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!
By Eric Lindstrom
The R/V Revelle expedition has been the opening round in a yearlong effort to understand the upper ocean physical processes in the eastern tropical Pacific. We put moorings in place to collect a time series of upper ocean measurements over the year. We launched the first round of Lagrangian drifters and floats. Lady Amber will be servicing these assets at regular intervals and launching new drifters and floats into the array.
It is with some caution and caveats that I try to summarize our findings from the last six weeks of effort. Ideas are still young and data processing is still in its early phases. Only data from shipboard measurements are complete but still require careful screening, calibration, and validation. Despite the caveats, some of our questions and challenges are much clearer now than before we left Honolulu.
The Conductivity, Temperature and Depth (CTD) work, led by Janet Sprintall, charting the variations of temperature, salinity, and oxygen in the upper ocean, revealed some quite interesting features. Janet and her team will be looking at salinity-compensated temperature inversions in the upper ocean that seem to be closely associated with the edges of the east Pacific fresh pool.
Jim Edson and Raymond Graham have a wonderful three-week time series of 80 atmospheric profiles from their radiosonde launches via weather balloons every six hours. Ray will be working these up for his MS degree research project, so I won’t steal any of his thunder. Needless to say, we all think he will have an awesome project because it is such a rich data set!
Ray also assembled all the rainfall data daily and found that during SPURS-2 we had about 10 inches of rainfall in our 3 weeks on site near 10N, 125W.
Carol Anne Clayson has collected more than 1,500 air-sea flux estimates (20-minute averages) to be analyzed in conjunction with the upper ocean data sets from numerous platforms. She has already been able to run her mixed layer model using initial conditions from early in the expedition and the raw flux estimates to compare with later expedition measurements. It gives us great optimism for new discoveries out of this data set.
Michael Reynolds brought the Remote Ocean Surface Radiometer (ROSR, from Andy Jessup) and the Infrared Sea surface temperature Autonomous Radiometer (ISAR, from Carol Anne Clayson) to SPURS-2 to examine the surface skin temperature of the ocean during rainfall. Michael successfully engineered the instruments for this purpose (normally a fair weather measurement). He has put together some exciting compilations of data comparing his measurements with other temperature measurements made on the ship.
Julian Schanze from Earth & Space Research in Seattle is the man with the Salinity Snake. It has provided a virtually continuous record of the salinity in the top 2 inches of the water column. Julian has identified nearly 40 fresh lenses where salinity at the surface is significantly lower than ship intakes at 6.5 feet (2 meters), 9.8 feet (3 meters), and 16.4 feet (5 meters depth). These measurements, when further combined with the Surface Salinity Profiler data from the upper 3.3 feet (1 meter), will constitute a rich data set for analysis of fresh water lenses induced by rainfall.
Ben Hodges from Woods Hole Oceanographic Institution (WHOI) has been following the three Wavegliders deployed near the SPURS-2 central mooring. They have salinity sensors near the surface and at 19.7 feet (6 meters) depth and will be hard at work over the entire coming year. One of the Wavegliders had an experimental package of sensors on it called the salinity “Rake” with sensors at every 3.9 inches (10 centimeters) depth from the surface to 3.3 feet. The Rake, invented by Raymond Schmitt at WHOI, recorded data internally and was recovered after a few days of operation to check functionality (it has not been to sea before). The data is amazing; but it only lasted one day before mechanical failure and short circuits took it out of commission. However, that vertical resolution and the interesting features that it saw were a new peek at the ocean surface salinity that really has not been seen before. More engineering work needs to be done at home before it can be re-deployed. The team at Woods Hole will be highly motivated to get this instrument to sea again soon, based on what we saw in just one day. The Waveglider was re-deployed without the Rake.
The Surface Salinity Profiler (SSP) team led by Kyla Drushka has a very successful run with 18 deployments (not counting various tests and trials). The data is still being assembled and examined but, like the Rake measurements, the SSP focus on the top 1 m of the ocean is going to provide new insights on ocean processes. The SSP has the added benefit of microstructure probes to provide information on turbulent mixing. The biggest difference in salinity seen over 3.3 feet by SSP was 9 units!
Eric Chan had the rare opportunity to focus a study on the air-sea exchange of carbon dioxide during rain events. The simultaneous analysis of his gas exchange data with the salinity snake and meteorological data will be enlightening. Certainly the raw carbon dioxide data show the dip in pCO2 expected during rain events when the salinity drops.
Finally, I’d like to heap praise on our chief scientist, Andy Jessup, who managed execution of all the projects and requirements with great skill and diplomacy. The whole SPURS-2 team owes Andy a great deal for making the R/V Revelle expedition such a successful initiation of the SPURS-2 Program.
Next blog post: PORT!
By Eric Lindstrom
A six-week voyage on the open ocean is not for everyone. On this trip we had plenty of veterans and few first timers. Channel fever is commonly considered something that happens at the end of a voyage as you head for port. It is maybe easier for those of you ashore to picture as akin to spring fever at the end of winter. I would like to describe a more comprehensive theory of voyage feelings that is more akin to the five stages of grief. Maybe it should be called the five stages of channel fever?
For grief, the five stages are denial, anger, bargaining, depression and acceptance. For channel fever, the five stages are sickness, interest, boredom, excitement, and port. Like grief, they are not some stops along a linear timeline (except maybe port!), but tools to help us recognize what we are thinking and feeling. In this theory of channel fever it occupies the entire voyage.
Getting your sea legs is the first hurdle of the voyage. It starts in the harbor channel and impacts people in different ways. Headaches, queasiness, and overwhelming sleepiness are all symptoms. This phase is definitely a downer and modern medicine has sought to treat it with drugs. Some unfortunates never get past this stage.
A core feeling early in voyages is interest in all the stuff that other people are doing that of which you have not yet become familiar. The ship is small, so any new things to see or do certainly focus your attention. Good mariners can make the simplest chores and routines the subject of great interest and focus. They know that you should hold this feeling as long as possible. It’s deadly if you move on to boredom too soon. Maybe my blogging style gains strength from this stage of channel fever?
Once you have mastered your work and everyone else’s chores, interest fades and boredom takes over. Ideally, you would like this feeling to be minimized. Therefore, sea veterans are adept at invention of new games, procedures, routines, and making anything that is even halfway interesting last as long as possible. You may have wondered why people come back from sea with weird new skills like knot tying or macramé. It’s because of trying to fight boredom!
This is the classic feeling of channel fever and its penultimate stage. Long after sickness, interest, and boredom, it is usually the time when all your hopes hang on finishing the trip and getting back to life ashore. Usually this stage alone is what people refer to as channel fever because the emotional symptoms are closely associated only with proximity to voyage end and no other known cause.
The final stage of channel fever and resolution (in my theory) of the malady come with arrival in port and being homeward bound. Resolution (port) is often a highly celebrated event. The modern cure for channel fever is solid ground and a cold beer. Really, we don’t know if beer has anything to do with this, however there seems to be a close association between beer and miraculous recoveries in port! The science party on R/V Revelle is hosting a post-voyage happy hour ashore later in the day we arrive, just to make sure everyone receives the cure.
By Eric Lindstrom
One of the challenges of oceanography (and many other sciences) is telling a coherent story of the environment across a vast space of space and time scales. For example, cosmologists tell the story of the universe from subatomic particles to the breath of the visible universe and from first nanoseconds of the big bang to billions of light years.
For SPURS-2, mixing is obviously an important factor in telling the story of how rainwater combines with seawater to bring about the east Pacific fresh pool that we see from space. That mixing primarily happens in the upper ocean at scales of centimeters, where turbulence is caused by phenomena such as wave breaking, current shears, convection in unstable layers, and the rain itself hitting the sea surface. In order to understand the big picture, we need to estimate the magnitude and location of the centimeter scale turbulent mixing.
Over many decades oceanographers have become quite adept at estimating mixing from measurements of centimeter scale temperature, salinity, and velocity variations – otherwise known as microstructure. Now, along with our standard instruments for measuring temperature and salinity, we also deploy microstructure probes – very fast sampling sensors of ocean variables.
It is beyond the scope of this blog to explain how microstructure measurements are transformed into ocean mixing estimates, but it is one of the more helpful developments in modern oceanography.
Caitlin Whalen of the University of Washington Applied Physics Laboratory (APL) is an expert in ocean mixing. While on the SPURS-2 expedition, she has contributed to a review paper on the subject for the Bulletin of the American Meteorological Society. During SPURS-2 she oversaw the addition of the Seagliders to the Lagrangian experiment.
The Seagliders will provide us with a picture of how the turbulence in the SPURS-2 region varies at deeper depths and over a longer time period than we will learn form our ship-based measurements. Over the next six months the Seagliders will repeatedly travel between the ocean surface and a depth of one kilometer, collecting data during each trip. From this data we will be able to determine how the turbulence in the ocean varies with depth and how it is related to other events such as heavy rain and the continuously changing density patterns of the water. Knowing where and when turbulence occurs will help us understand how the fresh rainwater eventually mixes deep into the salty ocean.
Kyla Drushka and Suneil Iyer, also from APL, have deployed microstructure probes on the Surface Salinity Profiler (SSP). They will try to determine, from these measurements and the vertical structure of salinity in the upper meter of the ocean, how quickly rain-formed low salinity lenses are mixed into the upper ocean during individual events. Their big challenge during SPURS-2 has been to get a snapshot of salinity lenses at various stages of their lifetime. Being in the right place (low wind conditions) at the right time (just as rain begins to fall) with the right gear (SSP) actually deployed has been challenging. Still, I am sure we have collected more such data this expedition than previously existed. Finally enough data to find great exemplars for discussion in the scientific community! This is a wonderfully “fresh” topic for a graduate student like Suneil to tackle.
Just about everyone doing analysis of SPURS-2 data will use estimates of mixing in some way or another in the telling of their part of the story of salinity in the eastern tropical Pacific. It will be part of any salinity budget calculations and used in the description of salinity fronts. It will be an essential part of the story in explaining the seasonal patterns of salinity we see from space. The story of the smallest scales in the ocean meets up with the story of the planet as seen from space!
By Eric Lindstrom
SPURS-2 on R/V Revelle has been a balloon bonanza. We have been profiling the atmosphere every six hours with radiosondes (AKA; sondes) attached to helium filled weather balloons. The sondes measure the temperature and humidity profiles in the atmosphere are transmitted via radio signal back to a receiver on the ship. They are tracked by GPS so also provide height and wind (via their changing position). The sondes are lost after the balloon pops in the upper atmosphere (over 12.4 miles –20 kilometers– up). The profile data of the atmosphere are key to studying convection, clouds, rain, and stability in the tropical atmosphere. Modern meteorology depends on hundreds of balloon launches worldwide every 12 hours. Such observations over the ocean are much less common and still provide for scientific discovery.
The regular weather balloon launches have also been a great way to send our birthday wishes home to friends and family. Today’s blog and balloon launch come with a hearty “Happy Birthday” to my daughter, Kelsey, in Everett, Washington! Kelsey, your birthday balloon made it to more than 21,000 meters (far into the stratosphere) and an atmospheric pressure of 44 millibars (1011.7 millibars at sea level here).
To study sea surface temperature variation on small scales, we have deployed the Lighter-Than-Air InfraRed System (LTAIRS). LTAIRS is a large, re-usable helium-filled balloon tethered to the ship with an instrument package hanging below it. The APL team lead by Andy Jessup has suspended a camera package that images the temperature patterns on the sea surface. The LTAIRS package is deployed when there are relatively steady light winds. It is quite a drama if the LTAIRS changes height or direction rapidly. This can happen, for example, if it is launched in the heat of the day and quickly loses lift in the rapid cooling after sunset (the balloon loses lift as the helium cools). Or, if the wind shifts rapidly during a rain shower the balloon can quickly drift back over the ship bringing its tether into the ship (think tangles!). We want no drama with an expensive ($50,000 worth) camera sitting just below the balloon. However, it is oceanography and any deployed equipment is at risk of loss. Innovative observations with potential for discovery (a bonanza!) are the reward for taking and managing the risk of the balloon acrobatics. So far there are very interesting variations and patterns in surface temperature during rain events. It will take considerable post-expedition analysis to pull the whole story together, but these results look extremely promising.
For ballooning we have quite a supply of helium aboard. For many years the world’s supply of helium has been under pressure, with usage depleting national reserves of this noble gas. Recently new supplies have been discovered in Africa, but helium is another one of those resources like oil, fresh water, or fish that have come under global management for human uses. Its supply closely parallels that of natural gas from which it is separated. Conservation activities and rising cost seems the logical outcome for the long term. Helium, many other resources, will see the times of bonanza and bust as we find and use our way through the reserves and discoveries.
Overall, the ballooning on R/V Revelle for SPURS-2 has been very successful and highly informative – a real bonanza of scientific information. Raymond Graham will get his Masters degree puzzling over the atmospheric profiles. Andy Jessup will spend weeks glued to the computer puzzling over the patterns in the LTAIRS IR images. And every one had fun at some point in the expedition filling or launching a balloon. Very uplifting all around!