Ernest F. Hollings Undergraduate Scholarship Program

Where Have All the Electrons Gone? Testing mechanisms proposed to explain the loss of high energy electrons from Earth's magnetosphere Christina Haig Space Environment Center Space Environment Center July 29, 2005 July 29, 2005

Monitors and forecasts Earth's space environmentMonitors and forecasts Earth's space environment Provides accurate, reliable, and useful solar-terrestrial informationProvides accurate, reliable, and useful solar-terrestrial information Conducts and leads research and development programsConducts and leads research and development programs Nation's official source of space weather alerts and warnings.Nation's official source of space weather alerts and warnings.

Science & Technology Infusion Branch Solar Terrestrial Models and TheorySolar Terrestrial Models and Theory Solar Terrestrial Instrumentation and DataSolar Terrestrial Instrumentation and Data Responsibilities for Data and InformationResponsibilities for Data and Information –Satellites –Rapid Prototyping Center –Cooperative Science Programs –Publications

Introduction and Research Outline Introduction to the Earth’s magnetosphereIntroduction to the Earth’s magnetosphere Introduction to the Earth’s radiation belts and our reasons for interestIntroduction to the Earth’s radiation belts and our reasons for interest Introduction to the potential mechanisms of electron lossIntroduction to the potential mechanisms of electron loss Testing of the currently applied explanationTesting of the currently applied explanation Conclusions about the theoryConclusions about the theory

Studying the Magnetosphere

Magnetosphere Solar Wind Magnetopause Solar Wind and Magnetic Field Lines

Earth’s Radiation Belts R E The electron belt is particularly important to satellites that reside in geosynchronous orbit (around 5.6 R E ) The Inner belt is around Earth radii, Outer belt around 3-10 R EThe Inner belt is around Earth radii, Outer belt around 3-10 R E Radiation belt electrons are relativistic (travel near the speed of light)Radiation belt electrons are relativistic (travel near the speed of light)

Motions of Radiation Belt Particles

Drift motion around Earth Gyro motion around magnetic field lines Gyro motion around magnetic field lines Bounce motion between poles Bounce motion between poles

The Challenge to Modelers Relativistic electron flux is extremely variable.Relativistic electron flux is extremely variable. Flux may increase or decrease on rapid timescales of less than one day.Flux may increase or decrease on rapid timescales of less than one day. Day of Year electron flux >2 MeV Electron Flux at Geosynchronous

Electron Radiation Belt Hazards Telestar Failure >1.5 MeV Electron dose High energy electrons can penetrate through shielding causing internal electrical charge to build up. A sudden discharge may cause minor problems, temporarily disabling satellites due to flipped program bits. More cataclysmic situations can permanently disable satellites due to damaged electronics, as in the loss of the Telestar satellite.

Magnetopause Loss Adiabatic motion can lead to real loss if electrons move out far enough to encounter the magnetopause. Kim and Chan [1997] examined one storm and based on theoretical calculations concluded that electrons at geosynchronous could be pushed out to the magnetopause. Currently, there is no observational support in favor of this loss mechanism. Earth Magnetopause e

Testing Magnetopause Loss Using the Geotail satellite data to build a statistical picture of the magnetopause:

Testing Magnetopause Loss Looking at electron flux during times of known magnetic field at the magnetopause: Geotail Crossing: 17-Feb :01: nT Median Field Outside: nT Median Field Inside: nT 4 day period surround magnetopause crossing of Geotail Magnetopause Field Magnetic Field at GOES 10 Electron Counts at GOES 10

Testing Magnetopause Loss Looking at electron flux during times of known magnetic field at the magnetopause: Geotail Crossing: 06-Nov :23: nT Median Field Outside: nT Median Field Inside: nT 4 day period surround magnetopause crossing of Geotail Magnetopause Field Magnetic Field at GOES 10 Electron Counts at GOES 10

Testing Magnetopause Loss Looking at dependency of electron flux on the pitch angle:

Testing Magnetopause Loss Looking at dependency of electron flux on the pitch angle:

Conclusions The characteristics of the magnetopause are highly variableThe characteristics of the magnetopause are highly variable The explanation of electron flux dropouts through the magnetopause does not fit well with observationsThe explanation of electron flux dropouts through the magnetopause does not fit well with observations The pitch angle data suggest another mechanism that preferentially loses electrons with pitch angles far from 90 degreesThe pitch angle data suggest another mechanism that preferentially loses electrons with pitch angles far from 90 degrees The theory of electron loss into the atmosphere fits better to the observed flux dropsThe theory of electron loss into the atmosphere fits better to the observed flux drops

Acknowledgements Special Thanks to: Janet Green (Mentor) Terry Onsager Ann Newman Jorgeann Hiebert Satellite Data Provided by: T. Onsager – NOAA SEC H. Singer – NOAA SEC S. Kokubun – STELAB, Nagoya University