The Saharan Air Layer and the Fate of African Easterly Waves—NASA's AMMA Field Study of Tropical Cyclogenesis

Zipser, Edward J.; Twohy, Cynthia H.; Tsay, Si Chee; Thornhill, K. L.; Tanelli, Simone; Ross, Robert S.; Krishnamurti, T. N.; Ji, Qiang; Jenkins, Gregory S.; Ismail, Syed; Hsu, N. Christina; Hood, Robbie E.; Heymsfield, Gerald M.; Heymsfield, Andrew J.; Halverson, Jeffrey B.; Goodman, H. Michael; Ferrare, R. A.; Dunion, Jason; Douglas, Michael W.; Cifelli, Robert; Chen, Gao; Browell, Edward V.; Anderson, B. E.

doi:10.1175/2009bams2728.1

Cited by 126 publications

(150 citation statements)

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“…In addition, much of the aerosol STORER ET AL. [Zipser et al, 2009], similar to that modeled in Storer and van den Heever [2013]. Shown in Figure 1a is the frequency of occurrence of DCCs in the region.…”

Section: Methodsmentioning

confidence: 58%

“…This region of the east Atlantic was chosen due to the frequent dust events that occur off the west coast of Africa within the Saharan Air Layer (SAL) [Carlson and Prospero, 1972;Zipser et al, 2009]. In addition, much of the aerosol STORER ET AL.…”

Section: Methodsmentioning

confidence: 99%

“…Observations of aerosols in this region [e.g., Zipser et al, 2009] show that it is characterized largely by dust, often mixed with sulfate aerosols. Dust particles have been known to act as CCN, giant CCN (GCCN), and ice nuclei (IN) [DeMott et al, 2003;Twohy et al, 2009].…”

Section: 1002/2013jd020272mentioning

confidence: 99%

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Observations of aerosol‐induced convective invigoration in the tropical east Atlantic

2014

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Four years of CloudSat data have been analyzed over a region of the east Atlantic Ocean in order to examine the influence of aerosols on deep convection. The satellite data were combined with information about aerosols taken from the Global and Regional Earth-System Monitoring Using Satellite and In Situ Data model. Only those profiles fitting the definition of deep convective clouds were analyzed. Overall, the cloud center of gravity, cloud top, and rain top were all found to increase with increased aerosol loading. These effects were largely independent of the environment, and the differences between the cleanest and most polluted clouds sampled were found to be statistically significant. When examining an even smaller subset of deep convective clouds likely to be part of the convective core, similar trends were seen. These observations suggest that convective invigoration occurs with increased aerosol loading, leading to deeper, stronger storms in polluted environments.

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Section: Methodsmentioning

confidence: 58%

Section: Methodsmentioning

confidence: 99%

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Observations of aerosol‐induced convective invigoration in the tropical east Atlantic

2014

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“…The transition from dry to relatively moist conditions occurs on average in the 700-600-hPa layer, although considerable variability likely exists in individual SAL events. Although not described in this context, Lidar Atmospheric Sensing Experiment (LASE), rawinsondes, and dropsonde measurements obtained during the NASA African Monsoon Multidisciplinary Activities experiment in 2006 (Zipser et al 2009;Ismail et al 2010) suggest that this vertical structure of humidity is often found at the west coast and downstream of Africa over the eastern Atlantic as well.…”

Section: Datamentioning

confidence: 99%

Reevaluating the Role of the Saharan Air Layer in Atlantic Tropical Cyclogenesis and Evolution

Braun

2010

Monthly Weather Review

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The existence of the Saharan air layer (SAL), a layer of warm, dry, dusty air frequently present over the tropical Atlantic Ocean, has long been appreciated. The nature of its impacts on hurricanes remains unclear, with some researchers arguing that the SAL amplifies hurricane development and with others arguing that it inhibits it. The potential negative impacts of the SAL include 1) vertical wind shear associated with the African easterly jet; 2) warm air aloft, which increases thermodynamic stability at the base of the SAL; and 3) dry air, which produces cold downdrafts. Multiple NASA satellite datasets and NCEP global analyses are used to characterize the SAL's properties and evolution in relation to tropical cyclones and to evaluate these potential negative influences. The SAL is shown to occur in a large-scale environment that is already characteristically dry as a result of large-scale subsidence. Strong surface heating and deep dry convective mixing enhance the dryness at low levels (primarily below ;700 hPa), but moisten the air at midlevels. Therefore, mid-to-upper-level dryness is not generally a defining characteristic of the SAL, but is instead often a signature of subsidence. The results further show that storms generally form on the southern side of the jet, where the background cyclonic vorticity is high. Based upon its depiction in NCEP Global Forecast System meteorological analyses, the jet often helps to form the northern side of the storms and is present to equal extents for both strengthening and weakening storms, suggesting that jet-induced vertical wind shear may not be a frequent negative influence. Warm SAL air is confined to regions north of the jet and generally does not impact the tropical cyclone precipitation south of the jet.Composite analyses of the early stages of tropical cyclones occurring in association with the SAL support the inferences from the individual cases noted above. Furthermore, separate composites for strongly strengthening and for weakening storms show few substantial differences in the SAL characteristics between these two groups, suggesting that the SAL is not a determinant of whether a storm will intensify or weaken in the days after formation. Key differences between these cases are found mainly at upper levels where the flow over strengthening storms allows for an expansive outflow and produces little vertical shear, while for weakening storms, the shear is stronger and the outflow is significantly constrained.

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“…Recent years have seen several field campaigns aimed at understanding the science of tropical cyclone formation. These include the National Aeronautics and Space Administration (NASA) Tropical Cloud Systems and Processes (TCSP) experiment in 2005 (Halverson et al 2007), the NASA African Multi-Disciplinary Monsoon Analyses (NAMMA) project in 2006 (Zipser et al 2009), and the Tropical Cyclone Structure experiment in 2008 (TCS-08;Elsberry and Harr 2008). Adding the results of earlier efforts such as the Tropical Experiment in Mexico (TEXMEX; Bister and Emanuel 1997;Raymond et al 1998) and even serendipitous observations of the early intensification of Hurricane Ophelia in the Hurricane Rainband and Intensity Change Experiment (RAINEX; Houze et al 2006), and occasional observations from reconnaissance aircraft (Reasor et al 2005), we have a collection of studies that have sampled pieces of a large and complex scientific puzzle.…”

mentioning

confidence: 99%

The Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT) Experiment: Scientific Basis, New Analysis Tools, and Some First Results

Montgomery¹,

Davis²,

Dunkerton³

et al. 2012

Bull. Amer. Meteor. Soc.

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153

132

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The Saharan Air Layer and the Fate of African Easterly Waves—NASA's AMMA Field Study of Tropical Cyclogenesis

Cited by 126 publications

References 42 publications

Observations of aerosol‐induced convective invigoration in the tropical east Atlantic

Observations of aerosol‐induced convective invigoration in the tropical east Atlantic

Reevaluating the Role of the Saharan Air Layer in Atlantic Tropical Cyclogenesis and Evolution

The Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT) Experiment: Scientific Basis, New Analysis Tools, and Some First Results

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