines with semi-circles pointing in direction of movement. Warm, moist air is overriding more stationary, cold, dry air
102
Occluded fronts
Denoted by purple linewith alternating triangles and semicircles pointing in direction of movement Cold front “catches up” with a warm front
103
Extra-tropical (Mid-latitude) Cyclones:
Weather phenomenon characterized by surface low, ~1000-2000 km horizontal scale, warm / cold fronts, and associated weather.
104
Extra-tropical (Mid-latitude) Cyclones:
(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
Key ingredients for cyclogenesis
– 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
Alberta Clipper
–  Develop over western Canada, move southeastward to Great Lakes
107
Nor-easter
Develop over Gulf Stream – pummel N.E. U.S
108
If a system tilts westward with height =\>
it will strengten
109
Temperature advection
–  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
Upper level divergence / convergence
–  Divergence above a surface low causes the low to deepen –  Convergence above a surface high causes the high to strengthen
111
Total Effect
Cold advection beneath trough =\> trough intensifies Warm advection downstream of trough =\> ridge develops NET EFFECT: TROUGH CURVATURE INCREASES
112
Vertically stacked cyclone
low pressure aloft is directly above low pressure at the surface
113
Divergence aloft (above a low)
Loss of mass (above a low) Low pressure deepens
114
Air tends to __________ upstream of a trough
converge
115
Air tends to ___________ downstream of a trough
diverge
116
Cold advection beneath trough =\>
trough intensifies
117
Warm advection downstream of trough =\>
ridge develops
118
If divergence aloft \> surface convergence
Loss of mass Low intensifies
119
If convergence aloft \> surface divergence
Accumulation of mass High intensifies
120
Vorticity
'spin' of air around its vertical axies
121
Stretching:
increases relative vorticity
122
Squashing
Decreases relative vorticity
123
Absolute vorticity =
Relative + Planetary
124
Cold advection under an upper level trough causes:
trough to intensify
125
Warm advection under an upper level ridge causes:
the ridge to intensify
126
Sea Level Pressure
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
Geostrophic balance
An equilibrium achieved when the horizontal pressure gradient and Coriolis forces push equallly in opposite directions
128
westerly wind
A wind that is coming from the west
129
Eastward ocean current
A current that moves toward the east
130
Cp
Winter: very cold and dry Summer: cool and dry
131
mT
Winter: warm and humid Summer: warn amd humid
132
Lake-effect snow is more common in the \_\_\_\_\_\_\_\_\_\_
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

Weather and Climate (10 decks)

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