Westward Currents Research Articles

Seasonal dispersion of petroleum contaminants in the Gulf of Thailand

Six oceanographic moorings were maintained in 1993 and 1994 and provided data on the water circulation and the flushing characteristics of the Gulf of Thailand. The concentration of dissolved and dispersed petroleum hydrocarbons (DDPH) was measured at 78 sites in 1994 and 1995 in coastal waters of the Gulf. The water circulation was sluggish and the Gulf was poorly flushed; the mean currents were generally <0.07 m s -1. Under the influence of the South China Sea, an anticyclonic gyre existed in the southeast monsoon, a cyclonic gyre in the northwest monsoon, and sluggish currents the rest of the time. Even in the dry season brackish water was found inshore; this suggests that freshwater, that arrived in the Gulf in the previous wet season, was trapped along the coast and that little mixing occurred between offshore and coastal waters. In coastal waters of the Inner Gulf and the Eastern Sea Board there were occasional acute pollution events (DDPH>40 μg l -1), superimposed 25% of the time upon chronic pollution (DDPH≈4 μg l -1) due to limited flushing of the Inner Gulf and the Eastern Sea Board, and the presence of slightly contaminated water elsewhere (DDPH<1.2 μg l -1) 75% of the time. Only the Outer Gulf seems relatively uncontaminated (DDPH≈0.01–0.1 μg l -1). The seasonal distribution of the DDPH appeared to be controlled by the water circulation; indeed the highest DDPH values in the Inner Gulf occurred in November–December because of the net currents were weak and variable. The highest DDPH values on the Eastern Sea Board occurred in April–August when the region simultaneously received contaminated coastal water from the Inner Gulf. The smallest DDPH values on the Eastern Sea Board occurred in September–November because strong westward currents prevailed which flushed the contaminants. The observed currents and DDPH data were used to drive an oil spill model which predicted that acute contamination occurs at least once a year everywhere in the Inner Gulf.

On the existence of prevalent westward shifts in the solar atmosphere

A statistical analysis of the deviations of the sideral angular rotation velocities Ω(ϕ) of single sunspot groups from the averaged rotation curve \(\overline {\Omega (\phi )} \), shows that positive deviations tend to be greater than negative ones: we can therefore deduce the existence of prevalent westward shifts in the solar atmosphere. This effect is only partially due to the sunspot group proper motions at the beginning of their evolution, and it could indicate the prevalence of westward currents in the solar photosphere.

On the Annual Cycle of Upper-Ocean Circulation in the Eastern Equatorial Pacific

Abstract An oceanic general circulation model is used to investigate the annual cycle of the near-surface currents in the eastern equatorial Pacific Ocean; in particular, the causes of the springtime increase of eastward momentum that reverses the westward surface flow and intensifies the Equatorial Undercurrent are examined. A set of process experiments are carried out that isolates effects due to three forcing mechanisms: local zonal and meridional winds, and remote zonal winds. It is demonstrated that the springtime weakening of the local easterly trades is the primary cause of the eastward-momentum increase. In addition, due to meridional advection, the local southerly wind drives a westward current on the equator throughout the year; this flow is weakest in the spring, and therefore this process also contributes to the anomalous eastward flow. On the other hand, remote forcing tends to weaken the springtime momentum increase: Anomalous easterlies in the far-western and central Pacific during the wint...

Average terrestrial ring current derived from AMPTE/CCE‐CHEM measurements

The present study attempts to analyze the average ring current density and pressure in the magnetospheric equatorial plane (as a function of geocentric distance and local time) based on the AMPTE/CCE‐CHEM proton distributions according to two different AE ranges, corresponding to a low (AE&lt;100 nT) and a moderate (100 nT&lt;AE&lt;600 nT) geomagnetic or auroral activity. In order to obtain a statistically significant database for a high spatial resolution, the data were averaged over 2 years. The results provide a trend of the ring current and show its general average features as a function of geomagnetic activity. In particular, the total ring current is dominated by the pressure gradient term, resulting in an eastward current in the inner magnetosphere (L&lt;4.5) and an extended westward current at higher altitudes. The westward current is always stronger than the eastward current. Moreover, the ring current system is a function of magnetic local time, exhibiting a noon‐midnight asymmetry in general, as well as a function of geomagnetic activity exhibiting an enhancement of about 20% during active times (in midnight‐dusk region only). The location of the total current peak in the midnight sector is at about MLT=2300, and its changes with magnetic activity are interpreted as an effect of the particles injection from the tail during the storms/substorms. The derived current values are compared to previous model predictions and observations.

High‐latitude Hall and Pedersen conductances during substorm activity in the SUNDIAL‐ATLAS campaign

Simultaneous high time resolution observations of the Hall and Pedersen conductances, ΣH and ΣP, respectively, the ionospheric electric field and the ground magnetic field during a magnetospheric substorm are reported. The measurements discussed here were taken during the SUNDIAL/ATLAS 1 campaign of March 24 to April 2, 1992. The European Incoherent Scatter (EISCAT) UHF special programme SP‐UK‐ATLAS, which operated on March 27, 1992, provided continuous measurements of the electron density and the ion vector velocity from which ΣH and ΣP and the ionospheric electric field were calculated. During the substorm growth phase, ΣP and ΣH were less than 10 S and the ratio, R = ΣH/ΣP, was less than 1. Although both ΣH and ΣP increased at the onset of the expansion phase, R remained close to 1. This ratio provides information on the mean energy of the precipitating particles responsible for the enhanced conductances. A ratio of 1 implies a mean energy of the particles of 2.56 keV. Two distinct expansion phases were identified, the second of which included a number of intensifications. Both ΣH and ΣP increased toward the end of the second expansion phase with peak values of 71 S and 34 S, respectively. The ratio R also increased to values exceeding 2, equivalent to mean energies of more than 5.78 keV. The largest value of R was 3.25, which occurred during the substorm recovery phase and is equivalent to mean energies of more than 10 keV. The increase in mean energy as the substorm progresses may be interpreted in terms of changes in the acceleration processes in the magnetosphere. The maximum zonal (east‐west) current during this interval was 2.20 A m−1 and occurred toward the end of the second substorm expansion phase. At a number of intensifications, reversals or enhancements in the zonal current were observed, for which the electric field was responsible in most cases. While the peak value of the Pedersen conductance of 40 S is similar to recent published results, the Hall conductance peak of 75 S is less than recent published measurements. Furthermore, the westward current during the initial part of the expansion phase is dominated by the electric field, in contrast to a previously published model which suggested that this current would be conductivity‐dominated. It is suggested that further spatial structure of the current is necessary to explain these observations.

Substorm activity precursors in the dayside magnetic perturbations

Magnetic data from a meridional chain of stations in Greenland and AL-indices of magnetic activity have been used to study the relationship between magnetic perturbations in the dayside cleft region and substorm activity in the night-time auroral zone. The analysis of 14 substorms, isolated and prolonged, has shown that intensification of westward currents in the postnoon sector of the cleft precedes or accompanies substorm development in the night-time auroral zone. Westward currents appear in the northern cleft as substorm precursors even under the adverse influence of the IMF positive B y component. These currents trend to extend in the prenoon sector. To explain the relationship between the cleft currents and auroral electrojet the connection between neutral layer currents and noon Birkeland currents is proposed. This connection can be realized by means of the source region acting just inside the daytime magnetopause owing to stationary reconnection of geomagnetic field and IMF, the source region flowing downstream to the tail magnetopause.

Geostrophic transport of the Pacific‐Indian Oceans throughflow

For the dynamic balance of the world ocean circulation, the flow through the Indonesian archipelago needs to be quantified. Part of the Java Australia Dynamic Experiment program was to occupy hydrographic sections during the two opposite seasons. Here we present and discuss the February 1992 geostrophic estimate of the throughflow. The appearance of the east‐flowing Java Current, flowing in the 80 km off the Indonesian coast, led to a net total transport of a few 106 m3 s−1 eastward, opposite to the expected sense of net transport. Uncertainty in this transport, estimated from the repeated casts, reaches 9 106 m3 s−1. This large error could be attributable to internal wave motions. Estimates of the transport from the conductivity‐temperature‐depth data and from the temperature profile associated to the Levitus [1982] data set have been compared. Comparison with August 1989 results shows that the main westward current, corresponding to the South Equatorial Current, is located north of the hydrological front in both seasons. The largest transport variation between the two cruises is located along the Indonesian coast, with the reversal of the Java Current. The mesoscale current variability is enhanced in the southern part of the section in February 1992. These transport evaluations, made in the two opposite seasons and in two different years, 18 ± 7 106 m3 s−1 westward in August 1989 and 2.6 ± 9 106 m3 s−1 eastward in February 1992, give an extreme range of the net throughflow.

Modeling the dispersal of Levantine Intermediate Water and its role in Mediterranean deep water formation

This paper demonstrates the importance of Levantine Intermediate Water (LIW) in the deep water formation process in the Mediterranean using the modular ocean general circulation model at 0.25° resolution, 19 vertical levels, over the entire Mediterranean with an open Gibraltar strait. LIW formation is strongly prescribed in the Rhodes Gyre region by Haney [1971] relaxation, while in other regions, surface salinity relaxation is much reduced by applying the ‘mixed’ thermohaline surface boundary conditions. Isopycnal diagnostics are used to trace water mass movements, and volume fluxes are monitored at straits. Low viscosity and diffusion are used to permit baroclinic eddies to play a role in water mass dispersal. The overall water budget is measured by an average flux at Gibraltar of 0.8 Sv, of which 0.7 Sv is exchanged with the eastern basin at Sicily. LIW (density around 28.95) spreads rapidly after formation throughout the entire Levantine due to baroclinic eddies. Toward the west, LIW accumulates in the northern and central Ionian, with some entering the Adriatic through Otranto and some mixing southward in eddies and exiting to the western Mediterranean through Sicily. LIW is converted to deep water in the south Adriatic at an average rate of 0.4 Sv. Water exchange through the Otranto strait appears to be buoyancy driven, with a strong bias to the end of winter (March–April), while at Sicily the exchange has a strong symmetric seasonal cycle, with maximum transport of 1.1 Sv in December indicating the effects of wind driving. LIW pathways in the west are complex and variable. In the Tyrrhenian, intermediate water becomes uniform on isopycnal surfaces due to eddy stirring. West of Sardinia, two LIW boundary currents are formed in the Balearic basin; one flows northward up the west coast of Sardinia and Corsica, and one westward along the northern African coast. The northward current is consistent with observations, while the westward current is intermittent for the first 10 years, often breaking up into eddies which enter the basin interior. Some observations of high‐salinity waters near the African coast may support this interpretation. LIW retains a subsurface salinity maximum of 38.4–38.5 practical salinity units (psu) when reaching the northwestern Mediterranean, contrasting with surface waters fresher than 38.0 psu. West Mediterranean deep water is formed below 1500 m depth with climatological characteristics, when it is mixed and cooled during winter convection in Lions Gyre.

Interannual variability of surface currents in the tropical Pacific during 1987–1993

Buoy drifts and current meter records between January 1987 and December 1993 are used to investigate the interannual variability of the equatorial Pacific currents at a depth of 15 m. The sampling is coarse until mid‐1988 but more complete afterward, so that the large‐scale features of the anomaly currents can be documented on the seasonal to yearly timescale. Using objective analysis, bimonthly current anomalies are mapped between 20°N and 20°S on a 1° × 5° grid, and the error covariance matrix of the analyzed fields are estimated. The current anomalies are primarily zonal, with largest amplitudes within about 8° from the equator, and they are largely linked to the El Niño‐Southern Oscillation phenomenon. In particular, broad, basin‐wide westward anomaly currents were encountered during the 1988 La Niña, and strong eastward currents persisted from July–August 1991 to January–February 1992, followed by westward currents from May–June to July–August 1992. An empirical orthogonal function (EOF) analysis shows that the first EOF of zonal current anomaly is largely uniform in the equatorial band, while the next two EOFs describe large‐scale currents of opposite sign across the equator and across 160°W, respectively. The EOFs are rather smooth and the errors on the principal component time series relatively small, which indicates that the sampling is adequate to describe the large‐scale, low‐frequency zonal current fluctuations. As the dominant EOFs of meridional current are noisy and the relative errors on the principal components larger, the meridional current fluctuations are not as well captured by the data set. Correlation analysis and a singular value decomposition are used to investigate the influence of advection by the large‐scale, low‐frequency currents on sea surface temperature (SST) anomalies during 1987–1993. Although the data set is noisy and other terms play an important role in the SST anomaly equation, the effect of zonal, and, to a lesser extent, meridional advection is seen in much of the central and eastern equatorial Pacific. The dominant terms are the anomalous zonal advection of mean SST, the mean zonal, and, intermittently, meridional advection of SST anomalies.

平塚観測塔に現れる黒潮による８０日周期潮位変動と急激な水温変化

The tidal data analysis from 1989 to 1994 in Hiratsuka revealed that the long period variation of sea level was influenced by variability of the Kuroshio, which flows in the neighborhood of the southern part of Sagami Bay. The spectral analysis for the Hiratsuka tidal data showed strong well-separated spectral peaks with typical time scales of 1 year, 80 days, 50 days, 33 days, and 24 days. The variability of 80 days is induced by the mesoscale variation of the Kuroshio and propagates from the southern part: Hachijyo and Miyake islands. The sea level affected by the variation with this period rises as the Kuroshio approaches to the Nojimazaki, to the Irozaki and vice versa. This result suggests that the oceanic conditions of Sagami Bay are affected from down stream side of the Kuroshio. In particular, when the Kuroshio front approaches to the Nojimazaki in wrinter, the rapid temperature rise occurs: the sea level rises rapidly before the rapid rise of the temperature. In this case, the strong westward currents were observed in Hiratsuka. This phenomena developed to the Kyuu-Chou, which damaged the Yellowtail fixed nets, in January 9, 1994. When the Kuroshio front is away from the Nojimazaki in summer, the sea level falls with the fall of the temperature. These phenomena may propagate to Hiratsuka as the Kelvin waves and may play an important role for the mixing in Sagami Bay.

Cloud albedo feedback and the super greenhouse effect in a global coupled GCM

Two competing cloud-radiative feedbacks identified in previous studies i.e., cloud albedo feedback and the super greenhouse effect, are examined in a sensitivity study with a global coupled ocean-atmosphere general circulation model. Cloud albedo feedback is strengthened in a sensitivity experiment by lowering the sea-surface temperature (SST) threshold in the specified cloud albedo feedback scheme. This simple parameterization requires coincident warm SSTs and deep convection for upper-level cloud albedos to increase. The enhanced cloud albedo feedback in the sensitivity experiment results in decreased maximum values of SST and cooler surface temperatures over most areas of the planet. There is also a cooling of the tropical troposphere with attendant global changes of atmospheric circulation reminiscent of those observed during La Nina or cold events in the Southern Oscillation. The strengthening of the cloud albedo feedback only occurs over warm tropical oceans (e.g., the western Pacific warm pool), where there is increased albedo, decreased absorbed solar radiation at the surface, stronger surface westerlies, enhanced westward currents, lower temperatures, and decreased precipitation and evaporation. However, the weakened convection over the tropical western Pacific Ocean alters the large-scale circulation in the tropics such that there is increased upper-level divergence over tropical land areas and the tropical Indian Ocean. This results in increased precipitation in those regions and intensified monsoonal regimes. The enhanced precipitation over tropical land areas produces increased clouds and albedo and wetter and cooler land surfaces. These additional contributions to decreased absorbed solar input at the surface combine with similar changes over the tropical oceans to produce the global cooling associated with the stronger cloud albedo feedback. Increased low-level moisture convergence and precipitation over the tropical Indian Ocean enhance slightly the super greenhouse effect there. But the stronger cloud albedo feedback is still the dominant effect, although cooling of SSTs in that region is less than in the tropical western Pacific Ocean. The sensitivity experiment demonstrates how a regional change of radiative forcing is quickly transmitted globally through a combination of radiative and dynamical processes in the coupled model. This study points to the uncertainties involved with the parameterization of cloud albedo and the major implications of such parameterizations concerning the maximum values of SST, global climate sensitivity, and climate change.

A magnetospheric magnetic field model with flexible current systems driven by independent physical parameters

A tilt‐dependent magnetic field model of the Earth's magnetosphere with variable magnetopause standoff distance is presented. Flexible analytic representations for the ring and cross‐tail currents, each composed of elements derived from the Tsyganenko and Usmanov (1982) model, are combined with the fully shielded vacuum dipole configurations of Voigt (1981). The ring current, consisting of axially symmetric eastward and westward currents fixed about the dipole axis, resembles that inferred from magnetic field observations yet permits easy control of inner magnetospheric inflation. The cross‐tail current contains a series of linked current sheet segments which allow for the tilt‐dependent flexing of the current sheet in the x‐z plane and arbitrary variations in current sheet position and intensity along the length of the magnetotail. Although the current sheet does not warp in the y‐z plane, changes in the shape and position of the neutral sheet with dipole tilt are consistent with both MHD equilibrium theory and observations. In addition, there is good agreement with observed ΔB profiles and the average equatorial contours of magnetic field magnitude. While the dipole field is rigorously shielded within the defined magnetopause, the ring and cross‐tail currents are not similarly confined, consequently, the model's region of validity is limited to the inner magnetosphere. The model depends on four independent external parameters, namely, (1) the dipole tilt angle, (2) the magnetopause standoff distance, (3) the midnight equatorward boundary of the diffuse aurora, and (4) the geomagnetic index Dst. In addition, we present a simple but limited method of simulating several substorm related magnetic field changes associated with the disruption of the near‐Earth cross‐tail current sheet and collapse of the midnight magnetotail field region. These include the classic dipolarization of the near‐Earth field and the reduction of the far‐tail equatorial field accompanying current sheet thinning. This feature further facilitates the generation of magnetic field configuration time sequences useful in plasma convection simulations of real magnetospheric events.

The source of 90‐day oscillations at Wake Island

Energetic 90‐day oscillations of sea level have been intermittently observed at Wake Island in the western tropical Pacific during the past 2 decades. The oscillations tend to occur about 1.5 years after El Niño‐Southern Oscillation events, to have amplitudes of 10–15 cm, and to persist for about 1 year. Sea surface heights from the Geosat altimeter are used to establish that these signals take the form of Rossby waves and have an energy source near the Big Island of Hawaii, which lies 40° of longitude to the east. Sea level and upper layer currents from an eddy‐resolving numerical model are examined and suggest that the energy source is eddies generated off the Big Island of Hawaii. These eddies appear to be associated with westward currents that intermittently impinge on the island. Several alternate hypotheses are also discussed and rejected.

Double structure of ionospheric conductivity in the midnight auroral oval during a substorm

Measurements of precipitating particles on board DMSP F7 spacecraft are used to analyze the distribution of ionospheric conductance in the midnight auroral zone during substorms. The distribution is compared with the meridional profile of ionospheric currents calculated from magnetic data from the Kara meridional chain. Two regions of high Hall conductance are found; one of them is the traditional auroral zone, at latitudes 64–68°, and the other is a narrow band at latitudes 70–73°. The position of high conductance zones is in agreement with the location of the intense westward currents. The accelerated particle population is typical of electrons E e > 5 keV in the high conductance region.

Hybrid state of the tail magnetic configuration during steady convection events

Previous observations have shown that during periods of steady magnetospheric convection (SMC) a large amount of magnetic flux crosses the plasma sheet (corresponding to ∼10° wide auroral oval at the nightside) and that the magnetic configuration in the midtail is relaxed (the current sheet is thick and contains enhanced BZ). These signatures are typical for the substorm recovery phase. Using near‐geostationary magnetic field data, magnetic field modeling, and a novel diagnostic technique (isotropic boundary algorithm), we show that in the near‐Earth tail the magnetic configuration is very stretched during the SMC events. This stretching is caused by an intense, thin westward current. Because of the strongly depressed BZ, there is a large radial gradient in the near‐tail magnetic field. These signatures have been previously associated only with the substorm growth phase. Our results indicate that during the SMC periods the magnetic configuration is very peculiar, with co‐existing thin near‐Earth current sheet and thick midtail plasma sheet. The deep local minimum of the equatorial Bz that develops at R ∼ 12 RE is consistent with steady, adiabatic, Earthward convection in the midtail. These results impose constraints on the existing substorm theories, and call for an explanation of how such a stressed configuration can persist for such a long time without tail current disruptions that occur at the end of a substorm growth phase.

Filamentary structure of the westward electrojet in the midnight sector auroral distribution during substorms: comparison with Viking auroral observations

The relationship between equivalent electric currents, auroral absorption and aurora structures in the midnight auroral distribution is examined using the ground magnetic and riometer observations along the Kara meridional chain of stations and auroral images obtained by the Viking spacecraft. Equivalent currents are calculated by the method of Kotikov et al. [(1987) Geophysica 23, 143] on the basis of the magnetic data. A filamentary structure of westward currents is found in the midnight auroral electrojet during substorm expansion phase. This structure develops in the poleward part of the auroral distribution only in those cases when intense auroral absorption spreads to the appropriate latitudes, and these structured westward currents are observed in areas where the UV auroral luminosity is high. Justifications that the calculated equivalent currents are real ionospheric currents are presented. Calculation of the ionospheric conductivity based on the measurements of precipitating electrons from DMSP-F7 shows that the conductivity in the regions of the westward filaments is enhanced.

Thermal excursions in the ocean at the Cretaceous—Tertiary boundary (northern Morocco): δ 18O record of phosphatic fish debris

High precision oxygen isotope analyses were made of phosphate extracted from 17 samples of nektonic and benthic fish debris sampled across the stratigraphic Cretaceous—Tertiary boundary in northern Morocco. A refinement of the silver phosphate method was used to isolate phosphate from biogenic materials. Measured δ 18O values of 18.6–20.5‰ are interpreted as reflecting high-resolution thermal variations that affected the ocean water column of the western Tethys. The warm (27°C) water masses that characterized Maastrichtian times underwent rapid cooling and stabilized at an average temperature of 19°C during the Dano-Montian and Thanetian. This period of constant and cool temperature was followed by a relatively rapid but more gradual warming to about 25°C achieved in the Middle Ypresian. Significant small shifts in δ 18O values between nektonic and benthic fauna recorded only during the stages of rapid warming or cooling may correspond to averaged thermal differences within the water column that developed in response to global climatic changes. The indicated temperature distribution could have been caused by thermal changes in the atmosphere rather than some signal carried by deep ocean currents. The oxygen isotope data coupled with previous measurements of REE and ϵ Nd(T) on the same samples support the suggestion that paleo-Pacific westward currents progressed as far as the northwestern part of the African platform at the end of the Cretaceous period.

Altitude variations of ionospheric currents at auroral latitudes

On the basis of updated EISCAT experiments, the first full derivation of the ionospheric current density of the auroral electrojets at six different altitudes are presented. It is found that current vectors at different altitudes are quite different, although the eastward and westward currents prevail in the evening and morning sectors, respectively, once the currents are integrated over altitude. The eastward electrojet becomes almost northward whilst the westward electrojet becomes almost southward, at the highest altitude, 125 km, in this study. The physical implications of these characteristics are discussed.

1993 author index

Assessments of hurricane-induced environmental impacts are important to coastal management and risk analysis of ecosystems. In this study, a previously-developed remote sensing model for non-hurricane conditions by Wang et al. [Wang, H. Q., Hladik, C. M., Milla, K., Huang, W. R., Edmiston, L., Harwell, M. A., & Schalles, J. F. (in press). Detecting and mapping water quality indicators in Apalachicola Bay, Florida using MODIS Terra 250-m imagery. International Journal of Remote Sensing] has been substantially enhanced to investigate the impact of Hurricane Frances on total suspended solid (TSS) concentrations in Apalachicola Bay, Florida, USA. The remote sensing model uses 250-m Moderate Resolution Imaging Spectroradiometer (MODIS) to map TSS concentrations in the Bay. Eleven additional satellite imageries of MODIS were used in the model improvement and calibration. TSS concentration computation in the present model has been substantially improved by using a two-step process: firstly producing atmospheric correction intercept by an approach of in-water reflectance regression, and then building the regression model (R2 = 0.8534, n = 25) between 250-m MODIS reflectance and observed TSS concentrations, which includes an extreme high TSS concentration data of 208 mg/L for severe storm or hurricane condition. Also, we carried out the validation of model (RMSE = 5.5 mg/L, n = 21). MODIS-derived TSS maps show substantial increases of TSS concentrations in the Bay during the passage of Hurricane Frances (the average TSS and maximum concentration about 54.3 mg/L and 165 mg/L in the Bay respectively) compared to under no-storm or -hurricane condition ( the average TSS and maximum concentration were approximately 24–27 mg/L and 58–64 mg/L). In comparison to those before and 5-days after the passage of the hurricane, the average TSS concentration in the Bay was twice higher while the maximum TSS concentration increased almost three times during the hurricane. This indicates that strong winds during the hurricane have caused strong sediment re-suspension. The spatial variations of TSS concentrations were analyzed by applying the hydrodynamic characteristics of wind-induced flow and tidal currents as described by Huang [Huang, W., Jones, K., & Wu, T. (2002). Modeling surface wind effects on subtidal salinity in Apalachicola Bay. Estuarine, Coastal and Shelf Science, 55(1), 33−46; Huang, W., Sun, H., Nnaji, S., & Jones, K. (2002). Tidal hydrodynamics in a multiple inlet estuary: Apalachicola Bay. International Journal of Coastal Research, 18(4), 674−684], which show westward currents in the Bay under westward wind condition. Therefore, the southwestward wind (about 50° from the north) during the hurricane induced southwestward currents and transport that resulted in the high TSS concentrations near West Pass in the Bay and the Gulf. Within the Bay, TSS concentrations were generally higher in the southern portion of the Bay, which was due mainly to transport by the combination of southwestward wind and southward residual flow from the Apalachicola River.

Magnetospheric equilibrium with anisotropic pressure

Self‐consistent magnetospheric equilibria with anisotropic pressure are obtained by employing an iterative metric method for solving the inverse equilibrium equation in an optimal flux coordinate system. A method of determining plasma parallel and perpendicular pressures from either analytic particle distributions or particle distributions measured along a satellite's path is presented. The numerical results of axisymmetric magnetospheric equilibria including the effects of finite beta, pressure anisotropy, and boundary conditions are presented for a bi‐Maxwellian particle distribution. For the isotropic pressure cases the finite beta effect produces an outward expansion of the constant magnetic flux surfaces in relation to the dipole field lines, and along the magnetic field the toroidal ring current is maximum at the magnetic equator. The effect of pressure anisotropy is found to further expand the flux surfaces outward. Along the magnetic field lines the westward ring current can be peak away from the equator owing to an eastward current contribution resulting from pressure anisotropy. As pressure anisotropy increases, the peak westward current can become more singular. The outer boundary flux surface has a significant effect on the magnetospheric equilibrium. For the outer flux boundary resembling the dayside compressed flux surface due to solar wind pressure, the deformation of the magnetic field can be quite different from that for the outer flux boundary resembling the taillike flux surface.