Abstract. This work presents the outline and so far completed design of the Aalto-1 science mission. Aalto-1 is a multi-payload remote-sensing nanosatellite, built almost entirely by students. The satellite aims for a 500-900 km sunsynchronous orbit and includes an accurate attitude dynamics and control unit, a UHF/VHF housekeeping and S-band data links, and a GPS unit for positioning (radio positioning and NORAD TLE's are planned to be used as backup). It has three specific payloads: a spectral imager based on piezoactuated Fabry-Perot interferometry, designed and built by The Technical Research Centre of Finland (VTT); a miniaturised radiation monitor (RADMON) jointly designed and built by Universities of Helsinki and Turku; and an electrostatic plasma brake designed and built by the Finnish Meteorological Institute (FMI), derived from the concept of the e-sail, also originating from FMI. Two phases are important for the payloads, the technology demonstration and the science phase. The emphasis is placed on technological demonstration of the spectral imager and RADMON, and suitable targets have already been chosen to be completed during that phase, while the plasma brake will start operation in the latter part of the science phase. The technology demonstration will be over in a relatively short time, while the science phase is planned to last two years. The science phase is divided into two smaller phases: the science observations phase, during which only the spectral imager and RADMON will be operated for 6-12 months and the plasma brake demonstration phase, which is dedicated to the plasma brake experiment for at least a year. These smaller phases are necessary due to the drastically different power, communication and attitude requirements of the payloads. The spectral imager will be by far the most demanding instrument on board, as it requires most of the downlink bandwidth, has a high peak power and attitude performance. It will acquire images in a series up to at least 20 spectral bands within the 500-900 nm spectral range, forming the desired spectral data cube product. Shortly before an image is acquired, the parallel visual spectrum camera will take a broader picture for comparison. Also stereoscopic imaging is planned. The amount of data collected by the spectral imager is adjustable, and ranges anywhere from 10 to 500 MB. The RADMON will be on 80 % of an orbit period on average and together with housekeeping data will gather around 2 MB of data in 24 h. An operational limitation is formed due to the S-band downlink capability of 29-49 MB per 24 h for a 500 900 km orbit altitude, as only one ground station is planned to be available for the satellite. This will limit both type and quantity of spectral imager images taken during the science phase. The plasma brake will in turn be within an angle of 20 • over the poles for efficient use of the Earth's magnetic field and ionosphere during its spin-up and operation.

This work presents the outline and so far completed design of the Aalto-1 science mission. Aalto-1 is a multi-payload remote sensing nanosatellite, built almost entirely by students. The satellite aims for a 500–900 km sun-synchronous orbit, and includes an accurate attitude dynamics and control unit, a UHF/VHF housekeeping and S-band data links, and a GPS unit for positioning (radio positioning and NORAD TLE's are planned to be used as backups). It has three specific payloads: a spectral imager based on piezo-actuated Fabry–Perot interferometry, designed and built by The Technical Research Center of Finland (VTT); a miniaturized radiation monitor (RADMON) jointly designed and built by Universities of Helsinki and Turku ; and an electrostatic plasma brake designed and built by the Finnish Meteorological Institute (FMI), derived from the concept of the e-sail, also originating from FMI. Two phases are important for the payloads, the technology demonstration and the science phase. Emphasis is placed on technological demonstration of the spectral imager and RADMON, and suitable targets have already been chosen to be completed during that phase, while the plasma brake will start operation in the latter part of the science phase. The technology demonstration will be over in relatively short time, while the science phase is planned to last two years. The science phase is divided into two smaller phases: the science observations phase, during which only the spectral imager and RADMON will be operated for 6–12 months, and the plasma brake demonstration phase, which is dedicated to the plasma brake experiment for at least a year. These smaller phases are necessary due to the drastically different power, communication and attitude requirements of the payloads. The spectral imager will be by far the most demanding instrument on board, as it requires most of the downlink bandwidth, has a high peak power and attitude performance. It will acquire images in a series up to at least 20 spectral bands within the 500–900 nm spectral range, forming the desired spectral data cube product. Shortly before an image is acquired, the parallel visual spectrum camera will take a broader picture for comparison. Also stereoscopic imaging is planned. The amount of data collected by the spectral imager is adjustable, and ranges anywhere from 10 to 500 MB. The RADMON will be on 80% of an orbit period in average and together with housekeeping data will gather around 2 MB of data in 24 h. An operational limitation is formed due to the S-band downlink capability of 29–49 MB per 24 h for a 500 900 km orbit altitude, as only one ground station is planned to be available to the satellite. This will limit both type and quantity of spectral imager images taken during the science phase. The plasma brake will in turn be on within an angle of 20° over the poles for efficient use of the Earth's magnetic field and ionosphere during its spin-up and operation

Abstract. 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 Kp 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.

Rapid magnetic fluctuations are known to be closely linked to the high-latitude geomagnetic activity, in particular, to geomagnetic pulsations and subtorms. Increasing amount of commercial activity in the arctic regions requires better monitoring capability and improved understanding on the effects of geomagnetic hazards to infrastructure. In this study, we analyze rapid, 1-s fluctuations in Greenland. To measure high-frequency geomagnetic fluctuations in the auroral oval and polar cap, we use high time resolution data of 1 s from 12 stations covering a large latitudinal range of 64 to 84 quasi-dipole geomagnetic latitude (QDGMlat). We found out that the large magnetic field fluctuations exceeding 0.2 nT/s are observed 10-30% of the time in auroral oval latitudes, depending on the solar cycle phase and station location. The latitudinal differences are much larger in fluctuation coverage (fractional derivative rate, FDR) than in fluctuations amplitude (dH∕dt). The highest |dH∕dt| and FDRs at noon are observed at the northern stations from 72 to 84 QDGMlat, while in south Greenland from 72 to 65 QDGMlat, the highest |dH∕dt| and FDRs are recorded at midnight. The largest differences in seasonal variation between noon and midnight are observed in the polar cap, where a summer increase is seen at noon and almost flat seasonal profile at midnight. Plain Language SummaryWe analyze Earth's magnetic field measurements from Greenland in 2011-2013. We use high time resolution measurements obtained from 12 stations, covering a large geographic area. We use the rate of change of the magnetic field as the basis of our analysis, and we have developed a new method called the fractional derivative rate for this purpose. Differences between the years, time of day, and geographic location along the north-south axis are studied separately. We found out that there are significant differences between the stations, with the northernmost stations being more magnetically active during noon and the southernmost stations more active during midnight. The largest differences in these activity patterns are seen in the northernmost area, the polar cap. Understanding these variations in activity between the geographic locations will help us prepare more accurate and better targeted space weather forecasts in the future.