High-resolution Beijing mesosphere–stratosphere–troposphere (MST) radar detection of tropopause structure and variability over Xianghe (39.75° N, 116.96° E), China

摘要

As a result of partial specular reflection from the atmospheric stablelayer, the radar tropopause (RT) can simply and directly be detected by VHFradars with vertical incidence. Here, the Beijing mesosphere–stratosphere–troposphere (MST) radar measurements areused to investigate the structure and the variabilities in the tropopause inXianghe, China, with a temporal resolution of 0.5 h from November 2011 toMay 2017. The high-resolution radar-derived tropopause is compared with thethermal lapse-rate tropopause (LRT) that is defined by the World MeteorologicalOrganization (WMO) criterion from twice-daily radiosonde soundings and withthe dynamical potential vorticity tropopause (PVT) that is defined as theheight 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 thisstudy 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 correlationcoefficient of ≥0.74. Statistically, weaker (higher)tropopause sharpness seems to contribute to larger (smaller) differencebetween the RT and the LRT in altitude. The RT agrees well with the PVT inaltitude during winter and spring, with a correlation coefficient of≥0.72, while the correlation coefficient in summer is only0.33. As expected, the monthly mean RT and LRT height both show seasonalvariations. Lomb–Scargle periodograms show that the tropopause exhibitsobvious diurnal variation throughout the seasons, whereas the semidiurnaloscillations are rare and are occasionally observed during summer and laterspring. Our study shows the potential of the Beijing MST radar to determinethe tropopause height as well as present its diurnal oscillations.