Tingdi Chen

Lidar observations of thermospheric Na layers up to 170 km with a descending tidal phase at Lijiang (26.7°N, 100.0°E), China

We report the first lidar observations of thermospheric Na layers up to 170 km at Lijiang (geomagnetic 21.6°N, 171.8°E), China, in March, April, and December 2012. The Na densities inside the layers are low, ranging from ~1 to ~6 cm−3 at altitudes of 130–170 km, about 3 orders of magnitude lower than the Na peak density in the mesopause region. All of these layers exhibit an apparent downward phase progression with a descending rate of 11–12 km/h or ~3 m/s, consistent with the vertical phase speed of semidiurnal tides around 140 km. We have identified at least 12 events from the total 37 nights of lidar observations with four shown in this report, giving an occurrence frequency of ~33% over Lijiang. These thermospheric layer events correspond to strong to moderate equatorial fountain effects, bolstering our hypothesis that the deposit of metallic ions from the equatorial region to low latitudes via the fountain effect provides the Na+ ions in the thermosphere over Lijiang. Adopting the theory by Chu et al. (2011) and the hypothesis by Tsuda et al. (2015), we further hypothesize that the thermospheric Na layers are formed through the neutralization of the tidal-wind-shear-converged Na+ layers via direct electron-Na+ recombination Na+ + e− → Na + hν. An envelope calculation using reasonable ion and electron densities shows good consistency with the observations.

Estimation of mesopause temperatures at low latitudes using the Kunming meteor radar

In this study, mesopause temperatures over a low-latitude station were derived by applying the temperature gradient model technique to data from a meteor radar installation located in Kunming (25.6°N, 103.8°E), China. The estimated temperatures are in good agreement with Sounding of the Atmosphere by Broadband Emission Radiometry (SABER) temperatures and exhibit clear seasonal and interannual variations with dominant spectral peaks at annual, semiannual, quasi 90 day, and terannual oscillations. However, the amplitudes of the temperature fluctuations and the dominant spectral peaks are larger than those from SABER. An improved method that accounts for the temperature sensitivity of the slope estimated from the meteor radar data was developed to calibrate the larger fluctuations obtained using the temperature gradient model technique. The resulting calibrated temperatures are more consistent with SABER observations, and the accuracy of the derived temperatures is significantly improved.

Mobile Rayleigh Doppler wind lidar based on double-edge technique

We describe a mobile molecular Doppler wind lidar (DWL) based on double-edge technique for wind measurement of altitudes ranging from 10 to 40 km. A triple Fabry-Perot etalon is employed as a frequency discriminator to determine the Doppler shift proportional to the wind velocity. The lidar operates at 355 nm with a 45-cm-aperture telescope and a matching azimuth-over-elevation scanner that provides full hemispherical pointing. To guarantee wind accuracy, a single servo loop is used to monitor the outgoing laser frequency to remove inaccuracies due to the frequency drift of the laser or the etalon. The standard deviation of the outgoing laser frequency drift is 6.18 MHz and the corresponding velocity error is 1.11 m/s. The wind profiles measured by the DWL are in good agreement with the results of the wind profile radar (WPR). Evaluation is achieved by comparing at altitudes from 2 to 8 km. The relative error of horizontal wind speed is from 0.8 to 1.8 m/s in the compared ranges. The wind accuracy is less than 6 m/s at 40 km and 3 m/s at 10 km.

First observation of mesosphere response to the solar wind high‐speed streams

We present a first analysis of 9 and 6.75-day periodic oscillations observed in the neutral mesospheric density in 2005 and 2006. Mesospheric densities near 90 km are derived using data from the Davis meteor radar (68.5°S, 77.9°E; magnetic latitude, 74.6°S), Antarctica. Spectral analysis indicates that the pronounced periodicities of 9 and 6.75 days observed in the mesosphere densities are associated with variations in solar wind high-speed streams and recurrent geomagnetic activity. Neutral mesospheric winds and temperatures, simultaneously measured by the Davis meteor radar, also exhibit 9- and 6.75-day periodicities. A Morlet wavelet analysis shows that the time evolution of the 9- and 6.75-day oscillations in the neutral mesosphere densities and winds are similar to those in the solar wind and in planetary magnetic activity index, Kp in 2005 and 2006. These results demonstrate a direct coupling between Suns Corona (upper atmosphere) and the Earths mesosphere.

Response of neutral mesospheric density to geomagnetic forcing

We report an analysis of the neutral mesosphere density response to geomagnetic activity from January 2016 to February 2017 over Antarctica. Neutral mesospheric densities from 85-95 km are derived using data from the Davis meteor radar (68.5°S, 77.9°E) and the Microwave Limb Sounder (MLS) on the Aura satellite. Spectral and Morlet wavelet analyses indicate that a prominent oscillation with a periodicity of 13.5-day is observed in the mesospheric density during the declining phase of solar cycle 24 and is associated with variations in solar wind high-speed streams and recurrent geomagnetic activity. The periodic oscillation in density shows a strong anti-correlation with periodic changes in the auroral electrojet (AE) index. These results indicate that a significant decrease in neutral mesospheric density as the geomagnetic activity enhances.

Gravity waves observation of wind field in stratosphere based on a Rayleigh Doppler lidar

Simultaneous wind and temperature measurements in stratosphere with high time-spatial resolution for gravity waves study are scarce. In this paper we perform wind field gravity waves cases in the stratosphere observed by a mobile Rayleigh Doppler lidar. This lidar system with both wind and temperature measurements were implemented for atmosphere gravity waves research in the altitude region 15-60 km. Observations were carried out for two periods of time: 3 months started from November 4, 2014 in Xinzhou, China (38.425°N,112.729°E) and 2 months started from October 7, 2015 in Jiuquan, China (39.741°N, 98.495°E) . The mesoscale fluctuations of the horizontal wind velocity and the two dimensional spectra analysis of these fluctuations show the presence of dominant oscillatory modes with wavelength of 4-14 km and period of around 10 hours in several cases. The simultaneous temperature observations make it possible to identify gravity wave cases from the relationships between different variables: temperature and horizontal wind. The observed cases demonstrate the Rayleigh Doppler Lidars capacity to study gravity waves.