Large-scale SST anomalies associated with subtropical fronts in the western North Atlantic during FASINEX

We describe the large-scale variability of sea surface temperature (Ts) and fronts in the western North Atlantic Subtropical Convergence Zone from January–June 1986 within an approximately 11° longitude by 10° latitude domain. Fronts were primarily found within interconnected bands separated by \u3c500 km that tended to be located on the periphery of anisotropic Ts spatial anomaly features that propagated westward at about 3 km day–1. Relatively weak and strong (small or large |∇Ts|) segments of the dominant zonally-oriented frontal band (the Subtropical Frontal Zone, or SFZ) shifted westward with these anomaly features, which had characteristic peak-to-peak space scales of up to ≈800 km in the minor axis direction (NW-SE) and time scales of up to ≈275 days, both larger than the scales of mesoscale eddies observed during earlier experiments. Both the main and seasonal thermoclines tended to be elevated (depressed) by several tens of meters beneath cold (warm) anomaly features, suggesting that the influence of eddies on Ts and fronts extends to larger space and longer time scales than those resolved in earlier studies. Because of the very limited spatial and temporal coverage of available subsurface data, however, this relationship could not be verified conclusively. Properties of the anomaly features were consistent with the dispersion of lowest-mode internal Rossby waves, and they were apparently not generated or significantly influenced by wind-driven Ekman transport. A much longer data set, including altimetry and subsurface data, will be required to verify that eddies influence Ts and fronts at these large scales, and if so, to determine the physical processes behind this influence

Large-Scale SST Variability in the Western North Atlantic Subtropical Convergence Zone during FASINEX. Part II: Upper Ocean Heat Balance and Frontogenesis

We analyzed the influence of wind-deriven horizontal heat advection on the large-scale [O(1000) km wavelength] variability of both the upper-ocean mixed-layer heat content and the subtropical frontal zone (SFZ) within an 11° by 10° domain in the western North Atlantic Ocean during FASINEX (January through June 1986). By estimating heat advection due to both Ekman transport and interior geostrophic (Sverdrup minus Ekman) transport from a slab mixed layer heat balance equation using satellite-derived sea surface temperature (Ts) and wind analysis maps, it was found that these processes could not account for the observed variability in either beat content or the SFZ. The annual cycle of surface vertical heat flux had the dominant influence on the heat content. Even when the average heat balance was analyzed during a 4-month time interval when the net influence of the annual cycle was nearly zero (mid-January to mid-May 1986), westward-propagating Ts spatial anomaly features with peak-to-peak scales of several hundred kilometers apparently had the dominant influence on heat content. The influence of Ekman transport appeared to become marginally detectable only when terms in the heat equation were zonally averaged across the entire analysis domain, apparently reducing the influence of the propagating anomaly features. Ekman transport did act to maintain the SFZ during the 4-month interval, and thus may have been ultimately responsible for its existence, but the large-amplitude variability in heat content and the SFZ driven by other processes made this impossible to prove conclusively in the FASINEX region

Problem of Time in Quantum Gravity

The Problem of Time occurs because the `time' of GR and of ordinary Quantum Theory are mutually incompatible notions. This is problematic in trying to replace these two branches of physics with a single framework in situations in which the conditions of both apply, e.g. in black holes or in the very early universe. Emphasis in this Review is on the Problem of Time being multi-faceted and on the nature of each of the eight principal facets. Namely, the Frozen Formalism Problem, Configurational Relationalism Problem (formerly Sandwich Problem), Foliation Dependence Problem, Constraint Closure Problem (formerly Functional Evolution Problem), Multiple Choice Problem, Global Problem of Time, Problem of Beables (alias Problem of Observables) and Spacetime Reconstruction/Replacement Problem. Strategizing in this Review is not just centred about the Frozen Formalism Problem facet, but rather about each of the eight facets. Particular emphasis is placed upon A) relationalism as an underpinning of the facets and as a selector of particular strategies (especially a modification of Barbour relationalism, though also with some consideration of Rovelli relationalism). B) Classifying approaches by the full ordering in which they embrace constrain, quantize, find time/history and find observables, rather than only by partial orderings such as "Dirac-quantize". C) Foliation (in)dependence and Spacetime Reconstruction for a wide range of physical theories, strategizing centred about the Problem of Beables, the Patching Approach to the Global Problem of Time, and the role of the question-types considered in physics. D) The Halliwell- and Gambini-Porto-Pullin-type combined Strategies in the context of semiclassical quantum cosmology.Comment: Invited Review: 26 pages including 2 Figures. This v2 has a number of minor improvements and correction

Westward-propagating SST Anomalies and Baroclinic Eddies in the Sargasso Sea

Previous studies have documented the existence of a zonal band of strong, persistent, westward-propagating sea surface temperature (Ts) anomalies with zonal wavelengths of ≈800 km and periods of ≈200 days that are confined to the subtropical convergence zone (STCZ, roughly 26°–32°N). Two years of satellite-derived sea surface temperature (Ts) and sea surface elevation anomaly (η) maps of the Sargasso Sea (22.5°–33.5°N, 71.5°–59.5°W) are analyzed to determine how these anomalies are forced and why they an confined to the STCZ. A simple anomaly model forced by horizontal eddy currents and damped by a linear feedback mechanism explains many properties of the anomaly response. At wavelengths exceeding several hundred kilometers, forcing by horizontal eddy currents becomes less important relative to atmospheric forcing with increasing wavelength. The anomalies are confined to the STCZ partly because the large mean Ts gradient there enables the horizontal eddy currents to be relatively effective at forcing anomalies. Also, the eddies that force these anomalies, wavelike features with wavelengths of ∼800 km and periods of ∼200 days, are themselves confined to the STCZ. These wavelike eddies were not detecting during earlier experiments such as MODE because the domains within which they were conducted were too small. Within the STCZ, zonal dispersion properties of the eddy field are consistent with baroclinic Rossby wave variability. To the north and south of the STCZ, however, zonal dispersion properties differ substantially from the properties observed within the STCZ. The eddy dispersion properties change abruptly across transition zones 1–2 degree wide centered at 32.5° and 25.5°N. A simple linearized reduced-gravity model is used to demonstrate that interaction between eddies and zonal mean currents can qualitatively account for the change is dispersion properties south of the STCZ, but not to the north within the Gulf Stream recirculation region

Westward-propagating SST Anomaly Features in the Sargasso Sea, 1982–88

Sea surface temperature (Ts) maps of the region from 59.5° to 75.5°W, 22.5° to 33.5°N containing the western North Atlantic Subtropical Convergence Zone (STCZ) were derived from AVHRR/2 images. The 7- year mean annual cycle was removed and the maps were filtered in space and time to represent anomaly variability with wavelengths ≥ 220 km and periods ≥ 50 days. Warm and cold anomaly features were observed cast of 71°W between 26° and 32°N that propagated westward at 3–4 km day−1 and that occasionally exceeded ±1°C in amplitude. They are generally strong and persistent from fall to spring and are only marginally detectable during summer. During 1981–82, 1982–83, and 1985–86, individual features could be followed through the entire fall-spring interval. During 1983–84,1986–87,and 1987–88,they could typically be followed for 2–4 months, and during 1984–85, for only 1–2 months. The features were anisotropic during all fall-spring intervals except 1986–87, and they had characteristic wavelengths of ∼800 km in the minor axis direction and periods of ∼200 days. Local forcing by synoptic atmospheric variability alone could not amount for the existence of these features. Anomaly features propagated westward in a manner consistent with theoretical zonal dispersion properties of first-mode baroclinic Rossby waves, suggesting that the anomalies may be coupled to a field of wavelike eddies. Since the anomalies were confined to the zonal hand of large mean meridional Ts gradients associated with the STCZ, where meridional eddy currents are relatively effective at forcing anomalies these eddy currents could be largely responsible for their existence. In one case, however, the influence of eddies an vertical heat flux at the mixed layer base appeared to be important. The relatively strong and persistent 1985–86 anomaly features appeared during a several-day interval at the onset of relatively stormy fall weather and (presumably) rapid mixed-layer deepening

Quantum Cosmology of Kantowski-Sachs like Models

The Wheeler-DeWitt equation for a class of Kantowski-Sachs like models is completely solved. The generalized models include the Kantowski-Sachs model with cosmological constant and pressureless dust. Likewise contained is a joined model which consists of a Kantowski-Sachs cylinder inserted between two FRW half--spheres. The (second order) WKB approximation is exact for the wave functions of the complete set and this facilitates the product structure of the wave function for the joined model. In spite of the product structure the wave function can not be interpreted as admitting no correlations between the different regions. This problem is due to the joining procedure and may therefore be present for all joined models. Finally, the {s}ymmetric {i}nitial {c}ondition (SIC) for the wave function is analyzed and compared with the ``no bouindary'' condition. The consequences of the different boundary conditions for the arrow of time are briefly mentioned.Comment: 21 pages, uses LaTeX2e, epsf.sty and float.sty, three figures (50 kb); changes: one figure added, new interpretation of quantizing procedure for the joined model and many minor change

The Code large-scale meteorological, sea surface temperature, and coastal sea level data set, 1980-84

Meteorological, sea surface temperature, and coastal sea level data were collected along the west coast of North America from northern Baja California to the Alaska/British Columbia border from 1980 to mid-1984 for the large-scale component of the Coastal Ocean Dynamics Experiment (CODE). This report presents statistical summaries and plots of selected meteorological variables, sea surface temperature, and coastal sea level from this data set

A low-voltage activated, transient calcium current is responsible for the time-dependent depolarizing inward rectification of rat neocortical neurons in vitro

Intracellular recordings were obtained from rat neocortical neurons in vitro. The current-voltage-relationship of the neuronal membrane was investigated using current- and single-electrode-voltage-clamp techniques. Within the potential range up to 25 mV positive to the resting membrane potential (RMP: –75 to –80 mV) the steady state slope resistance increased with depolarization (i.e. steady state inward rectification in depolarizing direction). Replacement of extracellular NaCl with an equimolar amount of choline chloride resulted in the conversion of the steady state inward rectification to an outward rectification, suggesting the presence of a voltage-dependent, persistent sodium current which generated the steady state inward rectification of these neurons. Intracellularly injected outward current pulses with just subthreshold intensities elicited a transient depolarizing potential which invariably triggered the first action potential upon an increase in current strength. Single-electrode-voltage-clamp measurements reveled that this depolarizing potential was produced by a transient calcium current activated at membrane potentials 15–20 mV positive to the RMP and that this current was responsible for the time-dependent increase in the magnitude of the inward rectification in depolarizing direction in rat neocortical neurons. It may be that, together with the persistent sodium current, this calcium current regulates the excitability of these neurons via the adjustment of the action potential threshold

Fresh inflation and decoherence of super Hubble fluctuations

I study a stochastic approach to the recently introduced fresh inflation model for super Hubble scales. I find that the state loses its coherence at the end of the fresh inflationary period as a consequence of the damping of the interference function in the reduced density matrix. This fact should be a consequence of a) the relative evolutions of both the scale factor and the horizon and b) the additional thermal and dissipative effects. This implies a relevant difference with respect to supercooled inflationary scenarios which require a very rapid expansion of the scale factor to give the decoherence of super Hubble fluctuations.Comment: version with minor changes. To appear in Phys. Rev.

The Bohm Interpretation of Quantum Cosmology

I make a review on the aplications of the Bohm-De Broglie interpretation of quantum mechanics to quantum cosmology. In the framework of minisuperspaces models, I show how quantum cosmological effects in Bohm's view can avoid the initial singularity, isotropize the Universe, and even be a cause for the present observed acceleration of the Universe. In the general case, we enumerate the possible structures of quantum space and time.Comment: 28 pages, 1 figure, contribution to the James Cushing festschrift to appear in Foundations of Physic