WHU VHF radar observations of the diurnal tide and its variability in the lower atmosphere over Chongyang (114.14° E, 29.53° N), China

Abstract

The diurnal tide (DT) and its variability in the lower atmosphere over Chongyang (114.14° E, 29.53° N) were studied based on the newly established Wuhan University (WHU) VHF radar observations with the height intervals of 0.145 km (below 9 km) and 0.58 km (above 9 km) in the whole year of 2012. We find that the DT was the dominant tidal component and showed remarkable height and season variations. A prominent seasonally dependent height variability characteristic is that maximum DT amplitude usually occurs around 6 km in the winter and spring months, which might be due to the tidal wave energy concentration arising from the reflections from the strong eastward tropospheric jet around 13 km and the ground surface. Our results suggest that the background wind is a crucial cause for height variability and seasonal variability of DT. In April 2012, a notable strengthening of DT is observed. Meanwhile, the significant higher harmonics of tides, i.e., the semidiurnal, terdiurnal, and even quarterdiurnal tides, can also be observed, which has seldom been reported. Interestingly, these four tidal components displayed consistent short-term variability, implying that they were excited by the same dramatically varying tidal source. In addition, we identified two symptoms of the coupling of DT and planetary waves (PWs), which can also lead to the short-term DT variability. One is the sum and difference interactions between DT and PWs, causing the tidal amplitude short-term variability as a consequence of the energy exchange among the interacting waves. The other one is the modulation of DT by PWs, leading to that the amplitude of DT varies with the periods of the PWs.