Shcherbina A.Y.,University of Washington |
Sundermeyer M.A.,University of Massachusetts Dartmouth |
Kunze E.,Seattle |
D'Asaro E.,University of Washington |
And 34 more authors.
Bulletin of the American Meteorological Society | Year: 2015
Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1-10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m2 s-1 as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level. © 2015 American Meteorological Society.
Paka V.,RAS Shirshov Institute of Oceanology |
Zhurbas V.,Tallinn University of Technology |
Rudels B.,Finnish Meteorological Institute |
Quadfasel D.,University of Hamburg |
And 2 more authors.
Ocean Science | Year: 2013
To examine processes controlling the entrainment of ambient water into the Denmark Strait overflow (DSO) plume/gravity current, measurements of turbulent dissipation rate were carried out by a quasi-free-falling (tethered) microstructure profiler (MSP). The MSP was specifically designed to collect data on dissipation-scale turbulence and fine thermohaline stratification in an ocean layer located as deep as 3500 m. The task was to perform microstructure measurements in the DSO plume in the lower 300 m depth interval including the bottom mixed layer and the interfacial layer below the non-turbulent ambient water. The MSP was attached to a Rosette water sampler rack equipped with a SeaBird CTDO and an RD Instruments lowered acoustic Doppler current profiler (LADCP). At a chosen depth, the MSP was remotely released from the rack to perform measurements in a quasi-free-falling mode. Using the measured vertical profiles of dissipation, the entrainment rate as well as the bottom and interfacial stresses in the DSO plume were estimated at a location 200 km downstream of the sill at depths up to 1771 m. Dissipation-derived estimates of entrainment were found to be much smaller than bulk estimates of entrainment calculated from the downstream change of the mean properties in the plume, suggesting the lateral stirring due to mesoscale eddies rather than diapycnal mixing as the main contributor to entrainment. Dissipation-derived bottom stress estimates are argued to be roughly one third the magnitude of those derived from log velocity profiles. In the interfacial layer, the Ozmidov scale calculated from turbulence dissipation rate and buoyancy frequency was found to be linearly proportional to the overturning scale extracted from conventional CTD data (the Thorpe scale), with a proportionality constant of 0.76, and a correlation coefficient of 0.77.
Ward B.,National University of Ireland |
Landwehr S.,National University of Ireland |
Sutherland G.,National University of Ireland |
O'Sullivan N.,National University of Ireland |
And 9 more authors.
European Space Agency, (Special Publication) ESA SP | Year: 2012
The Surface Ocean Lower Atmosphere Study (SOLAS) regards the ocean and atmosphere as coupled system which should be studied in unison. One of the main foci of SOLAS is to achieve an understanding of air-sea exchange of heat, gases momentum aersols, and water. In order to fully understand the processes governing these air-sea fluxes, the small scale processes on both sides of the air-sea interface need to be measured. These measurement techniques also need to be modelled in order to quantify some of the errors associated with the measurements. In this paper, we describe some of the techniques that we have available for studying the SOLAS domain. These include the Air-Sea Interaction Profiler (ASIP); eddy covariance direct air sea fluxes; and computational fluid dynamics (CFD). © 2012 European Space Agency.
Schirber S.,Max Planck Institute for Meteorology |
Manzini E.,Max Planck Institute for Meteorology |
Alexander M.J.,NorthWest Research
Journal of Advances in Modeling Earth Systems | Year: 2014
In order to simulate stratospheric phenomena, such as the Quasi-Biennial Oscillation (QBO), atmospheric general circulation models (GCM) require parameterizations of small-scale gravity waves (GW). In the tropics, the main source of GWs is convection, showing high spatial and temporal variability in occurrence and strength. In this study, we implement in the GCM ECHAM6 a source parameterization for GWs forced by convection. The GW source parameterization is based on the convective heating depth, convective heating rate, and the background wind. First, we show that the heating depth distribution of convective properties strongly influences the waves' source spectra. The strong sensitivity of spectral wave characteristics on heating property distributions highlights the importance of a realistic parameterization of convective processes in a GCM. Second, with the convection-based GW scheme as the unique source of GWs, the GCM simulates a QBO with realistic features. While the vertical extent of the easterly jet shows deficiencies, the wind speeds of the jet maxima and the variance of wind alteration show a clear improvement, compared to the standard model which employs a parameterization with constant, prescribed GW sources. Furthermore, the seasonality of the QBO jets downward progression is modeled more realistically due to the seasonality of physically based gravity wave sources. Key Points Implementation of a convection-based GW source parameterization into a GCM Explore physical aspects of convection-based GW source parameterization Physical GW parameterization improves QBO © 2014. American Geophysical Union. All Rights Reserved.
Miyagawa K.,Japan Meteorological Agency |
Petropavlovskikh I.,University of Colorado at Boulder |
Evans R.D.,National Oceanic and Atmospheric Administration |
Long C.,National Oceanic and Atmospheric Administration |
And 5 more authors.
Atmospheric Chemistry and Physics | Year: 2014
Analyses of stratospheric ozone data determined from Dobson-Umkehr measurements since 1977 at the Syowa (69.0° S, 39.6° E), Antarctica, station show a significant decrease in ozone at altitudes higher than that of the 4 hPa pressure level during the 1980s and 1990s. Ozone values over Syowa have remained low since 2001. The time series of upper stratospheric ozone from the homogenized NOAA SBUV (Solar Backscatter Ultraviolet Instrument)(/2) 8.6 overpass data (±4°, 24 h) are in qualitative agreement with those from the Syowa station data. Ozone recovery during the austral spring over the Syowa station appears to be slower than predicted by the equivalent effective stratospheric chlorine (EESC) curve. The long-term changes in the station's equivalent latitude (indicative of vortex size/position in winter and spring) are derived from MERRA (Modern Era Retrospective-analysis for Research and Applications) reanalyses at ∼ 2 and ∼ 50 hPa. These data are used to attribute some of the upper and middle stratospheric ozone changes to the changes in vortex position relative to the station's location. In addition, high correlation of the Southern Hemisphere annular mode (SAM) with polar upper stratospheric ozone during years of maximum solar activity points toward a strong relationship between the strength of the Brewer-Dobson circulation and the polar stratospheric ozone recovery. In the lower stratosphere, ozone recovery attributable to CFCs (chlorofluorocarbons) is still not definitive, whereas the recovery of the upper stratosphere is slower than predicted. Further research indicates that dynamical and other chemical changes in the atmosphere are delaying detection of recovery over this station. © Author(s) 2014.
Spooner C.M.,NorthWest Research |
Mody A.N.,BAE Systems |
Chuang J.,BAE Systems |
Anthony M.P.,BAE Systems
Proceedings - IEEE Military Communications Conference MILCOM | Year: 2013
We present novel tunnelized second- and higher-order cyclostationary signal processing algorithms to simultaneously detect and characterize RF signals. Techniques that exploit second- and higher-order cyclostationary features to detect and classify signals possess many desirable properties. However, their pervasive use and hardware implementation have been hampered because such features are highly complex, and consume substantial processor energy. In this paper we present a novel concept, where we observe that severe but purposeful under-sampling of the signals through tunneling preserves sufficient exploitable cyclostationarity, even when the tunnel bandwidth is much smaller than the signal bandwidth. This phenomenon is then exploited to create a low complexity and flexible suite of algorithms to simultaneously detect and characterize signals using their tunneling-distorted cyclostationary features. We also demonstrate that such algorithms can detect and characterize signals for a highly adverse signal-to-interference-plus-noise ratio, even when multiple signals completely overlap in time and frequency. © 2013 IEEE.