A Mechanism Involving Solar Ultraviolet Variations for Modulating the Interannual Climatology of the Middle Atmosphere

In years of low solar activity, free traveling wave modes in the upper stratosphere are dominated by atmospheric normal modes such as the 16-day wave. However, within a 4-year interval centered on the 1980 to 1981 solar maximum, cross-spectral analyses of zonal mean satellite temperature data versus the solar UV flux demonstrate significant power near 27 and 13 days, providing indirect evidence that short-term UV variations were capable of exciting traveling planetary-scale waves in the upper stratosphere. Previous theoretical and observational work has indicated that interference between traveling waves and stationary waves forced from below (and the resulting oscillating latitudinal heat transports) plays a likely role in the initiation of stratospheric warmings. Researchers therefore hypothesize that the initiation of a major stratospheric warming in the upper stratosphere and lower mesosphere may depend to some extent on the amplitude of longer-period 27-day traveling waves in the upper stratosphere. This would represent a new mechanism for solar UV effects on stratospheric climatology that may be relevant to the interpretation of some recent long-term correlative results

A Probable Approx. 2400 Year Solar Quasi-cycle in Atmospheric Delta C-14

A 2200 to 2600 year quasi-periodicity is present in atmospheric delta C-14 records after removal of long-term trends due to the geomagnetic dipole amplitude variation. This periodicity consists of both a long-term variation of the mean and a superposed, approximately recurring pattern of century-scale variations. The strongest of these latter variations occur near maxima of the approx. 2400 year delta C-14 cycles. The residual record can be modeled to first order as an amplitude modulation of a century-scale periodic forcing function by a approx. 2400 year periodic forcing function. During the last millennium, the largest century-scale variations (occurring near the most recent 2400 year delta C-14 maximum) are known to be mainly a consequence of the pronounced Maunder, Sporer, and Wolf solar activity minima, as verified by independent proxy solar activity records. Therefore, during this period, amplitude modulation has been occurring primarily in the sun and not in the terrestrial radiocarbon system. It is therefore inferred that the approx. 2400 year forcing function is mainly solar although some secondary terrestrial feedback into the delta C-14 record is likely. This conclusion has implications for the predictability of future pronounced solar activity minima and for the interpretation of certain minor Holocene climatic variations

Solar cycle variations of stratospheric ozone and temperature in simulations of a coupled chemistry-climate model

The results from three 45-year simulations of a coupled chemistry climate model are analysed for solar cycle influences on ozone and temperature. The simulations include UV forcing at the top of the atmosphere, which includes a generic 27-day solar rotation effect as well as the observed monthly values of the solar fluxes. The results are analysed for the 27-day and 11-year cycles in temperature and ozone. In accordance with previous results, the 27-day cycle results are in good qualitative agreement with observations, particularly for ozone. However, the results show significant variations, typically a factor of two or more in sensitivity to solar flux, depending on the solar cycle. <br><br> In the lower and middle stratosphere we show good agreement also between the modelled and observed 11-year cycle results for the ozone vertical profile averaged over low latitudes. In particular, the minimum in solar response near 20 hPa is well simulated. In comparison, experiments of the model with fixed solar phase (solar maximum/solar mean) and climatological sea surface temperatures lead to a poorer simulation of the solar response in the ozone vertical profile, indicating the need for variable phase simulations in solar sensitivity experiments. The role of sea surface temperatures and tropical upwelling in simulating the ozone minimum response are also discussed

Superradiance for atoms trapped along a photonic crystal waveguide

We report observations of superradiance for atoms trapped in the near field of a photonic crystal waveguide (PCW). By fabricating the PCW with a band edge near the D$_1$ transition of atomic cesium, strong interaction is achieved between trapped atoms and guided-mode photons. Following short-pulse excitation, we record the decay of guided-mode emission and find a superradiant emission rate scaling as $\bar{\Gamma}_{\rm SR}\propto\bar{N}\cdot\Gamma_{\rm 1D}$ for average atom number $0.19 \lesssim \bar{N} \lesssim 2.6$ atoms, where $\Gamma_{\rm 1D}/\Gamma_0 =1.1\pm0.1$ is the peak single-atom radiative decay rate into the PCW guided mode and $\Gamma_{0}$ is the Einstein-$A$ coefficient for free space. These advances provide new tools for investigations of photon-mediated atom-atom interactions in the many-body regime.Comment: 11 pages, 10 figure

Tests of an NACA 66,2-420 Airfoil of 5-Foot Chord at High Speed, Special Report

This report covers tests of a 5-foot model of the NACA 66,2-420 low-drag airfoil at high speeds including the critical compressibility speed. Section coefficients of lift, drag, and pitching moment, and extensive pressure-distribution data are presented. The section drag coefficient at the design lift coefficient of 0.4 increased from 0.0042 at low speeds to 0.0052 at a Mach number of 0.56 (390 mph at 25,000 ft altitude). The critical Mach number was about 0.60. The results cover a Reynold number range from 4 millions to 17 millions

Building one molecule from a reservoir of two atoms

Chemical reactions typically proceed via stochastic encounters between reactants. Going beyond this paradigm, we combine exactly two atoms into a single, controlled reaction. The experimental apparatus traps two individual laser-cooled atoms (one sodium and one cesium) in separate optical tweezers and then merges them into one optical dipole trap. Subsequently, photoassociation forms an excited-state NaCs molecule. The discovery of previously unseen resonances near the molecular dissociation threshold and measurement of collision rates are enabled by the tightly trapped ultracold sample of atoms. As laser-cooling and trapping capabilities are extended to more elements, the technique will enable the study of more diverse, and eventually more complex, molecules in an isolated environment, as well as synthesis of designer molecules for qubits

Two minor determinants of myelin basic protein induce experimental allergic encephalomyelitis in SJL/J mice

Experimental allergic encephalomyelitis (EAE)' is an autoimmune inflammatory demyelinating disease in the central nervous system (CNS) of animals immunized with myelin basic protein (MBP). The disease is directly mediated by Thelper cells that recognize MBP in the context ofclass II antigens of the MHC (1-3). In nude mice, a single clone of adoptively transferred MBP-reactive T helper cells can cause EAE (4), suggesting that these are the only T cells required for disease induction. As a prototypic model of T helper cell-mediated autoimmune disease, observations in EAE could likely be applicable to other T helper cell-mediated diseases such as murine lupus (5), thyroiditis (6), collagen arthritis (7), and adjuvant arthritis (8), as well as human autoimmune diseases. The MBP epitope is determined in part by the MHC. Using proteolytic peptide fragments of MBP, SJL/J (H-2s) and BIO.T(6R) (H-2q) mice were found to develop EAE to the COOH-terminal peptide of MBP, whereas PL/J (H-2u) and A/J (H-2k) mice developed EAE to the NH2-terminal peptide of MBP (9). Recently, by using synthetic peptides that overcome the difficulties of obtaining pure uncontaminated proteolytic peptides, a single T cell encephalitogenic epitope for PL/J mice has been identified . This epitope consists of the first nine NH2-terminal amino acid residues of MBP which must be acetylated at the a amino group to induce disease (10). Similar fine mapping of the encephalitogenic T cell epitope(s) for SJL/J mice has not been done, in part because of the large size of the COOH-terminal peptic fragment of MBP (residues 89-169 of rat MBP, reference 9). MouseMBP consists offour major forms due to differential RNA splicing of exons II and VI (11), resulting in molecular masses of 21, 18.5, 17.5, and 14 kD, in the relative amounts of 1 :10:3.5:35 . Since EAE can also be induced with the small form of rat MBP (14 kD), which has exons II and VI of the MBP gene deleted (12), the COOH-terminal encephalitogenic determinant for SJL/J mice must be present within a segment ofonly 42 amino acid residues . Consistent withthis notion is the observation that this peptide sequence is identical among the MBPs of several mammalian species, including mouse, rat, bovine, guinea pig, and porcine, all of which can induce EAE in SJL/mice (13, 14). To identify the SJL/J encephalitogenic T cell epitope(s), overlapping peptides to the COOH-terminal region ofthe small form of mouse MBP were synthesized. Two overlapping peptides encompassing an 18-amino acid region were found to elicit EAE in SJL/J mice. The finding of a single peptide region of MBP that is responsible for encephalitogenic T cell epitopes in SJL/J mice is analogous to that of the PL/J mice and has implications for the development of specific therapy for T cell-mediated autoimmune diseases

Surface spin-flop phases and bulk discommensurations in antiferromagnets

Phase diagrams as a function of anisotropy D and magnetic field H are obtained for discommensurations and surface states for a model antiferromagnet in which $H$ is parallel to the easy axis. The surface spin-flop phase exists for all $D$. We show that there is a region where the penetration length of the surface spin-flop phase diverges. Introducing a discommensuration of even length then becomes preferable to reconstructing the surface. The results are used to clarify and correct previous studies in which discommensurations have been confused with genuine surface spin-flop states.Comment: 4 pages, RevTeX, 2 Postscript figure