EGS MANUSCRIPT INTRO ===== If i were to conclude what we've seen so far in one sentence, "the ring current is NOT a ring". Give a review of our current understanding of the ring current from ENA images obtained by the ENA imager HENA onboard IMAGE. TOC ===== ASTRID/PIPPI: out of the ordinary. show a remarkable observation of the quiet-time magnetosphere IMAGE/HENA: give samples of the rich data set. show storms, how the ring current responds to rapid changes in IMF, and the effects of ring-current plasmasphere interactions. there's lot to show so I will not dwell on one observation. feel free to ask SHORT questions during the talk if i miss anything. keep in-depth questions to after. ASTRID/PIPPI ============ [VUGRAPH GEOMETRY AND OBSERVATIONS] Let's start back in 1995 with the swedish microsatellite Astrid and its ENA imager PIPPI. Astrid was located at the equator close to midnight imaging the sunward and the antisunward hemisphere. What we see is quite remarkable: first image: astrid staring in to the earth. see a narrow region of plasma along the field lines shown here in blue. second image: astrid staring down the tail. see the continuation 'flux tube' following the field line. it is essentially a narrow flux tube glowing in ENAs, if you will. [EBIHARA'S SNAPSHOT] We've succeded in modeling this event and we believe this is a narrow flow channel from the plasmasheet. During this event the magnetosphere experienced a weak, but steady convection. We realized that this unusual vantage point 'below' the ring current is very useful when it comes to resolving the PADs. REPRINTS OVER THERE!! Now to HENA! LATEST STORM (MOVIE) ================================= You've probably heard alot about the IMAGE spacecraft and what it can do and you probably expect me to show you the latest ring current in almost real-time. .... I cant show you real time, but let's start out with the latest storm that took place just before i left. [LASCO MOVIE] This is the CME that started out from the sun on the morning of the 16 march... This shock then arrived at the earth 1020 UT 19 March. [HENA MOVIE] Here is IMF Bz. Image above the north pole and sun to your right. CAUTION: this is level 0 and quicklook data and still needs processing. So e.g. the blob in the upper left corner is NOT a strong reconnection site on the magnetopause. please disregard it. The black gap is where a shutter closes in front of the aperture to protect HENA from direct sunlight. Sometimes this also cuts bits of the ring current. First we see some plasma on the nightside. Now, at 1020 UT the shock arrived at earth and note the sudden enhancement in ring current intensity...really interesting. The sudden commencement was about 1200 UT and we can see an enhancement of the ENA flux just as IMAGE goes into the radiation belts. Now we get a dip down to -20 nT which convects plasma into low L shells and when when the Bz goes back up, the convection should turn OFF and the grad.-curv. drift should keep the ring current on closed trajectories....and indeed so, and we can even maybe pick out a peak on the nightside, which should be the point where the convected plasma is energized the most due to the minima in electric potential at that point. Going further, we have a long period of negative Bz, and we can see that there's a bit more "banana" shape to the ring current which implies that the drift paths are probably open for this period. The Bz now goes to positive values slowly, and we get a more closed and ring formed ring current. and in the next orbit we see that it has decayed in intensity probably due to charge exchange. As you can see there's a wealth of information here. Now let us look at some events we HAVE analyzed. (GOTO 23 MAY) (15 July) ========= This is a "classic" storm to start with. goto mainphase. IMF Bz plotted here with a nice and sharp dip to -60 nT. Above the norht pole and sun is down. See intense ENA emission squeezed up close to the earth, and the reason is that the sharp dip enhanced the convection in the magnetosphere so that plasma was brought into low L-shells. Now, as the Bz goes positive the convection turns OFF and grad.-curv. drifts will dominate with the ring current "locked" on closed drift paths. You will see this clearly in the next pass. In the next orbits you'll see the decay in intensity, but it is still perfectly happy drifitng on closed paths. ...in a sense pretty boring and we only have a couple of these "texbook" storms. The rest are much more intruiging... 23 MAY [MOVIE] ============== Now let's look at some events we've studied. This one shows a nice relation with the IMF Bz. This starts out above the norht pole and sun is to your lower left. Just watch the gradual increase upto 1912 UT... and then a sudden evacutation of the dayside fluxes during about 10 min when IMF Bz goes negative. [TRAJECTORY PLOT VUGRAPH] The reason for this sudden decrease is quite clear: When IMF Bz is positive, convection is very weak and the gradient-curvature drifts dominate and the drift trajectories are almost closed. When IMF Bz goes negative we get strong convection with trajectories out through the magnetopause. This is from a Ebihara's kinetic ring current model. An unsolved mystery is how the evacuation can take place in only 10 min. Ebihara's model predicts that it takes approximately 30 min. REPRINTS OVER THERE!! 12 AUG [MOVIE] ============== The 12 aug was unusual in that the IMF By was large at the same time Bz was strongly negative for a whole day!! Plotted here is By. Above north pole and sun to lower right. We see large fluxes almost at dawn which seems to sit there happily the entire day. This indicates that there's probably a minimum in the electric potential in this region that energizes the plasma as it is convected in from the tail region. This is what we think is going on: The strongly negative Bz makes sure convection is strong enough to bring plasma close to the earth. The strongly positive By alters the merging lines on the flanks of the magnetosphere so that the potential pattern in the magnetosphere gets twisted in LT. The minimum potential will no longer be at dusk, but almost at dawn. We will investigate this in more detail right after this meeting. 24 MAY [VUGRAPH] ================ Now to some peculiar effects of dealing with a anisotropically emitting medium. What I mean by this is that e.g. an ion distribution with a pancake PAD will not emit as many ENAs in the field aligned direction as it will in the perpendicular direction. Therefore the ENA intensity from the same blob of plasma will depend on where we view it from. [HENA ONLY] Over north pole and sun to lower left. Ignore the emissions from the earth and focus on the emissions coming from around noon. One would guess that the 'blob' on the dayside is simply an injected blob of plasma that has drifted around to the dayside....BUT this blob stays in the same place for half a day! [HENAEUV] This led us to suspect interaction with the plasmasphere. This image shows the previous ENA image on top of an image of the plasmasphere (in EUV). The dashed line is the plasmapause and note the plasmaspheric tail. Note the apparent spatial relation between plasmasphere and ENA emissions. We have only ENA emissions outside the plasmapause. Now, why can this be? POLAR measurements reveal that inside the plasmapause we have pancake PADs and on the dayside they are isotropic, but the peak ion intensities are the same. So we have a full blown ring current but the PADs change as a function of LT. We believe that the reason why the PADs are modified are due to interactions with ion cyclotron waves. REPRINT OVER THERE!! END === If you somehow felt that this has been a commercial for IMAGE and HENA, you're probably right. We would like to stress that this IS a OPEN data set and we're doing everything to make it avialable interactively ONLINE. thankyou. sd-www......