ATPL Tropical Met Flashcards
Explain what’s meant by equatorial trough (meteorological or thermal equator)
The meteorological equator is the annual mean latitude of the intertropical convergence zone (ITCZ)
•Meteorological equator located at 5°N
•The thermal equator is a different line joining all points of highest mean annual surface temperature
Explain the inter-tropical convergence zone (ITCZ)
Marks the place where trade winds from norther and Southern Hemispheres converge
Centered on the thermal equator
Explain what’s meant by South Pacific convergence zone (SPCZ)
Formed where the outflow from the walker cell clashes with the semi-permanent highs at 30° south
•Is the birth place for all south pacific tropical cyclones
State the region where maximum convergence and convention and maximum cloud development are
20ºN 15ºS
Max convergence = when ITCS moves away from equator by about 5º or more while remaining in the tropics. Causing the south east trade winds to go into the northern hemisphere deflecting them west cos of coriolis force making them clash into each other. North east trade winds become north west and clash with southeast trade winds.
Max convection = same as convergence and further enhanced over large continental land masses. Cos of increased surface heating ( due to higher specific heat of land).
Max cloud development = same as above.
Describe the following weather associated with active and inactive ICTZ
Active = thunderstorms and heavy showers of rain up to 600km (300nm) wide
•Most active in the afternoon during summer
•Inactive = some showers, light winds. 500km wide
•Least active over ocean in the winter
Describe icing in active and inactive ICTZ
Active = Moderate to severe icing above the freezing level, especially within the first 10,000 to 15,000ft above it
•Inactive = light to none
Describe turbulence in ICTZ
Active = moderate to severe due to Cb clouds
•Can’t fly under turbulence because cloud bases are 1,000ft
•Can’t fly over turbulence as clouds too high
•Inactive = light to none
Describe cloud related factors associated with ITCZ
Active = Wall of Cu, Cb, Tcu clouds going all the way up into the stratosphere.
•Large deviations required if wanting to go around an active ITCZ
•Inactive = Various oktas of cumulous
Describe the preferred location and characteristics of the South Pacific converge zone
Papa New Guinea to French Polynesia
Use diagrams to explain the following aspects of the trade winds in both hemispheres of the Pacific Ocean relating to anticyclonic subsidence and associated met conditions
Semi-permanent highs occur between 25° to 35° latitude in both hemispheres and travel eastward
•Clear skies, light winds that are deflected by the Coriolis force
•Causes trade winds to be NE in northern hemisphere and SE in southern hemisphere
Where are the approximate latitudinal and vertical limits of the trade winds
Between 30ºN and S
Vertical limit of 8000ft AMSL
Describe the seasonal changes in location and their effect on wind direction on trade winds
Follows the sun
•Moves north in NZ winter and south in summer
•Southern hemisphere = SE in NZ summer, SW in winter
•Northern hemisphere = NW in NZ summer, NE in winter
Describe the typical wind strengths, including variation from summer to winter regarding trade winds
Steady and persistent in strength
•Wind strength = 10-20kts occasionally 30kts
•Trade winds slightly stronger in winter than summer
•Winds above are generally light westerly
Explain the effect of the trade winds on the wx experienced in island groups and northern Australia on trade winds
Increased rain in summer on south east coasts of islands and Australia, drier on the west coasts or inland
•In winter trade wind strength is reduced due to land breeze
•Winter might still have some cloud on the SE coasts from the trade winds but overall much drier and stable
Outline how tropical convection can occur as individual convective cells or as organised clusters
Individual cells caused by turbulence in the friction layer creating long streets of cumulus aligning itself parallel to the trade winds
•Organised clusters are mesoscale convective areas. Caused by heating and instability through deep layers
Describe the factors involved in wet monsoons in terms of seasonal factors
The wet monsoon occurs in summer for either hemisphere
•Enhanced more over land than over sea due to specific heat differences
Describe the effect of large land masses and orographic obstructions on monsoons
The larger the land mass, the greater the difference in temperature between the land and the sea increasing the wet monsoon in summer
•Mountains and hills encourage rising of air so that the moist air reaches its dew point, increasing rainfall
Describe the location of major monsoon regions
Concentrated along the south Asia continent
•Moist air from Indian ocean causes monsoons in India, Pakistan, Myanmar etc
•Northern hemisphere monsoon from June to September
•Also the north Australian continent in summer
State where tropical cyclones, typhoons and hurricanes are in relation to oceans
Cyclones - South Pacific Ocean, Indian ocean (all Southern Hemisphere)
Typhoons - north west Pacific Ocean
Hurricanes - North Atlantic Ocean, north east Pacific Ocean
With regard to formation and development of tropical cyclones, describe the relationship with the equatorial trough and/or the SPCZ
A pre-existing disturbance at low levels provides a focal point for rotation of large masses of thunderstorms
•The wave disturbance is caused by convergence zones or quasi-stationary fronts
•These are most likely to occur in the equatorial trough or south pacific convergence zone
Describe the requirement for and supply of sensible and latent heat in regard to cyclones
Sensible heat is the increase in temperature of a body as more heat is added
•Latent heat is released as clouds form increasing instability and sensible heat
•This sensible heat is delivered to the center of the storm through radial flow
Describe the effect of upper-level divergence
Subsiding air in the storm eye should increase pressure
•Upper-level divergence removes air from the column at the top of the troposphere faster than it is entering the system at the surface
•This reduces surface pressure increasing convergence
Describe the characteristics of the cyclone e’ye
Light winds
•Subsiding air causes adiabatic warming which dissipates clouds
•Clear skies
•Where the lowest surface pressure exists
Describe the requirement for a warm core in regard to tropical cyclones
Instrumental as it encourages the development of an upper level high-pressure zone
•This creates more upper level divergence and therefore more low level convergence
State the stages of development of tropical cyclones
- Tropical disturbance
•Tropical depression
•Tropical storm
•Tropical cyclone
For each stage of the development describe the atmospheric pressure tendency
Tropical disturbance – Pressure starts reducing
•Tropical depression (formative) – Approaching 1,000 hPa starts to fall by about 4-8hpa
•Tropical storm (immature) – Below 1,000 hPa pressure near centre falls dramatically,
•Tropical cyclone (mature) – At its lowest, around 950 hPa
For each stage of development describe the typical wind strengths, including variation in wind velocity in and either side of the Cyclone eye
(formative) depression – One quadrant increases to gale force (sustained 34kt wind)
•(immature) storm – Hurricane force (sustained 64kt wind)
•(mature) cyclone – Hurricane force or stronger
Describe the typical wind strengths, including variations in wind velocity around the eye
•Light winds and clear skies within the eye
•Around the eye is dense wall of cloud about 16km high known as the eye wall. Marks the belt of heaviest winds and strongest rainfall
Where is the strongest wind? In hurricanes (relation to 4 quadrants of storm)
Front left of storm in Southern Hemisphere
Front right of storm in northern hemisphere
Describe the typical radii of the affected areas of a hurricane
(formative) – few closed isobars have a radius of 50 km
•(immature) – Defined eye forms with radius of 40km, hurricane force winds felt within 50km of the eye
(mature) - hurricane force winds felt within 200km of the center, gale force winds are experienced out to 500km
•Life span of tropical cyclones is 10 days
Describe the associated weather and location of the most severe conditions within different stages of the hurricane
(formative) – clear rotation of cloud mass begins and pulls in surrounding Cb clouds intensifying storm
•(immature) – heavy frequent showers with no gaps, the heaviest rain around the eye wall
(mature) – flooding caused by heavy rainfall, huge ocean swells and extreme winds
•Most severe weather located in the forward left quadrant of the storm in the southern hemisphere and forward right in the northern hemisphere
Describe the mechanism for the decay of tropical cyclones.
Movement over substantial land area removing water source.
Moving to higher latitude us where water is to cold for evaporation
Ingestion of cold air or dry air
Separation from high level divergence
Strong windshear aloft
Move over sea thats colder than 27 degrees
State seasons which tropical cyclones are expected
SH - October to march peaks in feb
NH - June to November peaks in sept
Describe the walker cell in the South Pacific Ocean
Entire Pacific Ocean south of the equator is influenced by the walker circulation
•Caused by two areas. One off the coast of Peru and the other, seas around the Indonesian islands/Northern Australia
•Westbound air traveling at low levels and easterly up top
Define the ENSO index
•Method used to characterize the intensity of an El Niño Southern Oscillation (ENSO) event
•It is an irregularly variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean
•Can be La Nina, El Nino or Neutral depending on surface pressures
Outline the characteristics of positive La Niña and negative El Niño phases of the ENSO index including the effect on prevailing winds in tropical and mid-latitude regions
La Niña – Pressure is 4hPa or more higher in the east pacific
•Increases strength of easterly trade winds, reduces westerlies in mid-latitudes
•Neutral Index is when pressure difference is less than 4hPa but still positive/higher in the Eastern Pacific
El Niño – Pressure higher in the Western Pacific
•Easterly trade winds weaken or reverse direction and become westerlies
•Increases strength of mid-latitude westerlies
Outline the characteristics of La Niña and El Niño phases of the ENSO index including the meteorological conditions in Australasia
La Niña - storms and bad weather on east coast of pacific islands, australia and NZ
El Niño - bad weather on west coasts, dry on east
How are cyclones formed
Surface temp 27 degrees or more
Enough coriolis force to create low pressure system that rotates
Pre existing disturbance at low level to provide a focal point for rotation
Increasing atmospheric instability
High humidity at low-mid levels of troposphere
Low vertical winder shear
Strong upper level divergence
