We characterise the origin and evolution of a mesoscale wave pattern in Jupiters North Equatorial Belt (NEB), detected for the first time at 5 $mu$m using a 2016-17 campaign of `lucky imaging from the VISIR instrument on the Very Large Telescope and the NIRI instrument on the Gemini observatory, coupled with M-band imaging from Junos JIRAM instrument during the first seven Juno orbits. The wave is compact, with a $1.1-1.4^circ$ longitude wavelength (wavelength 1,300-1,600 km, wavenumber 260-330) that is stable over time, with wave crests aligned largely north-south between $14$ and $17^circ$N (planetographic). The waves were initially identified in small ($10^circ$ longitude) packets immediately west of cyclones in the NEB at $16^circ$N, but extended to span wider longitude ranges over time. The waves exhibit a 7-10 K brightness temperature amplitude on top of a $sim210$-K background at 5 $mu$m. The thermal structure of the NEB allows for both inertio-gravity waves and gravity waves. Despite detection at 5 $mu$m, this does not necessarily imply a deep location for the waves, and an upper tropospheric aerosol layer near 400-800 mbar could feature a gravity wave pattern modulating the visible-light reflectivity and attenuating the 5-$mu$m radiance originating from deeper levels. Strong rifting activity appears to obliterate the pattern, which can change on timescales of weeks. The NEB underwent a new expansion and contraction episode in 2016-17 with associated cyclone-anticyclone formation, which could explain why the mesoscale wave pattern was more vivid in 2017 than ever before.
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