Coastal Air-Ocean Coupled System (CAOCS) for the East Asian Marginal Seas (EAMS) by LCDR Mike Roth Thesis Presentation 07SEP01
Feb 23, 2016
Coastal Air-Ocean Coupled System (CAOCS) for the East Asian Marginal
Seas (EAMS)by
LCDR Mike RothThesis Presentation
07SEP01
SignificanceFocus of METOC support for the littoral region at the mesoscale level
Emphasis on Air-sea interaction
EAMS is a critical operating area of the USN, especially 7th Fleet
The objective of METOC’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) developed by NRL
Purposes
To provide further support that CAOCS does perform well in simulating EAMS surface current circulation, SST structure, and SSS structure.
To provide support that CAOCS does perform well in simulating EAMS surface wind stress and low level atmospheric forcing.
Purposes (cont.)
Through analysis of CAOCS output: To show how the atmosphere and ocean behave in a way that cannot be described climatologically due to the small temporal scales of numerous mesoscale features present at the surface of the ocean and in the lower levels of the atmosphere even during a period following the onset of the summer monsoon. This will provide support regarding the usefulness of CAOCS over an uncoupled, climatologically forced ocean or atmospheric model.
Purposes (cont.)
Through analysis of CAOCS output: To show the significance of the air-sea interaction processes that occur between the lower atmosphere and the surface of the ocean and that CAOCS is indeed handling these air-sea interaction processes.
To emphasize the near-real time capability of CAOCS.
Purposes (cont.)
To show that CAOCS is an excellent tool for USN METOC community personnel because the accurate, near-real time model output will contribute to increased meteorological, oceanographic, and acoustic forecasting skill in a littoral environment.
The EAMSThe EAMS is comprised of:
Japan/East Sea (JES)
Yellow Sea/East China Sea (YES)
South China Sea (SCS)
The EAMS
YS/ECS (YES)
SCS
JESBohai Sea
Japan
China
KoreanPeninsula
Russia
Taiwan
Philippines
Borneo
Indonesia
Malaysia
Gulf ofThailand
Vietnam
Gulf ofTonkin
Components of the the EAMS
JESOceanography
JES
KoreanStrait
TsugaruStrait
Soya Strait
Tatar Strait
Honshu
KoreanPeninsula
Vladivostok Hokkaido
Kyushu
JESViewed as a miniature prototype ocean:
Basin wide circulation pattern
Boundary currentsA Subpolar Front (SPF)Mesoscale eddy activity
Deep water formation
JES CurrentsTsushima Warm Current (TsWC)
Flows northward from the ECS through the Korean Strait
Carries warm water into the JES
Separates north of 35°N into eastern/western channels
JES CurrentsJapan Nearshore Branch (JNB)
Flows northward as the eastern branch of the TsWC along the Japanese west coast
JES CurrentsEast Korean Warm Current (EKWC)
Flows northward as the western branch of the TsWC
Bifurcates at 37°N into an eastern and western branch
The western branch makes a cyclonic turn in the East Korean Bay
JES CurrentsLiman Current and North Korean Cold Current
(NKCC)Flows southward from the
Sea of Okhotsk through the Tatar Strait and along the Russian and North Korean west coast
Brings cold water into the JES
JES CurrentsThe Subpolar Front (SPF)
The southward flowing NKCC and the northward flowing eastern branch of the EKWC converge at approx. 38°N
The SPF stretches across the JES in a northeasterly direction and extends to the west coast of Hokkaido
YESOceanography
YES
Ryuky
u Isla
nds
Taiwan Strait
Yangtze R.
Yellow R.
Han R.
Liao R.
YES BathymetryYS quite shallow
Most water depth < 50 m
N-S oriented trench in central portion of YS
Broad/shallow continental shelf – water readily affected by varying atmospheric forcing (heating, cooling, wind stress)
YES BathymetryE/W asymmetry:
Extensive shoals <20 m in western YS and and not in eastern YS
50-m isobath > 100 km from Chinese coast but only 50 km from South Korean coast
Plays a crucial role in the shoaling of the MLD
YES Thermal StructureMonsoon atmospheric
forcing greatly alters SST and MLD depth:
Winter:
Cold northerly winds
SAT<SST
Surface heat lost from ocean to atmosphere resulting in upward buoyancy flux
YES Thermal StructureWinter (continued):
Thermal Forcing (cooling) and Mechanical Forcing (wind stress) generate turbulence
Mixing of surface water with deep water
Deepening of MLD that often extends to bottom
YES Thermal StructureSummer:
Warm southerly winds
SAT>SST
Strong downward net radiation
Leads to downward buoyancy flux
MLD shoals
Multi-layer structure (MLD, thermocline, and sublayer)
YES CurrentsKuroshio Current (KUC)
Strong WBC
Flows northward along the shelf break in the southern ECS
YES CurrentsTaiwan Warm Current (TWC)
Enters ECS through the Taiwan Strait
Flows northward inshore of the KUC.
YES CurrentsTsushima Warm Current (TsWC)
Flows northward from the KUC west of Kyushu and passes through the Korean Strait
Splits in the vicinity south of Cheju Island
YES CurrentsYellow Sea Warm Current (YSWC)
Flows northward beneath the surface into the YS
Brings warm water into the YS
YES CurrentsKorean Coastal Current
Flows southward along the Korean Peninsula
YES CurrentsChinese Coastal Current
Flows southward around the tip of the Shandong peninsula and along the Chinese coast
SCSOceanography
SCSGulf ofTonkin
LuzonStrait
TaiwanStrait
Balabac Strait
Mindoro Strait
SCS BathymetryStraits are relatively
shallow except the Luzon Strait (sill depth = 2,400 m)
Broad shallows of the Sunda shelf in the S/SW
Continental shelf in the N extends from Gulf of Tonkin to the Taiwan Strait
LuzonStrait
TaiwanStrait
SCS BathymetryExtensive continental
shelves (< 100 m deep) in W and S
Deep slopes w/ almost no shelves in the E
Deep eliptical shaped basin in the center of the SCS extends to over 4,000 m
Numerous reef islands and underwater plateaus scattered throughout SCS
LuzonStrait
TaiwanStrait
SCS CurrentsComplex dynamics
involved in the flow of the SCS are related to:
geometry of the SCS
its connectivity with the Pacific Ocean
strongly variable atmospheric forcing
water exchange between the SCS/ECS via the Taiwan Strait
LuzonStrait
TaiwanStrait
SCS CurrentsKuroshio Current (KUC) – bifurcation regime
Originates from the North Equatorial CurrentFlows northward as a WBC east of LuzonEnters ECS through the Luzon Strait, bifurcates into northward and northwestward branches to the northeast of a cyclonic eddy that is located northwest of Luzon (NWL eddy)
E
SCS CurrentsKuroshio Current (KUC) – bifurcation regime
The northward branch flows northward along the western coast of Taiwan
EThe northwestward branch makes a cyclonic turn around the NWL eddy
SCS CurrentsKuroshio Current (KUC) – loop regimeOriginates from the North
Equatorial Current
Flows northward as a WBC east of Luzon
Enters ECS through the southern Luzon Strait, loops around an anticyclonic eddy northwest of Luzon, and exits through the northern Luzon Strait
E
SCS CurrentsWinter upper ocean circulation
A southward coastal jet off the Vietnam coast and a cyclonic circulation throughout the SCS
SCS CurrentsSummer upper ocean circulation
A northward coastal jet off the Vietnam coast and an anticyclonic circulation throughout the SCS
SCS CurrentsSCS Eddies
Several cold core and warm core eddies are often found in the SCS
Generally, cold core are more common
Bottom topography is a key factor in their lifetime/trajectory
EAMSAtmospheric Forcing – the winter and summer
monsoon
YES
Atmospheric Forcing – Winter MonsoonNovember through March
Siberian High over East Asia continent
Polar Front positioned north of the Philippines
Relatively stronger, cold, and dry NW/N/NE winds flow over the EAMS
Equatorial Trough located south of equator
H JES
SCS
Polar Front
YES
Atmospheric Forcing – Transition Period
Polar Front moves northward toward Korea
Winter to Summer: March through May
YS SST increases by 10°C
The Siberian High rapidly weakens in April
Frontally generated events often occur in the YES during late April and May that cause highly variable winds, cloud amount, and precipitation (Mei-Yu Trough due to cyclonic shear between NE and SW).
Yellow dessert sand is often carried into the YS by eastward migrating surface lows originating in Mongolia
An atmospheric low pressure system forms in the north YS in late May/early June and migrates westward over Manchuria
Atmospheric Forcing – Summer Monsoon
Heat Lows over East Asia continent due to high solar insolation
Mid-May through Mid-September
Higher pressure over Pacific Ocean but subtropical ridge is displaced poleward
Equatorial Trough lies over central Philippines and extends NW to Tibetan Plateau.
JES
YES
SCS
H
L
L
Atmospheric Forcing – Summer Monsoon
JES
YES
SCS
L
LAir flows SE south of equator and turns SW over the SCS due to Coriolis Force
Polar Front moves north ivo 30-35°N
Relatively weaker, warm, and moist SW/S/SE winds flow over the northern SCS and the remainder of the EAMS
H
A Tropical Easterly Jet is found at 125-mb between the subtropical ridge and the Equatorial trough
Atmospheric Forcing – Transition Period
Polar Front begins to move southward away from the Korean Peninsula
Summer to Winter: Mid-September through October
SST steadily decreases
Southerly winds weaken as the Manchurian Low is replaced by the Siberian High
The Atmospheric Component of the
CAOCS
Mesoscale Model Fifth Generation (MM5)
Developed by Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR)
Limited-area, non-hydrostatic, terrain-following sigma- coordinate model
Designed to simulate or predict mesoscale and regional-scale atmospheric circulation
Area for Atmospheric Model
Distribution of Vegetation
The Oceanic Component of the
CAOCS
Princeton Ocean Model (POM)Developed at Princeton University
Time dependent, primitive eqn circulation model on a 3-D
Specifically designed to accommodate mesoscale phenomena, including the often non-linear processes commonly found in estuarine and coastal environments
Includes realistic topography and a free surface
Ocean Bottom
CAOCS Numerics
• MM5V3.4– Resolution
• Horizontal: 30 km• Vertical: 16 Pressure Levels
– Time step: 2 min• POM
– Resolution• Horizontal: 1/6o × 1/6o
• Vertical: 23 σ levels– Time Steps: 25 s, 15 min
Coupling of the Oceanic and Atmospheric
Components of the CAOCS
Ocean-Atmospheric Coupling
• Surface fluxes (excluding solar radiation) are of opposite signs and applied synchronously to MM5 and POM
• MM5 and POM Update fluxes every 15 min
• SST for MM5 is obtained from POM • Ocean wave effects (ongoing)
Lateral Boundary Conditions
• MM5: ECMWF T42
• POM: Lateral Transport at 142oE from the climatological data
MM5 Initialization
• Initialized from: 30 April 1998 (ECMWF T42)
Three-Step Initialization of POM• (1) Spin-up
– Initial conditions: annual mean (T,S) + zero velocity– Climatological annual mean winds + Restoring type thermohaline
flux (2 years)• (2) Climatological Forcing
– Monthly mean winds + thermohaline fluxes from COADS (3 years)
• (3) Synoptic Forcing– Winds and thermohaline fluxes from NCEP (1/1/96 – 4/30/98)
• (4) The final state of the previous step is the initial state of the following step
Reality Check of the Oceanic Output of the
CAOCS
Reality Check of the Oceanic Output of the
CAOCS
Liman/NKCC
JNBEKWC
SPF
Reality Check of the Oceanic Output of the
CAOCS
Reality Check of the Atmospheric Output of
the CAOCS
Reality Check of the Atmospheric Output of the CAOCS
JES
YES
SCS
L
LH
H
L
850-mb Winds and GHTFor 12Z July 19, 1998
JES
YES
SCS
Reality Check of the Net Radiation Output of the
CAOCS
Reality Check of the Net Radiation Output of the
CAOCS
Reality Check of the Net Radiation Output of the
CAOCS
Surface Long Wave Radiation Flux did not verify in position nor in magnitude.
This discrepancy will be corrected in future work with CAOCS.
APPROACH
APPROACHCAOCS model output was examined for the entire May through July 1998 with the intention of identifying the following:A time period prior to the onset of the summer monsoon that involved:
A significant weather event over the EAMS as well asan oceanic event that could be forcing flow at the lower levels of the atmosphere
APPROACHA time period after the onset of the summer monsoon that involved:
A significant weather event over the EAMS as well asan oceanic event that could be forcing flow at the lower levels of the atmosphere
Results Using the JES as an Example
Regions of JES
Example of Air-Sea Interaction:
Low level Atmospheric Wind Stress Driving the
Oceanic Surface Currents in the JES
12Z MAY 16 through12Z MAY 17, 1998
Example of Air-Sea Interaction:
LH
L
L
L
H
L
00Z MAY 30 through12Z MAY 31, 1998
L
H
L
H
L
H
L
H
L
00Z MAY 24 through12Z MAY 25, 1998
L
H
L
H
L
L
L
00Z through12Z MAY 27, 1998
Coastal Upwelling off the Russian Coast inthe Northern JES
Due to strong southerlies leading to cyclonic turning and offshore flow of the
normally southwestward, along-shore flowing Liman Current
L
H
15°C isotherm
26 MAY 1998
Old 15°C isotherm
1527 MAY 1998
00Z through12Z July 24, 1998
Warm Currents enforcingupward vertical motion of a
developing cyclonein the YES
Weaknesses of CAOCSCAOCS possesses an erroneous Surface
Longwave Radiation FluxCAOCS has trouble with the open ocean
boundary
Conclusions
In general, the oceanic component of CAOCS performs well in simulating the EAMS surface current circulation, SST structure, and SSS structure.
Surface winds of the atmospheric component of CAOCS verified well against NCEP surface wind fields during May through July 1998.
Conclusions (cont.)
The impact of the atmosphere on the ocean sea surface temperature is also significant but to a lesser degree.
The impact of wind stress on surface current is significant.
Oceanic SSS fields are altered due to atmospheric forcing but to a lesser degree than SST and surface velocity fields.
Conclusions (cont.)CAOCS atmospheric and oceanic output is indicative of the impact of ocean thermal structure on the lower level of the atmosphere.
Conclusions (cont.)CAOCS output clearly demonstrates the presence of numerous atmospheric mesoscale features that either develop over the EAMS or transit over the EAMS on relatively small temporal scales both during periods prior to summer monsoon onset and during periods following summer monsoon onset.
Conclusions (cont.)CAOCS output clearly demonstrates the presence of numerous oceanic mesoscale features that develop over the EAMS with a relatively small temporal scale both during periods prior to summer monsoon onset and during periods following summer monsoon onset.
Conclusions (cont.)Results clearly show that a climatologically forced atmospheric (oceanic) model will be far less representative of the actual atmosphere (ocean) than a coupled system because air-sea interaction plays such a crucial role at a relatively short temporal scale. The climatologically forced model will be misrepresentative of the low-level atmospheric wind stress and the oceanic surface velocity, SST, and SSS fields.
Conclusions (cont.)Although an atmospheric (oceanic) model that is forced with previously analyzed oceanic (atmospheric) model output is useful for research purposes, the experienced delay during the process is insufficient for METOC support to the Fleet.
Conclusions (cont.)CAOCS has the potential to be an extremely useful tool for USN METOC personnel because of its verification and near-real time capability at the mesoscale level of a littoral region.
CAOCS support the concept behind NRL’s COAMPS future capability.
Recommendations for further researchComparison of winter and summer monsoon using the CAOCS
The inclusion of an acoustic prediction system as part of the CAOCS and comparison with an uncoupled acoustic prediction system
Impact of air-sea interaction at lower depths of the ocean using the CAOCSA detailed study that focuses solely on the comparison of coupled model output versus uncoupled model output