G. Siscoe et G. Lu, ENERGY-TRANSFER VIA REGION-2 CURRENTS - A TEST OF THE STANDARD MAGNETOSPHERE-IONOSPHERE COUPLING THEORY, J GEO R-S P, 103(A3), 1998, pp. 4637-4647
The magnetosphere-ionosphere coupling theory associated with the names
of Fejer, Vasyliunas, Swift, Wolf, and others can be used to predict
that in steady state the region 2 currents transfer no net energy betw
een the ionosphere and the magnetosphere, but when the transpolar pote
ntial drop increases, region 2 currents transfer energy away from the
ionosphere into the magnetosphere. Both properties are counterintuitiv
e and differ from the ''normal'' properties exhibited by region 1 curr
ents, which in steady state or otherwise consistently deliver energy t
o the ionosphere to feed Joule dissipation. We extend the theory to in
clude the effects of charge exchange so that it can be applied to magn
etic storms. We conclude that charge exchange also extracts energy fro
m the ionosphere via region 2 currents. To test these predictions of u
nexpected properties, we use the technique of assimilative mapping of
ionospheric electrodynaics (AMIE). From AMIE-derived values of ionosph
eric electrical potentials and field-aligned currents for a well docum
ented magnetic storm, we compute the direction and flux of energy flow
ing between the ionosphere and the magnetosphere. Region 2 currents in
deed transfer energy out of the ionosphere during the storm main phase
, when the transpolar potential drop increases to its storm time value
. The rate of energy transfer is greatly suppressed late in the recove
ry phase when conditions approximate steady state. Also the data are c
onsistent with charge exchange acting to extract energy from the ionos
phere via region 2 currents. Thus the test confirms two of the predict
ions and is consistent with the third. For this storm the region 2 upw
ard energy flux is at most about 30% of the energy that goes into the
ring current to;account for the growth of Dst.