1The best explanation for the cause of atmospheric pressure is
the weight of the air above
2The primary cause of wind is:
Not atmospheric pressure but atmospheric pressure differences
3The primary force which causes ALL winds is
pressure gradient force
4The Coriolis effect inlfuences wind by
Changing the direction of wind
5High pressure air zones are usually associated with
relatively dry conditions
6Planetary scale flow such as trade-winds are best classified as
macroscale
7Winds are usually named for
the direction or place from which they are blowing
8The United States is effected by monsoons
9The greater strength of jet stream winds during winter is due to
greater horizontal temperature contrasts
10Concerning rainfall patterns, areas of persistent high pressure tend to cause
desert regions
11The two most important properties that should be relatively homogeneous at the same altitude in an air mass are
- moisture content
- temperatures
12The typical amount of time it takes for an air mass to pass over a given area is on the order of a few
days
13An air-mass source region is characterized by
a general stagnation of atmospheric circulation
14"Lake-effect" snow is associated what type of air mass?
cP
15A region dominated by cyclones is more likely to produce an air mass than a region dominated by anticyclones
16On a weather map what type of fronts are shown with blue triangular points along a blue line?
Cold fronts
17Which of these is common to both cold and warm fronts?
Lifting of warm air over cold
18In the United States, the air mass most commonly found at the back of a cold front is
cP
19Compared to warm fronts, cold fronts have
a steeper gradient and a faster advance rate
20Thunderstorms can be generated wehn a cT air mass meets an mT air mass and creates a frontal boundary called a
dryline
21Thunderstorms form when _____, humid air rises in an _______ environment
warm; unstable
22There are three stages involved in the development of air mass thunderstorms. They are:
cumulus stage, mature stage, and dissipating stage
23At what time of day is an air-mass thunderstorm more likely to develop?
Midafternoon
24About what percent of thunderstorms in the United States become severe?
10%
25The gust front occurs
at the leading edge of a thunderstorm downdraft
26What is the difference between a typhoon and a hurricane?
They occur in different ocean basins
27Why do hurricanes initially form only in the tropics?
Warn water temperatures are found there
28Hurricane wind speeds are fastest near the center of the eye
29Wind speeds at the eye of a hurricane are relatively calm
30The initial detection and monitoring of tropical storms that may become hurricanes is accomplished by
satellites
31Air moves
vertically if over a barrier or if it's warmer than its environment
32Air flows from
areas of higher pressure to low pressure
33Air pressure is measured in
millibars
34Air pressure is measured with a
mercury barometer
35What is the process for measuring air pressure?
- Air pressure pushes on a pool of mercury and forces mercury up a tube
- High Pressure: The mercury goes further up the tube
- Low Pressure: The mercury stays lower
36What is another way to measure air pressure?
Aneroid Barometere
37What is falling pressure associated with?
Increasing clouds and storms
38What is rising pressure associated with?
Generally clearing conditions
39Why must air pressure be converted to sea-level equivalents?
Because measurements don't account for changes in elevation
40Values of pressure are displayed on maps using isobars. How are these values represented?
- Lines of equal pressure
- Close isobars identify highs (blue "H" and lows red "L")
41What is the average sea level pressure?
1013.25 mb
42High Pressure Systems are
- Anti-cyclones and often associated with dry weather
- the Big Blue "H"
43Low Pressure Systems are
- Cyclones or mid-latitude cyclones and usually produce stormy weather
- the Big Red "L"
44What direction does wind flow around an anti-cyclone?
Clockwise in Northern Hemisphere, counterclockwise in southern hemisphere
45What direction does wind flow around a cyclone?
Counterclockwise in Northern Hemisphere, clockwise in southern hemisphere
46Upper air data is provided by
radiosondes
47500 mb chart represents the middle atmosphere, with
half the air below, half the air above
48Why is the 500 mb chart at middle atmosphere significant?
Major weather systems tend to travel in the direction of winds at that level
49What are lines of equal pressure called?
Isobars
50What does it mean when isobars are close together?
Pressure is changing rapidly in that area -- can be caused by a warm front, cold front, low or high pressure system
51The difference in pressure between isobars creates a
pressure gradient which sets air in motion and causes stronger winds
52What do ridges represent on a pressure map?
High pressure warm air moving poleward
53What do troughs represent on a pressure map?
Low pressure cool air moving toward equator
54Differences in pressure generate
Local and global winds that produce our weather
55What are the four primary factors that contribute to changes in air pressure?
- Altitude
- Temperature
- Humidity
- Movement of mass from one location to another
56Air pressure ________ with altitude
decreases
57Air pressure _______ with depth
increases
58Air moves from higher pressure in warm column toward area of low pressure in the cold column. As the air aloft leaves the column
Mass decreases, causing a decrease in surface pressure
59Air moving from warm column to the cold column increase the pressure in the cold column. This higher pressure near the surface of the cold column generates
a surface flow from the cold column to the warm column. Loss of air from cold column causes air above to sink and air in warm column to rise
60Convergence
occurs when a net airflow into a region causes pressure to rose
61Divergence
occurs when there is a net outflow of air from a region and surface pressure drops
62Pressure gradient force
when air is subject to greater pressure on one side than another (directed from high to low pressure)
63If isobars are close together
a steep gradient and high winds result
64If isobars are far apart
a low gradient and lower wind speeds result
65Geostrophic flow occurs when
the pressure gradient force and the coriolis force are balanced. This provides a useful estimate of winds aloft.
66Vertical airflow is associated with
cyclones and anticyclones
67Microscale winds
Small and chaotic circulation from seconds to minutes (gusts, downdrafts, dust devils)
68Mesoscale winds
Minutes to hours (thunderstorms, tornadoes, locals winds such as sea breezes that can last hours to days) less than 60 miles
69Macroscale winds
largest wind patterns extending around entire globe. These planetary scale patterns can remain unchanged for weeks at a time.
70Synoptic scale winds
smaller macroscale circulations (tropical storms, hurricanes) 600 miles
71Valley Breeze
During the day air above mountain slopes is heated and rises creating a valley breeze
72Mountain breeze
At night air above the mounain slopes cools rapidly and drains into the warm valley below creating a mountain breeze
73Chinook Winds
Warm dry winds that sometimes move down slopes of moutains, can bring drastic changes in temperature
74Katabatic (fall) winds
winds originate when cold, dense air begins to move
75Country breezes
Mesoscale winds caused by uneven heating or urban and country areas. Results in the flow from country to urban areas
76Monsoons
Seasonal reversal of winds. Winter: wind blows offshore (drier) Summer: wind blows from sea to land (rainy season)
77Jet Streams
Embeded in westerlies.
78Polar jet stream
Moves faster in winter due to larger temperature contrast. Provides energy that drives storms and also directs path fo storms
79Subtropical jet stream
semipermanent jet stream in tropics. Mainly winter phenomenon that is slower than the polar. Caused by earth's rotation, not temperature contrast
80El Nino
gradual warming of eastern pacific waters in December or January . Noted for catastrophic impact on weather and is recognized as part of the global atmospheric circulation pattern
81La Nina
opposite of el nino and is colder-than-normal ocean temperatures
82Global air circulation
Caused by uneven heating of Earth's surface by solar radiation. They are importnat because they transport heat that affects the water cycle, clouds, and weather events. Brings us our daily weather
83What two things must be uniform when defining an air mass?
Similar temperatures and humidity throughout
84Source Regions
where air masses originate. Characterized by a stagnation of atmospheric circulation
85Classifying air masses depends on
the latitude and surface area
86cP
continental polar- very cold and dry
87cA
continental arctic - cold and dry
88cT
continental tropic - warm and dry
89mA
marine arctic - cold and wet
90mT
marine tropic - warm and wet
91A warm air mass would have more moisture
92Lake-effect snow
result of cold air mass over warm water. Leeward side is impacted
93dryline
narrow zone that can trigger severe thunderstorms should it encounter warm, moist maritime tropical air masses
94What are fronts?
Fronts are boundary surfaces between different air masses
95Warm front
occurs when warm air moves into a region of colder air. gentle slope that glides over air. As warm air moves into cold air it expands and cools. moisture condenses to form clouds and precipitation. cirrus clouds precede a warm front and short duration
96Cold fronts
Air advances into warm air and travels much faster, forcing air upward more violently. Precipitation is mroe intense than warm fronts but shorter in duration
97Stationary Fronts
occurs when airflow is neither toward cold air nor a warm air mass. Flow is almost parallel. May remain over an area for a long time. Depending on which air mass moves first, they can become warm or cold fronts
98Occluded front
When rapidly moving cold air overtakes a warm front, an occluded front occurs
99What is the duration of a cold front
short and violent. Weather is more violent because they lift up warmer and moist air more violently
100What is the duration of a warm front
steady and long
101Overrunning
Weather pattern in which a relatively warm air mass is in motion above another air mass of greater density at the surface.
102Midlatitude cyclones
synoptic-scale low pressure systems. Travel west to east, lasting from a few days to more than a week. Frequently produce precipitation.
103Where is the warm front in a midlatitude cyclone?
extenidng from the center usualy to the east
104Where is the cold front in a midlatitude cyclone?
extending from the center to the west of low pressure
105How do midlatitude cyclones form?
Clash of two air masses ofdifferent temperatures move parallel to a front in opposite directions
106Development of cyclonic flow
warm air advances polewarm and forms a warm front, cold air moves towards equator and forms a cold front. air begins counter-clockwise circulation toward the center of the low. Once circulation develops convergence results in a forceful lifting especially where warm air is overrunning colder air
107Mature stage of midlatitude cyclone
warm and cold fronts strengthen and the pressure surrounding the low drops. Cold front produces sever weather and warm frontestablishes cloud layer with precipitation. Cold front gradually overtakes warm front at the end producing occluded front
108occlusion at "the beginning of the end" of the midlatitude cyclone
cold air overtakes warm air. Early occluded stage often produces most hazardous weather
109Blocking Highs
High pressure that persists over an area for days to weeks. can be responsible for droughts or stagnant weather
110Cut-off lows
Low pressure that is cut off from the jet stream, can lead to blocking. Often leads to dreary weather and large quantities of precipitation
111Air mass thunderstorms
associated with warm, humid air that rises in convectively unstable environments. Form when warm, humid air is lifted in a conditionally unstable environment. Daytime heating contributes significantly to development. Occur most often in humid summer afternoons
1123 Stages of thunderstorm development
cumulus, mature, and dissipating stage
113Cumulus stage
Moisture is transported aloft and moistens up atmosphere. Air becomes humid enough for clouds to develop , precipitation occurs
114Mature stage
Updrafts and downdrafts coexist and enlarge the cloud. When they reach tropopause, updrafts spread laterally giving anvil shape.
115Dissipating stage
Rain turns updraft into another downdraft. Cuts the storm off from its source of rising air. Cooling effect makes precip and colder air aloft making end of thunderstorm activity
116Overshooting top
Top of cloud enters troposphere
117what defines a sever thunderstorm?
hail, tornado, or 58 mph winds
118How does wind shear and tilting of the updraft help the storm?
Wind shear helps to tilt a storm such that the updraft and downdraft are displaced from one another. Without competition of moving air, they can strengthen and last much longer than airmass thunderstorms.
119How do roll clouds form?
Roll clouds are horizontal tube shaped clouds. Form between areas of cold downdraft and warm air flowing into the storm
120Shelf clouds
Wedge type clouds accompanied by strong, cool winds of gust front
121Gust front
Acts as a mini cold front, providing lift needed for additional thunderstomr development
122Squall lines
Narrow bands of thunderstorms, often produced by lifting along or ahead of a cold front or dry line
123Mesoscale convective complexes (MCC)
an MCC consists of many individual thunderstorms, organized into an oval cluster. Development requires low-level flow of warm and moist air enhancing instability and cloud development
124Mesocyclone
Directional wind shear that develops vertically may cause updraft to rotate which forms cyclonic rotating air
125Lightning
Part of cloud develops excess negative charge while another part develops excess positive charge. lightning equalizes these charge differences producing a region fo excess negative to position charge or vice versa
126Most commmon type of lightning
Within one cloud or from one cloudto another
127Tornadoes
Violent windstorms with a rapidly rotating column or air or vortex. Drawn by lower presure in the center of vortex, air near the ground rushes in from all directions
128What direction do tornadoes most often move
Northeast
129Maximum wind speeds of tornadoes
less than 90 to more than 300 miles per house
130Lightning Strokes
The flash (total discharge) lasts a fewminutes
The leader is the ionized air which forms a conductive path
A step leader extends earthward in a short, nearly invisible burst
Return stroke develops and extends upward from ground to cloud
131Microburst
Column of sinking air (downdraft) in a thunderstomr
132Downburst
Strong downward and outward gushing wind system (downdraft) that causes damaging winds
133Heat lightning
Doesn't exist, but is light produced by a distant thunderstorm that is reflected off higher-level clouds making it visible
134EF Scale
rates tornado intensity based on severity of damage. Used to classify tornadoes and estimate wind speeds
135What is responsible for the strong wind speeds in tornadoes?
Air pressure is significantly lower than air pressure outside the storm
136What type of thunderstorms do tornadoes develop in?
Supercell thunderstorms (aka rotating thunderstorms), which are characterized by a rotating updraft and form in environments of vertical wind sheer
137Hurricanes
Intense centers of low pressure that form over tropical / subtropical oceans. Have intesne convective activity, rotary circulation, and sustained wind speeds equal to or in excessof 74 mph
138What is a hurricane's source of energy?
Huge volume of warm, moist air. Fueled by latent heat of condensed water vapor, most form late summer to early fall. Sea-surface temps of 80 or higher provide necessary heat and moisture
139How are hurricanes named?
NW pacific: typhoons SW pacfic/indian ocean: cyclones
140How does a hurricane work?
Warm humid air spirals in toward the center in a cyclonic counterclockwise pattern
eye in center, eye wall surrounds storm. ciruclar rain bands trail away. Air rises in the eye wall and exits the storm at the top rotating in the opposite direction. in the center air sinks to from the eye . the center of the storm is the warmest part at all levels
141Eye wall
Most destructive part of the storm, wall of towering thunderstorms whirl around eye of the storm
142Hurricane Formation
Tropical disturbances such as cloud arrays and thunderstorms grow larger adn develop strong cyclonic rotation
143Tropical storm
name of sotmr before it reaches hurrican status. has winds of 39 to 74 mph
144Saffir Simpson Scale
established to rank the intensities of hurricanes based on pressure, winds, and storm surge. 5 is worst
145What casues the fast wind speeds in a hurricane?
Conservation of mass and momentum. as air flows in eye it gets squeezed in and travels faster