ATPL Tropical Met

Question 1

Explain what’s meant by equatorial trough (meteorological or thermal equator)

Answer 1

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

Question 2

Explain the inter-tropical convergence zone (ITCZ)

Answer 2

Marks the place where trade winds from norther and Southern Hemispheres converge

Centered on the thermal equator

Question 3

Explain what’s meant by South Pacific convergence zone (SPCZ)

Answer 3

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

Question 4

State the region where maximum convergence and convention and maximum cloud development are

Answer 4

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.

Question 5

Describe the following weather associated with active and inactive ICTZ

Answer 5

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

Question 6

Describe icing in active and inactive ICTZ

Answer 6

Active = Moderate to severe icing above the freezing level, especially within the first 10,000 to 15,000ft above it

•Inactive = light to none

Question 7

Describe turbulence in ICTZ

Answer 7

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

Question 8

Describe cloud related factors associated with ITCZ

Answer 8

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

Question 9

Describe the preferred location and characteristics of the South Pacific converge zone

Answer 9

Papa New Guinea to French Polynesia

Question 10

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

Answer 10

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

Question 11

Where are the approximate latitudinal and vertical limits of the trade winds

Answer 11

Between 30ºN and S

Vertical limit of 8000ft AMSL

Question 12

Describe the seasonal changes in location and their effect on wind direction on trade winds

Answer 12

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

Question 13

Describe the typical wind strengths, including variation from summer to winter regarding trade winds

Answer 13

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

Question 14

Explain the effect of the trade winds on the wx experienced in island groups and northern Australia on trade winds

Answer 14

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

Question 15

Outline how tropical convection can occur as individual convective cells or as organised clusters

Answer 15

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

Question 16

Describe the factors involved in wet monsoons in terms of seasonal factors

Answer 16

The wet monsoon occurs in summer for either hemisphere

•Enhanced more over land than over sea due to specific heat differences

Question 17

Describe the effect of large land masses and orographic obstructions on monsoons

Answer 17

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

Question 18

Describe the location of major monsoon regions

Answer 18

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

Question 19

State where tropical cyclones, typhoons and hurricanes are in relation to oceans

Answer 19

Cyclones - South Pacific Ocean, Indian ocean (all Southern Hemisphere)

Typhoons - north west Pacific Ocean

Hurricanes - North Atlantic Ocean, north east Pacific Ocean

Question 20

With regard to formation and development of tropical cyclones, describe the relationship with the equatorial trough and/or the SPCZ

Answer 20

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

Question 21

Describe the requirement for and supply of sensible and latent heat in regard to cyclones

Answer 21

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

Question 22

Describe the effect of upper-level divergence

Answer 22

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

Question 23

Describe the characteristics of the cyclone e’ye

Answer 23

Light winds
•Subsiding air causes adiabatic warming which dissipates clouds
•Clear skies
•Where the lowest surface pressure exists

Question 24

Describe the requirement for a warm core in regard to tropical cyclones

Answer 24

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

Question 25

State the stages of development of tropical cyclones

Answer 25

• Tropical disturbance
  •Tropical depression
  •Tropical storm
  •Tropical cyclone

Question 26

For each stage of the development describe the atmospheric pressure tendency

Answer 26

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

Question 27

For each stage of development describe the typical wind strengths, including variation in wind velocity in and either side of the Cyclone eye

Answer 27

(formative) depression – One quadrant increases to gale force (sustained 34kt wind)
•(immature) storm – Hurricane force (sustained 64kt wind)
•(mature) cyclone – Hurricane force or stronger

Question 28

Describe the typical wind strengths, including variations in wind velocity around the eye

Answer 28

•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

Question 29

Where is the strongest wind? In hurricanes (relation to 4 quadrants of storm)

Answer 29

Front left of storm in Southern Hemisphere

Front right of storm in northern hemisphere

Question 30

Describe the typical radii of the affected areas of a hurricane

Answer 30

(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

Question 31

Describe the associated weather and location of the most severe conditions within different stages of the hurricane

Answer 31

(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

Question 32

Describe the mechanism for the decay of tropical cyclones.

Answer 32

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

Question 33

State seasons which tropical cyclones are expected

Answer 33

SH - October to march peaks in feb

NH - June to November peaks in sept

Question 34

Describe the walker cell in the South Pacific Ocean

Answer 34

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

Question 35

Define the ENSO index

Answer 35

•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

Question 36

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

Answer 36

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

Question 37

Outline the characteristics of La Niña and El Niño phases of the ENSO index including the meteorological conditions in Australasia

Answer 37

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

Question 38

How are cyclones formed

Answer 38

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