Saturn 2010 Giant North Tropical Storm
by Marc Delcroix


Approximative storm meridian transit ephemerides(based on drift rates calculations with WinJupos):

2010 NTrZ Storm zone center ephemerides (worldwide, unfiltered) (updated Jan. 13th 2011) - best to plan observations of the whole storm complex
2010 NTrZ Storm core ephemerides (worldwide, unfiltered) (updated Dec. 23rd 2010) - best to plan observations of the brightest part

activity analysis 

Analysis based on amateur images received and SED activity information given by Georg Fischer in mails calling for observations

Second analysis from 2010.12.20-2010.12.30
Evolution to a Giant Storm

The storm evolved very rapidly. As soon as Dec. 22nd, in the splendid hi-res image of A.Wesley  details appear, showing a bright core elongated in longitude, separated into 3 zones, one bright, one bluish and a second bright zone. North East of this zone, the storm shows the birth of a tail in a bright yellowish spot (WS6), followed by a long tail extending to the east (almost 50° in longitude) with 2 other bright spots WS5 and WS4, and two faint spots WS3 and WS2.

These spots can be followed on the best next images, WS2 and WS3 being more difficult to image though. The Cassini probe in 2 sessions offered us a very nice view of the western and eastern part of the zone, showing how complex the tail is and the 3 lobes morphology of the brightest part.

Only 8 rotations later, two others hi-res images from A. Wesley again show how the tail as been elongated to the east, and how the bright part drifted to the west while spreading. At this date the whole zone is spread over 100° in longitude (System III), that is around 100 000 km long (and 10 000 km in latitude) !

A detailed drift analysis shows that the spots in the tails have slow drifts (WS2 and WS3 eastward, WS4 and WS5 westward), while the beginning of the tail WS6 has a higher westward drift, and the bright core follows the westward jet in the North Tropical zone around 2.3° LIII/day. This makes this atmospheric feature a truly giant one on Saturn's scale.

2010 NTrZ Storm 2010.12.20-30 analysis

First analysis from 2010.12.05-2010.12.19
Birth of a Great North Tropical Storm

Georg Fischer issued an alert in December as Cassini's RPWS detected again lightning in Saturn on Dec. 5/6th. Question was were would be the storm located in latitude (information not given by RPWS). The answer confirmed what Georg Fischer suspected, the new storm is located in Saturn tropical zone, but not south as what has been observed by amateurs since 2003  and Cassini ISS since 2004, but North! This shows clearly a seasonality effect of lightning on Saturn, as the northern hemisphere has just entered the spring after 2009 equinox.
The Saturn Electrostatic Discharges detected were very strong, and it turned out that the storm observed by amateurs was the brightest feature seen on Saturn since probably at least 14 years, very easy to image by amateurs and even visible on individual raw frames!
From the single Cassini Imaging Science System image session showing the storm at the very beginning, the storm rapidly grew more than 10 times bigger, so spread in latitude that due to the difference in wind speed upon this latitude range it probably left a long tail preceding it.
If we consider that the very bright zones are associated to lightning, the lightning zone is now very spread - with even maybe a white spot further east of the main zone.
Contrary to most of the previous storms observed, this one is brighter in visible wavelengths than in infrared.

That is a fantastic start for Saturn's 2010-2011 apparition...

2010 NTrZ Storm 2010.12.05-19 analysis

If you image Saturn, don't hesistate to send your images for this kind of work!