The Impact of the Saharan Air Layer on Atlantic Tropical Cyclone Activity

Dunion, Jason; Velden, Christopher S.

doi:10.1175/bams-85-3-353

Cited by 552 publications

(569 citation statements)

References 14 publications

(18 reference statements)

Supporting

Mentioning

524

Contrasting

Unclassified

Order By: Relevance

“…Previous studies on the impacts of the Saharan air layer on tropical cyclone genesis and intensification have yielded mixed results, with some studies (Karyampudi and Carlson 1988;Karyampudi et al 1999;Karyampudi and Pierce 2002) suggesting that the SAL can have a positive influence on development and other studies (Dunion and Velden 2004;Jones et al 2007;Shu and Wu 2009) suggesting that the SAL may be a negative influence. Dunion and Velden (2004) described several ways by which the SAL can inhibit tropical cyclone growth, including increased vertical wind shear associated with 6 A problem with the Wu et al study, discovered by this author (who was a coauthor on the Wu et al paper) was that the AIRS moisture data had been assimilated as if the assigned height (the bottom of the layer) was the height of the midpoint of the moisture layer, resulting in the introduction of a dry bias.…”

Section: Discussionmentioning

confidence: 99%

“…Dunion and Velden (2004) described several ways by which the SAL can inhibit tropical cyclone growth, including increased vertical wind shear associated with 6 A problem with the Wu et al study, discovered by this author (who was a coauthor on the Wu et al paper) was that the AIRS moisture data had been assimilated as if the assigned height (the bottom of the layer) was the height of the midpoint of the moisture layer, resulting in the introduction of a dry bias.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

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

Braun

2010

Monthly Weather Review

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

Braun

2010

Monthly Weather Review

View full text Add to dashboard Cite

show abstract

“…An estimated 150 to 320 million tons of African dust are transported from Africa to the Atlantic Ocean every year [1,2]. Extensive seasonal dust variability occurs between June and October every year over West Africa and moves toward the tropical Atlantic.…”

Section: Introductionmentioning

confidence: 99%

“…Satellite data analysis and research of dust aerosol effects on hurricanes are comparatively new, it is still difficult to conclusively understand the impacts of dust on hurricane's intensity and lifetime. Although the detailed mechanisms linking dust amount to hurricane activity is still unclear, there is considerable evidence showing the suppression of hurricane development [2] by the dry and dust-laden Saharan Air Layer (SAL) [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

A Study of Dust Aerosols Impact on Hurricanes with Multi-Sensors Measurement from Space

Kamal¹

2012

TORMSJ

View full text Add to dashboard Cite

MODerate resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Thickness (AOT) and the Atmospheric Infrared Sounder (AIRS) atmospheric profiles (temperature and moisture) Level 2 products are studied to investigate dust aerosols impacts on hurricanes through spatial analysis. Spatial regions were selected based on two concentric circles (an annulus) and segmented by left and right regions of 180° each around the hurricanes center. Statistical relationships between MODIS AOT, AIRS temperature and percent relative humidity (RH) of the hurricanes Isabel (2003), Frances (2004), Katrina (2005) and Helene (2006) are presented. The variation of temperature and RH values represented in static-left, static-right, dynamic-left and dynamic-right for the 500 mb, 700 mb and 850 mb pressure levels are analyzed to determine the impacts of dust aerosols on temperature and RH. Average AOT was found highest in Helene (0.27) than Isabel (0.23), Frances (0.18) and Katrina (0.16). Negative impacts on the atmospheric moisture levels and positive on the temperature was found by dust aerosols. This study concludes that in 2006 dust dampened the force of hurricane Helene contributing towards extremely dryer atmosphere and inhibiting the conductive to intensify the hurricane.

show abstract

“…Scattering from aerosols can produce a diffuse component that lowers the contrast. Particularly in calima conditions, when the Saharan air layer, an elevated (1000−5500 m) layer of dry air and mineral dust originating from the Saharan desert, forms over large parts of the northern equatorial Atlantic (e.g., Dunion & Velden 2004). The polarizing effects from the atmosphere are visible in the blue sky but are small in direct sunlight.…”

Section: Atmosphere and Telescopementioning

confidence: 99%

CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter

Rodríguez

Löfdahl

Sütterlin

et al. 2014

A&A

171

View full text Add to dashboard Cite

The production of science-ready data from major solar telescopes requires expertise beyond that of the typical observer. This is a consequence of the increasing complexity of instruments and observing sequences, which require calibrations and corrections for instrumental and seeing effects that are not only difficult to measure, but are also coupled in ways that require careful analysis in the design of the correction procedures. Modern space-based telescopes have data-processing pipelines capable of routinely producing well-characterized data products. High resolution imaging spectropolarimeters at ground-based telescopes need similar data pipelines. We present new methods for flat-fielding spectropolarimetric data acquired with telecentric Fabry-Perot instruments and a new approach for accurate camera co-alignment for image restoration. We document a procedure that forms the basis of current stateof-the-art processing of data from the CRISP imaging spectropolarimeter at the Swedish 1 m Solar Telescope (SST). By collecting, implementing, and testing a suite of computer programs, we have defined a data reduction pipeline for this instrument. This pipeline, CRISPRED, streamlines the process of making science-ready data. It is implemented and operated in IDL, with time-consuming steps delegated to C. CRISPRED will also be the basis for the data pipeline of the forthcoming CHROMIS instrument.

show abstract

The Impact of the Saharan Air Layer on Atlantic Tropical Cyclone Activity

Cited by 552 publications

References 14 publications

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

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

A Study of Dust Aerosols Impact on Hurricanes with Multi-Sensors Measurement from Space

CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter

Contact Info

Product

Resources

About