Research ArticleCLIMATOLOGY

On the decadal scale correlation between African dust and Sahel rainfall: The role of Saharan heat low–forced winds

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Science Advances  09 Oct 2015:
Vol. 1, no. 9, e1500646
DOI: 10.1126/sciadv.1500646

Figures

  • Fig. 1 Seasonal (June to August) time series of Zhl (blue), precipitation (P, green), and τd (red).

    The monthly mean precipitation series is averaged over 5°W to 20°E, 10° to 20°N, and τd is averaged over 10° to 65° W and 0° to 30°N. The thin lines are the seasonal means, and the thick lines are the five-season smoothed time series (via a 1-4-7-4-1 filter).

  • Fig. 2 Climatology and regressed precipitation and winds.

    (A) Shown is a map of long-term mean dust emission (shading), seasonal mean precipitation (magenta contour lines, mm day−1), and seasonal mean 925-hPa climatological wind vectors (June to August). Dust emission rates are in nondimensional units of % of total annual mean of North Africa dust emission rates. The red circle indicates the location of the mean seasonal (June to August) position of the SHL. The brown boxes are the major dust hotspots of the Bodélé depression (14° to 24°E, 14° to 21°N), the depression in the lee of the Aïr and Adrar Mountains (2° to 10°E, 16° to 24°N), and the Mauritania and Western Sahara source region (12° to 2°W, 18° to 27°N, dashed lines). (B) Map of the coefficients of the regression of 925-hPa meridional and zonal winds (vectors and shading) and precipitation onto Zhl, for June to August and 1979 through 2012. Vectors are all unit length to indicate anomalous wind direction, and the shaded regions are the wind speed coefficients, where only coefficients statistically significant at the 90% level are shown.

  • Fig. 3 Wind speed histograms.

    (A to C) Histogram counts (per 0.2 m s−1) of 10-m wind speed from ERA-Interim reanalysis for the 300 strongest (red) and weakest (blue) phases of the SHL in the Bodélé Depression (A), a depression in the lee of the Aïr and Adrar Mountains (B), and the Mauritania and Western Sahara (C) in the summertime from 1979 through 2012. The mean values of the wind speed for the strong and weak SHL are statistically significantly different in (A), (B), and (C) based on the t score from a two-tailed t test. (D to F) Wind speed histogram differences for the warm minus cool SHL cases. The gray-shaded region represents wind speed threshold for dust emission. A qualitatively identical shift in the wind speed distribution is also observed during the month of May (not shown).

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