Link between Hurricanes and Climate Change: SST

Transcription

1 Link between Hurricanes and Climate Change: SST FRIDAY: PROJECT 2 Proposals due! Bring laptops on weds (at least one per group)! Discuss assessment on Weds. Roger Francois will talk on Friday about the paleotemperature record of the ocean Quiz part 1: -Take this one on your own - Keep track of your answers on a separate page - 5 questions, 5 minutes. 1) A collection of thunderstorms can become organized into a hurricane in the presence of a strong wind shear that interacts with an additional atmospheric disturbance under which of the following conditions: a) A sea-surface temperature greater than 26 deg C b) Enhanced evaporation c) Low pressure at the sea surface d) a, b, and c e) A hurricane will not form in the presence of a strong wind shear 2) Most hurricanes form in the tropics because: a) There is high humidity b) Most of the suns energy is absorbed in this region c) The tropics are characterized by an unusually high concentration of atmospheric disturbances d) The Atlantic multidecadal oscillation has a particularly big effect there. e) a and b 1

2 3) A thunderstorm is an atmospheric disturbance that forms because rising moist air condenses to form rain drops. The process of droplet condensation: a) Extracts heat from the atmosphere resulting in strong updrafts b) Extracts heat from the atmosphere resulting in strong downdrafts c) Releases heat to the atmosphere resulting in strong updrafts d) Releases heat to the atmosphere resulting in strong downdrafts e) Releases heat to the atmosphere resulting in strong downdrafts that circulate because of the Coriolis force. 4) Choose the most accurate statement: a) Human-induced global warming corresponds to an increase in both the frequency and intensity of hurricanes. b) Human-induced global warming has caused an increase in both the frequency and intensity of hurricanes. c) Human-induced global warming corresponds to an increase in hurricane intensity. d) Human-induced global warming, combined with the Atlantic multidecadal oscillation, and modulated my El Nino/ La Nina cycles has caused an increase in the frequency of hurricanes over the last 100 years. e) The annual cycle of Atlantic hurricanes is not observed before the industrial revolution. 5) If an El Nino forms during the summer a) The jet stream in the Pacific splits, favoring hurricanes in the Pacific and Indian oceans. b) The enhanced temperature gradient across the Pacific leads to conditions that do not favor the formation of hurricanes in the Atlantic. c) The jet stream dips southward over North America and the resulting increased trade winds cause hurricanes to form in the Pacific. d) The jet stream dips southward over North America and the weaker trade winds allow hurricanes to form in the Caribbean. e) None of the above. Quiz part 2: - Pass your answer sheet to your neigbir on your left -Take this one with your group. - ONE answer per group - Keep track of your answers on a separate page - 5 questions, 10 minutes. 2

3 1) A collection of thunderstorms can become organized into a hurricane in the presence of a strong wind shear that interacts with an additional atmospheric disturbance under which of the following conditions: a) A sea-surface temperature greater than 26 deg C b) Enhanced evaporation c) Low pressure at the sea surface d) a, b, and c e) A hurricane will not form in the presence of a strong wind shear 2) Most hurricanes form in the tropics because: a) There is high humidity b) Most of the suns energy is absorbed in this region c) The tropics are characterized by an unusually high concentration of atmospheric disturbances d) The Atlantic multidecadal oscillation has a particularly big effect there. e) a and b 3) A thunderstorm is an atmospheric disturbance that forms because rising moist air condenses to form rain drops. The process of droplet condensation: a) Extracts heat from the atmosphere resulting in strong updrafts b) Extracts heat from the atmosphere resulting in strong downdrafts c) Releases heat to the atmosphere resulting in strong updrafts d) Releases heat to the atmosphere resulting in strong downdrafts e) Releases heat to the atmosphere resulting in strong downdrafts that circulate because of the Coriolis force. 4) Choose the most accurate statement: a) Human-induced global warming corresponds to an increase in both the frequency and intensity of hurricanes. b) Human-induced global warming has caused an increase in both the frequency and intensity of hurricanes. c) Human-induced global warming corresponds to an increase in hurricane intensity. d) Human-induced global warming, combined with the Atlantic multidecadal oscillation, and modulated my El Nino/ La Nina cycles has caused an increase in the frequency of hurricanes over the last 100 years. e) The annual cycle of Atlantic hurricanes is not observed before the industrial revolution. 3

4 5) If an El Nino forms during the summer a) The jet stream in the Pacific splits, favoring hurricanes in the Pacific and Indian oceans. b) The enhanced temperature gradient across the Pacific leads to conditions that do not favor the formation of hurricanes in the Atlantic. c) The jet stream dips southward over North America and the resulting increased trade winds cause hurricanes to form in the Pacific. d) The jet stream dips southward over North America and the weaker trade winds allow hurricanes to form in the Caribbean. e) None of the above. Let s talk about some of the answers 1) A collection of thunderstorms can become organized into a hurricane in the presence of a strong vertical wind shear that interacts with an additional atmospheric disturbance under which of the following conditions: a) A sea-surface temperature greater than 26 deg C b) Enhanced evaporation c) Low pressure at the sea surface d) a, b, and c e) A hurricane will not form in the presence of a strong wind shear 1) A collection of thunderstorms can become organized into a hurricane in the presence of a strong wind shear that interacts with an additional atmospheric disturbance under which of the following conditions: a) A sea-surface temperature greater than 26 deg C b) Enhanced evaporation c) Low pressure at the sea surface d) a, b, and c e) A hurricane will not form in the presence of a strong wind shear 4

5 Concept: A hurricane is not easy to build The collection of T-storms must be large enough spatially that the Coriolis force causes them to rotate together as a vortex. Strong vertical wind shear due, say to enhanced westerlies, can either tear apart nascent vortexes or prevent them from forming (more about this in a bit) 2) Most hurricanes form in the tropics because: a) There is high humidity b) Most of the suns energy is absorbed in this region c) The tropics are characterized by an unusually high concentration of atmospheric disturbances d) The Atlantic multidecadal oscillation has a particularly big effect there. e) The Coriolis force is strongest near the equator. 2) Most hurricanes form in the tropics because: a) There is high humidity b) Most of the suns energy is absorbed in this region c) The tropics are characterized by an unusually high concentration of atmospheric disturbances d) The Atlantic multidecadal oscillation has a particularly big effect there. e) The Coriolis force is strongest near the equator. 3) A thunderstorm is an atmospheric disturbance that forms because rising moist air condenses to form rain drops. The process of droplet condensation: a) Extracts heat from the atmosphere resulting in strong updrafts b) Extracts heat from the atmosphere resulting in strong downdrafts c) Releases heat to the atmosphere resulting in strong updrafts d) Releases heat to the atmosphere resulting in strong downdrafts e) Releases heat to the atmosphere resulting in strong downdrafts that circulate because of the Coriolis force. 5

6 3) A thunderstorm is an atmospheric disturbance that forms because rising moist air condenses to form rain drops. The process of droplet condensation: a) Extracts heat from the atmosphere resulting in strong updrafts b) Extracts heat from the atmosphere resulting in strong downdrafts c) Releases heat to the atmosphere resulting in strong updrafts d) Releases heat to the atmosphere resulting in strong downdrafts e) Releases heat to the atmosphere resulting in strong downdrafts that circulate because of the Coriolis force. To start a hurricane: 3 concepts Thermodynamics: Droplet condensation in rising moist air releases (latent) heat to surrounding air. Mechanics (buoyancy): Warm air rises depending on the total flux of this latent heat. More droplets = faster rising air. A Critical condition for disturbance to grow in to a hurricane - The rate of rise must be sufficiently large to draw other T-storms to form a mass big enough for the Coriolis force to cause it to rotate en masse as a cyclone. - Vertical wind shear must be small Effects of strong wind shear on the growth of hurricanes: Deforms ( tears ) vortexes; prevents the development of stable cyclones. A more detailed picture that relies on the same 3 concepts Spreads out cumulus material (i.e. condensed water); Latent heat flux related to droplet condensation is thus vented away; No concentrated source of buoyancy to drive updrafts = a storm that does not grow. Tropical storm Gabrielle,

7 4) Choose the most accurate statement: a) Human-induced global warming corresponds to an increase in both the frequency and intensity of hurricanes. b) Human-induced global warming has caused an increase in both the frequency and intensity of hurricanes. c) Human-induced global warming corresponds to an increase in hurricane intensity. d) Human-induced global warming, combined with the Atlantic multidecadal oscillation, and modulated my El Nino/ La Nina cycles has caused an increase in the frequency of hurricanes over the last 100 years. e) The annual cycle of Atlantic hurricanes is not observed before the industrial revolution. 4) Choose the most accurate statement: a) Human-induced global warming corresponds to an increase in both the frequency and intensity of hurricanes. b) Human-induced global warming has caused an increase in both the frequency and intensity of hurricanes. c) Human-induced global warming corresponds to an increase in hurricane intensity. d) Human-induced global warming, combined with the Atlantic multidecadal oscillation, and modulated my El Nino/ La Nina cycles has caused an increase in the frequency of hurricanes over the last 100 years. e) The annual cycle of Atlantic hurricanes is not observed before the industrial revolution. Hurricane Frequency: What do we really know about it? If reliable records of hurricanes only go back to 1944, how can we say there were not more intense and more frequent hurricanes before 1944? How can we say with total accuracy that the upswing in the past few decades is solely a result of global warming? How can we say with total accuracy that the upswing in the past few decades is solely a result of global warming? Concepts: Natural variability such as AMO cannot explain the increase in hurricane frequency and intensity. This increase can be explained as a result of a long-term rise in the average sea surface temperature. The data do not demand that the human influence on climate is the underlying cause. 7

8 Hurricane Frequency: Paleo-record Varve sediments near Boston (GRL, 2008) Why was Katrina especially intense? Katrina and the Gulf Stream loop current What does this observation potentially imply about the next 200 years of hurricanes? 5) If an El Nino forms during the summer a) The jet stream in the Pacific splits, favoring hurricanes in the Pacific and Indian oceans. b) The enhanced temperature gradient across the Pacific leads to conditions that do not favor the formation of hurricanes in the Atlantic. c) The jet stream dips southward over North America and the resulting increased trade winds cause hurricanes to form in the Pacific. d) The jet stream dips southward over North America and the weaker trade winds allow hurricanes to form in the Caribbean. e) None of the above. 5) If an El Nino forms during the summer a) The jet stream in the Pacific splits, favoring hurricanes in the Pacific and Indian oceans. b) The enhanced temperature gradient across the Pacific leads to conditions that do not favor the formation of hurricanes in the Atlantic. c) The jet stream dips southward over North America and the resulting increased trade winds cause hurricanes to form in the Pacific. d) The jet stream dips southward over North America and the weaker trade winds allow hurricanes to form in the Caribbean. e) None of the above. 8

9 Concept: SST vs. SST GRADIENTS If higher SSTs increase wind shear, what effect will this have on hurricane formation, and could this also lead to a decrease in hurricane frequency as the planet warms? With rising SST is it possible to see cyclones in areas that were thought not to be vulnerable? Does increased SST have any influence on the formation rate of hurricane formation? i.e. Will it require a longer duration to detect and forcast the formation of an intense larger hurricane? Concept: ENSO / hurricane coupling-- How does it work? Shouldn't understanding the phenomena of El nino and la nina be more of a priority because they explained the dramatic differences between hurricane activities of 2005 and 2006? If El Nino and La Nina were the cause of a quiet 2006 season, what is the cause for the quiet 2007 and 2008 hurricane seasons? Net Mean Heat flux to Earth from the Sun This is: Solar abs - IR emitted; Key: NO zonal (latitudinal) or meridional (longitudinal) heat transfer related to ocean/atmo stirring Mean tropical Pacific climatology: Normal State Solar heating, ocean/atmo stirring 9

10 So why is there an El Nino state? A better question might be why there is a normal state Normal Pacific Normal Pacific Strong easterly trade winds lead to strong westerly winds at the ocean surface and a significant temperature gradient across the Pacific. El Nino Pacific El Nino Pacific This is close to what you would guess based on the solar heating alone! I.e. intuition = el nino not normal The key issues for ENSO: Surface wind stresses and upwelling Normal Condition: Depth to the thermocline is governed by the magnitude of the wind stress. The deeper the thermocline the colder the upwelling water. Strong westerly wind at the ocean driven by the large lateral temperature difference surface across the Pacific = deep thermocline. Upwelling water is cold. Topex Satellite Imagery: Growth of El Nino through SSH El Nino condition: The lateral temperature difference declines, surface winds slacken, the depth to the thermocline becomes less. Upwelling water is relatively warm. Warmer upwelling reinforces weakening of trades smaller delta-t). Weakening of trades reduces thermocline depth. 10

11 Growth of El Nino: SSH (indicates SST) Westerly triggers Kelvin-wave Wave reaches S. America Strong El Nino The Oscillation and Growth of La Nina Warm water piling up: El Nino start Weakening El Nino Weakening El Nino The Oscillation and Growth of La Nina The Death of La Nina Not a simple process. ENSO complex Slide 5 Weakening El Nino Overshoot : Strong La Nina El Nino in retreat A hot and cold Pacific? Normal Pacfic 11

12 K-waves also trigger El Nino A Kelvin wave. Pushes surface up Wave reaches S. America ENSO and Atlantic Wind Shear: Transient dynamic effects on hurricane production Warm water piling up: El Nino start Wind shear related to jet stream tears up nascent hurricanes! Katrina and a loop current Can global warming also potentially change the direction in which hurricanes move and lead to hurricanes hitting areas of the world that rarely/never are affected by these kinds of storms? Will climate change cause hurricanes to emerge in different locations? With rising SST is it possible to see cyclones in areas that were thought not to be vulnerable? 12