Contribution of IASI to the Observation of Dust Aerosol Emissions (Morning and Nighttime) Over the Sahara Desert

Abstract

Observing the planet at global scale, twice a day, and measuring the whole infrared atmospheric spectrum (8,461 channels at 0.50 cm−1 resolution), Infrared Atmospheric Sounder Interferometer (IASI)/METOP can concurrently detect clouds, determine the 3‐D atmospheric structure (temperature, water vapor, ozone, etc.), surface properties (emissivity and temperature), as well as dust aerosol AOD and altitude. Observing morning (0930 hr) and nighttime (2130 hr), IASI is in relatively good phase with the most frequent times of occurrence of the main Saharan dust uplift mechanisms reported in the literature. Here we classify IASI dust observations according to both the dust loading (AOD) and the dust layer height, providing a more comprehensive picture of dust characteristics. This classification is analyzed at daily scale and its capability to detect dust uplift events is evaluated through comparisons with results from the particularly well documented June 2011 Fennec campaign. Then, a Dust Emission Index (DEI), specific to IASI, is constructed by selecting AOD‐altitude bins with largest AODs and smallest altitudes likely indicative of freshly emitted dust. Applying this to the 12‐year 2007–2018 period, we determine climatological DEI maps and comparisons are made with other equivalent existing results derived from ground‐based or other satellite observations. Results of these comparisons demonstrate the capability of IASI to document the dust distribution over the whole Earth desert areas over a long period of time. The present approach is also suitable to the processing of the at least hourly observations of the coming Infrared Sounder instrument (IRS), planned on board Meteosat Third Generation (2021).

“Seeing” Beneath the Clouds—Machine‐Learning‐Based Reconstruction of North African Dust Plumes

“…The local maximum of the dust occurrence frequency from the reconstructed satellite images in the Nubian Desert (close to Sudan's Red Sea coast) is not represented by the CAMS reanalysis (see Figure 11). The Nubian Desert is a known dust source region as identified earlier in SEVIRI images (Schepanski et al., 2012), and also seen in other aerosol data, for example, the dust emission index derived from data of the Infrared Atmospheric Sounding Interferometer (Chédin et al., 2020) and the Aerosol Index using observations of the Total Ozone Mapping Spectrometer (N. J. Middleton & Goudie, 2001). Since the local maximum is also present in the dust frequency from non‐reconstructed observations, the feature is not an artifact of the reconstruction.…”

“…Comparing the reconstructed and the directly observed dust occurrence frequencies during 2021 and 2022 for 9, 12, and 15 UTC (see Figure 9) indicates, that previous studies of the dust occurrence frequency and by extension the dust source activation frequency derived from SEVIRI and other satellite observations underestimate the dust occurrence and dust source activation due to the presence of clouds (e.g., Chédin et al, 2020;Heinold et al, 2013; Schepanski et al, 2012). Our results suggest that at least 0.78% of observations in the spatial mean over the entire region of interest miss dust plumes due to cloud coverage.…”

Arctic amplification–induced decline in West and South Asia dust warrants stronger antidesertification toward carbon neutrality

“…Following Chédin et al ( 103 ), we defined monthly dust emission index (DEI) as the frequency of occurrence, normalized by the proportion of cases observed with simultaneous high DOD (≥0.5) and low dust layer mean altitude (≤1.1 km), because this simultaneous occurrence helps distinguish newly emitted dust from the aged dust transported at higher levels. To quantify horizontal transport of dust, we adopted the approach of Yu et al ( 40 ) and developed an approximate estimation of dust flux in the zonal direction by combining averaged zonal wind (from ERA5) beneath the dust layer height (from IASI) with total IASI DOD since we have limited information of vertical profiles of dust mass.…”

“…CESM v2.1.3 was used to explore global dust radiative effects. The chosen component set (compset) for this study was FWHIST, the robustness of which has undergone extensive validation ( 103 ). Detailed settings of FWHIST can be found in our previous study ( 104 ), and here we incorporated a diagnostic calculation to quantify dust radiative influences by turning off dust radiative effect in CESM.…”