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We present an analysis of a quarterdiurnal tide (QDT) during the 2019 Arctic sudden stratospheric warming (SSW) event. The analysis is based on data obtained from a meteor radar located at Mohe (MH, 53.5°N, 122.3°E), China. The enhancement of the QDT amplitude is observed during the SSW and the maximum QDT amplitude is about 10 m/s in both neutral wind components. Using the meter radar measurements at MH in the period from August 2011 to April 2019, a probability density function of the QDT amplitude is estimated. The probability of the QDT amplitude larger than 8 m/s is less than 1% at MH. A clear seasonal variability of the QDT amplitude is apparent with the maximum amplitudes that appeared in winter. Based on our analysis, the seasonal variability of the QDT is not the main reason that amplified the QDT. According to the bispectral and bicoherence analyses, nonlinear interaction between tidal waves may contribute to the enhancement of the ODTs. The nonlinear interaction between two semidiurnal tides (SDTs) is important, while the effect of the nonlinear interaction between the diurnal tide and the terdiurnal tide is secondary. It may be possible that the effect of the 2019 SSW amplifies the SDT first and then the QDT is generated via nonlinear interaction of SDTs. Key Points: Strong quarterdiurnal tides (QDTs) are observed in the mesosphere and lower thermosphere during the 2019 Arctic sudden stratospheric warming (SSW)The nonlinear interaction between tidal waves may contribute to the enhancement of the QDTsThe effect of the 2019 Arctic SSW may play an important role in the amplification of the QDTs [ABSTRACT FROM AUTHOR]

Mesospheric winds from three longitudinal sectors at 65°N and 54°N latitude are combined to diagnose the zonal wave numbers (m) of spectral wave signatures during the Southern Hemisphere sudden stratospheric warming (SSW) 2019. Diagnosed are quasi‐10‐ and 6‐day planetary waves (Q10DW and Q6DW, m = 1), solar semidiurnal tides with m = 1, 2, 3 (SW1, SW2, and SW3), lunar semidiurnal tide, and the upper and lower sidebands (USB and LSB, m = 1 and 3) of Q10DW‐SW2 nonlinear interactions. We further present 7‐year composite analyses to distinguish SSW effects from climatological features. Before (after) the SSW onset, LSB (USB) enhances, accompanied by the enhancing (fading) Q10DW, and a weakening of climatological SW2 maximum. These behaviors are explained in terms of Manley‐Rowe relation, that is, the energy goes first from SW2 to Q10DW and LSB, and then from SW2 and Q10DW to USB. Our results illustrate that the interactions can explain most wind variabilities associated with the SSW. Plain Language Summary: Sudden stratospheric warming events occur typically over the winter Arctic and are well known for being accompanied by various tides and Rossby waves. A rare SSW occurred in the Southern Hemisphere in September 2019. Here, we combine mesospheric observations from the Northern Hemisphere to study the wave activities before and during the warming event. A dual‐station approach is implemented on high‐frequency‐resolved spectral peaks to diagnose the horizontal scales of the dominant waves. Diagnosed are multiple tidal components, multiple Rossby normal modes, and two secondary waves arising from nonlinear interactions between a tide component and a Rossby wave. Most of these waves do not occur in a climatological sense and occur around the warming onset. Furthermore, the evolution of these waves can be explained using theoretical energy arguments. Key Points: Mesospheric winds from multiple longitudes in the NH are combined to diagnose zonal wave numbers of waves during the Antarctic SSW 2019Diagnosed are Q6DW, Q10DW, M2, SW1, SW2, SW3, and LSB and USB of Q10DW‐SW2 nonlinear interactionsLSB and USB are generated asynchronously, during which their parent waves evolve following the Manley‐Rowe energy relations [ABSTRACT FROM AUTHOR]