Tropical Met Flashcards
State the latitude limits of the tropics
Between the Tropic of Capricorn 23.5°S (southern hemisphere)
•Tropic of Cancer 23.5°N (northern hemisphere
Describe the Hadley cell
A large-scale atmospheric convection cell in which air rises at the equator and sinks at medium latitudes
•Sinks at around 30°N/S
•Responsible for the trade winds in the Tropics and control low-latitude weather patterns
Describe what’s meant by horse latitudes
Located between 30-40º in both hemispheres.
Light winds, little rain due to anticyclones that form here.
Describe what’s meant by doldrums
Exists with the intertropical convergence zone
•Between 5°N/S
•Trade winds converge resulting in light winds
•Frequent heavy thunderstorms due to convection caused by sun and moist air
Describe the equatorial trough and inter-tropical convergence zone (ITCZ)
The trough is centered on the thermal equator, its a Near continuous belt of low pressure around the low latitudes and which has a very high dew point therefore large amounts of moisture in the air
•Contains the doldrums, ITCZ and part of the trade winds
ITCZ - narrow band of convection Cb’s surrounding the glove resulting from the convergence of the NE trade winds from the northern hemisphere with the SE trades from the Southern Hemisphere.
State the seasonal location of the equatorial trough and ITCZ
Both move with the sun into the warmer hemisphere
•Causes the trade winds to change from SE to SW when crossing over the equator in northern hemisphere summer
•NE trade winds become NW in southern hemisphere summer
•Smaller movements over the ocean than land
State the typical low-mid level weather in active and inactive ITCZ
If trade winds meet head on theres a strong convergence, e.g NE wind converging with SW trade wind.
Weaker/inactive ITCZ caused by winds meeting at similar angles . E.g ene meeting ese wind
State the typical low and mid-level weather In an active and inactive ITCZ
Active = extensive Cu, TCu, Cb and thunderstorms with heavy showers, icing and strong up/downdraughts
•Inactive = Low level fair weather cumulus, light winds
Explain the origin and common location of the South Pacific convergence zone
Most active in Southern Hemisphere summer.
Caused by semi-stationary high in eastern pacific and anticyclones originating/travelling east from Australia/NZ.
NE wind meets SE wind creating zone of intense cloudiness between Papa New Guinea and French Polynesia.
Describe weather associated with the SPCZ
Summer = convective thunderstorms and tropical disturbances
Winter = weaker convective thunderstorms or fair weather Cu
Regards to trade winds describe the mechanism that drive the trade winds.
Pressure differential between the anti-cyclones at 30º and depressions at the equator.
As it moves from high to low, Coriolis force deflects the wind left in SH and right in NH but ultimately caused by the sun and aid in heat distribution.
Describe the latitudinal and vertical limits of the trade winds
Between 30ºN and 30ºS
8000ft amsl
Regards to trade wind describe seasonal location and direction
Follow the sun.
Moves north in NZ winter and south in summer.
Southern H = SE in NZ summer, SW in winter
Northern H = NW in NZ summer, NE in winter
Regards to trade wind, describe associated weather
Weather associated with high pressure systems closer to 30° latitude
•The closer to the equator the trade winds get, the more unstable the weather and clouds become
•Wind strength = 10-20kts occasionally 30kts
•Trade winds stronger in winter than summer
Regard to trade winds, winds and weather usually experience above the trade winds
Above trade wind inversion at closer to 30° = good visibility, dry air and clear skies
•Closer to the equator moisture content and instability increase creating TCu and Cb cloud at altitude
•Above the trade winds = light westerlies
Describe the topographical influences on the trade winds
•Land heats up and cools down faster than the ocean which Increases instability in summer on coasts exposed to SE trade wind and increases cloud development
•Steeper terrain will also cause orographic rising
•In winter stability is increased reversing the effects
Define monsoon
Derived from Arabic word mausim
•Means season and can be ‘wet’ or ‘dry’
•Caused by continental highs and lows creating giant land breezes or sea breezes
Describe the mechanisms involved with regard to wet monsoons
Occurs when land is heated up in spring/summer. Creates intense instability causing air to rise.
Replacement air from oceans travel inland and create large thunderstorms, heavy precipitation and squalls.
Mountain barriers increase the development as they push the air up.
State the seasons during which Australian monsoon occur
Occurs between November and April, peaks in February
•Summer
•Occurs when moist NW trade wind blows onto northern Australia, inter tropical convergence zone causing Coriolis force to deflect it the other way when it crosses over the equator
•In winter the dry monsoon blows from the SE trade wind bringing dry weather
Describe the requirements for the formation and development of tropical cyclones
Sea temperature must be 26.5ºC or higher.
Associated with low pressure area known as equatorial trough.
Between 5-20ºC latitude due to Coriolis force being to weak Above 5 and 20º latitude due to coriolis force being too weak above 5º
Must develop over ocean due to moisture requirement
Little to no vertical windshear
Must be high-level divergence just below the tropopause and requires a warm core created by release of latent heat. Warm core creates the upper level high pressure zone.
A cyclone eye to reduce pressure below 1000hPa through adiabatic warming
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Describe the weather conditions associated with tropical cyclones
Air pressures as low as 950 hPa
•Hurricane forces winds of 64kts or greater are sustained
•Torrential rain, thunderstorms and violent squalls
•Can last up to 2 weeks and travel west
Explain El Niño events
•Caused by the collapse of the Walker Cell
Occurs when pressure increases in the west near Darwin and decreases in the east near Tahiti, meaning Trade winds can reverse in direction and it can enhance westerlies in mid-latitudes
Explain factors causing La Niña events
Caused by the Walker Cell and Humboldt current
•Occurs when pressure decreases in the west near Darwin and increases in the east near Tahiti
•Trade winds enhanced
•Westerlies in mid-latitudes reduced or even reversed into easterlies
Describe how El Niño and La Niña events influence the weather in New Zealand
El Nino causes more rain on the west coast and dryer conditions on the east coast
•La Nina causes more rain on the east coast and dryer conditions on the west coast
•Higher chance of ex-tropical cyclones in summer months with La Nina
