The landlocked developing countries (LLDC) are developing countries that are landlocked. The economic and other disadvantages experienced by such countries makes the majority of landlocked countries the least developed countries (LDCs), with inhabitants of these countries occupying the bottom billion tier of the world's population in terms of poverty. Outside of Europe, there is not a single highly developed landlocked country as measured by the Human Development Index (HDI), and nine of the twelve countries with the lowest HDI scores are landlocked.
Landlocked European countries are exceptions in terms of development
outcomes due to their close integration with the regional European
market.
Landlocked countries that rely on transoceanic trade usually suffer a
cost of trade that is double that of their maritime neighbours. Landlocked countries experience economic growth 6% less than non-landlocked countries, holding other variables constant.
32 out of the world's 44 landlocked countries, including all the landlocked countries in Africa, Asia, and South America, have been classified as the Landlocked Developing Countries (LLDCs) by the United Nations. As of 2012, about 442.8 million people lived in these LLDCs.
The United Nations
has an Office of the High Representative for the Least Developed
Countries, Landlocked Developing Countries and Small Island Developing
States (UN-OHRLLS). It mainly holds the view that high transport costs
due to distance and terrain result in the erosion of competitive edge
for exports from landlocked countries.
In addition, it recognizes the constraints on landlocked countries to
be mainly physical, including lack of direct access to the sea,
isolation from world markets and high transit costs due to physical
distance.
It also attributes geographic remoteness as one of the most significant
reasons why developing landlocked nations cannot alleviate
themselves, while European landlocked cases are mostly developed
because of short distances to the sea through well-developed countries.
One other commonly cited factor is the administrative burdens
associated with border crossings as there is a heavy load of
bureaucratic procedures, paperwork, custom charges, and most
importantly, traffic delay due to border wait times, which affect
delivery contracts. Delays and inefficiency compound geographically, where a 2 to 3 week wait due to border customs between Uganda and Kenya makes it impossible to book ships ahead of time in Mombasa, furthering delivery contract delays.
Despite these explanations, it is also important to consider the
transit countries that neighbour LLDCs, from whose ports the goods of
LLDCs are exported.
Dependency problems
Although Adam Smith
and traditional thought hold that geography and transportation are the
culprits for keeping LLDCs from realizing development gains, Faye, Sachs
and Snow hold the argument that no matter the advancement of
infrastructure or lack of geographic distance to a port, landlocked
nations are still dependent on their neighbouring transit nations.
Outlying this specific relationship of dependency, Faye et al. insist
that though LLDCs vary across the board in terms of HDI index scores,
LLDCs almost uniformly straddle at the bottom of HDI rankings in terms
of region, suggesting a correlated dependency relationship of
development for landlocked countries with their respective regions.
In fact, HDI levels decrease as one moves inland along the major
transit route that runs from the coast of Kenya, across the country
before going through Uganda, Rwanda and then finally Burundi.
Just recently, it has been economically modeled that if the economic
size of a transit country is increased by just 1%, a subsequent increase
of at least 2% is experienced by the landlocked country, which shows
that there is hope for LLDCs if the conditions of their transit
neighbours are addressed.
In fact, some LLDCs are seeing the brighter side of such a
relationship, with the Central Asian nations geographic location between
three BRIC nations (China, Russia and India) hungry for the region's oil and mineral wealth serving to boost economic development.
The three major factors that LLDCs are dependent on their transit
neighbours are dependence on transit infrastructure, dependence on
political relations with neighbours, and dependence on internal peace
and stability within transit neighbours.
Burundi
Burundi
is shown in blue. Its possible export routes were: *dependent on
infrastructure of transit neighbour Tanzania (yellow), or *dependent on
political relations with transit neighbour Kenya (orange), or
*dependent on internal stability of transit neighbour Mozambique (red).
When all three routes were unavailable, Burundi had to rely on the port
of Durban in South Africa (brown).
Burundi
has relatively good internal road networks, but it cannot export its
goods using the most direct route to the sea since the inland
infrastructure of Tanzania is poorly connected to the port of Dar es Salaam. Thus Burundi relies on Kenya's port of Mombasa for export; but this route was severed briefly in the 1990s when political relations with Kenya deteriorated. Further, Burundi's exports could not pass through Mozambique around the same time due to the Mozambican civil war (1977-1992).
Thus, Burundi had to export its goods using a 4500 km route, crossing
several borders and changing transport modes, to reach the port of Durban in South Africa.
The mineral resource-rich countries of Central Asia and Mongolia
offer a unique set of landlocked cases to explore in more depth, as
these are nations where economic growth has grown exceptionally in
recent years. In Central Asia, oil and coal deposits have influenced development: Kazakhstan’s GDI per capita in purchasing power parity was five times greater than Kyrgyzstan's in 2009.
Despite substantial development growth, these nations are not on a
stable and destined path to being well developed, as the exploitation of
their natural resources translates into an overall low average income
and disparity of income, and because their limited deposits of resources
allow growth only in the short term, and most importantly because
dependence on unprocessed materials increases the risk of shocks due to
variations in market prices. And though it is widely conceived that free trade can permit faster economic growth, Mongolia is now subjected to a new geopolitical game about the traffic on its railway lines between China and Russia. Russian Railways
now effectively owns 50% of Mongolia's rail infrastructure, which could
mean more efficient modernization and the laying of new rail lines, but
in reality also translates into powerful leverage to pressure the
government of Mongolia to concede unfair terms for license grants of
coal, copper, and gold mines. Thus, it can be argued that these nations with extraordinary mineral wealth should pursue economic diversification. All of these nations possess education qualifications, as they are inheritors of the Soviet Union's
social education system. This implies that it is due to poor economic
policies that more than 40% of the labour force is bogged down in the
agricultural sector instead of being diverted into secondary or tertiary
economic activity.
Yet, it cannot be ignored that Mongolia benefits exceptionally from its
proximity to two giant BRIC nations, resulting in a rapid development
of railway ports along its borders, especially along the Chinese border,
as the Chinese seek to direct coking coal from Mongolia to China's
northwestern industrial core, and, as well as for transportation
southeast towards Japan and South Korea, resulting in revenue generation through the seaport of Tianjin.
Armenia
The
Republic of Armenia is a landlocked country having geographic
disadvantages and faces limitations on foreign policy options. It needs
to
transport its goods via coastal neighbors to access ports to participate
in international trade, to which Azerbaijan and Turkey are hostile and
deny its access. Therefore, Armenia mainly depends on the Georgian ports
of Batumi and Poti and the Georgian train system to participate in
international trade. Armenia also shares a small border with neighboring
Iran, through which it trades despite American sanctions. Armenia
remains heavily dependent on imports from and export of moderately
unsophisticated goods to Russia. While Russia stayed Armenia's dominant
trade partner, in 2020, trade with the EU accounted for around 18% of
Armenia's total trade. As of 2020, European Union is Armenia's third
biggest export market, with a 17% share in total Armenian exports, and
the second largest source of Armenian imports, with an 18.6% share in
total Armenian imports.
Nepal
Nepal
is another landlocked country with extreme dependency on its transit
neighbour India. India does not have poor relations with Nepal, nor does
it lack relevant transport infrastructure or internal stability.
However, there have been two cases of economic blockades imposed by the government of India on Nepal – the official 1989 blockade and the unofficial 2015 blockade
– both of which left the nation in severe economic crisis. In the
1970s, Nepal suffered from large commodity concentration and a high
geographic centralization in its export trade: over 98% of its exports
were to India, and 90% of its imports came from India. As a result of all this, Nepal had a poor trade bargaining position. In the 1950s, Nepal was forced to comply with India's external tariffs as well as the prices of India's exports.
This was problematic since the two countries have different levels of
development, resulting in greater gains for India which was larger, more
advanced and with more resources.
It was feared that a parasitic relationship might emerge, since India
had a head start in industrialization, and dominated Nepal in
manufacturing, which could reduce Nepal to being just a supplier of raw
materials.
Because of these problems, and Nepal's inability to develop its own
infant industries (as it could not compete with Indian manufactures)
treaties were drafted in 1960 and 1971, with amendments to the equal
tariffs conditions, and terms of trade have since progressed.
Almaty Ministerial Conference
In
August, 2003, the International Ministerial Conference of Landlocked
and Transit Developing Countries and Donor Countries on Transit
Transport Cooperation (Almaty Ministerial Conference) was held in Almaty,
Kazakhstan, setting the necessities of LLDCs in a universal document
whereas there were no coordinated efforts on the global scale to serve
the unique needs of LLDCs in the past.
Other than acknowledging the main forms of dependency that must be
addressed, it also acknowledged the additional dependency issue where
neighbouring transit countries are often observed to export the same
products as their landlocked neighbours.
One result of the conference was a direct call for donor countries to
step in to direct aid into setting up suitable infrastructure of transit
countries to alleviate the burden of supporting LLDCs in regions of
poor development in general. The general objectives of the Almaty Program of Action is as follows:
Reduce customs processes and fees to minimize costs and transport delays
Improve infrastructure with respect to existing preferences of local
transport modes, where road should be focused in Africa and rail in
South Asia
Implement preferences for landlocked countries’ commodities to boost their competitiveness in the international market
To establish relationships between donor countries with landlocked
and transit countries for technical, financial and policy improvements
Numerous accidents have occurred in the vicinity of thunderstorms due to
the density of clouds. It is often said that the turbulence can be
extreme enough inside a cumulonimbus to tear an aircraft into pieces,
and even strong enough to hold a skydiver. However, this kind of
accident is relatively rare. Moreover, the turbulence under a thunderstorm can be non-existent and is usually no more than moderate. Most thunderstorm-related crashes occur due to a stall
close to the ground when the pilot gets caught by surprise by a
thunderstorm-induced wind shift. Moreover, aircraft damage caused by
thunderstorms is rarely in the form of structural failure due to
turbulence but is typically less severe and the consequence of secondary
effects of thunderstorms (e.g., denting by hail or paint removal by
high-speed flight in torrential rain).
Thus, cumulonimbus
are known to be extremely dangerous to air traffic, and it is
recommended to avoid them as much as possible. Cumulonimbus can be
extremely insidious, and an inattentive pilot can end up in a very
dangerous situation while flying in apparently very calm air.
While there is a gradation with respect to thunderstorm severity,
there is little quantitative difference between a significant shower
generated by a cumulus congestus
and a small thunderstorm with a few thunderclaps associated with a
small cumulonimbus. For this reason, a glider pilot could exploit the
rising air under a thunderstorm without recognising the situation –
thinking instead that the rising air was due to a more benign variety of
cumulus. However, forecasting thunderstorm severity is an inexact
science; in numerous occasions, pilots got trapped by underestimating
the severity of a thunderstorm that suddenly strengthened.
General hazards to aircraft
Even
large airliners avoid crossing the path of a cumulonimbus. Two
dangerous effects of cumulonimbus have been put forward to explain the
crash of flight AF447 that sank into the sea on 31 May 2009 about 600 kilometres (370 mi) northeast of Brazil. It encountered a mesoscale convective system in the Intertropical Convergence Zone (known by sailors as the "doldrums"), where cumulonimbus rise to more than 15 kilometres (49,000 ft) in altitude.
However, the aircraft did not disintegrate in flight. A different
hypothesis was put forward and later confirmed: accumulation of ice on
the aircraft's pitot tubes.
The inconsistency between the airspeeds measured by the different
sensors is one of the causes of the accident according to the final
report.
The US FAA
recommends that aircraft (including gliders) stay at least 20 nautical
miles away from a severe thunderstorm, while a glider pilot could be
tempted to use the updraughts below and inside the cloud. There are two sorts of danger for this type of aircraft. One is related to the shear effects between updraughts and downdraughts inside the cloud – effects that can smash the glider. This shear creates a Kelvin-Helmholtz instability
that can generate extremely violent sub-vortices. The second danger is
more insidious: the strong updraughts below a supercell cumulonimbus can
cover a large area and contain little or no turbulence as explained
below. In this case, the glider can be sucked into the cloud, where the pilot can quickly lose visual reference to the ground, causing conditions to quickly become Instrument meteorological conditions (IMC), meaning that pilots are forced to fly by instruments alone, without visual reference of the ground or sky.
In these conditions, the aircraft (if not equipped for IMC flight and
flown by a pilot experienced in IMC flight) is likely to enter a graveyard spiral
and eventually break up by exceeding the wing load limit. In this
situation, the cause of the disintegration of the aircraft is not atmospheric turbulence
but is the inability of the pilot to control the aircraft following the
loss of visual reference to the ground. In the case of an instrument flight, cumulonimbus can catch a pilot by surprise when embedded in a more benign cloud mass. For example, nimbostratus can originate from the spreading of a cumulonimbus (nimbostratus cumulonimbogenitus), making the presence of active convective cells likely. Small private airplanes are generally not equipped with on-board weather radars; and during an IFR approach, they can be sent accidentally by air traffic control to non-obvious active cells.
Updraft characteristics
Figure 1 : Forward area of a severe cumulonimbus moving to the west. This area is precipitation-free and the site of widespread updrafts.
The updrafts under a cumulonimbus can be extremely laminar, extensive, and uniform, this is particularly true during the buildup of the thunderstorm. They can last more than one hour and correspond to a steady state of the cumulonimbus.
The updraft under the cloud is mostly due to buoyancy,
but there is also a large pressure difference between the base and the
top of the cumulonimbus (larger than would be found in this height range
outside the cloud) and local low-level mechanical lifting such as the
lifting generated by a downburst.
The two last phenomena can overcome a stable air zone close to the
surface by lifting cooler air parcels to a level where they are
eventually warmer than the surrounding air. This can happen if these
mechanical phenomena lift the parcel above the lifted condensation level (LCL), above which height the parcel's temperature Tp(z) decreases less with height (due to the release of latent heat and at approximately 6.5 K/km) than the surrounding air temperature Ts(z) decreases with height in the case of a conditionally unstable lapse rate aloft. In other words, the parcel can be lifted to a height where ,
where the former is the cooling rate of the parcel and the latter is
the ambient lapse rate. In these conditions, the rising parcel may
eventually become warmer than the surrounding air; in other words, there
may exist a level above which .
This scenario's conditionally unstable lapse rate aloft is relatively
common when thunderstorms exist. In effect, at low level, such air
parcels are sucked into the cloud as if by a vacuum cleaner. Soaring pilots refer to this near-base sucking as "cloud suck",
a phenomenon known to generally be more intense the taller the cumulus
cloud – and to thus be at maximum intensity with a cumulonimbus. Since
the dynamic updraft is wide, the updraft velocity varies little
laterally and thus the turbulence is minimised. So, it is said:
The observations reported by Marwitz (1973), Grandia and Marwitz (1975), and Ellrod and Marwitz (1976)
indicate that the updraft air entering the base of cumulonimbi is
smooth and relatively free of turbulence and remains so through a
significant depth of the WER.
In fact, Ellrod and Marwitz's paper
is more general. These authors state that in general, the buoyancy
beneath the cumulonimbus cloud base is often negative. This explains why
updrafts underneath the base of a cumulonimbus are often laminar. This phenomenon is well known by glider pilots. (see below). The phenomenon is enhanced under the weak echo region of a supercell thunderstorm that is extremely dangerous. At approximately 4 kilometres (13,000 ft) these smooth updrafts become suddenly very turbulent.
In general, updrafts reach their maximum intensity at 6
kilometres (20,000 ft) above the ground. At this altitude, a phase
change occurs where water droplets become ice crystals and therefore
release energy in the form of latent heat and thus the updraft strength
increases. Supercell thunderstorms or derechos
can have gigantic updrafts at this altitude, updrafts with speeds that
can exceed 40 metres per second (78 kn). Such an updraft speed
corresponds to the wind speed of a small hurricane. The speed can even exceed 50 metres per second (97 kn). The maximum number in the Beaufort scale is 12 ("hurricane force" wind) and is assigned to wind speeds of 64 knots or greater. If the Beaufort scale were extended, these updrafts would have a Beaufort number of 14 in the vertical direction. The turbulence is then extreme at this altitude.
Moreover, the diameters of the updraft columns vary between 2 km (air mass thunderstorm) and 10 km (supercell thunderstorm).
The height of the cumulonimbus base is extremely variable. It varies
from a few tens of meters above the ground to 4000 m above the ground.
In the latter case, the updrafts can originate either from the ground
(if the air is very dry – typical of deserts) or from aloft (when altocumulus castellanus degenerates into cumulonimbus). When the updraft originates from aloft, this is considered elevated convection.
Figure 2: Spreading of a downburst close to the ground.
Downbursts are dangerous for many reasons.
First, downdraughts under cumulonimbus can be severe and extensive. A
sailplane flying at 50 knots in a downdraught of 15 knots has an
approximate glide ratio of 3, meaning that it covers only about three
metres of ground for every metre it descends. Assuming that the glider
is at cloud base height at 2,000 metres (6,600 ft), if it remains in the
downdraught the entire time, it will only be able to glide 6 kilometres
(3.7 mi) before being forced to land – likely under difficult and
dangerous conditions. Even if the glider lands safely, it could be
destroyed later by a wind gust. So when a rain curtain shows a
downburst, it is of paramount importance to not land in this area.
Downdraughts of 50 knots are possible and can generate wind gusts of 60 knots or more.
Safely landing a light aircraft in these conditions can be virtually
impossible. Moreover, close to the ground, a glider or airplane pilot
can be caught by surprise by a sudden reversal of the wind direction and
transition from an upwind to a downwind situation. If the airspeed
becomes too low, the aircraft will stall
and may crash into the ground due to the altitude lost recovering from
the stall. As a consequence of famous instances of crashes of this
nature in the United States, a network of wind profilers and Terminal Doppler Weather Radars
was developed in the vicinity of airports to monitor this wind shear.
Based on FAA rules, every pilot must inquire about the wind speed and
direction before landing.
Compared to airliners, sailplanes fly at low airspeeds. The usual
approach speed of a sailplane is around 50 knots, but let's assume that
the pilot is extra "careful" and flies his approach at 65 knots. William
Cotton claims that the wind shear can be as high as 50 knots. In such a
case, if the shear direction is such that the airspeed is reduced by
the shear amount, this pilot's airspeed will drop to 15 knots, which is
well below his glider's stall speed (typically 35–40 knots). If this
airspeed drop occurs during the transition from the base leg to the final approach, the aircraft may enter into a spin from which there isn't enough altitude to recover. The exact quotation is the following:
Upon
encountering a downburst with say a 50 kt tailwind component, airspeed
can drop from say 65 kts to more like 15 kts. If the sailplane is making
a turn from baseleg to final, the pilot finds himself (herself) in one
of the deadliest situations a pilot can encounter, a "stall-spin"
situation with no chance to recover since the aircraft is close to the
ground on final approach.
So when the pilot encounters benign cumulonimbus, it may be a better choice to stay aloft and use the updraughts under the cumulus in front of the thunderstorm along the flanking line
(or even under the cumulonimbus itself in its laminar region) and wait
for the thunderstorm to dissipate instead of attempting a landing in the
presence of possible downbursts.
Flight inside cumulonimbus
Soaring
In some countries, sailplanes are permitted to fly inside clouds. For example, during the 1972 World Soaring Championship at Vršac, Yugoslavia, Helmut Reichmann attempted to use the violent updraughts associated with cumulonimbus.
Initially, he found an updraught of +8 m/s. After half a circle, he was
in a downdraught of −15 m/s. He had to land very shortly afterward. The
thunderstorm was in its mature stage. In another example, Terry Delore
got trapped in a severe thunderstorm. He entered a seemingly innocuous cumulus
at 2,000 feet (610 m). This cumulus evolved into a large cumulonimbus.
At first, the flight inside the cloud was turbulence-free. Then his
glider suddenly became uncontrollable. He was either inverted, in a
nosedive, or in a chandelle. The airbrakes became stuck open due to hailstones blocking the orifices. When he landed, the airfield
was still covered by hailstones. The wind gusts were between 30 and
40 knots. Everyone on the ground feared for the pilot's life. In the same book, the author narrates that an Italian instructor at Rieti had his students climb 10,000 metres (33,000 ft) inside cumulonimbus so that they get accustomed to them.
As mentioned above, a climb inside a cumulonimbus can be
initially very smooth (due to the negative buoyancy of the air parcel)
and suddenly become horribly turbulent. As an example, a glider pilot
found initially very laminar updraughts and got sucked into the cloud
where he encountered accelerations of 18 g and became unconscious.
Due to the phase change of water droplets (to ice), the cumulonimbus top is almost always turbulent.
The glider can become covered with ice, and the controls can freeze and
remain stuck. Many accidents of this kind have occurred. If the pilot
bails out and opens their parachute, they may be sucked upward (or at
least held aloft) as happened to William Rankin after ejecting from an F-8 fighter jet and falling into a cumulonimbus (within which his parachute opened).
A skydiver or paraglider pilot
under a cumulonimbus is exposed to a potentially deadly risk of being
rapidly sucked up to the top the cloud and being suffocated, struck by
lightning, or frozen. If they survive, they may suffer irreversible
brain damage due to lack of oxygen or require amputation as a
consequence of frostbite. German paraglider pilot Ewa Wiśnierska barely survived a climb of more than 9,000 metres (30,000 ft) inside a cumulonimbus.
Commercial aviation
Heavy transportation airplanes may occasionally have to cross a thunderstorm line associated with a cold front or a squall. They may not be able to overfly the cumulonimbus, because at 36,000 feet, the aircraft may be in or near what is known as the coffin corner
(stall speed is close to speed of sound), thus making it structurally
dangerous to climb higher. However, some cells can rise to 70,000 feet.
Another option would be to navigate around the cells. This is strongly
discouraged, however, because in the opening, new cells can grow very
rapidly and engulf the aircraft.
Whenever an aircraft moves to the west and crosses a thunderstorm line,
the pilot will first encounter a line of powerful and laminar
updraughts (that are not thermal but dynamic). The pilot should refrain
from pushing the stick to try to maintain a constant altitude (similar
to mountain waves),
because pushing the stick can cause the airspeed to increase to the
point of hitting the yellow arc (on the airspeed indicator). An airspeed
this high is not permissible in turbulent conditions and may lead to
break-up of the aircraft.
When the pilot exits the updraught zone, he will encounter very strong
turbulence due to the shear between rising and sinking air. If the
airspeed is too high at this point, the airplane will break apart. The
crash of Flight AF 447
is indirectly related to this situation: the pilot opted for the
shortest path while crossing the thunderstorm line associated with the Intertropical Convergence Zone, and the pitot tubes iced over. What followed is known.
On-board radars can be deceiving. Hail shafts generate weak radar
echoes, which means radar would guide the pilot there—but, they're
significantly more dangerous than cloudbursts.
Close to the ground, heavy rain (or snow at altitude) tends to dampen
turbulence (it is said that when rain comes, most of the danger is
gone). So another counter-intuitive recommendation is to fly toward the
zone of heavy precipitation or toward the darkest area of the thunderstorm line.
This recommendation contradicts the usual use of on-board radars to
avoid areas of strong precipitation, which is usually the best course of
action. There is no "miracle" solution, and the best option is to avoid
these thunderstorm systems by having enough fuel on board, thus
reducing the temptation to take a more dangerous route in the interest
of fuel savings.
Also, St. Elmo's fires
while flying inside cumulonimbus can burn out the on-board electronic
equipment and even pierce a wing by melting the metal skin.
Figure 3 : Picture of a supercell with its characteristicsFigure 4 : Picture of the forward area of a supercell that seems usable by a glider. It is made of small cumulonimbus and an arcus. This area is treacherous because the updraughts will be laminar.
The updraughts inside a cumulonimbus associated with a supercell thunderstorm can reach 45 metres per second (87 kn).This corresponds to the wind speed of a weak hurricane. Moreover, the turbulence inside a cloud can become extreme and break apart an aircraft. Thus, it is extremely dangerous to fly inside such a system.
The thunderstorm system can be divided into two zones in the
figure to the left: the precipitation-free zone, located on the left
where the airmass has a widespread up motion, and the precipitation
zone, on the right where the airmass is sinking. At the point where the
two zones meet, there is a wall cloud that could initiate tornadoes.
Moreover, even the cumulus congestus associated with a supercell
thunderstorm can be very dangerous. Tornadoes can be produced up to 36
kilometres (22 mi) from the main cell.
In the updraught area, the air has a negative buoyancy and is
sucked up by a low pressure zone at altitude. Turbulence is annihilated. In particular, in the forward area of the supercell, one can find a flanking line made of cumulus congestus or small cumulonimbus. The cloud base of the flanking line is higher than the base of the main cumulonimbus.
Since the updraught under these clouds (in the flanking line) is
mainly dynamic, the airmass being smooth and the cloud base higher, a glider pilot could be tempted to fly in this zone. However, conditions can rapidly become dangerous, since the wall cloud can generate a tornado
that will pulverise any aircraft. Moreover, since the rising air is
widespread, the glider pilot (especially if flying a low-speed,
low-performance glider like a paraglider) may be unable to escape and
may be sucked into the cloud up to its top. Thus, the FAA recommends
that aircraft should never be closer than 20 miles from severe
thunderstorms.
Other dangers pertaining to cumulonimbus
Lightning
Although it rarely happens, a glider can be struck by lightning. Metal sailplanes are Faraday cages
and thus should not be destroyed by a lightning strike. However,
gliders made of wood or fibreglass can be destroyed. Moreover, modern
sailplanes are filled with electronic devices that can be damaged by
lightning. Also, any winch launch is discouraged when a thunderstorm is
less than 20 kilometres (12 mi) away, because the air is electrified,
and the cable will act as a lightning rod.
Hail
Hail can
shred a sailplane canopy and seriously damage the wings and fuselage.
Hail is barely visible and can be encountered in the updraught zone
under the cloud. On 5 August 1977, an airplane pilot was taken by
surprise in the vicinity of Colorado Springs by a supercell thunderstorm
that produced 20 tornadoes. The pilot was flying in eerily calm air
(the updraught zone can be laminar) when he saw the sky transitioning
from pale grey to inky black. The pilot heard a loud sound that
reoccurred more and more frequently. Then a hailstone pierced the
windshield, rendering the pilot semi-unconscious. Eventually, the pilot
landed his shredded airplane in a field.
Tornadoes
An
EF5 tornado can generate ground winds of unbelievable speed; common
sense dictates that an aircraft should never be close to such a
meteorological phenomenon. Indeed the wind speed can reach 130 metres
per second (250 kn), and one can easily guess that the aircraft can be
torn into pieces in such conditions. However, airline transportation
aircraft have overflown tornadoes
by more than 8,000 feet (2,400 m) without damage. The fact that an
airliner does not get destroyed can be explained as follows: tornadoes
are violent phenomena only close to the ground and become weaker at
height. A glider dared to cross a weak tornado during a soaring contest
in Texas in 1967.
The cumulonimbus base was at 12,000 feet (3,700 m). The glider crossed
an extremely turbulent zone and ended up in a turbulence-free zone
inverted. The controls were not responding, and the pilot contemplated
abandoning the aircraft. After some time and a big fright, the controls
started to respond again, and the pilot was able to continue his flight.
Pilots in the vicinity did not notice anything.
On 6 October 1981 a Fokker aircraft hit a tornado which occurred
in a supercell near the town of Moerdijk in the Netherlands, all 17
occupants of the aircraft were killed.
An empirical criterion for tornado formation has been developed by Dan Sowa from Northwest Orient Airlines as follows: the cumulonimbus overshooting top must enter into the stratosphere by at least 10000 feet. This criterion is, however, incorrect and the Sonnac tornado
is a counter-example. It reached level EF2 while being generated by a
small cumulonimbus that did not attain 9,000 metres (30,000 ft).
Myths and truth about cumulonimbus
Figure 5 : Picture of a tornado in South Oklahoma City, Oklahoma shortly before it entered Moore
shot from a precipitation-free sunlit area. An absent-minded glider
pilot would probably have found smooth and moderate updraughts in this
sunlit zone.
Conventional wisdom
As a result of a faulty generalisation, it is very often incorrectly said that cumulonimbus and the updraughts under them are always turbulent. This fallacy
originates from the fact that cumulonimbus are actually extremely
turbulent at high altitude, and therefore, one might falsely deduce that
cumulonimbus are turbulent at all altitudes. Reliable studies
and glider pilots' experience have demonstrated that updraughts under
cumulonimbus were generally smooth. As seen above, updraughts under a
cumulonimbus are often dynamic and thus will be very smooth. The phenomenon is enhanced under the weak echo region of a supercell thunderstorm that is extremely dangerous.
However, this phenomenon is little known in the aviation world. Thus, a
widespread view in the aeronautical community is that cumulonimbus are
always associated with very strong turbulence (at all altitudes) and severe thunderstorms. For example, Gil Roy, in a book endorsed by the fr:Fédération française de vol à voile, claims that:
Les cumulo-nimbus [sic] sont le
siège de très violents orages. La partie avant, baptisée " front d'orage
" est le théâtre de très fortes turbulences mais aussi de puissantes
ascendances. (Translation:
The cumulo-nimbus [sic] are always the seat of very violent
thunderstorms. The forward area called thunderstorm front is the site of
very strong turbulence but also of powerful updraughts.)
Also, the author talks about cumulo-nimbus [sic] of gigantic size that can reach a height of several thousand metres. While the word "several" isn't very precise, a thickness of 8000 metres is fairly typical for a cumulonimbus,
with some as thick as 20000 metres or more. Moreover, the majority of
cumulonimbus are associated with weak pulse thunderstorms or even simple
showers without electric phenomena.
The reference to the thunderstorm front corresponds to the outflow boundary associated with downbursts that are indeed very dangerous and are the site of vortices associated with the Kelvin-Helmholtz instability
at the junction between updraughts and downdraughts. However, in front
of the thunderstorm, updraughts are generally laminar due to the
negative buoyancy of air parcels (see above).
Also, the LUXORION web site states:
Les cumulonimbus provoquent
toujours une turbulence sévère [...] Elle peut être rencontrée dans les
basses couches et devancer le cumulonimbus de 10 à 25 km. (Translation:
The cumulonimbus always generate a severe turbulence [...]. It can be
encountered in the lower layers and get ahead of the cumulonimbus by 10
to 25 km.)
Such a claim is too broad and again contradicts the fact that
updraughts in front of a thunderstorm are often laminar. However, it is
true that the upper layers are almost always turbulent. However, in most
cases, the aforesaid turbulence is not extreme. Along the same lines,
Didier Morieux states:
Le cumulonimbus [...] est aussi
le siège d'ascendances et de descendances pouvant atteindre des vitesses
de 15 à 20 m/s donnant lieu à une turbulence considérable, susceptible
de mettre en péril la structure des avions les plus solides.(Translation:
The cumulonimbus is also the site of updraughts and downdraughts of
speeds of 15 to 20 m/s generating considerable turbulence, likely to
imperil the structure of most robust airplanes.)
Dennis Pagen is even more explicit. He states:
All the updrafts and downdrafts
in a thunderstorm create considerable turbulence due to shear. All we
have to do is think of the velocities involved and you can imagine the
severity of the turbulence. Thunderstorm turbulence can (and has) tear
apart airplanes.
The International cloud atlas soothes these claims: it simply states that "la turbulence is often very strong " below the cloud.
Serious hazard to glider pilots
A
glider pilot convinced that cumulonimbus are always violent risks
getting a nasty surprise. If he flies under the flanking line of a supercell thunderstorm
and finds that the air is very smooth and updraughts are moderate, he
may falsely infer that he is safe and not under a cumulonimbus; since he
believes cumulonimbus are always turbulent. He may thus not realise
when he is under a secondary cumulonimbus that can suck him inside the
cloud, and he may encounter a wall cloud that could generate a tornado that could disintegrate his fragile skiff as shown in Figure 5. Dominique Musto cautions paraglider
pilots (that might otherwise be swayed by the above myth) against the
false sensation of safety in a region of extended updraughts that are
rather weak as follows:
Pourtant malgré un ciel sombre et l'absence de soleil, les ascendances sont douces et généralisées dans tout le secteur. Quelque chose cloche ! Si nous ne réagissons pas très vite pour descendre, une main invisible risque de nous happer et de nous jeter en enfer! (Translation: However, notwithstanding a dark sky and lack of sunlight, the updraughts are smooth and extended in the entire area. Something is wrong. If we do not react quickly and descend, an invisible hand is likely to grab us and throw us into hell!)
This quotation summarises in three sentences the often-insidious
dangers associated with cumulonimbus, dangers that are exacerbated for
paraglider pilots, as German paraglider pilot Ewa Wiśnierska
experienced. She survived climbing above 9,000 metres (30,000 ft)
inside a cumulonimbus. A nearby fellow pilot caught in the same weather
event wasn't so fortunate.
As well, in 2014, the 66 years old general Paolo Antoniazzi died
after its paraglider got sucked into a cumulonimbus up to the altitude
of 9,300 metres (30,500 ft).
Forerunners of a thunderstorm
The
above quotation puts informally the harbingers of a thunderstorm. So a
cumulonimbus acts as an enormous thermal machine that sucks up the air
in the front (left side of Figure 3) and violently throws it out in the
back through downbursts
(right side of Figure 3). Consequently, a broad area of updraughts will
be located in front of the thunderstorm. Typically, in a humid airmass,
the updraughts will be on the order of 1 m/s; and in a dry air mass,
they will be on the order of 2 to 3 m/s. Therefore, when a glider pilot is in an area where "updraughts are everywhere" and he is close to large clouds (that can be cumulus congestus), he is likely in the vicinity of a building thunderstorm.
Associated gravity waves
The downbursts associated with cumulonimbus can generate gravity waves far way from thunderstorms.
These gravity waves can be felt up to 50 kilometres (31 mi) away and in
some conditions several hundreds of kilometres away. A severe
thunderstorm generating these gravity waves located at more than 40
kilometres (25 mi) away (according to Federal Aviation Administration
recommendations) should not affect the safety of aircraft this far from
the thunderstorm. These gravity waves can be modelled in the same
manner as mountain waves and can be usable by a glider pilot.
Utilising cumulonimbus in cross-country flight or other
Exploitation of "small" cumulonimbus
Small
cumulonimbus can relatively safely be exploited by experienced glider
pilots. They generate moderate updraughts that are generally laminar. Thus, pulse-like summer thunderstorms can be used during cross-country flights,
since the glider will move away from the cumulonimbus after having (in
theory) climbed up to 500 feet below the cloud base (the maximum
permissible height in the United States) and the passage of the glider
in the proximity of the thunderstorm will be short. For example, during
an official contest of the Soaring Society of America, pilots openly played with the cumulonimbus (and even with the updraughts contiguous to downbursts) and boasted about it.
However, a rule of thumb says that the distance between two thermals is
equal to three times the height of the cloud. Consequently, a
cumulonimbus that is 13 km thick will eliminate any convective activity
over a radius of approximately 40 km. Most gliders cannot perform such
long glides, and therefore, an encounter with a pulse-like thunderstorm
in a glider will often be followed soon by the end of the flight.
Shear exploitation in the vicinity of a downburst
Figure 3.22 from this reference shows the presence of a rotor outside a downburst.
A more-than-foolhardy pilot could easily locate this updraught and
exploit it. However, this photograph will dissuade any sensible pilot
from using such monstrosities. Downbursts are the most significant
hazard pertaining to thunderstorms. Moreover, if for any reason the
pilot must land (hail storm or other), he will have to cross the downburst
immediately above him and there will be a greatly increased chance of
crashing – due to the unpredictable decrease of the airspeed. Moreover,
if the glider transitions from the updraught to the downdraught, severe
turbulence will occur due to the Kelvin-Helmholtz instability in the shear area. However, pilots have nonetheless exploited such updraughts.
Exploitation of flanking lines
Reckless pilots have exploited squalls by flying in front of thunderstorm systems as if flying along a ridge. The pilot really must land at an airport and put the glider in a hangar; the squall line will catch him again soon and imperil the glider if it is not protected. Dennis Pagen performed a similar flight in front of a supercell cumulonimbus during the Preliminaries of the hang glider 1990 World championship in Brazil
where he was able to fly 35 km at high speed without a turn. Pagen
acknowledges that his achievement was very risky, since hang gliders
(and even more so paragliders) are significantly slower than sailplanes and can much more easily be sucked inside the cloud.
Conclusion
The
only cumulonimbus clouds that could be usable by a glider pilot,
subject to all necessary reservations, might be isolated small
cumulonimbus or at a pinch the flanking lines associated with strong
thunderstorms. However, examples above show that a seemingly innocuous
cloud can rapidly become very dangerous. Squalls and supercell thunderstorms are definitely deadly hazards to uninformed pilots. Based on visual flight
rules, flights in pre-storm areas must be visual; the pilots must be
able to watch the evolution of a thundercloud and take the necessary
actions of avoidance or to quickly land when appropriate.
The above examples demonstrate that the different phenomena
associated with cumulonimbus can jeopardise any type of aircraft and its
occupants when the pilot flies in the vicinity and especially inside a
thundercloud. An airplane pilot should never come near a cumulonimbus.
The unit cell of rutile,
an important oxide of titanium. Ti(IV) centers are grey; oxygen centers
are red. Notice that oxygen forms three bonds to titanium and titanium
forms six bonds to oxygen.
Oxides are extraordinarily diverse in terms of stoichiometries
(the measurable relationship between reactants and chemical equations
of an equation or reaction) and in terms of the structures of each
stoichiometry. Most elements form oxides of more than one stoichiometry.
A well known example is carbon monoxide and carbon dioxide. This applies to binary
oxides, that is, compounds containing only oxide and another element.
Far more common than binary oxides are oxides of more complex
stoichiometries. Such complexity can arise by the introduction of other
cations (a positively charged ion, i.e. one that would be attracted to
the cathode in electrolysis) or other anions (a negatively charged ion).
Iron silicate, Fe2SiO4, the mineral fayalite,
is one of many examples of a ternary oxide. For many metal oxides, the
possibilities of polymorphism and nonstoichiometry exist as well.
The commercially important dioxides of titanium exists in three
distinct structures, for example. Many metal oxides exist in various
nonstoichiometric states. Many molecular oxides exist with diverse
ligands as well.
For simplicity sake, most of this article focuses on binary oxides.
Formation
Oxides
are associated with all elements except a few noble gases. The pathways
for the formation of this diverse family of compounds are
correspondingly numerous.
Metal oxides
Many
metal oxides arise by decomposition of other metal compounds, e.g.
carbonates, hydroxides, and nitrates. In the making of calcium oxide,
calcium carbonate (limestone) breaks down upon heating, releasing carbon
dioxide:
The reaction of elements with oxygen in air is a key step in corrosion
relevant to the commercial use of iron especially. Almost all elements
form oxides upon heating with oxygen atmosphere. For example, zinc
powder will burn in air to give zinc oxide:
The production of metals from ores often involves the production of
oxides by roasting (heating) metal sulfide minerals in air. In this way,
MoS2 (molybdenite) is converted to molybdenum trioxide, the precursor to virtually all molybdenum compounds:
Noble metals (such as gold and platinum) are prized because they resist direct chemical combination with oxygen.
Non-metal oxides
Important and prevalent nonmetal oxides are carbon dioxide and carbon monoxide.
These species form upon full or partial oxidation of carbon or
hydrocarbons. With a deficiency of oxygen, the monoxide is produced:
With excess oxygen, the dioxide is the product, the pathway proceeds by the intermediacy of carbon monoxide:
Elemental nitrogen (N2) is difficult to convert to oxides, but the combustion of ammonia gives nitric oxide, which further reacts with oxygen:
These reactions are practiced in the production of nitric acid, a commodity chemical.
The chemical produced on the largest scale industrially is sulfuric acid. It is produced by the oxidation of sulfur to sulfur dioxide, which is separately oxidized to sulfur trioxide:
Finally the trioxide is converted to sulfuric acid by a hydration reaction:
Structure
Oxides have a range of structures, from individual molecules to polymeric and crystalline
structures. At standard conditions, oxides may range from solids to
gases. Solid oxides of metals usually have polymeric structures at
ambient conditions.
Molecular oxides
Some important gaseous oxides
Carbon dioxide is the main product of fossil fuel combustion.
Carbon monoxide is the product of the incomplete combustion of carbon-based fuels and a precursor to many useful chemicals.
Nitrogen dioxide is a problematic pollutant from internal combustion engines.
Nitrous oxide ("laughing gas") is a potent greenhouse gas produced by soil bacteria.
Although most metal oxides are crystalline solids, some oxides are molecules. Examples of molecular oxides are carbon dioxide and carbon monoxide. All simple oxides of nitrogen are molecular, e.g., NO, N2O, NO2 and N2O4. Phosphorus pentoxide is a more complex molecular oxide with a deceptive name, the real formula being P4O10. Tetroxides are rare, with a few more common examples being iridium tetroxide, ruthenium tetroxide, osmium tetroxide, and xenon tetroxide.
Reduction of metal oxide to the metal is practiced on a large scale
in the production of some metals. Many metal oxides convert to metals
simply by heating, (see Thermal decomposition). For example, silver oxide decomposes at 200 °C:
Most often, however, metals oxides are reduced by a chemical reagent.
A common and cheap reducing agent is carbon in the form of coke. The most prominent example is that of iron ore smelting. Many reactions are involved, but the simplified equation is usually shown as:
Some metal oxides dissolve in the presence of reducing agents, which can include organic compounds. Reductive dissolution of ferric oxides is integral to geochemical phenomena such as the iron cycle.
Hydrolysis and dissolution
Because
the M-O bonds are typically strong, metal oxides tend to be insoluble
in solvents, though they may be attacked by aqueous acids and bases.
Dissolution of oxides often gives oxyanions. Adding aqueous base to P4O10 gives various phosphates. Adding aqueous base to MoO3 gives polyoxometalates. Oxycations are rarer, some examples being nitrosonium (NO+), vanadyl (VO2+), and uranyl (UO2+2). Of course many compounds are known with both oxides and other groups. In organic chemistry, these include ketones and many related carbonyl compounds. For the transition metals, many oxo complexes are known as well as oxyhalides.
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