Meteorology and Air-Sea Fluxes from Ocean Reference StationsAl Plueddemann and Bob Weller, WHOI, Woods Hole, MA

ORS provide accurate surface meteorology and air-sea fluxes at key sites

The goals are to:

• Quantify air-sea exchanges of heat, freshwater and momentum

• Describe the local oceanic response to atmospheric forcing

• Assess and motivate improvements to NWP and satellite products

• Provide anchor points for the development of new, basin scale flux fields

Geographic Distribution

Three ORS are presently operational:

• STRATUS (initiated Oct 2000)• NTAS (initiated March 2001)• WHOTS (initiated August 2004)

UOP is also operating ASIMET meteorological systems on three VOS lines (see Weller, Bahr and Hosom poster)

Stratus

First long-term, high quality surface flux measurements beneath the Peru/Chile stratus deck

Key issues:

• Cooling influence of stratus clouds on local and global heat balance

• Role of stratus clouds in maintaining the equatorial asymmetry of sea surface temperatures and winds

NTAS

Long-term surface flux record in NE trade wind region of tropical Atlantic

Key issues:

• Air-sea interaction processes controlling local SST variability and the cross-equatorial SST gradient

• Modulation of the annual cycle of ITCZ migration and its role in regional climate dynamics

WHOI-HOT Site (WHOTS)

• Deployment of HOT site ORS accelerated as a result of cooperation between NOAA/OCO and NSF

• First 9 months of meteorological data available on UOP web site, mooring turnaround scheduled for July 2005

• Key addition to a long-standing, interdisciplinary ocean observatory

Partnerships/Collaborations

• WHOTS: Fluxes for HOT; Ocean sensors from R. Lukas, UH (NSF)

• Stratus: Chilean Universities; Chilean and Ecuadorian Naval Hydrographic Offices; DART buoy servicing; Focal point for CLIVAR VOCALS process study

• NTAS: Co-located with GAGE/ MOVE transport array; Dialog with NHC/TPC for data exchange

• ECMWF: Data Exchange

• ORS Concept: Expansion to be proposed to NSF/ORION

• NCEP: Routinely acquire and examine reanalysis products.

• ETL: Field intercomparisons

• Argo: Drifter and float deployments

• Participation in international planning and management activities through: CLIVAR, CCSP, OOCP, GOOS, GWEX, SOLAS, ORION, OceanSITES

• With links to: NRC, WCRP, JCOMM, POGO, SURFA, CPT-Clouds, CPT-EMILIE, …

• Radiometer data: Instruments on NDBC buoys, Chesapeak Light Tower (BSRN); Data to PCMDI; CERES-ARM Validation Exp; Establishment of GEWEX Radiation Panel - Ocean Subgroup

Sensor Calibration

• Pre- and post-calibration at WHOI and by sensor manufacturers

• Field intercomparisons: buoy vs. ship and buoy vs. buoy

• Adjustment of bias and drift prior to flux calculation by bulk formulas

Sensor Accuracy

• First-generation IMET systems evaluated by Hosom et al., 1995

• Second-generation ASIMET presently being evaluated (Colbo, et al.)

The Seasonal Cycle of Surface Heating

NTAS

Stratus

Seasonal Cycle: NTAS

Comparison with NWP products and climatology

Qnet: NWP biased low, 2 yr means are <0 whereas buoy shows +40 W/m2

Timing of zero-crossings differ by 1-2 months

Climatology better than any of the model products

: NWP typically within 0.01 of buoy and clearly better than climatology

Seasonal Cycle: Stratus

Comparison with NWP products and climatology

Heat flux components:

Qsw: NCEP1 biased low, NCEP2 seasonal high-bias

Qlw: NCEP2 biased low

Qlat: Both NCEP1 and 2 show low bias

Qsen: NCEP1 low bias

Qnet: NCEP1 low, NCEP2 high

Annual Mean Heat Flux

Comparison with NWP and reanalysis products

NTAS

Stratus

• ECMWF Qnet disagrees with buoy by ~25 W/m2 in both years

• Interannual variability at buoy not reflected in ECMWF

• ECMWF agrees well with climatology

• NWP products under-estimate buoy Qnet by 40-50 W/m2

• Latent and shortwave fluxes are the primary contributors to discrepancy

• NWP products do not agree well with climatology

Improved Regional Flux Fields

• Evaluation of in-situ data vs. NWP products (Sun, Yu and Weller, 2003)

• Improved fluxes using NWP and satellite data: Synthesis using objective analysis, Validation with in-situ data (North Atlantic: Yu, Weller and Sun, 2004)

• Diagnosis of climate trends in the synthesized fluxes(Yu, Weller, and Jin, in progress)

Heat Budget Estimates

Annual mean heat budget estimated at the Stratus site(Colbo and Weller, in progress)

• Non-local cooling is required to balance the surface fluxes

• Upwelled coastal water has little impact at the mooring site

• Eddy flux divergence is important even though overall eddy KE is relatively low

Synergy with the global observing system

Colbo and Weller heat budget estimate uses a combination of:

• ORS mooring fluxes and heat content

• Satellite SST (Reynolds, TRMM/TMI)

• Satellite winds (QuikSCAT SeaWinds scatterometer)

• Surface drifter trajectories (Pazan and Niiler, MEDS/AOML)

• Climatology (World Ocean Atlas)

• Satellite altimetry (TOPEX/Poseidon)

Recommendations

Improvements to ORS

• Portable shipboard met standard

• High latitude sites

• Direct covariance fluxes and motion packages on buoys

• Near real-time heat content from moorings

Improved regional and global flux fields

• Continued validation, assessment and synthesis studies