A tale of two theories: How the adiabatic response and ULF waves affect relativistic electrons

Using data from the Comprehensive Energetic Particle and Pitch Angle Distri bution (CEPPAD)-High Sensitivity Telescope (HIST) instrument on the Polar s pacecraft and ground magnetometer data from the 210 meridian magnetometer c hain, we test the ULF wave drift resonance theory proposed to explain relat ivistic electron phase space density enhancements. We begin by investigatin g changes in electron flux due to the "Dst effect." The Dst effect refers t o the adiabatic response of relativistic electrons to changes in the magnet ic field characterized by the Dst index. The Dst effect, assuming no loss o r addition of new electrons, produces reversible order of magnitude changes in relativistic electrons flux measured at fixed energy, but it cannot acc ount for the flux enhancement that occurs in the recovery phase of most sto rms. Liouville's theorem states that phase space density expressed in terms of constant adiabatic invariants is unaffected by adiabatic field changes and thus is insensitive to the Dst effect. It is therefore useful to expres s flux measurements in terms of phase space densities at constant first, se cond and third adiabatic invariants. The phase space density is determined from the CEPPAD-HIST electron detector that measures differential direction al flux of electrons from 0.7 to 9 MeV and the Tsyganenko 96 field model. T he analysis is done for January to June 1997. The ULF wave drift resonance theory that we test proposes that relativistic electrons are accelerated by an m=2 toroidal or poloidal mode wave whose frequency equals the drift fre quency of the electron. The theory is tested by comparing the relativistic electron phase space densities to wave power determined at three ground sta tions with L* values of 4.0, 5.7 and 6.2. Comparison of the wave data to th e phase space densities shows that five out of nine storm events are consis tent with the ULF wave drift resonance mechanism, three out of nine give am biguous support to the model, and one event has high ULF wave power at the drift frequency of the electrons but no corresponding phase space density e nhancement suggesting that ULF wave power alone is not sufficient to cause an electron response. Two explanations of the anomalous event are investiga ted including excessive loss of electrons to the magnetopause and wave dura tion.