  This paper presents research on polar cap ionosphere space weather phenomena
conducted during the European Cooperation in Science and Technology (COST)
action ES0803 from 2008 to 2012. The main part of the work has been directed
toward the study of plasma instabilities and scintillations in association with
cusp flow channels and polar cap electron density structures/patches,which is
considered as critical knowledge in order to develop forecast models for
scintillations in the polar cap. We have approached this problem by
multi-instrument techniques that comprise the EISCAT Svalbard Radar, SuperDARN
radars, in-situ rocket, and GPS scintillation measurements. The Discussion
section aims to unify the bits and pieces of highly specialized information
from several papers into a generalized picture. The cusp ionosphere appears as
a hot region in GPS scintillation climatology maps. Our results are consistent
with the existing view that scintillations in the cusp and the polar cap
ionosphere are mainly due to multi-scale structures generated by instability
processes associated with the cross-polar transport of polar cap patches. We
have demonstrated that the SuperDARN convection model can be used to track
these patches backward and forward in time. Hence, once a patch has been
detected in the cusp inflow region, SuperDARN can be used to forecast its
destination in the future. However, the high-density gradient of polar cap
patches is not the only prerequisite for high-latitude scintillations.
Unprecedented high resolution rocket measurements reveal that the cusp
ionosphere is associated with filamentary precipitation giving rise to
kilometer scale gradients onto which the gradient drift instability can operate
very efficiently... (continued)
