Monday, 27 February 2012

Long Distance Storm Chasing - A Plea for Help!

Last spring, Saturn’s gigantic springtime disturbance was characterised for the first time in the infrared, allowing us to measure the vertical temperature structure of a Saturnian storm system.  Our paper (Fletcher et al., 2011, Thermal Structure and Dynamics of Saturn’s Northern Springtime Disturbance, Science, 332, 1413--1417,, showed that the thermal infrared imaging yielded some surprises - not least was the dramatic effect that this churning, tropospheric storm system had on the usually calm and quiescent stratosphere (see Saturn image on the far right).  It spawned two warm airmasses, which we termed ‘beacons’ because of their impressive emission at infrared wavelengths.  These heated airmasses were tracked throughout 2011 by Cassini, the Very Large Telescope in Chile, and the Infrared Telescope Facility in Hawai’i.

Today (February 2012), a single large hot airmass remains in Saturn’s stratosphere, but there’s a big question remaining - does this have any impact on the visible cloud tops?  Indeed, one of the big challenges for giant planet science is relating visible changes in albedo and cloud colouration to environmental changes (e.g., changes in temperature, cloud formation or chemistry).  So far, our comparisons with visible light observations have suggested that the effects of the hot stratospheric beacon are completely invisible.  The chart above shows the expected longitude (System III West) of the beacon, and an Excel spreadsheet listing the longitude on each date through the rest of 2012 can be found here:  

As Saturn reaches opposition on April 16th 2012, the next few months provides an excellent opportunity to search for any unusual goings-on beneath the hot beacon.  To find the System III Longitude visible from Earth at any time, use the JPL Horizons Ephemeris Generator (with option 14 for the table settings).

Wishing you clear skies and happy storm chasing!


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