Based on the long‐term observations of the Wuhan and Beijing Mesosphere‐Stratosphere‐Troposphere (MST) radars, the statistic characteristics of the mesospheric vertical winds at midlatitudes are investigated for the first time. The vertical wind data come from the Wuhan MST radar (29.51°N, 114.13°E) during 2012–2017 and from the Beijing MST radar (39.75°N, 116.96°E) during 2012–2014. The subdaily, seasonal, and annual variations of the mesospheric vertical winds at Wuhan and Beijing are presented. No obvious subdaily and seasonal variations are found and the annual variations of the mean vertical winds are downward in most of time. The mean vertical winds at Wuhan become smaller in summer and turn to upward at some heights, while those of Beijing only become smaller in summer. The difference of summer vertical winds over Wuhan and Beijing is closely related to the gravity wave activity. The Wuhan MST radar is located to the east side of the Qinghai‐Tibet plateau and also in the East Asian monsoon region, thus the mesospheric winds over Wuhan may experience more influence of gravity waves compared with those over Beijing. The possible bias sources in the vertical wind measurement of the two MST radars are carefully analyzed and the presented wind velocities are proved to be credible. The measured velocity magnitude is similar to other Very High Frequency radar observations, but much larger than that of the WACCM simulation. The Stokes drift, multicellular circulation structures, the wave influence on the radar echoes are raised as the potential sources for this discrepancy.

The present study investigates the ionospheric F‐layer scintillation responses in the American sector (90°W–0°, ±50° dip latitude) during the Northern Hemisphere winter sudden stratospheric warming events of 2007–2008, 2008–2009, 2009–2010, and 2012–2013. The scintillation data used in this work are obtained from the radio occultation observations of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission. The important results of this study are described as follows: the occurrence altitude and rate of ionospheric F‐layer scintillation over the American sector decrease by an average of 13.48 km and 17%, respectively, during the sudden stratospheric warming (SSW) periods compared with the pre‐SSW periods. We find that ionospheric F‐layer scintillation over the American sector shows similar inhibitory responses to each SSW event, although these SSW events have diversities in some aspects, such as SSW types and solar and geomagnetic activities. To our knowledge, this study is the first to discover that an SSW event under low solar activity, including a minor warming event, can obviously affect the generation of ionospheric irregularities. Additionally, the types of SSW events may influence the decrease in altitude but not the occurrence rate. The decreased plasma vertical drift during prereversal enhancement, together with the changed meridional wind, are the possible mechanisms for the above results. In addition, we find that the enhanced planetary wave and lunar semidiurnal tide activities may be responsible for the decreases in the occurrence rate of ionospheric F‐layer scintillation before the peak warming of the 2008–2009 and 2009–2010 SSW events.

The Wuhan mesosphere–stratosphere–troposphere (MST) radar is a 53.8 MHz monostatic Doppler radar, located in Chongyang, Hubei Province, China, and has the capability to observe the dynamics of the mesosphere–stratosphere–troposphere region in the subtropical latitudes. The radar system has an antenna array of 576 Yagi antennas, and the maximum peak power is 172 kW. The Wuhan MST radar is efficient and cost-effective and employs more simplified and more flexible architecture. It includes 24 big transmitter–receiver (TR) modules, and the row or column data port of each big TR module connects 24 small TR modules via the corresponding row or column feeding network. Each antenna is driven by a small TR module with peak output power of 300 W. The arrangement of the antenna field, the functions of the timing signals, the structure of the TR modules, and the clutter suppression procedure are described in detail in this paper. We compared the MST radar observation results with other instruments and related models in the whole MST region for validation. Firstly, we made a comparison of the horizontal winds in the troposphere and low stratosphere observed by the Wuhan MST radar with the radiosonde on 22 May 2016, as well as with the ERA-Interim data sets (2016 and 2017) in the long term. Then, we made a comparison of the observed horizontal winds in the mesosphere with the meteor radar and the Horizontal Wind Model 14 (HWM-14) model in the same way. In general, good agreements can be obtained, and this indicates that the Wuhan MST is an effective tool to measure the three-dimensional wind fields of the MST region.

As a result of partial specular reflection from the atmospheric stable layer, the radar tropopause (RT) can simply and directly be detected by VHF radars with vertical incidence. Here, the Beijing mesosphere–stratosphere–troposphere (MST) radar measurements are used to investigate the structure and the variabilities in the tropopause in Xianghe, China, with a temporal resolution of 0.5 h from November 2011 to May 2017. The high-resolution radar-derived tropopause is compared with the thermal lapse-rate tropopause (LRT) that is defined by the World Meteorological Organization (WMO) criterion from twice-daily radiosonde soundings and with the dynamical potential vorticity tropopause (PVT) that is defined as the height of the 2 PVU (PVU – potential vorticity units; 1 PVU = 10⁶ m² s⁻¹ K kg⁻¹) surface. We only consider tropopauses below 16 km in this study because of limitations with the radar system. During all the seasons, the RT and the LRT in altitude agree well with each other, with a correlation coefficient of ≥0.74. Statistically, weaker (higher) tropopause sharpness seems to contribute to larger (smaller) difference between the RT and the LRT in altitude. The RT agrees well with the PVT in altitude during winter and spring, with a correlation coefficient of ≥0.72, while the correlation coefficient in summer is only 0.33. As expected, the monthly mean RT and LRT height both show seasonal variations. Lomb–Scargle periodograms show that the tropopause exhibits obvious diurnal variation throughout the seasons, whereas the semidiurnal oscillations are rare and are occasionally observed during summer and later spring. Our study shows the potential of the Beijing MST radar to determine the tropopause height as well as present its diurnal oscillations.

With the support of the second phase of the Chinese Meridian Project, a new mesosphere-stratosphere-troposphere observation radar (MST radar), called Qinzhou MST radar, located in Qinzhou City, Guangxi Province, China (22°7'55''N,108°16'20''E) is under construction. The Qinzhou MST radar is a large VHF monostatic pulse Doppler radar with an active phased array antenna system, mainly using Doppler beam swinging technique for observation. The capability of multibeam observation, space antenna observation, and frequency- and spatial-domain interferometry are also employed. The main scientific objective of this radar is to explore the atmosphere dynamical processes at low latitudes of China. The observation of ionospheric field-aligned irregularities (FAIs) is also an important function of the radar. The radar applies a circular array composed of 1261 3-element crossed Yagi antennas with a diameter of 153 m and an aperture of near 2×10 ⁴ m ² . Thereinto, 997 elements connect both transmitting and receiving channels and 264 elements distributed near the edge connect only receiving channels. The peak power of the transmitter in each transmitting/receiving (T/R) module is 2 kW. The central frequency and bandwidth of the output signal are 50 and 4 MHz, respectively. The peak power of the whole system will be close to 2 MW. This article presents the initial design of the Qinzhou MST radar, and the construction will be completed at the end of 2022.

Based on long-term observations from Wuhan and Beijing MST (Mesosphere-Stratosphere-Troposphere) radars, we analyzed the climatological properties of mid-latitude mesospheric winds and evaluated them against the Horizontal Wind Model (HWM14). Measurements of zonal and meridional winds were collected from 2012 to 2021 using these two MST radars. The seasonal daily and monthly variations and periodic oscillations in mesospheric zonal and meridional winds are presented. Monthly mean and seasonal zonal winds recorded by two MST radars have similar height-time distributions to the HWM14. However, there are differences in zonal wind speeds, especially between summer and winter measurements and HWM14. The agreement between model results and actual radar measurements is poorer for meridional winds than for zonal winds. Through harmonic analysis, it is revealed that the zonal and meridional winds display significant Annual Oscillation (AO) between 65 and 85 km, while Semi-Annual Oscillation (SAO) is not readily apparent. It is found that there is no significant correlation between solar activity and the wind variations or data acquisition rate from MST radar. Overall, these studies help us better understand atmospheric changes in the mesosphere and provide ground observation references for models.