- Weekly Seminar (Kepko)
- Weekly Seminar (Stanier)
- Weekly Seminar (Roebber)
- Weekly Seminar (Guikema)
Weekly Seminar (Kepko)
February 4, 2016 - 3:30 pm
Larry Kepko of the Goddard Space Flight Center will present a seminar.
Title: Dynamics of the Sun-Heliosphere Connection
Connecting the solar wind structure and dynamics observed near Earth back to their origins in the Sun’s corona has long been one of the central goals of Heliophysics. Achieving this goal is essential both for understanding the basic physical processes driving solar/heliospheric activity and for developing predictive space weather models. The challenge, however, is that the two sets of data are very disparate: global-scale, lower resolution remote sensing of the corona and high resolution, in situ point measurements at 1 AU.
We present new analysis of high temporal resolution in situ ACE measurements of quasi-periodic (~90 minute) density structures and demonstrate that these structures are created by quasi-periodic magnetic reconnection that occurred back in the solar atmosphere. Our results impose severe new constraints on slow solar wind origin, and provide new compelling evidence that the slow wind results from the sporadic release of closed-field plasma via magnetic reconnection at the boundary between open and closed flux in the Sun's atmosphere.
In addition, we link the in situ measurements with new studies using STEREO coronagraph and heliospheric imager observations of quasi-periodic density variations in the slow wind that propagates along the so-called streamers that connect back to the large-scale closed field regions at the Sun. We conclude by showing numerical simulations of the dynamics of coronal streamers using both 2.5D and 3D MHD numerical models. The numerical simulations show that the interface between open and closed magnetic flux in the corona is inherently unstable due to reconnection, resulting in the quasi-periodic ejection of plasmoids along streamers. We conclude by discussing the implications of the simulations for interpreting the observations.close
Weekly Seminar (Stanier)
February 11, 2016 - 3:30 pm
Charles Stanier of the University of Iowa will present a seminar.
Title: Fine and Ultrafine Particles in the Atmosphere: Aerosol-Cloud Interactions and Midwestern Haze
Atmospheric chemistry and physics studies over the Midwestern U.S. and Great Lakes will be discussed and related to the improving air quality of the region. Results from the 2009 LADCO Winter Nitrate Study will be shared; the study elucidated meteorological and chemical drivers for wintertime haze episodes that impact the entire upper Midwest. Ground-based measurements of nitric acid, ammonia, and other components are discussed together with modeling of the haze episodes using the Community Multiscale Air Quality model (CMAQ). The integrated process rate (IPR) and integrated reaction rate (IRR) tools within CMAQ are used to apportion reactive nitrate formation to heterogeneous conversion of N2O5, the reaction of OH and NO2, and homogeneous conversion of N2O5.
The second case presented is a 10 month field campaign monitoring the aerosol number size distribution that was conducted in 2013 and 2014 at the long-term reference site in Bondville, Illinois. Results from this study, including diurnal and seasonal patterns and the influence of new particle formation and growth events on the size distribution, will be discussed. The site is representative of a wide region of the Midwestern U.S. and is home to many long-term monitoring stations of NASA, NOAA, and the US EPA, including a 20+ year record of particle number concentration and aircraft vertical profiles of optical properties, number concentration and particle number size distribution. Model results from the explicit WRF-Chem will be presented and discussed in terms of feedbacks between particle nucleation, air quality metrics, and aerosol-cloud interactions.close
Weekly Seminar (Roebber)
February 18, 2016 - 3:30 pm
Paul Roebber of the University of Wisconsin-Milwaukee will present a seminar.close
Weekly Seminar (Guikema)
February 25, 2016 - 3:30 pm
Seth Guikema of the University of Michigan (IOE) will present a seminar.close