| The low-level jet have important influence on rainstorms, air pollution, sandstorms and other weather and climate phenomena. Using the ERA-Interim reanalysis data during 2000 to 2013, we analyzed the wind profile over the Taklimakan. desert, verify the existence of this low-level jet, and give its characteristics and the seasonal variations, then we analyze the relative height of the low-level jet and the inversion layer top, the impact of this low-level jet on surface wind, and its influence on dust emission. The main results are as follows:1. There is a wind speed maximum center in the low-level boundary layer, and wind speed exceeds 6.5m/s. This indicates that a low-level jet (LLJ) may widely exist all year long. We defined a criterion to identify the low-level jet by considering the height of maximum wind speed, inversion and wind shear.:1, the maximum wind speed located within 1km above ground level (agl); 2, there is a temperature inversion, and the inversion height must be at least 50m (agl); 3, the wind speed minimum above the jet maximum fall off 40% within 5km above ground level.2. There is an easterly LLJ persistently appearing over the Taklimakan Desert, and has a high frequency of occurrence, the maximum appears in August for 68.4%, and the minimum is in December for 54.5%. Both the LLJ maximum wind speed and the jet core height have a significant seasonal variation:the LLJs appear highest in summer with a mean value of 339.6m above ground level (agl), and lowest in winter (237.7m agl). In spring and autumn, LLJs are approximately situated at 294.0 and 280.1 m, respectively. The strongest LLJs wind speed appear in spring and summer with a value larger than 7.5 m/s. In autumn, it decreases to 6.3m/s, and has a minimum value about 5m/s in winter. Furthermore, it shows a tendency for stronger LLJs to occur higher at low levels and then it performs an opposite tendency after reaching a certain height range. In spring and summer, LLJ wind speed median reach a maxima both greater than 9.5m/s at about 550m (agl). In autumn and winter, LLJ wind speed median maxima located at about 400m (agl),8m/s and 6.5m/s respectively.3. The maximum average height of inversion top over Taklimakan appears in December (608.4m), and the minimum is in July (236.5m). The trend of annual jet core height variation is opposite to the inversion. The LLJ core is highest in summer with a maximum value of 359.1m in August, it’s lowest in winter with a minimum value of 229.1m. The LLJs in summer mostly appear above the inversion top, but in winter, the LLJs mainly below the top of the inversion.4. The LLJ has important influence on surface wind, if the LLJ is higher than the inversion top, the corresponding surface wind speed is largest. By analysis the height of mixing layer top, the result shows that the mixing layer develops highest in summer, it can be about 1400m in June and July, and it’s lowest in winter with the minimum value of about 200m in December and January, this indicate that the turbulence in summer day can be more conducive to the downward transfer of upper LLJ momentum. |
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