Vol. 82, No. 1, January 2, 2001, p. 2.
Software Simplifies Air-Sea Data Estimates
Rich Pawlowicz, Bob Beardsley, Steve Lentz, Ed Dever, and Ayal Anis
For more information, contact Rich Pawlowicz, University of British Columbia, Vancouver, B.C., Canada; E-mail: rich@ocgy.ubc.ca.
Copyright 2001 American Geophysical Union
The atmosphere and oceans interact at the ocean surface through thin boundary layers. Processes at work here are crucial in controlling the coupling between air and ocean and, as such, are important both in studies of the ocean or atmosphere in isolation, and in studies of the coupled system. However, attempts to generate flux estimates from particular observational data sets often involve a great deal of effort, since the relevant parameterizations are scattered throughout the literature; may have only limited applicability to certain locations and regimes; and are found using algorithms that are often complex and iterative. This can be especially frustrating when boundary layer theory is only peripheral to the main scientific or educational interest.
The AIR_SEA toolbox is a software package of subroutines with a consistent user interface that can be used to estimate parameters important in atmosphere/ocean coupling using the best available theory. The toolbox will be updated from time to time as new and better parameterizations emerge. Other workers are invited to add to this collection to more widely disseminate their results.
The toolbox consists of a collection of MATLAB m-files that are distributed as source code. It is designed in a modular fashion so that different components can be combined as necessary, depending on the specific measurements available and flux parameters desired. MATLAB is available on a wide variety of operating systems and platforms and it is widely used in the oceanographic community. In addition, the vectorized nature of MATLAB lends itself to a more transparent presentation of the underlying algorithms. The toolbox structure is designed to facilitate quality-control checks at intermediate stages in the processing of a particular data set. Literature references are provided in the documentation so the user can evaluate the original work.
Figure 1 illustrates the data flow through the most basic routines. The heart of the toolbox is HFBULKTC.m, which is used to estimate sensible and latent heat fluxes, wind stress, and a number of other parameters such as the Monin-Obukhov length and exchange coefficients, according to similarity theory described in Fairall et al. [1996]. Various input parameters are required and there are different ways of measuring some of these. For example, relative humidity can be determined either through "direct" measurements using an electronic sensor, or "indirectly" from traditional wet/dry thermometer readings. It is also possible to estimate other parameters, such as "cool-skin" effects and the heat fluxes due to rain, with other routines.
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Estimates of long- and short-wave radiative fluxes can be made in many different ways depending on the data at hand. For example, if measurements of downwelling long-wave radiation are made using a pyrgeometer, then LWHF.m can be used to compute the net radiation. If no long-wave measurements are made, then bulk estimates based on measured air and sea surface temperatures, relative humidity, and cloudiness can be made using any of a number of formulas evaluated by Fung et al. [1984] and contained in the routine BLWHF.m.
The toolbox also includes a large number of utility routines that can be used to estimate time of sunrise, air density, saturation humidity, albedo, and drag coefficients according to various workers. Physical parameters and constants such as the acceleration due to gravity, von Karman's constant, and the long-wave emissivity of sea water are specified in a separate routine (AS_CONSTS.m) for maximum flexibility.
The toolbox is available via the World Wide Web at the SEA-MAT site maintained by Rich Signell of the U.S. Geological Survey (http://crusty.er.usgs.gov/sea-mat/).
Acknowledgments
We thank Dick Payne for advice on the radiation fluxes and Jim Edson for advice about TOGA/COARE parameterizations. Steve Anderson, Jay Austin, Roy van Ballegooyen, Chris Fairall, Carl Friehe, Bill Large, Reiner Onken, Dave Rogers, Rich Signell, and Bob Weller also contributed to the development of this toolbox. Agencies supporting this work include the U.S. National Science Foundation, the U.S. Office of Naval Research, the U.S. National Oceanographic and Atmospheric Administration, the U.S. Geological Survey, and the Natural Sciences and Engineering Research Council of Canada.
References
Fairall, C. W., E. F. Bradley, D. P. Rogers, J. B. Edson, and G. S. Young, Bulk parameterization of the air-sea fluxes for Tropical Ocean Global Atmosphere Coupled-Ocean Atmosphere Response Experiment, J. Geophys. Res., 101, 3747-3764, 1996.
Fung, I. Y., D. E. Harrison, and A. A. Lacis, On the variability of the net longwave radiation at the ocean surface, Rev. Geophys., 22, 177-193, 1984.
