Weather Prediction in Babylonia

This paper addresses developments in the prediction of weather phenomena in Late Babylonian scholarly texts. Previously published and unpublished texts are analyzed and the underlying methods are compared with omen-based weather prognostication, developments in Babylonian astronomical prediction and reporting practices in the astronomical diaries. It is found that some texts combine long-term astronomical prediction with inferential methods for predicting weather phenomena. It is argued that these new methods for predicting weather phenomena are part of a larger Babylonian effort to predict and explain non-astronomical phenomena by relating them to predictable astronomical phenomena

Introduction

This article introduces a double issue comprising 11 papers about Babylonian and Egyptian priests and scholarship between ca. 600 bce and 200 ce. They constitute the proceedings of the workshop “Scholars, Priests, and Temples: Babylonian and Egyptian Science in Context”, which was held at the Humboldt University Berlin, 12–14 May 2016, with support of the Excellence Cluster TOPOI. The workshop brought together Assyriologists and Egyptologists with expertise in Babylonian and Egyptian scholarship, priesthoods and temple institutions. All contributions have been revised and updated since then. The present contribution offers a brief introduction on previous research, cross-cultural interactions, economic aspects, royal patronage, and internal developments of Babylonian and Egyptian temple scholarship, followed by short summaries of the papers

Performative Aspects of Assyrian Celestial Divination and Babylonian Astronomical Diaries

This contribution explores performative aspects of Assyrian celestial divination and Babylonian astronomical diaries and related texts during the first millennium BCE. While the sources for Assyrian celestial divination contain much evidence about observational and ritual performances, astronomical diaries and related texts are mainly concerned with observation and prediction. It is argued that the Assyrian evidence can shed light on some poorly docu-mented performative aspects of astronomical practices in Babylon

Geodynamo alpha-effect derived from box simulations of rotating magnetoconvection

The equations for fully compressible rotating magnetoconvection are numerically solved in a Cartesian box assuming conditions roughly suitable for the geodynamo. The mean electromotive force describing the generation of mean magnetic flux by convective turbulence in the rotating fluid is directly calculated from the simulations, and the corresponding alpha-coefficients are derived. Due to the very weak density stratification the alpha-effect changes its sign in the middle of the box. It is positive at the top and negative at the bottom of the convection zone. For strong magnetic fields we also find a clear downward advection of the mean magnetic field. Both of the simulated effects have been predicted by quasi-linear computations (Soward, 1979; Kitchatinov and Ruediger, 1992). Finally, the possible connection of the obtained profiles of the EMF with mean-field models of oscillating alpha^2-dynamos is discussed.Comment: 17 pages, 9 figures, submitted to Phys. Earth Planet. Inte

Helicity Observation of Weak and Strong Fields

We report in this letter our analysis of a large sample of photospheric vector magnetic field measurements. Our sample consists of 17200 vector magnetograms obtained from January 1997 to August 2004 by Huairou Solar Observing Station of the Chinese National Astronomical Observatory. Two physical quantities, $\alpha$ and current helicity, are calculated and their signs and amplitudes are studied in a search for solar cycle variations. Different from other studies of the same type, we calculate these quantities for weak ($100G1000G$) fields separately. For weak fields, we find that the signs of both $\alpha$ and current helicity are consistent with the established hemispheric rule during most years of the solar cycle and their magnitudes show a rough tendency of decreasing with the development of solar cycle. Analysis of strong fields gives an interesting result: Both $\alpha$ and current helicity present a sign opposite to that of weak fields. Implications of these observations on dynamo theory and helicity production are also briefly discussed.Comment: accepted for publication in ApJ Lette

Magnetoconvection and dynamo coefficients: II. Field-direction dependent pumping of magnetic field

We study the pumping of magnetic flux in three-dimensional compressible magnetoconvection in the context of stellar dynamos. The simulation domain represents a rectangular section from the lower part of a stellar convection zone plus the underlying stably stratified layer, with a total depth of up to five pressure scale heights. Once convection has attained a statistically stationary state, a magnetic field is introduced. The magnetic field is subsequently modified by the convective motions, and the resulting pumping effects are isolated by calculating various coefficients of the expansion of the electromotive force, uxb, in terms of components of the mean magnetic field. The dependence of the pumping effects on rotation, latitude and other parameters is studied. First numerical evidence is found for the existence of pumping effects in the horizontal directions, unless the rotation axis coincides with the vertical axis, as is the case on the poles. Evidence is found that the pumping effects act differently on different components of the mean magnetic field. Latitudinal pumping is mainly equatorward for toroidal field, and can be poleward for poloidal field. Longitudinal pumping is mainly retrograde for the radial field but prograde for the latitudinal field. The pumping effect in the vertical direction is found to be dominated by the diamagnetic effect, equivalent to a predominating downward advection with a maximum speed in the turbulent case of about 10 percent of the rms convective velocity. Where possible, an attempt is made to identify the physical origin of the effect. Finally, some consequences of the results for stellar dynamos are discussed.Comment: 12 pages, 9 figures, submitted to A&A; version