Quantitative Estimations On The Gravity Wave Extraction Methods From Night-Time Lidar Observation

According to temporal and spatial ranges and resolutions of night-time lidar observations,we construct a synthetic data with known background temperature(consisting of constant background,planetary waves and tides)and gravity waves.The existing nightly mean method and the temporal running mean method are used to extract gravity waves from the synthetic data.On the basis of this,this paper proposes a harmonic fitting method that uses a harmonic function to approximately represent the background temperature changes to extract gravity waves.Based on the spectral response defined by the ratio between the extracted gravity waves and the known gravity waves,we quantitatively analyze the reliable range of periods and wavelengths of gravity waves extracted by each method.Our results show that,the nightly mean method always overestimates the amplitudes of gravity waves since it is particularly sensitive to background temperature components and the length of nighttime;the temporal running method is sensitive to semidiurnal tides and can be used to extract gravity waves with periods less than 1.15 times the window width or wavelengths less than 20.0 km;the harmonic fitting method is not sensitive to background temperature components and can be used to extract gravity waves with periods less than 0.4 times the night time or wavelengths less than 20.0km.Finally,the temporal running mean method and the harmonic fitting method can get reliable gravity waves from the temperature data observed by Na lidar during nighttime.