MET1010: Final Exam Review
Cretaceous Warm Greenhouse
- Breakup of Pangaea led to large outgassing of CO2 from increase in volcanic activity along spreading continental plates - 120-90 million years ago - CO2 concentrations four times current levels - Global mean temperature 11.2°F warmer than present - Very little ice; very warm period; sea level about 100 m higher than present
Volcanic eruptions
- Can alter climate of Earth for both short and long periods of time - Average global temperature dropped about 0.5°F for 2 years after eruption of Mt. Pinatubo in 1991 - Volcanic activity over thousands of years is associated with worldwide warming in average temperatures
Supercell thunderstorms
- Type of rotating single-cell thunderstorm that can persist for hours - One additional ingredient: wind shear - Updraft is tilted so that rain (and cold air) is downwind of storm's source of moisture and instability - Main threats: large and long-lived tornadoes, large hail, strong winds, flash flooding - Produce strongest tornadoes (EF4-EF5) - Has two primary downdrafts
Saffir-Simpson Scale
- Used to describe intensity and possible damage from hurricane - Wind speed is used: easier to measure; based on max winds in the eyewall - Cat 1: 74-95 mph wind; minimal damage; 4-5 feet of storm surge - Cat 3: 111-130 mph wind; extensive damage; 9-12 feet of storm surge - Cat 5: more than 155 mph wind; catastrophic damage; greater than 18 feet storm surge
Tornado
- Violently rotating column of air descending from a thunderstorm and in contact with the ground - May have wind speeds over 300 mph - Nearly 1,000 tornadoes occur in US each year, with an average of 62 fatalities - Usually brief, but may last more than an hour and travel for tens of miles - Rate on Enhanced Fujita scale - Occur typically away from equator, tropical regions, and poles - Occur in US most often in May and June - Most deaths in North Florida occurred with six F3 tornadoes
Groundwater flooding
- Water table rises to surface during prolonged wet periods - Occurs most in low-lying areas, areas near aquifers, and in basements/cellars - Rising very slowly and lasting for a month or more
Winter storms
- Weather event that features snow, sleet, and/or freezing rain (winter precipitation) - Occur during winter, but can happen during fall/spring - Associated with extratropical cyclones - Snowfall criteria: 6 in or higher in 12 hr or 8 in or higher in 24 hours - Sleet criteria: 1/2 inch or higher - Freezing rain criteria: 0.25 (1/4) inch or higher; when rain enters sub-freezing temperatures too close to the ground, it leads to freezing rain
Single-cell thunderstorms
- Can't last long because it exists away from jet stream - Cumulus stage: usually little if any rain; lasts about 10 minutes; occasional lightning; least likely to be seen on radar - Mature stage: likely heavy rain, lightning, strong winds, hail and tornadoes; lasts 10-20 min but may last longer - Dissipating stage: rainfall decreases in intensity; some produce burst of strong winds; lasts 10-15 mins
Hurricane damage categories
- Category 1: little damage - Category 2: roof and tree damage - Category 3: some structural damage - Category 4: widespread damage, some structural failure - Category 5: complete structural failures - Cat 3-5 account for 83% of damage, but are only 21% of US landfalling hurricanes
Multicell thunderstorm - squall line
- Cause "squalls" of strong wind and heavy rain - Need a stronger jet stream to maintain squall line - "Rear-inflow jet" is strong enough to push part of line forward and form a "bow echo": behind bow echo can be very strong winds - Air rising over gust front will condense prior to moving up updraft: will form a "shelf cloud"
Hurricane watch vs. warning
- Hurricane watch: hurricane conditions are possible within 48 hours - Hurricane warning: hurricane conditions are expected within 36 hours; provide adequate time for evacuation
Flooding from thunderstorms
- If ground is saturated from previous rainfall, a less-intense storm can cause flooding - Extended periods of rain can result in river flooding - Water rises more slowly but flooding may last for days or weeks - Average 127 deaths per year
Forecasting winter precipitation - snow depth
- If we want to forecast snow accumulation we need to estimate how much precipitation falls in the form of snow - Usually, models only output estimates of liquid water equivalent (amount of liquid we'd get if we melted all the snow) - Have to convert liquid amount to snow depth
Wind in extratropical cyclones
- Rated on Beaufort scale - Force: 0 = speed (mph) 0-1 = calm; glassy (like mirror) - Force: 6 = speed (mph) 25-31 = strong breeze; large waves, white foam crests - Force: 12 = speed (mph) 73+ = hurricane; huge waves, thundering white spray, no visibility - Wind fields are broader, asymmetric, and weaker than with hurricanes
River flooding
- River or stream overflows its banks due to recent heavy rainfall or prolonged rainfall over a basin - Cause of flood (ex. heavy rain, snowmelt) can be located well away from areas of impact - River gradually transports excess water downstream - Occurs near body of water and lasts for about a week
Ensemble forecast
- Set of forecasts that represent several possible weather forecasts - Use multiple model forecasts to evaluate range of possible conditions - Tells us what range of possibilities are, and what may be most likely
Process of tropical cyclone formation
1. Converging surface winds pick up HEAT and MOISTURE from the ocean 2. Thunderstorms release lots of latent heat and warm the core of the developing hurricane 3. Upper level winds diverge. They move from high pressure at the top center toward low pressure at the edges 4. Upper level divergence lowers the surface pressure. When the surface pressure decreases, the storm intensifies
Ten indicators of a warming world
1. Decreasing sea ice 2. Decreasing glaciers and ice sheets 3. Decreasing snow cover 4. Increasing sea surface temperature 5. Increasing ocean heat content 6. Increasing temperature over oceans 7. Increasing water vapor 8. Increasing sea level 9. Increasing air temperature near surface (troposphere) 10. Increasing temperature over land
What do forecasters do?
- 24-7 shift job: rotate between three shifts (8am-4pm, 4pm-12am, 12am-8am) - Review observations and model data, release forecasts, and issue watches and warnings for significant weather - Communicate weather via social media, emergency management, transportation agencies - Update climatological records
Pleistocene Glaciation
- 30% of land surface was covered by ice (only 10% is covered today) - Northern US was covered by one kilometer thick ice sheet
Snowball Earth
- 600-800 million years ago; geologic data show abundant glacial deposits globally - Solar luminosity ~6% less than today; possibly large land area at low latitudes helped ice sheets to expand to low enough latitudes to start runaway albedo effect - Global freezing may have lasted for up to 100 million years - Active volcanism added CO2 to atmosphere and eventually extreme greenhouse interrupted cooling - "Cambrian Explosion" of life followed
Summary comments of climate change and variability
- 98% of today's climate scientists worldwide agree warming/CO2 increase results from human activity - World's most vulnerable populations, resources, and systems likely will suffer most damaging consequences of climate change - Mitigation (ex. reducing emissions) is necessary but not sufficient: adaptation to climate change is required
Easterly waves in the Atlantic
- African easterly waves originate over North Africa, generated by an instability in African easterly jet - Usually begin in late spring, continue until late fall
Ingredients for snow storms
- Air must be below freezing through deep layer of atmosphere, and at surface - Moisture must be present to produce clouds and precipitation - Mechanism to generate rising motion
Enhanced Fujita (EF) scale
- An EF rating (and wind speed) is associated with each damage indicator - Ratings can be adjusted up or down for particularly strong or weak versions of these structures - EF 1 = small barns, farm outbuldings - EF 2 = one- or two-family residences - EF 16 = school- junior or senior high school - EF 17 = low-rise (1-4 story) building - EF 26 = free standing pole (light, flag, luminary) - EF 28 = tree - softwood
El Nino/Southern Oscillation (ENSO)
- Change in pattern of Walker circulation over equatorial Pacific Ocean resulting from warmer or cooler sea-surface temperatures across that region, usually occurs every 3-7 years - Southern Oscillation: surface air pressure differences at Darwin and Tahiti that seesaw over time - El Nino: westerly winds; weaker trade winds; weak upwelling near Peru; warm water near Tahiti - La Nina: strong trade winds; colder eastern Pacific waters; more upwelling near Peru, stronger easterly winds near equator
Impacts of climate change
- Changing rain and snow patterns - Changes in animal migration and life cycles - Less snow and ice - Stronger storms - Higher temperatures and more heat waves - More droughts and wildfires - Thawing permafrost - Damaged corals - Rising sea level - Warmer oceans - Changes in plant life cycles
Multicell thunderstorm - multicell clusters
- Contain multiple individual cells clustered together - Can persist for many hours, but individual cells constantly form and die out as system moves - Typically associated with: fronts (ex. along a cold front) or drylines; areas of low-level wind convergence - Have a little stronger tornadoes (EF2-EF3)
Formation of Himalaya Mountain Range
- Creation of Himalaya Mountains and Tibetan Plateau began ~50 million years ago - May be what sent Earth into an "icehouse" climate - Led to increased chemical weathering and removal of CO2 from atmosphere
Sting jet impact from extratropical cyclones
- Curled around low pressure system - Core of strong winds forming in rapidly deepening low pressure systems - Produces very high surface winds - Is a narrow feature relative to the size of the storm - Sting jets are 10s of kilometers wide while extratropical cyclones are 1000s of kilometers
Drought
- Defined by its impacts: a societal phenomenon - Occurs when water resources are insufficient to meet water needs (ex. water deficit)
Forecasting tornadoes
- Doppler radar: storm structure through where precipitation is falling, and can get an idea of wind speed and direction; gives clues but can't be sure - Dual-polarization radar: identify shapes of things in air; can see debris in the air from tornado damage; can know if tornado is occurring, but not as helpful in predicting
Pollution
- Either concentrated (bad) or dispersed (good) - Two main controlling conditions: (1) wind speeds and directions (transport); (2) stability- whether air can move or becomes trapped - Capping inversion: can keep air from rising and creating thunderstorms; can keep pollution near ground in city; common at night
Most important controls on global climate
- External factors: solar radiation amount (luminosity); Earth's orbital mechanics; and meteorite, asteroid, or comet impact events - Internal factors: plate tectonic activity (leads to land distribution); ocean temperatures and currents; atmospheric composition (greenhouse gas concentration); human activities
Weather conditions for flooding - thunderstorms
- Flash flooding most often occurs when thunderstorms move slowly, or continue to form and move over same areas (known as 'training') - Thunderstorm rain rates can be very high: typically >1 inch/hr - Gainesville Reg. Airport in 2018 once had 3.7 inches in 40 minutes
Hail from thunderstorms
- Forms by collision of supercooled drops: rain drops that are still liquid even though air around them is below freezing - The stronger the updraft, the bigger the hail size - Most very large hail associated with supercell storms - Hail sizes: based on diameter, measured by ruler - Severe when greater than 1 inch ('quarter size')
Weather models
- Global Forecast System (GFS): forecast for whole world; can see fronts, hurricanes, and broad clusters of precipitation - North American Mesoscale Model (NAM): forecast for North America; can see clusters of precipitation in more detail - High Resolution Rapid Refresh (HRRR): forecast for US; can see individual thunderstorms
Main tropical cyclone threats
- Inland flooding: may drop several feet of rain in a few days; responsible for 60% of deaths - Storm surge: moves ocean water onto coast, raising water level by 15 feet or more - Winds: sustained winds over 160 mph with gusts over 200 mph recorded in most intense hurricanes; winds can extend 30-600 miles outward - Tornadoes: often occur in right-front quadrant of hurricane, embedded within rainbands
IPCC and what does it do
- Intergovernmental Panel on Climate Change (IPCC): scientific intergovernmental body under UN established in 1988; provide world with clear scientific view on current state of knowledge in climate change and potential environmental and socio-economic impacts - Does not conduct research or measure climate change, rather reviews and assesses the state-of-the-science
Lightning - sprites, jets, and elves
- Known as transient luminous events (TLEs) - Sprites: massive dim flashes, typically red; last for a few millionths of a second; occur with positively charged lightning - Jets: conical shaped, blue, can be seen by naked eye but faint; occurs during frequent/vigorous lightning - Elves: faint red halo, cannot be seen by eye; occur in ionized upper atmosphere; formed as lightning generates electromagnetic pulse
Plate tectonics
- Large-scale motions of Earth's lithosphere (outermost shell) - Includes processes of upwelling magma, lithosphere plate movements, sea-floor spreading and subduction, earthquakes, volcanoes, and deformation - 3 major influences on climate: 1. Amount and location of land areas 2. Volcanoes and outgassing adds greenhouse gases and/or aerosols into atmosphere 3. Weathering of silicate rocks removes carbon dioxide from atmosphere
Thunderstorms
- Local storm produced by a cumulonimbus cloud, with lightning and thunder - Usually produces heavy rain, strong wind speeds, and sometimes hail or tornadoes - Can form as: single-cell, multi-cell clusters, multi-cell lines, supercells - Ingredients: sufficient moisture, lift, and instability
Citizen measurements for precipitation
- Meteorological Phenomena Identification Near the Ground (mPING): public can report precipitation type in their location - CoCoRaHs: specifically surrounds rain, but also for snow and hail
Ingredients for tropical cyclones
- Moist air throughout the troposphere - Warm ocean waters (26°C, 79°F) - Pre-existing surface low pressure (storms) - Unstable atmosphere - Very little vertical wind shear - At least 300 miles from equator (5° latitude)
Flooding
- More water coming in than leaving a region - Usually caused by heavy or prolonged rain, and/or rapid snowmelt - Severity is controlled by characteristics of surface or watershed: basin size, topography, drainage, vegetation or surface type, soil type and thickness, geology
Weather conditions for flooding - tropical cyclones
- Most tropical cyclones are huge rainmakers - Slower-moving the storm, the greater the potential for inland flooding (typically river and flash) - At coast, flooding is often result of storm surge
Making fossil fuels
- Mostly occurred during Carboniferous Period (355-300 mya): 55 million year process - Some contribution during Pre-cambrian era (mostly ocean algae), which is 3 billion year process - Burning fossil fuels began in 1760, which has been a 259 year process - Started with steam engine powered by wood to make textiles. Britain had coal on shore, but most was underground. People liked not traveling by horse and sail
North Atlantic Oscillation
- NAO: anomalous sea-level pressure difference between Icelandic Low and Azores High; atmospheric phenomenon - Positive NAO: large pressure gradient force leads to increased westerlies across North Atlantic; intensifies North Atlantic Current and advects warm and moist air from over ocean across much of northern Europe - Negative NAO: small pressure gradient force; weakens North Atlantic Current; weakened jet stream and increased frequency of Arctic outbreaks across northern Europe and northeast US
Naming of tropical cyclones
- Naming system designed to keep track and differentiate between multiple storms occurring at same time across a region - World Meteorological Organization (WMO) is responsible for generating name lists over each ocean - Names are alphabetical and rotated from year to year: storms with large impacts are permanently retired - Until 1979, all Atlantic hurricanes were 'female'
Weather conditions for flooding - atmospheric rivers
- Narrow flowing columns of atmospheric water vapor responsible for producing significant amounts of rain or snow - Typically associated with mid-latitude cyclones
Milankovitch Theory
- Obliquity: angle of Earth's tilt changes between 22 and 25 degrees (~41,000 years); changes in seasonal distribution of radiation at high latitudes - Precession (of equinoxes): the wobble, or variation of the spin of the Earth around it's axis; change in timing of perihelion (~22,000 years); changes difference between seasons across hemispheres - Orbital eccentricity: shape of Earth's orbit (ex. roundness) varies (~100,000 and ~400,000 years); affects total amount of radiation and difference in energy received at aphelion and perihelion
Flash flooding
- Occurs very quickly (generally < 6 hours in single day) after a period of intense rainfall, dam/levee break, or mudslide - Tends to occur in regions where ground is less permeable and where surface runoff dominates - Roads designed to act as urban rivers during large floods - Ex. urban areas, regions of hard bedrock, steep-sloped areas
Tornado outbreaks
- Outbreaks are events with 6 or more tornadoes - Activity occurs within a several hour period - Typically occur over a wide area, but should be meteorologically related to each other
Ingredients of a tornado
- Presence of wind shear through lower-mid troposphere (speed and direction) - An unstable atmosphere - A reason for surface air to rise: front, low-level convergence, etc. - Low-level moisture: but dry in middle and upper levels of troposphere
Air pollution types and sources
- Primary: emitted directly into atmosphere - Secondary: result from chemical reaction with some other element in atmosphere (natural or manmade) - Principal pollutants: particulates - PM 10, PM 2.5; aerosols; carbon monoxide; sulfur dioxide (sulfuric acid); VOCs (hydrocarbons); nitrogen dioxide, nitric oxide (nitric acid, NOx) - PM-10 or less have less distinct health impacts: PM-2.5 or less are worse for health with special regulations for limitations
'Cone' in tropical cyclones
- Probably forecast track of center of the storm up to 5 days out from its current position - About two-thirds of the time, the center of the storm will remain in the cone - Doesn't tell: size of storm, impacts both within cone and outside cone; impacts often occur well outside cone
National Weather Service
- Provide weather, hydrologic, and climate info and forecasts and warnings for US - Protection of life and property and enhancement of national economy - Form national info base and infrastructure - May be used by other agencies, private sector, public, global community
Weather radar
- Radar gathers info on precipitation by sending out pulses of energy and measuring characteristics of return energy - Single radar: determine where most rain fell across large area - Reflectivity: amount of power returned to radar dish - Velocity: shift in wavelength - Dual-polarization radar: sends out energy in both horizontal and vertical orientations; tells us about the shape of precipitation; use to measure type of precipitation across large area
Gust front
- Rain-cooled air surges in front of storm creating gust front - Caused by thunderstorm instead of big air mass - Front causes new cells to rise - Turns single cells into multicell thunderstorms
National Climate Assessment
- Similar (but not replace) IPCC process, but US only - Required by Global Change Research Act of 1990 - Discusses observed changes, current status of climate in US, impacts of climate change, and projected future trends - Latest (fourth) assessment released on November 23, 2018
Weather conditions for flooding - rapid snowmelt
- Spring snowmelt is normal course of events in areas with snowpack: this feeds rivers and springs - Conditions can promote rapid snowmelt leading to downstream river flooding - Can occur when: snowmelt is initially delayed until later in spring when warmer air is more abundant; heavy rainfall is co-timed with snowmelt
Tornado formation
- Start with supercells, mT air gets lifted over gust front - Air going 2 different directions creates horizontal spin along forward flank gust front (creates rotation) - Spin gets brought toward and around north of the updraft's low pressure center by the PGF - With enhanced updraft speed, air at ground is brought toward the low: this converging wind tightens and speeds up rotation - Increase in rotation at ground eventually reaches tornadic speeds and pressure drops until water condenses
Weather conditions for flooding - stalled-out fronts
- Stationary front in atmosphere w/ abundant moisture available - Precipitation will develop and persist over given area: it can be mixture of moderate/heavy stratiform rain and thunderstorms - Can result in flash flooding and river flooding
Seasonal and climate forecasting
- Statistical models: built using known relationships between climate variability and local weather conditions - Dynamic models: simulate full behavior of Earth's atmosphere and climate system
Tornado forecasts (SPC)
- Storm Prediction Center (SPC) produces probabilistic outlooks for tornadoes - Not just tornadoes, also wind and hail - Yellow area is the SPC forecasting there is a 10% chance a tornado will occur within 25 miles of any point in that area - Black hatching is 10% chance an EF2 or higher tornado will occur within 25 miles of any point in that area
Anatomy of tropical cyclone
- Surface air pressure decreases toward center of storm - Wind speed increases to a maximum in eyewall and goes to zero in the eye - Light and moderate rain and showers in rain-bands - Rain increase in intensity toward eyewall, where the heaviest rain tends to occur - Eye is free of rain
Extratropical cyclone: The "Bomb"
- Term for extratropical cyclone that has a pressure change of -24 mb or more in 24 hours - Results in very strong winds - System undergoes rapid intensification - Mostly occurs during cool season months (fall-spring)
Measuring precipitation
- Tipping bucket: 8 in diameter collecting surface, funneling into narrow tube; calibrated stick can be inserted to obtain rain amounts; as water collects, it is stored in one of two pivoting buckets - Rain gauges: 'on the ground' measurements; only provide a precipitation estimate for one single location - Snow depth is reported by human observer using ruler
Tornado watch vs. tornado warning
- Tornado watch: be aware of conditions over next few hours; forecasters seeing ingredients for supercells and tornadoes are assembling - Tornado warning: issued by local NWS office; means to take action as tornadoes are indicated or have been spotted; typical warning lasts 30 mins
Walker circulation
- Tropical South America, tropical Africa, and Australia/Oceania warmer than equatorial oceans during December-February (DJF) (lower albedo, lower specific heat) - Low pressure and rising motion over warmer land masses results in east-west circulations in DJF - Over equatorial Pacific: Easterly trade winds push water toward western Pacific; sea level is higher in Philippines than off west coast of Panama - Westward flowing water stays near surface and warms; warmest ocean waters on Earth in western Pacific (normally 8-10°C warner than eastern tropical Pacific)
Tropical cyclones
- Tropical cyclone: large low pressure system that originates over tropical oceans; no fronts, temperature gradients, extratropical lows, polar air masses; includes tropical depressions, tropical storms, and hurricanes - Tropical depression: tropical cyclone with winds between 23 and 38 mph (20-33 knots) - Tropical storm: tropical cyclone with winds between 39 and 73 mph (34-63 knots) - Hurricane: tropical cyclone with winds exceeding 74 mph (64 knots); typhoon in western Pacific, cyclone in Indian Ocean or South Pacific
Hurricane risk
- Tropical cyclones account for bulk of natural catastrophe US insurance losses - Losses vary roughly as cube of maximum wind speed - Ex. Katrina caused >1300 deaths and >130+ billion in damage - Hurricane Katrina (2005) - $161.3 billion - Hurricane Harvey (2017) - $125 billion - Hurricane Maria (2017) - $90 billion - Hurricane Sandy (2012) - $70.9 billion
Coastal flooding impact from extratropical cyclones
- Two mechanisms: A - low pressure increases sea level below it. B- higher water level transported toward shore, in addition to the wind-driven piling of water - Low pressure at center of ETC -> sucking up of sea level - High winds pile up sea water against coast (wind from high to low)
Weather vs. climate
- Weather: state of atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness; short-term - Climate: statistical collection of weather conditions at a place over a period of years; long-term - Climate is what you expect. Weather is what you get - Climate trend: based on changes in underlying average climate; anthropogenic climate change is cause of trend - Climate variability: shorter-term variations that occur due to natural processes; some can last years and amplify or reduce longer term trend over that period
Coastal flooding
- When coast is flooded by sea - Occurs once/twice a month - Rising and falling slowly but lasts for less than 3 hours - Two main reasons: (1) storm surge associated w/ storms and hurricanes; (2) sea level rise and/or subsidence of land - Ex. 'King' Tide street flooding in Miami, FL
Extratropical cyclone impacts
- Wind: pressure gradients, sting jets - Coastal flooding - Rain: measuring rain - rain gauges, radar - Winter - Thunderstorms: tornadoes - Floods
Regions unfavorable for tropical cyclone formation
- Within 5° latitude from equator: Coriolis force is near zero, so there is minimal rotation - Mid-latitudes: wind shear is too strong (jet streams) and often water is too cold - South Atlantic: few tropical disturbances are generated (minimal surface convergence), wind shear is too strong, and there are cold currents on west coast of Africa - Western coast of South America: ocean waters too cold (from Humboldt Current)
Pangaea Supercontinent
- ~300-250 million years ago, continents collided and formed supercontinent of Pangaea, much of it at high latitudes - Lots of mountain building, causing more chemical weathering that removed CO2 from atmosphere and extensive cooling
Storm Prediction Center - Outlook Products
1. Marginal (MRGL): isolated severe thunderstorms possible; limited in duration and/or coverage and/or intensity 2. Slight (SLGT): scattered severe storms possible; short-lived and/or not widespread, isolated intense storms possible 3. Enhanced (ENH): numerous severe storms possible; more persistent and/or widespread, a few intense 4. Moderate (MDT): widespread severe storms likely; long-lived, widespread and intense 5. High (HIGH): widespread severe storms expected; long-lived, very widespread and particularly intense
Drought types
1. Meteorological: when precipitation is below normal, often for an extended period of time; ex. place in Northern Europe w/ less precipitation, but grass is still green 2. Agricultural: soil and/or groundwater deficits that affect vegetation; typically when precipitation has been low for a month or more 3. Hydrological: insufficient water levels in rivers and watersheds; precipitation has been low for long time and agricultural drought is ongoing; ex. Cape Town, South Africa 4. Ecological: most extreme; prolonged and widespread deficit in naturally available water supply; creates multiple stresses across ecosystems
Ingredients of extratropical cyclones
1. Temperature gradient: stronger the polar and tropical air masses, stronger the extratropical cyclone between them 2. Moisture: high amounts of moisture flow into developing system make air unstable and buoyant