Pressure and Winds Flashcards
1
Q
Define Air Pressure:
A
Atmospheric pressure is the force per unit area exerted against a surface by the weight of air above that surface.
2
Q
Wind results from a _________ difference in air pressure.
A
horizontal
3
Q
Differences in_________ dictate the movement of air.
A
air pressure
4
Q
Define Wind:
A
Wind refers to the horizontal motion of air across Earth’s surface. Air moving to equalized pressure.
5
Q
What adds a vertical component to wind?
A
Turbulence
6
Q
What are the two principal properties of wind?
A
-Speed
-Direction
7
Q
How are winds named?
A
From the direction from which they originate (e.g., westerly wind, easterly wind).
8
Q
How is wind direction measured?
A
With a wind vane
9
Q
How is wind speed measured?
A
Anemometer
10
Q
What is a Sonic Anemometer?
A
Transmits (and receives) sound (ultrasonic) waves. Wind speed and direction are accurately recorded based on how the wind is impacting the speed of the sound (through transit time) as it travels through the air. Very precise way of measurement.
11
Q
What units are wind symbols measured in?
A
Knots, previously km/h
12
Q
What is 1 knot=_____?
A
1.852 km/h
13
Q
What are the four driving forces within the atmosphere?
A
-Gravitational Force
-Pressure Gradient Force
-Coriolis Force
-Friction Force
14
Q
What is an Isobar?
A
An isobar is an isoline, connecting areas of equal pressure.
15
Q
What is the Mean Sea Level Pressure?
A
Adjusted measure of station pressure, where station pressure is a raw measurement. It accounts for the elevational differences.
16
Q
What is the Pressure Gradient?
A
The rate of pressure changes across a given distance (ex. 1mb/100km).
17
Q
The closer the spacing of isobars, the ______ the pressure gradient, and the stronger the wind.
A
higher
18
Q
True or False: A very strong vertical pressure gradient is always present.
A
True.
19
Q
True or False: Gravity cancels out the natural pressure gradient force as we move up through the atmosphere.
A
True
20
Q
What is the Pressure Gradient Force?
A
The force that results from the difference in pressure across a given distance.
21
Q
How is the Pressure Gradient Force directed?
A
Always directed from where the pressure is higher to where the pressure is lower (Trying to reach equilibrium/equal pressure between the two.)
22
Q
What do Pressure Gradient’s determine?
A
Wind Speed
23
Q
What are strong pressure gradients associated with?
A
Strong wind speeds.
24
Q
Are isobars close or far apart when wind speeds are strong?
A
Close together
25
What was the strongest wind on record?
407km/h
26
What is the most important part about weather maps?
The Pressure Variation
27
What are High Pressure readings called?
Anticyclones
28
What are low pressure readings called?
Cyclones
29
What is the Coriolis Force?
The Coriolis force is an effect of Earth’s rotation.
30
Which direction does the Coriolis force direct in the northern hemisphere?
To the right
31
Which direction does the Coriolis force direct in the Southern hemisphere?
To the left
32
True or False: the Coriolis Force varies at different latitudes. The Coriolis force is zero along the equator and reaches maximum near poles.
True
33
____________ force: that is forced in a particular horizontal direction, along a straight path, will appear to curve from the perspective of someone on the surface, because the earth is rotating beneath the body while the body moves over the surface.
Coriolis
34
In what latitudes does the earth rotate faster?
Lower Latitudes (equatorial region)
35
True or False: The Coriolis force is a force that pushes objects.
False, There is not an actual force pushing this object, it is just an appearing force.
36
What type of winds have more apparent reflection?
Fast winds.
37
Where on earth is the Coriolis force strongest?
The poles.
38
What is the Geostrophic Wind?
The deflection increases until the Coriolis force is balanced by the pressure gradient force. At this point, the wind will be blowing parallel to the isobars. When this happens, the wind is referred to as the "geostrophic wind".
39
What is a Geostrophic wind combined of?
Pressure Gradient Force + Coriolis Force creates geostrophic wind
40
Where do Geostrophic winds mostly occur?
Upper Troposphere, ~1km
41
Geostrophic winds are ________ to the isobars.
Parallel
42
What are surface winds combined of?
Pressure Gradient + Coriolis + Friction Forces (surface winds)
43
Surface winds cross isobars at __________.
an Angle
44
Where do surface forces mostly occur?
~500m altitude
45
What two movements create Vertical Movement?
Converging and Diverging winds.
46
How does vertical movement impact cloud formation and weather?
Rising air cools, as water vapor cools it loses energy and we get condensation, involving latent heat, which is where we get clouds. Descending air warms, promotes clear skies around areas of high pressure. Which is why wind influence weather patterns.
47
What happens when air is converged into low areas?
Air is sent aloft. As we know, rising air cools, and as water vapor cools / loses energy, we might get condensation and the release of latent heat, counterclockwise in the northern hemisphere.
48
What happens when air is diverging from an area of high pressure?
Surface air is replaced by the air above. As we know, descending air warms, this promotes clear skies.
49
True or False: We have variable insolation and heating across the surface.
True.
50
How are the following areas important to pressure patterns on a MSL pressure map?
-Icelandic Low -Aleutian Low
-Pacific High -Siberian High
-Azores High
They show how certain factors (thermal or mechanical) influence pressure patterns.
51
What two factors influence Primary High-Pressure and Low-Pressure Areas?
-Temperature (thermal)
-Mechanical (dynamic)
52
What two pressure systems are driven by thermal factors?
-Equatorial low-pressure trough
-Polar high-pressure cells
53
What happens in the Polar High-Pressure cells?
Cold dense air sitting over these areas, leading to high pressure.
54
What two pressure systems are driven by mechanical factors?
-Subtropical high-pressure cells (dynamic factors)
-Sub-polar low-pressure cells. (Dynamic factors)
55
What do dynamic/mechanical factors influence on the system?
The physical displacement (Convergence and divergence) of air.
56
Define the Equatorial Low-Pressure Trough:
Constant high sun altitude and consistent daylength = large amounts of solar energy.
57
Define Trade Winds:
Named during the era of sailing ships that carried merchandise for trade across the seas. The most consistent winds on earth.
58
What direction do converging trade winds go?
Converging towards the equatorial low-pressure trough (toward intertropical convergent zone).
59
Why are there Northeasterly winds in the northern hemisphere and Southeasterly winds in the southern hemisphere?
Because of Coriolis, it acts during and near the Intertropical Convergent Zone.
60
What does ITCZ stand for?
Intertropical Convergent Zone
61
Where do Subtropical High-Pressure Cells sit in terms of latitude?
Between 20 – 35° Latitude in both hemispheres.
62
Subtropical High-Pressure Cells are driven by ______ factors.
Mechanical
63
What regions fall in the Subtropical High-Pressure Cell zone? (3)
-Azores high
-Bermuda high
-Pacific high
64
What mechanical factors drive the Subtropical High-Pressure Cells?
As air above the subtropics is pushed downward (mechanically) rather than being driven by thermal factors, it is driven by colliding/converging air.
65
Where do earths major desserts sit?
Earth’s major deserts generally occur within the subtropical belt (except antarctica).
66
Why do earths major desserts sit in the subtropical belt?
Air is warmed as it descends through the atmosphere. For this reason, the air is dry and hot.
67
Where do Trade Winds and Westerly Winds originate?
The trade winds originate from these areas of surface divergence.
68
Where do we find Sub-Polar Low-Pressure Cells?
Around 60° Latitude in both hemispheres
69
What two key locations are found in the Sub-Polar Low-Pressure Cells?
-Aleutian Low
-Icelandic Low
70
What type of weather is associated to the Sub-Polar Low-Pressure Cells?
Associated with cool / moist air
71
What type of weather is associated to the Polar High-Pressure Cells?
Frigid and dry air, thermal factors
72
What are two Mechanically driven primary pressure areas?
-Subtropical high-pressure
-Sub-polar low-pressure
73
What is a Front?
Front = Where air masses with different characteristics meet.
74
What is the Polar Front?
The Polar Front is where cold northern air, flowing in easterly winds, meet warm southern air flowing in westerly winds from subtropical highs.
75
How is a front formed?
Wherever we have a collision of different air masses, a front is formed.
76
Why is pressure at the surface higher?
The pressure at the surface is still high because of this strong convergence in the upper atmosphere, because of mechanical factors.
77
Why is pressure at the surface high?
The pressure at the surface is high because of the strong convergence in the upper atmosphere.
78
What does high pressure at the surface create?
The high pressure at the surface causes air at the surface to be pushed away at the surface...creating trade winds on the equator side of the highs and westerlies on the polar side of the highs.
79
What is the jet stream in the upper atmosphere over each of the subtropics called?
the subtropical jet stream.
80
Why is there a strong convergence at the latitude where Jet Streams occur?
Because the upper flow moving away from the ITCZ is becoming more and more affected by the Coriolis Force (it gets stronger away from the equator).
81
What is the polar front jet stream driven by?
Thermal Factors
82
What is a Jet Stream?
The jet stream is an irregular and concentrated band of fast-moving westerly wind, at altitude (usually at or near the tropopause) between 7600-10700m above the surface.
83
Where do we often find jet streams?
Near the Tropopause.
84
Which is stronger, the Polar Front Jet Stream or the Subtropical Jet Stream?
Polar Jet Stream
85
True or False: Winds in the in the upper atmosphere are consistent.
False, they are constantly shifting.
86
Where is the Polar Jet Stream commonly found?
Between 30-70 degrees N latitude.
87
Where is the Subtropical Jet Stream commonly found?
Between 20-50 degrees N latitude.
88
Where do Monsoons often occur? Why?
These often occur in the tropics, where we have a migrating ITCZ (intertropical convergent zone).
89
How do Monsoons occur?
In the summer, wet and humid air flows from south to north, bringing monsoonal rains.
90
What are dynamic highs?
even though the temperatures are warmer at the surface, the pressure at the surface is high because of the strong convergence in the upper atmosphere.
91
Where are jet streams found?
in the upper atmosphere over each of the subtropics, there is a jet stream...the subtropical jet stream.
92
Why are jet streams there?
there is strong convergence at this latitude/altitude.
93
Why is there a strong convergence at the latitude/altitude where jet streams occur?
Because the upper flow moving away from the ITCZ is becoming more and more affected by the Coriolis Force (it gets stronger away from the equator)
94
Where do we find the polar jet stream?
in the upper troposphere over each of the midlatitudes, there is a jet stream...the polar front jet stream. Driven more by thermal factors.
95
What factors create a jet stream?
In the upper atmosphere, where the air is not very dense, and where friction is negligible, very strong winds can be formed...a jet stream!
96
Which jet stream is stronger?
The polar jet stream is usually stronger than the subtropical jet stream.
97
Why aren't jet streams stationary?
Winds of the upper atmosphere are constantly shifting. Like waves within the ocean, the atmosphere is constantly responding to changing conditions. For this reason, jet streams are not stationary.
98
Where do we often find monsoons?
These often occur in the tropics, where we have a migrating ITCZ (intertropical convergent zone).
