1. Coastal Air-Ocean Coupled System (CAOCS) for the East Asian Marginal Seas (EAMS) by LCDR Mike Roth Thesis Presentation 07SEP01

2. Significance Focus 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 7 th Fleet The objective of METOC’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) developed by NRL

3. 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.

4. 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.

5. 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.

6. 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.

7. The EAMS The EAMS is comprised of: Japan/East Sea (JES) Yellow Sea/East China Sea (YES) South China Sea (SCS)

8. The EAMS YS/ ECS (YES) SCS JES Bohai Sea Japan China Korean Peninsula Russia Taiwan Philippines Borneo Indonesia Malaysia Gulf of Thailand Vietnam Gulf of Tonkin Components of the the EAMS

9. JES Oceanography

10. JES Korean Strait Tsugaru Strait Soya Strait Tatar Strait Honshu Korean Peninsula Vladivostok Hokkaido Kyushu

11. JES Viewed as a miniature prototype ocean: Basin wide circulation pattern Boundary currents A Subpolar Front (SPF) Mesoscale eddy activity Deep water formation

12. JES Currents Tsushima 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

13. JES Currents Japan Nearshore Branch (JNB) Flows northward as the eastern branch of the TsWC along the Japanese west coast

14. JES Currents East 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

15. JES Currents Liman 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

16. JES Currents The 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

17. YES Oceanography

18. YES Ryukyu Islands Taiwan Strait Yangtze R. Yellow R. Han R. Liao R.

19. YES Bathymetry YS 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)

20. YES Bathymetry E/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

21. YES Thermal Structure Monsoon 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

22. YES Thermal Structure Winter (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

23. YES Thermal Structure Summer: Warm southerly winds SAT>SST Strong downward net radiation Leads to downward buoyancy flux MLD shoals Multi-layer structure (MLD, thermocline, and sublayer)

24. YES Currents Kuroshio Current (KUC) Strong WBC Flows northward along the shelf break in the southern ECS

25. YES Currents Taiwan Warm Current (TWC) Enters ECS through the Taiwan Strait Flows northward inshore of the KUC.

26. YES Currents Tsushima 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

27. YES Currents Yellow Sea Warm Current (YSWC) Flows northward beneath the surface into the YS Brings warm water into the YS

28. YES Currents Korean Coastal Current Flows southward along the Korean Peninsula

29. YES Currents Chinese Coastal Current Flows southward around the tip of the Shandong peninsula and along the Chinese coast

30. SCS Oceanography

31. SCS Gulf of Tonkin Luzon Strait Taiwan Strait Balabac Strait Mindoro Strait

32. SCS Bathymetry Straits 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 Luzon Strait Taiwan Strait

33. SCS Bathymetry Extensive 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 Luzon Strait Taiwan Strait

34. SCS Currents Complex 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 Luzon Strait Taiwan Strait

35. SCS Currents Kuroshio Current (KUC) – bifurcation regime Originates from the North Equatorial Current Flows northward as a WBC east of Luzon Enters 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

36. SCS Currents Kuroshio Current (KUC) – bifurcation regime The northward branch flows northward along the western coast of Taiwan E The northwestward branch makes a cyclonic turn around the NWL eddy

37. SCS Currents Kuroshio Current (KUC) – loop regime Originates 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

38. SCS Currents Winter upper ocean circulation A southward coastal jet off the Vietnam coast and a cyclonic circulation throughout the SCS

39. SCS Currents Summer upper ocean circulation A northward coastal jet off the Vietnam coast and an anticyclonic circulation throughout the SCS

40. SCS Currents SCS 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

41. EAMS Atmospheric Forcing – the winter and summer monsoon

42. YES Atmospheric Forcing – Winter Monsoon November 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

43. 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

44. 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

45. Atmospheric Forcing – Summer Monsoon JES YES SCS L L Air 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

46. 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

47. The Atmospheric Component of the CAOCS

48. 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

49. Area for Atmospheric Model

50. Distribution of Vegetation

51. The Oceanic Component of the CAOCS

52. 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

53. Ocean Bottom

54. CAOCS Numerics MM5V3.4 –Resolution Horizontal: 30 km Vertical: 16 Pressure Levels –Time step: 2 min POM – Resolution Horizontal: 1/6 o × 1/6 o Vertical: 23 σ levels –Time Steps: 25 s, 15 min

55. Coupling of the Oceanic and Atmospheric Components of the CAOCS

56. 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)

57. Lateral Boundary Conditions MM5: ECMWF T42 POM: Lateral Transport at 142 o E from the climatological data

58. MM5 Initialization Initialized from: 30 April 1998 (ECMWF T42)

59. 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

60. Reality Check of the Oceanic Output of the CAOCS

61. Liman/NKCC JNB EKWC SPF

62. Reality Check of the Oceanic Output of the CAOCS

63. Reality Check of the Atmospheric Output of the CAOCS

64. JES YES SCS L L H H L 850-mb Winds and GHT For 12Z July 19, 1998 JES YES SCS

65. Reality Check of the Net Radiation Output of the CAOCS

68. Surface Long Wave Radiation Flux did not verify in position nor in magnitude. This discrepancy will be corrected in future work with CAOCS.

70. APPROACH

71. CAOCS 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 as an oceanic event that could be forcing flow at the lower levels of the atmosphere

72. APPROACH A time period after the onset of the summer monsoon that involved: A significant weather event over the EAMS as well as an oceanic event that could be forcing flow at the lower levels of the atmosphere

73. Results Using the JES as an Example

74. Regions of JES

75. Example of Air-Sea Interaction: Low level Atmospheric Wind Stress Driving the Oceanic Surface Currents in the JES

76. 12Z MAY 16 through 12Z MAY 17, 1998

77. Example of Air-Sea Interaction: L H L

78. L

79. L

81. H

82. L

83. 00Z MAY 30 through 12Z MAY 31, 1998

84. L H

85. L H

86. L H

87. L H

89. L

91. 00Z MAY 24 through 12Z MAY 25, 1998

92. L H

93. L H L

94. L

95. L

99. 00Z through 12Z MAY 27, 1998 Coastal Upwelling off the Russian Coast in the Northern JES Due to strong southerlies leading to cyclonic turning and offshore flow of the normally southwestward, along-shore flowing Liman Current

100. L H

101. 15°C isotherm 26 MAY 1998

102. Old 15°C isotherm 15 27 MAY 1998

103. 00Z through 12Z July 24, 1998 Warm Currents enforcing upward vertical motion of a developing cyclone in the YES

113. Weaknesses of CAOCS  CAOCS possesses an erroneous Surface Longwave Radiation Flux  CAOCS has trouble with the open ocean boundary

114. 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.

115. 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.

116. Conclusions (cont.) CAOCS atmospheric and oceanic output is indicative of the impact of ocean thermal structure on the lower level of the atmosphere.

117. 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.

118. 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.

119. 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.

120. 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.

121. 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.

122. Recommendations for further research Comparison 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 CAOCS A detailed study that focuses solely on the comparison of coupled model output versus uncoupled model output