Atmospheric Circulation and ENSO - Lecture 3

Question 1

What is atmosphere mainly composed of?

Answer 1

Nitrogen, oxygen and water vapour (4%)

Question 2

What determines the density of air?

Answer 2

Temperature + water content. Cooler air can hold less water, so the water vapour condenses into clouds.

Question 3

What does the atmosphere move in response to?

Answer 3

Uneven solar heating (Solar heating of the earth caries with latitude), and the earth’s rotation (the coriolis effect deflects air movement eastward).

Question 4

What is the earth’s tilt?

Answer 4

23 1/2 degrees.

Question 5

What are the three cells that drive global atmospheric circulation?

Answer 5

Polar
Ferrel
Hadley

Question 6

What are the duldrums?

Answer 6

The duldrums are the calm equitorial areas where two hadley cells converge (Intertropical convergence zone - ITCZ)

Question 7

What are the Horse Latitudes?

Answer 7

The horse latitudes are the area between hadley and ferrel cells.

Question 8

What reasons does cell circulation have for following the meteorological equator rather than the geographical?

Answer 8

1. NH contains less ocean than SH
2. Land masses have lower specific heat capacity than oceans.
3. Seasonal differences in temperature ans atmospheric cell circulations are more extreme in NH.
4. Because of greater heat capacity of water, season N -> south movement of ITCZ is generally less over ocean than land.

Question 9

What is a Monsoon?

Answer 9

A pattern of wind circulation that changes with the season.

Question 10

What are the typical conditions of a monsoon?

Answer 10

Locations typically have wet summers and dry winters.

Question 11

What is a storm? and what are the typical conditions associated with one?

Answer 11

A variation in large-scale atmospheric circulation. Areas typically experience high wind speeds, precipitation, and rotating masses of low-pressure air.

Question 12

Where do extra-tropical cyclones occur?

Answer 12

In Ferrel cells and are typically winter weather disturbances.

Question 13

What are the dynamics of a Tropical cyclone?

Answer 13

The core rotates left (counter clockwise). The air in a tropical cyclone starts moving toward the center (A zone of low pressure) and the veers off course to the right due to the coriolis effect.

Question 14

Why do tropical cyclones not form in the South Atlantic of Southeast Pacific oceans?

Answer 14

There are cold water currents in those areas that prevent optimum conditions forming.

Question 15

Why do tropical cyclones not form in the duldrums?

Answer 15

The coriolis effect in these areas is very subtle and not enough air movement is created.

Question 16

What is the typical path of a tropical cyclone?

Answer 16

The tropical cyclone forms either side of the equator, it then follows a curving path, first moving westward with the trade winds. The cyclone will then die over land or turn eastward until they lose power over the cooler mid-latitude oceans.

Question 17

What does ENSO stand for?

Answer 17

El Nino Southern Oscillation

Question 18

What is the El Nino southern oscillation?

Answer 18

A mode of inter-annual climate variability which effects a band of sea surface temperatures in the tropical pacific.

Question 19

What is the time period between El Nino and La Nina phases?

Answer 19

3-8 Years.

Question 20

Where are the effects of ENSO felt?

Answer 20

The major effects are on the pacific marine environment, but climate effects can be felt through out much of the world.

Question 21

What are the normal wind and current flow patters across the tropical pacific?

Answer 21

The thermocline is deeper in the west and rises in the east, as a result upwelling occurs along the west coast of Central and South America.

Question 22

What effects does an El Nino year have on wind and current flow?

Answer 22

The trade winds diminish and then reverse, this leads an eastward movement of warmer water along the equator. As a result surface waters of the central and eastern pacific become warmer and storms over land may increase.

Question 23

What is the Southern Oscilation Index?

Answer 23

A measurement of the pressure difference between Tahiti and Darwin.

Question 24

What do sustained values >8 on the Southern Oscillation index indicate?

Answer 24

La Nina.

Question 25

What do sustained values <-8 on the Southern Oscillation index indicate?

Answer 25

El Nino.

Question 26

What are the typical conditions experienced during El Nino?

Answer 26

Changes in atmospheric circulation and weather patterns. Low atmospheric pressure south of Alaska allows storms to move unimpeded to the pacific coast of North America. The weather is wet and cool to the south, and warm and dry in the north.

Question 27

What are the typical conditions experienced during La Nina?

Answer 27

High pressure south of Alaska blocks the storm track. Winds veer north, and lose their warmth over Canada then speed down as cold blasts. The pacific NW gets its usual rain, but the SW suffers drought.

Question 28

What are some examples of El Nino Impacts?

Answer 28

• Floods in peru
• Drought in Papua New Guinea
• Reduced productivity of Eastern Pacific waters - flow on effects (e.g. fisheries, seabirds)