------ Michel.J Report -----
This dark spot at about B"=32° is visible since February 16th on the my images and those I received for the JUPOS project. 
It is retrograding at +0.8°/d (see attached plate and graph).




------ Michel.J Report -----

------ John H. Rogers Report -----

That’s indeed a notable and interesting dark spot: thanks to Dave Tyler 
for spotting it, and to Anthony and Michel for assembling those sets of 
images, and to everyone else who has observed it.  Anthony and Michel 
have shown that it is a meteorological feature which developed over 
several weeks, although it was certainly worth investigating a possible 
impact origin for such a notable dark spot.  From it's latitude of 32 
deg.N, it's an anticyclonic dark spot.
 
Attached is a more extensive set of images, with the feature(s) of 
interest marked.  In deference to the people who provided the great 
majority of these images, and to professional interest in this, north is 
up in this set!  But I can send a version with south up, or a version 
without labels, if required.
 
This seems to be another example where small-scale but intense 
turbulence in the cyclonic belt gives rise to retrograding disturbance 
which feeds dark material into the adjacent anticyclonic zone.  This is 
happening at other longitudes in the N. Temperate domain at present, in 
the aftermath of the 2012 NTB revival, as small cyclonic rifted regions 
produce dark material which comprises a ‘North Temperate Disturbance’ in 
the NTZ [refs. 1 & 2].  It also sometimes happens in the S. Temperate 
domain, in the ‘Sf. tail’ of a dark STB segment, generating an 
anticyclonic dark spot [ref.3].
 
In the present case, the best images show a small turbulent outbreak 
developing in the NTB in early Feb., then the very dark spot developing 
f. it, initially on Feb.16 when you can see tiny dark spots enveloping a 
tiny white spot, which I suggest was an anticyclonic vortex.  The small 
black arrowheads are suggested identifications of subsequent tiny dark 
spots which I think were arising from the turbulent outbreak (so 
small-scale that it is barely visible in some images) and retrograding 
to merge with the very dark spot, making it especially dark on Feb.21 
and Feb.28 and thereafter.
 
best regards,
 
John
 
-------------------------------
References to our recent bulletins:
[1] 2013/14 Report no.4  
(http://www.britastro.org/jupiter/2013_14report04.htm)
[2] Set of images sent out last month, showing the bright new outbreak 
in NTB (I’ll post an updated version soon).
[3] ‘Jupiter’s South Temperate domain: Behaviour of long-lived features 
and jets, 2001-2012’
   (http://www.britastro.org/jupiter/stemp2013.htm)
-------------------------------
------ John H. Rogers Report -----

------ mike wong Report -----

here is a screenshot of the IRTF/CSHELL data viewer. 
gordy bjoraker is PI of our time at IRTF, and tilak 
hewagama the other observer.
 
on the left you see a 5-micron image, on the right a 
1.60-micron continuum image. we were imaging through 
clouds, and the instrument is designed for 
spectroscopy, so these are not the prettiest of 
images.
 
the location of the feature is 33 +/- 3 deg N 
(planetographic) and 220 +/- 6 deg W (sys III).
 
we do have some methane images at 1.64 microns, but we 
are still analyzing calibration issues with that. 
but combined with the pic du midi result, it seems 
pretty clear that this is not an impact.
 
these were taken last night, UT march 8 at about 
08:33.
------ mike wong Report -----

------ Glenn Orton Comment -----

I've not seen Mike Wong's CSHELL images, 
but it will be instructive to see the relative brightness temperature of the dark features.   
We normally see dark-albedo regions as relatively bright at 5 microns, although not as bright as genuine 5-micron 'hot spots'.   
But there were plenty of dark regions, as I recall, in the SEB revival sequence where this was not at all the case.


------ Glenn Orton Comment -----

[Michel Jacquesson : Sevigny-Waleppe (Ardennes) France]