2025 Summer Observation Campaign off Sanriku

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Overview
Comments from ECHOES Participants
NEWS during the Observation Campaign

Overview

To clarify the impact of higher sea temperatures on meteorological phenomena like “Yamase” in the Sanriku offshore region, where marine heatwaves persist, atmospheric and oceanic observations were conducted using two vessels, R/V Shinsei-maru (JAMSTEC) and T/V Seisui-maru (Mie Univ.), and at the Otsuchi Coastal Research Center (AORI, Univ. Tokyo).

Shinsei-maru: Yokosuka (Jun. 20) → Hakodate (Jul. 4)
Seisui-maru: Matsusaka (Jun. 25) → Shiogama (Jul. 1), Shiogama (Jul. 5) → Matsusaka (Jul. 8)
Otsuchi: Jun. 27 – Jul. 2

In the intensive observation for 61 hours from 17:00 on June 27 to 06:00 on June 30, radiosonde observations (as well as XCTD observations on ships) were conducted hourly, obtaining high-resolution atmospheric and oceanic data. R/V Shinsei-maru and T/V Seisui-maru moved north-south, traversing between warm and cold water areas, conducting grid-like observations of the Sanriku offshore region. This observation captured various phenomena, such as heavy fog and sudden wind changes in the lower atmosphere. (Hatsumi Nishikawa@Team for Observation Coordination)

Cruise tracks of Shinsei-maru and Seisui-maru

Observation points and cruise tracks during the intensive observation

Comments from ECHOES Participants

HOU HungChun (Tohoku Univ., M2)

I joined the KS-25-5 cruise on the research vessel Shinsei-maru from June 20 to July 4, 2025. The main goal of the cruise was to study how the northward shift Kuroshio Extension and warm-core eddies which broke off from Kuroshio influence the ocean and atmosphere. From June 27 to 30, we even carried out a special three-point observation off Sanriku, working together with the Seisui-maru and a land team in Ōtsuchi, Iwate.

During the cruise, we did CTD casts, XCTD drops, and radiosonde launches. Although I had some experience with radiosondes before, it was my first time to actually take part in CTD and XCTD work. Seeing with my own eyes how the huge amount of data I usually use for research is collected gave me a whole new appreciation for both the effort behind it and the value of the data itself.

At first, radiosonde launches felt difficult, but after several tries I got the hang of it. Shinsei-maru has a container that can automatically launch sondes, so I even had the chance to experience that for the first time. Still, depending on the wind, hand launches were sometimes necessary—which was quite exciting.

I also tried water sampling after CTD casts for the first time. It was nerve-wracking to realize how even small mistakes, like letting in bubbles, could affect measurements such as dissolved oxygen. It made me pay extra attention to every detail.

Of course, not everything went smoothly—there were a few troubles along the way. But thanks to teamwork and some creative problem-solving, we managed to overcome them and complete all the planned stations. It taught me how important flexibility and quick thinking are when you’re at sea with limited resources.

One of the best parts of the cruise was meeting and working with students, professors, and researchers from other universities. Being able to talk, share ideas, and work side by side with people at the forefront of ocean research was an unforgettable experience for me.

“Angel’s Ladder” seen from the Shinsei-maru

NAKAO Masami (Niigata Univ., B4)

From June 25 to July 8, 2025, I participated in the observation voyage of the Mie University training ship “Seisui-maru”. The purpose of this observation was to investigate the impact of the anomalous northward shift of the Kuroshio Extension off the coast of Sanriku, and to concentrate on observing the ocean front between the Kuroshio Extension and the Oyashio Extension. Observations were conducted using radiosonde, XCTD, CTD, and other instruments.

I was in charge of various roles, including preparing observation equipment such as radiosonde and XCTD, making observations, and analyzing data. I had little experience with preparation and observation, so I was a bit confused at first. However, as I observed several times, I began to feel more comfortable and was able to observe until the end. On the other hand, in data analysis, we were able to gain valuable experience by being the first to analyze data that we had obtained ourselves and that no one had ever seen before. Furthermore, through discussions with the researchers and students on board, I was able to gain a lot of knowledge and information that would be useful in my research activities.

In addition, this time we conducted multiple observations, including intensive hourly observations alternating between warm and cold seawater areas for over 60 hours, observations near the Sanriku coast, and observations from off the coast of Sanriku toward the Kuroshio Current. Through these observations, I was able to feel the ever-changing weather around the ship. One thing I particularly remember is the difference between the temperature difference, when it was warm above the warm seawater areas and so cold above the cold seawater areas that I wanted a jacket.

This voyage was a very valuable experience, as I was able to collect data myself and interact with my peers and seniors. I was really glad to be able to take part in this voyage.

YOSHIDA Ibuki (Mie Univ.)

In the summer of 2025, I took part in an observation campaign off the Sanriku coast. Our target was the offshore Sanriku waters, which have shown unusually high temperatures in recent years. We investigated the actual state of sea surface temperature and how the temperature fronts formed there affect the atmosphere.

From June 25 to July 8, I was on board the Seisui-maru for two weeks. On the ship, we carried out atmospheric observations using radiosondes, and ocean observations using XCTDs and bucket sampling. Many of the people on board were students, and the observations were all done manually. We organized shifts to cover nearly 100 observation sites, including an intensive 62-hour observation period. My responsibility was the midnight-to-morning shift.

What I found most fascinating was the chance to experience the phenomena directly through hands-on work. With my senses sharpened, I set off from Matsusaka Port toward the observation sites.

The ship was affected by a tropical depression and the Kuroshio Current, reaching the peak of rough seas off the coast of Chiba. Even while trying to sleep, I was awakened by the rolling of the ship and the sounds of loud crashes and seasick groans. As the voyage went on, however, the sea gradually became calmer.

During the first half of the intensive observation, strong winds posed a challenge. Since radiosondes are attached to balloons and released, wind direction is critical to prevent them from colliding with the ship. The crew constantly adjusted the vessel to make our work easier. However, during the final launch of our first observation shift, the radiosonde was caught in a downdraft surrounding the ship and fell into the sea, forcing us to attempt a re-launch. Under the pressure of knowing that a failed launch could create gaps in the data, we adjusted the balloon size, release position, and timing. This time, the radiosonde successfully rose in a graceful arc, skimming just above the troughs of the waves.

Observations are not enjoyable unless one engages with them, so we tried to “feel” the temperature front together. As we plotted the water temperatures obtained from bucket sampling and saw the front gradually becoming clearer, cheers went up. Although the ship’s route was determined with reference to reanalysis data from agencies such as the Japan Meteorological Agency, our actual measurements often revealed differences. We proceeded with the campaign through repeated real-time discussions. I stayed out on deck in short sleeves to sense the temperature changes, but it turned out to be colder than expected. While it was hot and humid on land, the sea air was surprisingly cool.

The latter part of the voyage was calm, with the sea surface so smooth it looked like a mirror. I remember being surprised to see such a quiet face of the ocean. At night, however, we encountered many fishing vessels at work. Since they were also targeting the tide fronts, it made sense. We continued our work by adjusting observation points as needed. Looking at the maps afterward, it was clear that the fishermen’s ability to identify the tide fronts based on experience was truly remarkable. On board, we even commented that “if we could observe from that boat, it would be perfect.”

Another objective of the Seisui-maru cruise was biologging. We released large turtles (up to 150 kg) that had been protected in Otsuchi into waters of various temperatures to study which directions they swam toward. During transport, we fed them jellyfish, their natural diet, which provided a welcome source of comfort during the long voyage.

This was a truly valuable experience. Moving forward, I will analyze the observation data to turn this experience into tangible results. I hope that as many outcomes as possible can be obtained from it.

Radiosonde release on a calm water surface with the morning sun

OGAWA Taisei (Kyoto Univ., M2)

From Jun 25 to Jul 2, 2025, we had the amazing opportunity to conduct an intensive radiosonde observation at the Otsuchi Coastal Research Center of the Atmosphere and Ocean Research Institute, University of Tokyo. The mission was to launch radiosondes at a high frequency, in sync with two research vessels, the Shinsei-maru and the Seisui-maru, as they navigated off the Sanriku coast. Our goal was to capture the detailed space-time variability of the atmospheric boundary layer over the oceanic frontal zone! I heard that a simultaneous observation by three ships in the East China Sea was carried out in the Hotspot2 Project, but this time, the key was our “two ships and one fixed station” setup. Having a stationary point makes it easier to distinguish between temporal and spatial variability. It also seemed to open the door for more people to join the observation, as I heard some participants joined the Otsuchi observation to avoid seasickness.

Our Otsuchi observation team had 13 members, made up of 3 professionals, 8 master’s students, and 2 undergraduate students. We worked around the clock, splitting into three shifts: 0-4, 4-8, and 8-0. I was on the 4-8 shift, and I have to say, it was the best one! We got to see both sunrise and sunset, and the weather was not too hot. I was a little jealous of the other two shifts, though, as they got to see some incredible star-filled night skies.

Since the 4-8 shift was almost always during the daytime, we witnessed all sorts of atmospheric phenomena. Or rather, our members helped me notice them. T-san pointed out some wave-like clouds, wondering if they were atmospheric gravity waves. A-san was always the first to spot “angel’s ladders.” And one morning, K-san and H-san were thrilled by a thick blanket of fog, snapping tons of photos. It turns out that this fog likely formed due to very specific weather and ocean conditions unique to that time and day, and H-san was fired up for doing detailed analysis. In an age where we’re glued to our phones, I discovered the simple happiness of having friends to gaze at the sky and talk about its wonders with.

We also got inspiration from the members of the Behaviour, Ecology and Observation Systems lab, AORI, U-Tokyo, who were staying at the center at the same time (We nicknamed them the “Sea Turtle Team.”). Their day started bright and early, heading out to receive sea turtles incidentally caught in fishermen’s nets. They would take measurements, attach a logger, and then release them back into the ocean. The turtles provide continuous records of the ocean interior conditions, which is valuable for our physics-based researchers, too. Unfortunately, our schedules were so different that we had limited chances to interact, but I hope we can connect more in the future to deepen our understanding of the Sanriku offshore region. Watching the Sea Turtle Team skillfully prepare their own meals, including expertly filleting fish, I was struck by the vibrant energy of field researchers.

I’ve been fortunate to participate in several observation campaigns before, but this one has left a particularly lasting impression. I find myself diving into data analysis, excited about the results. It was a precious experience that reminded me of the primitive joy of research.