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Moss is the name given to low lying (3000 km), hot (1 MK) solar coronal plasma that has recently been observed by the Transition Region and Coronal Explorer (TRACE). This paper investigates two hypotheses regarding the nature of the moss: (1) emission from small, million degree loops; (2) emission from the legs of 3-10 million degree loops. We update the coronal radiative loss curve, using the most recent results for coronal abundances, and use an analytical loop model to nd that the rst hypothesis requires a lling factor close to unity to reproduce the observed emission measure, while the second hypothesis results in a lling factor of about 0.1, in agreement with other independent multi-wavelength analyses of moss. We nd that the vertical extent and the height of the moss layer above the limb are also very well reproduced with the second hypothesis. We further show that the observed brightness of the moss scales linearly with the loop pressure and lling factor, independent of the loop length, and we derive a general expression for the conversion factor.

Direct observations over the past four centuries show that the number of sunspots observed on the Sun's surface varies periodically, going through successive maxima and minima. Following sunspot cycle 23, the Sun went into a prolonged minimum characterized by a very weak polar magnetic field and an unusually large number of days without sunspots. Sunspots are strongly magnetized regions generated by a dynamo mechanism that recreates the solar polar field mediated through plasma flows. Here we report results from kinematic dynamo simulations which demonstrate that a fast meridional flow in the first half of a cycle, followed by a slower flow in the second half, reproduces both characteristics of the minimum of sunspot cycle 23. Our model predicts that, in general, very deep minima are associated with weak polar fields. Sunspots govern the solar radiative energy and radio flux, and, in conjunction with the polar field, modulate the solar wind, the heliospheric open flux and, consequently, the cosmic ray flux at Earth.