Zonal Resolution Research Articles

Unexpected Regional Zonal Structures in Low Latitude Ionosphere Call for a High Longitudinal Resolution of the Global Ionospheric Maps

This study reports unexpected strong longitudinal structures from Global Navigation Satellite System (GNSS) derived total electron content (TEC) observations in the low-latitude ionosphere over Asia. The observations during 2019–2020 show diverse patterns in the zonal difference of regional TEC, even under geomagnetically quiet conditions. The TEC in the northern hemisphere occasionally exhibits drastic zonal gradients. The intense regional gradients in TEC span a longitudinal extent of about 20°. The higher values may appear on the east or the west side. Strong zonal gradients may appear in all seasons, regardless of geomagnetically quiet or active conditions. The 15 December 2019 and 16 March 2020 cases depict an intense zonal differences cluster in the narrow latitudinal band of 16°N to 28°N, spanning a regional scale smaller than the normal longitudinal structures. In contrast, the Global Ionospheric Maps (GIMs) with a longitudinal resolution of 5° show a much flatter zonal picture. Such intense and regional-scale zonal structures in the low-latitude ionosphere call for a high zonal resolution of GIMs in terms of better geographically distributed observations. Notably, no counterpart regional structures are found at the conjugated points in the southern hemisphere during the two cases. Although the physical drivers are not certain, the appearance only in the northern hemisphere possibly excludes the dominant contribution to forming the regional structures from the equatorial electric field.

THE APPLICATION OF THE 't' TEST AND MARKOV CHAIN ANALYSIS IN BIOSTRATIGRAPHY OF 'X' WELL

There is no habit in biostratigraphers to apply the statistic methods to solve problems in their jobs, whereas in fact these methods are very useful when conventional ways failed. The use of this method has become very important in reservoir scale where microfossil content is low and indicator species is rare or absent. Applying biozonation in reservoir scale is much less reliable since reservoir layers are mostly below zonal resolution, so that the application of high resolution biostratigraphy is needed. In this case, the integration of biometric study and 't' or 'f' test can be used to define bioevent precisely. In sequence stratigraphy, data of depositional environment in various system tracts that determined using microfossil assemblage are very important. However, for the reasons of barren or no samples, this information might not be obtained by biostratigraphy or other methods. Due to the geological cycle and repeatable nature of depositional sequence, Markov Chain analysis can be used to predict the lost information about environment of deposition.

Topographical and zonal patterns of T2 relaxation in osteoarthritic tibial cartilage by low- and high-resolution MRI

PurposeThis study aimed to establish the topographical and zonal T2 patterns of multi-resolution MRI in medial tibial cartilage in a canine model of osteoarthritis (OA), initiated by the anterior cruciate ligament (ACL) transection surgery, and studied after 8-weeks and 12-weeks post-surgery. MethodsArticular cartilage from healthy, two stages of contralateral, and of OA knees were quantitatively imaged by the MRI T2 protocols at two imaging resolutions (100 and 17.6 μm/pixel). The zonal T2 changes at five topographical locations (anterior (AMT), exterior (EMT), posterior (PMT), central (CMT) and interior (IMT) medial tibia) and subsequent two averaged regions (covered by meniscus and exposed) were analyzed. At each location, full-thickness cartilage was studied in four sub-tissue zones (superficial, transitional, upper and lower radial zones). ResultsTissue degradation can be detected by measurable changes of T2, which is resolution- and orientation-dependent. T2 changes ranging from +28.82% increase (SZ, PMT) to −23.15% decrease (RZ1, AMT) in healthy to disease (8C), with the largest increase of T2 in the surface tissue. Various location-dependent patterns of degradation are found over the tibial surface, most commonly shown in early-stage OA (8C) on the anterior site, different from the posterior. Finally, the contralateral cartilage has specific degradation patterns, different from those in OA cartilage. ConclusionsThis is the first quantitative and highest multi-resolution characterization of cartilage at five topographical locations over the medial tibial plateau with fine zonal resolution in an animal model of OA, which would benefit future investigation of human OA in clinics.

Palynology and depositional environments of the Middle – Late Triassic (Anisian – Rhaetian) Kobbe, Snadd and Fruholmen formations, southern Barents Sea, Arctic Norway

The Middle to Upper Triassic series in the Norwegian Barents Sea represents an important target for hydrocarbon exploration. However, the dating and correlation of these rocks are problematic due to the scarcity of age-diagnostic macrofossils, lateral facies variation and the overall thickness of the succession. Palynology has proven to be a useful dating tool but further work is necessary to improve the zonal resolution, particularly for the Upper Triassic Series. The current paper presents a detailed palynostratigraphy of the Middle – Upper Triassic succession in four exploration wells (7120/12-2, 7228/2-1s, 7-1a and 9-1s) drilled in the Hammerfest and Nordkapp basins. Eleven informal palynological zones are described from the stratigraphic interval spanning the Kobbe, Snadd and Fruholmen formations, which constitute regionally significant hydrocarbon source and reservoir rock facies. The results of this study contribute to a higher resolution palynostratigraphy for the Middle to Upper Triassic strata of the southern Barents Sea (SBS), and an improved correlation with the stratigraphy of the Svalbard Archipelago. Palynofacies data for the succession, presented here for the first time, indicates depositional environments ranging from fluvio-deltaic to offshore marine.

Gradual rasterization: redefining spatial resolution in transport modelling

It is a challenge to find the appropriate level of spatial resolution in transport modelling. While the zone system has substantial influence on model results, the resolution and design of zones is rarely analyzed systematically, and even less commonly adjusted to a specific modelling need. In this paper we present a new methodology to automatically create a new zone system based on the quadtree algorithm specific to transport modelling. Gradual raster cells are generated, where smaller raster cells tend to be used in urban areas and larger raster cells dominate in low-density, rural areas. As changing the zonal resolution affects the number of intrazonal and interzonal trips, an algorithm has been developed that adjusts intrazonal trips in line with the network resolution. Trip tables of a travel demand model for the state of Georgia, USA were disaggregated using this new zone system of gradual raster cells. The traffic assignment results validate significantly better than when using the original zone system.

230Th and 231Pa on GEOTRACES GA03, the U.S. GEOTRACES North Atlantic transect, and implications for modern and paleoceanographic chemical fluxes

The long-lived uranium decay products 230Th and 231Pa are widely used as quantitative tracers of adsorption to sinking particles (scavenging) in the ocean by exploiting the principles of radioactive disequilibria. Because of their preservation in the Pleistocene sediment record and through largely untested assumptions about their chemical behavior in the water column, the two radionuclides have also been used as proxies for a variety of chemical fluxes in the past ocean. This includes the vertical flux of particulate matter to the seafloor, the lateral flux of insoluble elements to continental margins (boundary scavenging), and the southward flux of water out of the deep North Atlantic. In a section of unprecedented vertical and zonal resolution, the distributions of 230Th and 231Pa across the North Atlantic shed light on the marine cycling of these radionuclides and further inform their use as tracers of chemical flux. Enhanced scavenging intensities are observed in benthic layers of resuspended sediments on the eastern and western margins and in a hydrothermal plume emanating from the Mid-Atlantic Ridge. Boundary scavenging is clearly expressed in the water column along a transect between Mauritania and Cape Verde which is used to quantify a bias in sediment fluxes calculated using 230Th-normalization and to demonstrate enhanced 231Pa removal from the deep North Atlantic by this mechanism. The influence of deep ocean ventilation that leads to the southward export of 231Pa is apparent. The 231Pa/230Th ratio, however, predominantly reflects spatial variability in scavenging intensity, complicating its applicability as a proxy for the Atlantic meridional overturning circulation.

Impact of ocean model resolution on CCSM climate simulations

The current literature provides compelling evidence suggesting that an eddy-resolving (as opposed to eddy-permitting or eddy-parameterized) ocean component model will significantly impact the simulation of the large-scale climate, although this has not been fully tested to date in multi-decadal global coupled climate simulations. The purpose of this paper is to examine how resolved ocean fronts and eddies impact the simulation of large-scale climate. The model used for this study is the NCAR Community Climate System Model version 3.5 (CCSM3.5)—the forerunner to CCSM4. Two experiments are reported here. The control experiment is a 155-year present-day climate simulation using a 0.5° atmosphere component (zonal resolution 0.625 meridional resolution 0.5°; land surface component at the same resolution) coupled to ocean and sea-ice components with zonal resolution of 1.2° and meridional resolution varying from 0.27° at the equator to 0.54° in the mid-latitudes. The second simulation uses the same atmospheric and land-surface models coupled to eddy-resolving 0.1° ocean and sea-ice component models. The simulations are compared in terms of how the representation of smaller scale features in the time mean ocean circulation and ocean eddies impact the mean and variable climate. In terms of the global mean surface temperature, the enhanced ocean resolution leads to a ubiquitous surface warming with a global mean surface temperature increase of about 0.2 °C relative to the control. The warming is largest in the Arctic and regions of strong ocean fronts and ocean eddy activity (i.e., Southern Ocean, western boundary currents). The Arctic warming is associated with significant losses of sea-ice in the high-resolution simulation. The sea surface temperature gradients in the North Atlantic, in particular, are better resolved in the high-resolution model leading to significantly sharper temperature gradients and associated large-scale shifts in the rainfall. In the extra-tropics, the interannual temperature variability is increased with the resolved eddies, and a notable increases in the amplitude of the El Nino and the Southern Oscillation is also detected. Changes in global temperature anomaly teleconnections and local air-sea feedbacks are also documented and show large changes in ocean–atmosphere coupling. In particular, local air-sea feedbacks are significantly modified by the increased ocean resolution. In the high-resolution simulation in the extra-tropics there is compelling evidence of stronger forcing of the atmosphere by SST variability arising from ocean dynamics. This coupling is very weak or absent in the low-resolution model.

Meridional changes in water mass distributions off NW Africa during November 2007/2008

An optimum multiparameter analysis was applied to a data set for the eastern boundary of the North Atlantic subtropical gyre, gathered during November of two consecutive years and spanning from 16 to 36º N. This data set covers over 20º of latitude with good meridional and zonal resolution over the whole coastal transition zone. The contribution from six water types in the depth range between 100 and 2000 m is solved. In the 100 to 700 m depth range the central waters of southern and northern origin meet abruptly at the Cape Verde Frontal Zone. This front traditionally has been reported to stretch from Cape Blanc, at about 21.5º N, to the Cape Verde Islands, but in our case it penetrates as far as 24º N over the continental slope. South of 21º N latitude we actually find a less saline and more oxygenated variety of South Atlantic Central Water, which we ascribe to less diluted equatorial waters. In the 700 to 1500 m depth range the dominant water type is a diluted form of Antarctic Intermediate Water (AAIW), whose influence smoothly disappears north of the Canary Islands as it is replaced by Mediterranean Water (MW); at latitudes where both water masses coexist, we observe MW offshore while AAIW is found near-shore. North Atlantic Deep Water is the dominating water type below about 1300/1700 m depth south/north of the Canary Islands; this abrupt change in depth suggests the existence of different paths for the deep waters reaching both sides of the archipelago.

Predicting the performance of an office under climate change: A study of metrics, sensitivity and zonal resolution

Climate change is expected to have significant impact on the future thermal performance of buildings. Building simulation and sensitivity analysis can be employed to predict these impacts, guiding interventions to adapt buildings to future conditions. This article explores the use of simulation to study the impact of climate change on a theoretical office building in the UK, employing a probabilistic approach. The work studies (1) appropriate performance metrics and underlying modelling assumptions, (2) sensitivity of computational results to identify key design parameters and (3) the impact of zonal resolution. The conclusions highlight the importance of assumptions in the field of electricity conversion factors, proper management of internal heat gains, and the need to use an appropriately detailed zonal resolution.

A conservative Fourier-finite-element method for solving partial differential equations on the whole sphere

Solving transport equations on the whole sphere using an explicit time stepping and an Eulerian formulation on a latitude–longitude grid is relatively straightforward but suffers from the pole problem: due to the increased zonal resolution near the pole, numerical stability requires unacceptably small time steps. Commonly used workarounds such as near-pole zonal filters affect the qualitative properties of the numerical method. Rigorous solutions based on spherical harmonics have a high computational cost. The numerical method we propose to avoid this problem is based on a Galerkin formulation in a subspace of a Fourier-finite-element spatial discretization. The functional space we construct provides quasi-uniform resolution and high-order accuracy, while the Galerkin formalism guarantees the conservation of linear and quadratic invariants. For N2 degrees of freedom, the computational cost is 𝒪(N2logN), dominated by the zonal Fourier transforms. This is more than with a finite-difference or finite-volume method, which costs 𝒪(N2), and less than with a spherical harmonics method, which costs 𝒪(N3). Differential operators with latitude-dependent coefficients are inverted at a cost of 𝒪(N2). We present experimental results and standard benchmarks demonstrating the accuracy, stability and efficiency of the method applied to the advection of a scalar field by a prescribed velocity field and to the incompressible rotating Navier–Stokes equations. The steps required to extend the method towards compressible flows and the Saint-Venant equations are described. Copyright © 2009 Royal Meteorological Society

Evolution of the Asian monsoon and the coupled atmosphere-ocean system in the tropics associated with the uplift of the Tibetan Plateau – A simulation with the MRI coupled atmosphere-ocean GCM

Large-scale orographies, such as the Tibetan Plateau and the Rocky mountains, play an important role to form the present global climate system (Kutzbach et al. 1993). The large-scale orography has dynamical and thermodynamical effects to the atmosphere, which in turn influences the ocean circulation through the atmosphere-ocean interaction. Many previous studies investigated the effect of mountains on the Asian summer monsoon using atmospheric general circulation models (AGCMs), by comparing the equilibrium climate states with and without mountains (Tibetan Plateau) and that without mountains (e.g., Hahn and Manabe 1974). However, these studies could not reveal to what degree the change of mountain height affects a climate and monsoon. It can also be postulated that the effect of mountains does not necessarily change linearly with increasing mountain heights. In addition, the Asian summer monsoon has been noted to have an active role of the interannual variability of the coupled atmosphereocean system in the tropical Pacific through the east-west circulation (e.g., Yasunari 1990, Yasunari and Seki 1992). The coupling of the Asian summer monsoon with the tropical Pacific Ocean system may, therefore, be crucial for the formation and variability of the tropical climate. An essential issue may be to investigate to what extent and how the tropical climate system, which is a coupled system of the Pacific/Indian Oceans and the Asian monsoon, is regulated by the uplift of the Tibetan plateau and other large-scale orographies. Thus, to understand changes of the atmosphere/ocean coupled system associated with gradual uplift of the orography, a numerical experiment was conducted using the Meteorological Research Institute (MRI) coupled atmosphere–ocean general circulation model I (CGCM-I) (Abe et al. 2003). The MRI CGCMI is the global grid model. Horizontal resolution of atmospheric part of the CGCM is 5° in longitude and 4° in latitude, and the vertical is 15 layers. The oceanic part has nonuniform meridional resolution ranging from 0.5° to 2.0°, with a finer grid in the tropics, fixed zonal resolution of 2.5°, and 21 layers vertically.

Calibrating the Devonian Time Scale: A synthesis of U–Pb ID–TIMS ages and conodont stratigraphy

The recalibrated Devonian time scale represents an important improvement of Devonian chronology regarding two aspects. Firstly, a data set of 13 biostratigraphically well-bracketed U–Pb ID–TIMS zircon and monazite ages constitutes the framework of the scale. Secondly, approximately time-linear biostratigraphic scales have been used for the interpolation between the isotopic ages. The new construction thus represents a ‘biochronometric’ time scale, which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary. The method of interpolation applied also enables the projection of the geochronological error onto the time scale. According to the newly calibrated scale, the Devonian lasted 57.4 ± 5.7 Ma from 418.1 ± 3.0 to 360.7 ± 2.7 Ma. This is, compared to previously published time scales, the longest time span ever calculated for this period. The age interpolations for the eight stage boundaries are: Famennian–Tournaisian (= Devonian–Carboniferous) 360.7 ± 2.7 Ma Frasnian–Famennian 376.1 ± 3.6 Ma Givetian–Frasnian 383.7 ± 3.1 Ma Eifelian–Givetian 388.1 ± 2.6 Ma Emsian–Eifelian 391.9 ± 3.4 Ma Pragian–Emsian 409.1 ± 3.8 Ma Lochkovian–Pragian 412.3 ± 3.5 Ma Pridolian–Lochkovian (= Silurian–Devonian) 418.1 ± 3.0 Ma The duration of the Middle Devonian is calibrated here as quite short with 8.2 Ma and the Emsian and the Famennian are the longest stages with interpolated durations of 17.2 and 15.4 Ma, respectively. Together, all Devonian stages contain 57 conodont zones (including subzones, according to the standard conodont zonation) giving a mean duration of about 1 Ma. In the highly resolved part of the time scale (mid-Eifelian to the Devonian–Carboniferous boundary), zonal resolution averages 0.6 Ma. In contrast, the lowest resolution is shown in the early Emsian to mid-Eifelian interval with zonal durations of up to 5.5 Ma ( serotinus Zone).

Waves and Instabilities for Model Tropical Convective Parameterizations

Models of the tropical atmosphere with crude vertical resolution are important as intermediate models for understanding convectively coupled wave hierarchies and also as simplified models for studying various strategies for parameterizing convection and convectively coupled waves. Simplified models are utilized in a detailed analytical study of the waves and instabilities for model convective parameterizations. Three convection schemes are analyzed: a strict quasi-equilibrium (QE) scheme and two schemes that attempt to model the departures from quasi equilibrium by including the shorter timescale effects of penetrative convection, the Lagrangian parcel adjustment (LPA) scheme and a new instantaneous convective available potential energy (CAPE) adjustment (ICAPE) scheme. Unlike the QE parameterization scheme, both the LPA and ICAPE schemes have scale-selective finite bands of unstable wavelengths centered around typical cluster and supercluster scales with virtually identical growth rates and wave structure. However, the LPA scheme has, in addition, two nonphysical superfast parasitic waves that are artifacts of this parameterization while such waves are completely absent in the new ICAPE parameterization. Another topic studied here is the fashion in which an imposed barotropic mean wind triggers a transition to instability in the Tropics through suitable convectively coupled waves; this is the simplest analytical problem for studying the influence of midlatitudes on convectively coupled waves. For an easterly barotropic mean flow with the effect of rotation included, both supercluster-scale moist Kelvin waves and cluster-scale moist mixed Rossby‐gravity waves participate in the transition to instability. The wave and stability properties of the ICAPE parameterization with rotation are studied through a novel procedure involving complete zonal resolution but low-order meridional truncation. Besides moist Kelvin, mixed Rossby‐gravity, and equatorial Rossby waves, this approximation retains other slowly propagating moist gravity waves in a consistent fashion.

Equatorial Circulation of a Global Ocean Climate Model with Anisotropic Horizontal Viscosity

Horizontal momentum flux in a global ocean climate model is formulated as an anisotropic viscosity with two spatially varying coefficients. This friction can be made purely dissipative, does not produce unphysical torques, and satisfies the symmetry conditions required of the Reynolds stress tensor. The two primary design criteria are to have viscosity at values appropriate for the parameterization of missing mesoscale eddies wherever possible and to use other values only where required by the numerics. These other viscosities control numerical noise from advection and generate western boundary currents that are wide enough to be resolved by the coarse grid of the model. Noise on the model gridscale is tolerated provided its amplitude is less than about 0.05 cm s−1. Parameter tuning is minimized by applying physical and numerical principles. The potential value of this line of model development is demonstrated by comparison with equatorial ocean observations. In particular, the goal of producing model equatorial ocean currents comparable to observations was achieved in the Pacific Ocean. The Equatorial Undercurrent reaches a maximum magnitude of nearly 100 cm s−1 in the annual mean. Also, the spatial distribution of near-surface currents compares favorably with observations from the Global Drifter Program. The exceptions are off the equator; in the model the North Equatorial Countercurrent is improved, but still too weak, and the northward flow along the coast of South America may be too shallow. Equatorial Pacific upwelling has a realistic pattern and its magnitude is of the same order as diagnostic model estimates. The necessary ingredients to achieve these results are wind forcing based on satellite scatterometry, a background vertical viscosity no greater than about 1 cm2 s−1, and a mesoscale eddy viscosity of order 1000 m2 s−1 acting on meridional shear of zonal momentum. Model resolution is not critical, provided these three elements remain unaltered. Thus, if the scatterometer winds are accurate, the model results are consistent with observational estimates of these two coefficients. These winds have larger westward stress than NCEP reanalysis winds, produce a 14% stronger EUC, more upwelling, but a weaker westward surface flow. In the Indian Ocean the seasonal cycle of equatorial currents does not appear to be overly attenuated by the horizontal viscosity, with differences from observations attributable to interannual variability. However, in the Atlantic, the numerics still require too large a meridional viscosity over too much of the basin, and a zonal resolution approaching 1° may be necessary to match observations. Because of this viscosity, increasing the background vertical viscosity slowed the westward surface current; opposite to the response in the Pacific.

Factors Affecting Heat Transport in an Ocean General Circulation Model

A global ocean general circulation model with idealized geometry and coupled to a simple representation of atmospheric energy fluxes is used to investigate which physical factors determine meridional heat transport. A particular focus is on causes for the common underestimation of heat transport in ocean general circulation models. The model is also forced by an idealized wind stress and moisture flux profiles. The zonal average of surface heat flux is obtained from a simple radiation parameterization and the divergence of observed atmospheric heat transport. In addition, zonal mixing in the atmosphere is implied by the relaxation of the sea surface temperature (SST) to its zonal average. A finite relaxation timescale results in a substantial increase in the meridional mass overturning in the “Atlantic” basin compared to the case with “infinitely efficient” zonal atmospheric mixing, owing to the admittance of zonal SST gradients. However, heat transport changes only by a small amount. When atmospheric zonal mixing is changed to interbasin mixing, meridional heat transport increases significantly. Doubling the width of the Pacific basin leads to a large increase in the Pacific heat transport, induced by both the meridional overturning and the horizontal gyre circulations. If the horizontal viscosity is decreased and the zonal resolution is increased near the boundaries, the resulting larger speed of the western boundary currents causes a noticable increase in the Atlantic basin’s heat transport. The introduction of the Gent–McWilliams eddy parameterization leads to a substantial decrease in the strength of the overturning circulation in the Atlantic basin, presumably because the overall amount of diapycnal mixing is reduced. However, the decrease in the heat transport is much smaller because the thermocline is sharper and the deep ocean colder, resulting in enhanced vertical temperature contrast. Apparent disagreements with and among previous results are explained through the different effects of diapycnal mixing in the North Atlantic and elsewhere in the model.

The Rate Zonal Separation of Organelles from Dilute Suspensions: The Problem of a Large Sample Volume

Transport vesicles that deliver proteins to the cell surface can be isolated by incubating cells that have been permeabilized by mechanical or chemical techniques in a high-K medium containing an ATP regenerating system. The vesicles released from permeabilized cells are, however, obtained as a very dilute suspension in the incubation solution. This presents a problem for the preparative separation of specific populations of vesicles by velocity sedimentation, because the small sample volume capacity of traditional glycerol or sucrose velocity gradients requires that the vesicles first be concentrated by sedimentation or that very small amounts of vesicles be loaded onto a gradient. We have addressed the problem of the loss of zonal resolution produced by the loading of large sample volumes, and we propose that high-viscosity Ficoll gradients can be used effectively to restore the resolution of zones when substantially larger sample volumes of dilute suspensions must be loaded onto velocity gradients.

Total ozone/UVB monitoring and forecasting: Impact of clouds and the horizontal resolution of satellite retrievals

This study compares the horizontal resolution of solar backscatter ultraviolet 2 (SBUV2) total ozone (Ω) fields with those from the new NASA earth probe (EP) and Advanced Earth Observing Satellite (ADEOS) total ozone mapping spectrometer (TOMS) side‐scanning photometers. The latter instruments provide high resolution, easily resolving the medium‐scale waves (4–7 wavelengths around the Earth at a fixed latitude) that dominate day‐to‐day midlatitude Ω fluctuations. In contrast, SBUV2 instruments do not, since these devices measure only at nadir (straight downward), yielding ∼14 measurements daily at a given latitude. This method has consequences not only for global monitoring of Ω and ultraviolet B (UVB, 290–320 nm), but also for short‐timescale Ω and UVB predictions in summer because timescales of a few days are coupled to medium horizontal scales (several thousand kilometers) by baroclinic waves that typically force the observed Ω variations. We use a simple Ω prediction model to test the use of Ω fields from TOMS and SBUV instruments and show that the higher zonal resolution from side‐scanning TOMS instruments results in sizeable reductions in Ω prediction errors, whereas predictions using SBUV2 Ω are no better than persistence (where tomorrow's Ω is taken to be today's) in the biologically important summer months. Daily variabilities (equivalent to errors in 24‐hour persistence forecasting of Ω) in high‐resolution TOMS midlatitude ozone during summer are shown to sometimes exceed 50 Dobson units, producing daily changes of 20% or greater in computed ground‐level clear‐sky UV index. This study demonstrates that even these large daily changes in measured or predicted clear‐sky UV are usually smaller than daily UV changes associated with transient clouds. While surface UVB variability is dominated by local cloudiness variations, Ω forecasts can enhance UVB prediction in relatively cloud free regions such as the U.S. desert southwest and in stagnant high‐pressure regimes that can persist for 1–2 weeks in summer. Furthermore, as weather forecast models increase in accuracy of forecasted cloudiness, accurate predictions will allow more accurate UVB forecasts for cloud free regions, the locations where they are most needed. Results from the present paper show, however, that high‐resolution TOMS‐like side‐scanning Ω measurements are required for ozone and UVB monitoring and prediction, rather than SBUV‐type nadir observations.

Indonesian throughflow in a coupled general circulation model

The Indonesian throughflow is analyzed in an extended simulation with a coupled ocean‐atmosphere model. The model, developed by the Max‐Planck‐Institut für Meteorologie, Hamburg, Germany, combines an atmospheric general circulation model at T42 resolution (2.8° latitude by 2.8° longitude) and a primitive equation ocean model with zonal resolution of 2.8° and a meridional resolution of 0.5° in the tropics and is coupled without flux correction equatorward of a latitude of 60°. The onset and strength of the monsoon in the Indonesian waters agree well with climatology, and many aspects of the observed temperature fields in the eastern Indian Ocean and Timor Seas are found in simulation. Differences between simulation and observations of temperature occur in mean and seasonal cycles in the far western Pacific. The annual cycles of sea level along the coast of Sumatra and Java are simulated satisfactorily. The simulated throughflow transports on average 13.8 Sv (106m3S−1) from the Pacific to the Indian Ocean. The vertically averaged (barotropic) component of the throughflow has a seasonal range of 13.1 Sv and is weakest in February and strongest in July. In contrast, deviations from the vertical average of the throughflow (baroclinic) are strongest in March and September. The average and seasonal cycle of the barotropic component of the throughflow are forced by winds over the Pacific and along the western coasts of Australia and South America, as described by the island rule. For closed Torres Strait, the contribution of the average bottom pressure torque is small, and friction closes the vorticity balance. For annual timescales, baroclinic flows affect the throughflow transport through the bottom pressure torque. The annual cycle of the baroclinic component of the throughflow is forced predominantly by winds over the Indonesian Seas. The throughflow exports 0.9 PW of heat from the Pacific into the Indian Ocean and is an important heat sink for the western Pacific. The throughflow is a major heat source for the Indian Ocean and is associated with reversal of the divergence of the meridional transport of heat south of 10°S that is balanced by heat fluxes from the ocean to the atmosphere.

Eustatic Curve for the Middle Jurassic--Cretaceous Based on Russian Platform and Siberian Stratigraphy: Zonal Resolution

We have used the stratigraphy of the central part of the Russian platform and surrounding regions to construct a calibrated eustatic curve for the Bajocian through the Santonian. The study area is centrally located in the large Eurasian continental craton, and was covered by shallow seas during much of the Jurassic and Cretaceous. The geographic setting was a very low-gradient ramp that was repeatedly flooded and exposed. Analysis of stratal geometry of the region suggests tectonic stability throughout most of Mesozoic marine deposition. The paleogeography of the region led to extremely low rates of sediment influx. As a result, accommodation potential was limited and is interpreted to have been determined primarily by eustatic variations. The central part of the Russian latform thus provides a useful frame of reference for the quantification of eustatic variations throughout the Jurassic and Cretaceous. The biostratigraphy of the Russian platform provides the basis for reliably determining age and eustatic events. The Mesozoic section of the central part of the Russian platform is characterized by numerous hiatuses. In this study, we filled the sediment gaps left by unconformities in the central part of the Russian platform with data from stratigraphic information from the more continuous stratigraphy of the neighboring subsiding regions, such as northern Siberia. Although these sections reflect subsidence, the time scale of variations in subsidence rate is probably long relative to the duration of the stratigraphic gaps to be filled, so the subsidence rate can be calculated and filtered from the stratigraphic data. We thus have compiled a more complete eustatic curve than would be p ssible on the basis of Russian platform stratigraphy alone. Relative sea level curves were generated by backstripping stratigraphic data from well and outcrop sections distributed throughout the central part of the Russian platform. For determining paleowater depth, we developed a model specifically designed for this region based on paleoecology, sedimentology, geochemistry, and paleogeography. The curve describes a series of high-frequency eustatic events superimposed on longer term trends. Many of the events identified from our study can be correlated to those found by Haq et al. (1988) and other sea level studies from other parts of the world, but there are significant differences in the relative magnitudes of events. Because the eustatic curve resulting from this study is based on a stable reference frame, the curve can be used in sedimentary basin modeling and as a tool for quantifying subsidence history from the stratigraphy of passive margins, basins, and other active regions.

Microstructure activity within a minifilament in the coastal transition zone

This paper presents observations of a dynamic minifilament and summarizes the findings of three microstructure surveys across and within the meandering current structures of the Coastal Transition Zone (CTZ). An actively turbulent minifilament is discussed and possible consequences of the small‐scale processes with regard to frontal dynamics are examined. Four different frontal structures were observed as part of the CTZ microstructure program, two resembling meanders and two characterized as filaments. Microstructure measurements included continuous rapid sampling vertical profiler (RSVP) (Caldwell et al., 1985) and acoustic Doppler current profiles (ADCP) profiling along meridional lines bisecting the frontal features. Common features of the two meanders observed in 1986: (Moum et al., 1988) and 1987: (Dewey and Moum, 1990) include offshore and onshore flow patterns (consistent with meridional sections through meanders), rapid temporal evolution of the frontal structures between consecutive (10–24 hour) transects, no elevated turbulent activity below the pycnocline, despite the enhanced current shears (quiescent core within central region where pycnocline is near surface), and approximate geostrophy of the dominant currents at scales > 10 km. A large filament, or jetlike feature observed in 1988 (Dewey et al., 1991) was characterized by off‐shore geostrophic flow, no enhanced turbulent activity, and significant asymmetry in the temperature, salinity and current fields, with stronger vorticity on the south (upwelled) side of the velocity maximum. An actively turbulent minifilament was also observed in 1988, and exhibited some characteristics not common to the larger meanders or filaments. A strongly divergent velocity signature was confined to the near‐surface layer (< 60 m), with a cool, uplifted core, possibly a result of localized upwelling and subsurface turbulent mixing. Below the surface mixed layer, elevated turbulent dissipation rates were coincident with regions of high shear and correspondingly low Ri. However, the buoyancy flux from turbulent mixing was estimated to be too low to have formed the cool surface signature of the minifilament. The estimated Rossby number (R0 = 1.3) for the minifilament suggests that significant departures from geostrophy are likely. However, due to the limited temporal and zonal resolution of the minifilament, no definitive ageostrophic analysis can be performed. Corresponding satellite images indicate that the observed structure, although narrow (10 km), may be as long as 100 km, be evolving over periods of days, and a common submesoscale feature in the swirling patterns revealed by advenced very high resolution radiometer (AVHRR).