// lecture 19

Question 1

pacific decadal oscillation

Answer 1

related to ENSO, but lower frequency and more concentrated in the middle latitudes.

Question 2

impacts of the PDO:

Answer 2

• affects US winter weather in the same way ENSO does. for example, a negative PDO encourages drought in California.
• affects salmon abundance on the west coast because of its influence on the ocean.
• affects the global mean temp. when in its cold phase, the cold SST in the tropics can lower the global mean temp. because the ocean stores more heat and cools the atmosphere. by transition from cold to warm during 2015 El Nino caused global warming to accelerate after long period of very slow warming.

Question 3

atlantic multi-decadal oscillation (AMO)

Answer 3

average SST over north atlantic, subtract linear trend. warm SST in tropical atlantic makes more and bigger hurricanes, all else being equal.

Question 4

impacts of AMO:

Answer 4

• arctic seems to be warmed by warming of North Atlantic Ocean.
• hurricanes in Atlantic respond to local warming of subtropical atlantic ocean.
• PDO and AMO are low frequency (decade time scales) natural variability that can be confused with, but also interact with, global warming.

Question 5

profile of tropical cyclone

Answer 5

• eye - clear area in the center.
• eyewall - clouds immediately surrounding the eye (highest winds and rain).
• spiral rain bands - outer raining areas.
• rising areas have rain and clouds; sinking areas are dry.

Question 6

hurricanes occur over the

Answer 6

warmest waters, but not right at the equator because the coriolis force is required.

Question 7

saffir-simpson hurricane scale

Answer 7

higher category = higher winds = more storm surge = lower pressure in the eye.

Question 8

category 1 (ss hurricane scale)

Answer 8

74 mph, 980+ mbars; minimal

Question 9

category 2

Answer 9

96 mph, 979 mbars; moderate

Question 10

category 3

Answer 10

111 mph, 964 mbars; extensive

Question 11

category 4

Answer 11

121 mph, 944 mbars; extreme

Question 12

category 5

Answer 12

156+ mph, <920 mbars; catastrophic

Question 13

many strong hurricanes are around

Answer 13

Taiwan, Philippines.

Question 14

tropical cyclone Yasi

Answer 14

155 mph winds, 930 mbar min. pressure. among top ten strongest cyclones to hit australia soil is already saturated from floods. la nina (extremely warm ocean in w. pacific)

Question 15

water vapor

Answer 15

fuels a hurricane. when water vapor condenses, heat is released.

Question 16

heat released from a hurricane:

Answer 16

• 1.5 cm/day of average rainfall in a circle of radius 660 km.
• the heat released from this condensation is 52 quintrillion joules per day of energy.
• 200 times the world electricity generating capacity.

Question 17

condensation is the ____ and evaporation provides the ____

Answer 17

energy source; fuel. the strong winds in hurricanes causes more evaporation from the ocean surface.

Question 18

warmer air can hold more

Answer 18

moisture. also evaporation can occur more easily from a warmer ocean.

Question 19

warm ocean temps.:

Answer 19

first requirement for hurricanes. hurricanes weaken when they pass over land due to lack of evaporation.

Question 20

requirements for hurricanes

Answer 20

• SSTs must be above 26 C (79 F). this will shift to a warmer temp. threshold in a warmer climate though.
• must be a least 5 degrees off the equator. Coriolis force is required (why storms rotate opposite in N. and S. hemispheres).
• not much wind sheer (when the winds change with height). this rips hurricanes apart.
• can’t be too cold below the surface either.

Question 21

when hurricanes pass by, they

Answer 21

churn up colder water from below.

Question 22

damages in hurricanes are caused by:

Answer 22

winds, storm surge (high winds pushing towards the land), and flooding.

Question 23

financial damages from hurricanes is

Answer 23

increasing, but this is primarily due to more people living on the coast.

Question 24

1991 Bangladesh cyclone

Answer 24

144,000 fatalities. left 10 million homeless.

Question 25

superstorm sandy

Answer 25

deadliest and most destructive storm of the 2012 season in the USA.
- only category 3, but was the largest Atlantic hurricane by diameter, about 1,800 km, 1,100 miles.
- hit caribbean islands and affected 24 states, especially NJ and NY, where the storm surge hit hard.
233 deaths, mostly in US (157) and Haiti (54).
- about $68 billion in damage.
- track featured unusual left turn in midlatitudes to hit US coast.

Question 26

sandy and grace

Answer 26

in oct. of 1991, a similar juxtaposition of a troopical storm and a midlatitude low brought a very strong storm off shore that sank fishing boats - Andrea Gail Sword boat.

Question 27

strong shear would be when the

Answer 27

wind speed increases or changes direction with height.

• midlatitude storms can deal with this shear and actually like it.
• tropical storms tend to be ripped apart, since the upper part needs to be connected to the lower part for an intense tropical storm.

Question 28

increased shear over the

Answer 28

gulf of mexico would act to weaken hurricanes. would offset some of the increase in strength due to increased temps. also the atmosphere tends to stabilize when there’s more moisture.

Question 29

in 2005, in the atlantic, there were:

Answer 29

• 3 of the 6 strongest storms ever (Wilma, Rita, and Katrina).
• 27 named storms (previous record: 21). doesn’t use letters Q, U, X, Y, and Z. uses alpha, beta, gamma, delta, epsilon, and zeta.
• but only 10% of the world’s hurricanes occur in the atlantic.

Question 30

claim that category

Answer 30

4 and 5 have increased 80%.

Question 31

power dissipation index

Answer 31

better measure of strength that combines frequency, intensity, and duration.

Question 32

PDI in the atlantic is

Answer 32

highly correlated with atlantic ocean temps.

Question 33

study suggests that hurricanes will

Answer 33

continue to strengthen with global warming.

Question 34

observational record of hurricanes with full coverage is

Answer 34

relatively short because before 1970s we didn’t have satellite data.

Question 35

recent models suggest more

Answer 35

really strong storms in warmer climate, but fewer storms overall.

Question 36

indian ocean dipole

Answer 36

difference between the east and west indian ocean.

Question 37

1994 event of indian ocean dipole

Answer 37

wind blows along coast of sumatra, upwelling of cold water, suppression of precipitation (rains more where SST is higher).

Question 38

tornadoes are

Answer 38

smaller in scale and shorter in duration than hurricanes. hurricanes often spawn tornadoes when they make landfall.

Question 39

tornadoes occur with

Answer 39

thunderstorms, hurricanes contain many thunderstorms.

Question 40

tornadoes occur most often

Answer 40

over land in springtime, usually, hurricanes occur exclusively over tropical oceans.

Question 41

observed changes in tornadoes are even more

Answer 41

uncertain than observed changes in hurricanes.

Question 42

hard to predict future tornados.

Answer 42

still warming means more energy in the form of latent heat of water vapor, and release of latent heat is what drives tornadoes, so this causes worry.