ATOC10001
hydrologic cycle
the movement of water through the biosphere
environmental lapse rate
the rate of temperature decrease with increasing height in the troposphere - unstable: air temp decreases with height pressure decreases, speed of molecule decrease; when aire expands it cools
Tides
the regular rise and fall of the ocean's surface influenced by the moon's gravity pulling on earth - are waves
Mature stage
the second phase of a thunderstorm, where downdrafts move from the base of a cumulonimbus cloud and produce heavy precipitation. Tornadoes touch down during this phase of the storm. - Eventually clouds deepen to reach a level where rising parcels are neutrally buoyant (LNB) and an anvil is formed - As rain is generated in cloud, may fall down through the convective updraft. As the cloud entrains some dry air from outside the cloud, some of the precipitation may evaporate, causing evaporative cooling, negative buoyancy, and generation of downdraft - When the downdrafts reach the surface, the near-surface air is cooled (stabilising the atmosphere) - Gust fronts are generated at the leading edge of the cold air as they hit the ground and spread out
agricultural drought
usually occurs when precipitation cannot supply enough moisture to the ground to support an area's crops
Psychrometer
An instrument used to measure humidity - One measurement gives temperature of air, other gives moisture; as it evaporates, goes down and shows dew point
South vs North pole regions
Antartica: elevated continent centred on pole, surrounded by open oceans Arctic: centred on pole, surrounded by flat continents
Paris Climate Agreement
An agreement within the United Nations Framework Convention on Climate Change dealing with greenhouse gas emissions mitigation, adaptation and finance starting in the year 2020. - December 2015 was signed with the aim of 'Holding the increase in the global average temperature to well below 2 degrees C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 degrees C above pre-industrial levels'
Ordinary Single Cell Thunderstorm
One updraft, one downdraft
Pressure equation
P=dRT; R= 287J/kg/K
radiation, advection, upslope
Radiation: produced by earth's radiational cooling (at night as the air above the ground cools and stabilises) Advection: warm, moist air moves over a sufficiently colder surface; the moist air may cool to its saturation point Upslope: forms as moist air flows up along an elevated plain, hill or mountain
December solstice
Winter in the Northern Hemisphere - axial tilt around 23 degrees - June solstice: summer in NH
Peru Current
a cold ocean current off the coast of western south america. - coast of Peru is cold because of current - Coast of Peru is dry - Because cold surface of ocean means no rising hot air and so no condensation - Lima, Peru - On coast, close to equator - Relatively cool, almost rainless climate
Ice-albedo feedback
a feedback mechanism that accelerates melting of sea ice and amplify warming
Stevenson screen
a type of shelter which contains meteorological instruments and keeps them from getting damaged by weather - contains thermometers, barometers and other instruments
Mammatus
form at base of cumulonimbus clouds; associated with severe thunderstorms, form by cool air sinking down
Ozone Hole
- Caused by chemical reactions between ozone and chlorine or bromine introduced by CFCs and halons - Chlorine and bromine radicals are catalysts; they speed up reactions causing ozone destruction - Reaction only proceeds in presence of ice clouds, low temp and sunlight; forms in spring in Antarctica
Collapse of Larsen B ice shelf
- 2002 (Feb. - March); 3,250 square km disintegrated - Shelf at edge was 220m thick - Occurred in only 1 month
A68
- 5,800 square kms - Around 330m thick - Weighs a trillion tonnes - Among the few largest icebergs ever recorded - Only about half the size of the largest ever iceberg, which broke away from the Ross Ice Shelf in 2000 - Represented about 10% of Larsen C shelf
Ice
- A high latent heat of fusion, the energy required to melt ice - Less dense than water - Because fixed crystal structure of ice takes up more space than liquid structure of water - Highest density occurs at 4˙C - Water is an excellent solvent Things dissolve very easily
Farmers and weather
- Accurate rapid warnings for extreme weather - Short-term forecasts for frosty nights - Accurate heatwave forecasts to protect livestock and crops - Useful seasonal outlooks for decisions on which crops to plant
Barometer
- Aneroid barometer - Constant pressure inside cell; expands or contracts depending on outside pressure, then moves dial - measures air pressure - Tells you whether you have stormy conditions, nice, etc
Urban temperature
- Anthropogenic heat release - Heat derived from industry and domestic vehicles and air conditioning exhaust radiates from cities - Materials: heat retaining and emitting properties means absorb much of incident radiation; released as heat - Lack of vegetation, less light intercepted, less evapotranspiration, thus less vapour released - Urban street canyons trapping heat energy
Nocturnal boundary and residual layer
- Approx 1/2 hour before sunset, thermals shut down due to thermal surface cooling - Residual found above stable boundary - Nocturnal boundary layer below (0-200m)
Arctic vs Antarctic sea ice extent
- Arctic declining - Antarctic was increasing but sharp decline after 2014
Sky view factor
- Atmosphere is heated from ground by long-wave terrestrial radiation, and the amount of radiation that is lost from the ground is proportional to amount of sky that is visible - Sky is cooler than the ground so more sky that is visible the more long-wave radiation is lost, the cooler the vicinity - Main causes of the urban heat island phenomena due to lower SVF in built up areas than the vastly treeless agricultural countryside
Atmospheric circulation
- Atmospheric circulation is the combined effect of the pressure gradients and the Coriolis effect (plus friction if close to surface) - Never get Highs and Lows to disappear If earth stopped moving, highs would move to low pressure system
Sleet
- Aus; mix of rain and snow that occurs when melting level is near the surface - North America; means ice particles that have refrozen near the surface having melted higher up
AUS BoM ACCESS produces
- Aviation forecasts for airports and flight routes -Forecasts for emergency services in preparation for extreme events -Frost potential forecasts - Streamflow forecasts -UV forecasts
Strong subsidence inversion
- Base of stable inversion acts as cap or lid on pollutants below by preventing them from escaping into the warmer air above. If the inversion lowers, the mixing depth decreases, and the pollutants are concentrated within a smaller volume
Modern Weather forecasting
- Based on NWP ideas - Conducted by multiple agencies around world; BoM (Australia) - Utilises some of most powerful computers in the world - Observations from weather stations, balloons, radar and satellite data used to help set up initial conditions for weather forecast simulation - Initial conditions partially set by previous simulation - Blending of previous weather simulation and new observations to set up next forecast = data assimilation
Phenomena we see due to scattering of light
- Blue haze caused by vegetation releasing particles which interact with ozone - These particles are very small and selectively scatter more shorter wavelength light at the blue end of the visible spectrum - Crepuscular rays; caused by the scattering of light in broken clouds
Low pressure
- By definition, a region of lower pressure than normal at the surface must be a region of typically rising air - Since rising air would decrease the surface pressure, while falling air would raise it - Think of air parcels - Rising air cools - Since atmosphere pressure is greatest close to the surface (due to gravity), the atmospheric pressure decreases as the 'parcel' of air rises - Thus, the 'parcel' expands. Expansion requires work, and so energy for this work needs to be found from somewhere. It is taken from the average speed of motion of the molecules in the parcel, which then decreases - Since the temp of a gas is just a measure of its typical molecular speed, the temperature decreases
Generating wind
- Can trigger rain and even thunderstorms - If surrounded by flat land, there can be an urban cool island due to shadows from buildings
Rainbows
- Caused by total internal reflection of light in raindrops - Light at different ends of visible portion of the electromagnetic spectrum is refracted to different angles - This causes the white sunlight to separate into its constituent colours and reflect at different points within the raindrop - Needs to be enough sunlight and it needs to enter the atmosphere at an angle that allows total internal reflection to separate the colours within the visible spectrum - Second rainbow forms due to additional reflection within the raindrops, causes the secondary rainbow to be shifted from primary rainbow and weaker
Differences in climate model
- Centres around the world, including BoM and CSIRO in Australia, produce climate models and whilst they are governed by the same equations, have some differences; - Varying sizes and heights of grid boxes (model resolution) -Different treatment of aerosols -Different ways of managing processes that occur on small scales - Results in models having different amounts of warming given the same external influences
Greenhouse gases
- Co2 not only greenhouse gas; methane, CFCs and water vapour - Their importance to overall greenhouse effect depends both on their ability to absorb energy and the exact wavelengths they absorb that energy at - Methane is released in agriculture - CFCs (chlorofluorocarbons) are banned and were used in cooling systems - fewer people in southern hemisphere, carbon dioxide emissions are lower
Impact of coastal storms
- Coastal storms cause much damage - Strong winds, storm surges, flooding, erosion - Local impact of coastal storms is magnified by three main factors: 1. On-shore winds push water toward the coast increasing ocean height 2. This effect can increase sea level by 0.5m 3. Massive waves cause by strong winds are superimposed by tides
Thunderstorm
- Convection storm - Cumulonimbus cloud - Trigger mechanisms: ○ Fronts ○ Low-level convergence ○ Low-level warm air advection ○ Low-level moisture advection ○ Outflow and sea-breeze boundaries ○ Orographic upslope ○ Frictional convergence ○ Vorticity ○ Jet streak
ECLs in Australia
- Damaging weather systems affecting coastal NSW and SE QLD -Third of AUS population - Significant monetary costs, human costs - A major risk for shipping; strong winds, turbulent seas - Coastal erosion from ECLs adds risk for planners - Intense rainfall adds to water storage levels - Nearly a quarter of rainfall along NSW coast is ECLS - 80% extreme rain events = ECLS
Precipitation
- Defined as any form of liquid that falls from a cloud and reaches the ground - Water vapour condenses onto CCN and eventually they fall once they become too heavy to be held in the cloud - Rain drops form through collision and coalescence of water vapour onto CCN - Clouds contain both water vapour and ice crystals even when they're below freezing - Water vapour in a liquid state but below freezing exists in the cloud due to a lack of CCN to freeze onto - Water vapour is said to be supercooled when in this state
Tropical cyclone effects
- Destructive winds - Heavy rainfall with flooding - Damaging storm surges - Tide/ water level higher; less pressure - A lot of waves caused by wind
Surface layer
- Direct contact with surface - Lowest few cm is the interfacial layer where molecular transport more effective - Above this, turbulent transport is dominant - Lapse rate is normally super-adiabatic
Afternoon and night pollution
- During arvo, when atmosphere most unstable, pollutants rise, mix and disperse downwind - At night when radiation inversion exists, pollutants from shorter stacks are trapped within the inversion, while pollutants from the taller stack, above the inversion, are able to rise and disperse downwind
Temperatures in Antarctic
- During the summer in Antarctic surface temperatures tend to follow the solar input, with the warmest temperatures in January - The temperature is then the net result of the balance of energy inputs and outputs, namely - Solar radiation + poleward transport of atmospheric energy = emitted infrared radiation - Both highs and lows transport: - Warm air towards the pole - Cool air towards the tropics - That is, a net transport of atmospheric energy - During the winter solar radiation = 0 - Over those places the balance of energy inputs and outputs is then: - Poleward transport of atmospheric energy = emitted infrared radiation
Seasons
- Earth's surface in the SH more perpendicular to Sun's rays in Dec than the NH - Thus, more solar energy per square metre - Seasons are not related to variation in distance of earth from the sun - This effect is not zero but it is small compared with the effect of the axis tilt - Max energy in December solstice - Melbourne 38 degrees south - Tropic of Capricorn goes through north of Australia - Antarctic circle defined as latitude on December solstice 24 hours of daylight
Urban/ rural energy budget
- Energy budget of urban areas differs from rural, mainly due to the lack of moisture retention in artificial surfaces
Extra heating in regions close to equator
- Extra heating in regions close to the equator must be brought into balance - On a planet, this extra heat would just go into causing a very high surface temp near equator - On earth, part of the excess heat is transported poleward by winds and ocean currents until a new heat balance is achieved - By itself, the new heat balance would lead to this pattern of rising motion due to hot air near equator, and falling motion at the poles - This is what happens on slowly rotating planets like Venus - But this ignores the effect of rotation
Difficulties defining droughts
- Extreme variations in the climate - Not a distinct event: not well-defined or end - Creeping phenomenon - Complex interaction of many processes
Why do ECLs occur?
- Form several reasons - Summer: can form ex-tropical cyclones, while decaying and moving south - Other reasons: - Often form rapidly offshore - Can form inside an existing low pressure trough - Temperature gradient due to cold air in the upper atmosphere and air warmed by East Australian Current - Rising air intensifies the low pressure - The rising moist air cools, condenses leading to rain - Can develop in wake of cold front passing over Victoria into Tasman Sea
Synoptic chart
- Giving an account of events from the same point of view or at the same time - Must be collected at the same 'absolute' times, not local - Standard reference for global time is the mean solar time at 0˙ longitude - Tine is Universal Coordinated Time (UTC) AEST = UTC plus 10 hours
Multicell storms
- Group or cluster of ordinary cells at different stages in their life cycles - Most convection ends up organised as multi-cells - Individual cells last 15-30 minutes, but the entire system can last many hours
Warm currents
- Gulf stream - Kuroshio - East Australian current
Importance of currents for climate
- Gulf stream: January temperatures in northern part of North Atlantic much Owarmer than they would be otherwise - crucial for mild winter climate of Norway, Ireland - Peru current: west coast of South America near equator much colder than should be at that latitude
3 heat system
- Heat balance plus Coriolis gives three 'cells' per hemisphere, instead of one in the case of no rotation - The three cells cause alternating latitudes of upward air movement (thus lower surface pressure) and downward air movement (thus higher surface pressure) - Ferrel cell - Polar cell - Hadley cell
Transport and weather
- Heat extremes can cause chaos on train network - Temps above 42 degrees C, Melbourne trains are limited to 70km/hr - Expansion of metal; deform, buckle - Risk of derailment - If heatwaves are well forecasted, preparations can be made -Revise schedule - Give notice much earlier in advance
homosphere heterosphere
- Homo: gases are will mixed due to turbulence in the atmosphere - Hetero: gases are quite different
Diagram of atmosphere
- Homosphere located from Stratosphere down - Hetero and Iono located Stratosphere and above
Factors that affect air pollution
- Ingredients - Many sources of pollution - Stationary deep high-pressure area - Pollution sits there - Light surface winds - Subsidence inversion - Shallow mixing layer - Valley - Clear night - Smog - If chimney emits puff of smoke every second, then low wind speed, smoke puffs are closer together and more concentrated - Windy = more turbulent = more mixing = more spread into atmosphere
Cause of Larsen B ice shelf collapse
- Intense storm in South Atlantic at the time - Temperatures had been rapidly warming in the Antarctic Peninsula region - Over a few years summer temps over Larsen B had started to exceed 0 degrees C - Induces surface melting, and water percolated into the crevasses - Even if conditions were not right for break up a specific year, the shelf had been weakened - End of summer the melted water, snow, etc. refreezes and cracks - The refrozen ice has different structural properties from the rest of the shelf - Makes unit more vulnerable to failure in next summer - South Atlantic storm may have provided the trigger - Dramatic disintegration was very rapid
Thermosphere
- Ionisation because electrons are excited by solar radiation and there is a greater absorption at higher level; Aurora - fewer particles - above 100km no effective mixing
Key ingredients for ozone depletion
- Key ingredients for ozone depletion - Cold, descending air; vortex 'cutting off; air from horizontal mixing - Polar stratospheric clouds - Chlorine and bromine (CFCs and Halons) - Sunlight to energise reactions leading to ozone depletion and cause chemical release from the clouds once the vortex has been established
Severe thunderstorm
- Large hail >2cm in diameter - Damaging wind gusts >90km/hr - Heavy rainfall conducive to flash flooding - Lightning is a hazard of thunderstorms but not definition of severe
Increase in computing power
- Larger ensembles - Weather forecasts provided for longer lead-times; currently 7 days - More skilful forecasts in general and for extreme events specifically
Troposphere
- Layer where most action occurs - 80% of mass of the atmosphere and almost all water vapour is in this layer
Diffracted light
- Light diffracted - Appears as rings around the sun or moon - Light passes through near uniforms sized particles
Mixing layer
- Located above surface - Uniform mixing of heat, moisture and momentum - Grows approximately half an hour after sunrise - Entrainment of warmer, drier air from above into the mixed layer
GPS radio occultation
- Magnitude of refraction depends on density gradient, depending on temperature, pressure and humidity - Refraction measured as low-earth orbit satellite passes into or out of view from GPS satellite - Provides important weather: - Stable, all-weather operation - 40km to the surface
SH line always lower in forecast skill
- Major forecasting agencies, best forecasting agencies are in - Europe, north America and Japan Where efforts are being focused
Salinity
- Measured in parts per thousand - Ocean well-mixed but salinity not uniform; some oceans more saline than others - Salinity low near land because of fresh water run off from rivers and melting glaciers - Low near polar regions because of low evaporation, precipitation, snow and ice melt - Low near equator because of (almost) daily showers in many equatorial regions - Freezing increases salinity of water - Salt is rejected from ice and goes into water and then, creates dense salty water - Rainfall reduces salinity - Evaporation increases salinity
Ingredients for a thunderstorm
- Moisture - Instability; air needs to be less dense than its surroundings to rise to high elevations - lift - thunderstorms most common near equator; tropical regions
Decay
- Moving over land - Loses main source of moisture and heat - Moves into a region of cool sea temps - Moves into region of high vertical wind shear - Many TCs experience extratropical transition - Systems among the strongest extratropical cyclones
Hadley cell
- Name for the overturning circulation nearest the Intertropical Convergence Zone (ITCZ) - Around the latitude of maximum incoming solar radiation, the strongest surface heating leads to rising air - Balanced by sinking air at higher latitudes - Hadley cell is mixing air - a large-scale atmospheric convection cell in which air rises at the equator and sinks at medium latitudes, typically about 30° north or south.
Mirages
- Occur due to light refraction that appears to displace objects - Mirages can be inferior (appearing to shift an object downwards) - Or superior (higher than they are) - Can occur when we have a temp inversion i.e. the temperature is colder nearer the surface and there is a change in density for refraction to occur
Sudden Stratospheric Warmings
- Occurs in Northern Hemisphere on average once every two winters and can trigger severe cold weather - 'Beast from East' = extreme winter in Europe - Normally in the stratosphere there are strong westerly wind, rapid warming events in the stratosphere called SSWs, are associated with these winds turning easterly
Land and sea breeze
- Occurs in boundary layer - Driven by temp contrast between land and sea - Only present when not too windy - Can slow down or increase synoptic wind - Most common in summer when land/ sea contrast greatest
Reasons for ocean controlling temperature
- Oceans have high specific heat - Light penetrates oceans (doesn't just get absorbed at surface) - The upper ocean undergoes mixing so heat is not trapped at surface (unlike ocean) - Evaporation uses up energy that would otherwise go into heating ocean - At equator variation not very big - High lateral, inland has biggest temp difference
heat island and pollution
- On clear, calm night, weak country breeze carries pollutants from outskirts of city, where they concentrate and rise due to city's urban heat island. - Effect may produce pollution dome from suburbs to centre of town
Waves
- Oscillations that form along the interface between fluids of different characteristics - Mass movement is vertical only - Also wind-driven ocean waves - Waves do not transport mass horizontally - Mass transport is vertical - Crest of a wave; 'the propagation' rather than movement - ocean wave types: wind-driven, tsunamis, tide waves
Dry air on plane
- Outside temperature about -60 degrees - low temperature means easy to condense moisture out - therefore not much moisture in the cold air outside the plane - when warmed to room temperature inside plane, the air has very little moisture so very low humidity
Oceans
- Over 70% of earth's surface is covered by oceans - Large effect on climate - Source of moisture and precipitation - Ocean currents transport warm or cold water and alter climate - the wind drives the ocean currents - Currents can travel from equator poleward (warm currents) or from the poles towards the equator (cold currents)
Cold currents
- Peru current - Benguela current - California current
Health and weather
- Prepared for extreme events like heatwaves, thunderstorm asthma - might cause spikes in hospital admissions - Hot and cold temps increase mortality
Climate prediction
- Produce estimates of how global and regional climate will change over next few years, decades, centuries - Use same basic principle but serve different purpose - NWP concerned with chaos which causes skill to decline -Not an issue for climate prediction because don't care about particular weather, want seasonal, annual averages
Heatwaves
- Prolonged period of excessive heat - Extremes defined by fixed threshold - T>35 degrees - Dependent on location
Why is the sky blue?
- Rayleigh scattering describes how the scattering of light by particles is a function of wavelength - At shorter wavelengths scattering is more effective, so that's why if you look up at the sky and away from the sun you see blue light - Humans are less sensitive to violet
Atmospheric halos
- Rings of light that appear around the sun and occur due to the refraction of light by ice crystals - 22 degrees
Supercell
- Rotating updraft - Can last several hours
Shallow waves
- Shallower than 1.20 of a wavelength - C = 3.13(d)^1/2 - D = depth of water - Bigger waves feel ocean floor more and are slowed down until all waves travel at same speed - Tides are shallow waves - Water depends on the ocean depth - Tide wavelength is about 20,000km (half the Earth's circumference) - Because there are two tidal bulges - Tides will be shallow water waves if ocean depth is less than 1,000km
Direct/ indirect effect of aerosols
- Short-wave insolation is absorbed by urban air pollution, lowering amount received at surface, reduces the urban heat island intensity during the day - During the night, air pollution particles such release long-wave heat radiation into the air, warming the urban temperature, which increases the rural to urban differences - Direct effect and indirect effect: suppression of rain out can invigorate convection by more freezing = more latent heat release
Dissolved salts and sources
- Sodium chloride, breaks up into ions - dissolved salt tends to reduce 'stickiness' of water molecules, thereby lowering the freezing point - Earth's crust - Outgassing from mantle - Most salts enter ocean from rivers and streams and leave ocean through deposits of sediments; the rest comes from ocean floor vents
Stratosphere
- Stable - 20% of atmosphere's mass - Much drier than troposphere but some water vapour - As temp rises with height this layer is very stable; relatively little vertical motion Temp increase with height is due to ozone absorbing shortwave solar radiation
Entrainment layer
- Stable layer above mixed layer - Acts as lid (cap) to rising thermals - Often an inversion layer - Entrainment of warmer, drier air from above into the mixed layer
Rotation in supercell
- Strong horizontal rotation due to vertical wind shear can be tilted into the vertical updraft - Rotating updraft with supercell thunderstorms is often the formation location for wall clouds and tornadoes
Western Australia
- Supposed to be a cold current there, like on eastern side of the other ocean basins - But climate of Perth is not a desert at all, although summers are dry - Perth gets more rain than Melbourne - There is a cold current, but it is far offshore - There is a warm current, the Leeuwin current - The Leeuwin current is caused by sea level difference between the pacific (which is higher due to winds pushing the water west) and the Indian ocean (which has lower sea level) - Warm water changes the climate of Perth: more rainfall - If no Leeuwin current, would not be a nice place to live
Inverse barometer effect
- Surface pressure (force per unit area) = weight of air above a point - For a pressure of 1000hPa, weight of air is same as that of 10m of water - Pressure at depth 100m = 11 atmospheres - A 1hPa increase in pressure = pressure exerted by 1cm of water
Urban surface
- Surfaces artificial - Warmer than naturally surfaced green space
Ferrel and Hadley
- The region of descending air where the Ferrel and Hadley cells meet is associated with predominant high pressure systems at the surface
Urban heat island
- Trees in built up area act as temp control - Reduce 'heat sink' created by building materials adsorption of sunlight, by providing shade - Average 2 degrees lower
Why need meteorologists?
- Understand biases and deficiencies - Can intervene to change forecast - Add value to the forecast - E.g. a model might be known to have a sea breeze comes into Melbourne too early under some synoptic patterns -Delay timing of sea breeze in official forecast
Supercell characteristics
- Updrafts often so strong, region below the mesocyclone is rain-free. Rain is not heavy enough to fall through updraft - Produce heavy rain, large hail, high surface winds and majority of tornadoes - Prevalent in Great Plains in spring - Large amount wind sheer, moist warm flow at surface - updraft = rotation
Urban canyon
- Urban canyons are building walls and the elements in between - Width to height ration controls amount of insolation received within canyon - Orientation makes big different Energy exchanges at different aspects, varies considerably with space and time, depending on where the sun could reach during the day
Norwegian Cyclone Model
- Used observations around Norway to propose a theory for how a cyclone progresses through its lifetime and how and where the winds move within the weather system
Climate change and affecting extreme weather
- Using climate model simulations we can estimate the role of climate change in specific extreme weather events - Done by comparing model simulations of the world including human and natural influences with simulations where the human influences are removed - We can construct statistical distributions of our weather interest e.g. Melbourne summer temperatures, in our two groups of model simulations - Can then estimate how much climate change has altered the probability of an extreme event - Field called event attribution and it allows scientists to make quantitative statements about the role of human-caused climate change in extreme weather events
Valleys and pollution
- Valleys prone to pollution are completely encased by mountains and hills - Air pollution concentrations in mountain valleys tend to be greatest in cold months - Pollution problem in several large cities is, at least, partly due to topography - At night, cold air and pollutants drain downhill and settle in low-lying valleys
Park cool island
- Vegetated urban parks are likely to be cooler than their surrounding built environment - Due to sinking air from above park, and the effect of being away from the conductive and radiating surfaces of buildings plus cooling by evaporation
Tornado
- Violently rotating column of air touching the ground usually attached to base of thunderstorm - few seconds - over an hour - multiple vortices - often produced by supercells - enhanced Fujita scale = damaged based - winds can exceed 322km/h - most frequent late spring/ early summer - strong vertical wind shear - warm, most air from Gulf of Mexico near surface - cooler drier continental air aloft
Greenhouse effect
- Warm our planet - Without the natural greenhouse effect on earth; its average surface temperature would be -17 instead of 15 - Radiation from sun is shortwave whereas earth emits a longwave - Due to lower temp of earth compared to sun - Energy emitted by a body is higher if the body is hotter (Boltzmann) and amount of energy emitted is inversely proportional to wavelength (Planck) - Key part of earth's energy balance - Human-induced climate change is creating an imbalance
El Nino
- Warm water in eastern pacific - Colder water in western pacific - Usually associated with more rain east, less west - in neutral phase (average conditions) we have easterly trade winds in the pacific - Leads to upwelling and cooler temps in east pacific - Warmer surface waters are pushed to the west - There is an associated circulation called the Walker Circulation - During El Nino the trade winds weaken moving the ocean heat and disrupting the Walker Circulation - During La Nina, there is a strengthening of the neutral phase - Can cause problems because brings certain climates to regions that don't have that - Disrupts weather patterns, cost a lot - El Nino = lower rainfall, droughts, bushfires
Why doesn't the land just cool off or warm up the adjacent ocean, making the ocean irrelevant to local land climate?
- Water molecule highly polar, negative charges on one side and positive on the other - Makes it easier for water molecules to attract each other - The fact that water molecules attract each other easily makes it hard to sperate water molecules and make then move (by heating them) - Gives water very strong ability to absorb heat without moving around and thereby displaying higher temperature - Means oceans are slow to heat up and slow to cool off, compared with either land or air - Reduces daily and seasonal variations of temperature in ocean regions, sometimes by a large amount
Mesophere
- Where meteors burn up - much lower ozone concentrations in this layer compared to stratosphere, means that temperature decreases with height again
Polar and ferrel
- Where the polar and Ferrel cells meet ascending air is linked to the low pressure at the surface - Ferrel and Polar are less well defined than the Hadley; harder to detect when we look at atmospheric fields
Planetary boundary layer
- Where we experience weather - Boundary between earth and free atmosphere - Also known as atmospheric boundary layer - Lowest part of atmosphere - Varies from several hundred metres to 1-2km depending on season, time of day, etc - Characterised by lots of eddies, turbulence - Draft in house = pressure difference between two sides of the house - Eddies are important for distributing air pollution - Geostrophic wind altered in boundary layer by friction force - Why its less windy at surface - LAMINAR FLOW above boundary layer
Multicell thunderstorms characteristics
- Wind shear - Stops precipitation falling into updraft - Wind shear can help tilt updraft - Helps warm, moist air going up into updraft stay isolated from precipitation-driven downdrafts - Storms last longer - Outflow boundary = boundary between the downdraft air that reaches the surface and the environmental air - Convection can be so vigorous that 'overshooting tops' may occur, in which convection overshoots its level of neutral buoyancy at cloud top
Urban wind
- Wind speed in green space faster than urban area - More built-up are, more wind is retarded/ altered - Channelling between buildings can increase the local speed
Role of wind and inversions
- advection of poor air quality - Dispersion: strong winds tend to lower concentration of pollutants - Role of stability and inversions -Vertical mixing - Radiation and subsidence inversions - Mixing layers and depths
external influences
- are external to Earth's climate system and effect input and output of energy to system - influences outside earth entirely - how much energy the Sun is producing and characteristics of Earth's orbit - volcanic eruptions which produce particles that can prevent some solar energy entering the climate system are also an external influence
Low skill forecast
- based on noticing patterns in weather to guess what sequence would happen next - persistance
Shelf cloud
- can form above gust front - air that hasn't reached its level of natural buoyancy - when warm moist air is forced to ascend by outflow boundary, but parcels are still cooler than LFC
Radiosondes
- carry instruments aloft in balloons - temp, pressure and humidity sensors - gives information on upper atmospheric conditions - Satellites and radar can be used to measure weather 'remotely' ○ i.e. the temp, rainfall or other variables is inferred through the transmission and reflection of radiation - Dual pole radar = infer the velocity of individual air parcels
Effects of climate change
- changing rainfall patterns - rising sea levels - coral bleaching - retreating glaciers - changes in weather extremes - melting sea ice
Climate analogues
- compares different local temperatures - helps people envisage the future climate
Impacts on ecosystem
- coral bleaching - 2014 heatwave, 40,000 flying foxes die in QLD
Dew point
- dew point the temperature to which the atmosphere must be cooled for saturation to occur - good measure
Boundary layer: daily cycle
- diurnal cycle of boundary layer - capping inversion, where temperature is inverted
Combat chaotic atmosphere
- don't know exactly the initial conditions therefore still an element of unpredictability - Deal with this by running forecast many times with slight changes made to initial conditions - Produces an ensemble group of model simulations from which we can make our forecasts
Temp increasing with height
- due to ozone at higher levels in the stratosphere absorbs radiation before it can reach lower stratosphere - deep convection can spill over into the stratosphere transferring water vapour from troposphere - moisture from clouds spilling up into the stratosphere; tropical regions convection passes through tropopause
Equations of MWP
- few mathematical equations that describe the horizontal and vertical motion of air and its thermodynamic state -Equations, with idea that mass and energy conserved, used to estimate change in the state of the atmosphere - Ideal Gas Law - Newton's second law of motion -F=ma - Weather forecast model uses these equations to estimate state of atmosphere - Process is repeated again and again as forecast simulation runs for about a week
Stationary fronts
- fronts with no movement - winds tend to blow parallel but opposite directions
Inverse Barometer Effect
- highest winds on eastern side of storm - stronger winds on eastern side will likely cause the highest storm surge and most damage
Condensation
- if molecules moving slow enough, start to attract each other and form a liquid - cooling air can cause condensation to occur - low pressure and resulting ascending air can cause rain
Troughs
- indicate a wind change rather than temperature change - may or may not be associated with weather
Weaker pressure gradient force
- indicated by isobars further apart - weaker winds
Instability with positive and negative feedback
- initial impulse amplified - initial impulse is damped
Relationship between fronts and lows
- initially cold and warm fronts separate - cold front catches up to warm front, intensifies upward motion and decreases surface pressure - creates 'occluded low' - more common in NH
Problems with radar
- insects = precipitation - mountains can block reception
Internal influences
- internal to Earth's climate systems - atmosphere, ocean, land surface, ice - they govern transfer between different parts of the climate system and include things like El Nino-Southern oscillation - ENSO involves the transfer of energy between the atmosphere and ocean, it modulates the global average surface air temperature we measure
Haze
- layer of particles dispersed through a portion of the atmosphere - haze becomes a cloud resting near the ground when visibility lowers to 2-5km - forms in very stable conditions
Fog
- less than 1km visibility - forms in one of two ways - 1. air is cooled below its dew point - 2. water vapour is added to the air by evaporation, and the moist air mixes with relatively dry air. - fog formation needs some wind but not too much, therefore difficult to forecast
Satellites
- like radars but above - Pulse of radiation from the satellite reflected back from clouds or the surface of the earth - Because tops of clouds are a lot colder than earth's surface, radiation reflected back to sunlight is at a different wavelength (much longer) -Can infer temperature of tops of clouds -Infer heights of clouds
Drought
- long period (month/ decades) deficiency in available moisture compared to normal 'conditions' - not a normally dry/ arid environment - Meteorological - months - Agricultural - years - Hydrological - decades - Socio-economic - Decades
Cold powerful currents
- low sea surface temperature - strong wind shear that disrupts convection
Condensation and lapse rate
- makes lapse rate less - saturated adiabatic lapse rate - because in clouds there is more condensation aloft, warms the parcel - difference between two lapse rates governs calculations of instability
Heat engine
- may be viewed as a heat engine that converts heat energy into mechanical energy
Convection
- means parcels moving upwards - can either move upwards because they are warmer and therefore less dense than the surrounding air (free convection) or they can be pushed up by an obstacle (forced convection); caused by mountains
Nimbus
- means rain
Wind speeds and directions
- measured at a standard 10m height worldwide because less friction than at surface, keeps it constant - wind speed from anemimeter - wind direction from wind vane
Ozone
- most concentrated in stratosphere - protects us from ultraviolet radiation but near surface is pollutant - formed via interaction with UV radiation - occurs naturally in stratosphere
Weather of tropical cyclone
- non-frontal low pressure systems - pressures at centres of tropical cyclone among lowest ever observed at sea level - eye = centre of tropical cyclone ○ Area of light winds and clear skies ○ 40km diameter - Eye surrounded by dense ring of clouds ○ 16km high ○ Eye wall - Marks the strongest winds and heaviest rain - Developed over warm water of tropical oceans - Highly organised convection (fuel for TC) - Intense rainfall - Distinct eye - Strong cyclonic wind near surface - Strong pressure gradient near eye directly associated with strong winds - Hurricane Ivan = more than 7 days - winds greater than 33km/h - Lasts for many days - Unstable atmosphere - Moist middle atmosphere - Low vertical wind shear Coriolis needed! - MORE TROPICAL CYCLONES DURING LA NINA
SH winter vs NH winter
- not as cold - not as far south as UK is north, equivalent latitude of Spain - no big land masses, more oceans
Frontal uplift
- occurs as cold air wedges under warmer air ahead of a cold front - precipitation does occur also behind a front but may be the result of moist, unstable airflow
Sunrises and sunsets
- often red - Mie scattering: due to larger particles - Sunrise/ sunset: the sun appears redder as passes through more of the atmosphere; more of the dense part of the atmosphere near the surface - Scattering of blue and green light leaves only the longer wavelength light (redder) to reach us at the surface - More aerosols lead to more scattering, so sunsets are often redder in cities
Wind Chill factor
- one of the dangers of the Antarctic environment is associated with 'wind chill factor' - High winds can increase the rate at which unprotected flesh loses heat, and can quickly lead to hypothermia and frostbite - This increased rate of loss makes the environment feel colder
Socio economic drought
- physical water shortages to affect social systems or the economy - health, well-being, quality of life - supply and demand of economic product
Absolute vs relative threshold
- relative = extreme temperatures defined by the tails of distribution, advantages are comparable at all locations, meaningful in a climate context
The atmosphere
- relatively thin barrier that separates us on the Earth's surface from outer space - Troposphere, Stratosphere, Mesosphere, Termosphere
Ensemble
- represents a range of equally possible outcomes for weather - Can make probabilistic forecasts - E.g. 100 forecasts and 20 produce precipitation; 20% chance of rain - poor man's ensemble: compare forecasts on different agencies' deterministic simulations
Low pressure
- rising air cools - Since atmospheric pressure is greatest close to the surface (due to gravity), the atmospheric pressure decreases as the 'parcel' of air rises - Thus the 'parcel' expands - Expansion requires work, and so the energy for this works needs to be found somewhere - It is taken from the average speed of motion of the molecules in the parcel; which then decreases - Since the temperature of a gas is just a measure of its typical molecular speed, the temperature decreases
Instability
- rising motion in atmosphere - Surface heating - Uplift of winds over mountains - Pushing upwards of air by cold fronts (frontal) - Convergence of winds at the surface - Turbulence - Free convection
Observing the weather
- satellite radiosonde wind profiler weather radar observation surface observation aviation weather observation
Thunderstorms
- storm containing thunder and lightning - convective storms that form with rising air - several triggers (unstable air, lift + moisture) - need moisture: condensation occurs = lots of energy released to atmosphere and the storms uses this energy
Future consequences
- storms surges will be worse with tropical cyclones - Lots of low lying islands; especially pacific and Indian; nothing above 3m of sea level; very damaging for these communities - More risk of storm surges - Freshwater stores become less resilient - More heatwaves and fewer cold extremes - More intense, short-duration, extreme rainfall: a warmer atmosphere holds more moisture - More droughts - warming increases evaporation from the surface and precipitation patterns change - Atmosphere can take more water from surface - Further melting of sea ice; removal of sea ice further warms system - further bleaching and death of coral due to marine warming
Cold surface winds
- tend to become increasingly unstable as they move equator-ward - lower part of air warmed by oceans - difference in temperature between lower and upper part of air increases - environmental lapse rate increases - instability decreases
Errors in measurment
- the instrumentation we use to measure the state of the atmosphere is often less precise during extremes ○ Stevenson screen's are less reliable during high temperatures - Especially in Europe, air becomes very still; box is not ventilated and artificially become too high recorded by the thermometers - less idea at equator than at tropics - Australia has a reduction of weather stations since the 80s - Rainfall not measured on a Sunday in Australia causes problems when trying to look at past Australian climate
Saturation
- total number of molecules escaping from liquid (evaporation) are balanced by number returning (condensing)
katabatic winds
- very intense 'downslope' wind - Over Antarctica in the winter, no solar radiation, but significant amounts of infrared radiation escaping surface - Causes surface to cool, and a strong surface 'temperature inversion' is established - This temp inversion creates a layer of very cold, dense air in the lowest few 100m of atmosphere - When this occurs over regions of steep slopes, strong gravity currents are formed - Such katabatic flows are found in many parts of the world (e.g. strong downslope valley winds occur in the surrounds of Adelaide on clear nights
Buoyancy
- warmer air finds itself surrounded by colder air, so therefore rises until it is no longer warmer than its surroundings (unless being forced to rise even further) - uplift can be initiated by one of the previous mechanisms
Regions of strong pressure gradients
- where isobars are close together - regions of strong winds - means pressure is changing over smaller difference - wind stronger = Coriolis force stronger
Hail
-Pieces of ice that can be opaque or transparent and have a large range in size - Hail forms in clouds with strong updrafts which allow enough time for the accretion of large amounts of water vapour - Updrafts take hail above the freezing level in the cloud where the water vapour freezes. Process repeats to form layering on hail and increase size
Cause of prolonged periods of heat
1. Persistent high pressure systems (blocking) 2. Warmer than average conditions due to natural variability - El Nino Southern Oscillation 3. Dry soil - Dependent on rainfall
cumulus stage
1st stage of a thunderstorm, strong updraft creates towering clouds with suspended droplets that release latent heat to raise temp so the cloud keeps growing up - Typically occur in weak vertical wind shear - *wind shear = change of wind speed with height - Common in many areas of the globe, including the SE of united states - Cumulus stage = small cumulus clouds bubble up into dry conditionally unstable atmosphere, gradually moistening the atmosphere above for subsequent deeper clouds - Clouds are too shallow for precipitation to form Lifting Condensation level (LCL) = the level at which a parcel becomes saturated (RH=100%)
Antarctic ice
3 main types: - Ice sheet: ice mass that covers a large land area - Sea ice: frozen ocean water (and floats on ocean) 2-3m thick - Ice shelf: permanent floating sheets of ice that connects to a landmass; outflow of 'ice sheet' and can be >800m thick
Cold front
A front where cold air moves in under a warm air mass. - causes transition from warmer to colder air at a fixed location - warm front is opposite - not so many warm fronts due to generally weaker temperature contrasts - represents a transition at a location from warm air to cold air - 10 knots = 18.5km/h
Extratropical cyclone
A low-pressure mid-latitude weather system characterised by converging winds and ascending air rotating counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. An extratropical cyclone forms at the front between the polar and Ferrel cells.
High pressure
A mass of sinking cool air that usually bring fair weather.
Tropical cyclone
A severe storm with high winds that spiral around a calm center - derives its energy from the heat that is released when water vapour that has been evaporated from the ocean surface condenses in the middle of the atmosphere - strongest winds near surface - between 100-2000km in diameter - at least 500km from equator
Gulf stream
A warm ocean current that flows from the Gulf of Mexico northward through the Atlantic Ocean - discovered earliest - strongest of the 'western boundary currents' (currents on the west side of the ocean basin - many meanders and eddies - Very large heat loss from the ocean surface as warm water meets very cold winter air from North America
Claudius - Clapeyron relation
A warmer atmosphere can hold more moisture meaning that when we have the right conditions for an extreme rainfall event, climate change can intensify the rainfall - exponential relationship between temperature of air and how much moisture it can hold - for every 1 degree of C warming, the air can hold about 7% more moisture
Stratus
Clouds that form in flat layers and often cover much of the sky. - means layered
Dew and frost
Dew forms on objects near the ground surface when they cool below the dew point, more likely on clear nights - white frost forms when the dew point is at or below freezing, forms on cold, clear, calm mornings
Numerical Weather Prediction (NWP)
Forecasting the weather based upon the solutions of mathematical equations by high-speed computers.
Temperature and height
Generally, decreases with height but very near the surface this isn't always the case; often due to overnight surface cooling
Human influences (external)
Greenhouse gas emissions which enhance the greenhouse effect and aerosols which reduce incoming solar radiation, also an external influence
Storm terms and locations
Hurricane (North Atlantic or South-Western Pacific) - typhoon (NW Pacific) - Tropical cyclone (S Pacific and Indian Ocean)
Inversion
Increase in temperature with height
East Coast Low
Intense low pressure system, slow moving and occasionally a remnant of a tropical cyclone.
urban heat island
Local heat buildup in an area of high population density
Deep water waves
Move in water deeper than one-half their wavelength - Wave speed (c ) = 1.25(L)^1/2 L = wavelength
Coriolis effect
Rotation causes air parcels to deflect - to right of their direction in NH - left SH - at equator, there is no Coriolis force
Meteorological seasons
SH: austral summer, autumn, winter and spring - In the NH; opposing times with word boreal used instead of austral - Seasons don't really suit every part of the world - Indigenous Australians different season
Humidity
The amount of water vapour in the air - specific humidity: mass of water vapour divided by total mass of air - mixing ratio: mass of water vapour divided by mass of dry air - relative humidity: amount of water vapour divided by maximum possible amount expressed as percentage
tropopause
The boundary between the troposphere and the stratosphere. - higher in equatorial regions and lower at the poles, due to convection and surface heating in the tropics making the layer where there is air turning thicker
Dissipation stage
The final stage of a thunderstorm in which rain gets lighter and downdrafts get less powerful - rain into updraft= cooling down updraft, cut off source of warm moist air, storm dies
La Nina
The opposite of El Nino, with a lesser effect.
Relative humidity
The percentage of water vapour in the air compared to the maximum amount of water vapour that air can contain at a particular temperature - poor indicator because it is relative to saturation vapour pressure, which increases sharply with temperature due to higher evaporation - good indicator if moisture transfer from materials: if RH too high, once some moisture gets into material, hard to evaporate out
data assimilation
The process of incorporating various types of atmospheric observations into the initial stages of a forecast produced by a computer model. - use observations around the world to help form initial conditions for weather prediction models - some places have less observations
dry adiabatic lapse rate
The rate at which the temperature of a parcel of dry air decreases as the parcel is lifted in the atmosphere.
Equinox
The time or date at which the sun crosses the celestial equator, when day and night are of equal length - maximum solar radiation at equator and minimum at poles
Kuroshio Current
This current is warm flowing along the western side of North America - means black current as it is warm and biologically unproductive - many eddies and a sharp boundary between cold and warm water - Interacts with cold current
Front
Transition between two air masses of different densities
Formation of tornado
Usually form as cool, dry air meets warm, moist air. When these two types of air masses meet, it causes a thunderstorms. Then a tornado can form when high winds in the upper atmosphere push against the thunderstorm clouds causing a rotation within the storm. - stretching of vorticity leads to an increase in horizontal wind speeds
apparent temperature
What the air temperature "feels like" for various combinations of air temperature and relative humidity. AT = atmospheric temp - 0.70(wind speed) + 0.33(water vapour pressure) - 4.00
climate sensitivity
amount of global warming we would expect after a doubling of atmospheric CO2 concentrations
Hygrometer
an instrument for measuring the humidity of the air or a gas.
East Australian Current
an ocean current that moves warm water in a counter clock-wise fashion down the east coast of Australia
Climate model
attempt to simulate processes and interactions in/ between the atmosphere, ocean, land surface and cryosphere over long periods of time - computationally expensive - reducing uncertainty in climate sensitivity is central to improving climate projects
Sun pillars
caused by reflection of sunlight from ice crystals
Cumulus
clouds that look like fluffy, rounded piles of cotton - means heat - summer time
contrails
come from planes, fuel releases water vapour and sulphur particles which enhance formation of droplets
Ordinary thunderstorms stages
cumulus, mature, dissipation
meteorological drought
defined by comparing an area's current precipitation with the area's typical precipitation and by analysing how long the dry period lasts
Noctilucent
high latitudes, only visible at night
Lenticular
moist, stable air going over mountain that cools, water vapour condenses and as it comes back down mountain it evaporates, water drops condensing and re evaporating
Hydrological drought
occurs when a meteorological drought affects an area' ground water, streams, lakes, and reservoirs
Principal pollutants
ozone aerosols carbon monoxide and sulphur dioxide nitrogen dioxide and nitric oxides VOCs: hydrocarbons
Air pollution types
primary and secondary fixed and mobile sources
Deterministic forecasting
run our model for a given forecast based on best available data for initial conditions that we have at the time
Graupel
small snow covered in thin layer of ice
fog cloud
stratus cloud at surface Fog often forms in anticyclonic conditions and is more likely in polluted air and after bonfire and fireworks celebrations where there are CCN for water vapor to condense onto.
Ionosphere
the lower part of the thermosphere, where electrically charged particles called ions are found - encompasses parts of the thermosphere and mesosphere - atoms are stripped of their electrons - consequence of absorption of energy due to cosmic rays and solar winds = aurora borealis/ australis
cloud formation
we need water vapour and particles for the vapour to condense on to, called cloud condensation nuclei (CCN) - Clouds are white due to the scattering of light in all directions from lots of cloud droplets Rain clouds appear greyer because they are thicker, so less light penetrates through the cloud
Solstice
when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days.
