ALBERT

Description: In this letter, first observations of ion-scale magnetic island from the Magnetospheric Multiscale (MMS) mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized by bipolar variation of magnetic fields with magnetic field compression, strong core field, density depletion and strong currents dominated by the parallel component to the local magnetic field. The estimated size of magnetic island is about 8 d i , where d i is the ion inertial length. Distinct particle behaviors and wave activities inside and at the edges of the magnetic island are observed: parallel electron beam accompanied with electrostatic solitary waves and strong electromagnetic lower hybrid drift waves inside the magnetic island; bidirectional electron beams, whistler waves, weak electromagnetic lower hybrid drift waves and strong broadband electrostatic noise at the edges of the magnetic island. Our observations demonstrate that highly dynamical, strong wave activities and electron-scale physics occur within ion-scale magnetic islands in the magnetosheath turbulent plasma.

Description: Estimates of the recent decline in Arctic Ocean summer sea ice extent can vary due to differences in sea ice data sources, in the number of years used to compute the trend, and in the start and end years used in the trend computation. Compounding such differences, estimates of the relative decline in sea ice cover (given in percent change per decade) can further vary due to the choice of reference value (the initial point of the trend line, a climatological baseline, etc.). Further adding to the confusion, very often when relative trends are reported in research papers, the reference values used are not specified or made clear. This can lead to confusion when trend studies are cited in the press and public reports.

Description: Abstract An experimental investigation of droplet generation by a plunging breaking wave is presented. In this work, simultaneous measurements of the wave crest profile evolution and of droplets ranging in radius down to 50 μm for a mechanically generated plunging breaker during many repeated breaking events in freshwater are performed. We find three distinct time zones of droplet production, first when the jet impacts the free surface upstream of the wave crest, second when the large air bubbles entrapped by the plunging jet impact reach the free surface and burst, and third when smaller bubbles burst upon reaching the free surface later in the breaking process. These subprocesses account for 22%, 44%, and 34%, respectively, of the average of 653 droplets produced per breaking event. The probability distributions of the ranges of large and small droplet radii are well represented by power law functions that intersect at a radius of 418 μm.

Description: Abstract A full‐spectrum characterization of past interglacial climate is a necessary prerequisite for the detection and attribution of climate changes during the current interglacial. Here we present a speleothem record of Asian summer monsoon (ASM) during Marine Isotope Stage (MIS) 11 interglacial (MIS 11c), from Yongxing cave, China. The record's unprecedented chronologic constraints and decadal‐scale temporal resolution allow a precise and direct comparison of ASM between the MIS 11c and the Holocene. Our data suggest that orbital‐centennial patterns of ASM were remarkably similar during both interglacial, including their pacing and structure. Notably, a multi‐millennial stronger monsoon late in MIS 11c, the “Late‐MIS 11c shift,” is similar to the Late Holocene strengthening of the ASM, the “2‐Kyr shift.” Thus, the multicentennial ASM weakening at the end of the Late‐MIS 11c shift could imply that the current century‐long ASM waning trend may persist into the future, if only natural forcings are considered.

Description: The impact of sandwich foehn on air pollution in Urumqi, a gap town located on the northern leeside of the Tianshan Mountains of China, is analyzed. The results show that during days with high pollution, the boundary layer over the city and the down-valley area can be divided into a three-layer structure, with the southeasterly foehn sandwiched between the northwesterly winds on top and the cold-air surface pool beneath. The southeasterly foehn at heights between 480 and 2,100 m results in a very stable boundary layer structure. In combination with the decoupling between the foehn flow and cold air pool, such boundary layer structure prevents vertical mixing of atmospheric pollutants. In the up-valley area from the northern leeside flank to the southern urban area, the ground-based foehn confronts the thermally driven valley breeze and forms a “mini-front,” which moves northwards in the morning and retreats southwards in the afternoon. Although the mini-front disappears in the early evening, the wind shear of the mountain breeze between the southern suburb and downtown areas is still remarkable, which is favorable for a convergence line to persist around the city all day long. In this case, air pollutants emitted from the up-valley and down-valley areas are transported toward the urban area. Therefore, the air pollutants accumulate daily, leading to the frequent occurrence of heavy pollution events in Urumqi. This indicates that the sandwich foehn plays a critical role in the formation of heavy air pollution events in Urumqi.

Description: Using global magnetohydrodynamic(MHD) simulation, we investigate the effect of the interplanetary magnetic field(IMF) on the location of the open-closed field line boundary(OCB), in particular the dusk- and dawn- side OCB and their asymmetry . We first model the typical OCB-crossing events on 22 October 2001 and 24 October 2002 observed by DMSP. The MHD model presents a good estimate of OCB location under quasi-steady magnetospheric conditions. We then systemically study the location of the OCB under different IMF conditions. The model results show that the dawn- and dusk-side OCB respond differently to IMF conditions when B Y is present. An empirical expression describing the relationship between the OCB latitudes and IMF conditions has been obtained. It is found that the IMF conditions play an important role in determining the dawn-dusk OCB asymmetry, which is due to the magnetic reconnection at the dayside magnetopause. The differences between the dawn and dusk OCB latitudes from MHD predictions are in good agreement with the observations.

Description: ABSTRACT Empirical statistical downscaling methods are becoming increasingly popular in climate change impact assessments that require downscaling multi-global climate model (GCM) projections. Here, empirical statistical downscaling methods are classified based on calibration strategies [bias correction (BC) and change factor (CF)] and statistical transformations (mean based, variance based, quantile mapping, quantile correcting and transfer function methods). Ten combinations of calibration strategies and transformation methods are used to represent a range of empirical statistical downscaling methods. To test the performance of these methods in downscaling daily precipitation and temperature, an inter-model cross-validation is carried out using an ensemble of 16 GCMs from the Coupled Model Intercomparison Project Phase 5 (CMIP5) dataset over the Huai River Basin in China. These downscaling methods are further applied to downscale the climate for the future period to assess the associated uncertainties. The results show that the CF-based methods outperform the BC-based methods in projecting the probability distribution of downscaled daily temperature, while both calibration strategies give comparable results in the case of precipitation. With the CF calibration strategy, simply adding (for temperature) or multiplying (for precipitation) the mean CF is sufficient to represent most of the relative changes projected by GCMs. The use of quantile-based methods appears to be advantageous only at the tails of the distribution. More sophisticated BC methods are needed to remove the biases in the higher-order statistics of the GCM outputs. The two calibration strategies lead to fundamentally different temporal structures and spatial variability of the downscaled climatic variables. The BC-based methods produce larger uncertainty bands of inter-annual variability than the CF-based methods. For downscaled future precipitation, the uncertainty arising from the downscaling methods is comparable to the uncertainty arising from GCMs, while more uncertainty is introduced by calibration strategies than by statistical transformation methods.

Description: A summary of methods for process intensification in stirred reactors is presented, based mainly on the experience from R&D in the minerals processing industry. The process intensification concept is broadened to include innovations which lead to dramatically increased throughput for large-scale processing reactors, in contrast to the traditional definition of reactor size reduction, which has so far been ignored by the minerals industry. Methods enabling operating at high solids concentrations in processing tanks are reviewed to increase the throughput. It is proposed that the agitation power constraint at a high solids loading can be overcome by removal of baffles, for slowly reacting slurry systems typical in minerals processing. It is also suggested that the difficulty of pumping of high-concentration slurry feed can be overcome by operating with stratification, such that the solids residence time is made longer than the bulk flow residence time. Production loss through tank downtime is common in the mineral process industry, thus, a need to reduce the tank downtime should not be underestimated in the context of process intensification. Methods including the swirl flow technology developed by CSIRO and Queensland Alumina Ltd in Australia to suppress the scaling growth, and agitator design principles to reduce erosion are introduced. Enhanced mass transfer toward process intensification is also discussed. The concept of process intensification is extended to include innovations leading to a significantly increased throughput for processing reactors. Operating at high solids concentrations in processing tanks is recommended. The agitation power constraint can be overcome by removal of baffles. Solutions for mass transfer limiting problems, poor mixing, and reduction of the tank downtime are summarized.

Description: Abstract Traditionally, the magnetotail flow burst outside the diffusion region is known to carry ions and electrons together (Vi = Ve), with the frozen‐in condition well satisfied (E + Ve × B = 0). Such picture, however, may not be true, based on our analyses of the high‐resolution MMS (Magnetospheric Multiscale mission) data. We find that inside the flow burst the electrons and ions can be decoupled (Ve ≠ Vi), with the electron speed 5 times larger than the ion speed. Such super‐Alfvenic electron jet, having scale of 10 di (ion inertial length) in XGSM direction, is associated with electron demagnetization (E + Ve × B ≠ 0), electron agyrotropy (crescent distribution), and O‐line magnetic topology but not associated with the flow reversal and X‐line topology; it can cause strong energy dissipation and electron heating. We quantitatively analyze the dissipation and find that it is primarily attributed to lower hybrid drift waves. These results emphasize the non‐MHD (magnetohydrodynamics) behaviors of magnetotail flow bursts and the role of lower hybrid drift waves in dissipating energies.