THE URANIAN AURORA AND ITS RELATIONSHIP TO THE MAGNETOSPHERE

About 32 h of Voyager Ultraviolet Spectrometer (UVS) observations of U ranus H-2 band airglow emission (875 less-than-or-equal-to lambda less -than-or-equal-to 1115 angstrom) have been analyzed using the singular value decomposition (SVD) approach to inversion, producing an intensi ty map showing aurora at both magnetic poles. An H Lyman alpha aurora may also be present but is difficult to separate from scattered solar and local interstellar medium components. SVD analysis of variance sho ws that the intensity estimate is significantly larger than the error estimate over both Uranographic poles and part of the equatorial regio n, fortuitously including both magnetic polar regions. The Goddard Spa ce Flight Center Q3 magnetic field model correctly predicts that the a urora should be larger in area and emit more power at the weaker N mag netic pole than at the stronger S magnetic pole. However, the auroral emissions are quite localized in magnetic longitude and so do not form complete auroral ovals. The brightest auroral emission at each magnet ic pole is confined to a range of almost-equal-to 90-degrees of magnet ic longitude centered on the magnetotail direction, at moderate magnet ic L parameter (5 less-than-or-equal-to L less-than-or-equal-to 10), b ut some emission at each pole is distributed over a range of more than 180-degrees of longitude. The S polar auroral intensity maximum is co incident with the source of the broadband bursty and broadband smooth Uranian kilometric radio emission (UKR), while the N polar auroral int ensity maximum may coincide with the dayside UKR source. The N and S a uroral intensity maxima also lie at the conjugate magnetic footprints of the maximum intensities of whistler-mode plasma wave emission and 2 2- to 35-keV electron fluxes observed by Voyager. The magnetic longitu des of the aurora are completely inconsistent with the ''windshield wi per'' effect for either ions or electrons, indicating that some other effect, such as rapid depletion of the population of precipitating par ticles or highly localized strong pitch-angle diffusion, may be acting to localize emission. The low apparent L of the precipitating particl es indicates that their energies may be < 10 keV. Hence magnetospheric convection is likely to be important, and thus particles exciting the aurora may not remain on constant L shells. The precipitating particl es may be a relatively low-energy population at high L that is heated to aurora-exciting energy by adiabatic compression during convection t o low L. We estimate that the total auroral power output at H Lyman al pha and shorter wavelengths is about 3 x 10(9) to 7 x 10(9) W, requiri ng about 10 times that much power for excitation.