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  • Author or Editor: Meric A. Srokosz x
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Roman E. Glazman
and
Meric A. Srokosz

Abstract

For a well-developed sea at equilibrium with a constant wind, the energy-containing range of the wavenumber spectrum for wind-generated gravity waves is approximated by a generalized power law β(U 2/g) k −4+2μ Y(k,θ), where Y is the angular spread function and μ can be interpreted as a fractal codimension of a small surface patch. Dependence of μ on the wave age, ξ=C 0/U, is estimated, and the “Phillips constant,” β, along with the low-wavenumber boundary, k 0, of the inertial subrange are studied analytically based on the wave action and energy conservation principles. The resulting expressions are employed to evaluate various non-Gaussian statistics of a weakly nonlinear sea surface, which determine the sea state bias in satellite altimetry. The locally accelerated decay of the spectral density function in a high-wavenumber dissipation subrange is pointed out as an important factor of wave dynamics and is shown to be also highly important in the geometrical optics treatment of the sea state bias. The analysis is carried out in the approximation of a unidirectional wave field and confined to the case of a well-developed sea characterized by ξ>1.

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Graham D. Quartly
and
Meric A. Srokosz

Abstract

The retroflections of the East Madagascar Current and Agulhas Current are complex rapidly evolving systems, the latter controlling the passage of warm salty water from the Indian Ocean to the Atlantic. The TRMM Microwave Imager (TMI) provides frequent observations of sea surface temperature through clouds, allowing one to monitor the evolution of these systems. The authors develop a simple feature-tracking system that obviates the need for user intervention, and use its results to guide more focused studies. In the period 1997–99, westward progradation of the Agulhas retroflection (associated with ring shedding) is observed about eight times per year, agreeing with previous estimates from infrared data, and many rings move westward or northwestward. However, this behavior is seen to change in the 2000–01 time period, with the Agulhas retroflection occurring farther to the east. A few Natal pulses are seen, but cannot be linked conclusively to the spawning of rings due to TMI's limited latitudinal coverage. The majority of features originating at the East Madagascar retroflection appear to migrate southwestward. A new observation from the data is that, although the first northward meander of the Agulhas Return Current is constrained by bathymetry, its position does vary intermittently, remaining fixed in a given location for up to six months at a time. Southward propagation of features is noted along two ridges: although eddies have been found before along the eastern slope of the Mozambique Ridge, the new results for the Madagascar Ridge indicate an extra pathway for the eddies. Eddylike features are also found leading from the Agulhas Return Current back toward the Agulhas Current. The narrow “corridor” of these features suggests that it is controlled by the gyre recirculation in the southwest Indian Ocean.

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Trevor H. Guymer
,
Graham D. Quartly
, and
Meric A. Srokosz

Abstract

An investigation into a potentially important, but little-studied effect on altimeter data—rain contamination—has been carried out using ERS-1. The method involves identifying large changes in the radar backscatter coefficient and relating these to atmospheric liquid water estimates obtained from an onboard microwave radiometer. The latter is found to provide a useful means of distinguishing between wind and rain events. In general, the backscatter coefficient is reduced most when the liquid water content is high, and by an amount that is consistent with atmospheric attenuation at the radar frequency in use. However, some examples of enhanced backscatter were also observed indicating a possible reduction in surface roughness by the impact of raindrops on the ocean surface. Examination of return pulse shapes across significant rain events reveals behavior consistent with published theoretical work and shows how rain may lead to loss-of-lock in extreme conditions. The results of this study have implications for improved data quality flagging procedures and correction of ERS-1 altimeter winds.

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Robin W. Pascal
,
Margaret J. Yelland
,
Meric A. Srokosz
,
Bengamin I. Moat,
,
Edward M. Waugh
,
Daniel H. Comben
,
Alex G. Cansdale
,
Mark C. Hartman
,
David G. H. Coles
,
Ping Chang Hsueh
, and
Timothy G. Leighton

Abstract

Waves and wave breaking play a significant role in the air–sea exchanges of momentum, sea spray aerosols, and trace gases such as CO2, but few direct measurements of wave breaking have been obtained in the open ocean (far from the coast). This paper describes the development and initial deployments on two research cruises of an autonomous spar buoy that was designed to obtain such open-ocean measurements. The buoy was equipped with capacitance wave wires and accelerometers to measure surface elevation and wave breaking, downward-looking still and video digital cameras to obtain images of the sea surface, and subsurface acoustic and optical sensors to detect bubble clouds from breaking waves. The buoy was free drifting and was designed to collect data autonomously for days at a time before being recovered. Therefore, on the two cruises during which the buoy was deployed, this allowed a variety of sea states to be sampled in mean wind speeds, which ranged from 5 to 18 m s−1.

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Ian M. Brooks
,
Margaret J. Yelland
,
Robert C. Upstill-Goddard
,
Philip D. Nightingale
,
Steve Archer
,
Eric d'Asaro
,
Rachael Beale
,
Cory Beatty
,
Byron Blomquist
,
A. Anthony Bloom
,
Barbara J. Brooks
,
John Cluderay
,
David Coles
,
John Dacey
,
Michael DeGrandpre
,
Jo Dixon
,
William M. Drennan
,
Joseph Gabriele
,
Laura Goldson
,
Nick Hardman-Mountford
,
Martin K. Hill
,
Matt Horn
,
Ping-Chang Hsueh
,
Barry Huebert
,
Gerrit de Leeuw
,
Timothy G. Leighton
,
Malcolm Liddicoat
,
Justin J. N. Lingard
,
Craig McNeil
,
James B. McQuaid
,
Ben I. Moat
,
Gerald Moore
,
Craig Neill
,
Sarah J. Norris
,
Simon O'Doherty
,
Robin W. Pascal
,
John Prytherch
,
Mike Rebozo
,
Erik Sahlee
,
Matt Salter
,
Ute Schuster
,
Ingunn Skjelvan
,
Hans Slagter
,
Michael H. Smith
,
Paul D. Smith
,
Meric Srokosz
,
John A. Stephens
,
Peter K. Taylor
,
Maciej Telszewski
,
Roisin Walsh
,
Brian Ward
,
David K. Woolf
,
Dickon Young
, and
Henk Zemmelink

As part of the U.K. contribution to the international Surface Ocean-Lower Atmosphere Study, a series of three related projects—DOGEE, SEASAW, and HiWASE—undertook experimental studies of the processes controlling the physical exchange of gases and sea spray aerosol at the sea surface. The studies share a common goal: to reduce the high degree of uncertainty in current parameterization schemes. The wide variety of measurements made during the studies, which incorporated tracer and surfactant release experiments, included direct eddy correlation fluxes, detailed wave spectra, wind history, photographic retrievals of whitecap fraction, aerosolsize spectra and composition, surfactant concentration, and bubble populations in the ocean mixed layer. Measurements were made during three cruises in the northeast Atlantic on the RRS Discovery during 2006 and 2007; a fourth campaign has been making continuous measurements on the Norwegian weather ship Polarfront since September 2006. This paper provides an overview of the three projects and some of the highlights of the measurement campaigns.

Full access
Ian M. Brooks
,
Margaret J. Yelland
,
Robert C. Upstill-Goddard
,
Philip D. Nightingale
,
Steve Archer
,
Eric d'Asaro
,
Rachael Beale
,
Cory Beatty
,
Byron Blomquist
,
A. Anthony Bloom
,
Barbara J. Brooks
,
John Cluderay
,
David Coles
,
John Dacey
,
Michael Degrandpre
,
Jo Dixon
,
William M. Drennan
,
Joseph Gabriele
,
Laura Goldson
,
Nick Hardman-Mountford
,
Martin K. Hill
,
Matt Horn
,
Ping-Chang Hsueh
,
Barry Huebert
,
Gerrit De Leeuw
,
Timothy G. Leighton
,
Malcolm Liddicoat
,
Justin J. N. Lingard
,
Craig Mcneil
,
James B. Mcquaid
,
Ben I. Moat
,
Gerald Moore
,
Craig Neill
,
Sarah J. Norris
,
Simon O'Doherty
,
Robin W. Pascal
,
John Prytherch
,
Mike Rebozo
,
Erik Sahlee
,
Matt Salter
,
Ute Schuster
,
Ingunn Skjelvan
,
Hans Slagter
,
Michael H. Smith
,
Paul D. Smith
,
Meric Srokosz
,
John A. Stephens
,
Peter K. Taylor
,
Maciej Telszewski
,
Roisin Walsh
,
Brian Ward
,
David K. Woolf
,
Dickon Young
, and
Henk Zemmelink

Abstract

No Abstract available.

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