Abstract
Dust mass concentrations have been measured daily at Miami, Florida, in the summer months, and biweekly throughout the remaining months, since 1974. The 43‐year record of dust mass concentrations indicate large daily, seasonal, and interannual variations, with most of the dust arriving within 5–8 episodes each summer. On average, dust arrives to Miami, Florida, 10 days after emission from North Africa, with measured concentrations depending on characteristics of the lower free‐tropospheric winds due to the vast travel distance. Daily dust mass concentrations from July and August, the months that contribute the most to the annual mean, are used to characterize the synoptic conditions most favorable for dust transport. Two key regions are linked with the highest daily dust mass concentrations above Miami: (i) easterly winds, averaged over 850–500 mb, over the Tropical West Atlantic [15–25°N, 45–80°W], and (ii) southerly winds, similarly averaged, over the Florida Peninsula [20–30°N,75–80°W]. Winds within these two regions are enhanced when the North Atlantic subtropical high is displaced south and zonally elongated, relocating the western edge over Florida. A dust‐transport‐efficiency index, based on the maximum potential for dust to arrive above Miami with limited loss to deposition or mixing, identifies high‐dust loading cases on the subseasonal scale. Monthly dust‐transport‐efficiency values agree well with the monthly dust trends over the 43‐year time span. While seasonal dust loadings have been decreasing over Florida in the past decade, the transport efficiency has been increasing, possibly due to trends in the North Atlantic subtropical high.
Plain Language Summary
Winds over the Saharan desert lift small dust particles into the air, which remain airborne for a few weeks, and slowly fall to the ground and ocean thousands of kilometers away. The dusty‐air is carried across the Atlantic Ocean to Miami, Florida, during the summer months, disrupting hurricane development, cloud features, and affecting human health. Dust is measured at the Rosenstiel School of Marine and Atmospheric Science each summer day since 1974 and twice weekly in other seasons. We compare days with the largest and smallest measured values of dust in July and August to identify wind regions that are most important for bringing dusty‐air, and what causes them to be stronger some years but not others. We located two regions of wind, which are critical for large amounts of dust to reach Miami: (i) east‐to‐west winds over the Tropical West Atlantic and (ii) south‐to‐north winds over the Florida Peninsula. By averaging the monthly wind speeds in the two critical regions, we can estimate the amount of dust which reaches Miami, Florida, each summer. This may improve future forecasts, warnings, and hurricane products.
Key Points
Strengthened easterlies over the West Tropical Atlantic and southerly winds over the Florida Peninsula linked to high Saharan dust at Miami
The North Atlantic subtropical high (NASH) is displaced southward and elongated to the west during these periods of favorable flow
Newly defined dust transport efficiency correlates well with increases in dust mass concentrations at subseasonal and seasonal time scales
