There is an important research contribution that reports on a natural and human climate forcing that has a direct and indirect effect on tropical cyclones, as well as other climate effects such as radiative forcing. The paper is
Amato T. Evan and Sujoy Mukhopadhyay, 2010: African dust over the northern tropical Atlantic: 1955–2008. Journal of Applied Meteorology and Climatology 2010 ; e-View doi: 10.1175/2010JAMC2485.1
African dust results both from natural landscapes but also land that has been degraded by overgrazing as in the Sahel region of Africa.
The abstract reads
“African dust outbreaks are the result of complex interactions between the land, atmosphere, and oceans, and only recently has a large body of work began to emerge that aims to understand the controls on -and impacts of- African dust. At the same time, long-term records of dust outbreaks are either inferred from visibility data from weather stations, or confined to a few in-situ observational sites. Satellites provide the best opportunity for studying the large-scale characteristics of dust storms, but reliable records of dust are generally on the scale of a decade or less. Here we develop a simple model for using modern and historical data from meteorological satellites, in conjunction with a proxy record for atmospheric dust, to extend satellite-retrieved dust optical depth over the northern tropical Atlantic form 1955–2008. The resultant 54-year record of dust has a spatial resolution of 1° and a monthly temporal resolution. From analysis of the historical dust data, monthly tropical northern Atlantic dust cover is bimodal, has a strong annual cycle, peaked in the early 1980s, and shows minimums in dustiness during the beginning and end of our record. We use these dust optical depth estimates to calculate radiative forcing and heating rates from the surface through the top of the atmosphere over the last half-century. Radiative transfer simulations show a large net negative dust forcing from the surface through the top of the atmosphere, also with a distinct annual cycle, and mean tropical Atlantic monthly values of the surface forcing range from −3 to −9Wm−2. Since the surface forcing is roughly three-times larger in magnitude than the top of the atmosphere forcing, there is also a positive heating rate of the mid-troposphere by dust.”
“There is reason to believe that African dust outbreaks may both directly and indirectly impact Atlantic hurricane genesis and intensification. As such, a summertime forecast of Atlantic dust cover may be a useful aid in predicting seasonal hurricane activity. Here I present a qualitative forecast of Atlantic main development region (MDR) dust cover for the 2010 hurricane season (July–November). Based on persistence in dust, and Sahelian rainfall anomalies during the previous year, MDR dust cover during the 2010 hurricane season will be near-normal to one standard deviation below-average (relative to 1982–2009). This is not to say that one month will not show anomalously high or low dust values, or that particularly strong dust outbreaks (or prolonged periods of no dust) won’t occur, but that averaged over the hurricane season dustiness will be near to below average.
Along with this report I am making available online an updated data set of tropical northern Atlantic dust optical depth that spans the period of January 1982 through May 2010.
The report starts with the text
“There is a wealth of recent publications making the case for either direct or indirect influences of African dust outbreaks on Atlantic tropical cyclones. Here I refer the reader to the following papers for further reading on this topic: Dunion and Velden (2004), Dunion and Marron (2009), Evan et al. (2006a, 2008), Wong and Desser (2005), and Wong et al. (2009).”
This study continues to add to the important papers and reports that document that climate variability and change are dominated by regional climate forcings and feedbacks, NOT a global average surface temperature trend.