Modeling atmospheric effects of the September 1859 Solar Flare

We have modeled atmospheric effects, especially ozone depletion, due to a solar proton event which probably accompanied the extreme magnetic storm of 1-2 September 1859. We use an inferred proton fluence for this event as estimated from nitrate levels in Greenland ice cores. We present results showing production of odd nitrogen compounds and their impact on ozone. We also compute rainout of nitrate in our model and compare to values from ice core data.Comment: Revised version including improved figures; Accepted for publication in Geophys. Res. Lett, chosen to be highlighted by AG

Initial conditions, Discreteness and non-linear structure formation in cosmology

In this lecture we address three different but related aspects of the initial continuous fluctuation field in standard cosmological models. Firstly we discuss the properties of the so-called Harrison-Zeldovich like spectra. This power spectrum is a fundamental feature of all current standard cosmological models. In a simple classification of all stationary stochastic processes into three categories, we highlight with the name ``super-homogeneous'' the properties of the class to which models like this, with $P(0)=0$, belong. In statistical physics language they are well described as glass-like. Secondly, the initial continuous density field with such small amplitude correlated Gaussian fluctuations must be discretised in order to set up the initial particle distribution used in gravitational N-body simulations. We discuss the main issues related to the effects of discretisation, particularly concerning the effect of particle induced fluctuations on the statistical properties of the initial conditions and on the dynamical evolution of gravitational clustering.Comment: 28 pages, 1 figure, to appear in Proceedings of 9th Course on Astrofundamental Physics, International School D. Chalonge, Kluwer, eds N.G. Sanchez and Y.M. Pariiski, uses crckapb.st pages, 3 figure, ro appear in Proceedings of 9th Course on Astrofundamental Physics, International School D. Chalonge, Kluwer, Eds. N.G. Sanchez and Y.M. Pariiski, uses crckapb.st

Long-term cycles in the history of life: Periodic biodiversity in the Paleobiology Database

Time series analysis of fossil biodiversity of marine invertebrates in the Paleobiology Database (PBDB) shows a significant periodicity at approximately 63 My, in agreement with previous analyses based on the Sepkoski database. I discuss how this result did not appear in a previous analysis of the PBDB. The existence of the 63 My periodicity, despite very different treatment of systematic error in both PBDB and Sepkoski databases strongly argues for consideration of its reality in the fossil record. Cross-spectral analysis of the two datasets finds that a 62 My periodicity coincides in phase by 1.6 My, equivalent to better than the errors in either measurement. Consequently, the two data sets not only contain the same strong periodicity, but its peaks and valleys closely correspond in time. Two other spectral peaks appear in the PBDB analysis, but appear to be artifacts associated with detrending and with the increased interval length. Sampling-standardization procedures implemented by the PBDB collaboration suggest that the signal is not an artifact of sampling bias. Further work should focus on finding the cause of the 62 My periodicity.Comment: Published in PLoS ONE. 5 pages, 3 figures. Version with live links, discussion available at http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004044#to

Small Scale Structure and High Redshift HI

Cosmological simulations with gas dynamics suggest that the Lyman-alpha forest is produced mainly by "small scale structure" --- filaments and sheets that are the high redshift analog of today's galaxy superclusters. There is no sharp distinction between Lyman-alpha clouds and "Gunn-Peterson" absorption produced by the fluctuating IGM -- the Lyman-alpha forest {\it is} the Gunn-Peterson effect. Lyman limit and damped Lyman-alpha absorption arises in the radiatively cooled gas of forming galaxies. At $z~2-3$, most of the gas is in the photoionized, diffuse medium associated with the Lyman-alpha forest, but most of the {\it neutral} gas is in damped Lyman-alpha systems. We discuss generic evolution of cosmic gas in a hierarchical scenario of structure formation, with particular attention to the prospects for detecting 21cm emission from high redshift HI. A scaling argument based on the present-day cluster mass function suggests that objects with M_{HI} >~ 5e11 h^{-1} \msun should be extremely rare at $z~3$, so detections with existing instruments will be difficult. An instrument like the proposed Square Kilometer Array could detect individual damped Lyman-alpha systems at high redshift, making it possible to map structure in the high redshift universe in much the same way that today's galaxy redshift surveys map the local large scale structure.Comment: 15 pages, latex w/ crckapb & epsf macros, ps figures; get ps version with all figures from ftp://bessel.mps.ohio-state.edu/pub/dhw/Preprints To appear in Cold Gas at High Redshift, eds. M. Bremer et al. (Kluwer, 1996

Characterizing the non-linear growth of large-scale structure in the Universe

The local Universe displays a rich hierarchical pattern of galaxy clusters and superclusters. The early Universe, however, was almost smooth, with only slight 'ripples' seen in the cosmic microwave background radiation. Models of the evolution of structure link these observations through the effect of gravity, because the small initially overdense fluctuations attract additional mass as the Universe expands. During the early stages, the ripples evolve independently, like linear waves on the surface of deep water. As the structures grow in mass, they interact with other in non-linear ways, more like waves breaking in shallow water. We have recently shown how cosmic structure can be characterized by phase correlations associated with these non-linear interactions, but hitherto there was no way to use that information to reach quantitative insights into the growth of structures. Here we report a method of revealing phase information, and quantify how this relates to the formation of a filaments, sheets and clusters of galaxies by non-linear collapse. We use a new statistic based on information entropy to separate linear from non-linear effects and thereby are able to disentangle those aspects of galaxy clustering that arise from initial conditions (the ripples) from the subsequent dynamical evolution.Comment: Accepted for publication in Nature. For high-resolution Figure 3, please see http://www.nottingham.ac.uk/~ppzpc/phases/n0colorphase.html, For the animations and the idea of this paper please see http://www.nottingham.ac.uk/~ppzpc/phases/index.htm