Forecasting auroras from regional and global magnetic field measurements

We use the connection between auroral sightings and rapid geomagnetic field variations in a concept for a Regional Auroral Forecast (RAF) service. The service is based on statistical relationships between near-real-time alerts issued by the NOAA Space Weather Prediction Center and magnetic time derivative (dB / dt) values measured by five MIRACLE magnetometer stations located in Finland at auroral and sub-auroral latitudes. Our database contains NOAA alerts and dB / dt observations from the years 2002-2012. These data are used to create a set of conditional probabilities, which tell the service user when the probability of seeing auroras exceeds the average conditions in Fennoscandia during the coming 0-12 h. Favourable conditions for auroral displays are associated with ground magnetic field time derivative values (dB / dt) exceeding certain latitude-dependent threshold values. Our statistical analyses reveal that the probabilities of recording dB / dt exceeding the thresholds stay below 50% after NOAA alerts on X-ray bursts or on energetic particle flux enhancements. Therefore, those alerts are not very useful for auroral forecasts if we want to keep the number of false alarms low. However, NOAA alerts on global geomagnetic storms (characterized with K-p values > 4) enable probability estimates of > 50% with lead times of 3-12 h. RAF forecasts thus rely heavily on the well-known fact that bright auroras appear during geomagnetic storms. The additional new piece of information which RAF brings to the previous picture is the knowledge on typical storm durations at different latitudes. For example, the service users south of the Arctic Circle will learn that after a NOAA ALTK06 issuance in night, auroral spotting should be done within 12 h after the alert, while at higher latitudes conditions can remain favourable during the next night.Peer reviewe

ELASTIC GUIDED WAVE MEDIATED INDUSTRIAL ULTRASONIC CLEANING

Industrial ultrasonic cleaning plays a crucial role in optimizing processes and production in various industrial equipment by eliminating the need for harmful chemicals and minimizing production downtime. While previous research has focused on optimizing ultrasonic cleaning for larger and complex geometries, by controlling acoustic pressure fields and cavitation, the potential contribution of online cleaning using elastic vibrations of the equipment wall remains insufficiently explored. To bridge this gap, this study employs a combination of simulation techniques and laboratory experiments to investigate the significance of elastic guided waves and evaluate the influence of different pulsed driving waveform properties on cleaning efficacy. Specifically, the study focuses on the delivery of ultrasonic energy along the pipe wall. While confirming the effective delivery of ultrasonic energy across the length of pipes, the mechanisms underlying scale removal are still open to interpretation. Notably, specific flexural wave modes of a fluid-filled pipe, e.g. F_FFP (n,1) mode family, are identified as potential carriers of the cleaning effect. The research highlights the significance of high momentary power and total effective power in achieving efficient cleaning. The presence of liquid introduces complexities such as mode conversions and the possibility of cavitation. Further investigations are recommended to explore the individual roles of normal and tangential vibration components at the wall-scale interface. The study emphasizes the need for comprehensive analysis to optimize ultrasonic cleaning processes for larger and complex geometries, determine effective parameters for particle detachment, and enhance overall cleaning efficiency