SCALING OF HEATING RATES IN SOLAR CORONAL LOOPS

THE gas of the solar corona is at a temperature of several million deg rees, orders of magnitude hotter than the underlying photosphere, The nature of the physical process that heats the solar corona (and the co ronae of solar-type stars more generally) has been a long-standing puz zle, A number of plausible heating mechanisms have been proposed, but observations have so far been unable to discriminate between them(1). Here we show that coronal heating exhibits scaling properties that sho uld provide a powerful diagnostic of the underlying mechanism. The cor onal magnetic field organizes the coronal plasma into loop-like featur es, which form the basic structural elements of the corona(2). We demo nstrate that the pressures and lengths of the coronal loops are statis tically related, suggesting that the heating rate scales inversely wit h approximately the square of the loop length. Existing coronal heatin g theories make different predictions about what this scaling should h e, and a model(3,4) of energy dissipation bg stressed coronal magnetic fields appears at present to be the most consistent with our observat ional result.