Meteorology and Air-Sea Fluxes from Ocean Reference Stations

1
Meteorology and Air-Sea Fluxes from Ocean
Reference Stations Al 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

2
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)
3
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

4
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

5
WHOI-HOT Site (WHOTS)

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

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

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

6
Partnerships/Collaborations

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

• ECMWF Data Exchange

• NCEP Routinely acquire and examine reanalysis
  products.

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

• ETL Field intercomparisons

• Argo Drifter and float deployments

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

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

• ORS Concept Expansion to be proposed to
  NSF/ORION

• 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,

7
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

8
Sensor Accuracy

• First-generation IMET systems evaluated by Hosom
  et al., 1995
• Second-generation ASIMET presently being
  evaluated (Colbo, et al.)

9
The Seasonal Cycle of Surface Heating
Stratus
NTAS
10
Seasonal Cycle NTAS
Comparison with NWP products and climatology
Qnet NWP biased low, 2 yr means are lt0
whereas buoy shows 40 W/m2 Timing of
zero-crossings differ by 1-2 months Climatology
better than any of the model products
t NWP typically within 0.01 of buoy and clearly
better than climatology
11
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
12
Annual Mean Heat Flux
Comparison with NWP and reanalysis products

• 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

Stratus

• 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

NTAS
13
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)

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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

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Synergy with the global observing system
Colbo and Weller heat budget estimate uses a
combination of

• ORS mooring fluxes and heat content

• Satellite winds (QuikSCAT SeaWinds scatterometer)

• Satellite altimetry (TOPEX/Poseidon)

• Satellite SST (Reynolds, TRMM/TMI)

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

• Climatology (World Ocean Atlas)

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Recommendations
Improvements to ORS

• Portable shipboard met standard

• Direct covariance fluxes and motion packages on
  buoys

• Near real-time heat content from moorings

• High latitude sites

Improved regional and global flux fields

• Continued validation, assessment and synthesis
  studies