Jupiter in 2024/25, Report no.5:  The NTBs jet outbreak

John Rogers¹, Shinji Mizumoto², Gianluigi Adamoli³, Rob Bullen³, Grischa Hahn³, Michel Jacquesson³, Hans-Jörg Mettig³, & Marco Vedovato³

(1) BAA; (2) ALPO-Japan; (3) JUPOS team

The NTBs jet outbreak has been very impressive and fascinating, so much so that we have not had time to post interim reports.  This report will combine everything that we have learnt about the process.  It will be finalised this month (2025 March), but meanwhile we post this abstract so that anyone interested can see a summary of it.  Meanwhile, complete charts and sets of maps covering the outbreak have been regularly posted by Shinji Mizumoto on ALPO-Japan. 

Summary

The NTBs jet outbreak, predicted to occur in 2024 or 2025, duly appeared on 2025 Jan.10 (see Report no.4). These events are currently occurring every 4-5 years, and are among the most spectacular, energetic, and fast-moving phenomena on Jupiter.   This one has unfolded in exactly the same way as previous such outbreaks, and given us new insights into the processes.

It began, as always, with the appearance of a small bright spot which rapidly grew to be the brightest feature on the planet at all wavelengths from UV to IR and in the methane absorption band, indicating that it was a convective plume rising to very high altitude. This plume accelerated over the first few days, then maintained a constant drift of -5.0 deg/day in System 1 from Jan.14-31, which is typical for these super-fast outbreaks.  Up to Jan.31 it was still super-bright at all wavelengths, esp. the methane band, and it created a long expanding wake following it like a comet’s tail.  The wake contained large dark patches which appeared periodically, and small bright spots on the north side, most of which moved with speeds close to System 1. There were also small bright, methane-bright spots arising at the following end, accelerating to speeds similar to the main plume but short-lived.  We show that these “wake-induced plumelets” are a typical feature of these outbreaks.

On Jan.27 a second such plume appeared, only 20º preceding the first, and rapidly became as bright as the first, with almost identical speed.

On Feb.1-4, the first plume caught up with the wake of the second, and disintegrated within a few days, leaving plume 2 leading a very long turbulent dark wake.  Meanwhile two more plumes (or plumelets) appeared shortly following the wake: no.3 only lasted a few days (Feb.1 to 3), but no.4 persisted from Jan.31 to Feb.8.  More such wake-induced plumelets appeared in the subsequent week, while on Feb.9, plume 5 appeared in a largely undisturbed sector, and grew to become another independent plume.  In total, we identified eight such storms, of which numbers 1, 2 and 5 were independent primary plumes, and the others were wake-induced plumelets, although number 4 could be an intermediate case.  Plumes 2 and 5 persisted until late February, when each caught up with the wake preceding it and rapidly faded, both disappearing by March 1.

All three primary plumes first appeared at 24.0-24.6ºN, then drifted south and accelerated within a few days, to remain at 23.3 (±0.3)ºN with sustained speeds of -5.0, -5.1, and -4.6 deg/day (plumes 1,2,5 respectively). As usual, they all broke up within a few days when they caught up with the wake of the next plume ahead.

The plumes and other white spots all fit a zonal drift profile which peaks at 23.3ºN, DL1 = -5.1 deg/day (u₃ = +166.6 m/s), and is similar to the zonal wind profile from Voyager (one year before a similar outbreak), but extends to faster speed and lower latitude than the profile from Cassini (peak u = 136.2 m/s).  Zonal wind profiles have now been produced by G. Hahn from amateur images just before and after the present outbreak. In 2024 Nov., the peak was 150 m/s at 23.5ºN (slightly faster than the long-lived grey streaks that were tracked at 23.3ºN).  In 2025 Feb. (across the wake of the outbreak), 4 profiles range from a narrow peak at ~141 m/s to a broad peak at ~126-136 m/s.  These profiles confirm that the super-fast plumes and plumelets erupted from and moved with a deeper super-fast jet, but other features at cloud-tops never achieved this speed; the jet at cloud-top level only showed modest acceleration before the outbreak, and modest deceleration in the wake.

It is thought that these outbreaks occur when sufficient available potential energy has accumulated below the thick cloud layer that whitens the NEB, and they consist of giant convective plumes erupting from the water-cloud layer, well below the visible cloud-tops.  In the 2025 outbreak, JunoCam on Jan.28/29 directly imaged lightning in plume 1.  The convection can no longer be sustained where these storms have disrupted the pre-existing vertical atmospheric layering, so the plumes break up when they reach the wake of the next plume. We suggest that the wake-induced plumelets (which we have also observed in some previous outbreaks) are similar plumes triggered by the approach of the following end of the wake, but in this situation they are less intense and are short-lived.

Full report to be posted soon….