Funding for this TPOS-2024 mission is provided by NOAA OMAO UxSOC in support of the Uncrewed Surface Vehicles (USV) Integrated within the Tropical Pacific Observing System (TPOS) transition plan.

Pre-mission plan: The TPOS-2024 mission had a planned launch date of September 10, 2024, with two saildrones departing Alameda for the first waypoint, the official start of the mission, in the eastern tropical Pacific at 10°N 125°W.  The approximately 110-day mission follows the GO-USV route, with a meridional transect from 10°N 125°W to the equator and a zonal transect along the equator to 0°N 140°W, where a coordinated frontal study with a Seaglider (PI & Pilot: Katie Kohlman, UW) will be performed. The saildrones will then head north to the ITCZ and transit eastward along the North Equatorial Counter Current.

A letter from sea: Reaching Our Study Site and Observing a Tropical Instability Wave

November 18, 2024

After a week-long transit from Honolulu, HI, we finally arrived at our study site near 2°N, 140°W. Our first task was deploying Mooring C, followed by several scientific instruments including Apex and Navis Argo Biogeochemical floats, and six CPIES (Current and Pressure Inverted Echo Sounders).

On November 13, we kicked off our first process study, just as a front on the leading edge of a tropical instability wave (TIW) began to approach our location. We deployed three drifting WireWalker moorings, designed to profile and move with the upper ocean currents. The idea is that these moorings will drift across the TIW, collecting valuable vertical profiles of temperature, salinity, chlorophyll, and water velocities. During one of the deployments, we had an unexpected visitor — a curious shark circled the Wire Walker, as if inspecting our equipment!

We have been closely monitoring sea surface temperature fronts using various satellite products and models to track the frontal edge of the TIW evolution and adapt our sampling strategies in real time. On November 14, we crossed the front, witnessing a sharp temperature jump recorded by the ship's underway intake system. We believe this spike marks one of two leading-edge fronts trailing the TIW.

R/V Sikuliaq's surface temperature and salinity by the leading edge of a TIW.

GHRSST Daily Sea Surface Temperature for November 13, 2024. Overlaid in the same color scale is the R/V Sikuliaq's intake temperature data, with the front identified on November 14th marked in cyan.

In the coming days, we’ll intensify our efforts with FastCTD (750-meter profiles every 10 minutes) and EpsiFish (750-meter profiles every 30 minutes). These tools will allow us to gather high-resolution profiles of temperature, salinity, chlorophyll, shear, and turbulence across the front.

Looking ahead, we’re eagerly awaiting the arrival of the Saildrones, which are ‘riding the wave’ towards our location. We hope their observations will complement our data, giving us an even clearer picture of the front’s behavior.

Follow the R/V Sikuliaq’s journey here.

Blog post by Katie Kohlman

Adjusting Course to Optimize Currents

November 12, 2024

Katie and the rest of the team on the MOTIVE cruise aboard the R/V Sikuliaq have made it to approximately 3°N, 140°W. We’re eagerly awaiting an update on their operations plans as they settle into their work in the region. There's still a possibility of coordinating with them near the end of their cruise, so we're keeping communication lines open.

Meanwhile, on our side, we made a strategic decision on Friday to sail west along approximately 6°N before turning back to the southwest today. This change came after several days of limited southward progress, with unfavorable currents and winds hampering boat speeds. With the new westward trajectory, we took advantage of westward currents over the weekend and are now riding the currents around an eddy to gain a helpful speed boost.

We’ll continue to adapt our path to the conditions as needed. Fingers crossed for potential collaboration with the R/V Sikuliaq crew soon!

Mercator Surface and Merged Ocean Currents Forecast (plotted are the “total currents” which sums together the general circulation, tides and waves on a 1/12° regular grid).

Blog post by Elizabeth McGeorge

One week down, 15 weeks to go

November 6, 2024

We're one week into the expedition, with 15 more to go. Yesterday, we cruised past the historical TAO buoy station at 8°N 125°W. In previous years, we might have been able to do a quick intercomparison here, but unfortunately the station was decommissioned in early 2023. It’s been a challenging start; strong easterly currents have slowed our progress south, holding our average speed to just under 1 knot. Despite that, the drones have maintained their transect along 125°W and haven’t been swept further eastward.

Katie has left to join the R/V Sikuliaq, which departed Honolulu yesterday, November 5. Their transit to station (3°N 140°W) is expected to take around 7 days. Follow the R/V Sikuliaq’s journey here.

Drone positions with GFS forecast winds in the background - 11/6/2024 22:00 UTC.

Blog post by Elizabeth McGeorge

MOTIVE Cruise and Underwater Glider "Pigeon" Coordination

November 1, 2024

As mentioned earlier, we hope to coordinate our drones with an underwater seaglider that will be deployed and piloted by UW PhD student Katie Kohlman aboard the R/V Sikuliaq MOTIVE cruise this November. The Mixing belOw Tropical Instability waVEs (MOTIVE) project is investigating the question: What processes govern the observed modulation of internal waves, and possibly turbulent mixing, by Tropical Instability Waves (TIWS) in the equatorial Pacific? The MOTIVE project is a collaboration across UW, Scripps, OSU, and WHOI. The MOTIVE cruise, led by chief scientist Caitlin Whalen, will use an array of subsurface moorings (one-year deployment), FastCTDs, and wirewalkers positioned nominally near 0-3°N, 140-138°W to observe subsurface mixing beneath TIWs.

Planned Saildrone - Glider Coordination with UW Student Katie Kohlman

Katie is investigating air-sea interactions and subsurface dynamics associated with the leading edge front (LEF) of TIWs. As part of this research, she plans to pilot a UW Student Seaglider Center Seaglider, to coordinate with our two Saildrones. The Seaglider has been aptly named Pigeon, as it will complete its mission in the tropics and, much like a homing pigeon, glide all the way back home (or in our case, Honolulu, HI). The glider will provide complimentary profiles of temperature, conductivity, backscatter (470 nm, 695 nm, and 700 nm), and oxygen from the surface to 990m. Using the data collected from the drones, the glider, and complimentary MOTIVE cruise data, she plans to analyze air-sea interactions, impacts on biogeochemistry, and currents and shear associated with TIW fronts.

“I’m thrilled to pilot Pigeon, a Seaglider given a second life through the dedicated work of UW undergraduates, off of the MOTIVE cruise. It is exciting to see this refurbished glider join a collaboration of diverse autonomous tools, all working together to reveal new insights into surface and subsurface interactions and ocean dynamics!” – Katie Kohlman

Katie Kohlman testing a Seaglider in the Puget Sound.

OCS is thrilled by this opportunity for collaboration and eagerly anticipates the deeper insights it will bring.

Blog post by Elizabeth McGeorge (with fact-checking and input from Katie Kohlman)

It's GO (USV) time!

October 30, 2024

With weather and wind always being hard to predict, our projected arrival to 10°N on Monday (28 October) was slightly off due to a combo of headwinds forcing the saildrones to tack their way south and currents stalling that minimal progress even further.

Strong north-easterly current (left) and southerly wind (right) making the transit south difficult.

No matter the slight delay, they reached the first way point (10°N, 125°W) and the 2024 PMEL TPOS Mission finally kicked off at 00:00 UTC October 30, 2024! Here’s to hoping for smooth seas and plenty of insights.

With the mission officially started, the USVs have had all sensors powered on and, battery allowing, they’ll be taking measurements every step (or splash) of the way. Each Saildrone is packed with scientific instruments designed to gather essential data on oceanic and atmospheric conditions which will help to fill gaps in our understanding of how the ocean and atmosphere interact. This year our saildrones are equipped with the following sensors:

Sensor table for the TPOS-2024 mission.

In our next blog, we’ll hear from UW PhD student Katie Kohlman who is about to head off to Honolulu to join the MOTIVE cruise on the R/V Sikuliaq (with PI Caitlin Whalen). Katie is hoping to coordinate an underwater glider with our USVs to investigate frontogenesis in Tropical Instability Waves. We’ll be keeping in touch with Caitlin and Katie once they’re onboard the Sikuliaq to facilitate an observing “party” between our USVs and their operations.

Stay tuned for updates! Our USV mission is just getting started, and who knows what surprises the ocean has in store next.

Photo from SD1033 near 17°N, 122°W on October, 20, 2024, 14:00 UTC (courtesy of Saildrone, used with permission).

Blog post by Elizabeth McGeorge

A (non)eventful transit

October 24, 2024

The past month has been quite the journey for our drones! After wrapping up the intercomparison with NDBC Station 1801593 (another saildrone!) back on September 20th, our drones have been steadily making their way south to 10°N, 125°W. As of today, they’ve just reached 13°N, 123°W, having covered 24 degrees of latitude in 34 days—that's about 1,440 nautical miles (or roughly 1,650 miles). Their average speed during the transit has been a modest 1.7 knots (nautical miles per hour).

Now, with only 180 nautical miles to go, we’re on track to hit our target of 10°N, 125°W by Monday, October 28th. Once there, all sensors will be turned on and we’ll officially kick off this year's mission. But it’s not all smooth sailing—there’s some extra excitement on the radar!

Hurricane Kristy in the Distance

Hurricane Kristy on approach to (and narrowly missing) the Saildrones of TPOS-2024.

Hurricane Kristy formed from the remnants of Tropical Storm Nadine, and intensified upon its approach from the east. From the National Hurricane Center:

"24 Oct 2024 - 15:00 UTC ...MAJOR HURRICANE KRISTY CONTINUES WESTWARD... As of 8:00 AM PDT Thu Oct 24 the center of Kristy was located near 14.1, -120.3 with movement W at 17 mph. The minimum central pressure was 933 mb with maximum sustained winds of about 150 mph."

While it's giving our drones a bit of a speed boost right now (now averaging a whopping 3.5 knots due to the increased wind on the hurricane edge), there’s no need for concern. The forecast shows Kristy moving northwest (black track in picture), staying a few hundred nautical miles away and safely passing behind us as the drones continue south (purple planned track in picture). So, we’re expecting to avoid any direct impact.

Blog post by Elizabeth McGeorge

And they are off!

September 20, 2024

The two saildrones (SD-1033 and SD-1090) performed an ADCP bottom tracking test outside of the Golden Gate Bridge and then a ~36+ hour intercomparison with the NDBC Station 1801593 (also a saildrone). There was some variability associated with a coastal eddy that could be seen in the HYCOM fields. The dewpoint measurements from the NDBC site were also difficult to compare. But otherwise, all data checked out. On to 10N.

Blog post by Meghan Cronin

Meet the TPOS-2024 Team at PMEL and UW!

September 5, 2024

TPOS-2024 Pre-Mission Photo of the Ocean Climate Stations team with a Saildrone (In main photo, left to right: Katie Kohlman, Nathan Anderson, Dongxiao Zhang, Meghan Cronin, Yolande Serra, and Patrick Berk. In upper right photo inset: Liz McGeorge, sailing in Lake Washington last summer). The pictured saildrone is from an earlier generation of drone, and certain characteristics may differ from the deployed 2024 drones.

As lead-PI for the TPOS-2024 mission, I'd like to introduce you to a few key people on the TPOS-2024 team. Dongxiao Zhang (UW/CICOES and PMEL), co-PI for the project, is the lead Mission Manager. Other Mission Managers include myself, UW/CICOES postdoc Elizabeth McGeorge, and co-PI Yolande Serra (UW/CICOES). We will be working on a daily basis to provide waypoints for the pilots at Saildrone, Inc.

Every mission we try to learn something new about the capabilities of the Uncrewed Surface Vehicles (USV) within the TPOS. Last mission, for example, we had one drone with an EK80 system instead of an ADCP and worked with co-PI Reka Domokos (NOAA/NMFS/PIFSC) to test how fisheries applications could be integrated within the TPOS. We also used the mission to go to the heart of the developing El Nino. 

In this coming TPOS-2024 mission, we will go to equatorial cold tongue region (0°N 140°W) where there will be an intensive field campaign - TEPEX - in late 2026-2028. On the northern edge of the equatorial cold tongue, extremely sharp and Abrupt! fronts can form. These fronts can undulate and have cuspy patterns as Tropical Instability Waves propagate westward. For TPOS-2024, we will perform a coordinated frontal study using our two saildrones and a Seaglider, an underwater profiling glider piloted by UW School of Oceanography graduate student Katie Kohlman. The glider will measure how the ocean stratification changes on either side of the front. The equatorial cold tongue's front is associated with air-sea fluxes that can impact the atmosphere, causing a front in the winds. These air-sea fluxes in turn can also impact the ocean. Having the glider's ocean stratification information is thus important for understanding the coupling between the ocean and atmosphere. However, we expect that coordinating the underwater glider and the saildrones will be very challenging in this frontal region due to the strong currents associated with the westward-flowing South Equatorial Current and strong currents associated with the tropical instability waves. Wish us luck!

I'd also like to introduce the team that contributes to instrumentation setup, data transfer and visualization, and engineering.  Nathan Anderson (UW CICOES) is the Ocean Climate Stations (OCS) group's data manager.  He will be on the front line in getting telemetered and delay mode data to users.  Patrick Berk (UW CICOES) is the OCS instrument technician coordinating instrument setup, shipping & receiving, and other pre- and post-mission logistics.  Those responsible for all aspects of the ASVCO2 systems aboard the Saildrones include Adrienne Sutton and Stacy Maenner (both of NOAA/PMEL).  Finally, Eugene Burger (NOAA/PMEL Science Data Integration Group) and Ellen Koukel (UW CICOES) both provide critical data services to successfully land data on PMEL servers, perform data integrity checks, configure data into ERDDAP, and curate the metadata.

Blog post by Meghan Cronin