The longer the polar night gets the more suitable time it is for ground-based auroral measurements in the north. During a couple of weeks before the 'Above The Poles' day, several space physicists from the University of Oulu, the Sodanky Geophysical Observatory and the Finnish Meteorological Institute, well wrapped to withstand the polar biting cold, were mobilized for the annual Finnish EISCAT measurement campaign.
During the campaign, series of measurements were taken, including every day measurements by using all three EISCAT radar systems consisting huge antennas: the tri-static UHF and the VHF radars in Tromsø and the EISCAT Svalbard Radars in Spitsbergen, far within the Arctic circle, being home to about 3,000 polar bears!
Among the main gang at Tromsø, Timo Pitkanen from the NISSE team was taking care of the radar measurements. This meant long hours watching the radar monitors in the radar control room and monitoring the current space weather from various sources like satellites in the solar wind via internet. Overnight runs could last eight hours from 7 PM in the evening to 3 AM the next morning. In addition, there were measurements during daytime. Fortunately nobody needed to stay awake every night but we could take turns so that everybody had enough sleep.
EISCAT test measurements for NISSE
A few hours of radar time were exclusively reserved for NISSE test measurements. At around noon local time, we pointed all three UHF antennas roughly to the region where the water in the NISSE experiment will be released — at about 95 km altitude about 35 km north-northwest of the rocket launch pad at the Esrange Space Centre, Sweden. Tests were carried out and everything worked well.
Preliminary data analysis of the test measurements revealed that, as expected, possible effects of the water release may be a challenge to measure. The release region will be at the lower part of the ionosphere (95 km) and a quite long distance away (~190 km) from the transmitting site, which means weak radar echoes. However, in early March the ionospheric conditions will be slightly better compared to the test conditions now in late November-early December. In March the sun will rise higher above the horizon and thus enhance somewhat the degree of background ionization, which in turn strengthens the backscattered radar signal.
Auroral displays in the night
Due to the solar activity minimum, geomagnetic activity stayed mainly at quiet level during the present EISCAT campaign. Luckily in few occasions, we could enjoy simultaneous clear sky and bright auroras in the sky above the EISCAT Tromsø site.
