The focus of our project was an investigation into fluctuations and oscillations in the brightness of images of the solar corona, the outermost layer of the Sun’s atmosphere. Previous research has shown that power spectra computed from time series of light intensity values from the solar corona can be modelled by a general background power law, representing a combination of stochastic processes, with an added ‘tail’ at high frequencies, which captures a transition to white noise. Recently, work by Ireland et al. (2015) has proposed a more comprehensive spectral model that includes an additional superimposed Gaussian component to capture periodic spectral features. We use this comprehensive spectral model to perform the first global survey of power spectra of the extreme ultraviolet (EUV) solar corona. The solar region used is a massive (1000×1000-arcsecond) region, corresponding to 35% of the visible solar disk, and data from five wavelengths are considered: 171Å, 193Å, 211Å, 304Å, and 1600Å. The different wavelengths correspond to observations at different heights from the solar surface. We find that for these wavelengths, the best-fit model parameters distinctly reflect the regions’ visually observed features and allow for insight into the dynamical processes thought to exist in the solar corona. We …
From a collaboration with Professor Zhang and Big Bear Solar Observatory
James M. McCracken and Robert S. Weigel
Phys. Rev. E 93, 022207 – Published 8 February 2016
We introduce new quantities for exploratory causal inference between bivariate time series. The quantities, called penchants and leanings, are computationally straightforward to apply, follow directly from assumptions of probabilistic causality, do not depend on any assumed models for the time series generating process, and do not rely on any embedding procedures; these features may provide a clearer interpretation of the results than those from existing time series causality tools. The penchant and leaning are computed based on a structured method for computing probabilities.
By Karl Battams (a scientist at NRL who is doing a PhD with a concentration in Space Weather at GMU)
I have a curious claim to fame. I have almost certainly seen more individual images of comets than any person in history. A good ballpark estimate would be around 50,000 unique images of comets, but that may be slightly on the low side. Either way, it’s a lot.
Our work examines the detectability of tidally distorted solid exoplanets in synchronous rotation. Previous work has shown that tidally distorted shapes of close-in gas giants can give rise to radius underestimates and subsequently density overestimates for those planets. We examine the assumption that such an effect is too minimal for rocky exoplanets and find that for smaller M Class stars there may be an observationally significant tidal distortion effect at very close-in orbits. We quantify the effect for different stellar types and planetary properties using some basic assumptions. Finally, we develop a simple analytic expression to test if there are detectable bulge signatures in the photometry of a system. We find that close in for smaller M Class stars there may be an observationally significant signature that may manifest itself in both in-transit bulge signatures and ellipsoidal variations.
James M. McCracken and Robert S. Weigel
Convergent cross-mapping (CCM) is a technique for computing specific kinds of correlations between sets of times series. It was introduced by Sugihara et al. [Science 338, 496 (2012).] and is reported to be “a necessary condition for causation” capable of distinguishing causality from standard correlation. We show that the relationships between CCM correlations proposed by Sugihara et al. do not, in general, agree with intuitive concepts of “driving” and as such should not be considered indicative of causality. It is shown that the fact that the CCM algorithm implies causality is a function of system parameters for simple linear and nonlinear systems. For example, in a RL circuit, both voltage and current can be identified as the driver depending on the frequency of the source voltage. It is shown that the CCM algorithm, however, can be modified to identify relationships between pairs of time series that are consistent with intuition for the considered example systems for which CCM causality analysis provided nonintuitive driver identifications. This modification of the CCM algorithm is introduced as “pairwise asymmetric inference” (PAI) and examples of its use are presented.
A.D. Kercher and R.S. Weigel
Numerical schemes for ideal magnetohydrodynamics (MHD) that are based on the standard finite volume method (FVM) exhibit pseudo-convergence in which irregular structures no longer exist only after heavy grid refinement. We describe a method for obtaining solutions for coplanar and near-coplanar cases that consist of only regular structures, independent of grid refinement. The method, referred to as Compound Wave Modification (CWM), involves removing the flux associated with non-regular structures and can be used for simulations in two- and three-dimensions because it does not require explicitly tracking an Alfvén wave. For a near-coplanar case, and for grids with 213 points or less, we find root-square-mean-errors (RMSEs) that are as much as 6 times smaller. For the coplanar case, in which non-regular structures will exist at all levels of grid refinement for standard FVMs, the RMSE is as much as 25 times smaller.
In response to the Government adding solar storms to the National Risk Register (NRR) of Civil Emergencies in 2011, the Met Office Space Weather Operations Centre (MOSWOC) was created to provide a UK operational space weather prediction centre to help protect the country from the serious threats posed by space weather events.
CMEs are often associated with flares and are eruptions of large amounts of matter and energetic particles from the solar atmosphere. These can take days to reach Earth, carrying a local magnetic field from the Sun, and their arrival time is the focus of space weather forecasting. We use the state of the art NOAA ‘ENLIL’ computer model to predict the arrival time of CMEs. This enables prediction of CMEs impacting Earth within plus or minus six hours (at best). While the Met Office can forecast a CME and its direction of travel, the capability to ascertain whether a CME will have an effect on the Earth is limited to one satellite. Depending on the speed of the CME, this observation will give 20 to 30 minutes warning before the CME has an effect …
Karl Battams: http://arxiv.org/abs/1409.8166
Modern advances in space technology have enabled the capture and recording of unprecedented volumes of data. In the field of solar physics this is most readily apparent with the advent of the Solar Dynamics Observatory (SDO), which returns in excess of 1 terabyte of data daily. While we now have sufficient capability to capture, transmit and store this information, the solar physics community now faces the new challenge of analysis and mining of high-volume and potentially boundless data sets such as this: a task known to the computer science community as stream mining. In this paper, we survey existing and established stream mining methods in the context of solar physics, with a goal of providing an introductory overview of stream mining algorithms employed by the computer science fields. We consider key concepts surrounding stream mining that are applicable to solar physics, outlining existing algorithms developed to address this problem in other fields of study, and discuss their applicability to massive solar data sets. We also discuss the considerations and trade-offs that may need to be made when applying stream mining methods to solar data. We find that while no one single solution is readily available, many of the …
11 AM – noon, Room 242 of Planetary Hall unless otherwise noted.
11 AM – noon, Room 242 of Planetary Hall
Lower-Upper Atmosphere Cooling — from Milliseconds to Decades
Erdal Yiğit and John Lear
Recent MAVEN-Mars results
Temporal evolution of the horizontal motion, buoyant velocity and magnetic field of an emerging active region
Graduate Institute of Space Science, National Central University, Chung-Li, Taoyuan, Taiwan
Abstract: We examined the emerging process of NOAA AR11645 from the
earliest detection of magnetic flux in the region. The observed horizontal
motion of the emerging flux is compared with its average magnetic field
strength and the vertical motion derived from the magnetic buoyancy theory.
The magnitude of the theoretically derived thick-tube buoyant velocity of
the inclined fields is comparable to that of the observed separation velocity
of two polarities. The thin-tube approximation results in an unreasonably
high buoyant velocity, indicating that the approximation is inappropriate
for emerging active regions. While the observed horizontal motion is not
found to directly correlate with either the magnetic field strength or the
derived buoyant velocities, the separation velocity of two poles, the temporal
derivative of the average magnetic field strength, and the percentage of the
inclined fields all show a similar decreasing profile. The results of this study
imply that the assumption …
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Tuesday at 11am, Room 242 Planetary Hall
Tuesdays (Jan 28; Feb 11, 25; Mar 18; Apr 1, 15, 29) from 12:00pm to 1:00pm in Planetary Hall room 242.
Alternate Tuesdays from 12:00pm to 1:00pm in Planetary Hall room 242.
The SWL journal club will meet ad-hoc in Fall 2012 on Tuesdays 1:00 pm – 2:30 pm in a room that will change from week-to-week. To receive announcements, register for the SWL student email list given at http://aurora.gmu.edu/spaceweather/index.php/Main_Page
Astrophysics Journal Club: This fall, the journal club will meet on alternate Wednesdays (Sep 5, 19; Oct 3, 17, 31; Nov 14, 28) from 3:00pm to 4:00pm in Planetary Hall (S&T I) room 306.
The SWL journal club will meet ad-hoc on Tuesdays 1:00 pm – 2:30 pm in Research Hall 302. To receive announcements, register for the SWL student email list given at http://aurora.gmu.edu/spaceweather/index.php/Main_Page
Astrophysics Journal Club: Jan 25; Feb 8, 22; March 7, 21; April 4, 18; May 2 from 1:30pm to 2:30pm in S&T I, room 306. To receive announcements, contact Joseph Weingartner firstname.lastname@example.org.
The SWL journal club will meet ad-hoc on Tuesdays from 12:00-1:00pm.
During the fall 2011 semester, the astrophysics journal club will meet on alternate Wednesdays (Sep 7, 21; Oct 5, 19; Nov 2, 16, 30) from 1:30pm to 2:30pm …
Please note that some of the locations have changed.
We are holding a new graduate student orientation on Friday August 16th. Note that the morning schedule differs between the Physics and CSI graduate students.
New and current students are welcome to attend any of the activities.
Please send either Prof. So (email@example.com) or Prof. Weigel (firstname.lastname@example.org) an email (if you have not already) if you plan on attending.
Physics students only: Showcase Room of Research Hall (room at ground level of the observatory tower).
09:30-10:15 New students meeting with Prof. So
10:30-12:30 New students placement evaluations (PHYS PhD students only)
CSI students only: Planetary Hall, room 242.
11:30-12:30 About the CSI graduate program (with Weigel and Camelli)
Physics and CSI PhD students
Showcase Room of Research Hall
12:30-01:30 Pizza Lunch
01:30-01:45 Prof. Summers welcoming note
01:45-02:00 About grad school
02:00-02:45 Research talks
03:00-04:30 Research talks
04:30-05:30 Reception with light food and drink
Brion’s Grill [http://www.brionsgrille.com/]
06:00-07:00 Social hour with current graduate students
The workshop is to improve the scientific understanding of the origin and propagation of solar transients, and develop the prediction capacity of these transients’ arrival and potential impact on the Earth.
This workshop is the activity of the ISEST program in CAWSES-II / Task Group.
The workshop engages coordinated international activities in observation, theory and modeling, involves scientists in both developed and developing countries, and provides an online platform for educational opportunities for students
We are working with the Office of Equity and Diversity Services to develop a plan to increase the number of underrepresented minorities in physics at all levels. We are meeting with Corey Jackson on the 20th of August to discuss our plans.
This workshop is the activity of the ISEST program in CAWSES-II / Task Group 3.
ISEST Workshop (International Study of Earth-Affecting Solar Transients)
Satellite observations of the space shuttle’s main engine exhaust plume: Unexpected global-scale transport and polar mesospheric cloud formation
March 26th, 2013