NOAA Teacher at Sea Wes Struble Aboard NOAA Ship Ronald H. Brown February 15 – March 5, 2012
Mission: Western Boundary Time Series Geographical Area: Sub-Tropical Atlantic, off the Coast of the Bahamas Date: March 2, 2012
Weather Data from the Bridge
Position: 26 degrees 19 minutes North Latitude & 79 degrees 55 minutes West Longitude (8 miles west of Florida’s coast)
Windspeed: 14 knots
Wind Direction: South
Air Temperature: 25.4 deg C / 77.7 deg F
Water Temperature: 26.1 deg C / 79 deg F
Atm Pressure: 1014.7 mb
Water Depth: 242 m / 794 feet
Cloud Cover: none
Cloud Type: NA
There are four different ship’s stations that are involved in a CTD (Conductivity, Temperature, & Depth) operation: the bridge, the survey team, the winch operator, and the computer room. The bridge is responsible to keep the ship on position and stable over a predetermined latitude and longitude. The survey team is responsible for preparing the CTD platform for deployment and securing it back on deck at the completion of the cast. The winch operator controls the actual motion of the CTD platform by the use of a hoist. The computer lab relays commands to the winch and survey team in reference to testing and sampling depths, and when to start and stop the ascent and descent of the platform. The CTD platform can carry many types of instruments depending upon the nature of the research being conducted. During this cruise our platform usually contained two each of a temperature gauge, conductivity gauge (from which you can obtain salinity), and oxygen gauge. In addition there is one pressure gauge and a transmissometer (that measures the turbity of water which is an indicator of the phytoplankton), 23 Niskin water sampling bottles, and two Acoustic Doppler Range finders – one pointing toward the surface and one pointing at the sea floor.
A CTD cast begins when the ship arrives at prearranged coordinates of latitude and longitude. The bridge will announce that we are “on station”.
The survey team acknowledges and then raises the CTD platform and places it is the water at the surface for a minute or two. Then after receiving a signal from the computer operator that all functions are operating within normal parameters the platform is lowered to 10 meters and held there for two minutes to allow the instruments to stabilize.
After the two minute hold at 10 meters the entire platform is brought back to the surface and the log is started as the package is lowered. The descent begins at about 30 meters/minute and eventually reaches 60 meters/minute. Many of the deep water casts on this cruise were between 4000 m and 5500 meters (about 13000 ft and 18,000 ft) and take over an hour to reach the bottom. While the descent takes place all the instruments are recording data which is stored and plotted in real time at the computer monitor. When the CTD platform is 10 meters from the bottom the descent is stopped and the first water sample is collected by sending a signal that closes the first Niskin bottle. At this point the CTD slowly begins its climb back to the surface (another hour or more) stopping at designated depths to collect water samples.After the last Niskin bottle is closed at the surface, the CTD platform is brought back on deck, the water samples are removed, and the entire platform is prepared for the next cast.
A CTD is a standard instrument used on ships to measure conductivity, temperature and depth. Three CTD systems are being used during Leg 3 of Project DYNAMO to measure CTD.
The Revelle deploys the ship’s CTD twice a day to a depth of 1,000 m. The CTD measurements can be viewed on a monitor in the computer room.
The Ocean Mixing group is using a specialized profiling instrument that was designed, constructed, and deployed by the microstructure group at the College of Oceanic and Atmospheric Sciences, Oregon State University. The instrument, called “Chameleon”, measures CTD and turbulence. Chameleon takes continuous readings to a depth of 300 m as it is lowered through the water column. The top of the instrument has brushes to keep the instrument upright in the water and make it hydrodynamically stable so that very precise measurements of turbulence can be achieved. These measurements allow computations of mixing, hence the name Ocean Mixing Group. The instrument freely falls on a slack line to a depth of 300 m after which it is retrieved using a winch. The Chameleon has been taking continuous profiles at the rate of about 150/day since we have been on station and will continue taking measurements for the next 28 days.
The T Chain CTD aboard the ship was also designed by the microstructure group at the College of Oceanic and Atmospheric Sciences, Oregon State University. This instrument measures CTD in the near-surface (upper 10 m) using bow chain-mounted sensors (7 Seabird microcats + 8 fast thermistors). The T Chain takes data every 3 seconds, and although that is not very fast, the data is extremely accurate (within 1/1000th of a degree – 3/1,000th of a degree). The T Chain is mounted on the bow and has been taking measurements continuously since we have been on station. These measurements focus on the daytime heating of the sea surface and the freshwater pools created by the extreme rainfall we have been observing and which is associated with the MJO.
NOAA High Resolution Doppler LIDAR (Light Detection And Ranging) Group
A Brief Introduction to LIDAR
The following introduction to LIDAR systems was provided by Raul Alvarez.
In LIDAR, a pulse of laser light is transmitted through the atmosphere. As the pulse travels through the atmosphere and encounters various particles in its path, a small part of the light is scattered back toward the receiver which is located next to the transmitter. (You may have seen similar scattering off of dust particles in the air when sunlight or a laser pointer hits them.) The particles in the atmosphere include water droplets or ice crystals in clouds, dust, rain, snow, aircraft, or even the air molecules themselves. The amount of signal collected by the receiver will vary as the pulse moves through the atmosphere and is dependent on the distance to the particles and on the size, type, and number of particles present. By keeping track of the elapsed time from when the pulse was transmitted to when the scattered signal is detected, it is possible to determine the distance to the particles since we know the speed of the light.
Once we know the signal at each distance, it is now possible to determine the distribution of the particles in the atmosphere. By measuring how the light was affected by the particles and the atmosphere between the LIDAR and the particles, it is possible to determine things such as the particle velocity which can yield information about the winds, particle shape which can indicate whether a cloud is made up of water droplets or ice crystals, or the concentration of some atmospheric gases such as water vapor or ozone. The many kinds of LIDARs are used in many different types of atmospheric research including climate studies, weather monitoring and modeling, and pollution studies.
An integrated motion compensation system is used to stabilize the scanner to maintain pointing accuracy. As you can see from the video below, the scanner maintains its position relative to the horizon while the ship moves.
The slides below represent a Doppler LIDAR data sample from Leg 3 of the Revelle cruise. The images and slides were provided courtesy of Ann Weickmann.
The R/V Revelle is not a NOAA ship. It is part of the University-National Oceanographic Laboratory System (UNOLS) and part of the Scripps Institution of Oceanography research fleet. A few crew members were kind enough to take time from busy schedules to talk with me about their careers. Students may find these interviews interesting especially if they are exploring career options.
The food aboard the Revelle is very good thanks to our cooks, Mark and Ahsha. They are very friendly crew members and always happy to accommodate the diverse eating schedules of scientists who have to work during meal hours.
Meanwhile back on the winch, I am beginning to get the hang of it. I will not say that I am comfortable, because I am always aware that I am in charge of a very expensive piece of equipment. I alternate between operating the winch, operating the computer, standby time (to assist as needed) and free time.
A lot of the scientists got very little work done today because the cloud cover was interfering with their instruments. The radar group from Colorado State University was in good spirits because they had a real opportunity to test their equipment during stormy conditions. They are still working out some of the bugs so that when we reach international water, they will be able to work efficiently.
This was the first day in a week that I felt somewhat seasick. I would like to take this opportunity to thank the makers of Meclizine for making a darn good product. We are in the middle of a storm, as you can see from the higher waves and lower visibility reported above. It certainly could be worse- I mean, the waves are only 8 feet, but it’s still an adjustment for my body since the trip has been so nice up until now. I saw a satellite image of this part of the world and you can see a huge storm brewing. I encourage you to search the Internet for current weather images (try a Yahoo search of “NCAR RAP”) and find our latitude and longitude on the map. It looks pretty impressive. It could easily develop into a tropical storm, but hopefully not until it has passed us a little. So what does it feel like to be in a storm? Well, the boat is rocking a LOT, and I’ve been losing my balance all day. I went outside to take some pictures, and was drenched in the few minutes I was there. The deck has about an inch of water sloshing around. And there’s no view of the sunset on the deck after dinner tonight.
Question of the day: What are the two factors that are used when classifying a storm as a tropical depression, tropical storm, or hurricane?
Photo Descriptions: Today’s photos include 5 shots relating to the storm we are in. You’ll see several pictures of the bow of the ship and the low visibility. At all times, there is someone on the bridge on lookout for “objects” in the water (boats, buoys, etc.) During low visibility conditions this job is even more important, since the Captain would have very little time to react if something was spotted. Of course, there is always the radar system, but it doesn’t catch everything. Finally, a picture of the Doppler radar dome, taken prior to the storm. This Doppler radar provides crucial data about the weather conditions around the ship.