GEOG220 Flashcards
How is pressure measured?
From above mean sea level
What direction does air circulate around low and high pressure systems?
Air flows clockwise around low pressure, anti-clockwise around high pressure.
Earth Circumference
40,000km
Earth Diameter
12,740km
Earth Surface Area
510 million km cubed, 70% ocean
Why does the difference between the Earth’s circumference and diameter matter in regards to rotation?
Because the earth rotates and completes a rotation every 24 hours, the equator has much further to travel than higher latitudes.
This creates a rotation speed gradient.
What forms the Coriolis Effect?
Objects at lower latitudes are moving at a greater velocity than objects at higher latitudes, due to the rotation speed gradient. Large-scale horizontal motion results in ‘apparent deflection’ of movement. This gradient creates the Coriolis effect, the deflection of horizontal movement.
Coriolis Effect
Deflection of horizontal movement. Causes air to circulate around high and low pressure systems, storm systems to spin, and different weather patterns and climate across latitudes.
Atmospheric Water (%)
0.001%
Why is atmospheric water important?
Responsible for energy transport (latent heat during phase transition), high heat storage, and is an extreme greenhouse gas - warming the earth.
What forms seasons?
The Earth is rotating on a tilted axis of 23.5* around the sun, meaning incoming solar radiation is targeted towards on hemisphere. When the rotation is perpendicular, neither hemisphere pointed towards or away, the Earth is in equinox to give spring/autumn. This gives us seasons.
True or False, distance from the sun influences seasons?
False, distance has no influence on seasonality.
What causes the tropics to be warmer?
The curvature of the Earth results in the uneven distribution of incoming radiation, with higher concentration at the equator. Tropics receive more direct radiation, giving warm tropics and cold poles.
Solar Zenith Angle
Angle of incoming radiation relative to the vertical. Near zero for direction radiation, near 90* for no radiation. This is why the tropics are warm and the poles are cold.
High Zenith Angle
= low net short-wave radiation = cooler climate
Energy
The ability or capacity to do work on matter.
Heat
Energy being transferred from one object to another because of temperature difference.
Celsius Scale
Based on freezing and boiling of pure water
Specific Heat
Heat energy needed to raise one gram of a substance one *C
Latent Heat
Heat energy required to change the state
Evaporation and Melt
Take in heat and cool surrounding environment
Condensation and freezing
Release heat and warm surrounding environment
Conduction
transfer of heat within a substance (solid).
Convection
transfer of heat by mass movement of a fluid (liquids and gases are able to move freely and form currents). Driven by differences in temperature.
Advection
horizontal transport of heat (warm ocean currents, cold southerlies). Driven by different processes of movement.
Thermal
rising bubble of air that carries heat energy upwards by convection (vertical movement).
Short-wave Radiation
UV, do not feel as heat, 50% absorbed by the earth and is reemitted as long-wave radiation.
Long-wave Radiation
feel as heat. It is reemitted by the earth, and absorbed by atmosphere and greenhouse gases.
Stefan-Boltzmann Law
The higher the temperature of the object emitting radiation:
- The greater the amount of radiation emitted
- The shorter the wavelength (higher the frequency) of the radiation emitted
Black body
perfect absorber and perfect emitter of radiation (incoming solar = outgoing terrestrial).
Hadley Cell - Thermally Direct (Temp Driven)
Circulation created by convection of heated surface air at the equator (ITCZ).
Air rising at equator turns poleward at the stable tropopause (deflected to the east forming westerly sub-tropic jets) –> air sinks/warms near 30*N/S (subtropical high pressure zones - creates deserts) –> surface winds return back to equator (surface trade winds converge at ITCZ).
Subtropic High Pressure Zone (30*N/S)
Thermally direct! Dominated by descending branch of the Hadley cell, producing warm and dry average climate conditions. Weak winds.
Ferrell Cell - Thermally Indirect
Fueled by the meeting and convergence of warm/cold air. Forms westerlies
Polar Cell - Thermally Direct (Temp Driven)
Warm air from tropics meets cold air from poles, different air mass properties create fronts and instability - storms.
Monsoon
land warmer than water
Continents heat (low pressure) and cool (high pressure) much faster than water, giving high pressure belt
Monsoon in NH Summer and Winter
Summer: Continents heat (low pressure) and cool (high pressure) much faster than water, giving high pressure belt. Westerlies move north. WET
Winter: Southward movement of ITCZ, farthest south over areas of continental heating. Westerlies move poleward. DRY
What controls ocean currents?
Wind. Gives rise to Gyres, Thermohaline.
What are the 4 climate types?
- Global
- Macro
- Meso
- Micro
Global Climate
the climate of entire planet
Macroclimate
climate of large area, size of state or country (1000km2)
Mesoclimate
small areas the size of few acres to hundreds kms (forests, valleys, cities, beaches)
Microclimate
very localised climate region (near ground vs metres above ground)
What are the 7 Climate Type Controls
I promise our wet pasta might accelerate.
- Intensity of insolation and variation
- Proximity of land/water
- Ocean currents
- Winds
- Position of high and low pressure systems
- Mountain barriers
- Altitude
Koppen-Geiger System
Classification of world climates based on annual/seasonal averages of temp and precipitation. Related to the distribution and type of vegetation.
Climate Zones - Koppen-Geiger System
(A) tropical moist climates
(B) dry climates (sub-tropical high pressure belt and rain shadows).
(C) moist mid-latitude climates with mild winters (western coasts of large continents and islands).
(D) moist mid-latitude climates with cold winters (interior regions of large continents)
(E) polar climates
Koppen-Geiger System: Moist Tropical Climate (A)
Within 20* latitude of equator. Warm and humid all year, with heavy precipitation.
Koppen-Geiger System: Dry Climate (B)
Cover 35% of Earth. North and South of humid tropical climates, within the descending Hadley Cell sub-tropical dry belt.
Divided into:
Hot (Bwh - BSh), annual temperature >18C
Cold (BWk - BSk), annual temperature <18C
Koppen-Geiger System: Temperate Mid-latitude Climate (C)
Middle latitudes of 40-60*.
Distinct summers and mild winters (never below 0*C).
Influenced by large bodies of water, with prevailing onshore winds.
Wet year-round with weather tied to fronts/mid-latitude storm track.
Koppen-Geiger System: Continental Mid-latitude Climate (D)
Very strong seasonal temperature variations, with hot humid summers and cold winters.
Located far from oceans relative to prevailing wind.
Precipitation year-round, but varies from convective thunder-storms in summer to snow in winter.
Koppen-Geiger System: Polar Climates (E)
Extremely cold winters and cold (short) summers, with warmest average temperature <10*C.
Little precipitation.
Differentiated by temperature alone.
Tundra (ET) - Warmest, 0-10C. Ice cap (EF) - <0C
Problems with Koppen-Geiger System
Too generalised (eg, NZ and topography)
Assumes sharp gradient between climatic zones (is gradual).
Synoptic Climatology
Relating surface climates to their regional atmospheric circulation patters.
Synoptic Types - Kidson Types (2000)
- Trough (low dominant - westerly winds)
- Zonal (high pressure over north, low pressure to south, but low stays south)
-Blocking (dominated by ridge, stopping other systems moving over)
Synoptic Kidson Type: Trough in NZ
SW - NW flow, cloudy, cool temperatures, exception is Hawkes Bay (sheltered by Mountains), very wet.
Synoptic Kidson Type: Zonal in NZ
Westerly, lows pass South, Warmer east and cooler on south, clearer skies, dry.
Synoptic Kidson Type: Blocking in NZ
NE flow, East coast cool and wet, west warm and dry.
Southern Annular Mode (SAM)
Intra-seasonal north-south movements of westerlies and storm-track.
Expand north towards NZ and contracting back to Antarctica
How Does NZ Topography Affect Wind Flow?
Predominant flow is westerly through troposphere. North-South orientation of mountains provides barrier, giving a windward side. Low-level winds will go around rather than over.
Vertical stability of flow important:
- More stable = winds will go around mountains
- More unstable = winds more likely to flow over mountains
Froude’s Number (Fr)
the influence of gravity on fluid motion.
High Fr: stable flow, blocking on windwards side
Low Fr: unstable and turbulent flow
Describe Christchurch Winds
Less frequent: NW, but most strong.
Most frequent: Easterlies, less strong.
El Nino in NZ
More trough and zonal westerlies. Dryer and hotter in the East, Wetter and cooler in the West.
La Nina in NZ
More blocking and northeasterlies. Wetter and cooler in the East, Dryer and warmer in the West.
+ SAM
Contracts towards Antarctica, storm track moves, gives effects similar to La Nina.
- SAM
Expands towards NZ, storm track moves, gives effects similar to El Nino.
East Coast Lows
Low pressure systems which develop along east (southeast) coast of Australia
Warm, oceanic air from the tropics + cold air from Southern Ocean collide. Runs into mountain, which causes column of air to compress, stretched and spins on leeward side.
How many cyclones does NZ get per year?
7-10
How do cyclones/severe local storms form?
Instability results in convection.
Temperature contrast between warm surface and cold air, air attempts to rise, strong vertical wind shear causes spin parallel to ground. Lifted vertically by updrafts. Storm forms
Scales of Motion
- Global
10,000kms, months to seasons, jet streams, overturning circulation cells (eg, Hadley).- Synoptic
1,000kms, days to weeks, surface highs/lows, upper-level ridges/troughs - Mesoscale
100skm, sub-daily, tropical cyclones, squall lines - Microscale
10skm, minutes to hours, thunderstorms, land-sea breezes.
- Synoptic
Jet Streams
Channel of strong flowing wind, to the east - consists of longwaves (Rossby Waves), with embedded shortwaves/disturbances
Troughs
Upper-level lows: ‘dig’ from high latitudes into lower latitudes and are associated with cyclonic flow.
Ridges
Upper-level highs: ‘build’ from low latitudes into higher latitudes and are associated with anti-cyclonic flow.
Bars, Millibars, and hPa
1 bar (1000 millibars) = pressure at sea level.
1b = 1000mb = 1000hPa
What pressure do upper-level troughs and ridges form?
300/500hPa
Upper-level convergence
promotes sinking air and surface high pressure
Upper-level divergence
promotes rising air and surface low pressure
Geostropic Flow
Upper-level winds flow in approximate geostrophic balance (where flow is parallel to height contours, pressure gradient force is balanced by the Coriolis force).
Ageostrophic Flow
Pressure gradient force is > or < Coriolis. This results in local ageostrophic flow, which is not parallel to height contours. This creates convergence and divergence in troughs.
Fronts
Boundaries marking the transition zone between air masses.
Four main types, named by the air mass moving into/replacing the air mass ahead of it.
Air Mass
Large body of air whose temperature and moisture are fairly similar. Source regions determine the air mass type.
Air Mass: C-Type
Air masses originating over land (continental air mass) = dry, can be cold or warm (Aus = warm, Antarc = cold). Gives cP = continental polar, cT = continental tropical
Air Mass: M-Type
Air massses originiting over water (maritime air mass) - moist, can be cold or warm. Gives mP = maritime polar, mT = maritime tropical
Stationary Front
Transition zone between two air masses that is not moving
Cold Front
Cold cP or mP air moving into and replacing warmer air, forces warm air over dense cold.
Rising motion along cold fronts can be heavy with precipitation and squall lines.
Warm Front
Warm cT or mT air is moving in and replacing colder air.
Warm air rises over colder, denser air. Approach creates high, wispy clouds with halo around sun/moon.
Occluded Front
Cold air is more dense than warm air, so cold fronts advance faster. Cold front eventually catches warm front. Occurs in later stage of cyclone development.
Four Types of Fronts
Stationary, Warm, Cold, Occluded
Mid-latitude Cyclone Development: Polar Front Theory
A stationary front exists, and a wave or ripple forms.
A frontal or ‘open wave’ forms with low pressure centre.
Warm sector narrows and cold front catches warm front.
Occlusion-cold front develops.
Temperature gradients dissipate, low weakens.
The Wind Barb
bards and triangles which point in the direction the wind is coming from, with different symbols to give speed in knots.
Types of Satellite Imagery
1) Visible (picture, detect the movement)
2) Infrared (measure of infrared radiation, detect temperatures)
3) Water vapour (measure of how much water content - detects upper level moisture sources and transport, identifying ridge/trough patterns)
True or false, atmospheric pressure decreases with height.
True, atmospheric pressure decreases with height - usually at environmental lapse rate
Stability
Refers to a state of equilibrium. Two types:
- Stable
- Unstable
Stable equilibrium
a resting object that is moved will return back to its resting position
Air parcel moved upwards will tend to sink back down.
Unstable equilibrium
a resting object moved will accelerate away from its original resting position
Air parcel nudged upward will continue to rise until it reaches the same temperature/density as its surrounding environment.
Atmospheric Stability
Air pressure and temp decreases with height, called the environmental lapse rate. On average around 6.5*C/1000m.
Environmental Lapse Rate
Rate air temperature decreases with height. 6.5*C/1000m.
Air parcels that are warmer than their surroundings…
are buoyant and will rise (unstable atmosphere).
Air parcels colder/drier than their surroundings…
will sink or not rise (stable atmosphere).
Air parcels rising and sinking without condensation/latent heat release…
cool and warm at dry adiabatic lapse rate (10*C/1000m)
Role Moisture
Air parcel contains moisture = dew point temperature. When dew point temp = actual temp, relative humidity increases to 100% and condensation occurs.
Air parcel continues to rise/cool at dry adiabatic lapse rate. Condensation creates cloud, and releases latent heat.
Latent heat release = warming of rising air parcel = slower cooling. Cools at moist/saturated adiabatic lapse rate (6*C/1000m)
Stable Environment Lapse Rate
Have very weak environmental lapse rate, meaning temperature does not cool much with height.
- environmental lapse rate = 4*C/1000m
Therefore, air parcels nudged to rise at either the dry (10C/1000m) or moist (6C/1000m) adiabatic lapse rate will always become and remain colder than surrounding air.
Unstable Environment Lapse Rate
The environment cools very quickly with height. Eg, environmental lapse rate = 11*C/1000m.
Air parcels nudged to rise at either the dry (10C/1000m) or moist (6C/1000m) aidatic lapse rate will remain warmer than the environment and continue to rise.
Conditionally Unstable Environment
The environment cools between the dry and moist adiabatic lapse rate. Eg, environmental lapse rate = 7*C/1000m
This is the most common type of environment.
Air parcels cooling at the dry (10*C/1000m) lapse rate (without condensation) will sink back down.
Skew-T chart
This plots temperature and dewpoint with height, alongside dry and moist adiabatic lapse rates.
Temperature for isotherms is skewed to the right for visualisation purposes.
Red (temp) and green (dew) are temperature and dew point temperature
3 Ways to Increase Instability
1) Warm the surface
2) Increase moisture at the surface (get to the saturated adiabatic lapse rate quicker
3) Cool temperatures aloft
Stable Environments: Skew-T
1) Weak environmental lapse rates
2) Temperature inversions
Cloud Development
1) Rising air parcels expand/cool and reach their dew point temperature at the adiabatic lapse rate, called the lifted condensation level (LCL). Marks base of the cloud
2) 2) Above the LCL, continued rising/cooling results in more condensation and cloud growth (while the air parcel cools more slowly at the saturated adiabatic lapse rate) If the parcel reaches a level where it becomes warmer than its surroundings, this marks the level of free convections (LFC)
3) 3) At the LFC, air parcel continues to rise until no longer warmer than surroundings, called equilibrium level (EL)
The parcel becomes colder than surroundings, stops rising
4 Mechanisms to Raise Air Parcels
1) Daytime surface heating (convection)
Pockets of warmer air from uneven heating. Short-lived, most common during afternoon.
2) Topography Physical barriers that force air to rise (mountains). Stationary, results in steady/heavy precip 3) Fronts Collision of air masses with different densities. Warm/moist air (low density) will rise over cold/dry air (high density) 4) Synoptic-scale convergence/divergence Convergence of surface air or divergence in upper-levels.
Marine Clouds
Less condensation nuclei, fewer and larger water drops (fuzzy edges)
Continental Clouds
More condensation nuclei, more and smaller water drops (sharper edges)
Cloud Types
Cumulus (upward developing): convection, taller than wide, cauliflower tops).
Stratus (horizontal developing): formed from gentle uplift over wide area, wider than tall.
Cirrus: high clouds, cold and thin, comprised mostly of ice crystals, can look wispy or give murky appearance.
Cloud Type Prefixes
Prefixes tell us height.
Strato = low-level
Alto = middle-level
Cirro = high-level
Nimbo = precip
Onshore sea/lake breezes
Develop when land heats up more than surrounding water during day. Land acquires lower surface pressure than water, and an onshore wind develops.
Offshore land breeze
During night, land cools - land acquires higher surface pressure and offshore wind develops.
Can be associated with culumus clouds and showers
Urban Heat Island Effect
Urban surfaces with low albedo readily absorb, emit, and retain heat. Strongest at night. Also have less evapotranspiration.
This means urban areas are warmer than adjacent rural areas, especially at night. Gives localised clouds and showers.
Daytime Anabatic Winds
Generated by sun heating up sloped surface. Form soon after sunrise. Usually shallow and confined to individual slopes, ceasing around sunset.
Move upwards.
Night-time Katabatic Winds
Generated by nocturnal cooling of slope. Onset soon after sunset. Stronger than anabatic winds as gravity is working with. Confined to invidiual slopes, ceasing after sunrise.
Move downwards
Valley Winds
Blow up-valley in daytime. Response of large-scale warming of the higher valley walls.
Mountain Winds
Blow down-valley at night. Quite strong. Advance down-valley in response to large-scale cooling of the higher valley walls.
Large-scale Variability
Global patterns, driving year-to-year variations in climate.
El Nino, Southern Oscillation (ENSO)
Annular (ring-shaped) modes (SAM)
ENSO
El Nino Southern Oscillation
- Weaker than normal trade winds (sometimes westerly bursts) - Warm SSTs and heavy rainfall shift east into central tropical Pacific near 180* Thermocline flattens
El Nino
- Weaker than normal trade winds (sometimes westerly bursts)
- Warm Sea and heavy rainfall shift east into central tropical Pacific near 180*
Thermocline flattens
- Warm Sea and heavy rainfall shift east into central tropical Pacific near 180*
La Nina
- Stronger than normal trade winds
- Warmer sea surface temperatures in west, wet over indonesia
- Cooler SSts in east
Thermocline steeper than normal
El Nino Impacts
- Warm
- Dry in west tropical Pacific and tropical South America
- Descending air drives global jet streams
Shifts storm tracks and creates cooler/stormier NZ
- Descending air drives global jet streams
La Nina Impacts
- Cold episode
- Wet in western tropical Pacific and tropical Southern America
- Intensified walker circulation
- Weaker sub-tropical jet
Warmer in NZ
ENSO and NZ
El Nino: More trough/zonal, more strong westerlies.
La Nina: More blocking, more NE
Southern Annular Mode (SAM)
leading pattern of pressure variability in the Southern Hemisphere mid-latitude circulation. Varies from week to week, emerges more prominently on monthly/seasonal time scales.
A result of the meandering/pulsing of the southern ocean storm track and jet stream.
SAM +
Mid-latitude jet and storm track contract poleward.
La Nina-like
SAM -
Mid-latitude jet moves equatorward
El Nino-like
GHG Concentration
420ppm
SAM vs ENSO
SAM: Affects Southern Hemisphere’s high latitudes, driven by changes in atmospheric pressure and atmospheric circulation, and fluctuating on shorter timescales.
ENSO: centered in the tropical Pacific Ocean, driven by sea surface temperature anomalies, and operates on longer timescales with widespread climate impacts
