A practical step-by-step guide to wavelet analysis is given, with examples taken from time series of the El Nino–Southern Oscillation (ENSO). The guide includes a comparison to the windowed Fourier transform, the choice of an appropriate wavelet basis function, edge effects due to finite-length time series, and the relationship between wavelet scale and Fourier frequency. New statistical significance tests for wavelet power spectra are developed by deriving theoretical wavelet spectra for white and red noise processes and using these to establish significance levels and confidence intervals. It is shown that smoothing in time or scale can be used to increase the confidence of the wavelet spectrum. Empirical formulas are given for the effect of smoothing on significance levels and confidence intervals. Extensions to wavelet analysis such as filtering, the power Hovmoller, cross-wavelet spectra, and coherence are described. The statistical significance tests are used to give a quantitative measure of change...

https://atoc.colorado.edu/research/wavelets/bams_79_01_0061.pdf

A Practical Guide to Wavelet Analysis.

Changes in Atmospheric Constituents and in Radiative Forcing

The presence of a Jupiter-mass companion to the star 51 Pegasi is inferred from observations of periodic variations in the star's radial velocity. The companion lies only about eight million kilometres from the star, which would be well inside the orbit of Mercury in our Solar System. This object might be a gas-giant planet that has migrated to this location through orbital evolution, or from the radiative stripping of a brown dwarf.

A Jupiter-Mass Companion to a Solar-Type Star

This chapter should be cited as: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Coordinating Lead Authors: Gunnar Myhre (Norway), Drew Shindell (USA)

Anthropogenic and Natural Radiative Forcing

We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA star. Improvements in MESA star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 M ? stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA star solves the fully coupled stellar structure and composition equations, and we show how this has improved the scaling of MESA's calculational speed on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit that packages all the required components needed to form a unified, maintained, and well-validated build environment for MESA. We also highlight a few tools developed by the community for rapid visualization of MESA star results.

/pdf/modules-for-experiments-in-stellar-astrophysics-mesa-planets-29j324a9bq.pdf

Modules for Experiments in Stellar Astrophysics (MESA): Planets, Oscillations, Rotation, and Massive Stars

The recent discoveries of extrasolar planetary systems around lower main-sequence stars such as tau Booe (HD 120136) has prompted further investigation into their stellar activity A cursory analysis of tau Booe for cyclic chromospheric activity, based on its 30-yr record of Ca 2 H and K fluxes obtained as part of the HK Project from Mount Wilson Observatory, finds an intermediate, sub-yearly period (approximately 117 d) in chromospheric activity in addition to, and separate from, both its rotation (33 d) and long-term variability As a persistent subyearly period in surface magnetic activity is unprecedented, we investigate this apparent anomaly further by examining chromospheric activity levels of other stars with similar mass, searching for variability in chromospheric activity with periods of less than one year, but longer than measured or predicted rotation An examination of the time series of 40 mid-to-late F dwarfs yielded one other star for further analysis: alpha Com (HD 114378, P approximately 132 d) The variations for these two stars were checked for persistence and coherence Based on these determinations, we eliminate the possibilities of rotation, long-term activity cycle, and the evolution of active regions as the cause of this variation in both stars In particular, for tau Booe we infer that the phenomenon may be chromospheric in origin; however, beyond this, it is difficult to identify anything further regarding the cause of the activity variations, or even whether the observed modulation in the two stars have the same origin

Persistent Sub-Yearly Chromospheric Variations in Lower Main-Sequence Stars: Tau Booe and alpha Com

We compiled and analyzed a daily time series of temperatures and precipitation totals from Mount Wilson, California from 1918 to 1998. Our results show a large decline in maximum temperature, no change or an upward trend in minimum temperature, and a substantial decline in the diurnal temperature range (DTR). The interannual variations in monthly maximum temperature and DTR are significantly correlated with monthly precipitation levels, sea-surface temperatures (SSTs) off the coast of Southern California, and the Southern Oscillation Index (SOI). El Nino periods and/or months with high SST anomalies tend to be wet with lower maximum temperatures and DTR while La Nina periods and/or months of lower SSTs are hotter and drier with higher DTR values. It is noteworthy that the SOI and SSTs have significant trends toward more El Nino-like conditions with higher SSTs off Southern California.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999GL006064

Large asymmetrical temperature trends at Mount Wilson, California

Sunlight supplies most of the energy that drives the dynamics of the terrestrial climate. Speculation on the role of changes in the sun and their influence on changes in the earth’s climate has been ongoing for centuries. Riccioli (1651, 1653) considered the possible connection of sunspot activity with weather in Italy, e.g., the warm and dry weather during September of 1632 when there were no spots in contrast to the cold June of 1642 when there were many spots. Herschel (1801) reported, “I am now much inclined to believe that openings with great shallows, ridges, nodules and corrugations, instead of small indentations, may lead us to expect a copious emission of heat, and therefore mild seasons. And that on the contrary, pores, small indentations, the absence of ridges and nodules, and of large openings and shallows, will denote a spare emission of heat, may induce us to expect severe seasons” (see, e.g., Schove 1983 for a review of the history of the sun-climate connection).

An Assessment of the Sun-Climate Relation on Time Scales of Decades to Centuries: The Possibility of Total Irradiance Variations

We have mounted an early adaptive optics system, the Atmospheric Compensation Experiment (ACE), on the 60-inch telescope at Mount Wilson Observatory in California in a program designed to investigate the performance of ACE at an astronomical site and to evaluate the usefulness of adaptive optics for astronomy. Despite its development as a non-astronomical instrument, ACE has produced positive results, including the obtaining of images of single and double stars with a resolution (full-width half-maximum) of 117 milliarcseconds at 700 nm. Improvement of image quality is obtained for guide objects with a B magnitude brighter than 5.9. To deepen this limiting magnitude, we have embarked on a low-noise high-speed CCD fabrication project jointly with JPL. First devices have been fabricated. We have applied post- processing techniques borrowed from speckle methodology to the adaptive optics images, and find that the pre- and post-processing techniques complement each other powerfully. We conclude that an adaptive optics system designed specifically for visible-wavelength astronomy would be a low-order system with good site thermal control, combined with post-processing. Such a system could be effective, robust and relatively low cost.

Sallie L. Baliunas

Papers

Persistent Sub-Yearly Chromospheric Variations in Lower Main-Sequence Stars: Tau Booe and alpha Com

Large asymmetrical temperature trends at Mount Wilson, California

An Assessment of the Sun-Climate Relation on Time Scales of Decades to Centuries: The Possibility of Total Irradiance Variations

Results of adaptive optics at Mt. Wilson Obseratory

Climatic and Environmental Changes of the Past 1000 Years