An improved parameterization of tidal mixing for ocean models

Two modifications to an existing scheme of tidal mixing are implemented in the coarse resolution ocean component of a global climate model. First, the vertical distribution of energy flux out of the barotropic tide is determined using high resolution bathymetry. This shifts the levels of mixing higher up in the water column and leads to a stronger mid-depth meridional overturning circulation in the model. Second, the local dissipation efficiency for diurnal tides is assumed to be larger than that for the semi-diurnal tides poleward of 30°. Both modifications are shown to improve agreement with observational estimates of diapycnal diffusivities based on microstructure measurements and circulation indices. We also assess impacts of different spatial distributions of the barotropic energy loss. Estimates based on satellite altimetry lead to larger diffusivities in the deep ocean and hence a stronger deep overturning circulation in our climate model that is in better agreement with observation based estimates compared to those based on a tidal model.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.geoscientific-model-development.net/home.html

Robust principal component analysis of electromagnetic arrays with missing data

We describe a new algorithm for robust principal component analysis (PCA) of electromagnetic (EM) array data, extending previously developed multivariate methods to include arrays with large data gaps, and only partial overlap between site occupations. Our approach is based on a criss-cross regression scheme in which polarization parameters and spatial modes are alternately estimated with robust regression procedures. The basic scheme can be viewed as an expectation robust (ER) algorithm, of the sort that has been widely discussed in the statistical literature in the context of robust PCA, but with details of the scheme tailored to the physical specifics of EM array observations. We have tested our algorithm with synthetic and real data, including data denial experiments where we have created artificial gaps, and compared results obtained with full and incomplete data arrays. These tests reveal that for modest amounts of missing data (up to 20 per cent or so) the algorithm performs well, reproducing essentially the same dominant spatial modes that would be obtained from analysis of the complete array. The algorithm thus makes multivariate analysis practical for the first time for large heterogeneous arrays, as we illustrate by application to two different EM arrays.Keywords: Time series analysis, Geomagnetic induction, Magnetotelluri

Ionospheric current source modeling and global geomagnetic induction using ground geomagnetic observatory data

Long-period global-scale electromagnetic induction studies of deep Earth conductivity are based almost exclusively on magnetovariational methods and require accurate models of external source spatial structure. We describe approaches to inverting for both the external sources and three-dimensional (3-D) conductivity variations and apply these methods to long-period (T≥1.2 days) geomagnetic observatory data. Our scheme involves three steps: (1) Observatory data from 60 years (only partly overlapping and with many large gaps) are reduced and merged into dominant spatial modes using a scheme based on frequency domain principal components. (2) Resulting modes are inverted for corresponding external source spatial structure, using a simplified conductivity model with radial variations overlain by a two-dimensional thin sheet. The source inversion is regularized using a physically based source covariance, generated through superposition of correlated tilted zonal (quasi-dipole) current loops, representing ionospheric source complexity smoothed by Earth rotation. Free parameters in the source covariance model are tuned by a leave-one-out cross-validation scheme. (3) The estimated data modes are inverted for 3-D Earth conductivity, assuming the source excitation estimated in step 2. Together, these developments constitute key components in a practical scheme for simultaneous inversion of the catalogue of historical and modern observatory data for external source spatial structure and 3-D Earth conductivity.This is the publisher’s final pdf. The article is copyrighted by the American Geophysical Union and published by John Wiley & Sons, Inc. It can be found at: http://agupubs.onlinelibrary.wiley.com/agu/jgr/journal/10.1002/%28ISSN%292169-9356/Keywords: simultaneous inversion, external source fields, mantle conductivity, global inductio

Long-term monitoring of ULF electromagnetic fields at Parkfield, CA

Electric and magnetic fields in the (10{sup -4}-1.0) Hz band were monitored at two sites adjacent to the San Andreas Fault near Parkfield and Hollister, California from 1995 to present. A data window [2002-2005], enclosing the September 28, 2004 M6 Parkfield earthquake, was analyzed to determine if anomalous electric or magnetic fields, or changes in ground conductivity, occurred before the earthquake. The data were edited, removing intervals of instrument malfunction leaving 875 days in the four-year period. Frequent, spike-like disturbances were common, but were not more frequent around the time of the earthquake; these were removed before subsequent processing. Signal to noise amplitude spectra, estimated via magnetotelluric processing showed the behavior of the ULF fields to be remarkably constant over the period of analysis. These first-order plots make clear that most of the recorded energy is coherent over the spatial extent of the array. Three main statistical techniques were employed to separate local anomalous electrical or magnetic fields from the dominant coherent natural fields: transfer function estimates between components at each site were employed to subtract the dominant field, and look deeper at the 'residual' fields; the data were decomposed into principal components to identify the dominant coherent array modes; and the technique of canonical coherences was employed to distinguish anomalous fields which are spatially broad from anomalies which occur at a single site only, and furthermore to distinguish anomalies which are present in both the electric and magnetic fields from those which are present in only one field type. Standard remote reference apparent resistivity estimates were generated daily at Parkfield. A significant seasonal component of variability was observed suggesting local distortion due to variations in near surface resistance. In all cases, high levels of sensitivity to subtle electromagnetic effects were demonstrated, but no effects which can be reasonably characterized as precursors to the Parkfield earthquake were found

Numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum

A hydrodynamic model incorporating a self‐consistent treatment of ocean self‐attraction and loading (SAL), and a physically based parameterization of internal tide (IT) drag, is used to assess how accurately barotropic tides can be modeled without benefit of data, and to explore tidal energetics in the last glacial maximum (LGM). M2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm RMS in the open ocean. This accuracy, and agreement with atlimetric estimates of energy dissipation, are achieved only when SAL and IT drag are included in the model. Solutions are sensitive to perturbations to bathymetry, and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations. The ≈100 m drop in sea level during the LGM results in significant changes in modeled M2 tides, with some amplitudes in the North Atlantic increasing by factors of 2 or more. Dissipation is also significantly changed by the drop in sea level. If IT drag estimated for the modern ocean is assumed, dissipation increases by about 50% globally, and almost triples in the deep ocean. However, IT drag depends on ocean stratification, which is poorly known for the LGM. Tests with modified IT drag suggest that the tendency to a global increase in dissipation is a robust result, but details are sensitive to stratification. Significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained

A Minimal Model of Metabolism Based Chemotaxis

Since the pioneering work by Julius Adler in the 1960's, bacterial chemotaxis has been predominantly studied as metabolism-independent. All available simulation models of bacterial chemotaxis endorse this assumption. Recent studies have shown, however, that many metabolism-dependent chemotactic patterns occur in bacteria. We hereby present the simplest artificial protocell model capable of performing metabolism-based chemotaxis. The model serves as a proof of concept to show how even the simplest metabolism can sustain chemotactic patterns of varying sophistication. It also reproduces a set of phenomena that have recently attracted attention on bacterial chemotaxis and provides insights about alternative mechanisms that could instantiate them. We conclude that relaxing the metabolism-independent assumption provides important theoretical advances, forces us to rethink some established pre-conceptions and may help us better understand unexplored and poorly understood aspects of bacterial chemotaxis

TOPEX/POSEIDON tides estimated using a global inverse model

Altimetric data from the TOPEX/POSEIDON mission will be used for studies of global ocean circulation and marine geophysics. However, it is first necessary to remove the ocean tides, which are aliased in the raw data. The tides are constrained by two distinct types of information: the hydrodynamic equations which the tidal fields of elevations and velocities must satisfy, and direct observational data from tide gauges and satellite altimetry. Here we develop and apply a generalized inverse method, which allows us to combine rationally all of this information into global tidal fields best fitting both the data and the dynamics, in a least squares sense. The resulting inverse solution is a sum of the direct solution to the astronomically forced Laplace tidal equations and a linear combination of the representers for the data functional. The representer functions (one of each datum) are determined by the dynamical equations, and by out prior estimates of the statistics of errors in these equations. Out major task is a direct numerical calculation of these representers. This task is computationally intensive but well suited to massively parallel processing. By calculating the representers we reduce the full (infinite dimensional) problem to a relatively low-dimensional problem at the outset, allowing full control over the conditioning and hence the stability of the inverse solution. With the representers calculated we can easily update out model as additional TOPEX/POSEIDON data become available. As an initial illustration we invert harmonic constants from a set of 80 open-ocean tide gauges. We then present a practical scheme for direct inversions of TOPEX/POSEIDON crossover data. We apply this method to 38 cycles of geophysical data records (GDR) data, computing preliminary global estimates of the four principal tidal constituents, M₂, S₂, K₁, and O₁. The inverse solution yields tidal fields which are simultaneously smoother, and in better agreement with altimetric and ground truth data, than previously proposed tidal models. Relative to the “default” tidal corrections provided with the TOPEX/POSEIDON GDR, the inverse solution reduces crossover difference variances significantly (≈20 -30%), even though only a small number of free parameters (≈1000) are actually fit to the crossover data

Long‐term monitoring of ULF electromagnetic fields at Parkfield, California

Electric and magnetic fields in the (10−4–1.0) Hz band were monitored at two sites adjacent to the San Andreas Fault near Parkfield and Hollister, California, from 1995 to 2007. A data window (2002–2005), enclosing the 28 September 2004 M6 Parkfield earthquake, was analyzed to determine if anomalous electric or magnetic fields or changes in ground conductivity occurred before the earthquake. The data were edited, removing intervals of instrument malfunction, leaving 875 days in the 4 year period. Frequent, spikelike disturbances were common but were not more frequent around the time of the earthquake; these were removed before subsequent processing. Signal‐to‐noise amplitude spectra, estimated via magnetotelluric processing, showed the behavior of the ultralow frequency fields to be remarkably constant over the period of analysis. These first‐order plots make clear that most of the recorded energy is coherent over the spatial extent of the array. Three main statistical techniques were employed to separate local anomalous electrical or magnetic fields from the dominant coherent natural fields: transfer function estimates between components at each site were employed to subtract the dominant field, and look deeper at the “residual” fields; the data were decomposed into principal components to identify the dominant coherent array modes; and the technique of canonical coherences was employed to distinguish anomalous fields which are spatially broad from anomalies which occur at a single site only, and furthermore to distinguish anomalies present in both the electric and magnetic fields from those present in only one field type. Standard remote reference apparent resistivity estimates were generated daily at Parkfield. A significant seasonal component of variability was observed, suggesting local distortion due to variations in near‐surface resistance. In all cases, high levels of sensitivity to subtle electromagnetic effects were demonstrated, but no effects were found that can be reasonably characterized as precursors to the Parkfield earthquake.Keywords: Parkfield, California, ULF electromagnetic field

948-46 Preserved Cardiac Baroreflex Control of Renal Cortical Blood Flow in Advanced Heart Failure Patients: A Positron Emission Tomography Study

Cardiac baroreflex (CBR) control of forearm blood flow (FBF) is blunted or reversed in humans with heart failure (HF). but little is known about CBR control of renal cortical blood flow (RCBF) in HF due to technical limitations. Positron emission tomography (PET) 0–15 water is a new, precise method to measure RCBF quantitatively. We compared CBR control of RCBF and FBF (venous plethysmography) in 8 patients with HF (mean age, 47±3 y, ejection fraction 0.25±0.02) and 10 normal humans (mean age 35±5 y) during CBR unloading with phlebotomy (450ml). In 5 normals, cold pressor test was used as a strong, non-baroreflex mediated stimulus to vasoconstriction.ResultsPhlebotomy decreased central venous pressure (p <0.001), but did not change mean arterial pressure or heart rate in HF patients or controls. The major findings of the study are: 1) At rest, RCBF is markedly diminished in HF vs normals (2.4±0.1 vs 4.3±0.2ml/min/g, p < 0.001). 2) In normal humans during phlebotomy, FBF decreased substantially (basal vs phlebotomy: 3.3±0.4 vs 2.6±0.3 ml/min/100 ml, p=0.021, and RCBF decreased slightly, but significantly (basal vs phlebotomy: 4.3±0.2 vs 4.0±0.3 ml/min/g, p=0.01). 3) The small magnitude of reflex renal vasoconstriction is not explained by the inability of the renal circulation to vasoconstrict since the cold pressor stimulus induced substantial decreases in RCBF in normals (basal vs cold pressor: 4.4±0.1 vs 3.7±0.1 ml/min/g, p=0.003). 4) In humans with heart failure during phlebotomy, FBF did not change (basal vs phlebotomy: 2.6±0.3 vs 2.7±0.2 ml/min/100 ml, p=NS), but RCBF decreased slightly but significantly (basal vs phlebotomy: 2.4±0.1 vs 2.1±0.1 ml/min/g, p=0.01). Thus, in patients with heart failure, there is an abnormality in cardiopulmonary baroreflex control of the forearm circulation, but not the renal circulationConclusionThis study 1) shows the power of PET to study physiologic and pathophysiologic reflex control of the renal circulation in humans, and 2) describes the novel finding of selective dysfunction of cardiac baroreflex control of the forearm circulation, but its preservation of the renal circulation, in patients with heart failur