When I launched a radiosonde at 0830 UTC (1730 SMT), August 20, I could confirm a balloon was traveling in the rainbow sky.
We have spent here on-station over two weeks and could obtain various observation data. The sky was decorated with this beautiful rainbow, as if they had celebrated us. I had better say rain-ball rather than rainbow to indicate this nice combination.
Now the time for telling surface drifter after two talks on TRITON buoy and wave-gliders, which all form a special observation array around the MIRAI.
Yesterday, I wrote wave glider can measure ocean surface condition without disturbances around wave glider owing to its slim and thin body. The surface drifter, I introduce today, is much easier to obtain data without such noises than wave glider. This is because simply we use a small (O(10cm)) float equipped with temperature/salinity sensors. Since it drifts, it does not create any disturbances around the instrument. After we deploy it, we recover the next day or so. Indeed, we deployed its first trial yesterday, and could recover it today.
Having said that, it is not an easy task than you expect. You may recall that currently we are conducting on-station observation. Namely, while we need to keep the position, we also have to recover the drifter, which moves several 10 km away. Thus, we need to arrange observation as well as personnel schedule.
In addition, although GNSS-receiver is equipped on the float, it is very tough to find such 10-cm diameter ball in the ocean using only GNSS information. Of course, we need to avoid hitting it by the ship. Thus, after we reach the expected area, while we look for the drifter using telescope and binoculars, we also use a small boat. As usual, ship crew can find it earlier than researchers. As shown in photo-2, finally we caught it by hand from the small boat.
I have to talk about science derived from this trial. As noted, this drifter can measure temperature and salinity in a couple of centimeters of the ocean surface, which is greatly influenced by atmospheric condition, and vice versa. Through this knowledge, we’d like to know a life cycle of cloud and associated large-scale features.
Today we recovered the drifter under the heavy clouds (but no rain). According to the satellite cloud images, it was part of cloud cluster of O(1,000 km). In addition, weather forecast says low pressure area was formed around here and then it is expected to move northward. Thus, while I will watch its first data obtained by the drifter, I may also be aware of cloud ensemble movement to see any relation to weather condition over Japan…
by M. K. (edited at J-Office for English ver.)
The drifter we use is called Surpact, which was developed by our French collaborators of LOCEAN. This observation is conducted under the framework of French-Japan Science and Technology Cooperation. Its details will be noted in the Cruise report.
During on-station period, we are deploying various observation systems around the Mirai. Yesterday, I introduced TRITON buoy, today I’d like to mention about wave-glider, autonomous surface vehicle.
A wave glider consists of float (yellow part in the photo-1) and glider (identified with many fins in the same photo). This photo does not show its exact configuration during its operation, because both are connected by 8-m long umbilical cable. As you can easily guess from its name, this ASV obtains propulsion power from waves. When the float moves up and down due to waves, its motion changes glider’s fin, so that it accelerates forward motion. The operator on land can control its direction via satellite. Various atmospheric and oceanic instruments are equipped, and solar energy is used for their operation. Namely, it is a nature-friendly new generation observation tool.
Photo-2 was taken when we launched. Owing to its slim configuration, it can measure ocean surface condition without significant turbulence around the vehicle.
This time in addition to standard surface meteorological sensors we have equipped GNSS-receiver, which can measure precipitable water vapor. Since water vapor plays an essential role in regulating convective activity and cloud development, this ASV equipped with various instruments can be used to monitor cloud formation from the viewpoint of air-sea interaction.
During this on-station period, we are deploying three wave gliders, which occupy west, north, and east 50 km away from the Mirai. As you may recall, we’ve already deployed one TRITON buoy at south of 50 km away from the Mirai. Namely, this time our observational configuration consists of six platforms within 50 km radius (five are fixed locations, and one is drifting, which will be mentioned later). This is irregular comparing to previous field campaigns, where we usually form an observation network over 100 km in space. I know, we should keep away from 3Cs on land to avoid any possible risk of COVID-19. However, we are challenging to conduct dense observation here. I believe this configuration will bring a new insight.
Note that after our one-month intensive observation here, we will recover all wave gliders as well as TRITON buoy. I do hope they work well and we can recover them. So do you.