Space Physics Seminar - fall-2015

Oct. 2, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Ying Zou - UCLA AOS

Understanding the occurrence of meso-scale enhanced auroras is critical for forecasting ionospheric scintillation and remote-sensing magnetospheric disturbances. One important nightside meso-scale aurora is poleward boundary intensifications (PBIs), which are intensifications along the poleward boundary of the nightside auroral oval and are produced by magnetotail reconnection. By combining white light and multi-spectral all-sky imagers (ASIs) with radars, we try to understand when and where PBIs and the associated magnetotail reconnection occur, spontaneously or driven by external forcing. We found that in radar measurements polar cap convection is structured and the embedded narrow fast flows highly (90%) correlate with PBI occurrence at the same longitude. Although radar field-of-view is limited, a polar cap multi-spectral ASI substantially expand our observing area by enabling flow tracing over long distance using airglow patches and polar cap arcs. It shows localized fast flows commonly occur deep in the polar cap, propagate at ~600 m/s as channels elongated in the noon-midnight meridian, and significantly contribute to magnetic flux convection across the polar cap. The mosaic images further show that as these fast flow propagate equatorward from the magnetic pole and impinge on the nightside auroral poleward boundary, they are followed by oval intensifications that are spatially connected to them and initiate within a few minutes delay. Such intensifications are major disturbances that do not occur until the impingement of polar cap flows, suggesting the intensifications to be triggered by these flows. Our results suggest that locally enhanced nightside auroras can be preceded by, and developed around, localized flow enhancements arriving at the auroral poleward boundary from the polar cap. This preceding signature is essential to understand the development of magnetotail reconnection, and gives the potential of forecasting the specific time and location of disturbances in the magnetosphere and ionosphere.

Oct. 9, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Paul Tenfjord - University of Bergen, Birkeland Centre for Space Science, Norway

Impact of the azimuthal component (By) of the Interplanetary Magnetic Field (IMF) on Magnetosphere-Ionosphere coupling

The solar wind’s IMF By component is believed to be the cause of a number of asymmetric features in both the magnetosphere and ionosphere. We investigate it's role in the generation of Birkeland currents, comparing observations from AMPERE and MHD simulations. When the IMF reconnects with the terrestrial magnetic field with a non-vanishing By flux transport is asymmetrically distributed between the two hemispheres. The magnetosphere then imposes asymmetric forces on the ionosphere, and the effects on ionospheric flow is characterized by distorted convection cell patterns, often referred to as "banana" and "orange" cell patterns. The flux asymmetrically added to the lobes results in a non-uniform induced By in the closed magnetosphere. By including the dynamics of the system we introduce a mechanism that predicts asymmetric Birkeland currents at conjugate footpoints. We argue that the induced By produces asymmetrical Birkeland currents as a consequence of asymmetric stress balance between the hemispheres. Associated with these currents we expect fast localized ionospheric azimuthal flows present in one hemisphere, but not necessarily in the other.

Oct. 16, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• John Linker - Predictive Science, Inc, San Diego

The origin of the slow solar wind is controversial. One group of theories argues that the slow wind primarily arises quasi-statically from the large magnetic expansion factor in these regions, while another set of theories contends that a significant portion of the slow solar wind arises dynamically via the reconnection of open and closed fields in the corona. In this talk, I describe modeling results that show that the dynamic interaction between open and closed fields is closely related to the evolution of coronal holes. Observations of coronal holes in the STEREO era may thus prove to be important discriminator between the different theories.

Oct. 23, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Bob Strangeway - UCLA IGPP

The Magnetospheric Multiscale Mission (MMS) is a four-spacecraft mission that was launched into a near equatorial orbit on March 13, 2015. The science investigation that is being carried out with the MMS spacecraft is "Solving Magnetospheric Acceleration, Reconnection, and Turbulence” (or SMART), led by James L. Burch of SwRI. To achieve the science objectives of SMART a comprehensive fields and particles instrument complement was built for each of the observatories. This instrument complement includes fluxgate magnetometers built by UCLA and the Institute for Space Research (Institut für Weltraumforschung, IWF), Graz.

The MMS spacecraft were initially launched into an orbit with post dawn apogee at around 12 Earth radii, and the magnetometers on board MMS were powered up on March 16. The booms were deployed on March 17. Since then the MMS orbit has precessed through midnight and dusk to the dayside, where MMS is now routinely crossing the magnetopause. In this talk I will summarize the scientific objectives of the MMS mission, and review examples of the many different phenomena observed so far by MMS, including substorms and ULF waves, as well as the magnetopause observations.

Oct. 30, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Xing Meng - JPL

The terrestrial ionosphere driven from above and from below: a modeling experience

The terrestrial ionosphere represents an interface between the magnetosphere and lower atmosphere. Conditions in the ionosphere depend on both the space weather from above and the neutral atmospheric dynamics from below. We perform numerical simulations of the ionosphere and look into the total electron content (TEC) disturbances induced by 1) geomagnetic storms 2) atmospheric gravity waves. For geomagnetic storms, we make TEC predictions with the Global Ionosphere-Thermosphere Model (GITM) to explore the feasibility of ionospheric forecasts with the current generation of physics-based models. A TEC metric has been developed to quantify forecasted storm-time TEC disturbances. The simulation results are compared with Global Positioning System satellite observations. For atmospheric gravity waves, we focus on upward propagating waves generated by tsunamis, which could cause traveling TEC perturbations in the ionosphere. To capture this process, we have implemented tsunami-generated gravity waves into GITM to construct a three-dimensional physics-based model Wave Perturbation-GITM. The model has been shown to reproduce the ionospheric signatures of a major tsunami event.

Nov. 6, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Madhulika Guhathakurta - NASA Ames

Interplanetary Space Weather: A New Paradigm

As human activity expands into the solar system, the need for accurate space weather and space climate forecasting is expanding, too. Space probes are now orbiting or en route for flybys of Mercury, Venus, Earth and the Moon, Mars, Vesta, Ceres, Saturn, and Pluto. Agencies around the world are preparing to send robotic spacecraft into interplanetary space. Each of these missions (plus others on the drawing board) has a unique need to know when a solar storm will pass through its corner of space or how the subsequent solar cycle will behave. Ultimately, astronauts will follow, traveling beyond Earth orbit, and their need for interplanetary space weather and climate forecasting will be even more compelling.

Until recently, forecasters could scarcely predict space weather in the limited vicinity of Earth. Interplanetary forecasting was even more challenging. This began to change in 2006 with the launch of the twin STEREO probes followed almost four years later by the Solar Dynamics Observatory. These three spacecraft along with SOHO now surround the sun, monitoring active regions, flares, and coronal mass ejections around the full circumference of the star. No matter which way a solar storm travels, the STEREO-SOHO-SDO fleet can track it. Missions like SDO and Kepler are giving us a better view of sun-like stars and their inner workings to understand their cyclic behavior, while missions like MAVEN and JUNO are investigating interaction of solar radiation and solar wind with Mar’s upper atmosphere and Jupiter’s intense auroras, a branch of heliophysics called “comparative heliophysics.”

To capitalize on the science that will naturally emerge from the growth and modernization of the observational assets, researchers from many different fields will have to work together. Interplanetary space weather and climate forecasting is essentially interdisciplinary. Progress requires expertise in astrophysics, plasma physics, solar physics, weather forecasting, planetary atmospheres, and more. In this talk I will summarize existing observational assets, other resources, and the challenges we have to face to move this interdisciplinary field forward.

Nov. 13, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Desheng Han - Polar Research Institute, China

Introduction to observations on upper atmospheric physics at the Polar Research Institute of China and of studies of the dayside diffuse aurora Ionosphere- magnetosphere coupling

The Polar Research Institute of China has carried out observations of upper atmospheric physics with various instruments, such as, optical cameras, HF radar, imaging riometers, digisonde, magnetometers, TEC receiver, and so on, in both Antarctic and Arctic since it was founded in 1989. This talk will briefly introduce these observations at first and then present a statistical study on dayside diffuse aurora (DDA) based on ground optical observations obtained at Yellow River Station. We found that the DDAs can be commonly observed in the dayside and present different forms in the morning, noon, and afternoon. The DDAs observed near the magnetic local noon often show stripy structure and the orientation of stripy DDA is consistent with the ionospheric convection. Most interestingly, we found that the poleward end of the stripy DDA can extend to equatorward of the discrete auroral oval and is always connected with a discrete auroral arc that is north-south aligned and perpendicularly connected to the discrete aurora oval. The north-south aligned discrete auroral arc was named throat aurora and was suggested to be projection of newly opened flux of magnetopause reconnection. We argue that our observational results may present the optical evidence for the physical process of cold plasmas flowing into the dayside reconnection site and this process has very important implications.

Nov. 20, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Paulett Liewer - JPL

Observations and Analysis of the Non-Radial Propagation of Coronal Mass Ejections near the Sun aurorae

The trajectories of coronal mass ejection (CME) are often observed to deviate from radial propagation from the source while within the coronagraph fields-of-view (R < 15 - 30 Rsun). To better understand non-radial propagation within the corona, we first analyze the trajectories of five CMEs for which both the source and 3D trajectory (latitude, longitude and velocity) can be well determined from solar imaging observations, primarily using observations from the twin Solar TErrestrial RElations Observatory (STEREO) spacecraft. Next we analyze the cause of any non-radial propagation using a potential field source surface (PFSS) model to determine the direction of the magnetic pressure forces exerted on the CME at various heights in the corona. In two cases, we find that the CME’s deviation from radial propagation occurs primarily before reaching the coronagraph field-of-view (below 1.5 solar radii). Based on the observations and the magnetic pressure forces calculated from the PFSS model, we conclude that for these cases the deviation is the result of strong active region fields causing an initial asymmetric expansion of the CME that gives rise to apparent rapid deflection and non-radial propagation from the source. For all five cases, within the limitations of the PFSS model, the magnetic fields appear to guide the CMEs out of the corona through the weak field region around the heliospheric current sheet even when the current sheet is inclined and warped.

Dec. 4, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Jiong Qiu - University of Montana

Probing Magnetic Reconnection in Solar Flare Observations

Energy release in solar flares is governed by magnetic reconnection taking place in the Sun's outer atmosphere, the corona. Yet in terms of observables, the immediate and more significant response usually occurs in the lower atmosphere, the chromosphere. Here, energy flux down along newly reconnected field lines (or flare loops) quickly heats up plasmas generating impulsive chromospheric emissions. The lower atmosphere is also the only place where reliable measurements of magnetic field are currently available. Whereas probes in fusion experiments or spacecrafts in the Earth's magnetosphere usually sample multiple points for direct in-situ measurements, all reconnection events in the Sun's corona resulting in significant atmosphere heating can be mapped in the chromosphere with imaging observations of the solar disk. This mapping allows us to track where reconnection takes place, and find out how much and how quickly magnetic flux is reconnected. High resolution observations reveal that fast reconnection responsbile for flare energy release is unsteady and intermittent, but at the same time organizable globally. We develop techniques to infer these properties and estimate how much energy is released by bursts of reconnection. This talk will discuss recent results and challenges in this practice.

Dec. 11, 2015
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Fulvia Pucci - University of Rome and Visiting Graduate Researcher, UCLA

Fast tearing: the transition to kinetic effects

By examining sheets with thicknesses scaling as different powers of the magnetic Reynolds number S, Pucci & Velli (2014) showed that the growth rate of the tearing mode increases as current sheets thin and, once the thickness reaches a scaling a/L=S1/3, the time scale for the instability to develop becomes of the order of the Alfvén time. That means that a fast instability sets in well before Sweet-Parker type current sheets can form. In addition, such an instability produces many islands in the sheet, leading to a fast nonlinear evolution and most probably a turbulent disruption of the sheet itself (Tenerani et al. 2015). This has fundamental implications for magnetically driven reconnection throughout the corona, and in particular for coronal heating and the triggering of coronal mass ejections. At high Lundquist numbers scales get smaller and the transition to kinetic physics becomes important: herewe consider first the Hall effect, showing that we can define a trigger relation as in the resistive case, and then the effect of electron skin depth reconnection. In particular we present a linear study aiming to show how an ”ideal tearing mode” is achieved when kinetic effects are included, including scaling laws for sheet aspect ratios and growth rates. We show that, taking into account this effect an ”ideal” growth rate where ??A ? 1 still defines the trigger condition for fast reconnection. These results provide a step towards identifying the proper conditions for reconnection to effectively occur in lab and space plasmas.