U-shaped type II solar radio bursts associated with the 1980 March 28 flare

Observations of the 1980 March 28, 2B flare in optical, radio microwave and metric and X-ray wavelengths are presented. In the dynamic radio spectrum, unusual and rare U-shaped type II radio bursts associated with this flare have been observed. The normal type II bursts display negative frequency drift, due to the flare-triggered shock wave travelling outwards in the solar corona. But in this case the type II emission first showed the usual negative frequency drift, and then after reaching a plateau level, showed a positive drift, thus giving the shape of an inverted "U". The authors propose a model for this type II emission.We suggest that the shock wave generated by the flare or the flare spray propagates through sucting and repeated reflections, which takes place within a large scale coronal loop or an arcade of loops, thus resulting in reverse frequency drift in type II emission

The importance of time-varying forcing for QBO modulation of the atmospheric 11 year solar cycle signal

We present results from three multidecadal sensitivity experiments with time-varying solar cycle and quasi-biennial oscillation (QBO) forcings using National Center for Atmospheric Research's Whole Atmosphere Community Climate Model (WACCM3.1). The model experiments are unique compared to earlier studies as they use time-varying forcings for the solar cycle only and the QBO, both individually and combined. The results show that the annual mean solar response in the tropical upper stratosphere is independent of the presence of the QBO. The response in the middle to lower stratosphere differs depending on the presence of the QBO and the solar cycle but is statistically indistinguishable in the three experiments. The seasonal evolution of the solar and the combined solar-QBO signals reveals a reasonable agreement with observations only for the experiment in which both the solar cycle and the QBO forcing are present, suggesting that both forcings are important to generate the observed response. More stratospheric warmings occur during solar maximum and QBO west conditions. This appears to be the result of a QBO modulation of the background zonal mean wind climatology, which modifies the solar signal. Depending on the background wind, the small initial early winter solar signal in the subtropical upper stratosphere/lower mesosphere is enhanced during QBO east and diminished during QBO west conditions. This consequently influences the transfer of the solar-QBO signal during winter and results in the observed differences during late winte

5He ternary fission yields of 252Cf and 235U(n,f)

The relative 4He and 5He ternary fission yields were determined from a careful analysis of the energy distribution of α spectra from a new measurement with a 252Cf source and from published data on 252Cf and 235U(n,f). The kinetic energies of the 5He and 4He ternary particles were found to be approximately 11 and 16 MeV, respectively. 5He particles contribute 10-20% to the total alpha yield with the remainder originating from 4He accompanied fission

Nano-sampling of solids with nanosecond and femtosecond lasers and tip enhanced near-field ablation

International audienceA method of near-field (NF) laser ablation for sampling of solids with a nm resolution was developed and applied. The method is based on the coupling of nanosecond or femtosecond laser pulses with an Atomic Force Microscope (AFM). The technique uses a tip enhancement effect obtained by interaction of laser radiation with a tip of the AFM maintained a few nm above a sample surface. In our experiments, craters of about 100 nm in diameter and a few nm in depth were obtained with a single laser pulse on gold and silicon samples. The elemental or isotope content of the ablated matter may be analyzed by a mass spectrometer with inductively coupled plasma source (ICP-MS). An electrostatic model of the NF created by an ellipsoidal tip with a coating was used in NF heating and ablation calculations. It allows one to take into account the effect of possible plasmonic resonance (both in the tip and the surface under study) on the NF enhancement factor. A two-temperature model of electron and lattice heating was used for temperature calculations for both heating and ablation regimes. A multi-parametric study was made to understand the effect of different experimental parameters (laser fluence, tip-to-sample distance, sample and tip nature) on NF laser ablation efficiency, crater dimensions and amount of ablated material. The developed combined model of the NF heating and ablation was used to test calculations and to study different interaction features. Numerical simulations of the NF localized heating with a 3-D code have offered a good explanation of nm crater diameters obtained in the experiments

The HAMMONIA Chemistry Climate Model: Sensitivity of the mesopause region to the 11-year solar cycle and CO₂ doubling

This paper introduces the three-dimensional Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), which treats atmospheric dynamics, radiation, and chemistry interactively for the height range from the earth’s surface to the thermosphere (approximately 250 km). It is based on the latest version of the ECHAM atmospheric general circulation model of the Max Planck Institute for Meteorology in Hamburg, Germany, which is extended to include important radiative and dynamical processes of the upper atmosphere and is coupled to a chemistry module containing 48 compounds. The model is applied to study the effects of natural and anthropogenic climate forcing on the atmosphere, represented, on the one hand, by the 11-yr solar cycle and, on the other hand, by a doubling of the present-day concentration of carbon dioxide. The numerical experiments are analyzed with the focus on the effects on temperature and chemical composition in the mesopause region. Results include a temperature response to the solar cycle by 2 to 10 K in the mesopause region with the largest values occurring slightly above the summer mesopause. Ozone in the secondary maximum increases by up to 20% for solar maximum conditions. Changes in winds are in general small. In the case of a doubling of carbon dioxide the simulation indicates a cooling of the atmosphere everywhere above the tropopause but by the smallest values around the mesopause. It is shown that the temperature response up to the mesopause is strongly influenced by changes in dynamics. During Northern Hemisphere summer, dynamical processes alone would lead to an almost global warming of up to 3 K in the uppermost mesosphere