Fig. 4
Observed dust responses to negative Sahel NDVI anomalies and corresponding dry soil anomalies during 1982–2011. a total dust emission (bars: climatology, referring to the left y axis; dots and open circles: significant (p < 0.1 based on Monte Carlo bootstrap test) and insignificant responses, respectively, referring to the right y axis). In a, labels on the x axis stand for 3-month seasons, e.g., JFM for January, February, and March. b spatial pattern of GEFA responses in dust emission (% climatology σNDVI −1, green-brown color), column dust concentration (kg m−2 σNDVI −1, stitching and hatching), column dust transport (kg m−1 per month σNDVI −1, vector), and regional dust frequency (defined in Methods section, fraction σNDVI −1, circles in blue-red color) in September-November. Only statistical significant (p < 0.1) responses are shown in b, according to the Monte Carlo bootstrap test. Open circles in b represent stations with insignificant responses in dust frequency
