This essay provides an insight into the formation of tropical cyclones in the Southern Hemisphere, with examples of cyclones in the past and the damage that they have wrought
ASSIGNMENT COVER PAGE
University of Johannesburg
Department of Geography, Environmental Management and Energy Studies
ASSIGNMENT COVER PAGE
Title of assignment: South Indian Ocean Tropical Cyclone Season 2018/19
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, 1. Introduction
There are various environmental events that are present on Earth which stray from the norm as they
represent anomalies that can wreak violent havoc that causes damage to both nature and the human race.
One of the most common disasters in the atmosphere are tropical cyclones. Tropical cyclones are named
according to the alphabet letters in a specific season and have different terms around the world, for
example, in the Southern hemisphere they are Tropical cyclones, in the USA they are Hurricanes and in
Asia they are known as Typhoons (Christopherson & Birkeland, 2015). As per Oliver and Hidore
(2002:159) a tropical cyclone is a strong “vortex” which circulates in a clockwise direction within the
Southern hemisphere and anticlockwise in the Northern hemisphere. These cyclones are low-pressure
storms which use latent heat from their surrounding oceans to gain vitality which allows them to possess
energy comparable to that of more than 10 000 atomic bombs and can extend up to a number of hundred
kilometres with the eye possessing a diameter of up to 65 km thereby being present over 52 000 km2 (Oliver
and Hidore, 2002:159). The Southern Hemisphere, specifically around the South Indian Ocean has been
home to a number of life-shattering and disparaging tropical cyclones. This discursive will discuss the
history of cyclones in the East Coast of Southern Africa to provide background to the present where the
South Indian Ocean Cyclone 2018/2019 season will be discussed, furthermore, the changes and reasons
behind such change between the past and present cyclonic seasons will be investigated. This discursive will
then focus on Cyclone Idai including its development, path and effects.
Figure 1: Map showing the oceans of the world with emphasis on the Indian ocean (On the world map, n.d).
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, 2. Formation of tropical cyclones in the Southern Hemisphere
Tropical cyclones require a specific environment to form, they only form in areas where there is an oceanic
presence of warm water and warm air resulting in them only forming in the summer period in tropical regions of
the world such as the South East Coast of Southern Africa and neighbouring Mozambique Channel (Oliver and
Hidore, 2002). As supported by Oliver and Hidore (2002) Tropical cyclones can only form in a particular region
over tropical water bodies between 5° and 20° Latitude and peak of cyclonic activity occurs when oceans have
the highest sea temperature and when displacement of the convergence zone is highest. It is said that they base
their foundation on a distribution of low pressure in wind which undulates from unstable air masses and varying
local heating. Once a tropical cyclone forms, the wet air surrounding the area comes together towards a centre
which will become the eye of the storm (Oliver and Hidore, 2002). An energized tropical cyclone moving from
the ocean over the land will dissipate as it loses energy due to more friction with the surface (Oliver and Hidore,
2002).
Gray (1998:38) speaks of six specific elements that are considered in the formation of tropical cyclones
including the necessary Coriolis force having an effect in global wind systems which is why tropical cyclones
will not form around the equator lacking Coriolis force, a “low-level relative velocity” which is a specific range
of speed and direction of air movement, a reverse of “tropospheric vertical wind shear”, oceanic energy of more
than 27°C that runs deeper than 60 metres, a variation in similar “potential temperature between the surface and
500mb” and lastly relative humidity in the troposphere must be supportive. A major characteristic of tropical
cyclones is that the pressure of the atmosphere is almost proportional around the eye (the centre of the cyclone)
and the pressure may decrease up to an exceptional 650 millibars (Oliver and Hidore, 2002). Tropical cyclones
in the Southern Hemisphere track from east to west and tend to track more Northerly but can also bounce
between higher and lower altitudes as it gains and loses energy, this is due to the fact that air circulates from
areas of high pressure to areas of low pressure, therefore cyclones move towards the Equatorial Low pressure
region as air is flowing in that direction to balance the atmospheric circulations (Oliver and Hidore, 2002).
It is important to remember that tropical cyclones start out as tropical waves where there is slight disturbance for
sustained amounts of time, thereafter it turns into a “tropical disturbance” that has maximum winds of 34 knots,
if it is sustained and gathers more energy it develops into a “tropical storm” where it is named and has winds up
to 63 knots until it can develop into a “tropical cyclone” with winds from 110 km/h where it can further be
categorized as level one to four based on its wind speeds and damage (Christopherson & Birkeland, 2015:240).
Tropical cyclones can track in their journeys and be constantly upgraded or downgraded as they gain or lose
energy (Christopherson & Birkeland, 2015). The tropical cyclones studied in this discursive are positioned in the
South Indian Basin region of tropical cyclone occurrence (Oliver and Hidore, 2002).
3. History of the presence of cyclones in the East Coast of Southern Africa
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