Astronomy Colloquium for 2019-09-18

Series: Astronomy Colloquium
Date: Wednesday 18-Sep-2019
Time: 16:05-17:00 (4:05-5:00 pm)
Location: ATL 2400
Speaker: Dr. Robert Leamon (GSFC)
Title: Terminators: the death of solar cycles: Implications in 2020 for Cosmic Rays, Gamma Rays, Stellar Dynamos and our Atmosphere

Sunspots are a canonical marker of the Sun's internal magnetic field which flips polarity every ~22 yr. The principal variation of sunspots, an ~11 yr variation, modulates the amount of the magnetic field that pierces the solar surface and drives significant variations in our star's radiative, particulate, and eruptive output over that period, and modulation of incoming cosmic rays. When the incoming hadronic cosmic rays interact with solar gas, the sun becomes a bright source of multi-GeV gamma rays. We will present observations from the Solar and Heliospheric Observatory and Solar Dynamics Observatory indicating that the 11 yr sunspot variation is intrinsically tied to the spatio-temporal overlap of the activity bands belonging to the 22 yr magnetic activity cycle. Using a systematic analysis of ubiquitous coronal brightpoints and the magnetic scale on which they appear to form, we show that the landmarks of sunspot cycles 23, 24 (and 25!) can be explained by considering the evolution and interaction of the overlapping activity bands of the longer-scale variability. We will also show how the activity band model can explain shorter cycles of activity, geomagnetic storms ("Space Weather"), and even drive climatic changes with real world consequences, such as hurricanes and agriculture.

Along the way we will discuss how I got to looking at things as seemingly disparate as gamma rays and crop prices, meandering through scientific disciplines, around the world, and through academia and government service.

Colloquia are usually preceded by espresso and ice cream at 1:45 pm outside room PSC 1150 and are followed by an informal reception at 5:15 pm in that room. Anyone interested in talking with the speaker, or being added to the colloquium announcement email list, should contact the colloquium organizer. Lunch will normally be reserved for the speaker to talk to graduate students. Anyone asking a question during a talk is asked to raise their hand and be acknowledged before speaking.

Colloquium Organizer: Prof. Richard Mushotzy


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


Directions and information about parking can be found here.

This page was automatically generated on: 12-Sep-2019.