The Polarization Signature of Local Bulk Flows

A large peculiar velocity of the intergalactic medium produces a Doppler shift of the cosmic microwave background with a frequency-dependent quadrupole term. This quadrupole will act as a source for polarization of the cosmic microwave background, creating a large-scale polarization anisotropy if the bulk flow is local and coherent on large scales. In the case where we are near the center of the moving region, the polarization signal is a pure quadrupole. We show that the signal is small, but detectable with future experiments for bulk flows as large as some recent reports.Comment: 5 pages, 3 figures. Accepted by Ap

Investigation of new systems for potential laser action Quarterly status report, 1 Dec. 1968 - 28 Feb. 1969

Electronic absorption spectra of mercuric iodid

Investigation of new systems for potential laser action Quarterly report, 1 Jun. - 30 Sep. 1969

Metal halides as new chemical system for laser actio

Comments on "Statistical guidance methods for predicting snowfall accumulation in the northeast United States"€� by McCandless et al. (2012)

McCandless et al. (2012) examine eight statistical methods for predicting the snowfall accumulation from the output of the Global Ensemble Forecast System. Some of these results have been previously tested by others, but were not discussed within their article. These comments demonstrate the importance of a thorough literature synthesis that accurately reflects the content of the paper

A 27 day persistence model of near-Earth solar wind conditions: a long lead-time forecast and a benchmark for dynamical models

Geomagnetic activity has long been known to exhibit approximately 27 day periodicity, resulting from solar wind structures repeating each solar rotation. Thus a very simple near-Earth solar wind forecast is 27 day persistence, wherein the near-Earth solar wind conditions today are assumed to be identical to those 27 days previously. Effective use of such a persistence model as a forecast tool, however, requires the performance and uncertainty to be fully characterized. The first half of this study determines which solar wind parameters can be reliably forecast by persistence and how the forecast skill varies with the solar cycle. The second half of the study shows how persistence can provide a useful benchmark for more sophisticated forecast schemes, namely physics-based numerical models. Point-by-point assessment methods, such as correlation and mean-square error, find persistence skill comparable to numerical models during solar minimum, despite the 27 day lead time of persistence forecasts, versus 2–5 days for numerical schemes. At solar maximum, however, the dynamic nature of the corona means 27 day persistence is no longer a good approximation and skill scores suggest persistence is out-performed by numerical models for almost all solar wind parameters. But point-by-point assessment techniques are not always a reliable indicator of usefulness as a forecast tool. An event-based assessment method, which focusses key solar wind structures, finds persistence to be the most valuable forecast throughout the solar cycle. This reiterates the fact that the means of assessing the “best” forecast model must be specifically tailored to its intended use

Probabilistic concepts in a changing climate: a snapshot attractor picture

The authors argue that the concept of snapshot attractors and of their natural probability distributions are the only available tools by means of which mathematically sound statements can be made about averages, variances, etc., for a given time instant in a changing climate. A basic advantage of the snapshot approach, which relies on the use of an ensemble, is that the natural distribution and thus any statistics based on it are independent of the particular ensemble used, provided it is initiated in the past earlier than a convergence time. To illustrate these concepts, a tutorial presentation is given within the framework of a low-order model in which the temperature contrast parameter over a hemisphere decreases linearly in time. Furthermore, the averages and variances obtained from the snapshot attractor approach are demonstrated to strongly differ from the traditional 30-yr temporal averages and variances taken along single realizations. The authors also claim that internal variability can be quantified by the natural distribution since it characterizes the chaotic motion represented by the snapshot attractor. This experience suggests that snapshot-attractor-based calculations might be appropriate to be evaluated in any large-scale climate model, and that the application of 30-yr temporal averages taken along single realizations should be complemented with this more appealing tool for the characterization of climate changes, which seems to be practically feasible with moderate ensemble sizes

Possible mechanisms of explosive maritime cyclogenesis

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1983.Microfiche copy available in Archives and Science.Bibliography: leaves 126-127.by Paul Joseph Roebber.M.S