Assessment of the effectiveness of POLYMODE data assimilation by a numerical barotropic model for synoptic motions

This paper considers the results of numerical experiments involving POLYMODE data assimilation by a barotropic model for synoptic ocean dynamics. The model's response the data assimilation for various space-time discretenesses of assimilation is studied. Results derived from the application of optimal interpolation algorithms and modified optimal filtration algorithms are compared. Qualitative similarity to the calculations carried out through the simulation modelling technique is noted. Optimal assimilation algorithms are determined, depending on the space-time discreteness used. An optimal sampling discreteness for the POLYMODE conditions is suggested.Translated by Vladimir A. Puchkin.     

A method for precise measurement of argon 40/36 and krypton/argon ratios in trapped air in polar ice with applications to past firn thickness and abrupt climate change in Greenland and at Siple Dome, Antarctica

We describe a method for measuring the ⁴⁰Ar/³⁶Ar ratio and the ⁸⁴Kr/³⁶Ar ratio in air from bubbles trapped in ice cores. These ratios can provide constraints on the past thickness of the firn layer at the ice core site and on the magnitude of past rapid temperature variations when combined with measured ¹⁵N/¹⁴N. Both variables contribute to paleoclimatic studies and ultimately to the understanding of the controls on Earth’s climate. The overall precision of the ⁴⁰Ar/³⁶Ar method (1 standard error of the mean) is 0.012‰ for a sample analyzed in duplicate, corresponding to ±0.6 m in reconstructed firn thickness. We use conventional dynamic isotope ratio mass spectrometry with minor modifications and special gas handling techniques designed to avoid fractionation. About 100 g of ice is used for a duplicate pair of analyses. An example of the technique applied to the GISP2 ice core yields an estimate of 11 ± 3K of abrupt warming at the end of the last glacial period 15,000 years ago. The krypton/argon ratio can provide a diagnostic of argon leakage out of the bubbles, which may happen (naturally) during bubble close-off or (artifactually) if samples are warmed near the freezing point during core retrieval or storage. Argon leakage may fractionate the remaining ⁴⁰Ar/³⁶Ar ratio by +0.007‰ per ‰ change in ⁸⁴Kr/³⁶Ar, introducing a possible bias in reconstructed firn thickness of about +2 m if thermal diffusion is not accounted for or +6 m if thermal diffusion effects are quantified with measured ¹⁵N/¹⁴N. Reproducibility of ⁸⁴Kr/³⁶Ar measured in air is about ±0.2‰ (1 standard error of the mean) but is about ±1‰ for ice core samples. Ice core samples are systematically enriched in ⁸⁴Kr/³⁶Ar relative to atmosphere by ∼5‰, probably reflecting preferential size-dependent exclusion of the smaller argon atom during bubble entrapment. Recent results from the Siple Dome ice core reveal two climate events during the last deglaciation, including an 18-m reduction in firn thickness associated with an abrupt warming at sometime between 18 and 22 kyr BP and a partial or total removal of the firn during an ablation event at 15.3 kyr BP.     

The first data on helium isotopy in a transitional clay layer at the cretaceous-paleogene boundary (Gams,Eastern Alps)

The paper presents preliminary results derived from the study of He isotopy in a transitional clay bed at the critical 65-Ma boundary in the Gams area (Eastern Alps). The ratio ³He/⁴He is shown to decrease from bottom to top of the transitional layer, and the difference between its values in the lower-and uppermost sublayers of the layer exceeds by more than ten times the measurement uncertainty (5%). The ratio ³He/⁴He is smallest in the upper part of the section, where all features of an impact event (spherules of pure nickel, diamonds, and awaruite) are established. The general inference of our study is that ³He enrichment in the lower part of the Gams section is related not to cosmic matter but to a change in the conditions in the source area, most likely, to volcanic activity. The effect of the latter has been established, independent of He isotopic studies, from anomalous concentrations of As, Pb, Cu, and Zn and from the presence of particles of gold, copper, and titanomagnetite similar in composition to its basaltic varieties.     

On the Determination of the Neutral Drag Coefficient in the Convective Boundary Layer

Based on the idea that free convection can be considered as a particular case of forced convection, where the gusts driven by the large-scale eddies are scaled with the Deardorff convective velocity scale, a new formulation for the neutral drag coefficient, C_Dn, in the convective boundary layer (CBL) is derived. It is shown that (i) a concept of C_Dn can still be used under strongly unstable conditions including a pure free-convection regime even when no logarithmic portion in the velocity profile exists; (ii) gustiness corrections must be applied for rational calculations of C_Dn; and (iii) the stratification function used in the derivation of C_Dn should satisfy the theoretical free-convection limit. The new formulation is compared with the traditional relationship for C_Dn, and data collected over the sea (during the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) and the San Clemente Ocean Probing Experiment (SCOPE)) and over land (during the BOREX-95 experiment) are used to illustrate the difference between the new and traditional formulations. Compared to the new approach, the traditional formulation strongly overestimates C_Dn and z_o in the CBL for mean wind speed less than about 2 m s^-1. The new approach also clarifies several contradictory results from earlier works. Some aspects related to an alternate definition of the neutral drag coefficient and the wind speed and the stress averaging procedure are considered.     

Angular fluctuations in the cosmic microwave background owing to initial perturbations in the radiation temperature

A new method is proposed to account for multiple scattering by electrons in calculations of the correlation functions describing the angular fluctuations in the cosmic microwave background radiation (CMBR). The apparatus of the theory of radiative transport with Rayleigh scattering is used. The problem is reduced to solving an integral equation for the vector source function (dependent only on time), along with differential equations for the other quantities (scalar potentials, baryon velocities, etc.) which show up in the problem. The quantities which describe the angular fluctuations in the CMBR (in the temperature and in the polarization) are then calculated by integrating the vector source function along the line of sight. As an illustration, the correlation functions and power spectra are calculated for the case where the fluctuations are produced by some initial gaussian perturbations of the CMBR. __________ Translated from Astrofizika, Vol. 50, No. 4, pp. 621–631 (November 2007).     

CMB recombination lines of hydrogen: The differential spectrum

We have calculated the distortions of the cosmic microwave background (CMB) spectrum in the wavelength range 2–50 cm due to the superposition of the CMB hydrogen recombination radiation in subordinate lines. The level populations were determined by numerically solving the equation of recombination kinetics together with the statistical equilibrium equations for a 60-level model hydrogen atom. The relative distortions are ≈10^?7–10^?6, with their wavelength dependence having a low-contrast, wavy pattern. However, the contrast increases severalfold and becomes pronounced when passing to the differential distortion spectrum. We study the dependence of the distortions on cosmological parameters.     

Space–VLBI observations of the OH maser OH 34.26+0.15: low interstellar scattering

We report on the first space–VLBI observations of the OH 34.26+0.15 maser in two main-line OH transitions at 1665 and 1667 MHz. The observations involved the space radio telescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The map of the maser region and images of individual maser spots were produced with an angular resolution of 1 mas, which is several times higher than the angular resolution available on the ground. The maser spots were only partly resolved and a lower limit to the brightness temperature     was obtained. The maser seems to be located in the direction of low interstellar scattering, an order of magnitude lower than the scattering of a nearby extragalactic source and pulsar.     

Exact and numerical solutions of the kompaneets equation: Evolution of the spectrum and average frequencies

The evolution of the spectrum of isotropic uniform radiation in an infinite space filled with a homogeneous, nonrelativistic electron gas is calculated by solving the Kompaneets equation. For an infinitely narrow initial spectrum, the time dependence of the average frequency and frequency dispersion is determined in a linear approximation of the equation. Characteristic times corresponding to changes in the character of this dependence are introduced. Two schemes are proposed for the numerical solution of the nonlinear equation: a nonconservative scheme with a grid that is uniform in frequency and a conservative scheme with automatic selection of an adaptive grid in frequency and time. For the linear equation the method yields results consistent with calculations of its solutions in terms of an eigenfunction expansion of the Kompaneets operator calculated in [D. I. Nagirner and V. M. Loskutov, Astrofizika, 40, 97 (1977)]. The influence of nonlinearity on the evolution of the spectrum of initially monochromatic radiation of various intensities is traced as an example of the application of the method.