ALBERT

Description: Recent observations on DIII-D have advanced the understanding of plasma response to applied resonant magnetic perturbations (RMPs) in both H-mode and L-mode plasmas. Three distinct 3D features localized in minor radius are imaged via filtered soft x-ray emission: (i) the formation of lobes extending from the unperturbed separatrix in the X-point region at the plasma boundary, (ii) helical kink-like perturbations in the steep-gradient region inside the separatrix, and (iii) amplified islands in the core of a low-rotation L-mode plasma. These measurements are used to test and to validate plasma response models, which are crucial for providing predictive capability of edge-localized mode control. In particular, vacuum and two-fluid resistive magnetohydrodynamic (MHD) responses are tested in the regions of these measurements. At the plasma boundary in H-mode discharges with n  = 3 RMPs applied, measurements compare well to vacuum-field calculations that predict lobe structures. Yet in the steep-gradient region, measurements agree better with calculations from the linear resistive two-fluid MHD code, M3D-C1. Relative to the vacuum fields, the resistive two-fluid MHD calculations show a reduction in the pitch-resonant components of the normal magnetic field (screening), and amplification of non-resonant components associated with ideal kink modes. However, the calculations still over-predict the amplitude of the measured perturbation by a factor of 4. In a slowly rotating L-mode plasma with n  = 1 RMPs, core islands are observed amplified from vacuum predictions. These results indicate that while the vacuum approach describes measurements in the edge region well, it is important to include effects of extended MHD in the pedestal and deeper in the plasma core.

Description: CloudSat observations have indicated that multiple scattering affects 94 GHz spaceborne radar observations. The ESA EarthCARE explorer mission scheduled to launch in 2015 features also a spaceborne 94-GHz radar with Doppler capability for providing a global data set of convective motions and particle sedimentation rates. Vertical velocity measurements will be collected in all cloud conditions, including deep convection where multiple-scattering is expected to contaminate the signal. Thus, before the spaceborne Doppler radars are used for science application, it is imperative to develop a method to identify radar range gates contaminated by multiple scattering contributions. Based on simulations, a criterion to identify the onset of multiple scattering is presented in this paper; the cumulative integrated reflectivity from the top of the atmosphere is a proxy of the multiple scattering enhancement and can be confidently used to detect the onset of multiple scattering. Analysis of a limited (two months) CloudSat data set reveals that, for deep tropical convective cores, the onset of significant multiple scattering typically occurs in the region between 9–10 km and more than 35% of the range bins above the freezing level height and with reflectivity above −20 dBZ are not affected by multiple scattering. This assessment offers a conservative upper limit for EarthCARE 94-GHz radar multiple scattering effects due to the narrower field of view of the Doppler radar compared to CloudSat's radar. Identification of multiple scattering contamination in the CloudSat and EarthCARE radar observations facilitates the following objectives: (1) to constrain the region of validity of currently developed CloudSat products based on single scattering theory (e.g. 2B-CWC-RO, 2B-CWC-RVOD) and (2) to filter out multiple scattering affected range bins in any analysis aimed at the assessment of the feasibility and of the accuracy of the EarthCARE Doppler estimates within deep convective cores.