Abstract
Dust aerosols impact global energy balance substantially by acting as efficient ice nuclei to alter cold cloud properties. However, the estimate of dust indirect effect remains uncertain due to simulating dust distributions poorly and lacking reliable dust observations, especially in the upper-troposphere. Here, we characterize and understand upper-troposphere dust sources and transport with an improved dust dataset derived from A-train satellite lidar and radar measurements and an air parcel trajectory model. The distinct upper-troposphere dust belt over the northern hemisphere has seasonally varying base and top heights of 3.65 ± 2.84 and 8.35 ± 1.50 km above mean sea level and its column loading is strongest during spring (March-April-May). The out-of-phase annual cycles of mid-level dust concentration and westerly wind over source regions control the seasonal upper-tropospheric dust loading variations. African deserts contribute the most (46.3%) to the upper-troposphere dust belt in spring and the synoptic trough is the leading (49%) dust lifting mechanism.
Highlights
Dust aerosols impact global energy balance substantially by acting as efficient ice nuclei to alter cold cloud properties
The concept of the Global Dust Belt (GDB)[37], which refers to dusty source regions stretching from the west coast of North Africa into Central Asia, was proposed long ago and has a great impact on our understanding of dust distributions[17] along with surface conditions and multi-scale dynamics
Besides the traditional GDB over source regions in the low troposphere, there is a noticeable high dust extinction region north of 30°N above 4 km above mean sea level (MSL). This feature stands out above 6 km MSL when dust layers are further detached from dust sources, and is defined as the upper troposphere dust belt (UTDB), which can be identified from dust occurrences[36]
Summary
Dust aerosols impact global energy balance substantially by acting as efficient ice nuclei to alter cold cloud properties. It is estimated that global net cloud radiative forcing increases by ∼1 W m−2 for each order of magnitude increase in INP concentrations[3] Despite their effectiveness to act as INPs and being the most abundant aerosol type by mass[4], the radiative forcing from dust aerosols remains[5,6] uncertain, due to poorly simulated multi-scale dynamical processes and the resulting vertical dust distribution, as well as associated cloud and precipitation systems[5]. Ground-based lidar measurements are extensively used to document the vertical distributions of dust aerosol[10,11,12], global dust aerosol characterization was not possible until the launch of CALIOP on board Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) in 200613.
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