Long-term persistence of solar activity

The solar irradiante has been found to change by 0.1% over the recent solar cycle. A change of irradiante of about 0.5% is required to effect the Earth's climate. How frequently can a variation of this size be expected? We examine the question of the persistence of non-periodic variations in solar activity. The Hürst exponent, which characterizes the persistence of a time series (Mandelbrot and Wallis, 1969), is evaluated for the series of¹⁴ C data for the time interval from about 6000 BC to 1950 AD (Stuiver and Pearson, 1986). We find a constant Hürst exponent, suggesting that solar activity in the frequency range of from 100 to 3000 years includes an important continuum component in addition to the well-known periodic variations. The value we calculate,H ≈ 0.8, is significantly larger than the value of 0.5 that would correspond to variations produced by a white-noise process. This value is in good agreement with the results for the monthly sunspot data reported elsewhere, indicating that the physics that produces the continuum is a correlated random process (Ruzmaikin et al., 1992), and that it is the same type of process over a wide range of time interval lengths. We conclude that the time period over which an irradiance change of 0.5% can be expected to occur is significantly shorter than that which would be expected for variations produced by a white-noise process. The full paper has been submitted to Solar Physics. Part of the research decribed here was carried out by JPL, Caltech under a contract with NASA.     

Merger histories in warm dark matter structure formation scenarios

Observations on galactic scales seem to be in contradiction with recent high-resolution N -body simulations. This so-called cold dark matter (CDM) crisis has been addressed in several ways, ranging from a change in fundamental physics by introducing self-interacting cold dark matter particles to a tuning of complex astrophysical processes such as global and/or local feedback. All these efforts attempt to soften density profiles and reduce the abundance of satellites in simulated galaxy haloes. In this paper, we explore a different approach that consists of filtering the dark matter power spectrum on small scales, thereby altering the formation history of low-mass objects. The physical motivation for damping these fluctuations lies in the possibility that the dark matter particles have a different nature, i.e. are warm (WDM) rather than cold. We show that this leads to some interesting new results in terms of the merger history and large-scale distribution of low-mass haloes, compared with the standard CDM scenario. However, WDM does not appear to be the ultimate solution, in the sense that it is not able to fully solve the CDM crisis, even though one of the main drawbacks, namely the abundance of satellites, can be remedied. Indeed, the cuspiness of the halo profiles still persists, at all redshifts, and for all haloes and sub-haloes that we investigated. Despite the persistence of the cuspiness problem of DM haloes, WDM seems to be still worth taking seriously, as it alleviates the problems of over-abundant sub-structures in galactic haloes and possibly the lack of angular momentum of simulated disc galaxies. WDM also lessens the need to invoke strong feedback to solve these problems, and may provide a natural explanation of the clustering properties and ages of dwarfs.     

THE IMPACT-FLOOD CONNECTION: DOES IT EXIST?*

In a recent article in Terra Nova, Kristan-Tollmann and Tollmann (1994) suggested that the Biblical Flood can be explained by seven fragments of a comet that impacted the ocean at seven locations on Earth at 03.00h (C.E.T.) on 23 September, 9545 yr BP. We demonstrate that all the ‘geological proofs’ that allegedly support their conclusions are not supported by the available data on impact cratering. Their hypothesis is based on insufficient and ambiguous data, selective citation, and incomplete comprehension of previous research.     

H4 and H5 chondrites from the Rub'al Khali Desert

Abstract Al-Jimshan is a highly weathered 11.45 kg chondrite that was found in 1955 in the Rub' al Khali Desert, Saudi Arabia (20*42′N, 52*50E) about 240 km south-east of the town of al-Hadidah. The main mass is now at UCLA. Based on texture and mineral composition (olivine Fa_17.7 ± 0.4; pyroxene Fs_15.7 ± 1.0 Wo₁₃ ± 0.4), al-Jimshan is classified as an H4 chondrite of shock stage S2. The Bir-Hadi and ad-Dahbubah H chondrites, which also were found in the Rub'al Khali (Holm, 1962), are probably not paired with al-Jimshan. They are classified as H5, shock stage S3 (Fa_18.1 ± 0.5, n = 10; Fs_16.0 ± 0.6, Wo_1.1 ± 0.4, n = 9) and H5, shock stage S2 (Fa_17.9 ± 0.3, n = 10; FS_15.5 ± 0.2 Wo_1.0 ± 0.4, n = 10), respectively.     

The youngest big impact on Earth deduced from geological and historical evidence

The comparison of events that followed the great impact at the Cretaceous/Tertiary boundary with those contained within the Flood myths suggests an analogous cosmic cause. This paper proposes that there is geological evidence to support this thesis which is also indicated by a careful analysis of the natural phenomena described in Flood traditions. The time, the sites, the cause, the detailed course of the events and the consequences of this catastrophe can hope to be reconstructed.