![]() The reference region is used as the key location ( Figure 1) for a composite analysis to investigate the possible influence of desert dust on AEW amplification. This region exhibits VORA standard deviations exceeding 0.5 × 10 −5 s −1 (not shown) and is observed on the northern side of the climatological position of the African easterly jet. To identify periods of enhanced AEW activity, we define an index based on the anomalies of relative vorticity at 700–hPa (VORA) spatially averaged in a reference region bounded by (22.5°N–17.5°N) and (50°W–30°W). The daily climatology was subtracted from the surface dust time series to produce surface dust anomalies (DUSTA). The smoothing is necessary to remove noise due to interannual variations. To remove the seasonal cycle, a daily climatology was first computed by averaging the 22 years at each day from 1 June to 30 September and smoothing 50 times with a 1-2–1 filter. Daily averaged surface dust concentrations generated by the model during June, July, August and September are used. For the desert dust modeling, we use NCEP/NCAR reanalysis at T62 resolution (∼1.8 × 1.8 degrees), using 28 sigma levels available every 6 hours. The transport model is the Model of Atmospheric Transport and Chemistry driven by meteorological fields from the NCEP/NCAR reanalysis. Dust variability is investigated with a 22–year simulation (1979–2000) of dust transport with the model described in Luo et al. AI's were computed as the difference analysis minus first–guess. To focus on the time scale of easterly waves, a Murakami band-pass recursive filter with cut-off periods of 2.5 and 10 days was applied (hereafter called anomalies). The following analysis and first–guess fields were analyzed: vertical component of relative vorticity (700–hPa), geopotential height (700–hPa) and temperature (1000, 925, 850 and 700–hPa). using NASA GEOS-1 to estimate the mean heating rates associated with African dust. A similar assumption was used by Alpert et al. Our hypothesis is that large values of AI in regions with high dust concentrations can provide important signatures of dust in the easterly waves development. We note that the NCEP/NCAR reanalysis model does not include appropriate parameterizations to account for the radiative and microphysical effects of mineral dust. The difference between analysis and model first–guess is called analysis increments (AI) and provide a quantitative measure of the quality of the reanalysis over regions with large number of observations. We use NCEP/NCAR reanalysis and model first–guess fields at 6–hourly intervals (00Z, 06Z, 12Z and 18Z) from 1 June to 30 September 1979–2000. Data and Dust Transport Model Experiments The objective of this paper is to show indirect observational evidence that mineral dust can modulate the intensity of easterly waves formed in western Africa and tropical Atlantic Ocean. Likewise, about 10% to 20% of the seasonal variability of desert dust concentrations across the North Atlantic is related to easterly waves, which indicates that easterly waves modulate the transport of dust. Their results indicate that ∼20% of dust entrainment into the atmosphere over a broad region of North Africa is associated with easterly wave activity, suggesting that easterly waves may regulate desert dust entrainment into the atmosphere. ![]() investigated the relationships between easterly wave activity and model simulations of desert dust entrainment and transport. African easterly waves (AEW) are frequent in the tropical Atlantic Ocean and western Africa during boreal summer and are important in modulating the variability of desert dust. They were able to statistically estimate that, for an average event, African dust plumes have a heating effect in the lower troposphere (1.5 to 3.5 km) of ∼0.2 K per day. They found that the spatial patterns of monthly mean IAU closely resemble the spatial patterns of dust in the eastern tropical Atlantic. examined satellite-derived dust events and the differences between NASA GEOS-1 reanalysis and first-guess fields (incremental analysis update–IAU). Desert dust from North Africa is an important source of mineral dust to the atmosphere. Although some substantial progress has been made, the sources, spatial and temporal distributions, radiative forcing and biogeochemical impacts are still not well understood. It has been widely recognized that mineral aerosols are an important component of Earth's climate through interaction with radiative, biogeochemical and photochemical processes.
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