Lecture 7

Question 1

Describe Earth’s energy balance

Answer 1

• there is an equilibrium between incoming radiation and outgoing radiation
• Earth intercepts only a small portion of the Sun’s radiation
• The Sun’s energy drives the hydrologic cycle and all weather phenomena on Earth
• Nearly all of the energy available at Earth’s surface comes from the Sun

Question 2

What is the atmosphere composed of?

Answer 2

• composed of nitrogen (78%) and oxygen (21%)
• the remaining 1% consists of water vapour, carbon dioxide, and other ‘trace’ gases
• water vapour in the atmosphere can result in cloud development and the formation of precipitation
• water vapour comes from evaporation from the oceans

Question 3

Where is weather confined in the atmosphere?

Answer 3

• all weather (ie. clouds and precipitation) is confined to the troposphere
• the ozone layer (25km above surface) protects us from the Sun’s harmful UV rays; it is found in the stratosphere

Question 4

How are clouds named?

Answer 4

Prefix:

• cirro (high cloud)
• alto (mid-level cloud)
• strato (low cloud)

Suffix:

• cumulus (puffy)
• stratus (flat)

“nimb”: clouds that produce precipitation

Question 5

What is cumulonimbus cloud?

Answer 5

-a cloud that produces lightning, thunder, and heavy rain

Question 6

What is atmospheric pressure?

Answer 6

• it is a force exerted on the Earth’s surface by the weight of air molecules
• it is also called barometric pressure and is measured with a barometer
• pressure decreases with increasing altitude

Question 7

What results from differences in pressure at Earth’s surface?

Answer 7

• causes wind to blow
• in the northern hemisphere: at areas of low pressure air circulates counter-clockwise and rises which results in clouds and precipitation, at areas of high pressure air circulates clock-wise and sinks which results in clear skies

Question 8

What is a front?

Answer 8

• a front marks the boundary between two air masses
• the name of the front describes the type of air behind that front
• at a cold front, dense cold air undercuts warm air
• at a warm front, the less dense warm air overrides cold air
• cold fronts violently force warm air up so they are associated with cumulonimbus clouds

Question 9

How is tornado formed?

Answer 9

• start as horizontal spinning columns in the clouds
• hot air rising off of hot ground moves the horizontal column vertically
• whole thing is called mesocyclone

Question 10

What is required for thunderstorm development?

Answer 10

• an unstable environment (steep vertical temperature gradient)
• water vapour
• rising air (or a lifting mechanism, eg. a front)

Question 11

What are the stages of thunderstorm development?

Answer 11

• cumulus
• mature
• dissipative
• most storms pass through all 3 stages

Question 12

What is hail?

Answer 12

• it is formed during thunderstorms in cumulonimbus clouds
• updrafts in the cloud repeatedly force a water droplet upward
• the droplet develops a ring of ice around it each time it enters the cold part of the cloud
• the ball of ice eventually becomes heavy enough to fall to the surface

Question 13

What is lightning?

Answer 13

• a spark of electricity occurring in a cloud
• the majority of lightning strikes within the cloud
• lightning heats the air causing the air to expand thus creating a shockwave (thunder)
• sometimes the atmosphere refracts thunder making it inaudible

Question 14

What is the main requirement for lightning?

Answer 14

• a cumulonimbus cloud containing a region of opposite charges
• the interaction of ice crystals, hailstones, and water droplets result in a separate distribution of charges in the cloud

Question 15

What is a tornado?

Answer 15

• a rotating column of air touching the ground that formed within a supercell thunderstorm
• a rotating column not touching the ground is called a funnel cloud

Question 16

What are characteristics of a tornado?

Answer 16

• on average they are approximately 300m wide
• they travel from the southwest toward the northeast at an average speed of 50km/h
• they tend to exist for less than 30 mins with a defined life cycle
• the most common season for tonadoes is Summer in Canada and Spring in the US

Question 17

What is the life cycle of a tornado?

Answer 17

Organizational stage:

• wind shear causes rotation to develop
• funnel cloud protrudes from above
• dust and debris rotates beneath

Mature stage:

-most severe damage occurs at this stage

Rope stage:

-the tornado stretches out and weakens

Question 18

What is a wind shear?

Answer 18

-a change in wind speed or wind direction over a horizontal or a vertical distance

Question 19

How are tornadoes classified?

Answer 19

• Enhanced Fujita Scale: tornadoes are classified on a scale of EF0 to EF5 based on the damage produced
• EF5 tornadoes: complete devastation; wind speed over 322km/h, less than 1% of all tornadoes are EF5

Question 20

Where are the tornado alleys located>

Answer 20

• the US experiences the most tornadoes on Earth
• Canada experiences the 2nd most
• US tornado alley: Kansas and Oklahoma
• Canada Tornado alley: Southwestern ontario

Question 21

Why do tornado alleys exist?

Answer 21

• they are areas where air masses commonly collide
• they are areas of relatively flat land (this allows for undistrubed rotation)

Question 22

How do tornadoes occur in Canada’s tornado alley?

Answer 22

• tornadoes in Ontario occur when a southwesternly wind brings warm, moist air from the Gulf of Mexico
• the warm moist air often interacts with cooler lake breezes

Question 23

Describe the 1974 Super Outbreak of tornadoes

Answer 23

-on this day 148 tornadoes touched down between Ontario and Alabama

Question 24

When did the largest tornado outbreak in world history occur?

Answer 24

• 2011 from April 25-28
• in the southeast US 358 tornadoes touched down and 324 people were killed (239 in Alabama)
• overall more people were killed by tornadoes in 2011 than any other year since 1925

Question 25

Describe the Joplin tornado

Answer 25

• May 22 2011
• an EF5 tornado killed 162 people in Joplin Missouri
• this tornado was the most costly in US history (2.2B) and the deadliest in the US since 1947

Question 26

Describe the Goderich tornado

Answer 26

• a tornado in Goderich killed 1 person and destroyed much of the town core on Aug 21 2011
• it was the first EF3 tornado to touch down in Ontario in 15 years
• the tornado was spotted over Lake Huron on RADAR and a warning was issued 12 minutes before it reached town

Question 27

Describe the Moore tornado

Answer 27

• on May 20, 2013 an EF4 tornado in Moore, Oklahoma killed 24 people
• a tornado warning was issued for the area 16 minutes in advance
• advances in weather technology have greatly improved warning systems over the past decade

Question 28

What is fog?

Answer 28

• it is a cloud with its base at the Earth’s surface that reduces visibility
• it occurs at night when the air cools to the dew point (at which point water vapour condenses into droplets)
• fog can also form when warm air moves over a cold body of water

Question 29

What conditions need to be met for blizzards?

Answer 29

• wind of at least 40km/h
• snow falling or blowing snow occurring
• visibility less than 400m
• all of these must occur for 4 hours
• pretty rare in southwestern ontario

Question 30

What is lake effect snow?

Answer 30

• lake effect snow is caused by cold air moving over relatively warm water
• heavy snow falls downwind of lakes
• snowbelts are found downwind of the lakes (in winter, the wind is often from the northwest)
• heavy snow falls downwind of lakes
• London and Guelph often receive lake effect snow from Lake Huron causing high annual snowfall
• Windsor occasionally receives lake effect snow from Lake Michigan

Question 31

What are lake effect clouds?

Answer 31

• all of southern Ontario frequently experiences lake effect clouds in winter
• both lake effect clouds and lake effect snow diminish when the lakes freeze (this can occur by February)

Question 32

What are haboobs?

Answer 32

• sandstorms that occur in arid and semi-arid regions
• downdrafts on the leading edge of a thunderstorm cause a haboob to form

Question 33

What are dust devils?

Answer 33

• a small spinning vortex of air formed over hot, dry land
• as hot air rises wind direction may change due to obstacles
• this may result in a spinning column of air

Question 34

What are ice storms?

Answer 34

• these are mainly caused by freezing rain
• the weight of the ice can pull down trees and power lines
• freezing rain is rain that freezes upon impacting the surface

Question 35

What are droughts?

Answer 35

• this is an extended period of unusually low precipitation
• droughts affect more people in NA than any other hazard
• they cause water shortages that can lead to crop failure
• in developing countries, this may lead to malnutrition and famine
• droughts are linked to global weather patterns and are a normal part of the climate system

Question 36

What is wind chill?

Answer 36

-it is a correction factor to a temperature reading caused by the presence of wind making the air feel cooler than the temperature suggests

Question 37

What is the humidex?

Answer 37

-it is a correction factor to a temperature reading caused by high levels of humidity making the air feel warmer than the temperature suggests

Question 38

How can we minimize severe weather hazards?

Answer 38

• forecasting has improved dramatically with better technology; 3 day forecasts are very accurate today
• weather satellites detect cloud cover and aid in forecasting hurricanes and mid-latitude cyclones
• RADAR detects precipitation (both the type of precipitation and intensity)

Question 39

What is a watch?

Answer 39

• an alert covering a wide area
• conditions favour the development of hazardous weather but none has been reported
• ex: tornado watch, winter storm watch

Question 40

What is a warning?

Answer 40

• an alert that usually covers smaller areas
• it indicates that hazardous weather is currently occurring in the area
• ex: severe thunderstorm warning

Question 41

What is an advisory?

Answer 41

• used to alert the public of less hazardous weather conditions
• dense fog advisory

Question 42

In which layer of the atmosphere are most clouds found?

Answer 42

troposphere