Hurricanes = Typhoons = Tropical Cyclones. A video Teaser, while students enter the classroom. YouTube clip Day5-02 Hurricane Harvey. Texas.

Transcription

1 Hurricanes = Typhoons = Tropical Cyclones A video Teaser, while students enter the classroom. (LG: 5d) YouTube clip Day5-02 Hurricane Harvey. Texas (4:22) 1 Storm Hazards (LG: 5d) Thunderstorm Hazards lightning tornado hail downpours (of rain) / local flooding downbursts (of air) / gustfronts Hurricane Hazards contain thunderstorms storm surge / coastal flooding high waves coastal erosion today 2

2 Today s Learning Goals By the end of this period, you should be able to: 5a) describe the anatomy of a hurricane, and how it looks in weather radar and satellite images 5b) explain how sea-surface temperature, winds, waves, condensation, and a "warm core" affect hurricanes 5c) describe the evolution and movement of hurricanes, and locate times and places of greatest risk 5d) explain the main hazards of a hurricane and appropriate safety procedures 5e) describe the nature and skill of hurricane forecasting, and explain why Canada has few hurricanes. 3 Road-map to Storm topics Learning Goals (LG): 1-5 Day Hazards Risk & Safety 1 Lightning 2 Rain Downpours, Air Downbursts 3 Tornadoes 4 Hail Fundamentals Appearance & Evolution Thunderstorm basics Supercells, mesocyclone. Observ.: radar, satellite Wall cloud, striations, Doppler radar Clouds at Tstorms: flanking line, mammatus Energy makes storms sun, radiation, surface heating moisture, condensation, latent heating heat to motion, forces, winds 5 Flooding, winds, waves, storm surge Hurricanes energy in warm ocean, Coriolis 4

3 (LG: 5d) Survey Question: If you have been in a hurricane, typhoon, or tropical cyclone, where were you at that time? (A) North America (B) an Atlantic island (C) a Pacific island (D) Asia (E) (I have not been in any of these storms.) 5 NASA A. Description 1. Anatomy of a hurricane 2. Observations by satellite and radar 3. Saffir-Simpson hurricane wind scale B. Processes 4. Tropical cyclones: organized to create their own fuel 5. Formation & movement 6. Warm core systems: the key to long life C. Hazards 7. Storm surge: the atmosphere drives an ocean disaster 8. Hurricane prediction and safety 9. Hurricanes in Canada Hurricanes = Typhoons = Tropical Cyclones Prof. Roland Stull Earth, Ocean & Atmos. Sciences Dept., UBC (LG: 5a-e) 6

4 A. Description (LG: 5a) Hurricane Sandy NASA, Oct Anatomy of a Hurricane (LG: 5a) Hurricane Floyd 14 Sep 1999 (from NASA GSFC) 8

5 Size: height = 15 km for both hurricanes & Tstorms. diameter = km for hurricanes. (compared to 15 km for Tstorms) (LG: 5a) Hurricane Isabel Thunderstorms from 9 Horizontal Structure (LG: 5a) Hurricanes & typhoons are tropical cyclones, with surface winds turning counterclockwise (in N. Hem.) & spiraling in. Simplified Diagram of a Hurricane Eye = center of hurricane relatively clear relatively calm low pressure at sea level bands of thunder eye eye wall storms Hurricanes are made of thunderstorms: eye wall = ring of thunderstorms around the eye. spiral bands = bands of Tstorms extending out from the eye wall. R photo by R. Stull R is radial distance from center of the eye, and arrows represent wind direction near the ocean surface. Gray represents bands of thunderstorms. 10

6 (LG: 5a,b) Vertical Cross-section Through a Hurricane cirrus troposphere stratosphere eye wall eye outflow subsidence spiral band stratus inflow warm sea surface trade cumulus rain rain intense T-storms Light blue represents clouds, red through green represents decreasing radar-echo intensity (proportional to precipitation rate), and dark blue is the ocean. image by R. Stull 11 The Eye Wall, a Ring of Tstorms (LG: 5a) Radar image, made from HRD aircraft in Isabel. (Red shows heavy precipitation in eye wall) 12

7 NOAA and The Eye, as viewed by Hurricane Hunters (Katrina, Aug 05) NOAA/AOML/ Hurricane Research Division Observations by satellite Hurricane Katrina

8 by Radar NWS photos compiled by Stull (LG: 5a,c) Katrina iclicker Question The hurricane eye wall is A) a region of near-calm conditions at the center of the hurricane. B) a band of thunderstorms spiralling out away from the storm center C) a circle of thunderstorms around the eye D) a high ocean wave formed near the storm center E) is a region of strong winds and heavy rain 16

9 (revised in 2010 by NHC) (LG: 5d) 3. Saffir-Simpson Hurricane Wind Scale Faster winds indicate stronger hurricanes. table by R. Stull Definition Typical Characteristics 17 B. Processes (LG: 5a,b) Katrina 2005 NASA 18

10 4. Tropical Cyclones Organized to Create their own Fuel Compare with individual thunderstorms: use the warm, humid boundary-layer air as fuel. consume nearby supplies of fuel. run out of fuel and die. are short lived (about minutes). Exceptions (longer-lasting thunderstorms) if properly organized: ambient atmosphere happens to have right amount of wind shear that: - continually blows fresh fuel into storm. - or blows Tstorm to new regions having boundary-layer fuel. namely, Supercell that can last for hours. photo by R. Stull (LG: 5b) 19 Hurricanes (& their Tstorms) can last for weeks, because... (LG: 5b) they manipulate the environment to continually create new fuel from heat stored in the ocean. NASA 20

11 Fuel Creation Method (LG: 5b) Low pressure in eye sucks in boundary-layer (BL) air (i.e., air in the bottom 1 km of the atmosphere) As air gets closer to eye, it moves faster Faster winds create larger ocean waves... Hurricane B.L. Warm Ocean T eye T waves Warm Ocean Cold Ocean photo by R. Stull 21 Fuel Creation Method (continued) (LG: 5b) from Evaporation from ocean surface is enhanced with spray from waves Adds significant amounts of moisture into boundary-layer air Finally, when boundary-layer air reaches base of eye wall, it is: warm exceptionally humid (near 100 % relative humidity) contains tremendous amounts of sensible and latent-heat fuel. 22

12 Warm Sea Surface is Needed (LG: 5b) Self-fueling method works (i.e., hurricanes form) ONLY if: ocean surface temperatures > 26 C, AND warm surface waters are > 60 m deep (so that turbulence within the ocean caused by surface waves doesn't mix cold waters up to surface) 23 Warm Sea Surface Shifts with Seasons (LG: 5b) Watch for regions where ocean surface temperatures > 26 C (shown in orange, red, and white here) 24

13 (LG: 5b) Hurricanes Cause Sea-Surface Temperature to Cool, Due to Waveinduced Turbulence in Upper Ocean NASA This is why the depth of warm surface waters should be > 60 m (to avoid having the hurricane kill itself by making SST < 26 C). 25 (LG: 5b) Q: For a hurricane to fuel itself, it needs to (A) add heat to the ocean. (B) remove heat from the ocean. (C) create strong winds that form high waves. (D) move over a waveless ocean to avoid the extra friction (drag) caused by high waves. (E) (none of the above) 26

14 Hurricane Season (in N. Hemisphere) (LG: 5c) late summer and in early Fall, when waters warmest with maximum extent and depth Official N. Atlantic hurricane season is June through November. Most N. Atlantic hurricanes occur August through October wikipedia (LG: 5c) Eastern N. Pacific Atlantic By Cyclonebiskit - Created using WikiProject Tropical cyclones/tracks. The background image is from NASA [1]. The tracking data is from the National Hurricane Center and the Central Pacific Hurricane Center's Northeast and North Central Pacific hurricane database, Public Domain,

15 5. Hurricane Formation & Movement (LG: 5b,c) Hurricanes form in the tropics, but NOT at the equator. International Space Station photo from 29 Favored Hurricane Locations Coriolis (earth s rotation) effect is stronger near poles (shown in blue). Earth Rotation (LG: 5b,c) Coriolis (earth s rotation) effect is stronger near poles (shown in blue). 30 NASA

16 Favored Hurricane Locations Coriolis (earth s rotation) effect is stronger near poles (shown in blue). Earth Rotation (LG: 5b,c) Warmest sea-surface temperatures near equator (shown in red). Coriolis (earth s rotation) effect is stronger near poles (shown in blue). NASA 31 Favored Hurricane Locations Coriolis (earth s rotation) effect is stronger near poles (shown in blue). Earth Rotation (LG: 5b,c) Favored hurricane formation latitudes (shown in green) are where there is BOTH warm SST & nonzero Coriolis Warmest sea-surface temperatures near equator (shown in red). Coriolis (earth s rotation) effect is stronger near poles (shown in blue). NASA 32

17 Favored Hurricane Formation Latitudes are (LG: 5b,c) Equator Wikipedia Commons/ NO hurricanes at equator, because no Coriolis effect there. 33 Hurricane Existence (LG: 5b,c) Hurricanes can persist only if : central pressure in eye remains low (to create wind, waves, and to suck in fuel of warm humid air), AND the hurricane remains over the warm ocean. Hurricanes weaken and die if : cannot generate sufficient fuel of warm, humid air. This happens when hurricanes move over: colder water, or land. larger-scale weather systems interfere. 34 WeatherStock.com, used under license

18 (LG: 5b,c) Hurricane Decay by Landfall JHU fermi.jhuapl.edu/ hurr/17/17.html 35 (LG: 5b,c) Hurricane Decay by Cold Water hurr/17/17.html JHU 36

19 iclicker Question To form and strengthen, hurricanes must A) be at the equator, where the ocean is warmest. B) not be at the equator, because Coriolis force is zero. C) be over land, to gain energy from supercell thunderstorms. D) not be over land, because of the extra frictional drag caused by trees, houses, hills. E) be over the ocean, so that sea spray from breaking waves can add humidity to the air. 37 L Hurricane Decay by Larger-scale System (LG: 5b,c) Cold Front Hurricane Isabel NWS 38

20 (LG: 5b,c) Hurricane Decay by Larger-scale System Water-Vapour Satellite Image Hurricane Isabel, Sep 2003 NWS 39 (LG: 5c) Hurricane Paths Stull 2011, used with permission Bermuda High Steered by the general circulation in the atmos. Westerlies Bermuda High Trade winds NASA Westerlies Trade Winds Trade Winds Westerlies 40

21 Hurricane Paths (continued) (LG: 5c) Net result: hurricanes strike USA at Gulf coast & SE Atlantic states. Canada USA Gulf Coast Atlantic Ocean 41 (LG: 5b, c) Hurricanes don t hit British Columbia because (A) the midlatitude winds blow Pacific hurricanes westward, away from BC. (B) the sea surface is too cold (below the 26 C that is needed). (C) BC is too close to the equator, where the Coriolis effect is too small. (D) the steep coast mountain range protects BC from hurricanes. (E) (They can hit BC, but would be called typhoons in the E. Pacific.) 42

22 (LG: 5b) 6. Warm Core - the key to long life Why can hurricanes last for weeks, in spite of all the air molecules continually being blown into the core? Answer: Hurricane Harvey Aug 2017 Heavy condensation and precipitation from thunderstorms in the eye wall cause the hurricane core (eye + eye wall) to become very warm relative to its surroundings. NWS 43 How eye-wall Tstorms warm the core (LG: 5b) Surroundings cirrus Core stratosphere Surroundings outflow The warm core creates High pressure at the core top, and Low pressure at the core bottom (recall from Day 4). troposphere eye wall eye subsidence spiral band stratus inflow warm sea surface photo by R. Stull 44

23 (LG: 5b) Result is a Vertical Circulation strong updrafts in the eyewall thunderstorms outflow at hurricane top away from core weak downward motion (subsidence) in the eye and outside the hurric. inflow at hurric. bottom towards core cycles back into base of eye-wall Tstorms as a complete circulation. cirrus troposphere trade cumulus rain spiral band stratosphere stratus rain eye wall eye intense T-storms H Vertical Cross-section Through a Hurricane H L outflow subsidence inflow warm sea surface photo by R. Stull 45 iclicker Question The warm core is important for hurricanes because A) it increases the heat stress for people near the core. B) warm air can hold more water vapour than cold air, thereby reducing condensation and rain. C) it causes high pressure at the top of the storm, which drives an outward spiralling wind at storm top. D) causes low pressure at the top of the storm, which drives an inward spiralling wind at storm top. E) (It is not important for hurricanes.) 46

24 Announcements For a fun first-year course on weather, consider taking ATSC 113 Applied Meteorology (Weather for Sailing, Flying and Snow Sports). Online. Offered every term. If you want to learn more about storms, consider ATSC 201 Meteorology of Storms, which I teach every Fall term. Designed for science & engr. majors -- uses a lot of algebra and trig. That course uses my free online textbook: Practical Meteorology: An Algebra-based Survey of Atmospheric Science. Consider majoring in Atmospheric Sciences (ATSC). Become a meteorologist. Stull s team provides a weather forecast service to Canadian companies. 47 C. Hazards. Hurricane Risk (LG: 5c,d) Wikipedia Commons 48

25 7. Storm Surge The atmosphere drives an ocean disaster (LG: 5d) Strong winds drag ocean water, raises sea level, & causes water to pile up against shore. Water pushed ashore This is called a storm surge, causing coastal flooding. Learn more about it in Waves segment of EOSC114. NOAA / AOML / HRD Hurricane Isabel September 2003 WeatherStock.com, used under license 49 Hurricane Flooding & Storm Surge (LG: 5d) photo by R. Stull YouTube clip: Day5-30 Storm surge in Philippines from Super Typhoon Haiyan (Yolanda) in 2013 (1:45). 50

26 (LG: 5d) Hurricane-caused Fatalities: Drowning & Disease Hurricane Harvey Aug 2017 Coastal flooding caused by the hurricane storm surge causes the most deaths. E.g., Bangladesh has been hard hit. In countries such as the USA, inland and urban flooding caused by heavy rains cause the 2nd most hurricane-related deaths. 51 YouTube Video (LG: 5c,d,e) Day Health Dangers after Hurricane Flooding (2:03) 52

27 (LG: 5c,d,e) 8. Hurricane Prediction & Safety Knowledge of past hurricane tracks is NOT the best predictor. Computer models of the atmosphere give conflicting forecasts. Therefore, there is uncertainty until the hurricane gets close to shore. NOAA Past hurricane tracks Computer forecasts of tracks, Hur. Isabel 53 (LG: 5c,d,e) Hurricane Prediction & Safety Hurricane Harvey Aug 2017 Predicted Path Hurricane predictions are inaccurate. Therefore, forecast maps of hurricane danger usually include probabilities. Recommendations for your Safety: Don t buy or build houses on or near the beach in SE USA. Plan in advance for evacuation. Don t ride out the storm. 54

28 (LG: 5c,d,e) 9. Canadian Hurricane Centre Example of Forecast Map Hurricanes are Rare in Canada (LG: 5c,d,e) On 15 Aug 2009, Hurricane Bill hit Nova Scotia and Newfoundland. as a Category 1 storm. 56

29 9. Hurricanes are Rare in Canada (LG: 5c,d,e) About 4 to 5 hurricanes per decade. Most of those rare hurricanes hit Atlantic provinces. Some former hurricanes cause heavy rain and flooding over ON & QC. Some other recent hurricanes include: Hurricane Earl - Cat. 1 at Nova Scotia Hurricane Igor - Cat. 1 at Newfoundland Hurricane Kyle - Cat. 1 at Nova Scotia former Hurricane Noel - Cat. 1 at Nova Scotia & New Brunswick former Hurricane Florence - Cat. 1 at Newfoundland Noteworthy Storms: Hurricane Juan - Cat. 1 to 2 at Nova Scotia. 20 m waves former Hurricane Hazel - Toronto 225 mm rain, killed 81 people. 57 The storm surge iclicker Question A) is caused near the eye because the inward-moving winds create inward-moving ocean currents. B) is often the greatest on the left side of the storm-center track in the Northern Hemisphere C) is often the greatest on the right side of the storm-center track in the Northern Hemisphere D) is a local rise of sea level as hurricane winds push ocean water and cause it to pile up against coastlines. E) is another name for the violent large wind-driven waves that break against the shore. 58

30 End of Storm Topics Prof. Roland Stull Earth, Ocean & Atmospheric Sciences Dept., UBC We covered: Thunderstorm Hazards lightning tornado hail downpours (of rain) / local flooding downbursts (of air) / gustfronts Hurricane Hazards contain thunderstorms storm surge / coastal flooding NASA Any Questions? 59