Xuewu Cheng

Occurrence and characteristics of sporadic sodium layer observed by lidar at a mid-latitude location

Na lidar observations of SSL during the past 5 years at a mid-latitude location (Wuhan, China, 31degreesN, 114degreesE) are reported in this paper. From 26 SSL events detected in about 230 h of observation, an SSL occurrence rate of 1 even/9 h at our location was obtained. This result, combined with that reported by Nagasawa and Abo (Geophys. Res. Lett. 22 (1995) 263) at Tokyo, Japan, reveals that the SSL occurrence can be relatively frequent at some mid-latitude locations. The statistical analyses of main parameters for the 26 SSL events were made, and the results were compared with those previously reported. By examining the corresponding data from a nearby ionosonde, it was found that there was a fairly good correlation between SSL and Es. Of the 18 pairs of SSL and Es events checked, 15 of SSL were accompanied by Es, and 8 pairs of them were correlated within 1 h in time and within 5 km in altitude. From the analyses of observed perturbations during SSL development, the role of dynamic processes of atmosphere in the SSL formations were emphasized

Double sodium layers observation over Beijing, China

The altitude of the sodium layer in the mesosphere and lower thermosphere is usually from 80 km to 105 km. In this paper, we report a set of double sodium layer (DSL) events observed by sodium lidar over Beijing, China. In these DSL events, the normal sodium layer and secondary sodium layer (SeSL) present separately. There were about 17 DSL events occurred in 319 observation nights during 2009 similar to 2011. All DSL events were observed in spring and summer. The SeSL appeared independently within the altitude range from 105 km to 130 km. The density of the SeSL is very high. The maximum ratio of peak density and the ratio of column density for the SeSL to the normal sodium layer are up to similar to 60% and similar to 47%, respectively. The SeSL lasted several hours, and then merged into the normal sodium layer. After the SeSL, a sporadic sodium layer occurred in the normal sodium layer. Citation: Wang, J., Y. Yang, X. Cheng, G. Yang, S. Song, and S. Gong (2012), Double sodium layers observation over Beijing, China, Geophys. Res. Lett., 39, L15801, doi:10.1029/2012GL052134.

A double sodium layer event observed over Wuhan, China by lidar

[1] A double sodium layer (DSL) structure was observed during the night of June 13, 2000 over Wuhan, China (31degreesN, 114degreesE) by our Na lidar. The unique feature of this DSL is that a normal sodium layer at altitudes of 80 similar to 105 km was accompanied by a secondary sodium layer at altitudes of 105 similar to 125 km for about 2 hours. The lidar observation result together with that obtained from the nearby ionosonde and geomagnetic equipments are presented. While the exact mechanism responsible for this DSL formation is still unclear, some possible explanations and corresponding observation evidences are discussed.

Photon Return On-Sky Test of Pulsed Sodium Laser Guide Star with D-2b Repumping

Sodium laser guide star (LGS) system has become one of the critical components in modern astronomical adaptive optics system (AOS), especially for the next-generation extremely large telescopes, such as the Thirty Meter Telescope and the European Extremely Large Telescope. Since the wavefront detection performance of AOS is directly related to the brightness of LGS, it is important for AOS to maximize its photon generation efficiency by all means. Sodium D-2b line repumping is such a technique that can greatly increase the returned photons for either sodium continuous wave (CW) laser or pulsed laser. This technique has been studied theoretically and field tested with a 20 W CW laser by European Southern Observatory team. However, field test results of a 20 W class pulsed laser with D-2b repumping have not been reported yet. In this paper, our latest field test results with theoretical comparison of D-2b repumping with a 20 W quasi-continuous wave (QCW) pulsed laser will be presented. With a linearly polarized beam, approximate 40% photon return enhancement was achieved when 10% of laser power was detuned to D-2b line, which agreed well with results from a rate equation-based Monte Carlo photon return simulation program. Both experiment and simulation results indicate that with a higher laser intensity projected at the sodium layer, the D-2b repumping will be more effective.

First report of sporadic K layers and comparison with sporadic Na layers at Beijing, China (40.6°N, 116.2°E)

A double-laser beam lidar was successfully developed to simultaneously measure K and Na layers at Beijing (40.6°N, 116.2°E) in 2010. Statistical analysis of the parameters of sporadic K (Ks) and sporadic Na (Nas) layers was performed over 2 years of lidar data, and different characteristics of them were found. The average Ks occurrence (2.9%) was lower than that of Nas (5.9%); the Nas occurrence had a maximum (19.3%) in May–June months and a minimum (1.6%) in January–February months, while the Ks occurrence had a maximum (4.9%) in January–February months and a minimum (1.0%) in September–October months; most Ks peaks tended to occur around 93 km, which was ~2 km lower than that of Nas (~95 km); the Ks peak density was often at least 1 order of magnitude lower than that of Nas; notably, two Ks with high peak densities (>1000 cm−3) were observed, which were much higher than K density (15–300 cm−3) reported before. The ascending time of Ks was often longer than its descending time, but an opposite trend occurred for Nas. During the 152 cases of joint observation for the K and Na layers, 21% (32/152) were cases in which Ks and Nas events simultaneously occurred, while 79% (120/152) were cases in which only one layer (K or Na) exhibited a strong Ks or Nas.

A Combined Rotational Raman–Rayleigh Lidar for Atmospheric Temperature Measurements Over 5–80 km With Self-Calibration

A combined lidar system on the basis of conventional Rayleigh lidar has been extended by two rotational Raman (RR) channels for nocturnal atmospheric temperature measurements from 5 to 80 km over Wuhan, China (30.5°N, 114.5°E). An overlapping altitude range of about 10 km is obtained with the RR-technique temperatures reaching upward to 40 km and the Rayleigh-integration-technique temperatures above 30 km. Temperature values obtained by two different mechanisms match nicely in the overlapping area. By using a data-merge method, complete temperature profiles covering widely from 5 to 80 km are obtained for the observation of the thermal structure and perturbations from the troposphere up to the mesosphere. Based on the overlapping-region (30-40 km) data obtained from this combined RR-Rayleigh lidar system and Rayleigh-integration-technique temperatures initialized with model data at an upper height (90 km), we develop a self-calibration method for the determination of the system-dependent constants for RR temperature retrieval. Compared with the conventional radiosonde calibration method, the self-calibration obtained in the overlap region of both lidar temperature measurement techniques can be extrapolated to the lower temperatures in the tropopause region by using the simpler two-constant calibration function. With this new calibration method, the combined lidar system can perform independent and accurate atmospheric temperature measurements when a coincident (in time and space) radiosonde is not available, as it is often the case. This combined RR-Rayleigh lidar thus has the potential for long-term studies of atmospheric thermal structure and associate perturbations.

Photon returns test of the pulsed sodium guide star laser on the 1.8 meter telescope

A microsecond pulsed sodium has been developed in TIPC laser physics research center, the power of this laser is around 20W and the length of the pulse is about 120 microseconds. In 2011, an experiment to project the TIPC prototype laser to the sky and measure the photon returns of the laser has been held on the 1.8 meter telescope in Yunnan observation site. During the sky test, an artificial sodium beacon has been successfully generated, and the brightness of the sodium beacon is around 8.7M in V Band. In the 2012 test campaign, the sodium column density facility has mounted on the telescope to test the local sodium density and structure and the sodium density test result is around 2.2x1013/m2.

Development of a solid-state sodium Doppler lidar using an all-fiber-coupled injection seeding unit for simultaneous temperature and wind measurements in the mesopause region

A solid-state sodium (Na) Doppler lidar developed at YanQing Station, Beijing, China (40°N, 116°E) aiming to simultaneous wind and temperature measurement of mesopause region was reported. The 589 nm pulse laser was produced by two injection seeded 1064 nm and 1319 nm Nd:YAG pulse lasers using the sum-frequency generation (SFG) technique. A fiber amplifier is implemented to boost the seed power at 1064 nm, enabling a robust, all-fiber-coupled design for seeding laser unit, absolute laser frequency locking, and cyclic three-frequency switching necessary for simultaneous temperature and wind measurements. The all-fiber-coupled injection seeding configuration together with the solid-state Nd:YAG lasers make the Na Doppler lidar more compact and greatly reduce the system maintenance, which is conducive to transportable and unattended operation. A preliminary observational result obtained with this solid-state sodium Doppler lidar was also reported in this paper.

Seasonal variations of meteoric potassium layer over Beijing (40.41°N, 116.01°E)

A dual-wavelength resonance fluorescence lidar facility, operating at 770 nm and 589 nm, was set up in the mid-latitude of East Asia, Beijing (40.41°N, 116.01°E) to detect the upper atmospheric potassium and sodium layers simultaneously. This fluorescence lidar system has been operational for 220 nights, clocking 1250 h in total from November 2010 to October 2011 and May 2013 to April 2014. The observations reveal that the potassium layer shows considerable semiannual seasonal variations. Specifically, the column and peak densities vary semiannually with maxima in winter and summer. The centroid height displays semiannual variation, reaching maxima in spring and autumn. The RMS width has a slight semiannual seasonality with maxima in July and December. The seasonal behavior of the potassium layer in Beijing is similar to that in other potassium lidar sties. However, the unexpected difference is that the column and peak densities of the potassium layer are extremely large in winter, compared to the maximum values in summer.

Joint observation results of Na layer and ionosphere in Wuhan during the Total Solar Eclipse

During the total solar eclipse on July 22, 2009 in Wuhan, the joint observation test of Na layer and ionosphere was conducted by using the daytime observation atmospheric lidar and the GPS ionosphere detector. The results show that the full width at half maximum (FWHM) of Na layer density slightly narrowed during the total solar eclipse and broadened after the eclipse, while the height of Na peak slightly decreased in the eclipse and increased after the eclipse. These implying that Na layer changes reflect the rapid process of sunrise and sunset. The ionosphere total electron content (TEC) and the sky background light noise also presented an obvious fluctuation characteristic with the changes of solar irradiation during the process of total solar eclipse. The difference lies in that the changes of FWHM of Na layer atoms are much slower than that of ionosphere, the reason for this might be that the Na layer, after being disturbed by the total solar eclipse, will generate a series of complicated photochemical reactions and momentum transport processes, and then recombine the Na atoms. The Na atoms to be detected by the lidar need a lag process, which rightly conforms to the theoretical simulated results.