SeaSoar Measurements in the Japan/East Sea
Craig M. Lee - APL, University of Washington
Overview Observational Program Spring 1999 Winter 2000 Results People

Pictures Reports Positions Met Data SST Sections AVHRR

Frequent storms mark wintertime atmospheric variability over the Japan/East Sea. These events occur on 3-5 day time scales and often involve cold, dry Siberian air channeled though the region around Vladivostok and out over the central basin. Such storms can drive intense heat loss and produce convective overturning in the upper ocean. Under the Office of Naval Research's JES Initiative, a wintertime cruise will focus on documenting the upper ocean response to these cold air outbreaks, with particular attention to processes associated with water mass formation and subduction in the region around the subpolar front.

The winter SeaSoar cruise was held from 16 January — 5 February 2000 aboard the R/V Roger Revelle. A team of U.S., Korean, Russian, German, Chinese and Polish scientists made physical, bio-optical and biological measurements of the upper ocean and both shipboard and balloon soundings of the atmospheric boundary layer. Sampling involved intensive surveys in and around the subpolar front and several longer sections taken in a line radiating away from Vladivostok towards the south side of the front. SeaSoar surveys were supplemented by intensive sections of hydrographic and bio-optical profiling casts. We adjusted our sampling strategy in response to real-time remote sensing (sea surface temperature and ocean color) and atmospheric forecast data that were available on board the Revelle Our intent was to characterize the atmospheric boundary layer and upper ocean in the region around the subpolar front before, during and after cold air outbreaks.

Here is a roster of the Science Party on the Revelle for the Winter 2000 Cruise.

Snapshots from the Japan/East Sea in Winter

Dawn, last day of sampling. Al Gordon, Matthew Ragan, Jeremy Bricker and Burt Jones move the bio-optical profiling package into position for deployment.

Choi Sung Ho, Frank Bahr and Paul La Violette recover the bio-optics package.

Frank Bahr, Craig Lee, Dong Won Park, Burt Jones, Steve Murray and Chief Engineer John Weaver move SeaSoar onto its launching cradle.

A nice, sunny, extremely cold day following our second cold air outbreak. Jeremy Bricker, Bos'n Vic Barnhart and Billy King chipping ice off the bow. Cold temperatures and copious spray produced a thick coating of ice during the outbreak.

Progress Reports from Chief Scientist Dr. Craig Lee, APL/UW

29 JANUARY 2000
Just after our last posting (22 Jan), we completed two lines extending from 39 N to 41 15" N along 134 58" E and 135 12" E. These sections show what appears to be a warm eddy just north of the subpolar front. Mixed layers within the eddy were deeper than those outside, extending below 100 m. Some of the deepest chlorophyll fluorescence and transmissivity signals we have observed were associated with the eddy's bottom edge. North of the eddy we entered the cold, deep mixed layer regime we originally expected to find just north of the subpolar front. At the end of the initial survey, we recovered SeaSoar in preparation for an intensive series of hydrographic and optical stations. Recovery revealed extensive fairing (small drag-reduction fins attached to the sea cable) damage, likely caused by rough operating conditions during the previous cold air outbreak. As usual, fairing repair was a lengthy endeavor, this time undertaken at night with air temperatures well below freezing. A large number of the science party turned out for this exercise, and we of the SeaSoar team are very grateful for their help. Had it not been for all the extra hands, it would have been a miserable, all-night affair.

With SeaSoar aboard, we began a highly resolved section of CTD and optical casts, running from 39 to 41 15" N along 134 28" E. The start of this section coincided with the onset of our second cold air outbreak, with winds gusting to 40 knots, 4-5 m seas and temperatures hovering near -11 C. This event produced a thick coat of ice over the bow, on the bulwark and across the fantail. Revelle provided a stable platform, enabling us to operate despite the conditions. The extreme cold played mischief with several aspects of CTD operations and taught us a few memorable lessons. Problems included frozen plumbing, frozen plugs clogging Nisken bottle drains and general icing of all of our handling gear. Nonetheless, we were able to sample all stations as planned.

Following the hydro section, we redeployed SeaSoar and begun our second intensive survey. This pattern focuses on the region directly around the front, reoccupying the sections sampled by the first survey but staying between 39 10" and 40 10" N. Shortly after deployment, the SeaSoar CTD ceased telemetering data, forcing us to recover for troubleshooting and repair. After an initial scare over shorting in the sea cable, Paul Fucile quickly tracked the fault to arcing in the winch's slip rings. Following slip ring replacement we redeployed SeaSoar and continued with the second intensive survey.

Our second cold air event ended the following day. Temperatures remained quite cold, but the sun reappeared and both winds and seas settled down. Various members of the science party joined the Revelle's crew to help chip and clear ice from Revelle's heavily encrusted bow. The second survey was completed on 28 January in the calm between cold air outbreaks. In general, mixed layers appear to have deepened and surface waters have cooled considerably since the initial survey, consistent with the response one might expect from several days of strong winds and intense net surface cooling.

We are currently executing a third intensive survey. This resembles the area of the first and second surveys, but extends northward to capture the southern half of the eddy observed north of the subpolar front. The series of repeated surveys, taken before, during and after cold air outbreaks, will allow us to investigate how the region around the front responds to strong forcing events.

22 JANUARY 2000
We've survived our first cold air outbreak! Following the last report (16 Jan), we reoccupied the west-east section sampled last spring. Weather remained good during this period. Just off the Korean Coast, the section passed through an eddy-like feature approximately 200 km in diameter. The eddy was warmer and more saline than surrounding waters, with a marked salinity maximum near its base. Near the end (134 E) of the zonal section along 37°45'N , we sampled a pycnostad similar to the feature observed near the same location during the spring cruise. The pycnostad sat between the 26 and 26.5 kg/m^3 isopycnals with waters near 10 C and 34 psu. Clouds continue to hamper remote sensing efforts, though we have received some clear images over the region sampled during the May cruise. The remainder of the front has been obscured from view. We thus chose to site the first intensive survey in the region we sampled the previous spring.

At 134 E, we turned north to make our initial section across the front. SeaSoar experienced mechanical difficulties as we neared the subpolar front, forcing a recovery near 39 45' N. Given an estimated 6-10 hours on deck for diagnosis and repair, we elected to steam southward back along the sampling line, executing four hydrographic casts between the recovery point and 39 N. These casts revealed a subsurface oxygen maximum/salinity minimum near 80 m, well beneath the surface mixed layer. A thin salinity maximum resided just beneath this. We traced SeaSoar's problems to a hydraulic unit leak. The component was replaced with a spare and a second dissolved oxygen sensor (Seabird SBE-23) was added to supplement the Langdon unit. SeaSoar was redeployed at 39 N following completion of the fourth hydrographic cast. That evening, winds picked up and temperatures dropped- the start of our first cold air outbreak.

We spent the next two days executing an intensive survey of the subpolar front in rough, cold conditions. (south - north section along 134°E) Wind speeds reached 40 knots, with 4-5 m seas and air temperatures well below freezing. Crew and science weathered the conditions well, though the weather certainly took its toll on general energy levels. Revelle was easily able to maintain the required 8 knot towing speed, and SeaSoar performed well despite the rough conditions. Extreme pitching of the ship impacted SeaSoar's performance, resulting in a slightly reduced profiling range when the waves were largest.

Between 134 E and 135 E, the subpolar front sat near 39 50' N with surface temperature gradients of 3 C in 20 km. Mixed layers south of the front were typically 20-40 m deep, with strong stratification at the base. In contrast to our expectations, waters north of the front were warm (5-6 C) with relatively shallow, 50-70 m deep mixed layers. North of 41 N, surface waters cooled to 3 C and the mixed layer deepened considerably. Stratification at the mixed layer base was weaker north of the front than south, but was extremely weak north of 41 N. Subsequent surveys will allow us to explore how the region around the front evolves in response to cold air outbreak events.

Today dawned on calmer seas, sunshine (!) and much, much weaker winds. Many in the science party spent part of the morning enjoying the ice sculptures left behind by the wind and spray of the last two days. A couple of calm days and several hours of undisturbed sleep will be welcome by all. We are currently finishing the first intensive survey, after which we will recover SeaSoar and execute a high-resolution hydrographic/bio-optical section across the front.

16 JANUARY 2000
After three days of intensive setup, we sailed at 16:00 today. All systems are operational. SeaSoar sits on the fantail ready for deployment. Installation of the additional meteorological sensors went well, and all are now logging data as we cruise north. The sonic anemometer's GPS returns time but no position, but this will be rectified by integrating the ship's P-code GPS stream in post-processing. Rob Pinkel is testing his two new sonar systems, which may give us velocities to 1000 m. The NRL group is receiving real-time AVHRR and SeaWiFS imagery. Unfortunately, we forgot to request a cloud-free central basin, so coverage over the study area has been limited. A recent image provided partial coverage of the subpolar front between 134 E and 135 E, essentially the same region we sampled in spring 1999. The image reveals sharp sea surface temperature contrasts near 40 N, with considerable small-scale structure in and around the front. Our current plan is to steam northward along the Korean coast to 37 45' N, at which point we will deploy SeaSoar and continue directly eastward. Unless tomorrow's images compel us otherwise, we will turn north at 134 E to make our initial section of the front. The weather remains quite good- hopefully everyone will have an opportunity to get their sea legs before we face our first storm.

Cruise Track Waypoints
Waypoints for JES-3 (R/V Revelle) for 16 January through 5 February 2000

Starting from Pusan harbor, steam to Waypoint #1 following 1000m isobath north along Korean coast.
1 37° 45.00'N 129° 06.00'E Deploy Seasoar (~200 m depth)
2 37° 45.00'N 134° 00.00'E This will take us into Russian waters
3 41° 15.00'N 134° 00.00'E
4 41° 15.00'N 134° 11.00'E
5 39° 00.00'N 134° 11.00'E
6 39° 00.00'N 134° 28.00'E
7 40° 10.00'N 134° 28.00'E
8 40° 10.00'N 134° 42.00'E
9 39° 00.00'N 134° 42.00'E
10 39° 00.00'N 134° 58.00'E
11 41° 15.00'N 134° 58.00'E Northern extent may change
12 41° 15.00'N 135° 12.00'E
13 39° 00.00'N 135° 12.00'E End of 1st survey, recover SeaSoar
14 39° 00.00'N 134° 28.00'E CTD cast 5/optics cast 1
15 39° 15.00'N 134° 28.00'E CTD cast 6/optics cast 2
16 39° 30.00'N 134° 28.00'E CTD cast 7/optics cast 3
17 39° 40.00'N 134° 28.00'E CTD cast 8/optics cast 4
18 39° 50.00'N 134° 28.00'E CTD cast 9/optics cast 5
19 40° 00.00'N 134° 28.00'E CTD cast 10/optics cast 6
20 40° 10.00'N 134° 28.00'E CTD cast 11/optics cast 7
21 40° 20.00'N 134° 28.00'E CTD cast 12/optics cast 8
22 40° 30.00'N 134° 28.00'E CTD cast 13/optics cast 9
23 40° 45.00'N 134° 28.00'E CTD cast 14/optics cast 10
24 41° 00.00'N 134° 28.00'E CTD cast 15/optics cast 11
25 41° 15.00'N 134° 28.00'E CTD cast 16/optics cast 12, deploy SeaSoar
26 39° 00.00'N 134° 28.00'E
27 39° 00.00'N 134° 00.00'E
28 40° 00.00'N 134° 00.00'E
29 40° 00.00'N 134° 14.00'E
30 39° 10.00'N 134° 14.00'E
31 39° 10.00'N 134° 28.00'E
32 40° 10.00'N 134° 28.00'E
33 40° 10.00'N 134° 42.00'E
34 39° 10.00'N 134° 42.00'E
35 39° 10.00'N 134° 58.00'E
36 40° 10.00'N 134° 58.00'E
37 40° 10.00'N 135° 12.00'E
38 39° 10.00'N 135° 12.00'E
39 39° 10.00'N 134° 00.00'E
40 40° 00.00'N 134° 00.00'E
41 40° 00.00'N 134° 14.00'E
42 39° 10.00'N 134° 14.00'E
43 39° 10.00'N 134° 28.00'E
44 40° 20.00'N 134° 28.00'E
45 40° 20.00'N 134° 42.00'E
46 39° 10.00'N 134° 42.00'E
47 39° 10.00'N 134° 58.00'E
48 40° 20.00'N 134° 58.00'E
49 40° 20.00'N 135° 12.00'E
50 39° 10.00'N 135° 12.00'E

Plotted Waypoints for JES-3 (R/V Revelle) for 16 January through 5 February 2000
Plotted Waypoints for JES-3

Hourly Average Meteorological Data
Daily ASCII data files including Position from the Revelle.
Please consider these data preliminary and use them with care. Many of the sensors have had severe icing problems.

Sea Surface Temperature (SST)
Satellite SST image of the region surveyed. The large SST contrast near 39 50' N is surface expression of the subpolar front. The four red north-south lines mark the SST sections displayed in the next two figures.
Satellite SST image
Meridional sections of AVHRR Sea Surface Temperature before (18 Jan) and after (21 Jan) a cold air outbreak. In both figures, the subpolar front sits near 39 45' N. Following the cold air outbreak, the subpolar front appears sharper and sea surface tempertures along the entire line have decreased. Dr. Christine Chan of the Naval Research Laboratory (NRL), Stennis Space Center produced the three figures from NOAA AVHRR imagery.

SeaSoar Vertical Contour Sections

West to East line along 37° 45'N

South to North line along 134°E

Recent AVHRR Imagery
AVHRR sea surface temperature as it appeared at the end of December, 1999- two weeks prior to the Winter 2000 Cruise. Extensive cloud cover limits the quality of remotely sensed imagery. Mid-basin, near 135 E, the subpolar front appears near 40 N, though the location of the front is difficult to discern through the cloud cover. These images are provided by Robert Arnone, Christine Chan and Richard Gould of NRL Stennis Space Center.

Japan/East Sea on 28 December 1999 - Click for full-size image

Japan/East Sea on 30 December 1999 - Click for full-size image

^ top