Introduction

1. Probing the Dayside Magnetosphere: Measurements by ACE soon after launch, August 25, 1997Travis GlinesHeather Briggs

2. Introduction • Launched on August 25, 1997 • It crossed through: • the dayside magnetosphere • entered a region around the magnetosphere called the magnetosheath (twice) • eventually crossed a weak bowshock into the interplanetary medium exposed to the solar wind. • WIND was also making measurements. • The three regions of Earth's dayside magnetosphere encountered by ACE are defined by different magnetic properties as observed by our data.

3. Normal Dipole • The Earth's magnetic field is nearly a dipole. • Figure 1 shows an ideal dipole (as the Earth would appear were it unaffected by the sun).

4. Dipole Formula • r = L*cos2() is the equation for a dipole. • = Invariant latitude, the angle at which the field leaves the earth's surface • L = the distance in Re at which a given field line crosses the equatorial plane

5. Solar Influence

6. ACE Trajectory

7. The dark line represents the Earth's magnetic field as measured by ACE from 6 Re to 14 Re The Earth's magnetic field follows a dipolar field until it enters the magnetosheath. Data collected of Dipole and Actual • The light line represents the original dipole field as obtained from the previous formula • The dipole is evaluated along the ACE trajectory

8. The Three Regions of Earth's Magnetic Environment • R1 is the inner regions of our magnetosphere. • R2 is called the magnetosheath, or the outer boundary of our magnetic field. • R3 is interplanetary medium, separated from our magnetic field by a bow shock.

9. Region 1- The Magnetosphere • The magnetosphere is approximately a dipole in which the field strength decreases at a rate of 1/r3 • r represents the distance from Earth

10. The second major drop showed the ACE trajectory across the magnetopause a second time after being forced to re-enter it Entering the Magnetosheath • The first dip shows where ACE entered the magnetosheath • The magnetic field then expands to encompass the satellite once again (the forced re-entry)

11. WIND Data • We compared this solar wind data with ACE's magnetic field data • WIND noted a pressure drop that had repurcussions for ACE half an hour later and caused the magnetosphere to then recapture the spacecraft

12. The field lines run parallel to the interplanetary magnetic field (IMF). Average field strength ~ 10 nT Region 2- The Magnetosheath • The field strength does not depend on it's distance from Earth. • The field lines oscillate significantly.

13. This graph shows a field strength no greater than 3 nT, thus a weak field and bow shock. Region 3- Interplanetary Medium • The average field strength of Interplanetary Medium is about 6 nT.

14. Bow Shock • The bow shock is a boundary area where the interplanetary wind slows down to subsonic speeds • This shock is produced when the wind slows down and is thus diverted around the Earth so it does not hit us head on • Our graph shows a weak bow shock due most likely to the unusually low magnetic field strength of the solar wind

15. Historical Viewpoint • The last time such an analysis was completed was in 1967 • One of the earliest was Explorer 12, with much lower time resolution.

16. Conclusion • Through ACE's measurements, we have verified that the three specific regions associated with the magnetosphere have difinitive properties singular to those areas • In correlation with data obtained by WIND, we have observed the effect of the solar wind on the magnetosphere and verified that it is a fluctuating boundary that is affected greatly by solar and interplanetary radiation.

17. THE END