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This paper is the second in a series on a study of the link between IMF and\udsporadic-E layers within the polar cap. In Paper I (Voiculescu et al., 2006),\udan analysis of the sporadic-E data from Thule and Longyearbyen was\udpresented. Here we concentrate on the electric field mechanism of sporadic-E\udgeneration. By means of model calculations we show that the mechanism is\udeffective even at Thule, where the direction of the geomagnetic field departs\udfrom vertical only by 4. The model calculations also lead to a\udrevision of the electric field theory. Previously, a thin layer was assumed\udto grow at a convergent null in the vertical ion velocity, which is formed\udwhen the electric field points in the NW sector. Our calculations indicate\udthat in the dynamic process of vertical plasma compression, a layer is\udgenerated at altitudes of high vertical convergence rather than at a null.\udConsequently, the layer generation is less sensitive than previously assumed\udto fluctuations of the electric field direction within the NW sector. The\udobserved diurnal variations of sporadic-E occurrence at Longyearbyen and\udThule are compared with the diurnal variations of the electric field, calculated\udusing a representative range of IMF values by means of the statistical APL\udmodel. The results indicate that the main features of Es occurrence can be\udexplained by the convection pattern controlled by the IMF. Electric fields\udcalculated from the IMF observations are also used for producing\uddistributions of sporadic-E occurrence as a function of electric field\uddirection at the two sites. A marked difference between the distributions at\udThule and Longyearbyen is found. A model estimate of the occurrence\udprobability as a function of electric field direction is developed and a\udreasonable agreement between the model and the experimental occurrence is\udfound. The calculation explains the differences between the distributions at\udthe two sites in terms of the polar cap convection pattern. The conclusion is\udthat the electric field is the major cause for sporadic-E generation and,\udconsequently, IMF has a clear control on the occurrence of sporadic E within\udthe polar cap

IMF effect on sporadic-E layers at two northern polar cap sites: Part II – Electric field