Salinity Processes in the Upper Ocean Regional Study (SPURS): R/V Revelle SPURS-2 EpilogueOctober 21st, 2016 by Maria-Jose Viñas
By Eric Lindstrom
Salinity Processes in the Upper-ocean Regional Study #2 is underway for the next year. Lots of science remains to be done, so it is very early to be writing an epilogue! However, the first big field campaign with a large research ship is completed and it seems right to sum up some of the operational conundrums be articulated as we plan for further operations with the Lady Amber over the coming year and the R/V Thomas Thompson in October 2017.
Conundrum#1: Finding “Just Right”
Like Goldilocks, the R/V Revelle team went in search of very special conditions. Conceptually, SPURS-2 is built around observing all the processes that lead to rainfall mixing into the ocean and the resulting large-scale variations of salinity that we detect from space.
One of the concepts is that rain falling into the ocean will reveal itself as low salinity “lenses” at the surface than mix into the ocean over time. Well, not unexpectedly, if the wind is anything but calm, the rain mixes quickly into the upper ocean mixed layer and cannot be seen as a lens – only tiny variations of salinity that build up over time. In order to see the strong signal of a lens of fresher water, one needs to observe the ocean during calm winds and rain. The difficulty with this is finding the simultaneous occurrence of rain and low wind conditions in a vast ocean with a platform with a top speed of about 12mph. During SPURS-2, it became apparent that the regions with more certain rainfall (those large cells and fronts visible from space) were also stormier and windier than ideal for measurement. In areas of calm winds, there are patches of rainfall but they don’t seem predictable (“It’s the tropics” says Jim Edson!)
So, the perfect observing condition for us were more difficult to find than we expected ahead of time. Probably no surprise that mother nature throws a great curve ball! In the end, we targeted the low-wind regime by following the surface wind forecasts and hoped to run into rain (which we did). After a few weeks at sea we learned and prevailed.
It is always tricky to balance risk and reward. Equipment deployed at sea is always at risk of loss. The reward for taking the risk is valuable data to expand our scientific understanding. We had several occasions to examine and balance these risks and rewards.
For example, the CODE drifter was an instrument that was modified ashore by addition of a salinity sensor but not tested prior to shipping five of them to R/V Revelle. In the parlance of oceanography, drifters float at the surface, while floats are neutrally buoyant and can sink and return to the surface to transmit profiles of the ocean. In a test deployment of one drifter, it appeared to stay at the surface (just), but when released from the ship it simply sank, never to be seen again! Not the behavior you like to see in a drifter! So, although modification to its four sister drifters were undertaken, it was eventually decided that these drifters were not ready for prime time. Lucky we tested one! The small experiment with CODE drifters will have to wait until next year.
The Lighter-Than-Air InfraRed System (LTAIRS) balloon deployments were quite complicated by variations in the balloon lift during rain and by variations in wind speed and direction. Dipping the balloon payload (expensive camera) in the water is a big risk. However, the data – infrared movies of the sea surface skin temperature in rain – are super interesting and scientifically novel. We learned a lot about making waterproof payloads, the best material and size of balloons, and weather characteristics unfavorable for ballooning. This knowledge was hard won with near misses and close calls and exhaustion of the helium supply. We all think it cost our chief scientist Andy Jessup some new gray hairs! However, the grin on his face when he shows you the data is priceless. Well worth the drama and risk in the process. LTAIRS work will go more smoothly next year on the R/V Thompson and the team will likely make some interesting discoveries about the thermal properties of the sea surface during rain.
It was a great pleasure to work with and support the scientists and crew on R/V Revelle. It is a capable ship and crew and the science party was very well prepared for the challenges and risks. Morale was high during the entire voyage – maintained by a busy schedule, everyone pitching in, and good food and fellowship. The teams from University of Washington Applied Physics Laboratory, University of Connecticut, Woods Hole Oceanographic, and Scripps Institution of Oceanography came to R/V Revelle super-prepared and ready for action. The schooner, Lady Amber, will be making periodic voyages during the coming year to service and renew out drifting (Lagrangian) experiment. As always, your blogger enjoyed every minute of our six weeks at sea. Its wonderful to watch scientists and engineers face the challenges of understanding the ocean while in its grip. I’ll keep you posted on developments during the coming year!