| Popis: |
While nocturnal Low-Level Jets (NLLJs) occur frequently in many parts of the world, the occurrence and other detailed characteristics of NLLJs over the Taklimakan Desert (TD) are not well known. This paper presents a climatology of NLLJs and coincident dust over the TD by analyzing multi-year ERA-Interim reanalysis and satellite observations. It is found that the ERA-Interim dataset can capture the NLLJs feature well by comparing with radiosonde data from two surface sites. 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. NLLJs above the inversion have a strong annual cycle with a maximum frequency in August. 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 emission and transport during the warm season over the Taklimakan. |
