Week 2: Greta Point

Cracking into my second week here at NIWA’s Greta Point Campus a quote from the great Sir Peter Blake himself was in my mind “the hardest point in any big project is beginning”. During this week I was got stuck into my research project on seasonal variation at NIWA’s Rainbow Mountain Site, knowing full well that the week ahead entailed tackling some sophisticated statistical analysis software with the extent of my STAT110 background.

Rainbow Mountain or Maungakakaramea is the newest NIWA atmospheric monitoring site, sitting alongside Baring Head, Lauder and Arrival Heights (Antarctica). Rainbow Mountain is the only NIWA atmospheric monitoring station with a forestry surrounding, with Lauder being based in grasslands, Baring Head facing the sea and Arrival Heights being on the ice. The site is about 25km south of Rotorua, is at an elevation of 743 metres and is on the north-western boundary of the Kaingaroa Forest. Rainbow Mountain also sits within the geothermally active Taupo Volcanic Zone with the Waiotapu thermal area being situated only a few kilometres away. Because of its unique position Rainbow Mountain gives NIWA a greater insight into carbon sinks and sources in the central North Island.

One of the most useful processes I’ve learnt about this week is that of photosynthetic uptake. The concept being that during seasons like summer and spring there is a higher plant growth rate, with more photosynthesis occurring which draws down more carbon dioxide from the atmosphere. In contrast in winter and autumn, with plant die-back and less photosynthesis occurring, there is a higher abundance of CO2 as it’s not being absorbed as readily by vegetation. This phenomenon is colloquially termed the ‘earth breathing’ as the Earth inhales CO2 in the warmer months and exhales CO2 in the cooler months. This effect is particularly pronounced in the Northern Hemisphere due to it having much more landmass (see Figure One).

Figure One: Seasonal variability shown through the monthly mean CO2 recorded at Mauna Loa, Hawaii (NOAA Pacific Marine Environmental Laboratory)

My Monday morning was spent doing some preliminary data analysis of the Rainbow Mountain data on Microsoft Excel. At Rainbow Mountain CO2 data is recorded every second and for three different levels the 5m, 17.5m and the 30m. This height set up is to give good insight into the diurnal mixing of the boundary layers, if you were to measure the CO2 at the different heights at night (a time with very little air mixing) they would quite likely read different values. For this reason I chose to work with a well-mixed time period of 3-4pm and with hourly averages of the data. The Rainbow Mountain site was established in late 2011, when considering what range of data I should use for my analysis there was a balancing up decision between how far back to go to ensure the data was consistent but also was a wide enough range to get an insight into the seasonal variation. I decided to measure three full year cycles from the 1st November 2013 through to 31st October 2016.

In the afternoon I was back in the Gas Lab to watch the mass spectrometer in action analysing carbonate samples from the Tangaroa. The acid drops weren’t working so we went into problem detection mode. Switching off valves, applying pressure to clear any blockages in the line and manually cleaning the highly sensitive instrumentation. Another interesting experience was refilling the liquid nitrogen tank. This required the full donning of safety gear and wheeling a massive tank to the pump at Greta Point. It was cool to see ice crystals forming as we refilled it despite it being a very hot day in Wellington.

On Tuesday, I was back to my Rainbow Mountain analysis. I was poring over some graphs which appeared to produce the opposite seasonal variation to what was anticipated with the photosynthetic uptake effect. After discussing it with Dr Sara Mikaloff-Fletcher, the TROPAC team’s resident statistical guru, she suggested that this may be an indication what’s called the ‘Rectifier effect’. Back to the books (well computer) I went to research this and try some different things to minimise its effect. Finally I got Figure Two below and it looked like I was on my way again in terms of exploring the seasonal variation cycle.

Figure Two: Preliminary data analysis of the Rainbow Mountain CO2 seasonal variation (Injy Johnstone)

In the afternoon on Tuesday I also had some intriguing interviews with some of the NIWA staff. I talked first to Dr Mike Harvey who is the Principal Scientist for Atmosphere about his projects, experiences and interests. I was particularly struck by how much interaction there is between the air, ocean life and water in terms of cloud formation. Next I interviewed Dr Guang Zeng who is an atmospheric scientist, we talked about her work on the Unified Model- an all-encompassing climate modelling and weather prediction system which she develops the atmospheric chemistry side of. Lastly I interviewed Dr Hinrich Schaefer an atmospheric scientist who has done some fascinating work unlocking the composition of methane isotopes; providing a unique insight into where our increasing methane levels originate from (for those wondering it’s from agriculture).

Wednesday and Thursday involved an insight into the statistical software called Matlab. This is software that can be advanced and complex analysis, and runs on code. Without spoiling too much of what I have found using Matlab before publishing my report, one of the things I been doing on there was footprint analysis where I was using a script that inverse models the airflow patterns around Rainbow Mountain for different months of the year. Figure Three gives you an idea of what this looks like.

Figure Three: Airflow analysis March 2013-2016 at Rainbow Mountain (Injy Johnstone)

I finished off the week by interviewing Dr Sam Dean who is the chief scientist for Climate, Atmosphere and Hazards. It was really interesting hearing of his pathway from physics to climate modelling and all the different things that he does as part of his role at NIWA. Finally I started pulling together my presentation which I’ll be doing as part of wrapping up the Greta Point part of my analysis next week. It’s hard to think my time at Greta Point is nearly over, these first two weeks with NIWA have flown by. I can’t wait to see what the last few weeks hold. Next stop Rainbow Mountain on Sunday!