bluuebunny/crossref_metadata_2025 huggingface dataset:
Haline circulation induced by formation and melting of sea ice
Authors: Hasumi Hiroyasu , Suginohara Nobuo
Published: February 2004

A three‐dimensional, coupled ice‐ocean model is developed, and basic numerical experiments for examining effects of freshwater budget associated with formation and melting of sea ice on the thermohaline circulation are performed. Motion of sea ice affects the freshwater budget in two ways. First, it horizontally transports freshwater in the form of sea ice. Second, it alters the conditions of sea ice, which influence heat budget at the sea surface and thus the rate of formation and melting. To separate such effects of ice motion, two experiments are designed. In one case, ice motion is removed, and in the other case it is included. There appear significant differences in the thermohaline circulation between the two cases. These differences are due to the difference in horizontal distribution of salinity, which is maintained by the cycle of formation, transport, and melting of sea ice and the corresponding freshwater budget. Experiments for investigating dependence of the thermohaline circulation on the distribution of winds and consequent ice motion are also carried out. It is demonstrated that wind‐induced ice motion has major influences on how saline water produced by sea ice formation at high latitudes extends.
Numerical studies of open ocean deep convection
Authors: Sander Johannes , Wolf‐Gladrow Dieter , Olbers Dirk
Published: February 2004

Open ocean deep convection is examined with a nonhydrostatic model based on primitive equations. Strong cooling on the surface of the ocean enforces vertical motion which takes place in the narrow regions of convective cells. Different equations of state are considered, and it is shown that a linear equation of state with a constant thermal expansion coefficient cannot represent the buoyancy field and fluxes properly. The inclusion of thermobaric effects leads to additional vertical acceleration in the whole water column. The parametrization of the convective fluxes by a convective adjustment algorithm represents the horizontal mean temperature quite well but suppresses the entire vertical mass transport within the convective cells. This mass transport may be important for the transport of other tracers. Investigation of an energy cycle of the convective motion sorts out sources and sinks and reveals the conversion between different forms of energy during convective events. Both the vertical and the horizontal component of the Earth rotation vector contribute to the time mean energy balance with the same order of magnitude, but the instantaneous amplitudes of the distinct terms may differ substantially. A sensitivity study with respect to eddy and thermal diffusion coefficients distinguishes two regions; at high values of the diffusivities the velocities and tracer distributions show that a strong dependence on this values occurs, while for sufficiently small coefficients, only a weak dependence is observed.
Surface layer response to weak winds, westerly bursts, and rain squalls in the western Pacific warm pool
Authors: Wijesekera Hemantha W. , Gregg Michael C.
Published: February 2004

In November–December 1992, we measured microstructure, the hydrographic field, and the velocity field in the western equatorial Pacific near 1°43′S and 156°E as the first part of the Tropical Ocean ‐ Global Atmosphere ‐ Coupled Ocean Atmosphere Response Experiment. During our stay, we observed two westerly wind bursts with maximum speeds of about 10 m s−1, rainfalls of about 20 mm h−1, and nearly 2 weeks of calm and dry weather. During wind bursts, mixing in the upper 1 MPa was dramatic and rapid, and the major turbulence in the thermocline was produced by near‐inertial shears following the wind bursts, during which dissipation rates and Richardson numbers were comparable to those in the central Pacific. By the end of the October–November westerly burst, the averaged eddy diffusivity of momentum in the mixed layer was about 10−2 m2 s−1. Below the mixed layer, a layer about 0.50–0.75 MPa thick with high shear and strain along with a high dissipation rate persisted even after the wind burst. During calm days, mixing was primarily driven by nighttime convection and was confined to the upper 0.1 or 0.2 MPa. In general, no diurnal deep cycle in dissipation rate was found below the mixed layer, unlike in the central equatorial Pacific. Entrainment below the mixed layer occurred when both wind work and convection were large. On average, the entrainment heat flux at the base of the mixed layer was about 6 (±2) W m−2. Salinity gradients were important to density between 0.3 and 0.6 MPa. However, the salinity stratification did not control entrainment mixing. During calm and dry weather, the mixed layer heat content was governed by the vertical divergence of the radiative flux, that is, the net surface heat flux minus the radiative flux out the bottom of the layer. Both the entrainment flux and the advective flux (which was estimated as the residual term) were smaller than uncertainties in the surface heat flux. During the October–November wind burst, however, the advective term was one of the most dominant terms in the heat budget. Although the entrainment heat flux was small over short timescales, it may be important in long‐term budgets because the long‐term net surface heating could also be small.
Southern Ocean fronts from the Greenwich meridian to Tasmania
Authors: Belkin Igor M. , Gordon Arnold L.
Published: February 2004

All available meridional sections have been analyzed to investigate the evolution of main fronts between 0° and 150°E. The central South Atlantic is featured by the Subtropical Frontal Zone (STFZ), bordered by the North and South Subtropical Fronts (NSTF and SSTF, respectively), and by the Polar Frontal Zone (PFZ), bordered by the Subantarctic and Polar Fronts (SAF and PF, respectively). This structure becomes more complex in the African sector as the Agulhas Retroflection and the bottom topography force a more convoluted pattern. The Retroflection and associated Agulhas Front (AF) press the SSTF from 38° to 42°–43°S. Strong interactions of the AF, SSTF, and SAF with topography shift the fronts but do not obliterate them. The AF can be traced reliably up to 52°E, sometimes up to 75°E. The SAF is deflected from 45° to 43°S by the Mid‐Ocean Ridge and converges with the SSTF north of the Prince Edward Islands to form a combined SSTF/SAF. This front intensifies east of 50°–52°E as a result of the confluence with the AF, and between 52° and 65°E a triple AF/SSTF/SAF (“the Crozet Front”) is observed. The PF continues along 49° and 50°S between the Crozet Plateau and the Ob‐Lena (Conrad) Rise, passing north of Kerguelen, nearly joining the triple Crozet Front. Downstream of the Kerguelen‐Amsterdam Passage, the canonical structure is being restored (SSTF, SAF, PF); however, the front parameters in the Australian sector are different from the African sector, largely because of strong air‐sea interaction and cross‐frontal exchanges in the Crozet‐Kerguelen region. The SSTF, squeezed between the AF and SAF, loses characteristics to both. The SSTF/SAF interaction results in the Australian SAF being warmer and saltier downstream, while the SSTF becomes shallower and weaker. The Australian STF derives its characteristics mostly from the AF, thus bringing the modified Agulhas waters to the Pacific Ocean. The newly defined North Subtropical Front (NSTF) was distinguished in the Indian Ocean between 31° and 38°S. The front marks the southern boundary of the subtropical salty, warm water pool of the central South Indian Ocean. The NSTF location is coincident with the position of the wind convergence between westerlies and easterlies, suggesting the possible wind‐driven frontogenesis.
Linear waves in a one‐layer ocean model with thermodynamics
Authors: Ripa P.
Published: February 2004

The simplest member of a family of ocean models with inhomogeneous layers is used to study the physics of an active mixed layer overlying a quiescent denser layer. The dynamical variables of the system are the depth‐averaged horizontal velocity u and buoyancy ϑ fields and the layer thickness h. The potential vorticity q is not conserved in these models, unless ϑ is constant. An integral of motion quadratic in the deviation from a steady and symmetric basic state is derived and shown not to be positive definite; that is, there is no formal stability theorem (except in the case of uniform flow). This is due to a term proportional to the square of the distance between the isolines of q and ν, which is a measure of the nonconservation of q. A reference state without mean currents must have ΘH2 = constant, where Θ and H are the buoyancy and layer thickness, respectively, in that state. Linear waves superimposed on this basic state are Poincaré and Rossby waves, analogous to those of a homogeneous layer problem but with a different topography. In addition, there is a force‐compensating mode (FCM), which corresponds to changes in buoyancy and layer thickness that represent a vanishing contribution to the depth‐averaged pressure force. The phase speed of gravity waves (in the absence of rotation effects) is
. Rossby waves are driven by the gradient of ƒ/c2 (where ƒ is the Coriolis parameter) rather than by the gradient of ƒ/H, as they are in the homogeneous layer case. The quadratic integrals of motion are used to classify the types of instability. First, this is done in an a priori sense, looking for properties of an unstable basic flow that constrain the structure of growing perturbations. Second, this is done in an a posteriori sense, through the evaluation of the rate change of selected parts of those integrals of motion, as a function of the perturbation fields. It is stressed that for this method to give unambiguous results it is necessary that the integrals of motion be quadratic, to lowest order, in the perturbation. Unlike the case of the classical shallow water equations, a uniform flow in a channel may be unstable, if the buoyancy increases toward its right (left) in the northern (southern) hemisphere. In the ƒ plane this necessary instability condition corresponds to mean flow in the direction opposite to that of the propagation of Rossby waves. A growing perturbation is very well represented by the combination of a Rossby wave and an FCM (from the system without currents), which interact due to the presence of the uniform flow.
Southern Ocean monthly wave fields for austral winters 1985–1988 by Geosat radar altimeter
Authors: Josberger Edward G. , Mognard Nelly M.
Published: February 2004

Four years of monthly averaged wave height fields for the austral winters 1985–1988 derived from the Geosat altimeter data show a spatial variability of the scale of 500–1000 km that varies monthly and annually. This variability is superimposed on the zonal patterns surrounding the Antarctic continent and characteristic of the climatology derived from the U.S. Navy [1992] Marine Climatic Atlas of the World. The location and the intensity of these large‐scale features, which are not found in the climatological fields, exhibit strong monthly and yearly variations. A global underestimation of the climatological mean wave heights by more than 1 m is also found over large regions of the Southern Ocean. The largest monthly averaged significant wave heights are above 5 m and are found during August of every year in the Indian Ocean, south of 40°S. The monthly wave fields show more variability in the Atlantic and Pacific Oceans than in the Indian Ocean. The Seasat data from 1978 and the Geosat data from 1985 and 1988 show an eastward rotation of the largest wave heights. However, this rotation is absent in 1986 and 1987; the former was a year of unusually low sea states, and the latter was a year of unusually high sea states, which suggests a link to the El Niño‐Southern Oscillation event of 1986.
Surface thermohaline forcing conditions and the response of the present‐day global ocean climate to global warming
Authors: Cai Wenju
Published: February 2004

I investigate the response of the present‐day thermohaline circulation to a greenhouse gas‐induced global warming under different surface thermohaline conditions in a global Bryan/Cox [Bryan, 1969;Cox, 1989] ocean general circulation model with realistic bathymetry and geometry. Initially the model is spun up with surface temperature and salinity relaxed toLevitus[1982] climatologies. The forcing condition for salinity is then switched to a diagnosed flux, while that for temperature is provided by a restoration with a timescale of either 30 days (strong relaxation) or 300 days (weak relaxation). The present‐day ocean climate is obtained under these two sets of thermohaline conditions. Under the strong restoration, the modeled North Atlantic Deep Water Formation (NADWF) settles to an intensified state. Under the weak relaxation, the model solution hardly differs from that of the spin‐up. The ocean states are then subject to a global warming at a rate similar to that of the double CO2experiment in a fully coupled model described byManabe and Stouffer[1993, 1994]. The global thermohaline circulations under the weak relaxation show an initial weakening and shallowing, continued weakening upon the cessation of the atmospheric warming, and eventual reestablishment of their strengths. These behavior patterns are not unlike those found in the fully coupled model but are in sharp contrast to those in the case under the strong restoration, where NADWF eventually collapses. The processes responsible for these differences are discussed.
Cool‐skin and warm‐layer effects on sea surface temperature
Authors: Fairall C. W. , Bradley E. F. , Godfrey J. S. , Wick G. A. , Edson J. B. , Young G. S.
Published: February 2004

To obtain bulk surface flux estimates approaching the ±10 W m−2 accuracy desired for the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (COARE) program, bulk water temperature data from ships and buoys must be corrected for cool‐skin and diurnal warm‐layer effects. In this paper we describe two simple scaling models to estimate these corrections. The cool‐skin model is based on the standard Saunders [1967] treatment, including the effects of solar radiation absorption, modified to include both shear‐driven and convectively driven turbulence through their relative contributions to the near‐surface turbulent kinetic energy dissipation rate. Shear and convective effects are comparable at a wind speed of about 2.5 m s−1. For the R/V Moana Wave COARE data collected in the tropical western Pacific, the model gives an average cool skin of 0.30 K at night and an average local noon value of 0.18 K. The warm‐layer model is based on a single‐layer scaling version of a model by Price et al. [1986]. In this model, once solar heating of the ocean exceeds the combined cooling by turbulent scalar heat transfer and net longwave radiation, then the main body of the mixed layer is cut off from its source of turbulence. Thereafter, surface inputs of heat and momentum are confined to a depth DT that is determined by the subsequent integrals of the heat and momentum. The model assumes linear profiles of temperature‐induced and surface‐stress‐induced current in this “warm layer.” The model is shown to describe the peak afternoon warming and diurnal cycle of the warming quite accurately, on average, with a choice of a critical Richardson number of 0.65. For a clear day with a 10‐m wind speed of 1 m s−1, the peak afternoon warming is about 3.8 K with a warm‐layer depth of 0.7 m, decreasing to about 0.2 K and 19 m at a wind speed of 7 m s−1. For an average over 70 days sampled during COARE, the cool skin increases the average atmospheric heat input to the ocean by about 11 W m−2; the warm layer decreases it by about 4 W m−2 (but the effect can be 50 W m−2 at midday).
The adjoint method of data assimilation used operationally for shelf circulation
Authors: Griffin David A. , Thompson Keith R.
Published: February 2004

A real‐time shelf circulation model with data assimilation has been successfully used, possibly for the first time, on the outer Nova Scotian Shelf. The adjoint method was used to infer the time histories of flows across the four open boundaries of a 60 km × 60 km shallow‐water equation model of Western Bank. The aim was to hindcast and nowcast currents over the bank so that a patch of water (initially 15 km in diameter) could be resampled over a 3‐week period as part of a study of the early life history of Atlantic cod. Observations available in near real time for assimilation were from 14 drifting buoys, 2 telemetering moored current meters, the ship's acoustic Doppler current profiler and the local wind. For the postcruise hindcasts presented here, data from two bottom pressure gauges and two more current meters are also available. The experiment was successful, and the patch was sampled over a 19‐day period that included two intense storms. In this paper we (1) document the model and how the data are assimilated, (2) present and discuss the observations, (3) demonstrate that the interpolative skill of the model exceeds that of simpler schemes that use just the current velocity data, and (4) provide examples of how particle tracking with the model enables asynoptically acquired data to be displayed as synoptic maps, greatly facilitating both underway cruise planning and postcruise data analysis. An interesting feature of the circulation on the bank was a nearly stationary eddy atop the bank crest. Larvae within the eddy were retained on the bank in a favorable environment until the onset of the storms. The variable integrity of the eddy may contribute to fluctuations of year‐class success.
Velocity profiles and surface roughness under breaking waves
Authors: Craig Peter D.
Published: February 2004

Recent measurements under wave‐breaking conditions in the ocean, lakes, and tanks reveal a layer immediately below the surface in which dissipation decays as depth to the power −2 to −4 and downwind velocities are approximately linear with depth. This behavior is consistent with predictions of a conventional, one‐dimensional, level 2.5 turbulence closure model, in which the influence of breaking waves is parameterized as a surface source of turbulent kinetic energy. The model provides an analytic solution which describes the near‐surface power law behavior and the deeper transition to the “law of the wall.” The mixing length imposed in the model increases linearly away from a minimum value, the roughness length, at the surface. The surface roughness emerges as an important scaling factor in the wave‐enhanced layer but is the major unknown in the formulation. Measurements in the wave‐affected layer are still rare, but one exceptional set, both in terms of its accuracy and proximity to the surface, is that collected by Cheung and Street [1988] in the Stanford wind tunnel. Their velocity profiles first confirm the accuracy of the model, and, second, allow estimation, via a best fit procedure, of roughness lengths at five different wind speeds. Conclusions are tentative but indicate that the roughness length increases with wind speed and appears to take a value of approximately one sixth the dominant surface wavelength. A more traditional wall‐layer model, which ignores the flux of turbulent kinetic energy, will also accurately reproduce the measured velocity profiles. In this case, enhanced surface turbulence is forced on the model by the assumption of a large surface roughness, three times that required by the full model. However, the wall‐layer model cannot predict the enhanced dissipation near the surface.
Hydrography and circulation in the western Bay of Bengal during the northeast monsoon
Authors: Shetye S. R. , Gouveia A. D. , Shankar D. , Shenoi S. S. C. , Vinayachandran P. N. , Sundar D. , Michael G. S. , Nampoothiri G.
Published: February 2004

The Bay of Bengal, a semienclosed tropical basin that comes under the influence of monsoonal wind and freshwater influx, is distinguished by a strongly stratified surface layer and a seasonally reversing circulation. We discuss characteristics of these features in the western Bay during the northeast monsoon, when the East India Coastal Current (EICC) flows southward, using hydrographic data collected during December 1991. Vertical profiles show uniform temperature and salinity in a homogeneous surface layer, on average, 25 m deep but shallower northward and coastward. The halocline, immediately below, is approximately 50 m thick; salinity changes by approximately 3 parts per thousand. About two thirds of the profiles show temperature inversions in this layer. Salinity below the halocline hardly changes, and stratification is predominantly due to temperature variation. The halocline is noticeably better developed and the surface homogeneous layer is thinner in a low‐salinity plume that hugs the coastline along the entire east coast of India. The plume is, on average, 50 km wide, with isohalines sloping down toward the coast. Most prominent in the geostrophic velocity field is the equatorward EICC. Its transport north of about 13° N, computed with 1000 dbar as the level of reference, varies between 2.6 and 7.1 × 106 m3 s−1; just south of this latitude, a northwestward flow from offshore recurves and merges with the coastal current. At the southern end of the region surveyed, the transport is 7.7 × 106 m3 s−1. Recent model studies lead us to conclude that the EICC during the northeast monsoon is driven by winds along the east coast of India and Ekman pumping in the interior bay. In the south, Ekman pumping over the southwestern bay is responsible for the northwestward flow that merges with the EICC.
The eddy field of the southeast Atlantic Ocean: A statistical census from the Benguela Sources and Transports Project
Authors: Rae C. M. Duncombe , Garzoli S. L. , Gordon A. L.
Published: February 2004

Data collected during the Benguela Sources and Transports project were examined to determine some statistical properties of the eddy field observed in the Cape Basin. Seven anticyclonic eddies were encountered during the hydrographic surveys. Two of these were shown to be of Brazil Current origin (this paper and Smythe‐Wright et al. [1996]). Inverted echosounder (IES) records of acoustic travel time were scaled to the depth of the thermocline, represented in the Cape Basin by the 10°C isotherm. These records indicate that a minimum of four to six eddies, assumed to be of Agulhas origin, entered the Cape Basin per year during the sampling period. They were associated with depressions in the 10°C isotherm records ranging from 100 to 400 m and of a duration between 30 and 100 days. The thermocline appears to shallow appreciably after the passage of an eddy before relaxing to the local mean. Estimates of the heat and salt contents of the hydrographically surveyed eddies indicated that the mean available heat and salt anomalies of the eddies were 0.55 × 1020 J and 3.5 × 1012 kg, respectively. Extrapolating the hydrographic data to the eddies detected in the IES record shows the eddy field responsible for the transfer of 2.2 to 3.3 × 1020 J yr−1 (0.007 PW), 14 to 21 × 1012 kg salt yr−1, and 2.6 to 3.8 × 106 m3 s−1.
The landslide tsunami of November 3, 1994, Skagway Harbor, Alaska
Authors: Kulikov Evgueni A. , Rabinovich Alexander B. , Thomson Richard E. , Bornhold Brian D.
Published: February 2004

We show that the tsunami of November 3, 1994 in Skagway, Alaska was generated by an underwater landslide formed during the collapse of a cruise ship wharf undergoing construction at the head of Taiya Inlet. This event occurred at a time of extreme low tide and was not associated with a regional seismic event or incoming oceanic tsunami. Persistent wave motions with an amplitude of 1 m and a period of 3 min recorded by a tide gauge in Skagway Harbor following the landslide are linked to the formation of a cross‐inlet seiche and quarter‐wave resonance within the harbor. The high Q factor for the harbor (Q ≈ 20) indicates weak dissipation and strong resonance within the harbor.
Evaluation of surface radiative flux parameterizations for use in sea ice models
Authors: Key Jeffrey R. , Silcox Robert A. , Stone Robert S.
Published: February 2004

The surface radiation budget of the polar regions strongly influences ice growth and melt. Thermodynamic sea ice models therefore require accurate, yet computationally efficient methods of computing radiative fluxes. In this study, a variety of simple parameterizations of downwelling shortwave and longwave radiation fluxes at the Arctic surface are examined. Parameterized fluxes are compared to in situ measurements over an annual cycle. Results suggest that existing parameterizations can estimate the downwelling shortwave flux to within 2% in the mean, with a root‐mean‐square error (RMSE) of about 4% for clear skies and 21% for cloudy conditions. Parameterized longwave fluxes are accurate to within 1% in the mean, with RMSE values of 6% for both clear and cloudy skies. On the basis of these results, two parameterization schemes are recommended to estimate radiation forcings in sea ice models for Arctic applications.
Response of a circular ice floe to ocean waves
Authors: Meylan Michael H. , Squire Vernon A.
Published: February 2004

A new model is presented to reproduce the behavior of a solitary, circular, flexible ice floe brought into motion by the action of long‐crested sea waves. The intended application of the work is ultimately a fully three‐dimensional analogue of a marginal ice zone (MIZ) through which ocean waves propagate, allowing the attenuation and directional advance to be forecast and validated against observations. (Existing theory does not treat directional changes correctly.) To enable a check to be made on the model, two independent methods are developed: an expansion in the eigenfunctions of a thin circular plate, and the more general method of eigenfunctions used to construct a Green's function for the floe. Displacement and three‐dimensional scattering patterns in the water surrounding the floe are given for several floe geometries. The model is also used to investigate the strain field generated in the floe, its surge response, and the energy initiated in the water encircling it. Finally, with the aim of understanding how floes herd together to form cohesive structures in the MIZ, the force induced on floes of various thicknesses and diameters is plotted.
Evidence for a North Pacific Deep Western Boundary Current
Authors: Hallock Zachariah R. , Teague William J.
Published: February 2004

Four current meter moorings arrayed across the Japan Trench near 35°N yielded 2 years of deep current velocities in the vicinity of the Kuroshio where it separates from the Japanese coast. One‐ and 2‐year means are interpreted in the context of other observations, including concurrent hydrography, as well as the results of earlier investigations. Principal findings are as follows: the presence of a persistent, southward deep western boundary current (1–2 cm s−1) along the slope (2000–4000 m) inshore of the Japan Trench; a generally northward deep flow (∼4 cm s−1) over the trench, beneath the Kuroshio; and southward and eastward deep flows farther southeast of the Kuroshio separation. These deep, mean flows, particularly the one inshore of the Japan Trench, may be partly of thermohaline origin. Eddy‐driven local recirculations and bottom intensification are also likely.
Changes in Antarctic Bottom Water properties in the western South Atlantic in the late 1980s
Authors: Coles Victoria J. , McCartney Michael S. , Olson Donald B. , Smethie William M.
Published: February 2004

Data collected in 1988–1989, as part of the South Atlantic Ventilation Experiment, have been combined with the historical database to study the circulation and water mass variability of the abyssal water in the Argentine Basin. A map of potential temperature at 4000 m used as an indication of geostrophic shear defines a south and western intensified crescent‐shaped abyssal recirculation. Within this recirculation, and its northward extension to the Brazil Basin, Antarctic Bottom Water (AABW) properties have undergone two modifications during the 1980s: (1) The water mass cooled (0.05°C) and freshened (0.008 in salinity ratio) on surfaces of constant density. (2) The densest layer of AABW was altered to less dense water through mixing or advection out of the study area. This water mass change does not appear to have affected the flow pattern. Data collected in 1983 and 1988 to the north in the Brazil Basin show penetration of the freshwater mass in the deep western boundary current to between 18°S and 10°S, indicating very rapid propagation of the anomaly from the Argentine Basin into the Brazil Basin as a deep western boundary current. It is suggested that open ocean convective events within the Weddell Sea contributed to the change in AABW documented here.
Thermocline stratification within the Indonesian Seas
Authors: Ilahude A. Gani , Gordon Arnold L.
Published: February 2004

An extensive suite of conductivity‐temperature‐depth stations was obtained from the Baruna Jaya I during the southeast monsoon of 1993 and northwest monsoon of 1994, as part of the Indonesian/U.S. Arlindo project. The main objective of these cruises was to determine sources, pathways, and mixing histories of the throughflow water masses for the monsoon extremes. Water mass analysis indicates that the most penetrating route followed by Pacific water occurs within the Makassar Strait. This supports the notion that this strait carries the bulk of the Pacific to Indian throughflow, consisting of North Pacific Subtropical Water (upper thermocline Smax) and North Pacific Intermediate Water (lower thermocline Smin). The more attenuated Smax core during the northwest monsoon relative to the southeast monsoon suggests that the throughflow may slacken in that season. There is only minor contribution within the possible throughflow pathway east of Sulawesi. However, relative salty water of South Pacific origin is observed in the lower thermocline within the Seram and southern Maluku Seas, particularly in the northwest monsoon. Density‐driven, sill depth overflow into the deep Banda Sea basin via the Lifamatola Passage also contributes to the total throughflow, though this contribution is likely to be minor. While some of the throughflow has been shown to pass through the Lombok Strait, water mass analysis clearly shows the Makassar throughflow turning into the Flores Sea and Banda Sea before curling southward into the Timor Sea and Indian Ocean.
The effect of the Indonesian throughflow on ocean circulation and heat exchange with the atmosphere: A review
Authors: Godfrey J. S.
Published: February 2004

A new version of the island rule, which relates transport around an island to wind and pressure forcing, provides a basis for comparing various published theoretical estimates of the long‐term mean Indonesian throughflow magnitude. It is found, among other things, that nonlinear effects near Halmahera and pressure gradients across New Zealand may modify the long‐term throughflow magnitude. Recent theoretical estimates of interannual throughflow variations are in approximate agreement with observation; Indian Ocean Kelvin waves play an important role. On still shorter timescales and for understanding flow details in different channels, consideration of the full details of the Indonesian region via numerical modeling becomes essential. Most of the throughflow enters from the Mindanao Current. The process by which the South Pacific waters eventually reach the Mindanao Current appears to involve some nonlinear retroflection process (particularly in northern summer) and subsequent freshening along long pathways in the North Pacific. Observed water mass transformations in Indonesian waters demand a vertical eddy diffusivity of about 10−4 m2 s−1, large enough to generate turbulent heat fluxes of order 40 W m−2 at the base of the mixed layer. According to numerical models, changes in ocean circulation associated with the throughflow are likely to affect patterns of heat exchange with the atmosphere in widely separated regions of the world ocean. In particular, an increased throughflow will result in more heat loss to the atmosphere in the subtropical Indian Ocean and less in the Pacific Ocean. Simple, physically reasonable mechanisms have been offered for these model results. Observational evidence to support or refute these mechanisms is rather fragmentary but is reviewed here. Our present understanding of the throughflow permits some informed speculations as to the possible role of the throughflow in coupled ocean‐atmosphere phenomena, such as the El Niño‐Southern Oscillation (ENSO). Earlier estimates of western Pacific reflectivity seem largely confirmed by recent observational results. However, it is suggested that tidal mixing in the Indonesian seas may generate ENSO‐related sea surface temperature anomalies there, possibly affecting the development of westerly wind bursts.
Coupled dynamics of the South China Sea, the Sulu Sea, and the Pacific Ocean
Authors: Metzger E. Joseph , Hurlburt Harley E.
Published: February 2004

The complex geometry, the seasonally reversing monsoon winds, and the connectivity with the Pacific Ocean all contribute to the coupled dynamics of the circulation in the South China Sea (SCS), the Sulu Sea, and the region around the Philippine Islands. The 1/2°, 1.5‐layer global reduced gravity thermodynamic Navy layered ocean model (NLOM) is used to separate these components and to investigate the role of each one. When forced by the Hellerman and Rosenstein [1983] (HR) monthly wind stress climatology, the basic features of the model solution compare well with observations, and with higher‐resolution NLOM versions. The dynamics of the flow from the Pacific Ocean into the SCS via the Luzon Strait are emphasized. The effects of Ekman suction/pumping due to wind curl are examined by forming monthly spatial averages of the winds over the SCS/Sulu Sea basins. This maintains a monthly varying stress but with a region of zero curl. Forcing the model with these modified winds leaves the mean Luzon Strait transport unchanged, and the variability actually increases slightly. These results suggest that it is the pressure head created by the pileup of water from the monsoonal wind stress that controls the variability of the Luzon Strait transport. The forcing for wind stress pileup effects could be either internal or external to the SCS/Sulu Sea basin. The effects of internal forcing are studied by applying monthly winds within this basin but annual HR winds outside the region. With this forcing the mean Luzon Strait transport is essentially unchanged, but the variability is only 44% of the standard case value. The external forcing is defined as zero stress in the SCS/Sulu Sea basins and HR monthly winds outside. Again, the mean Luzon Strait transport is unchanged, and here the variability is 60% of the standard case. The mean Luzon Strait transport is largely a function of the model geometry. When the Sulu archipelago is opened, a net cyclonic flow develops around the Philippines, which is essentially an extension of the northern tropical gyre. The bifurcation latitude of the North Equatorial Current (NEC) at the Philippine coast is also affected by the amount of transport through the Sulu archipelago. Opening this archipelago causes the NEC split point to move southward and increases the transport of the Kuroshio east of Luzon while decreasing the Mindanao Current. Opening or closing the Sunda Shelf/Java Sea or the Sulu archipelago does not affect the transport of the Pacific to Indian Ocean throughflow.
Electric field magnitudes and lightning initiation in thunderstorms
Authors: Marshall Thomas C. , McCarthy Michael P. , Rust W. David
Published: February 2004

Lightning may be initiated via an electron avalanche that may occur when energetic electrons (∼1 MeV) are accelerated by thunderstorm electric fields to velocities sufficient to produce new energetic electrons during ionizing collisions with nitrogen or oxygen molecules. For the avalanche to occur, the thunderstorm electric field must exceed a critical value called the breakeven field. At any altitude the breakeven field is substantially less than the field usually thought necessary either for dielectric breakdown or for streamer propagation. We show that 23 electric field soundings through thunderstorms seem to confirm that lightning occurs when the electric field exceeds the breakeven field. The soundings also show that the electric field inside storms tends to be limited to magnitudes less than or equal to the breakeven field. This breakeven mechanism may explain why electric field magnitudes greater than 150 kV m−1 are rarely found inside thunderstorms. It may also help explain the initiation of lightning and other types of discharges that either propagate upward from the tops of thunderstorms or occur above them.
Large‐scale pollution of the atmosphere over the remote Atlantic Ocean: Evidence from Bermuda
Authors: Dickerson Russell R. , Doddridge Bruce G. , Kelley Paul , Rhoads Kevin P.
Published: February 2004

Ozone acts as a greenhouse gas and controls much of the oxidizing capacity of the atmosphere. Photochemical production of ozone in urban areas (smog) is a serious environmental problem, but how far this process extends on regional or global scales remains a major unanswered question in atmospheric science. In summer, Bermuda basks in pristine marine air, but in the spring, episodes of high ozone are common. From meteorological analyses and observations of ozone, carbon monoxide, and reactive nitrogen compounds, we conclude that half or more of the excess ozone in Bermuda originates from air pollution over eastern North America.
Relative contributions of land and ocean processes to precipitation variability
Authors: Koster Randal D. , Suarez Max J.
Published: February 2004

A series of general circulation model simulations are used to quantify the relative contributions of land surface and ocean variability to variability in precipitation. The simulations show that land surface processes contribute significantly to the variance of annual precipitation over continents. In contrast, ocean processes acting alone have a much smaller effect, particularly in midlatitudes. The precipitation variability reflects local evaporation variability and associated hydrological persistence, and it responds most strongly to the land surface during summer, when moist convection dominates.
Volatility and size of cloud condensation nuclei
Authors: Hudson James G. , Da Xiaoyu
Published: February 2004

Cloud condensation nuclei (CCN) volatility and size versus critical supersaturation Sc measurements are presented for maritime, continental, and urban areas. The measurements included both hemispheres of the globe. Although this was a nonsystematic preliminary survey, some general trends are shown. CCN in cleaner air were smaller, characteristic of completely pure soluble substances, whereas the CCN in dirtier air were larger, characteristic of insoluble and/or different soluble material mixed internally. Volatility was generally characteristic of sulfate (i.e., ammonium sulfate) except in urban areas, where more volatile material was present, which is characteristic of unneutralized acids.
Airborne measurements of aqueous and gaseous hydrogen peroxide during spring and summer in Ontario, Canada
Authors: Macdonald A. M. , Anlauf K. G. , Banic C. M. , Leaitch W. R. , Wiebe H. A.
Published: February 2004

Measurements of H2O2, both in the gas phase and in cloudwater samples, were made over central Ontario during the summer 1988 and spring 1990 intensive measuring periods of the Eulerian Model Evaluation Field Study from a Twin Otter aircraft. Cloudwater concentrations range from less than 1.5 μM to greater than 100 μM; corresponding gaseous concentrations range from less than 0.1 parts per billion by volume (ppbv) to approximately 2.5 ppbv. Gas phase H2O2 data are corrected for instrument response and the interphase partitioning of H2O2 is examined. Ratios of the measured to predicted partitioning based on Henry's law equilibrium range from approximately 0.2 to 1. When the data correction is applied, most samples do not differ from equilibrium by more than 20%. Lower ratios are associated with samples from supercooled clouds or samples taken when interstitial SO2 is high. The measured aqueous fraction for the supercooled samples is approximately 20% of that expected by Henry's law equilibrium. The ratios are independent of liquid water content but show some dependence on pH.
Downward transport in the upper stratosphere during the minor warming in February 1979
Authors: Kouker W. , Beck A. , Fischer H. , Petzoldt K.
Published: February 2004

On February 6, 1979, a small region of dry air, referred to below as a dry tongue, appeared in Limb Infrared Monitor of the Stratosphere data directly below the stratopause at approximately 75°N when a zonal average between 40°E and 160°E was applied. Isentropic analysis of Ertel's potential vorticity and H2O mixing ratio does not support the hypothesis of the dry tongue being caused solely by adiabatic sinking from the dry mesosphere into the upper stratosphere. Therefore a three‐dimensional mechanistic model of the middle atmosphere, which is mainly driven by the net heating rate and the effects of breaking gravity waves, is used to simulate the minor warming in January and February 1979. The model data clearly support the existence of the dry tongue mentioned above as a real phenomenon. Moreover, they allow the dry tongue to be interpreted as the result of the combined adiabatic and diabatic downward movements east of the center of the polar vortex.
Comparison of measured and calculated aerosol properties relevant to the direct radiative forcing of tropospheric sulfate aerosol on climate
Authors: Quinn P. K. , Marshall S. F. , Bates T. S. , Covert D. S. , Kapustin V. N.
Published: February 2004

The accuracy of the estimated radiative forcing of tropospheric sulfate aerosol depends on the quality and spatial coverage of the aerosol chemical, physical, and optical data that serve as input to global climate models. To augment the available data and to provide a comparison of measured and calculated optical properties, surface measurements were made of the aerosol light scattering and backscattering coefficients, the number size distribution from 0.02 to 9.6 μm, and chemical mass size distributions during two Pacific Ocean field experiments. All measurements were made on an aerosol sample stream dried to 30% relative humidity and are reported as such. The first experiment took place during the Pacific Sulfur/Stratus Investigation at Cheeka Peak, Washington, in April and May of 1991 (PSI 91). The second occurred as part of the Marine Aerosol and Gas Exchange cruise in February and March of 1992 (MAGE 92) which was conducted from 33°N to 12°S along 140°W. The mass size distributions of nonseasalt sulfate and sodium varied widely both spatially and temporally. The shape of the number size distribution remained fairly constant throughout both experiments with an accumulation mode geometric number mean diameter of 0.19±0.03 μm and a geometric mean standard deviation of 1.4 ± 0.06. Measured light scattering and backscattering ranged from 3.7 to 19×10−6 m−1 and 0.64 to 2.8×106 m−1, respectively, resulting in an average backscattered fraction of 0.15 with a standard deviation of ±0.009. The light scattering and backscattering coefficients were calculated from a Mie model applied to the measured number size distributions. The mean of the calculated scattering values was 3% higher than the mean of the measured values with a 14% variance about the mean. This variance was within the uncertainty of the calculations indicating that the scattering characteristics of the aerosol were parameterized adequately by the model. The calculated backscattering values were about 40% lower than the measured values, however. The calculated light scattering apportioned to nonseasalt sulfate aerosol was 39±17% of the total calculated scatter. The scattering to mass ratio for sulfate aerosol averaged 5.0 m2 g−1 with a standard deviation of ±1.6 m2 g−1 and varied with variability in the number size distribution. Further measurements are needed that will allow for the formation of a global‐scale database to reveal the extent of the variability in the aerosol chemical, physical, and optical properties relevant to climate forcing.
Modeled response of photochemical oxidants to systematic reductions in anthropogenic volatile organic compound and NOx emissions
Authors: Roselle Shawn J. , Schere Kenneth L.
Published: February 2004

As an exercise in model sensitivity, the Environmental Protection Agency's regional oxidant model (ROM) was run for several simulations to study the impact of across‐the‐board reductions in anthropogenic volatile organic compound (VOC) and NOx emissions on the photochemical environment of the eastern United States. The ROM, which simulates most of the physical and chemical processes responsible for the formation of O3 on regional scales, was used to simulate a widespread high O3 episode in the eastern United States. Separate simulations were performed over the period July 2–10, 1988, for each of the sensitivity runs. An operational evaluation and several model diagnostics were performed on the base case simulation. The sensitivity runs reduced anthropogenic NOx and VOC emissions separately and in combination in increments of 25% of full scale emissions. Biogenic emissions were held constant across all sensitivity tests. Seventeen of the potential 25 nodes of the NOx, VOC emissions reduction matrix were simulated. In the analysis the modeled domain (the eastern half of the United States) is subdivided into several chemically coherent regions. Several chemical species, including afternoon average concentrations of O3, PAN, HNO3, OH, and HO2 + RO2, are examined to gain an understanding of how the reduction in emissions affected the overall chemical system for each sensitivity test. Results are presented as a series of statistical and graphical displays illustrating the response of the system within the selected subdomains to the emission reductions.
Scattered ultraviolet radiation in the upper stratosphere 1: Observations
Authors: Minschwaner K. , Thomas R. J. , Rusch D. W.
Published: February 2004

Observations of scattered solar near‐UV radiation in the upper stratosphere were obtained during a 1983 balloon flight at 31°N latitude. The instrument design was patterned after the UV ozone spectrometer on board the Solar Mesosphere Explorer satellite. The measurements cover the wavelength range 175 to 325 nm at a spectral resolution of 1.5 nm, spanning a range of viewing elevation angles from −3.3° to 14.6° with a field of view 1.65×10−5 sr. Observations began at midday near 46 km and continued to approximately 1700 LT near an altitude of 40 km. Calibrated radiances reported here are determined from the raw data using measured sensitivity characteristics of the spectrometer. A correction to account for the polarized nature of Rayleigh‐scattered radiation is included which employs the measured polarization response of the instrument and assumes single scattering of solar radiation. The single pass spectrometer was susceptible to a small but in some cases important contamination by stray light. This effect is quantified using observations obtained at low altitudes and low solar elevation angles, i.e., large optical paths. The uncertainty in radiances is determined by statistical and systematic errors (efficiency, polarization, and stray light determinations) and ranges typically from 15 to 30%. In contrast to previous observations, scattered radiances decrease rapidly at wavelengths shortward of 210 nm.