Validation Of ALADIN Winds And Study Of Stratospheric Gravity Waves Based On USTC Lidar

Wind speed and temperature measurements are fundamental to a comprehensive understanding of atmospheric dynamics and are essential for numerical weather prediction and atmospheric model parameterization.The means of observing wind fields in the altitude range 15-70 km are scarce and only expensive and discontinuous soundings are possible with sounding rockets.This altitude region is therefore known as the "radar gap".To fill the "radar blind spot",LIDAR technology has been developed and is now a very effective tool for tropospheric and stratospheric wind field detection.This thesis focuses on the study of Rayleigh Doppler lidar wind and temperature measurement technology,and introduces the development of the new generation USTC lidar.The thesis also presents two applications of lidar observations,the validation of space-borne wind measurement data and the study of gravity waves in the stratospheric atmosphere.This thesis firstly gave the development of the Rayleigh Doppler lidar system of USTC.According to the basic principle of doube-edge technology lidar,a system simulation was conducted so that the key parameters of each component were determined.To eliminate the wind error caused by zero-Doppler frequency shift,the optical structure and wind retrieve algorithm were promoted.A large amount of wind field and temperature data was acquired by this upgraded system in the Xinjiang region between 2017 and 2019.The accuracy of the observations and the reliability of the data were demonstrated by comparison with the European Centre for Mesoscale Weather Forecasting(ECMWF)model data and wind speeds measured by local radiosonde.This also demonstrates the considerable effectiveness of the new zero-Doppler shift calibration scheme given in this thesis.The world’s first wind measurement satellite,Aeolus,has enabled the first human observation of the global wind field.Its payload,ALADIN,is also a direct detection lidar.Due to the nature of incoherent lidars,their wind measurements must be validated and calibrated periodically.The European Space Agency has conducted numerous validation experiments on its wind field data,however,these experimental data are almost all in the tropospheric region below 10 km.This thesis validates stratospheric data above 10 km height from ALADIN using data measured in Xinjiang by the USTC lidar system in 2019.Selected Aeolus Level-2B Rayleigh wind data from June to December are compared by two data matching methods.In this thesis,data from the 2019 lidar measurements in Xinjiang are used to validate the data from the space-borne wind lidar.Selected Aeolus Level-2B Rayleigh wind data from June to December were compared by two data matching principles.We found a small discrepancy between the wind speeds for the upward and downward orbits.We also found that the wind biases deviate from zero and oscillate with height above 16 km.The analysis suggests that this oscillation may be related to the frequent occurrence of local gravity waves.Overall,this study demonstrates the reliability and accuracy of the satellite data in north-western China,which also provides experience for the data validation of future space-borne wind lidars in China.Another application of wind and temperature lidar in this thesis is the observation of atmospheric gravity waves.Conventional temperature data observations do not allow for the acquisition of all the key characteristics of gravity waves such as propagation direction,horizontal wavelength and intrinsic period.However,simultaneous temperature and wind velocity measurements from lidar can be used to obtain polarization relationships based on hodograph analysis and ultimately gravity wave characteristics.A large number of gravity wave phenomena were detected by the USTC lidar during its observations in September and October 2018.The modes of these gravity waves were not homogeneous,so spectral analysis and fluctuation equation fitting were used to extract the first-and second-dominant gravity waves.Information on the propagation direction,horizontal wavelength,and intrinsic period of a total of 184 first-dominant and 140 second-dominant gravity waves was calculated and counted from the polarization relationships of the zonal-meridional wind and the zonal wind-temperature perturbation vector hodograph.It is found that the background westerly wind,which is common in Xinjiang,influences the propagation direction of the gravity waves,and the propagation directions of the first-dominant gravity waves are concentrated in the east and west direction.In addition,wind shear at an altitude of 35-40 km was found to cause the reflection of the upward propagating primary gravity waves.At this altitude part of the gravity wave energy is absorbed by the background atmosphere and secondary gravity waves with complex patterns are generated above the extinction range.These secondary gravity waves generate atmospheric instabilities and these observations have important implications for the theory of atmospheric nonlinear theory.