Thursday, 7 February 2013

Final Night on IRTF: Fog and Ice on the Wrong Planet

Cheesy grins in front of the IRTF
It's 5.30 pm and we're up here at IRTF for my final night of observations with TEXES, before flying for home tomorrow.  The TEXES run will continue all the way through until February 11th, but they're only half nights on Jupiter and Io (i.e., 6pm-midnight), so a lot easier on the brain and body than these full nights.  Unfortunately, as soon as I woke up around 2pm I could tell that the weather was going to be a problem - the inversion that normally keeps all the moist maritime air below Hale Pohaku had broken down, and the clouds had surrounded us.  I hiked up a nearby cinder cone, and it was a rather eery experience to be amongst the clouds.  As we drove up to IRTF, we could see clouds over the summit of Mauna Loa, and Haleakala on Maui was completely obscured by thick cumulus clouds.  The  worse news for us was the very high water clouds we could see above Mauna Kea, which will really screw our chances of getting decent observations.  Here's what the forecast says:

Unstable low-level clouds filling in with the northeasterly trades are expected to interact with an upper-level trough passing overhead during the next 24-36 hours. This could saturate the air mass below 15 thousand feet, bringing fog, ice, clouds and/or flurries to the summit over the next 2 nights. Turbulence associated with this trough is also expected to degrade seeing, should observing be possible, during this time. Fortunately, the trough will slip east of the Big Island early Friday morning and a new ridge will fill in from the west around that time as well. This will help stabilize the air mass, push the bulk of the moisture toward the SE, and rebuild the tradewind inversion near 6 thousand feet through that day. This will lead to more normal dry/stable summit-level conditions.

Great sunset with Subaru just opening
in the foreground, February 6th 2013

The high cloud made for a rather spectacular sunset, as it moved below a couple of distinct layers of cloud and took on a deep red colour before it finally vanished.  The air was pretty still, but the clouds were pretty ominous all around us.  IRTF opened its dome, followed by Subaru, but the rest of the summit seemed pretty quiet.  We moved straight to Jupiter, with the plan to spend six hours mapping the planet for Glenn Orton.  With the humidity rising, and the risk of being clouded out, we just shot as many images in eight spectral settings as we could.  It takes about 90 minutes to run through all eight, if there are no hiccups.  Io moved into eclipse from Jupiter's eastern side at 05:40 UT (should reappear on the western side at 08:00 UT), and was a wonderful focusing source for Jupiter.  By 07:20 UT a fog bank had moved in between us in IRTF and the summit ridge, and the humidity spiked up to 95%.  We could tell there were clouds overhead as we were trying to image.

Closing the Dome

Once we reach 95%, we have to close.  We can only reopen once the humidity drops back below 90% for a significant portion of time.  But then the concern is ice build up - I'm told if you go outside and touch the metal handrails, you'll know that it's icing up.  Then you have to wait for the humidity to drop sufficiently for it to sublimate, which can take a while.  Finally, if the ground is cold enough that ice starts forming there too, your night is over.  It's no longer safe to be up here, and we'd head down.  But while we're waiting for all these decision points, we just sit with the dome closed and hope that conditions improve.  I stood outside for a while, and you can feel the moisture on your face, and see that the stars are being obscured.  We waited until near midnight, but there was no improvement, and everything had iced up.  So we took the decision to call it a night, and head back down the mountain.... a shame, but I think we've got some incredible data these past five nights, so I'm not too upset!
The shadow of Mauna Kea at sunrise on
February 6th 2013

Ending the Observing Run

Part of the night was spent strategising over how to publish all the data we've taken, and what our priorities should be in the coming months.  We should be able to produce maps of key meteorological variables on Jupiter (temperature, humidity, winds and cloud cover), measure abundances of isotopic species and hydrocarbons on Saturn, and study atmospheric waves, auroral hotspots and giant storms on both planets.  That's a lot of work for us!

It's been an absolute privilege to work up here at IRTF this week.  I've learned a tremendous amount about TEXES from Tommy Greathouse and John Lacy, and I'm fired up to start analysing data as soon as I return to Oxford.  The experience of being up here on the mountain top is one I'll never forget, and I can understand why Hawaiians believe this 'White Mountain' to be a sacred, special place.  This blog has been a bit of an experiment, so if anyone has read it, I hope you've enjoyed these O2-deprived ramblings from 14000 feet!

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