HTML
-
The Upper Stratosphere and Lower Mesosphere (USLM) is an important region in the Earth’s atmosphere. In this region, the amplitudes of atmospheric gravity waves (GW) and solar tides can be increased due to the decrease of air density with altitude[1]. When these waves propagate upwards, their energy and momentum can be deposited into the background and thereby modulate the atmosphere[2]. Long-term observations are important for studying the seasonal and inter-annual variability in the USLM region and for understanding global climate change[3-5]. Rayleigh scattering lidar has been proven an efficient means for making high-resolutionmeasurements of density and temperature in the USLM region[5].
The first Rayleigh lidar observation of neutral density and temperature profiles was made by Hauchecorne and Chanin at the Haute-Provence Observatory[6]. Gardner et al. used a Rayleigh lidar to study the gravity waves characteristics at Urbana, Illinois[7]. Wichwar et al. used 3 years of Rayleigh lidar data at Logan, Utah to study the climatology of mesospheric temperature[8]. Recently, Llamedo et al. used an 11-year lidar temperature dataset at the altitudes of 20-56 km at Rio Gallegos, Argentina to study gravity wave activities and found that GW specific potential energy inside the polar vortex is larger than the outside or the edge of the vortex[5].
In the Antarctica region, Di Donfrancesco et al. used Rayleigh lidar observations to show an interesting temperature behavior and variation at McMurdo station (78° S, 167° E)[9]. Then Pan and Gardner combined Fe/Rayleigh lidar and high-altitude balloonsonde data to characterize the seasonal variations of atmospheric temperature from surface up to 110 km at South Pole[10]. Klekociuk et al. reported the seasonal variations of temperature in the stratosphere and lower mesosphere using the lidar data at Davis station (68.6° S, 78.0° E) near the Antarctica Circle[11]. Then Alexander et al. used Rayleigh lidar at Davis station to study the wintertime gravity wave activities in the USLM region[12]. Recently, Chu’s group used 5 years (from 2011 to 2015) of lidar observation to characterize the GW between 30 km and 50 km at McMurdo station[3-4].
In China, Wu et al. firstly used a dual-beam Rayleigh lidar to obtain the air density and temperature profiles between 30 km and 43 km at Hefei[13]. After the system was upgraded, the lidar could measure the vertical distribution of atmospheric temperature from 22 km to 60 km[14]. From 2008, the Chinese meridian project deployed several lidars in China, including Rayleigh lidars at Beijing, Hefei, Wuhan, and Hainan[15]. Yue et al. used Rayleigh lidar data to analyze the middle atmosphere temperature structure at Beijing[16]. Qiao et al. and Dai et al. used a Rayleigh lidar measurements at Golmud, Qinghai to show the temperature and density profiles over the Tibetan Plateau region and analyzed the seasonal variations of atmospheric density[17-18].
The Rayleigh lidar presented in this paper is the first Rayleigh lidar deployed at Chinese stations in Antarctica. We will describe the lidar system configuration in Section 1, the data retrieval method in Section 2, our initial measurement results in Section 3, and then summarize in the last Section.
-
The Rayleigh lidar system at Zhongshan station consists of three units: laser transmitter, optical receiver, and time control & signal acquisition unit. Figure 1 shows lidar schematic diagram and the system configurations are listed in Tab.1.
Configuration Parameters Laser transmitter Wavelength/nm 532 Pulse energy/mJ 400 Repetition rate/Hz 30 Pulse width/ns 8 Lidar receiver Telescope diameter/m 0.8 Telescope f number 1.8 Fiber diameter/mm 1.5 Fiber NA 0.39 PMT quantum efficiency ~40% @ 532 nm Time control & signal acquisition Time generator DG645 Photon counting card P7882 Table 1. System configurations of Zhongshan station Rayleigh lidar
The lidar transmitter unit mainly consists of a neodymium-doped yttrium aluminum garnet (Nd:YAG) pulsed laser. The output laser is at the wavelength of 532 nm with single pulse energy ~400 mJ and repetition rate of 30 Hz. A high-precision beam controller is used to steer the laser beam to the zenith direction.
A prime focus telescope with the diameter of 0.8 m is used as lidar receiver. In order to perform well under the cold weather condition in Antarctica, the telescope's primary mirror was made of devitrified glass, which has relatively smaller thermal expansion coefficient. A multi-mode optical fiber with 1.5 mm core diameter and 0.39 numerical aperture (NA) is used to couple the telescope to the subsequent optical path. A mechanical chopper with the rotation rate of 5400 rpm is used to block the photon signal at lower altitudes for protecting the photon multiplier tube (PMT) from saturation. After passing through the chopper and an optical filter, received photons are finally detected by a PMT (Hamamatsu H7421-40, with the quantum efficiency ~40% at 532 nm).
The PMT converts optical photons to electrical signals being recorded by a digitizer (Fast ComTec MCA-3 Series/P7882). The timing control of the lidar is designed as follows. The primary timing is generated by the chopper in the receiving channel at the frequency of 180 Hz. Then the chopper triggers a digital delay/pulse generator (DG645) so that for every six pulses from the chopper, the DG645 is triggered once. Therefore a timing signal with the repetition rate of 30 Hz is produced to trigger the Nd:YAG laser's flash lamp. The same timing is also synchronized to the data acquisition unit.