Characteristics of Taklimakan Dust Distribution and Nocturnal Low Level Jet: A Satellite and Reanalysis Field Perspective

The Taklimakan Desert is one of the largest sources of dust globally. Dust particles from this region can be lofted vertically up to 10 km due to the unique topography and northeasterly winds associated with certain synoptic conditions. Then they can be transported horizontally to far downwind regions by westerlies. We combined Multi-angle Imaging SpectroRadiometer (MISR) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) to investigate the three-dimensional distribution of dust over the Taklimakan Desert and surrounding areas. During spring and summer, a dust belt with high aerosol optical depths (AOD) expends eastward from the Taklimakan Desert to the Loess Plateau along the Hexi Corridor, and southward to the Tibetan Plateau. However the dust extinction coefficients rapidly decrease from 0.340 km-1 near surface to 0.015 km-1 at 5 km in spring, while the extinction values vary within 0.100±0.020 between the altitudes of 1.6 and 3.5 km and decrease to 0.023 km-1 at 5 km in summer which indicates that dust aerosol is relatively well mixed in the vertical. After further analyzing multi-year ERA-Interim reanalysis and satellite observations, we found that nocturnal Low-Level Jets (NLLJs) occur frequently in the TD region. The NLLJs occur in more than 60% of nights, which are primarily easterly to east-northeasterly. They typically appear at 100 to 400 m above the surface with a speed of 4 to 10 ms-1. Most NLLJs are located above the nocturnal inversion during warm season while they are embedded in the inversion layer during cold season. We also quantify the convective boundary layer (CBL) height and construct an index to measure the magnitude of the momentum in the CBL. We find that the NLLJ contains more momentum than without NLLJ, and in warm season the downward momentum transfer process is more intense and rapid. The winds below the NLLJ core to the desert surface gain strength in summer and autumn, which are coincident with an enhancement of aerosol optical depth. It indicates that the NLLJ is an important mechanism for dust activity and transport during the warm season over the Taklimakan.