Volcanic eruptions produce ash clouds, which are a major hazard to population centers and the aviation community. Within the North Pacific (NOPAC) region, there have been numerous volcanic ash clouds that have reached aviation routes. Others have closed airports and traveled for thousands of kilometers. Being able to detect these ash clouds and then provide an assessment of their potential movement is essential for hazard assessment and mitigation. Remote sensing satellite data, through the reverse absorption or split window method, is used to detect these volcanic ash clouds, with a negative signal produced from spectrally semi-transparent ash clouds. Single channel satellite is used to detect the early eruption spectrally opaque ash clouds. Volcanic Ash Transport and Dispersion (VATD) models are used to provide a forecast of the ash clouds' future location. The Alaska Volcano Observatory (AVO) remote sensing ash detection system automatically analyzes satellite data of volcanic ash clouds, detecting new ash clouds and also providing alerts, both email and text, to those with AVO. However, there are also non-volcanic related features across the NOPAC region that can produce a negative signal. These can complicate alerts and warning of impending ash clouds. Discussions and examples are shown of these non-volcanic features and some analysis is provided on how these features can be discriminated from volcanic ash clouds. Finally, there is discussion on how information of the ash cloud such as location, particle size and concentrations, could be used as VATD model initialization. These model forecasts could then provide an improved assessment of the clouds' future movement.

Semi-diurnal oscillations are a ubiquitous feature of polar sea-ice motion. Over much of the Arctic basin, inertial and semi-diurnal tidal variability have similar frequencies so that periodicity alone is inadequate to determine the source of oscillations. We investigate the relative roles of tidal and inertial variability in Arctic sea ice using a barotropic ice-ocean model with sea ice embedded in an upper boundary layer. Results from this model are compared with 'levitated' ice-ocean coupling used in many models. In levitated models the mechanical buoyancy effect of sea ice is neglected so that convergence of ice, for example, does not affect the oceanic Ekman flux. We use rotary spectral analysis to compare simulated and observed results. This helps to interpret the rotation sense of sea-ice drift and deformation at the semi-diurnal period and is a useful discriminator between tidal and inertial effects. Results indicate that the levitated model generates an artificial inertial resonance in the presence of tidal and wind forcing, contrary to the embedded sea-ice model. We conclude that sea-ice mechanics can cause the rotational response of ice motion to change sign even in the presence of strong and opposing local tidal forcing when a physically consistent dynamic ice-ocean coupling is employed.