Full-scale spectra of 15-year time series of near-surface horizontal wind speed on the north slope of Mt. Everest

Abstract. Wind speed spectral analysis is of great importance for understanding boundary-layer turbulence characteristics, developing atmospheric numerical model, and assessing wind energy. 15-year time series of near-surface horizontal wind data from the national Observation and Research Station for Qomolongma Special Atmospheric Processes and Environmental Changes (QOMS) on the north slope of Mt. Everest has been used to investigate the full-scale wind spectrum in the frequency range from about 10 yr^-1 to 5 Hz. The annual average wind speed showed almost no detectable trend from 2006 to 2018 at the QOMS station. Three peaks were identified in the full-scale spectra at the frequencies of 1 yr^-1, 1 day^-1, and 12 hr^-1, respectively. The 12 hr^-1 peak is evident in spring and summer but disappears in winter, indicating the seasonal differences in local circulations at the QOMS station. The spectral density was the highest on the low-frequency side of the diurnal peak and in the microscale frequency range (f ≥ 1×10^-3 Hz) in winter, indicating frequent synoptic weather events and vigorous turbulent intensity generated by shear due to strong wind during winter. An obvious spectral gap around the frequency of 4.5×10^-4 Hz was observed in the composite seasonal and daily spectrum in winter, while the spectral gap disappeared in summer. The combination of low spectral density in the mesoscale frequency range, high spectral density in the microscale frequency range, and strong turbulence intensity contributes to the spectral gap in winter.