By Steff Gaulter
Living in Qatar, we know the effects of a desert environment only too well, the sand and dust gets everywhere. In the UK, if you didn’t clean for a few weeks, you’d see that fluffy dust particles had collected on surfaces. In Qatar, it’s a gritty substance that collects, and often within a few days.
In Qatar we endure both the raging dust storms, which sandblast our faces and coat our hair in dust, as well as the inert dust that hangs over Doha on a still day, hampering the view. The particles in the air are a type of air pollution, and the dust can irritate our respiratory systems or lead to asthma attacks.
However, there are many more effects of a desert’s dusty environment, and some of them are surprisingly beneficial.
Certainly those people living in the Caribbean and the western USA should be grateful for the desert dust. Over the past few months, we’ve been hearing about typhoons and hurricanes which have been battering parts of Asia and western Mexico. Just last Sunday, Typhoon Phanfong slammed into Japan triggering flooding and landslides. However, whilst the Pacific is producing storm after storm, the Atlantic hurricane season has been surprisingly quiet. Only five storms have been strong enough to be awarded names so far this year, making it the quietest hurricane season since 1986. At least part of the reason for this has been due to the dust from the Sahara Desert.
Not surprisingly, the air above the Sahara is dry and dusty. However, it doesn’t just stay over the desert. Every few days, a blast of this hot dry air forces its way west. These plumes of dusty air can be enormous.
Spacemen on the International Space Station often report seeing widespread haze from the Sahara, which can travel right across the Atlantic Ocean. The dust is generally at quite high levels in the atmosphere, over 5,000ft (1,500m), but despite its height it still has a distinctive effect on storms.
As you may know, many of the hurricanes that batter the Caribbean develop from storms that originate over Africa. Summer is the time of year that the rains reach their northernmost point over Mali, Niger and Chad. Within the general rain band are vigorous storms, which track west. The thunderstorms rage over Africa, then start to drift across the Atlantic, and it is these pulses of torrential rain which can develop into hurricanes.
For a cluster of thunderstorms to develop into a tropical storm, the thunderstorms need to be moving over warm seas. The magic temperatures is 26C (79F); if the temperature of the surface of the sea is below this, then a tropical storm will not be able to form. A warm sea should also ensure there is plenty of moisture in the air, which is another important factor in storm development.
A final consideration is the strength of the winds in the atmosphere; they need to be consistent. If the winds at the top of the atmosphere are much stronger than those near the surface of the sea, then they will effectively push the storm over, and prevent it from becoming organised and powerful.
Between late spring and early autumn, the dust from the Sahara normally tracks north of the equator and towards the Caribbean and North America. This dusty blast effectively works against the storms. The dry air in the upper atmosphere inhibits cloud formation, and the strong winds within the Saharan air also disrupt any development.
For much of this hurricane season, dry air has been sinking over the Atlantic, suppressing any potential storms. If you have ever been on the receiving end of a tropical storm or a hurricane, then you will certainly be grateful for anything that stops them, even if it is endless quantities of dust.
Later in the year, in the northern hemisphere winter, the dust from the Sahara takes a more southerly route. Instead of tracking towards the Caribbean, it heads towards the Amazon rainforest, where again it has a very positive effect.
The plumes of dry air bring millions of tonnes of dust to the Amazon rainforest every year. The nutrient-rich particles take approximately a week to reach South America, but they help to keep the soil fertile. Peculiarly, over half of this dust comes from just one place; the Bodele Valley. This valley is situated in southern Chad, on the south of the Sahara.
It’s located between two mountain ranges, which effectively turn the valley into a wind tunnel. As the air hurtles through the valley, it picks up a seemingly endless supply of dust, and all of this is transported across the Atlantic. It’s estimated that in the northern hemisphere winter, the valley produces an incredible 700,000 tonnes of dust every single day.
All of this goes to show that whilst here in Qatar we may complain about dust and dust storms, elsewhere that opinion isn’t shared. In fact, on a global level, desert dust is highly beneficial.
