Clarify the seasonal relationship between K1 and the diurnal tide

Clarify the relation between the Martian zonal-wavenumber-1 Kelvin mode K1 and the diurnal tide during periods other than Northern Hemisphere summer, including the dusty season.

Background

The paper explains that K1 is a free atmospheric normal mode whose eigenfrequency varies with the global-mean atmospheric temperature, whereas the diurnal tide is a solar-forced oscillation with a period of one sol. During Northern Hemisphere summer, K1 can approach the diurnal frequency and potentially resonate with the eastward nonmigrating diurnal tide DE1.

Previous observational studies had mainly examined DE1 or inferred K1 indirectly from phase changes in the diurnal signal. The authors identify the relationship between K1 and the diurnal tide outside Northern Hemisphere summer—particularly during dusty periods—as insufficiently understood, motivating direct K1 detection using InSight pressure observations.

References

In addition, the relation between the diurnal tide and K1 during periods other than the NH summer—such as the dusty season—remains largely unclear.

— Quasi-diurnal Kelvin Wave Observed in the Atmosphere of Mars by the Pressure Sensor on the InSight Lander  (2608.19892 - Asumi et al., 20 Aug 2026) in Section 1, Introduction

The reason why the K1 frequency is lower in the Mars PCM than in the InSight observations remains unclear, and a detailed investigation is beyond the scope of the present study.

— Quasi-diurnal Kelvin Wave Observed in the Atmosphere of Mars by the Pressure Sensor on the InSight Lander  (2608.19892 - Asumi et al., 20 Aug 2026) in Section 4, Results from Mars PCM simulations