Rain dust

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The leaves of this Schefflera show the dust stains of a rain dust (near Paris, France) Pluie saharienne sur Schlefflera 2.jpg
The leaves of this Schefflera show the dust stains of a rain dust (near Paris, France)

Rain dust or snow dust, traditionally known as muddy rain, red rain, or coloured rain, is a variety of rain (or any other form of precipitation) which contains enough desert dust for the dust to be visible without using a microscope.

Rain liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then become heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for hydroelectric power plants and crop irrigation.

Mineral dust

Mineral dust is atmospheric aerosols originated from the suspension of minerals constituting the soil. It is composed of various oxides and carbonates. Human activities lead to 30% of the dust load in the atmosphere. The Sahara Desert is the major source of mineral dust, which subsequently spreads across the Mediterranean and Caribbean seas into northern South America, Central America, North America, and Europe. Additionally, it plays a significant role in the nutrient inflow to the Amazon rainforest. The Gobi Desert is another source of dust in the atmosphere, which affects eastern Asia and western North America.



The rain dust phenomenon was studied by Italian scientist Giuseppe Maria Giovene (1753–1837), who managed to correctly explain the phenomenon as early as 1803. On 7 March 1803, rain dust fell over Southern Italy's region Apulia. At that time, people believed that the rain was caused by the explosions of Italy's volcanoes Mount Vesuvius or Etna, or that it was due to the transport of matter coming from the sea floor and raised by vapor. Giuseppe Maria Giovene brilliantly managed to relate the phenomenon to the wind which occurred prior to the rain event, and he came to the conclusion that the sand had come from Africa and that it had been pushed by the wind coming from south-east. [1] [2]

Giuseppe Maria Giovene was an Italian archpriest, naturalist, agronomist, geologist, meteorologist, entomologist and ichthyologist. He is best known for his studies on the "nitrosity" of Pulo di Molfetta, which made him famous abroad, so as to be cited and appreciated by many Italian and foreign scholars, including Eberhard August Wilhelm von Zimmermann in a French publication.

Southern Italy Economic macroregion of Italy

Southern Italy or Mezzogiorno is a macroregion of Italy traditionally encompassing the territories of the former Kingdom of the two Sicilies, with the frequent addition of the island of Sardinia and, historically, some parts of Lazio as well.

Apulia Region of Italy

Apulia is a region in Southern Italy bordering the Adriatic Sea to the east, the Ionian Sea to the southeast, and the Strait of Otranto and Gulf of Taranto to the south. The region comprises 19,345 square kilometers (7,469 sq mi), and its population is about four million.


Rain dust is common in the Western and Southern Mediterranean, where the dust supply comes from the atmospheric depressions going through the northern part of North Africa. The main sources of desert dust reach the Iberian Peninsula and the Balearic Islands in the form of dust transported by wind or rain from the Sahara, Atlas Mountains in Morocco and Central Algeria. [3]

Iberian Peninsula Peninsula located in southwest Europe

The Iberian Peninsula, also known as Iberia, is located in the southwest corner of Europe. The peninsula is principally divided between Spain and Portugal, comprising most of their territory. It also includes Andorra, small areas of France, and the British overseas territory of Gibraltar. With an area of approximately 596,740 square kilometres (230,400 sq mi)), it is both the second largest European peninsula by area, after the Scandinavian Peninsula, and by population, after the Balkan Peninsula.

Balearic Islands Archipelago in the Mediterranean, autonomous community, and province of Spain

The Balearic Islands are an archipelago of Spain in the western Mediterranean Sea, near the eastern coast of the Iberian Peninsula.

Sahara desert in Africa

The Sahara is a desert located on the African continent. It is the largest hot desert in the world, and the third largest desert overall after Antarctica and the Arctic. Its area of 9,200,000 square kilometres (3,600,000 sq mi) is comparable to the area of China or the United States. The name 'Sahara' is derived from a dialectal Arabic word for "desert", ṣaḥra.

Mud rains are relatively frequent and had been increasing in early 1990s in the Mediterranean Basin. [4]

Mediterranean Basin region of lands around the Mediterranean Sea that have a Mediterranean climate

In biogeography, the Mediterranean Basin is the region of lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation.

It also occurs in arid desert regions of North America such as west Texas or Arizona. It occasionally happens in the grasslands as it did in Bexar County, Texas on March 18, 2008.

Desert Area of land where little precipitation occurs

A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one-third of the land surface of the world is arid or semi-arid. This includes much of the polar regions where little precipitation occurs and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location.

North America Continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere

North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere; it is also considered by some to be a northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, and to the southeast by South America and the Caribbean Sea.

Texas State of the United States of America

Texas is the second largest state in the United States by both area and population. Geographically located in the South Central region of the country, Texas shares borders with the U.S. states of Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the west, and the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas to the southwest, while the Gulf of Mexico is to the southeast.

It may also occur in some regions of Southern Italy (sand coming from North Africa), but it is a very rare phenomenon.

North Africa Northernmost region of Africa

North Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Morocco in the west, to Egypt's Suez Canal and the Red Sea in the east. Others have limited it to top North-Western countries like Algeria, Morocco, and Tunisia, a region that was known by the French during colonial times as “Afrique du Nord” and is known by all Arabs as the Maghreb. The most commonly accepted definition includes Algeria, Sudan, Morocco, Tunisia, Libya and Egypt, the 6 countries that shape the top North of the African continent. Meanwhile, “North Africa”, particularly when used in the term North Africa and the Middle East, often refers only to the countries of the Maghreb and Libya. Egypt, being also part of the Middle East, is often considered separately, due to being both North African and Middle Eastern at the same time.

Dust composition

The rain dust is very alkaline. [3] Some of the large particles contain mixtures of chemicals such as sulfate and sea salt (chiefly with sodium, chlorine and magnesium). Major minerals in order of decreasing abundance are: illite, quartz, smectite, palygorskite, kaolinite, calcite, dolomite and feldspars. [3] In Majorca a study finds that the size, by volume, 89% of the particles from rain dust fraction corresponded to silt (between 0.002 mm and 0.063 mm) and that there was virtually no clay sized particles (less than 0.29%). [5]


Blood/red rain

Rain dust is the most common cause of blood rain.

Red rain is however not always rain dust, see for example the Red rain in Kerala.

See also

Related Research Articles

Sahara Desert (ecoregion) ecoregion

The Sahara Desert ecoregion, as defined by the World Wide Fund for Nature (WWF), includes the hyper-arid center of the Sahara, between 18° and 30° N. It is one of several desert and xeric shrubland ecoregions that cover the northern portion of the African continent.

Geography of Mauritania

Mauritania, a country in the western region of the continent of Africa, is generally flat, its 1,030,700 square kilometres forming vast, arid plains broken by occasional ridges and clifflike outcroppings. It borders the North Atlantic Ocean, between Senegal and Western Sahara, Mali and Algeria. It is considered part of both the Sahel and the Maghreb. A series of scarps face southwest, longitudinally bisecting these plains in the center of the country. The scarps also separate a series of sandstone plateaus, the highest of which is the Adrar Plateau, reaching an elevation of 500 metres. Spring-fed oases lie at the foot of some of the scarps. Isolated peaks, often rich in minerals, rise above the plateaus; the smaller peaks are called guelbs and the larger ones kedias. The concentric Guelb er Richat is a prominent feature of the north-central region. Kediet ej Jill, near the city of Zouîrât, has an elevation of 1,000 metres and is the highest peak.

Dust storm meteorological phenomenon common in arid and semi-arid regions

A dust storm is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transported by saltation and suspension, a process that moves soil from one place and deposits it in another.

Libyan Desert North-eastern part of the Sahara comprising desert areas in Egypt, Libya and Sudan

The Libyan Desert forms the northern and eastern part of the Sahara Desert. It describes that part of the Sahara that lies within the present-day state of Libya; it also historically describes the desert to the south of Ancient Libya, a territory which lay to the east of the present-day state. The Libyan Desert is one of the driest, harshest and most remote parts of the Sahara, the world's largest hot desert. This extended desert country is barren, dry and rainless.

Sirocco wind

Sirocco, scirocco, jugo or, rarely, siroc is a Mediterranean wind that comes from the Sahara and can reach hurricane speeds in North Africa and Southern Europe, especially during the summer season.

Aeolian processes Processes due to wind activity

Aeolian processes, also spelled eolian or æolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth. Winds may erode, transport, and deposit materials and are effective agents in regions with sparse vegetation, a lack of soil moisture and a large supply of unconsolidated sediments. Although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts.

Desert pavement A desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size.

A desert pavement, also called reg, serir, gibber, or saï is a desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. They typically top alluvial fans. Desert varnish collects on the exposed surface rocks over time.

Red rain in Kerala

The Kerala red rain phenomenon was a blood rain event that occurred from 25 July to 23 September 2001, when heavy downpours of red-coloured rain fell sporadically on the southern Indian state of Kerala, staining clothes pink. Yellow, green, and black rain was also reported. Coloured rain was also reported in Kerala in 1896 and several times since, most recently in June 2012, and from 15 November 2012 to 27 December 2012 in eastern and north-central provinces of Sri Lanka.

Saharan Air Layer

The Saharan Air Layer (SAL) is an extremely hot, dry and sometimes dust-laden layer of the atmosphere that often overlies the cooler, more-humid surface air of the Atlantic Ocean. In the Sahara Desert region of North Africa, where it originates, it is the prevalent atmosphere, extending from the surface upwards several kilometers. As it drives, or is driven, out over the ocean, it is lifted above the denser marine air. This arrangement is an inversion where the temperature increases with height. The boundary between the SAL and the marine layer suppresses or "caps" any convection originating in the marine layer. Since it is dry air, the lapse rate within the SAL itself is steep, that is, the temperature falls rapidly with height.

Terra rossa (soil) limestone-derived soil type of the Mediterranean region

Terra rossa is a well-drained, reddish, clayey to silty clayey soil with neutral pH conditions and is typical of the Mediterranean region. The reddish color of terra rossa is the result of the preferential formation of hematite over goethite. This soil type typically occurs as a discontinuous layer that ranges from a few centimeters to several meters in thickness that covers limestone and dolomite bedrock in karst regions. The high internal drainage and neutral pH conditions of terra rossa are a result of the karstic nature of the underlying limestone and dolomite. Terra rossa is also found associated with Mediterranean climates and karst elsewhere in the world.

Antonio Randa Italian painter

Antonio Randa was an Italian painter of the classicist period, active in Ferrara, Modena, Rovigo, Florence, Comacchio and his native Bologna.

Winds of Provence

The Winds of Provence, the region of southeast France along the Mediterranean from the Alps to the mouth of the Rhone River, are an important feature of Provençal life, and each one has a traditional local name, in the Provençal language.

DESERTEC was a large-scale project supported by a foundation of the same name and the consortium Dii created in Germany as a limited liability company (GmbH). The project aimed at creating a global renewable energy plan based on the concept of harnessing sustainable power from sites where renewable sources of energy are more abundant and transferring it through high-voltage direct current transmission to consumption centers. All kinds of renewable energy sources are envisioned, but the sun-rich deserts of the world play a special role.

Blood rain or red rain is a phenomenon in which blood is perceived to fall from the sky in the form of rain. Cases have been recorded since Homer's Iliad, composed approximately 8th century BC, and are widespread. Before the 17th century it was generally believed that the rain was actually blood. Literature mirrors cult practice, in which the appearance of blood rain was considered a bad omen. It was used as a tool foreshadowing events, but while some of these may be literary devices, some occurrences are historic. There is now a scientific consensus that the blood rain phenomenon is caused by aerial spores of green microalgae Trentepohlia annulata.

Nitrary place of production of potassium nitrate or saltpetre

A nitrary is a place of production of potassium nitrate or saltpetre used primarily for the manufacture of gunpowder. The saltpetre occurs naturally in certain places like the "Caves of Salnitre" (Collbató) known since the Neolithic. In the "Cova del Rat Penat", guano deposited over thousands of years became saltpetre after being leached by the action of rainwater.

July 1968 England and Wales dust fall storms

The July 1968 England and Wales dust fall storms were the most severe dust fall storms in the British Isles for over 200 years. A layer of mineral dust blowing north from the Sahara met cold, wet air over the British Isles, resulting in thick, dense clouds and severe thunderstorms across most of England and Wales. These clouds completely blotted out the light in some areas and the rain and hail resulted in property damage and flooding, and at least four people were killed. During the storm, Leeming Bar in North Yorkshire saw 35.7 millimetres (1.41 in) of rain in under 10 minutes – a UK record until 2003.


  1. elogio-storico, pag. 20
  2. pioggia-rossa
  3. 1 2 3 Avila, Anna; Queralt-Mitjans, Ignasi; Alarcón, Marta (1997). "Mineralogical composition of African dust delivered by red rains over northeastern Spain". Journal of Geophysical Research. 102: 21977. Bibcode:1997JGR...10221977A. doi:10.1029/97JD00485.
  4. Sala, José Quereda; Cantos, Jorge Olcina; Chiva, Enrique Montón (1996). "Red dust rain within the Spanish Mediterranean area". Climatic Change. 32 (2): 215. Bibcode:1996ClCh...32..215S. doi:10.1007/BF00143711.
  5. Fornós, Joan J., Crespí, Damià; Fiol, Lluís (1997). "Aspectes mineralogics i texturals de la pols procedent de les pluges de 1ang a les IIles Balears: la seva importancia en alguns processos geologics recents". Boll. Soc. Hist. Nat. Balears. 40: 114–122.CS1 maint: Multiple names: authors list (link)
  6. Papastefanou, C; Manolopoulou, M; Stoulos, S; Ioannidou, A; Gerasopoulos, E (2001). "Coloured rain dust from Sahara Desert is still radioactive". Journal of Environmental Radioactivity. 55 (1): 109–112. doi:10.1016/S0265-931X(00)00182-X. PMID   11381550.