NEW ARTICLE: The dune effect on sand-transporting winds on Mars

Sand ripples on Mars (Image: NASA/JPL-Caltech/University of Arizona)

Our latest article published in Nature Communications demonstrates that local dune topography exerts a strong influence on wind speed and direction above the surface of Mars. Ripple movement likely reflects steered wind direction for certain dune ridge shapes. These findings highlight the need to first model winds at high resolution before inferring regional wind patterns from ripple movement or dune orientations on the surface of Mars today.

 The full open access article is available here.

NEW ARTICLE

Patrick Hesp's and my latest collaboration  'Aeolian dynamics of beach scraped ridge and dyke structures'  has just been published in Coastal Engineering. Free access to the article, without registration or sign up, is available until May 5, 2015 so get clicking!

New Article!

Examples of wind flow steering over a foredune for three incident wind approaches

Chuffed to announce that my first article in collaboration with Patrick Hesp, Flow deflection over a foredune, is now available in press from Geomorphology. Patrick was the most cited author in my PhD thesis and its a real pleasure to be working with him here at Flinders. Here's to many more!

Sand dune migration in an arid coastal dune field

Maspalomas is a coastal dune field situated on the south coast of Gran Canaria. With an annual precipitation of less than 100 mm, the area is very arid with sparse vegetation. Predominant winds blow from the northeast, forcing the dunes to migrate toward the south west. Mapping of dune migration has found that those closest to the shoreline, move faster than those further inland.

Simulated wind speed 0.5 m above the surface of the study site. Vectors on the map represent wind speed and direction at 61 dune crests within the study area. 

To explore why dune migration is faster near the beach, a 3D computational fluid dynamics (CFD) simulation was applied over the surface of the dunes. The results found that although flow was faster on the taller, landward dunes, those dunes also created large zones of flow re-circulation which will cause sediment, transported from the windward slope and crest, to be deposited. Conversely wind in lee of the lower dunes created little to no flow reversal allowing sediment eroded from the dune to be transported further landward into the dune field.

Top image represents flow across a 640 m cross sectional profile of the study area. The middle image shows flow in lee of a large inland dune. note the large zone of flow separation and re-circulation. The bottom image is of a smaller dune close to the shoreline behind which flow slows, but remains attached.

This post is a summary of an article published by Jackson et al., 2013 in the Journal of Coastal Research. Please click the link below to view the full article:

Jackson, D.W.T., N., Cruz Avero, T.A.G., Smyth, L. Hernández Calvento (2013) 3D airflow modelling and dune migration patterns in an arid coastal environment, Journal of Coastal Research SI 65, 1301 - 1306

How do patterns of wind flow change with wind speed?

Complex blowout that wind flow was measured and simulated over. Each point denotes the location of a 3D ultrasonic anemometer

It is sometimes perceived that patterns of wind direction over dunes, including zones of flow reversal and acceleration, change with wind speed. A recent paper by Smyth et al., 2013 published in Aeolian Research found that that patterns of flow steering remained constant even during hurricane force winds.

Measured wind direction at 15 points 

Measurements made by 15 ultrasonic anemometers of wind flow at 1 m above the surface at 15 locations in a complex blowout during from fresh breeze to strong gale found that wind flow steering remained remarkably constant. A validated computational fluid dynamics (CFD) model was then used to simulate flow during hurricane force winds. Wind direction at the 15 points during hurricane force winds also did not vary from those at lower incident velocities.

Simulated wind direction in a blowout during fresh breeze to hurricane force winds

Full Article
Smyth, T.A.G., D.W.T., Jackson, J.A.G. Cooper (2013), Three dimensional airflow patterns within a coastal blowout during fresh breeze to hurricane force winds, Aeolian Research, 9, 111 - 123