bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation and circulation of dense water in the Persian/Arabian Gulf
Authors: Swift Stephen A. , Bower Amy S.
Published: May 2003

The nature and circulation of water masses in the Persian/Arabian Gulf (hereinafter referred to as the Gulf) is investigated by examination of a historic database of hydrographic observations. The densest water forms in winter at the northern end of the Gulf rather than along the warmer southern and western coasts. With the exception of small amounts of water directly above the seafloor, most water flowing out of the Gulf mixes across a density front that separates Gulf Deep Water within the Gulf from the Indian Ocean Surface Water (IOSW). Contrary to previous inferences, the seasonally variable incursion of IOSW into the Gulf peaks in late spring. This timing may be due to seasonal changes in sea surface slope driven by variations in evaporation rate. In order to explain mooring results published elsewhere that show relatively small seasonal changes in the volume flux through the Strait of Hormuz (hereinafter referred to as the Strait), we suggest that this flux is driven by the difference between the density of Gulf Deep Water in the interior of the basin and water at comparable depths outside the Gulf. This density difference varies less than 15% during the year. High rates of vertical mixing in the Strait extend about 200 km westward in response to topographic constriction of tidal flows by islands and shoals.
Spatial patterns of wind and sea surface temperature in the Galician upwelling region
Authors: Torres R. , Barton E. D. , Miller P. , Fanjul E.
Published: May 2003

Cape Finisterre is the most northwest point in the Galician region and separates the meridional west and zonal north coasts of Galicia. The wind field there has high spatial and temporal variability throughout the year. No clear seasonal signal is evident; upwelling and nonupwelling patterns alternate in all seasons. Two outstanding features of the Galician region are persistent upwelling near Cape Finisterre even when not present farther south and alternation of strong upwelling on north and west coasts. Up to now, explanations have relied upon particular dynamics of oceanic flow past Finisterre. We find that major features of upwelling around Finisterre are related to strong spatial structure in the wind field. Analysis of QuikScat wind data for July 1999 to May 2001 shows strong repeatable patterns in the synoptic wind field. These wind patterns emerge as the combination of the two dominant modes in a complex empirical orthogonal function (CEOF) analysis representing over 85% of the variance. Summer wind patterns give rise to characteristic distributions of upwelling along the coast and favor development of filaments in particular locations. The wind measured at Finisterre itself, often used as a general indicator of upwelling conditions around the Galician coast, is not always representative of the overall wind field. The relevant wind fields allowed a qualitative explanation of temperature structure seen in sea surface temperature images, and of differences in both the upwelling and downwelling regimes between the two years.
On the dynamics of an observed thermal front off central eastern Australia
Authors: Oke Peter R. , England Matthew H. , Middleton Jason H.
Published: May 2003

Results from a short observational program off central eastern Australia (28.4°S) are presented. A series of events involving sharp temperature fluctuations and strong pulses in the alongshore currents are measured by a mooring array over the inner shelf. With use of AVHRR images, ADCP, and CTD surveys, it is reasoned that these events correspond to the periodic advection of a thermal front past the inshore moorings. The front involves a temperature change of 1°–2°C, with a southward jet of greater than 0.5 m s−1 over a width of 1–2 km in 25 m of water. The dynamical balances of the momentum equations are examined. It is demonstrated that at the onset of each event the local tendency of alongshore velocity is balanced by across‐shore advection. Additionally, a quasi‐balance between the surface and bottom stress terms is noted throughout the experiment demonstrating the prominence of mixing over the inner shelf.
Influence of coastal effects, bottom topography, stratification, wind period, and mixing upon the propagation of internal waves and the profile of wind‐induced currents
Authors: Xing Jiuxing , Davies Alan M.
Published: May 2003

A three‐dimensional model in cross‐sectional form is used to examine the influence of wind period, stratification and bottom topography upon internal wave generation and wind‐induced current profiles in the coastal ocean. Calculations with fixed vertical diffusion coefficients and with a turbulence energy model are performed. These show that besides the wind period influencing the depth of penetration of the wind's momentum, as in a point model, it determines the offshore extent of internal waves generated at the coast. These waves together with elevation gradients modify the directly wind‐driven current profile found in a point model. For forcing at the subinertial frequency the internal wave field is trapped in the coastal region. Offshore the current can be derived from a point model incorporating wind forcing and an elevation gradient related to it. For wind forcing at the superinertial frequency the offshore extent of internal wave propagation increases with frequency. The local topography influences the offshore propagation of internal waves, leading at superinertial frequencies to regions of enhanced surface current magnitude in a similar manner to that found with internal tides. Calculations with the turbulence energy model show increased surface diffusion in these regions, which allows wind energy at both superinertial and subinertial frequencies to penetrate to depth in offshore areas. This process does not involve subinertial internal wave propagation. Conclusions are drawn as to the conditions under which a single point model can reproduce wind induced current profiles at an offshore location.
Interaction of lateral baroclinic forcing and turbulence in an estuary
Authors: Lacy Jessica R. , Stacey Mark T. , Burau Jon R. , Monismith Stephen G.
Published: May 2003

Observations of density and velocity in a channel in northern San Francisco Bay show that the onset of vertical density stratification during flood tides is controlled by the balance between the cross‐channel baroclinic pressure gradient and vertical mixing due to turbulence. Profiles of velocity, salinity, temperature, and suspended sediment concentration were measured in transects across Suisun Cutoff, in northern San Francisco Bay, on two days over the 12.5‐hour tidal cycle. During flood tides an axial density front developed between fresher water flowing from the shallows of Grizzly Bay into the northern side of Suisun Cutoff and saltier water flowing up the channel. North of the front, transverse currents were driven by the lateral salinity gradient, with a top‐to‐bottom velocity difference greater than 30 cm/s. South of the front, the secondary circulation was weak, and along‐channel velocities were greater than to the north. The gradient Richardson number shows that stratification was stable north of the front, while the water column was turbulently mixed south of the front. Time‐series measurements of velocity and salinity demonstrate that the front develops during each tidal cycle. In estuaries, longitudinal dynamics predict less stratification during flood than ebb tides. These data show that stratification can develop during flood tides due to a lateral baroclinic pressure gradient in estuaries with complex bathymetry.
Bayesian hierarchical modeling of air‐sea interaction
Authors: Berliner L. Mark , Milliff Ralph F. , Wikle Christopher K.
Published: May 2003

By means of Bayesian hierarchical modeling (BHM), we develop a model for aspects of vigorous air‐sea interactions on a basin scale. The approach relies on both physical reasoning and statistical techniques for data processing and uncertainty management. The theory and current practice of BHM of air‐sea interaction physics will be introduced and demonstrated in this paper. The demonstration is in the context of an observing system simulation experiment. An ocean “truth” simulation is driven by idealized surface winds in a testbed domain abstracted from the Labrador Sea. Artificial observations analogous to scatterometer and altimeter data are supplied to a BHM and comparisons made with the evolution of the “truth” simulation over a ten day experiment. Substantial attention is devoted to description of computational techniques.
Generation of seiches by cold fronts over the southern North Sea
Authors: de Jong M. P. C. , Holthuijsen L. H. , Battjes J. A.
Published: May 2003

Seiches affecting the Port of Rotterdam are generated in the Southern North Sea. Their generation is investigated with observations and numerical simulations. A wavelet analysis of the observations, both at sea and in the harbor, shows that low‐frequency energy (0.1–2.0 mHz) does indeed occur at sea prior to each seiche event in Rotterdam. An analysis of 6 years of weather charts indicates that all 51 seiche events in this period (with amplitude exceeding 0.25 m) coincided with the passage of a low‐pressure weather system. Some of these low‐pressure systems included a sharp cold front (classical or ana), whereas others included a more diffuse cold front (split or kata). Numerical simulations with a hydrodynamic model driven by meteorological observations reproduced the seiches for situations with the sharp cold fronts correctly. The seiches that were simulated for situations with the gradual cold fronts do not agree with the observations, which is ascribed to the inadequate atmospheric forcing of the hydrodynamical model.
Interaction of salt finger convection with intermittent turbulence
Authors: Wells M. G. , Griffiths R. W.
Published: May 2003

The diapycnal buoyancy fluxes due to the combined presence of salt finger convection and intermittent turbulent events are discussed. In a series of experiments, salt fingers, which were periodically stirred by a comb of vertical rods, were created in a continuous density gradient using the laboratory sugar/salt analog. Measurements of the buoyancy flux were made by measuring the rate of change of the density gradient. Particular attention was paid to how the time‐averaged buoyancy flux varied as the frequency of stirring was increased relative to the characteristic timescale for growth of the salt fingers. We found that the mean buoyancy flux was up gradient when the time between stirring events was longer than several e‐folding periods of the salt finger growth rate. When stirring was more frequent, the salt fingers were continuously disrupted, resulting in a mean down‐gradient buoyancy flux, characteristic of stratified turbulence. Using data for salt finger convection and intermittent turbulence in the oceanic thermocline and extrapolation of the laboratory results, we examine the sensitivity of salt finger buoyancy fluxes to intermittent turbulence in the oceans.
How realistic is the high‐frequency signal of a 0.1° resolution ocean model?
Authors: Tokmakian Robin , McClean Julie L.
Published: May 2003

This paper describes the results from a comparative wavelet analysis of a 0.1, 40‐level Parallel Ocean Program model simulation of the North Atlantic with coincident in situ measurements of sea surface height (SSH) and temperature. The wavelet analysis is used to examine the realism of the surface's variability and its high‐frequency signals (less than a year). Along the coast, it shows that the model's simulated fields of SSH are realistic with the correlations to tide gauge measurements on the order of 0.8. The wavelet spectra show that the model replicates the observations' frequency space. Comparisons of the model's temperatures to temperatures from NOAA buoys north and south of the Gulf Stream show that, while not replicating the location of mesoscale features all the time, the model's energy in the strong mesoscale regions compares favorably to data. Due to the TOPEX/POSEIDON's (T/P) sampling, which requires large areal averages and because of the model's spontaneous eddy field, the evaluation of the simulation in the open ocean is less conclusive. The model does show similarities to the T/P data at high latitudes where the sampling by the sensor is denser and also on the eastern side of the basin with its lower mesoscale activity. Spatially, there are similarities in the amplitude of the signals between the model and the observations in areas with a significant signal in a given spectral band.
Three‐dimensional seasonal‐mean circulation and hydrography on the eastern Scotian Shelf
Authors: Han Guoqi , Loder John W.
Published: May 2003

A three‐dimensional nonlinear finite element model with an advanced turbulence scheme is used in conjunction with historical current, temperature, and salinity observations to describe seasonal‐mean circulation and hydrography on the eastern Scotian Shelf (ESS). The model solutions consist of density‐, wind‐, and boundary‐driven currents, and associated elevation, hydrographic, and turbulence fields. The M2 and K1 tides are simultaneously computed to include the effects of tidally induced turbulent mixing and bottom friction, and tidal rectification. The circulation is dominated by surface‐intensified baroclinic nearshore and shelf‐break currents, both directed southwestward with prominent seasonal and alongshelf changes. These currents are primarily associated with the equatorward inflow of relatively fresh water from the Gulf of St. Lawrence and Newfoundland Shelf/Slope. Pronounced and persistent influences of outer‐shelf banks, inner‐shelf basins, and cross‐shelf channels are evident in the circulation fields. In particular, the Sable Gully features a year‐round cyclonic partial gyre, with a net onshore flow that is greatest in spring. A relatively strong anticyclonic gyre over Sable/Western Bank contrasts a weak partial gyre over Banquereau Bank. The model solutions are in approximate agreement with observed transports and currents for the primary flow features.
On dynamics and mixing of inflowing saltwater in the Arkona Sea
Authors: Lass H. U. , Mohrholz V.
Published: May 2003

Time series measurements of temperature, salinity and current at the sills and the rim of the Arkona Basin have been performed during the winter seasons 1998/1999 and 1999/2000 together with ship‐based measurements of stratification and currents covering the whole Arkona Basin. The well‐mixed brackish surface was separated from the stratified saline bottom water by a halocline at a mean depth of 30 m. The saline bottom water was contained in an up to 15 m thick pool filling the central part of the Arkona Basin. This stratification resulted in a 6 km wide Rossby radius and a phase velocity of 0.7 m/s for the first baroclinic mode. The mean stratification was disturbed by cyclonic geostrophic eddies with a characteristic radius equal to the first baroclinic Rossby radius and up‐ and downwelling processes in the coastal boundary layer. 90% of the variability of the vertical current profile can be described by the first and second EOF. The most pronounced feature of the current profile is the existence of an Ekman bottom friction layer found in both modes. The thickness of the Ekman layer of the barotropic mode is 10–15 m and that of the baroclinic mode is about 5m. The baroclinic circulation consists of a pulsating cyclonic motion in the bottom layer and an anticyclonic motion in the upper layer along the rim of the Arkona Basin, driven by the spilling of saline bottom water over the sills into the Arkona Basin. The saline bottom water is flowing as gravity current from the sills into the Arkona Basin which is in a first order balanced by gravity and the Coriolis force, whereas friction is smaller than the other two forces involved. The friction imposes a spiral motion into the center of the Arkona Basin where it contributes to the dense bottom water pool. The front of the dense bottom water moves with a phase speed of about 30 cm/s at the westerly rim and slows down to about 10 cm/s along the southerly and easterly rim of the Arkona Basin. Evidence was found that the dense bottom water plume mixes with the ambient water by wind induced entrainment in the vicinity of the sill. The main mixing mechanism of a propagating saltwater plume is mixing of the water ahead of its front with the bottom water behind the front by differential advection.
Effects of surface freshwater flux induced by sea ice transport on the global thermohaline circulation
Authors: Komuro Y. , Hasumi H.
Published: May 2003

Effects of surface freshwater flux induced by sea ice formation and melting on the thermohaline circulation are investigated by using a sea‐ice‐ocean coupled general circulation model forced by monthly climatology. Restoring to the observed sea surface salinity is not employed in order to evaluate precisely the sea ice effects. Because of the model's improper representation of interaction between sea ice and the Northern Hemisphere deep convection, the discussion is focused on the effect of sea ice in the Southern Hemisphere. In the control case, deep water formation around Antarctica occurs under compact sea ice cover, where positive annual mean sea ice production is an essential factor to induce deep convection. When sea ice motion is turned off, deep water formation is maintained primarily by thermal destabilization of water columns, as annual mean sea ice production is almost zero everywhere. Consequently, the deep ocean around Antarctica is warmer and less saline compared with that for the control case, and the Atlantic bottom circulation is weakened by 16%. Northward salt transport from the Southern Ocean in the bottom layer also decreases. The amount of the decrease is greater by 1 order of magnitude than that of the surface salt input associated with sea ice. In a case where the freshwater flux at the ice‐ocean interface is turned off, results are similar to the case without sea ice transport, although surface heat and momentum fluxes significantly differ between them. This suggests that the influence of sea ice on freshwater flux is more important than on heat and momentum fluxes in affecting the global thermohaline circulation.
Coupling between two inlets: Observation and modeling
Authors: Liu P. L.‐F. , Monserrat S. , Marcos M. , Rabinovich A. B.
Published: May 2003

The resonance coupling between two adjacent inlets is investigated. Field evidence of this natural phenomenon is found for two elongated inlets in the region of Ciutadella, Menorca Island, in the Western Mediterranean (Ciutadella and Platja Gran). To illustrate the fundamental features of the problem, analytical solutions for two rectangular inlets with constant depth are constructed and analyzed. The theoretical results mimic well the field data and demonstrate the resonance coupling characteristics of the inlet responses. The phenomenon is also examined with a numeric model so that the effects of real bathymetry can be considered. Numerical computations show the specific resonant features of local topography and the agreement between field data and numerical results is very good.
Comparison of optical and radar measurements of surf and swash zone velocity fields
Authors: Puleo Jack A. , Farquharson Gordon , Frasier Stephen J. , Holland K. Todd
Published: May 2003

Surf zone bore celerities and swash zone surface currents were measured on a shallow sloping, low‐energy beach using two remote sensing methods that differ fundamentally in their imaging mechanisms. Microwave Doppler radar measures electromagnetic backscatter from small‐scale ocean surface roughness while video‐based particle image velocimetry (PIV) relies on image texture resulting from variations in light reflectivity from the ocean surface. Imagery from the two methods showed high correlation, in which regions of high radar backscatter corresponded to visibly identifiable waves and bores propagating across the surf zone. Correlation coefficients between radial velocity time series sampled using the two methods at multiple locations across the surf zone were typically greater than 0.5 for frequencies less than a noise cutoff of 0.25 Hz. Similarly, spectra were found to be coherent at the 95% level with a nearly zero phase shift between the two signals near the broad spectral peak between 0.02 and 0.25 Hz. However, some significant differences were evident. PIV was capable of estimating both cross‐shore and alongshore surface velocities while the use of one microwave Doppler radar system restricted surface velocity estimates from that technique to line of sight (radial) only. PIV was found to be more capable of estimating swash zone (uprush and backwash) surface velocities as a smoother water surface in the swash zone adversely affected radar reflectivity. In contrast, microwave Doppler radar was found to be more capable of estimating the surface velocity between bores when insufficient image texture was recorded in the video imagery. Both techniques were capable of measuring surf zone bore celerities through comparison to a shallow water model and to independent celerity estimates extracted from the slope of individual bore trajectories. Typical normalized errors were roughly 25% for radar and 15% for PIV.
On the spring‐neap variability and age of the internal tide at the Hawaiian Ridge
Authors: Holloway Peter E. , Merrifield Mark A.
Published: May 2003

Observations and modeling have shown that an energetic M2 internal tide is generated by tidal flow over the Hawaiian Ridge. This paper presents numerical results that explore the variability of the internal tide over the spring‐neap cycle resulting from the combination of M2 and S2 constituents. The spring‐neap cycle is simulated from a superposition of separate model runs for M2 and S2, and from longer model runs with combined M2 and S2 forcing. There are only small differences between the two methods, indicating that at tidal frequencies and the 4‐km model resolution, the system is approximately linear. Energy fluxes at spring tides are substantially stronger than the sum of M2 and S2 fluxes, suggesting strong contrast from spring to neap tides in energy available for mixing. The baroclinic currents vary in amplitude over the spring‐neap cycle by approximately 50%, but tidal beams maintain their overall structure. The time of maximum spring amplitudes relative to the astronomical forcing is examined in terms of the age of the tide. Near the ridge where the internal tide is generated, the age is the same as that of the barotropic tidal currents, which is approximately 1 day older than the barotropic surface elevation. The age of the internal tide is approximately 1 day along the ridge and increases moving away from the ridge, consistent with the group velocity of the internal waves. Hence, away from the ridge, spring internal tides may occur 2 or 3 days after spring tidal elevations at the ridge.
A delayed action oscillator shared by biennial, interannual, and decadal signals in the Pacific Basin
Authors: White Warren B. , Tourre Yves M. , Barlow Mathew , Dettinger Mike
Published: May 2003

Biennial, interannual, and decadal signals in the Pacific basin are observed to share patterns and evolution in covarying sea surface temperature (SST), 18°C isotherm depth (Z18), zonal surface wind (ZSW), and wind stress curl (WSC) anomalies from 1955 to 1999. Each signal has warm SST anomalies propagating slowly eastward along the equator, generating westerly ZSW anomalies in their wake. These westerly ZSW anomalies produce cyclonic WSC anomalies off the equator which pump baroclinic Rossby waves in the western/central tropical North Pacific Ocean. These Rossby waves propagate westward, taking ∼6, ∼12, and ∼36 months to reach the western boundary near ∼7°N, ∼12°N, and ∼18°N on biennial, interannual, and decadal period scales, respectively. There, they reflect as equatorial coupled waves, propagating slowly eastward in covarying SST, Z18, and ZSW anomalies, taking ∼6, ∼12, and ∼24 months to reach the central/eastern equatorial ocean. These equatorial coupled waves produce a delayed‐negative feedback to the warm SST anomalies there. The decrease in Rossby wave phase speed with latitude, the increase in meridional scale of equatorial SST anomalies with period scale, and the associated increase in latitude of Rossby wave forcing are consistent with the delayed action oscillator (DAO) model used to explain El Niño. However, this is not true of the western‐boundary reflection of Rossby waves into slow equatorial coupled waves. This requires modification of the extant DAO model. We construct a modified DAO model, demonstrating how the various mechanisms and the size and sources of their delays yield the resulting frequency of each signal.
Validation of ocean wind and wave data using triple collocation
Authors: Caires S. , Sterl A.
Published: May 2003

Significant wave height and wind speed fields from ERA‐40 are validated against buoy, ERS‐1, and Topex altimeter measurements. To do so, we propose and apply a triple collocation statistical model. The model takes into account the random errors in observations and model results and allows the estimation of the variances of the errors. We first examine the case where the random errors of the different systems are independent, but situations where independence is not strictly observed are also considered. The results show that the ERA‐40 predictions underestimate high values of significant wave height and, contrary to what would be obtained by less sophisticated statistical methods, wind speed, that the variance of the errors associated with the ERA‐40 system is much higher than that of the errors of the measurements, and that the former shows a dependence on the value of the observations not present in the latter. The altimeter measurements of significant wave height are very precise, in contrast to the large uncertainty associated with the altimeter retrieved wind speeds.
A note on the deficiency of NCEP/NCAR reanalysis surface winds over the equatorial Indian Ocean
Authors: Goswami B. N. , Sengupta D.
Published: May 2003

The seasonal cycle and intraseasonal variability of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP) reanalysis surface winds over the Indian Ocean (IO) are assessed by comparing them with in situ surface observations from two moored buoys and winds from the SeaWinds scatterometer on the QuikSCAT satellite. The buoys are located in the central Bay of Bengal and eastern Arabian Sea. Both QuikSCAT and NCEP wind products reproduce closely the seasonal cycle and intraseasonal variability (10–60 day) in the in situ observations. In the equatorial IO, however, the seasonal mean NCEP wind speeds can be 2–3 m s −1 smaller and the amplitude of intraseasonal variability only about half that of QuikSCAT winds. The systematic errors of NCEP zonal winds are comparable to the annual mean or amplitude of the seasonal cycle in the equatorial IO. It is suggested that the systematic error of mean and intraseasonal variability of reanalysis winds is related to systematic error in the NCEP analysis of precipitation.
Case analysis of a role of ENSO in regulating the generation of westerly wind bursts in the Western Equatorial Pacific
Authors: Yu Lisan , Weller Robert A. , Liu W. Timothy
Published: May 2003

This study speculates that the low‐frequency ENSO might have a regulating effect on the activity of episodic westerly wind bursts (WWB) in the western equatorial Pacific (WEP) based upon the analysis of two contrasting El Niño‐Southern Oscillation (ENSO) phases during the 1996–2000 period and the onset of the 1982 El Niño. It suggests that ∇PWEP, the equatorial sea level pressure (SLP) gradient between 130°E and 160°E, could be a key parameter in relating ENSO to the WWB generation. ∇PWEP is a preconditioning index for the tropical cyclone formation associated with midlatitude atmospheric transient forcing (cold surges). The cyclonic circulation near the equatorial latitudes contributes to prolonged WWB events. ∇PWEP can be regulated by ENSO because the location of the low SLP center, which determines the strength of the ∇PWEP, correlates with the location of the warm water pool, and has an east‐west migration in response to the ENSO phases. Through ∇PWEP, the variability of WWB was linked to the ENSO phases. The study finds that ∇PWEP was promoted prior to the 1997 El Niño when the warm pool was large and extended to near the dateline, whereas it was suppressed during the follow on La Niña in 1999/2000 when the warm pool was small and displaced far westward. However, only westerly winds generated in the east of New Guinea could have potential importance to ENSO as the islands over the Indonesian Seas represent a significant blocking to the propagation of a Kelvin wave. It appears that the active WWB in the winter of 1996 were generated on a favorable background conditioned by pre‐El Niño state; they facilitated the development of the 1997 El Niño but may not be a sufficient onset mechanism. Further statistical analysis is required to test the veracity of the hypothesis derived from the case analysis of this study.
Chlorophyll dispersal by eddy‐eddy interactions in the Gulf of Mexico
Authors: Toner M. , Kirwan A. D. , Poje A. C. , Kantha L. H. , Müller‐Karger F. E. , Jones C. K. R. T.
Published: May 2003

A Lagrangian analysis of the transport and dispersal of plumes observed in satellite‐derived ocean color images was conducted using a data‐assimilating model of the Gulf of Mexico. The interaction between pervasive cyclonic and anticyclonic eddies in the Gulf generated advective paths that connect remote shelf regions. These paths aligned remarkably well with the plume events recorded with the chlorophyll‐a ocean color product from SeaWiFS. Two such events were studied. In one event material was transported in a thin strip between the northern wall of the Loop Current and an adjacent cyclone, connecting the eastern Campheche shelf (off the Yucatan Peninsula) and South Florida shelves. The other event began off the Louisiana shelf break as a small plume traced by chlorophyll and then developed into a long and thin feature which meandered to the shelf break off the northern Yucatan Peninsula, moving between a large anticyclone and several adjacent cyclones. These results indicate that inter‐eddy advection plays a crucial role in developing the ocean color patterns observed in the satellite ocean color data.
A global study of diurnal warming using satellite‐derived sea surface temperature
Authors: Stuart‐Menteth Alice C. , Robinson Ian S. , Challenor Peter G.
Published: May 2003

Ten years of global infrared satellite data from National Oceanic and Atmospheric Administration's advanced very high resolution radiometer are analyzed to investigate global variations of diurnal warming. Daily nighttime sea surface temperatures (SSTs) are subtracted from adjacent daytime SSTs to give an estimate of diurnal warming (ΔTday‐night). The results reveal large regions in the tropics and midlatitudes that are frequently susceptible to diurnal warming each year. A strong seasonal pattern exists, dictated by the wind and solar insolation variability. A simple ΔT regression model confirms that the observed warming is consistent with the right meteorological conditions of low winds and high insolation. The analysis also reveals how the spatial distribution and magnitude of ΔT varies with the drift of the satellite orbit as it shifts from a local overpass time of 1400 to 1600. The results highlight the importance of the diurnal cycle for SST measurements and suggest the need for the diurnal cycle to be included in numerical models.
Spatial structure of subsurface temperature variability in the California Current, 1950–1993
Authors: Mendelssohn Roy , Schwing Franklin B. , Bograd Steven J.
Published: May 2003

State‐space models are used to examine long‐term spatial patterns in a set of temperature time series representing the meridional and offshore extent of the California Current System (CCS). We use global one‐degree summaries from the World Ocean Database at 11 locations and 10 standard depths in the upper 200 m for the period 1950–1993. Four common trends account for most of the total variance and the important time‐dependent features of the temperature series. These trends also reveal that different geographical regions and depth strata within the CCS have clearly distinct temporal patterns of interannual to decadal thermal variability: the first common trend reveals a series‐long warming tendency at all locations, with the greatest changes occurring in the upper 50 m (75 m) for the coastal (offshore) stations; the second common trend delineates a cross‐shore separation, with the coastal locations having greater variance and a stronger impact from most El Niño events and decadal‐scale warming and cooling tendencies; the third common trend, with signals strongest in the thermocline, provides a measure of the northern extent of influence of El Niño events and reveals greater interannual variance south of 38°N; the fourth common trend separates the series by depth, revealing significant long‐term trends in thermal stratification. These spatially‐variant thermal fluctuations identify three characteristic patterns of El Niño influence in the CCS, reflecting both the meridional extent and depth structure of their signals. La Niña signals are less spatially variable in the CCS. We also describe the spatially heterogeneous anomaly structure associated with large‐scale decadal climate shifts, such as occurred around 1976. It is shown that this event was a coastal‐ and surface‐intensified acceleration of a warming trend that had begun several years earlier. We briefly discuss the biological consequences of the spatially and temporally varying thermal structure of the CCS revealed by this analysis.
Observing ocean heat content using satellite gravity and altimetry
Authors: Jayne Steven R. , Wahr John M. , Bryan Frank O.
Published: May 2003

A method for combining satellite altimetry observations with satellite measurements of the Earth's time‐varying gravity to give improved estimates of the ocean's heat storage is presented. Over the ocean the time‐variable component of the geoid can be related to the time‐varying bottom pressure. The methodology of estimating the ocean's time‐varying heat storage using altimetric observations alone is modified to include observations of bottom pressure. A detailed error analysis of the methodology is undertaken. It is found that the inclusion of bottom pressure improves the ocean heat storage estimates. The improvement comes from a better estimation of the steric sea surface height by the inclusion of bottom pressure in the calculation, over using the altimeter‐observed sea surface height alone. On timescales of the annual cycle and shorter the method works particularly well. However, long‐timescale changes in the heat storage are poorly reproduced because of deficiencies in the methodology and the presence of contaminating signals in the bottom pressure observations.
Numerical simulation of orographic rainbands
Authors: Anquetin Sandrine , Minsicloux Fabien , Creutin Jean‐Dominique , Cosma Stéphanie
Published: May 2003

This study, based on a statistical analysis of simulated warm rain event and radar data, aims at highlighting the main physical mechanisms that lead to organize shallow convection on the relief. The region of investigation, the Cévennes‐Vivarais, is located in the southeast part of France. Radar images from the Cévennes experiment (fall 1986–1988) reveal a characteristic and repetitive structure of the rain distribution organized in narrow bands or plumes, oriented south‐north in the case of stationary southerly Mediterranean flow. The event of 14 November 1986 has been selected and constitutes the data set of this numerical study. This work is closely associated with the previous work by Miniscloux et al. [2001] which presents in detail the results of a geostatistical analysis of the radar data set extracted from the Cévennes experiment data base. The main results highlight the physical characteristics and the dynamics of the rain patterns. Following the recent work of Cosma et al. [2002], high‐resolution (Δ = 1 km) simulations have been continued with the nonhydrostatic three‐dimensional (3D) atmospheric model MesoNH, in order to reproduce the observed rainbands over the Cévennes region. The numerical model correctly reproduces the structure and the dynamics of the rainbands. The geostatistical analysis has been applied for the simulated rain fields. The model slightly overestimates the northward advection velocity of the rain cells within the bands (75 km h−1 against 60 km h−1 for the observation), and the simulated rainbands are narrower and more organized around the N180° direction than the observed rain field. The comparison allows the qualification and validation of the choice of the numerical methodology and realism of the physical parameterizations. The analysis of the 3D simulated fields confirms the physical mechanisms responsible for the rain organization demonstrated by Cosma et al. [2002] through idealized simulations. The statistical analysis highlights the presence of mean topographic features under low‐level convergence zones composed of a succession of ridges and penetrating valleys orientated east‐west. The rainbands are generated upstream of these topographic features and enhanced on the leeside due to the convergence created by the flow deflection around the obstacle and its penetration into the valleys. The simulated triggering takes place further to the south than the observed one, and the triggering is active as soon as the relief is suitably described in the model.
An operational remote sensing algorithm of land surface evaporation
Authors: Nishida Kenlo , Nemani Ramakrishna R. , Running Steven W. , Glassy Joseph M.
Published: May 2003

Partitioning of solar energy at the Earth surface has significant implications in climate dynamics, hydrology, and ecology. Consequently, spatial mapping of energy partitioning from satellite remote sensing data has been an active research area for over two decades. We developed an algorithm for estimating evaporation fraction (EF), expressed as a ratio of actual evapotranspiration (ET) to the available energy (sum of ET and sensible heat flux), from satellite data. The algorithm is a simple two‐source model of ET. We characterize a landscape as a mixture of bare soil and vegetation and thus we estimate EF as a mixture of EF of bare soil and EF of vegetation. In the estimation of EF of vegetation, we use the complementary relationship of the actual and the potential ET for the formulation of EF. In that, we use the canopy conductance model for describing vegetation physiology. On the other hand, we use “VI‐Ts” (vegetation index‐surface temperature) diagram for estimation of EF of bare soil. As operational production of EF globally is our goal, the algorithm is primarily driven by remote sensing data but flexible enough to ingest ancillary data when available. We validated EF from this prototype algorithm using NOAA/AVHRR data with actual observations of EF at AmeriFlux stations (standard error ≅ 0.17 and R2 ≅ 0.71). Global distribution of EF every 8 days will be operationally produced by this algorithm using the data of MODIS on EOS‐PM (Aqua) satellite.
Hemispheric differences in the temperature of the summertime stratosphere and mesosphere
Authors: Siskind David E. , Eckermann Stephen D. , McCormack John P. , Alexander M. Joan , Bacmeister Julio T.
Published: May 2003

We study two processes which may govern interhemispheric differences in the temperature of the summertime middle atmosphere. The first is the direct radiative effect arising from the eccentricity of Earth's orbit. The second factor is the difference in gravity‐wave filtering due to the hemispheric asymmetries in the summertime mean winds of the troposphere and lower stratosphere. Using two different gravity‐wave drag parameterizations and a zonal wind climatology, we find greater gravity wave induced acceleration of the zonal flow in the southern summer lower stratosphere, which leads to weaker gravity wave drag in the southern upper mesosphere. Using a two‐dimensional chemical‐dynamical model, we evaluate the temperature changes caused by these drag differences and compare them with those caused by direct radiative asymmetry. The radiative asymmetry peaks in the upper stratosphere but is nonnegligible between 20 and 80 km. The dynamical asymmetry has a primary contribution in the upper mesosphere and a secondary contribution in the lower stratosphere. Overall, our results support the idea that poleward of 30° the southern middle atmosphere is warmer than the north by 3–8K between 20 and 85 km. As a result, our model suggests that the relative humidity of the northern summer mesopause region is greater than in the south. This implies that mesospheric clouds (PMCs and NLCs) should be more frequent and more extensive in the north than in the south.
Trace gas and particle emissions from fires in large diameter and belowground biomass fuels
Authors: Bertschi Isaac , Yokelson Robert J. , Ward Darold E. , Babbitt Ron E. , Susott Ronald A. , Goode Jon G. , Hao Wei Min
Published: May 2003

We adopt a working definition of residual smoldering combustion (RSC) as biomass combustion that produces emissions that are not lofted by strong fire‐induced convection. RSC emissions can be produced for up to several weeks after the passage of a flame front and they are mostly unaffected by flames. Fuels prone to RSC include downed logs, duff, and organic soils. Limited observations in the tropics and the boreal forest suggest that RSC is a globally significant source of emissions to the troposphere. This source was previously uncharacterized. We measured the first emission factors (EF) for RSC in a series of laboratory fires and in a wooded savanna in Zambia, Africa. We report EFRSC for both particles with diameter <2.5 μm (PM2.5) and the major trace gases as measured by open‐path Fourier transform infrared (OP‐FTIR) spectroscopy. The major trace gases include carbon dioxide, carbon monoxide, methane, ethane, ethene, acetylene, propene, formaldehyde, methanol, acetic acid, formic acid, glycolaldehyde, phenol, furan, ammonia, and hydrogen cyanide. We show that a model used to predict trace gas EF for fires in a wide variety of aboveground fine fuels fails to predict EF for RSC. For many compounds, our EF for RSC‐prone fuels from the boreal forest and wooded savanna are very different from the EF for the same compounds measured in fire convection columns above these ecosystems. We couple our newly measured EFRSC with estimates of fuel consumption by RSC to refine emission estimates for fires in the boreal forest and wooded savanna. We find some large changes in estimates of biomass fire emissions with the inclusion of RSC. For instance, the wooded savanna methane EF increases by a factor of 2.5 even when RSC accounts for only 10% of fuel consumption. This shows that many more measurements of fuel consumption and EF for RSC are needed to improve estimates of biomass burning emissions.
Vertical distribution of gaseous elemental mercury in Canada
Authors: Banic C. M. , Beauchamp S. T. , Tordon R. J. , Schroeder W. H. , Steffen A. , Anlauf K. A. , Wong H. K. T.
Published: May 2003

Measurements of gaseous elemental mercury (GEM) were made in three locations in Canada at altitudes from 0.1 to 7 km. In the summer in southeastern Canada, northwesterly winds bring air with a constant mixing ratio of GEM at altitudes up to 7 km, with a concentration near 1.5 nanograms per standard cubic meter of air (ng sm−3). In the winter in southern and central Ontario the mixing ratio is still approximately constant with altitude, but the concentration is 1.7 ng sm−3. In the spring in the Arctic the concentration of gaseous elemental mercury at altitudes above 1 km is near 1.7 ng sm−3; however, there is evidence of episodic depletion of elemental mercury near the surface with mixing of depleted air to altitudes of 1 km. Measurements of GEM in cloud interstitial air and of mercury in cloud water indicate that the influence of a single cycling of air through cloud has little effect on the concentration of GEM. The GEM in air masses transported over the relatively unpopulated terrain of northern Canada during the summer indicates a lower limit of 5000 ng m−2 for an atmospheric column from the surface to 5 km. This gives a global burden of at least 2500 t for that altitude range. These data demonstrate the existence of a vast pool of mercury aloft, provide evidence for a long atmospheric lifetime, and illustrate the potential for long‐range atmospheric transport of this metal at altitudes up to at least 7 km.
In situ HNO3 to NOy instrument comparison during SOLVE
Authors: Ballenthin J. O. , Thorn W. F. , Miller T. M. , Viggiano A. A. , Hunton D. E. , Koike M. , Kondo Y. , Takegawa N. , Irie H. , Ikeda H.
Published: May 2003

Measurements of HNO3 mixing ratios from the chemical ionization mass spectrometer have been critically compared with simultaneous measurements of total gas phase NOy from the NO chemiluminescence detector aboard the NASA DC‐8 aircraft during the SAGE 3 Ozone Loss and Validation Experiment (SOLVE). The data were obtained in the arctic upper troposphere and lower stratosphere in the winter of 1999–2000. A brief comparison to the NOy instrument aboard the NASA ER‐2 is also presented. The time responses, detection limits, relative precision, and stability of relative calibrations for the instruments were in excellent agreement throughout the mission. However, the average slope of the HNO3 to NOy correlation was 1.13 ± 0.03 overall and 1.06 ± 0.03 in stratospheric air, indicating that the two measurements had a systematic calibration offset. Possible sources for the offset error are presented, and methods to reduce the calibration error in future flights are suggested.
Trace gas emissions from the production and use of domestic biofuels in Zambia measured by open‐path Fourier transform infrared spectroscopy
Authors: Bertschi Isaac T. , Yokelson Robert J. , Ward Darold E. , Christian Ted J. , Hao Wei Min
Published: May 2003

Domestic biomass fuels (biofuels) were recently estimated to be the second largest source of carbon emissions from global biomass burning. Wood and charcoal provide approximately 90% and 10% of domestic energy in tropical Africa. In September 2000, we used open‐path Fourier transform infrared (OP‐FTIR) spectroscopy to quantify 18 of the most abundant trace gases emitted by wood and charcoal cooking fires and an earthen charcoal‐making kiln in Zambia. These are the first in situ measurements of an extensive suite of trace gases emitted by tropical biofuel burning. We report emission ratios (ER) and emission factors (EF) for (in order of abundance) carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), acetic acid (CH3COOH), methanol (CH3OH), formaldehyde (HCHO), ethene (C2H4), ammonia (NH3), acetylene (C2H2), nitric oxide (NO), ethane (C2H6), phenol (C6H5OH), propene (C3H6), formic acid (HCOOH), nitrogen dioxide (NO2), hydroxyacetaldehyde (HOCH2CHO), and furan (C4H4O). Compared to previous work, our emissions of organic acids and NH3are 3–6.5 times larger. Another significant finding is that reactive oxygenated organic compounds account for 70–80% of the total nonmethane organic compounds (NMOC). For most compounds, the combined emissions from charcoal production and charcoal burning are larger than the emissions from wood fires by factors of 3–10 per unit mass of fuel burned and ∼2 per unit energy released. We estimate that Zambian savanna fires produce more annual CO2, HCOOH, and NOxthan Zambian biofuel use by factors of 2.5, 1.7, and 5, respectively. However, biofuels contribute larger annual emissions of CH4, CH3OH, C2H2, CH3COOH, HCHO, and NH3by factors of 5.1, 3.9, 2.7, 2.4, 2.2, and 2.0, respectively. Annual CO and C2H4emissions are approximately equal from both sources. Coupling our data with recent estimates of global biofuel consumption implies that global biomass burning emissions for several compounds are significantly larger than previously reported. Biofuel emissions are produced year‐round, disperse differently than savanna fire emissions, and could strongly impact the tropical troposphere.