Japan/East Sea  Home Page

Department of Physical Oceanography
Woods Hole Oceanographic Institution
Woods Hole, Massachusetts 02543

ATMOSPHERIC FORCING and its SPATIAL VARIABILITY
over the JAPAN/EAST SEA
 

Robert Beardsley (WHOI)
Clive Dorman (SDSU)
Richard Limeburner (WHOI)
Alberto Scotti (UNC)

January, 2001








Table of Contents

Project Overview:

The overall goal of this project is to improve our understanding of the marine atmospheric boundary layer (MABL), its spatial structure and variability, and the resultant ocean surface forcing over the Japan/East Sea (JES).

Winter circulation and water mass formation in the Japan/East Sea are thought to be strongly driven by surface wind stress and heat fluxes. Strong winds off Siberia during cold-air outbreaks and local topographic effects associated with the Sikhote-Alin mountain range that boarder the western rim of the Japan/East Sea may give rise to large spatially-concentrated surface stresses and associated heat and moisture fluxes which have direct and possibly large effects on the ocean.

Our primary objectives are 1) to determine the structure and variability of the MABL over the JES on synoptic and seasonal time scales, 2) to estimate surface wind stress and heat flux time series during summer and winter conditions, and 3) to examine the role of the coastal mountain ranges along the western perimeter of the JES on the low-level air flow and surface forcing during winter, with special emphasis on cold-air outbreak events that cause the maximum surface wind stresses and air-sea heat flux losses.

This project is part of the ONR Japan/East Sea Directed Research Initiative to examine frontal processes, circulation, and water property evolution in the Japan/East Sea during 1999-2000.  The meterological data collected in this project and modeling directly complements two other components of the ONR JES program.  C. Friehe and D. Khelif (UCI) used an instrumented ONR Twin Otter aircraft to map the surface meteorological fields and study the MABL structure over the central JES during late January-February 2000 (one flight overflew the Revelle).  Flight patterns included low-level (~ 30m) transects, with soundings to map the vertical structure of the boundary layer.  Some flights were timed to sample cold-air outbreaks.  S. Chen (UMiami) has collected both land-based and satellite weather data in the JES region for 1999-2000 and used this data with global weather model data to force a regional weather model and produce more highly resolved surface weather fields for the study period.
Links to these two components are given below.
 

Scientific Background:

The surface winds over the Japan/East Sea show a marked seasonality, with weak and variable winds in summer and strong winds in winter.  The wintertime mean synoptic-scale weather pattern is dominated by the Siberian high, which forces northerly and northwesterly winds from the Asian continent over the JES.  Based on weather map analysis, Na et al.  (1992) report offshore monthly-mean surface wind stresses of order 1.5 dyn/cm^2 in the northern JES (Figure 1). Cold-air outbreaks are typical, occurring about 2-4 times per month on average.  Manabe (1957) found extremely large air-sea fluxes during a cold-air outbreak in winter 1954-1955, as implied from synoptic data and observations from USAF reconnaissance flights, with air-sea temperature differences exceeding 10 deg C (Figure 2). In the far northern JES, Martin et al. (1992) report local heat losses larger than 1000 W/m^2 during winter storms with strong northerly winds. Hirose et al. (1996) estimated from ship reports that the monthly mean heat loss from the JES to the atmosphere exceeds 200 W/m^2 during November, December and January, with an annual mean heat flux of about -50 W/m^2.  In a recent analysis by Kawamura and Wu (1998) using ECMWF forcasts and NSCAT winds, estimates of the total heat flux in January 1997 exceed 300 W/m^2 offshore of Vladivostok (Figure 3).
 
 !Click on the thumbnail to see a bigger version of the figure!
/mnt/alessi/japan_sea/index.html

Figure 1a

Figure 1b

Figure 2

Figure 3

Despite this past work, little is actually known about the marine boundary layer and surface forcing fields over the Japan/East Sea, especially during winter.  We know of no modern profile measurements through the marine layer or moored measurements which allow accurate estimation of the surface heat flux components.

Theoretical, numerical, and laboratory investigations of flow past two-dimensional ridges and isolated circular and elliptical obstacles have demonstrated a rich array of dynamical flow structures including lee waves, hydraulic jumps, wakes, eddy generation and shedding, and upstream blocking and recirculation.  Although the study of topographic effects in homogeneous and stratified flows is well-developed for idealized geometries, the role of the local orography in modifying and accelerating low-level winds during cold-air outbreaks in this region is unknown.  The mountain ranges along the North Korean and Russian coasts reach heights of 1000m and higher, and are separated by an orographic gap at Vladivostok (Figure 1(a)).  Manabe (1957) found that in this gap during one cold-air outbreak, the marine layer had a height of about 800m (with a strong inversion cap above), comparable to the height of the neighboring mountains.  This suggests that the coastal mountains may effectively channel the cold dry Siberian air through the Vladivostok gap during cold-air outbreaks, causing strong spatial variability in the wind stress and surface heat flux over the JES.  While there is some anecdotal evidence for this hypothesis, we know of no data collected to look at spatial variability in the surface forcing fields.

Approach:

This study is part of the ONR JES program.  Our approach is to (1) make ship and fixed-point meteorological measurements on selected JES cruises to investigate MABL structure and surface forcing variability during summer (1999) and winter (2000) conditions, (2) collect and analyze JMA buoy weather data, regional WMO surface and upper-air data, stationary weather satellite imagery, and ECMWF surface fields to determine the synoptic setting during our in-situ measurement periods, and (3) conduct a process-oriented  model study to gain dynamical understanding of the wintertime orographically modified flow, and to compare these model flows to observations and to results from more complex models.

Work Completed:

Ship-based Meteorological Measurements: (Beardsley, Dorman, Limeburner)

Meteorological data were collected on three R/V Revelle and two R/V Professor Khromov cruises during summer 1999 and winter 2000 in the JES (Table 1).  These measurements included a) basic shipboard measurements of surface variables (wind, air temperature, relative humidity, air pressure, incident short- and long-wave radiation, precipitation, and sea surface temperature) on all five cruises, b) balloon soundings (winds, air temperature, relative humidity, and air pressure) to 10 km on the two Revelle SeaSoar cruises, and c) high-frequency sonic measurements of wind velocity, temperature and relative humidity on the winter Revelle cruise.

The basic surface measurements were made on the Revelle using the ship's IMET system and on the Khromov using WHOI self-contained ASIMET units.  During the two Revelle SeaSoar cruises, two SDSU sensor sets were deployed on the bow mast below the IMET sensors, and one SDSU set near the top of the main mast, providing profile measurements over the maximum vertical sensor spacing available.  The winter Revelle cruise featured additional IMET and ASIMET radiation sensors and J. Edson?s 3-axis sonic anemometer/thermometer/motion sensor system (Edson et at., 1998) mounted on the bow mast to allow direct covariance estimation of surface forcing during high wind cooling events.

Despite some IMET and ASIMET failures, the overall data return and data quality of the surface measurements were good. These data plus some additional data collected during the cruises should allow a full description of the surface meteorological conditions during the five cruises, plus bulk estimation of the surface wind stress during the five cruises and the surface heat and moisture fluxes on the two Revelle SeaSoar cruises and both Khromov cruises. Atmospheric soundings made on both Revelle SeaSoar cruises from the surface to above 10 km captured changes in the vertical structure of the MABL during synoptic shifts and winter cold-air outbreaks.

Table 1.  JES cruises featuring meteorological measurements collected by this component. The surface met data sets are considered "complete" if accurate time series of wind velocity, air temperature, relative humidity, pressure, incident short- and long-wave radiation, and SST can be constructed using the best mix of IMET, ASIMET, SDSU, and other shipboard data.
 

Ship 
 Dates
Chief Scientist
Activity
Surface Met Data
Other Data
Revelle 
5/19-6/3/99
C. Lee (UW)
SeaSoar 
Complete
Sounding data 
Revelle
6/25-7/18/99
L. Talley (SIO) 
Hydrography 
No short-wave radiation
  
Khromov
7/20-8/9/99 
L. Talley (SIO) 
Hydrography 
Complete 
  
Revelle
1/16-2/4/00
C. Lee (UW) 
SeaSoar 
Complete 
Sounding, turbulence data
Khromov
2/28-3/17/00 
L. Talley (SIO) 
Hydrography
Complete
 

Land-based Meteorological Measurements: (Dorman)

Additional meteorological data were obtained from a new automatic weather station installed in Vladivostok(on the roof of the FERHRI laboratory) in late1999 with help from Y. Volkov (FERHRI), other fixed surface stations including Japanese Meteorological Agency buoy 21002, and the WMO upper air sounding stations surrounding the JES.  Weather satellite imagery and SST data were also collected and archived.
 

Numerical Modeling and Analysis: (Scotti)

We originally hypothesized that the Vladivostok ?Gap? in the coastal mountain range would tend to channel the eastward flow of cold surface air during cold-air outbreaks, thus affecting the surface wind field over the western JES (Figure 4). Using the Rogerson (1998) nonlinear shallow water MABL model, initial model simulations with idealized topography show a strong jet leaving the gap and veering westward, indicating topography, stratification, and rotation are tightly coupled as first thought.  Additional simulations indicate that time-dependent forcing (i.e., allowing the imposed upper-layer pressure field to vary in time) can cause the surface jet to vary in direction from initially southwestward towards the southeast, more consistent with the observed wind fields during cold-air outbreaks.
 
 

                         Figure 6.  Schematic of air flow over coastal ranges during a cold-air outbreak.

Results: Fall AGU 2000 Presentations

Beardsley, R., R. Limeburner, J. Edson, C. Dorman, and C. Lee (2000).  Shipboard Meteorological Measurements in the Japan/East Sea during January-March 2000.   POSTER

Dorman, C.E., S. M. Varlamov, and N.A. Dashko (2000).  Cold Air Outbreaks over the Japan Sea During Winter 2000. ABSTRACT

Khelif,D., and C.A. Friehe (2000).  Surface Forcing and Boundary-Layer Structure Over the Japan/East Sea During Winter Cold-Air Outbreaks.  ABSTRACT

Lee, C.M., B.H. Jones, K.H. Brink, R. Arnone, R. Gould, C. Dorman, R. Beardsley (2000). Upper Ocean Response to Cold Air Outbreaks in the Japan/East Sea: SeaSoar Surveys at the Subpolar Front
ABSTRACT

Scotti, A. and R. Beardsley (2000).  Hydraulically Controlled Flow Across the Vladivostock Gap. ABSTRACT

Data Inventory

This section provides links to the data and model results obtained in this project as they become available.  Descriptions of the methods used to process and produce "best" versions are included with the final data sets.  Please contact Bob Beardsley if you experience any problems getting the information or have questions and find errors in the data.

Shipboard surface meteorological data:
 
 
Cruise
Cruise Report
Final Data
Lee summer SeaSoar 
  
Revelle1
Talley summer survey - part 1
  
Revelle2
Talley summer survey - part 2
Report
Met Report
Khromov1
Lee winter SeaSoar
Met processing
Revelle3
Talley winter survey 
Met Report
Khromov2

Also available via ftp

Numerical model results

Related Program Links

ONR JES program main home page

Shuyi Chen (UMiami)

Craig Lee (UWash)

Carl Friehe (UCI)

Clive Dorman (SDSU)
 
 

Summary:

We plan to continue to process the meteorological data collected in this project and produce final "best" data sets for scientific analysis and use by other investigators.  Our intial focus will be on the winter measurements with special attention to the several cold-air outbreaks that occured during the January-March measurement period.   Analysis of these data will guide the numerical model studies, with the goal of producing detailed descriptions of the surface fields and MABL structure behavior during cold-air outbreaks and the dynamics governing these events.
 
 

References:

Hirose, N., C.H. Kim, and J. H. Yoon, 1996:  Heat budget in the Japan Sea.  J. Oceanography Soc. Japan, 52, 553-574.

Kawamura, H., P. Wu, 1998: Formation mechanism of Japan Sea Proper Water in the flux center off Vladivostok. J. Geophys. Res., 103(C10), 21611-21622. 

Manabe, S., 1957: On the Modification of air-mass over the Japan Sea when the outburst of cold air predominates. J. Met. Soc. Japan, 35(6), 311-326. 

Martin, S., E. Munoz, R. Drucker, 1992: The effect of severe storms on the ice cover of the northern Tatarskiy Strait. J. Geophys. Res., 97(C11), 17753-17764. 

Na, J.-Y., J.-W. Seo, S.-K. Han, 1992: Monthly-mean sea surface winds over the adjacent seas of the Korean Peninsula. J. Ocean. Soc. Korea, 27(1), 1-10. 
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