Changes in Atmospheric Constituents and in Radiative Forcing

Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production (NPP) of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans. Approaches based on satellite indices of absorbed solar radiation indicate marked heterogeneity in NPP for both land and oceans, reflecting the influence of physical and ecological processes. The spatial and temporal distributions of ocean NPP are consistent with primary limitation by light, nutrients, and temperature. On land, water limitation imposes additional constraints. On land and ocean, progressive changes in NPP can result in altered carbon storage, although contrasts in mechanisms of carbon storage and rates of organic matter turnover result in a range of relations between carbon storage and changes in NPP.

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Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components

A weekly 1° spatial resolution optimum interpolation (OI) sea surface temperature (SST) analysis has been produced at the National Oceanic and Atmospheric Administration (NOAA) using both in situ and satellite data from November 1981 to the present. The weekly product has been available since 1993 and is widely used for weather and climate monitoring and forecasting. Errors in the satellite bias correction and the sea ice to SST conversion algorithm are discussed, and then an improved version of the OI analysis is developed. The changes result in a modest reduction in the satellite bias that leaves small global residual biases of roughly −0.03°C. The major improvement in the analysis occurs at high latitudes due to the new sea ice algorithm where local differences between the old and new analysis can exceed 1°C. Comparisons with other SST products are needed to determine the consistency of the OI. These comparisons show that the differences among products occur on large time- and space scales wit...

An Improved In Situ and Satellite SST Analysis for Climate

The responses of vertebrate neurones to glutamate involve at least three receptor types. One of these, the NMDA receptor (so called because of its specific activation by N-methyl-D-aspartate), induces responses presenting a peculiar voltage sensitivity. Above resting potential, the current induced by a given dose of glutamate (or NMDA) increases when the cell is depolarized. This is contrary to what is observed at classical excitatory synapses, and recalls the properties of 'regenerative' systems like the Na+ conductance of the action potential. Indeed, recent studies of L-glutamate, L-aspartate and NMDA-induced currents have indicated that the current-voltage (I-V) relationship can show a region of 'negative conductance' and that the application of these agonists can lead to a regenerative depolarization. Furthermore, the NMDA response is greatly potentiated by reducing the extracellular Mg2+ concentration [( Mg2+]o) below the physiological level (approximately 1 mM). By analysing the responses of mouse central neurones to glutamate using the patch-clamp technique, we have now found a link between voltage sensitivity and Mg2+ sensitivity. In Mg2+-free solutions, L-glutamate, L-aspartate and NMDA open cation channels, the properties of which are voltage independent. In the presence of Mg2+, the single-channel currents measured at resting potential are chopped in bursts and the probability of opening of the channels is reduced. Both effects increase steeply with hyperpolarization, thereby accounting for the negative slope of the I-V relationship of the glutamate response. Thus, the voltage dependence of the NMDA receptor-linked conductance appears to be a consequence of the voltage dependence of the Mg2+ block and its interpretation does not require the implication of an intramembrane voltage-dependent 'gate'.

Magnesium gates glutamate-activated channels in mouse central neurones

Two new high-resolution sea surface temperature (SST) analysis products have been developed using optimum interpolation (OI). The analyses have a spatial grid resolution of 0.25° and a temporal resolution of 1 day. One product uses the Advanced Very High Resolution Radiometer (AVHRR) infrared satellite SST data. The other uses AVHRR and Advanced Microwave Scanning Radiometer (AMSR) on the NASA Earth Observing System satellite SST data. Both products also use in situ data from ships and buoys and include a large-scale adjustment of satellite biases with respect to the in situ data. Because of AMSR’s near-all-weather coverage, there is an increase in OI signal variance when AMSR is added to AVHRR. Thus, two products are needed to avoid an analysis variance jump when AMSR became available in June 2002. For both products, the results show improved spatial and temporal resolution compared to previous weekly 1° OI analyses. The AVHRR-only product uses Pathfinder AVHRR data (currently available from January 1985 to December 2005) and operational AVHRR data for 2006 onward. Pathfinder AVHRR was chosen over operational AVHRR, when available, because Pathfinder agrees better with the in situ data. The AMSR– AVHRR product begins with the start of AMSR data in June 2002. In this product, the primary AVHRR contribution is in regions near land where AMSR is not available. However, in cloud-free regions, use of both infrared and microwave instruments can reduce systematic biases because their error characteristics are independent.

Daily High-Resolution-Blended Analyses for Sea Surface Temperature

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Satellite images of warm core ring 82-B sea surface temperature and a chronological record of major physical events affecting ring structure

For a given short-ranged interatomic potential the density profile of an inhomogeneous fluid decays into bulk in the same fashion as the bulk radial distribution function g(r). General statistical mechanical arguments predict damped oscillatory decay of the liquid-vapour density profile into the saturated liquid for temperatures T removed from the critical value Tc. Explicit density functional calculations for a square-well model fluid near its triple point yield an oscillatory profile whose amplitude is about 2% of the bulk liquid density. The amplitude decreases for higher T and for T≥0.9 Tc only pure exponential decay is found. Capillary-wave fluctuations reduce the amplitude of the oscillations but do not change their period and decay length. The existence of density oscillations gives rise to an oscillatory binding potential for an adsorbed liquid film. This has significant repercussions for wetting transitions and allows the possibility of a sequence of layering transitions between adsorbed liquid layers. The same length scales which determine the decay of g(r) determine the asymptotic decay of the solvation force for a fluid confined between two planar walls. In the case of long-ranged interatomic potentials, density profiles exhibit power-law decay at longest range but, for liquid densities, their intermediate range damped oscillatory decay is governed by the same leading-order pole structure that describes short-ranged forces. Recent work on the decay of correlations in liquid mixtures is also described.

Oscillatory behaviour of density profiles: Relevance for fluid interfacial phenomena

We summarize the results of a recent positron annihilation study of the phase behaviour of confined in Vycor glass. Particular emphasis is placed on the phase diagram of the confined fluid and on the usefulness of the positron annihilation technique in determining the mechanisms underlying phase transitions of fluids in porous solids.

Positron and positronium annihilation studies of the phase behaviour of fluids in Vycor

Parry and Evans reply.

Using a simple density functional theory (DFT) we determine the height of the free energy barrier for forming a droplet of the liquid phase from the metastable gas phase for a model colloidal fluid exhibiting competing interactions. The pair potential has a hard core of diameter {\sigma}, is attractive Yukawa at intermediate separations, and is repulsive Yukawa at large separations. We find that even a very weak long-range repulsive tail in the pair potential has a profound effect on nucleation: increasing the amplitude of the repulsive Yukawa tail reduces significantly the free energy barrier height and therefore increases the liquid droplet nucleation rate. The method we introduce for calculating the droplet density profile and free energy employs a fictitious external potential to stabilize a liquid droplet of the desired size, i.e. with a given excess number of particles. For the critical droplet, corresponding to an extremum of the grand potential, this fictitious potential is everywhere zero. We examine the decay of the droplet density profiles into the bulk gas. For a range of nucleation state points the DFT predicts exponentially damped, long wavelength oscillatory decay for systems exhibiting long-range repulsion, contrasting sharply with the monotonic decay found when the pair potential has only an attractive Yukawa piece. The changes in nucleation properties that we find for small amplitudes of the repulsive Yukawa tail reflect the propensity of the fluid to form modulated structures such as clusters or stripes.

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Robert Evans

Papers

Satellite images of warm core ring 82-B sea surface temperature and a chronological record of major physical events affecting ring structure

Oscillatory behaviour of density profiles: Relevance for fluid interfacial phenomena

Positron and positronium annihilation studies of the phase behaviour of fluids in Vycor

Parry and Evans reply.

Nucleation of liquid droplets in a fluid with competing interactions