The characteristics of turbulence intermittency and its impact on surface energy imbalance over Loess Plateau

Turbulence intermittency is a challenge facing in the ffeld of atmospheric boundary layer (ABL) and micrometeorology. We employed an automated algorithm for the separation and reconstruction of Sub-Mesoscale and Turbulent motions (SMT) to examine the basic characteristics of turbulence intermittency driven by submesoscale motion over the complex underlying surface of the Loess Plateau. The ffndings revealed that submesoscale motion has a signiffcant inffuence on turbulence statistical parameters. We analyzed ffve cases and found that the turbulent intermittency events were characterized by quiescent and burst periods. During the quiescent (burst) period, the turbulent transport weakened (strengthened), turbulence ffuctuations weakened (strengthened), atmospheric stability increased (decreased), and turbulent energy decreased (increased). These bursts can be triggered by energy conversion from sub-mesoscale to turbulent motion. Actual observations revealed atmospheric conditions where turbulent intermittency events are more likely to occur: wind speed U < 3.5 ms &#8722; 1 , wind speed gradient &#916;U/&#916;Z < 0.2 s &#8722; 1 , temperature gradient &#916;T/&#916;Z > -5.1 K/100 m, or bulk Richardson number Rib > -0.1. The inffuence of turbulence intermittency on the classical energy non-closure issue over the Loess Plateau was explored further. The results show that the presence of sub-mesoscale motions contributed to energy closure, with an energy closure of 78 % during daytime and 36 % during nighttime. And different periods of turbulent intermittency events affected energy non-closure differently, the energy closure during the burst (quiescent) period was approximately 98 % (70 %) during daytime and 68 % (17 %) during nighttime, approaching closure and far exceeding the overall closure rate during the burst period, whereas signiffcantly low during the quiescent period. This suggests that turbulence intermittency is a very important factor causing energy non-closure over complex underlying surfaces, especially in stable boundary layer (SBL) during nighttime. The results are highly signiffcant for a better comprehension of turbulence intermittency and surface-atmosphere interactions over complex underlying surface.