| The middle and upper atmosphere temperature and wind fields are important parameters to study the atmospheric solar tides, gravity waves, and planetary waves and their mutual interactions, as well as the temperature structure and general circulation. Currently in China, the ground-based and space-borne instruments for simultaneously measuring the temperature and wind in the mesopause region are rare. Mostly, the meteor or medium frequency radars are used to measure mesopause region wind, while the Rayleigh lidars are used to retrieve temperature. As a high precision instrument, lidar has been widely used in remote sensing of atmospheric profile. This thesis describes in details the development of China first high spectral resolution sodium temperature/wind lidar, based on the sodium spectroscopy and lidar technology. Using the dataset measured by this lidar, we study the mesopause region semidiurnal tide and gravity wave momentum flux. This thesis is divided into the following two parts:The first part, including chapters1and2, mainly focuses on the introduction of atmosphere and lidar technology as well as the sodium temperature/wind lidar measurement theory. The chapter1introduces the atmosphere temperature structure and composition, the methods for measuring atmospheric temperature and wind, and the current status of sodium temperature/wind lidar. The chapter2describes the sodium fluorescence lidar equation, sodium hyperfine spectrum, and the theory for retrieving wind and temperature.The second part is my main research work and achievements during the Ph.D study. The main research results are as follows:(1) As a key member, I participated in building the China first high-spectra resolution sodium temperature/wind lidar. The development of transmitter, receiver, data acquisition system and timing system are described in details. We develop the seed CW laser source by using the ring dye laser pumped by a diode semiconductor laser, the absolute laser frequency locking and automatic tracing system, three frequency laser generator, pulse dye amplifier, auto-aligning system. For the receiver, we design the multi-dimension adjusting coupler and mechanical chopper system, and optimize the specification of coupling fiber, lens, filters and photomultiplier to improve system efficiency. (2) We study the mesopause region temperature and wind variability with the high-resolution lidar dataset. We discussed in details the analysis procedures of temperature and wind profile between80and105km retrieved from the three frequency backscattered photon signals.(3) We compare the sodium lidar observed temperature profile with SABER observed. The results are generally consistent in both structure and absolute value. We also compare the lidar wind profile and meteor radar wind measured at Wuhan, which is-300km west of Hefei.. The results are in good agreement. Both lidar and radar winds show clear downward phase propagation of maxima and minima, suggesting the dominance of solar tides on the variability in the mesopause region. All these demonstrate that the temperature and wind profiles observed by our sodium lidar are reliable and reasonable.(4) With the observed temperature and wind dataset, we studied the semidiurnal tidal structure in the mesopause region. On December3,2011, the semidiurnal amplitudes in temperature, zonal and meridional winds are～24K,～45and ～50m/s respectively. The estimated vertical wavelength in both winds is25-30m/s, shorter than the typical vertical wavelength of40-50km. Compared with the results obtained from meteor radar wind, the semidiurnal amplitudes of zonal and meridional wind retrieved from lidar profiles are slightly larger. We also found clear phase changes near90km. Both the short vertical wavelength and phase changes may indicate the gravity wave dissipation and breaking and thus interaction with semidiurnal tide.(5) The observations of gravity wave momentum flux is extremely important for us to understand the momentum budget and the middle and upper atmosphere general circulation. We use dual-beam method with each laser beam pointing either east or west both with20°from zenith to measure the momentum flux. The results show that the value of vertical flux of horizontal momentum is between-10m2s-2-10m2s-2, with either positive correlation or anti-correlation with mean zonal wind. The positive correlation between momentum flux and mean zonal wind may be due to gravity wave passing through an opposite wind shear below observed region and casuing the increase of momentum flux. On the other hand, the anti-correlation is likely due to the gravity waves filtered by mean zonal wind. The momentum flux in the same direction as wind shear is suppressed, while the flux in the opposite direction to wind shear is enhanced. Since the zonal wind as well as its shear is modulated by tides, the dissipation and breaking of gravity wave could eventually cause dramatic short-term tidal variation. On the contrary, the variability of tides further leads to the change of momentum flux and its divergence. |
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