Last month has been damn cold. Our last decent blow (87km/hr / 46 knot gusts) was the first few days of March, since then, the wind has averaged under eight knots. When we get the big weather systems come through, obviously the wind chill makes it unpleasant to go outside but in fact the temperature rises by a few degrees. This blow in March however had temperatures several degrees below freezing and we had some grease ice trails form, originating in the shallow sheltered water against the cold rocks and drifting off downwind. And so it began…
When I first saw this grease ice forming, on a still and cold morning, I didn’t think much of it. The next wind will blow this away. But really there hasn’t been much wind to speak of for four weeks (and counting)… and it has just gotten colder.
And then came the snow. We’ve had dustings of snow throughout the summer but if it settles at all, it doesn’t last long. As Bob’s party of four prepared for a walk to Watts hut we got a substantial dump that delayed their departure by a day, turned the last couple of kilometres to the hut into a four hour epic, and left them there another day still exhausted and recovering! Having said that, it sure did make the place look pretty.
Generally, immediately after a snow dump we get a decent blow that moves most of it, shaping blizzard trails behind rocks and clearing it away from exposed areas. But this snowfall was followed by only light to moderate winds, so we had a fairly evenly distributed loose powder which was great fun to walk though. Although it’s not necessarily quite as enthralling when you’re tired and you can’t see your footing on rough rocky ground and your survival pack is starting to feel heavy after carrying it all day.
The cover of snow has probably contributed to the colder temperatures by reflecting most of the sunlight. Certainly the Vestfolds convergence clouds seem to be a thing of the past. This, still settled air, and the dark nights we are now getting as we move past the equinox, means the sea ice has come in and is here to stay.
The sunlight meter is the much joked about “crystal ball” of meteorology. Sunshine is focussed onto a strip of cardboard, which burns a scorch mark (or in full sun, burns a gaping hole). One faces north for day time sunshine and one faces south, and each day we tally up the sunshine hours as we replace the cards. Now we’ve moved past equinox we will only need to replace the day time card. This day when it frosted up, stratocumulus dissipated and the full sun was enough to scorch the cardboard even as the frost melted.
I have every second weekend off and I’m always keen to get out and explore. On 23-24 March Rich and I planned to repeat the infamous Watts hut epic. In the fortnight since Bob’s party did the walk the snow had consolidated and now it was generally half the depth and proportionately better packed. It was overcast and really too cold to stop so we briskly knocked the walk over in a solid five hours and twenty minutes.
Thankfully the huts have gas heating and triple glazed windows, although it takes a long time to get them warmed up. The carbon monoxide detector is definitely worth it’s weight and it’s quite interesting to see the levels of CO got up to 30ppm or so. Having the vents open is absolutely mandatory, although we could probably have closed them off a little once we’d turned the heaters off for the night as it was damn cold in the morning.
Refilling the hut water was a bit of a mission. It was already cold just carrying the 20 litre plastic jerry containers to the rapids. I warmed up a bit as I used the ice axe to cut through 50-70mm of ice in a rectangle shape to fit the 20 litre dipping bucket. As the water was shallow I had to move a rock in the stream bed to get the bucket in at all. I did this with the ice axe and it came out with a coating of ice that remained there all day. I made sure to stand upwind as I poured water into the jerry cans, as any splashes on the plastic froze. As I expected, the lids snap froze on – but I thought two of us would be able to prize them off at the hut. In the end we needed to pour hot water over it. Luckily Rich had some ready in a thermos flask. This is why we always leave water in a saucepan at the hut – a solid lump of ice beats snow any day.
We walked back by a different route, a brisk walk again at the same pace got us back at Davis in the early afternoon. While we had some sun briefly in the morning by the time we returned it was looking like snow. A good opportunity for me to try the Davis spa.
In early summer the sea ice was closed and so far there has been no travel on the sea ice since. Having seen enormous elephant seals struggle to keep their access hole to the water open (it has since closed off, after someone missed the night shift?) we eventually went out to take some measurements. This is done both to maintain a historic record, and to justify opening the sea ice to travel earlier than May 15. For our first walking on water experience we used a specially designed floating platform, after watching the accompanying video of men in moustaches pulling kids out of half frozen lakes in Connecticut.
The sea ice measured a consistent 400mm – over a foot. The freeboard between the waterline and the top of the ice was around 20mm – indicating that the ice is 95% as dense as sea water. A good quality ice pack. If ice freezes slow enough the salt falls to the bottom, and the salt also gradually precipitates out over time. I tasted the shavings and they were distinctly brackish but not as salty as sea water. On the morning of 31 March we had an overnight minimum of -27.6C – a record low for March. I thought it was cold! That day was fine and clear and it remained cold, with the high of -20.0C a record low for March as well, this time equalled exactly 37 years earlier.
This is another physics in action trick, which I’ll do my best to explain off the top of my head. I used to clean my lunchbox at work by shaking a small amount of boiling water around inside it. This helps keep work “interesting” as what tends to happen is the lid explodes off and you get boiling water all over you. Basically you have rapidly heated the air in the lunchbox. Heated air expands. In the same way, -25C air explodes when suddenly heated by a jug of boiling water. Because of this explosion you have a lot of droplets with a lot of surface area to continue warming the air (whilst cooling the droplets). Therefore it is possible for the water to turn into a cloud (droplets small enough to suspend in the air) before it reaches the ground.
If you’re really keen and you want to understand the next paragraph, know this first:
- Steam that you see isn’t actually water vapour, it is tiny water droplets suspended in the air – exactly like in a cloud. Water vapour is invisible.
- Like many clouds it is quite possible that the water droplets are supercooled (they could be minus twenty five Celsius)
- For water droplets to form, the vapour needs to find a condensation nuclei (a certain type of dust particle)
- For ice crystals to form you need deposition nuclei, and there aren’t as many around. Hence the fact that supercooled water droplets are common
In this photo the majority of the cloud is water droplets (steam). This is probably why the ice crystals can be seen on the outside where they have had “first dibs”. They seem to be lead by droplets of water of normal size (too big and heavy to sit in a cloud). These zip past a lot of cold air so they leave freezing ice crystals in their path, but some may reach the ground. Now that I’ve dissected it in my mind instead of just listening to the bang and taking photos, I would like to try the experiment again and see how things change if I add a little salt or dust to the water, or if I use the purified water we use for making hydrogen. I’m sure temperature also makes a difference. Onto tide cracks…. they creak and squeak as the water moves them around. Sometimes I’ve even seen a visible swell in the first five or ten metres of ice from the shore. My other little project is seeing if I can tell the difference between flooding and ebbing tide based on the sound of the creaking tide crack. Wish me luck with that.