Scale-Dependent Transport of Saharan Dust by African Easterly Waves
The scale-dependent transport of Saharan dust aerosols by African easterly waves (AEWs) is examined analytically and numerically. The analytical analysis shows that the meridional and vertical wave transports of dust are modulated by the Doppler-shifted frequency, <inline-formula><math xmln...
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MDPI AG
2022-09-01
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| Online Access: | https://www.mdpi.com/2076-3263/12/9/337 |
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| author | Terrence R. Nathan Dustin F. P. Grogan |
| author_facet | Terrence R. Nathan Dustin F. P. Grogan |
| author_sort | Terrence R. Nathan |
| collection | DOAJ |
| description | The scale-dependent transport of Saharan dust aerosols by African easterly waves (AEWs) is examined analytically and numerically. The analytical analysis shows that the meridional and vertical wave transports of dust are modulated by the Doppler-shifted frequency, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>d</mi></msub></mrow></semantics></math></inline-formula>, and the wave growth rate, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>i</mi></msub></mrow></semantics></math></inline-formula>, both of which are functions of the zonal wave scale. The analytical analysis predicts that the AEW dust transports, which are driven by the Reynolds stresses acting on the mean dust gradients, are largest for the twin limits: <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>d</mi></msub><mo>→</mo><mn>0</mn></mrow></semantics></math></inline-formula>, which corresponds to flow near a critical surface, a <i>local</i> effect; and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>i</mi></msub><mo>→</mo><mn>0</mn></mrow></semantics></math></inline-formula>, which corresponds to the slowest growing waves, a <i>global</i> effect. The numerical analysis is carried out with the Weather Research and Forecasting (WRF) model, which is radiatively coupled to the dust field. The model simulations are based on an AEW spectrum consistent with observations. The simulations agree with the theoretical predictions: the slowest growing waves have the strongest transports, which are as much as ~40% larger than the transports of the fastest growing wave. Although the transports are highly scale-dependent, largely due to the scale dependence of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>i</mi></msub></mrow></semantics></math></inline-formula>, the location of the critical surface and thus the location of the maximum dust transports are not. |
| first_indexed | 2024-03-09T23:54:30Z |
| format | Article |
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| language | English |
| last_indexed | 2024-03-09T23:54:30Z |
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| spelling | doaj.art-5f3065846a424a08baefd534f7191d5f2023-11-23T16:27:01ZengMDPI AGGeosciences2076-32632022-09-0112933710.3390/geosciences12090337Scale-Dependent Transport of Saharan Dust by African Easterly WavesTerrence R. Nathan0Dustin F. P. Grogan1Atmospheric Science Program, Department of Land, Air, and Water Resources, University of California, Davis, CA 95616, USADepartment of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, NY 12222, USAThe scale-dependent transport of Saharan dust aerosols by African easterly waves (AEWs) is examined analytically and numerically. The analytical analysis shows that the meridional and vertical wave transports of dust are modulated by the Doppler-shifted frequency, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>d</mi></msub></mrow></semantics></math></inline-formula>, and the wave growth rate, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>i</mi></msub></mrow></semantics></math></inline-formula>, both of which are functions of the zonal wave scale. The analytical analysis predicts that the AEW dust transports, which are driven by the Reynolds stresses acting on the mean dust gradients, are largest for the twin limits: <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>d</mi></msub><mo>→</mo><mn>0</mn></mrow></semantics></math></inline-formula>, which corresponds to flow near a critical surface, a <i>local</i> effect; and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>i</mi></msub><mo>→</mo><mn>0</mn></mrow></semantics></math></inline-formula>, which corresponds to the slowest growing waves, a <i>global</i> effect. The numerical analysis is carried out with the Weather Research and Forecasting (WRF) model, which is radiatively coupled to the dust field. The model simulations are based on an AEW spectrum consistent with observations. The simulations agree with the theoretical predictions: the slowest growing waves have the strongest transports, which are as much as ~40% larger than the transports of the fastest growing wave. Although the transports are highly scale-dependent, largely due to the scale dependence of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>ω</mi><mi>i</mi></msub></mrow></semantics></math></inline-formula>, the location of the critical surface and thus the location of the maximum dust transports are not.https://www.mdpi.com/2076-3263/12/9/337African easterly wavesSaharan dust transportdust-dynamics interactions |
| spellingShingle | Terrence R. Nathan Dustin F. P. Grogan Scale-Dependent Transport of Saharan Dust by African Easterly Waves Geosciences African easterly waves Saharan dust transport dust-dynamics interactions |
| title | Scale-Dependent Transport of Saharan Dust by African Easterly Waves |
| title_full | Scale-Dependent Transport of Saharan Dust by African Easterly Waves |
| title_fullStr | Scale-Dependent Transport of Saharan Dust by African Easterly Waves |
| title_full_unstemmed | Scale-Dependent Transport of Saharan Dust by African Easterly Waves |
| title_short | Scale-Dependent Transport of Saharan Dust by African Easterly Waves |
| title_sort | scale dependent transport of saharan dust by african easterly waves |
| topic | African easterly waves Saharan dust transport dust-dynamics interactions |
| url | https://www.mdpi.com/2076-3263/12/9/337 |
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