The impact of dust aerosols on cyclone activity

With the recent cyclone in Mozambique and the huge floods in KZN it’s interesting to read this article on the impact that aerosols have on monsoon rainfall in India.  Could the same sort of thing be affecting the rainfall on the west coast of Africa?  And then also, do cyclones affect dust fallout?  Take a look at these articles below – for the full articles, please click on the links provided.

_______________________________ Geoscience

“The Indian summer monsoon is influenced by numerous factors, including aerosol-induced changes to clouds, surface and atmospheric heating, and atmospheric circulation. Most previous studies assessing the effect of aerosols on monsoon rainfall have focussed on the local impact of aerosols on precipitation on monthly to seasonal timescales. Here, we show that desert dust aerosol levels over the Arabian Sea, West Asia and the Arabian Peninsula are positively correlated with the intensity of the Indian summer monsoon, using satellite data and models; a lead–lag analysis indicates that dust and precipitation vary in concert over timescales of about a week. Our analysis of global climate model simulations indicates that by heating the atmosphere, dust aerosols induce large-scale convergence over North Africa and the Arabian Peninsula, increasing the flow of moisture over India within a week. According to these simulations, dust-induced heating of the atmosphere over North Africa and West Asia rapidly modulates monsoon rainfall over central India.”

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Image from - In this photo taken on Friday, March 15, 2019 and provided by the International Red Cross, an aerial view of the destruction of homes after Tropical Cyclone Idai, in Beira, Mozambique. Mozambique's President Filipe Nyusi says that more than 1,000 may have by killed by Cyclone Idai, which many say is the worst in more than 20 years. Speaking to state Radio Mozambique, Nyusi said Monday, March 18 that although the official death count is currently 84, he believes the toll will be more than 1,000. (Denis Onyodi/IFRC via AP)

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New evidence for a relationship between Atlantic tropical cyclone activity and African dust outbreaks Gate

“It is well known that Atlantic tropical cyclone activity varies strongly over time, and that summertime dust transport over the North Atlantic also varies from year to year, but any connection between tropical cyclone activity and atmospheric dust has been limited to a few case studies. Here we report new results that demonstrate a strong relationship between interannual variations in North Atlantic tropical cyclone activity and atmospheric dust cover as measured by satellite, for the years 1982 – 2005. While we cannot conclusively demonstrate a direct causal relationship, there appears to be robust link between tropical cyclone activity and dust transport over the Tropical Atlantic.

The recent upswing in Atlantic tropical cyclones(including both hurricanes and tropical storms) affectingNorth America has raised the awareness of their impact onsociety and the economy. Currently, there is a debatesurrounding the cause of this observed increase in cycloneactivity. Several recent studies have explored the relation-ship between long– term trends in tropical cyclone activity(either in terms of their number or intensity) and environ-mental factors that may or may not be influenced byglobal warming [Emanuel, 2005a, 2005b; Landsea, 2005;Trenberth, 2005; Webster e t al. , 2005]. Other studies,however, have concluded that different environmentalfactors – not necessarily related to global warming –control trends in cyclone activity [Goldenberg et al., 2001;Knutson and Tuleya, 2004].[3] In this paper, we explore another possible contributorto changing North Atlantic tropical cyclone activity: the role of atmospheric dust. This hypothesis was first suggested byDunion and Velden [2004], who showed that tropicalcyclone activity may be influenced by the presence of theSaharan Air Layer, which forms when a warm, well-mixed,dry and dusty layer over West Africa is advected over thelow-level moist air of the tropical North Atlantic [Carlsonand Prospero, 1972]. The Saharan Air Layer rides over themarine boundary layer and can be a significant feature ofthe atmosphere as it transits over the North Atlantic, oftenseen as far away as the Caribbean (7,000 km west of theSahara Desert) [Dunion and Velden, 2004]. The Saharan AirLayer’s longevity is likely enhanced by the persistenttemperature inversions that exist at its base and top: daytimethermal heating by dust entrained within the Saharan AirLayer tends to counter nighttime radiative cooling, thuskeeping the Saharan Air Layer relatively warm and stable asit traverses the North Atlantic [Prospero and Carlson,1972].”

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