christina j williamson

After Alaska, we flew to Hawaii and then Fiji on NASA ATom. The tropics are very dynamic, active areas in the atmosphere and this produces a lot of interesting phenomena that we study. These flight routes are also pretty remote, so it’s interesting to see where the air is super clean and where we still have influence from continental sources. There are also local influences, such as forest and agricultural fires on the islands where we land.

We spent one day on the ground in both Hawaii and Fiji. In Hawaii, my instruments were performing great, so after processing the data and sorting some other work stuff I had some hours free to explore. We made a short hike down a cliff to a beautifully verdant valley and black sand beach.

To measure the smallest particles in the air, I have a set on instruments with 10 different channels between them. Each channel counts all the particles larger than a given size, and by setting all the channels to different sizes I can calculate a size distributions of particles, that is, how many particles of each size are present. On the flight from Hawaii to Fiji one of these channels started having problems. It either counted more particles than made sense, or fewer, or had crazy-looking fluctuations. The particle concentration is a product of two measurements: flow, and optical counts. The flow of the troubled channel looked fine, so I figured the problem had to be with the optics.

The day after we landed in Fiji, I went back to the plane first thing in the morning to try and solve the problem. I had thought that perhaps some moisture or dirt was on the optics, giving me false counts. I cleaned them, and saw no improvement. I then examined the signal from the optics with an oscilloscope and saw that everything was wandering around in ways it should not be. On discussion with a colleague, we figured that this must mean that an intentional block in the optics was letting too much light through to the sensor and this was causing the wandering. The block must have slipped out of alignment.

To get the block realigned in the lab, I have a complex set up, where I take it out of the instrument, power it separately and use special equipment to test the signal as I realign. This was not possible in Fiji. I considered trying a version of this in my hotel room, perhaps butchering a phone charger that gives the correct voltage power to set it up, but it seemed unlikely to succeed. In the end I managed to leave it powered up in the instrument, but suspended above it so that I could access the necessary parts to move the block. With much caution, I slowly adjusted the block’s position while a colleague monitored the oscilloscope and told me when things wandered more or less than before. To our surprise, this worked well, and I got the block realigned and recovered that channel.

Working in the tropics, the heat and humidity present challenges – both to instruments and people. The airport had kindly supplied us with an air conditioning unit, which valiantly struggled for a few hours against the soaring temperatures and hot sun beating down on our steel tube of a plane. Then it made a dramatic exit in a puff of black smoke, and we were left to work on as the temperatures climbed. As I crouched behind the instrument, making delicate adjustments to the optics, I tried not to be distracted by the small rivers of sweat running down my back and legs.

But it is precisely when you’re struggling that you are reminded quite how lucky you are on this mission. Our crew are second to none, and as well as opening up the plane for us to work, when they’d rather be enjoying a down day by the beach, they did everything they could to help out even offering up phone chargers etc. to try and create a 5V power supply. A more experienced colleague stayed on the plane to help me diagnose and fix the problem, and my own team back in Colorado interrupted their weekend to message advice and chip in with the diagnostic process. It’s such a heartwarming feeling, to be part of a team that are all so dedicated to the same mission, who rally to help each other out, who celebrate each other’s wins and commiserate their difficulties.

With work done for the day, I got to enjoy a beautiful sunset stroll along the beach and some of Fiji’s amazing Indian cuisine, before and early night and 4am start to head off to New Zealand.