Research on 16-day Planetary Waves in the Mid-latitude Troposphere, Stratosphere, Mesosphere, and Lower Thermosphere with Langfang Dual-frequency ST-M Radar Data

Abstract. Horizontal wind observational data by the dual-frequency Stratosphere-Troposphere-Meteor (ST-M) radar at Langfang Observatory from March 2023 to February 2024, was used to investigate spatiotemporal variations, and propagation characteristics of planetary waves, as well as the relationship between planetary waves in the troposphere and stratosphere (ST) and the mesosphere and lower thermosphere (MLT) over Langfang mid-latitude regions. The quasi-16-day planetary wave’s activities are obtained by applying band-pass filtering on the daily averaged horizontal wind. Simultaneous MERRA-2 reanalysis wind data are used to derive the dominant zonal wavenumbers of 16-day waves in ST and mesosphere, and also the background zonal winds through which the planetary may propagate vertically. Results show that 16-day wave activity occurs all the year, its zonal component is stronger than the meridional component, and it is characterized by being strong in winter and weak in summer. It is newly found that the vertical phase propagation direction of 16-day wave got changed during autumn and winter that in autumn August–September it is upward in ST and downward in MLT, and upward in ST but upward in MLT in November–December, and downward in ST and upward in MLT after later December. The dominant zonal wavenumbers for the 16-day wave are (ST: -1, MLT: 2) in August–September, and (ST: 2, MLT: 4) in November–December, and (ST: -1, MLT: 4) in December–January respectively in MERRA-2 data. It can be derived with the information of vertical phase velocity and zonal wavenumber that the group velocity of the 16-days in radar data is downward in ST and downward in MLT in August–September, and upward in ST and upward in MLT in November–December, and downward in ST and Upward in MLT in December–January, respectively. Together with the zonal background winds from MERRA-2 and radar over the field site which provide the vertical propagation condition for planetary waves, it can infer that the observed 16-day wave in ST may be triggered by the jet at about 14km altitude and hence propagated downward in August–September, and the background wind do not allow upward propagating of the wave. So, the observed wave in MLT in August–September may be trigged by another unknown source above or refracted from low-or-high latitude regions. The observed 16-day wave in ST in November–December is not the same as that before, was generated in the lower atmosphere and propagated through the background winds upward maybe into the MLT regions as observed. In December–January, the observed 16-day wave in ST gets changed zonal wavenumber again, it is also generated in the lower atmosphere and propagate upward. However, its upward propagation will be blocked by the above winds and therefore cannot penetrate into the MLT above. The observed wave in MLT in December–January could be the one already existed there before. The newly observations and interpretations help us to further understanding the vertical coupling among the ST and MLT by planetary waves.