Atmospheric Turbulent Characteristics Under Summer Shamal in Coastal Qatar

摘要

Summer Shamal, a strong low-level northwesterly wind in the Middle Eastern, is the major trigger for dust storm activity with a broad impact on regional transport and human safety. However, near-ground turbulent mixing analysis under Shamal is still rare due to the lack of available high frequency data. The present study explores the near-surface turbulence characteristics under summer Shamal, compared with those of non-Shamal, in the coastal region of Qatar (26.08 degrees N, 51.36 degrees E). The results show that Shamal prevents the development of summer sea breezes in the Persian Gulf. A "Shamal day" (SD) is commonly defined as a day with a strong, continuous, north-northwesterly wind. Compared to non-Shamal days (NSD), SDs are characterized by higher surface sensible heat flux and turbulent kinetic energy (TKE) with lower humidity, especially around noon time. At night, the wind turbulence energy is contained in smaller eddies for SD due to the more stable atmospheric conditions. The streamwise velocity spectra analysis displays a power-law trend with a coefficient of -1.53 as compared to the traditional Kolmogorov -1.67 (-5/3) power law, indicating a higher TKE dissipation rate for SD. The smaller scatter of the normalized TKE dissipation rate observed for SD is related to lower streamwise turbulence intensity. A Weibull distribution is observed for probability distribution of TKE dissipation rate under SD in log scale for both stable and unstable conditions. This distribution for TKE dissipation rate is different than the results from other field measurements due to Shamal.