Finland’s R Index: Read the Station and the Ten-Minute Interval

Read the quantity before its colour

The Finnish Meteorological Institute explains R as a measure based on magnetic-field change over a ten-minute interval. That definition differs from the three-hour planetary Kp index. Even when both products use coloured graphics, their numbers cannot be exchanged as if they were the same scale. Begin with the product’s own explanation rather than a general aurora-app legend. A screenshot labelled only “activity high” loses the measurement being discussed. Keep the quantity name and the interval together in your notes so a later comparison does not quietly merge two different kinds of scientific information.

Station location is part of the result

A local station observation belongs to a particular measuring location. It does not automatically describe the magnetic conditions above every settlement in Finland or the wider Nordic region. FMI’s map provides station-based information, and its explanation associates thresholds with those locations. Select the relevant station and read the corresponding labels. A nearby place may be a useful geographical reference, but proximity alone does not make a station an exact measurement at your accommodation. When comparing stations, retain their names and times rather than copying only the strongest colour from a national map.

Interpret thresholds with their source legend

FMI describes lower and upper activity thresholds displayed through its service. The thresholds support the product’s interpretation of the local magnetic observations. They are not a guarantee that an observer will see a bright display through cloud, daylight or an obstructed view. Read the current legend because interface choices can change. Distinguish a threshold crossing from the length of time activity remains elevated. A brief highlighted interval and repeated highlighted intervals tell different observational stories, even if a cropped screenshot gives both the same colour. Keep a longer view when discussing the development of an event.

Treat missing observations as missing

A service can show that the latest observation is unavailable. That state must remain separate from low measured activity. Do not fill a blank with an assumed quiet value or interpret a missing station marker as proof that nothing happened there. Compare the last available timestamp with the time you are reading the page. If current data are absent, say that the product cannot answer the immediate station question. Other official observations may provide context, but they should be identified separately rather than silently substituted. This distinction is especially important when saving maps for later comparison with personal observations.

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