Definitions and names of meteorological phenomena of particular interest to Malawi

Chiperoni: Malawian name for influx of cool moist air from the south east, bringing overcast conditions with drizzle on windward slopes along the Northern lakeshore and in particular to many areas in the South of Malawi. This phenomenon can persist for up to a week but the usual duration is two to three days.

Mwera: Strong SE ly winds occur immediately before and occasionally during a Chiperoni outbreak. Lake Malawi is particularly affected by the Mwera due to the flat and obstruction free nature of its surface, allowing winds of considerable strength to develop. The onset of a Mwera can be quite sudden causing a rapid deterioration in the condition of the late itself. Amateur and weekend sailors are urged to pay particular attention to this phenomenon.

The Inter-Tropical Convergence Zone (ITCZ): The zone where air streams from both hemispheres converge oscillates with the sun from season to season and lies South of the equator, usually across or near Malawi between November and March. It is the main factor governing the increased convergence, which is responsible for Malawi s rainy season.

Technical meteorological terms, processes

High Pressure System, Anticyclone: An atmospheric pressure area where the highest pressure is in the centre, decreasing outwards. Winds flow around the high pressure in an anti-clockwise direction in the Southern Hemisphere. These systems are not regular in shape and occasionally bulge out to form Ridges of High Pressure.

Tropical Revolving Storms or Cyclones: Intense low pressure areas, which form over oceans such as the Indian Ocean during the Summer months, usually December to April. These disturbances have gale force winds blowing inwards and clockwise around the centre. Weather in association wit cyclone is usually violent with torrential rain. They occasionally move inland. Cyclones can cause severe flooding and disruption of public services, infrequently reaching disaster proportions.

Air Mass: A fairly homogenous mixture of air, in respect of temperature and humidity, covering a large area, which may extend over thousands of miles.

Fronts: In temperate climates air mass discontinuities are demarcated by Fronts . These are not featured on the Malawi weather map.

Surface convergence: An upwelling of excess air as air streams from different directions converge.

Convection: The over turning process which results when air which is warmer than its surroundings and therefore less dense rises, allowing colder air to take its place. This colder air may, in its turn, be heated by contact with ground causing the whole process to be repeated.

Clouds and their development: Clouds are formed when air is cooled sufficiently for invisible water vapour to be deposited out as visible water droplets. When these droplets are big enough they become heavier than their surroundings and fall as rain. The initial cooling is usually the result of air that has been forced to ascend by:

Convection
Forced ascent over higher ground or mountain ranges
Convergence of different air streams at the surface.

Low, Low Pressure Systems, Depression: opposite of high pressure system with the centre having the lowest pressure. Bulges and elongation in the circular pattern are known as Troughs of Low Pressure. The flow of wind around a depression is clockwise in the Southern Hemisphere.

Economic Benefits of Meteorological Information

There are many economic benefits that users of meteorological data and information can realise such as:-

Fuel saving in aircraft operation Increased crop yield by utilising correct planting dates. Saving lives by use of Mwera warnings over the lake. Saving lives and property by using tropical cyclone warnings. Food security through the use of rainy seasonal rainfall forecasts. Man-day savings in construction through use of rainy days information.

If you are interested in past weather and climate data and Information, you can obtain these only from the Meteorological Headquarters at Chileka at the address below:

The Director
Meteorological Services
P. O. Box 1808
BLANTYRE
Malawi
Tel: +265 1 822 014
Fax: +265 1 822 215
Email: metdept@metmalawi.com

Remember to remember: The weather is such a natural force t reckon with that it can not and should not be ignored in man s day to day operations because in any tussle between weather and man, the weather always wins!

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