Mineral dust over west and central Sahel: Seasonal patterns of dry and wet deposition fluxes from a pluriannual sampling (2006–2012)

Abstract

Total and wet mineral dust deposition has been monitored since 2006 at three Sahelian stations in Senegal, Mali, and Niger, respectively at the weekly and the event time scale. Average annual deposited mass fluxes range from 75 to 183 g m−2 yr−1, from west to east. Deposition fluxes exhibit a clear seasonal cycle in Mali and Niger. High wet deposition fluxes result from an optimum phasing between dust concentration and precipitation: the maximum occurring at the beginning of the wet season, after the maximum of dust concentration and before the precipitation maximum. The contribution of wet to total deposition varies from 67% in Mali to 8% in Senegal. It is the main factor of variability of the deposition fluxes from year to year and at the seasonal scale in Niger and Mali. Wet deposition fluxes in Mali and Niger are mainly due to the wash out of dust emitted by convective systems. In Senegal, the deposition fluxes are lower and dominated by dry deposition (92% of the annual deposition flux). This is due to the low occurrence of convective systems producing local dust emissions and intense wet deposition. The dry deposition fluxes are primarily driven by the variability of the dust concentration. The dry deposition velocities derived from our measurements are consistent with those estimated by theoretical models. Scavenging ratios computed from the measured wet deposition fluxes, dust concentrations, and precipitation are anticorrelated with precipitation amounts. This suggests that most of the atmospheric dust is scavenged at the very beginning of the precipitation events.

Dust Uplift Potential in the Central Sahel: An Analysis Based on 10 years of Meteorological Measurements at High Temporal Resolution

“…We observe that for both sites, there is almost no differences in the annual trend of the cumulative rainfall, number, and duration of rain events. This is consistent with the observations reported by Marticorena et al () who have shown that in this region the cumulative rainfall and the duration of the rain events are well correlated. On average over 10 years, the rainy season starts about 1 week earlier and ends 1 week later in Cinzana (1 April and 1 November on average) than in Banizoumbou.…”

Impact of Agropastoral Management on Wind Erosion in Sahelian Croplands

“…The field is cultivated by local farmers following their usual practices, and it is thus representative of cultivated fields in the area. Meteorological data (wind velocity, air temperature, relative humidity, and precipitation) were constantly monitored (except when technical problems) from 2006 to 2012 at 6·5‐m height with 5‐min time resolution (Marticorena et al ., ). There is considerable interannual variability of wind and rainfall within this period (Table ).…”

“…Mean annual precipitation ranges between 100 and 600 mm; most of it is brought by a few mesoscale convective systems that induce strong winds just before the start of the rain. Thus, most wind erosion occurs during the late dry season and beginning of the rainy season, when vegetation cover is low and strong winds are frequent (Abdourhamane Touré et al, 2011;Marticorena et al, 2016).…”

Size‐Resolved Dry Deposition Velocities of Dust Particles: In Situ Measurements and Parameterizations Testing

“…Most deposition data reported in the literature correspond to direct deposition measurements performed with collectors that separate, or not, wet from dry deposition. These data when acquired over a long period of time (e.g., Bergametti et al, ; Heimburger et al, ; Loÿe‐Pilot & Martin, ; Marticorena et al, ; Prospero et al, ; Uetmatsu et al, ; Vincent et al, ) provide information on the seasonality and on the orders of magnitude of dust deposition fluxes but rarely on the size of the deposited dust. They allow comparisons with the deposition simulated by dust transport models over periods ranging from 1 week to months.…”

“…They allow comparisons with the deposition simulated by dust transport models over periods ranging from 1 week to months. However, although a large fraction of the emitted dust mass is dry deposited along the first 1,000 km of transport (e.g., Schütz, ), only a limited number of deposition measurements were performed close to the dust source regions (for more details, see Marticorena et al, , and references therein). In addition, very few of these measurements provided relevant information on the dust dry deposition only mainly because of the technical difficulties one must overcome to perform these direct measurements.…”