ALBERT

Description: Activities of the Madden-Julian Oscillation (MJO) in boreal winter has recently been found to be stronger in easterly phases of the stratospheric quasi-biennial oscillation (QBO) than its westerly phases. This QBO-MJO connection was investigated in this study using a method that identifies individual MJO events by tracking their eastward propagating signals in precipitation. Stronger MJO activities in QBO easterly phases are a consequence of more MJO days, not larger amplitudes of individual MJO events as previously thought. More MJO days come from more MJO events initiated over the Indian Ocean and their longer duration because of a weaker barrier effect of the Maritime Continent on MJO propagation. Zonal heterogeneity exists in the connection between QBO, MJO, and tropical total precipitation in general. This poses a challenge to our current understanding of the MJO dynamics, which has yet to fully include upper-tropospheric and stratospheric processes.

Description: The Solar Wind Ion Detectors (SWIDs) on the Chang'E-1 spacecraft, while orbiting the Moon, occasionally observed two continuous flux peaks with energies not exceeding 8 and 4 times that of the prevailing solar wind proton energy. These form parallel curves (PCs) with an energy ratio of 2 in the energy-time spectrogram. The fluxes of the two curves are comparable, around 10−5 ∼ 10− 4 of the solar wind flux. The pitch angle distribution of PC particles is concentrated around 90°. The velocity space distribution of PC particles shows distinct double-ring feature, suggesting the existence of a pickup ion species with m/q = 2. Pickup ions from local interstellar medium, the inner sources and the lunar exosphere are investigated. We conclude that this observation may be the first in situ evidence for H2+ ions in the lunar exosphere, thus providing new insights on the evolution and fate of solar wind hydrogen in the solar system.

Description: The efficiencies of pathways of thermospheric heating via soft electron precipitation in the dayside cusp region are investigated using the coupled magnetosphere-ionosphere-thermosphere model (CMIT). Event-based data-model comparisons show that the CMITmodel is capable of reproducing the thermospheric mass density variations measured by the CHAMP satellite during both quite and active periods. During blackthe 24 Aug 2005 storm event (Kp = 6-) while intense Joule heating rate occurs in the polar cusp region, including soft electron precipitation is important for accurately modelling the F -region thermospheric mass density distribution near the cusp region. blackDuring the 27 Jul 2007 event (Kp = 2-) while little Joule heating rate occurs in the polar cusp region, the controlled CMIT simulations suggest that the direct blackpathway through the energy exchange between soft electrons and thermospheric neutrals is the dominant process during this event, which only has a small effecton the neutral temperature and mass density at 400 km altitude. blackComparisons between the two case studies show that the indirect pathway via increasing the F-region Joule heating rate is a dominant process during the 24 Aug 2005 storm event, which is much more efficient than the direct heating process.

Description: [1]  In this paper we compare observations of the high latitude cusp from DMSP data to simulations conducted using the Lyon-Fedder-Mobarry (LFM) global magnetosphere simulation. The LFM simulation is run for the 31 Aug 2005 to 02 Sep 2005 moderate storm, from which the solar wind data exhibits a wide range of conditions that enable a statistical representation of the cusp to be obtained. The location of the cusp is identified using traditional magnetic depression and plasma density enhancement at high altitude. A new diagnostic using the parallel ion number flux is also tested for cusp identification. The correlation of the cusp latitude and various solar wind IMF coupling functions is explored using the three different cusp identification methods. The analysis shows 1) the three methods give approximately the same location and size of the simulated cusp at high altitude; 2) the variations of the simulated cusp are remarkably consistent with the observed statistical variations of the low-altitude cusp. In agreement with observations a higher correlation is obtained using other solar wind coupling functions such as the Kan-Lee electric field. The MLT position of the simulated cusp is found to depend upon the IMF By component, with a lower linear correlation. The width of the simulated cusp in both latitude and MLT is also examined. The size of the cusp is found to increase with the solar wind dynamic pressure with saturation seen when the dynamic pressure is greater than 3 nPa.

Description: This paper investigates a possible physical mechanism of the observed dayside high-latitude upper thermospheric wind using numerical simulations from the coupled magnetosphere-ionosphere-thermosphere (CMIT) model. Results show that the CMIT model is capable of reproducing the unexpected afternoon equatorward winds in the upper thermosphere observed by the HIWIND balloon. Models that lack adequate coupling produce poleward winds. The modeling study suggests that ion-drag driven by magnetospheric lobe-cell convection is another possible mechanism for turning the climatologically-expected dayside poleward winds to the observed equatorward direction. The simulation results are validated by HIWIND, EISCAT and DMSP. The results suggest a strong momentum coupling between high-latitude ionospheric plasma circulation and thermospheric neutral winds in the summer hemisphere during positive IMF B z periods, through the formation of magnetospheric lobe-cell convection driven by persistent positive IMF B y . The CMIT simulation adds important insight into the role of dayside coupling during intervals of otherwise quiet geomagnetic activity

Description: Earthward propagating plasmoids in the Earth's magnetotail have been observed by satellites. Using a multi-fluid global magnetosphere simulation, earthward propagating plamoids are reproduced when ionospheric O + outflow is included in the global simulation. Controlled simulations show that without ionospheric outflow, the plasmoids generated in the magnetotail during a substorm-SMC cycle only propagate tailward. With ionospheric outflow, earthward plasmoids can be induced through the modification of magnetotail reconnection at multiple X-lines. When multiple X-lines form in the magnetotail, plasmoids may be trapped between multiple reconnection sites. When magnetic reconnection rate is reduced at the near-Earth X-line by the presence of ionospheric O + , the earthward exhaust flow of reconnection occurring at the mid-tail X-line forces the plasmoid to propagate earthward. The propagation speed and spatial size of the simulated earthward plasmoid are consistent with observations from the Cluster satellites.

Description: We describe a coupled geospace model that includes causally regulated ion outflow from a physics-based ionosphere/polar wind model. The model two-way couples the multi-fluid Lyon-Fedder-Mobarry (MFLFM) magnetohydrodynamics (MHD) model to the ionosphere/polar wind model (IPWM). IPWM includes the H  +  and O  +  polar wind as well as a phenomenological treatment of energetic O  +  accelerated by wave-particle interactions (WPI). Alfvénic Poynting flux from the MHD simulation causally regulates the ion acceleration. The WPI model has been tuned and validated with comparisons to particle-in-cell (PIC) simulations and empirical relationships derived from Fast Auroral SnapshoT (FAST) satellite data. IPWM captures many aspects of the ion outflow that empirical relationships miss. First, the entire coupled model conserves mass between the ionospheric and magnetospheric portions, meaning the amount of outflow produced is limited by realistic photochemistry in the ionosphere. Second, under intense driving conditions, the outflow becomes flux limited by what the ionosphere is capable of providing. Furthermore, the outflows produced exhibit realistic temporal and spatial delays relative to the magnetospheric energy inputs. The coupled model provides a flexible way to explore the impacts of dynamic heavy ion outflow on the coupled geospace system. Some of the example simulations presented exhibit internally-driven sawtooth oscillations associated with the outflow, and the properties of these oscillations are analyzed further in a companion paper.

Description: General methods for improving the specification of electron precipitation in global simulations are described and implemented in the Lyon-Fedder-Mobarry (LFM) global simulation model, and the quality of its predictions for precipitation is assessed. LFM's existing diffuse and monoenergetic electron precipitation models are improved, and new models are developed for lower energy, broadband and direct-entry cusp precipitation. The LFM simulation results for combined diffuse plus monoenergetic electron precipitation exhibit a quadratic increase in the hemispheric precipitation power as the intensity of solar wind driving increases, in contrast with the prediction from the OVATION Prime (OP) 2010 empirical precipitation model which increases linearly with driving intensity. Broadband precipitation power increases approximately linearly with driving intensity in both models. Comparisons of LFM and OP predictions with estimates of precipitating power derived from inversions of Polar satellite UVI images during a double substorm event (28-29 March 1998) show that the LFM peak precipitating power is 〉 4× larger when using the improved precipitation model and most closely tracks the larger of three different inversion estimates. The OP prediction most closely tracks the double peaks in the intermediate inversion estimate, but it overestimates the precipitating power between the two substorms by a factor 〉2 relative to all other estimates. LFMs polar pattern of precipitating energy flux tracks that of OP for broadband precipitation, exhibits good correlation with duskside region 1 currents for monoenergetic energy flux that OP misses, and fails to produce sufficient diffuse precipitation power in the prenoon quadrant that is present in OP. The prenoon deficiency is most likely due to the absence of drift kinetic physics in the LFM simulation.

Description: A new gas-around-liquid spray nozzle (GLSN) was designed, and the two-phase flow fluid field in this nozzle was simulated numerically. Flow characteristics under different structural parameters were obtained by changing the L / D ratio of the premixing chamber, incident angle, and inlet pressures. Increasing the L / D ratio and incident angle improved flow characteristics such as atomization flow, outlet velocity, and turbulence intensity. The nozzle performed optimally at an L / D ratio of 0.5 and incident angle of 60°. The atomization flow decreased with higher gas pressure and increased with higher liquid pressure. The outlet velocity mainly depended on the inlet gas pressure, not on the inlet liquid pressure. These results provide an indication for optimum structures and parameters of the GLSN. Since the atomization effect of spray nozzles plays a key role in wet flue gas desulfurization processes, an innovative gas-around-liquid spray nozzle was designed. The two-phase flow fluid field in this nozzle was simulated numerically and the flow characteristics were determined with different structural parameters to find the optimum conditions.

Description: This paper investigates the effects of magnetospheric mass loading on the control of dayside magnetic reconnection using global magnetospheric simulations. The study is motivated by a recent debate on whether the integrated dayside magnetic reconnection rate is solely controlled by local processes (local-control theory) or global merging processes (global-control theory). The local control theory suggests that the integrated dayside reconnection rate is controlled by the local plasma parameters. The global control theory argues that the integrated rate is determined by the net force acting on the flow in the magnetosheath rather than the local microphysics. Controlled numerical simulations using idealized ionospheric outflow specifications suggest a possible mixed-control theory, that is 1) a small amount of mass loading at the dayside magnetopause only redistributes local reconnection rate without a significant change in the integrated reconnection rate, and 2) a large amount of mass loading reduces both local reconnection rates and the integrated reconnection rate on the dayside. The transition between global-control and local-control dominated regimes depends on (but not limited to) the source region, the amount, the location and the spatial extension of the mass loading at the dayside magnetopause.