Workshop 1



Panel : In-situ Measurements


Rapporteur: M. Rothstein


S. Anderson:

  • scatter plot comparison of friction velocity from bulk aerodynamic and through direct covariance shows that the technology is here to utilize the direct measurement of friction velocity.

  • emphasized the need for inclusion of the ocean current velocity . . . typical speeds in the range of 25 em/sec . . . failure to include results in 5-10% error in momentum flux.


Discussion:

  • debate over whether estimation of U* accounts for ocean currents.

  • M. Bourassa pointed out that measurement of currents at 5m depth may not represent speeds closer to surface.


F. Bradley:

  • emphasized the interconnection of turbulent, radiative, and fresh water fluxes.

  • COARE bulk algorithm require all as input.

  • fresh water flux affects the stratification of mixed layer, depth, dynamics and surface current (very important if considering diurnal cycle) and contributes directly to sensible heat.

  • highlighted the poor accuracy of in-situ rainfall measurement due to spatial variability and limitations of instrumentation -- ship location reflecting wind distortion etc.


Discussion:

  • there was a question of whether averaging rainfall over several storms improved things.

  • P. Webster reiterated the importance of including fresh water in the upper ocean.

  • general discussion of goals of workshop to concentrate on turbulent fluxes.


C. Fairall:

  • presented a background on measurements from the beginning of system development in 1984, which emphasized inertial-dissipation method, to current development of the 3rd generation system.

  • gave a list of basic instrumentation:

    • sonic anemometer/thermometer

      • IR fast hygrometer

    • aspirated mean T/RH

    • floating near-surface ocean T

    • some cruises include rawinsondes, laser ceilometer, doppler wind profiler.

  • presented a list of cruises with data available . . . acknowledged a "spotty" coverage of locations/conditions.

  • demonstrated that through proper sampling, you can average the data from multiple cruises.

  • noted that each cruise uses its own format for data collection/reporting making the combination of cruises difficult.


Discussion:

  • T. Liu - inquired about efforts to coordinate data

  • Rossow — suggested attempting to coordinating some of the data and using that to demonstrate the difficulty and need for funding.


P. Taylor:

  • any new flux product must be verified over a range of climate conditions.

  • zonal means can be very misleading.

  • good in-situ reference measurements are needed.

  • verification must take the error characteristics of each data set into account.

  • potential surface flux reference data:

    • "flux" buoys which measure all variables needed to estimate the fluxes (IMET) good data, but few sites.

    • "operational" met. buoys (TAO, Triton, NOBC) worse data for longer periods, but often coastal sites.

    • air-sea interaction experiments (TOGA-COARE) good data, very restricted in coverage.

    • quality controlled voluntary observing ship data (VOS) poor data, good coverage in restricted regions, continual availability.

    • Future?

      • buoys that determine fluxes directly.

      • improved VOS subset.

    • advocated the use of all in-situ references — use as much as possible.


Discussion:

  • Rossow - questioned whether ship data should be used.

  • Taylor - if errors are understood, some use can be made of it.


R. Weller:

  • summarized the improvements made in reducing the errors in observed heat fluxes . . . a chart indicated errors in the early 80’s as large as 200 w/m2 for total heat flux and present error values under 10 w/m2.

  • announced that, although buoy coverage was limited, there was a project underway to coordinate data and distribute it over the web.

  • emphasized the need for a partnership to plan where observations are needed.


Discussion:

  • Beljaars - pointed out the difficulty in understanding the space-time variability.

  • M. Bourassa - added that assimilation of buoy data into GCM's don't work well.

  • P. Taylor - stated that perhaps GCM's shouldn't use the buoy data, but rather this data should be used to verify the GCM's.


J. Hare:

  • gave a description of some of the latest instrumentation, including:

    • sonic anemometer with strapdown navigation

    • IR and Oak Ridge hygrometers, CO2 sensor

      • K Gill-system with "spray finger," dry/wet bulb

    • in-situ SST thermistor

    • TSK wave-height recorder

  • noted that there was still great difficulty making in-situ measurements during high wind speed conditions and precipitation

  • discussed the rationale for measuring wave height in helping with this problem.


S. Planton:

  • stressed the importance of using in-situ measurements made at the mesoscale

  • in addition to FASINEX and TOGA-COARE, two recent experiments satisfy these requirements.

    • SEMAPHORE in the Azores region

      • aircraft, buoy and ship data 10/7/93-11/16/93

        • atmospheric analysis (Giordani 1998) and oceanic analyses done on in-situ data


    • CATCH (oceanic component of FASTEX)

      • has allowed re-evaluation at high-wind speeds

      • NW Atlantic (47oN, 40o W) 1/97-2/97

        • allowed analysis during significant ocean front and active atmospheric perturbations

  • datasets coming soon include:

    • FETCH

      • concentrates on conditions of limited fetch

      • West Mediterranean 2/98-3/98

    • EQUALANT

      • aimed at oceanic circulation in tropical Atlantic 7/99-8/99.



Panel Discussion:

  • J. Curry - can we fix the problem of making accurate measurements of flux parameters in high wind speed and/or precipitating conditions.

  • C. Fairall - thinks we can get there via "closed-path" instruments.

  • P. Taylor - thought the French were having some success with microwave instruments?

  • T. Liu - was wondering if any thought was given to just measure the fluxes directly or if we will always be reliant upon bulk algorithms.

  • C. Fairall - felt it was tough to beat the bulk methods at this time, but the future may be different.

  • J. Curry - suggested a need for both types of measurements.

  • C. Clayson - thought the variability would be difficult to measure without in-situ measurement of parameters.

  • M. Bourassa - pointed out that accelerating/decelerating ships will bias wind speed measurements and that some means by which to average the readings was needed to get the true wind speed . . . was wondering if ship maneuvers were recorded/reported.

  • P. Webster - again brought up the issue of inclusion of fresh water flux and debate ensued over the goals of the workshop.