Tropical Meteorology Flashcards
Describe the seasonal location of the equatorial trough in the Northern Hemisphere and explain the reason for the change in location?
SEE DIAGRAM
- Consistent with the meridional movement of the thermal equator north and south of latitude 0º each year.
- In the Northern summer (May to October), entire trough is located in Northern Hemisphere, but the latitudinal change in position and intensity of the trough varies greatly because of the differing nature of surface.
How do oceanic regions and continental landmasses influence the equatorial trough?
- Over oceanic regions, the equatorial trough is constant in terms of latitude, but the influence of continental landmasses (their differing mountainous natures and local pressures) cause the trough to shift considerably and fracture in a few places.
Describe the seasonal location of the equatorial trough in the Southern Hemisphere and explain the reason for the change in location?
SEE DIAGRAM
- In the Southern Summer (November to April), a large deflection takes the trough South through South Africa, while a smaller wave brushes the Northern parts of Australia (due to influence of variation in surface characteristics).
- The major difference is the position of the trough in the central Pacific and Atlantic where the equatorial trough remains in the Northern Hemisphere.
- This is because of the stronger trade wind strength in the North compared to the South, and also the influence of oceanic surface temperatures
What is the key difference between the equatorial trough and the ITCZ?
The equatorial trough is a more or less permanent feature of convergence and convection, whereas the ITCZ is a erratic feature, the presence and intensity of which depends on the variable degree of trade wind convergence.
What is the equatorial trough?
- The general term for the belt of comparatively low pressure around the globe in the tropics.
- The semi-continuous belt of low pressure lying between the sub-tropical high-pressure systems in the Northern and Southern Hemispheres.
What is the ITCZ?
The ITCZ is a synoptic or weather feature within the equatorial trough. the ITCZ is where Northern and Southern hemisphere trade winds converge.
Describe the origin of the SPCZ? Include where the converging airflows originate from
- Formed by the divergent easterlies of the high west of South America and the tradewinds in the Australasian region.
- The semi-stationary anticyclonic system in the eastern Pacific. The easterlies on the equator side of this system turn north-easterly on approaching the Western Pacific; and
- The anticyclones originating and travelling eastward from the Australia/New Zealand region. The southeasterlies preceding these systems extend to the region where the SPCZ forms.
- Thus when the North-easterlies meet, they form a convergence zone with weather characteristics very similar to the ITCZ.
Where is the preferred location of the SPCZ?
- Identified from the eastern tip of Papua New Guinea, to slightly southeast of French Polynesia.
- Fluctuations in its intensity may bring cloudiness and rainfall down into Australia’s Northern Territory and Northern Queensland from time to time.
Where does the position of the SPCZ stretch to? What are the latitudes of the SPCZ?
Its position also stretches from an area of warm tropical water near Papua New Guinea at approximately 140ºE into sub-tropics near 30ºS 120ºW in the East, sometimes as far as the Cook Islands.
When is the SPCZ is more active, summer or winter?
Summer.
What is the SPCZ associated with regards to air masses?
Associated with the northeast passage of mid-latitude cold fronts when the cloud band of the latter merges with that of the convergence zone.
What weather is the SPCZ responsible for?
- Intense rainfall
- Large storms
- Tropical cyclones
What are the latitudes of the trade winds?
General outflow from the high-pressure belts at average latitudes 30ºN and 30ºS towards the equatorial trough produces a steady wind in the lower troposphere.
What is the vertical extent of the trade winds?
Approximately 8000 ft AMSL.
What direction are the trade winds in the Northern and Southern Hemisphere respectively?
- Northern Hemisphere is north-easterly.
- Southern Hemisphere is south-easterly.
Where do the trade winds converge?
Equatorial trough.
What happens as the trade winds travel further from the highs towards to the equatorial trough with regards to anticyclonic subsidence?
As the trade winds penetrate into increasingly warm surface conditions, the effect of this subsidence decreases.
What is the weather at the trade wind zone largely influenced by? What heights do these vary at?
Influenced by subsidence inversion, varying in height from 6000 to 8000 ft above sea level.
What is the weather at trade wind zone like below a subsidence inversion?
- Good visibility with varying amounts of cumulus with bases between 2000 and 3000 ft, and tops at around 8000 ft.
What will happen when trade winds cross the windward side of islands?
The amounts and limits of the varying amounts of cumulus with bases at 2000 and 3000 ft are prone to increase when trade winds cross the windward side of islands so that increased wind speeds and shower activity are likely in those locations.
What is the moisture content below the subsidence inversion like with regards to the trade winds?
What is the weather like above 8000 ft?
- Moisture content greater than above.
- Good visibility and generally dry air and clear skies above 8000 ft.
What happens to the subsidence inversion as they approach the vicinity of the equatorial trough.
- It weakens and rises in height.
- Increased instability from warm surfaces and, especially over ocean areas, great abundance of moisture, cause the formation and development of instability cloud which ultimately includes TCU’s with associated thunder, squall and shower activity.
What are the typical wind velocity and direction found above the trade wind zone?
- Winds above the trade winds are usually from the west, often light.
Describe the seasonal changes in the location of the trade winds and the effect seasons has on the wind direction.
- In the mid pacific, the trough never enters the southern hemisphere, meaning that the trade winds (south-easterlies of the southern hemisphere) cross the equator to flow to the trough.
- Similarly, during the southern winter, the equatorial trough is in the Northern Hemisphere north of Australia, so that trade winds in that region also cross the equator.
- In summertime in Aussie, the trough is south of the equator so that the Northern Hemisphere trade winds will have to do the crossing.
- When the south-east trade winds cross the equator en-route to the equatorial trough in the Northern Hemisphere, they will be subjected to the Coriolis force applicable to the Northern Hemisphere (veer to the right). Strength of the force is weak. Thus the trade winds blow initially towards the trough from the south and then to the southwest.
- The northeast trades from the Northern Hemisphere towards the trough near Northern Australia in summer will initially become northerly and ultimately north-west.