Description

Kalima (or Calima) is a weather phenomena characterised by a suspension of dust or sand particles in the air, typically originating from the Sahara Desert. It is a hot, dry, and hazy wind that blows from the south or southeast, often reaching the Canary Islands.

Dust storms carrying dust across the Atlantic Ocean from the Sahara, as seen from space February 2001. [Source: Wikicommons. Author: NASA/Goddard Space Flight Center.]

Causes

Extreme diurnal heating leads to instability in the lowest level of the atmosphere over the Sahara, warming and drying the air near the surface and cooling while humidifying the air near the top of the layer through convective mixing. Kalima occurs when strong winds, associated with the high pressure system over the Sahara, transport dust and sand across the Atlantic.

The dust creates a dry, yellowish-brown haze or fog, reducing visibility and sometimes turning the sky an orange or reddish colour.

Kalima events can last from a few hours to a few days.

Kalima is most prevalent in the winter months but can also occur in the summer.

Sometimes a rare small depression forming south-west of the Canary Islands can increase the wind speed and intensity of a Kalima event. Such storms and the rising warm and humid air can lift dust up to 15,000 feet above the Atlantic blanketing hundreds of thousands of square miles of the eastern Atlantic Ocean with a dense cloud of Saharan sand, sometimes reaching as far as the Carribean.

Flight safety considerations

• Reduced visibility: Significant reduction in visibility can lead to disruption of aviation operations and has led to airport closures in the Canary Islands.
• Crew, ground staff, and passenger health: Dust particles can irritate the eyes, skin, and respiratory system causing sneezing, coughing and worsening asthma symptoms.
• Increased temperature: May affect aircraft performance.
• Component damage: Depending on size and concentration, dust particles may cause malfunction or damage to aircraft systems as well as ground handling equipment.