Friday, 1 July 2016

In freezing mode

Finally, we have not been lucky this austral winter. On 21 May, there was a huge storm, with hourly averages of wind speed up to 27 m/s and 6-min-peaks up to 38 m/s. In the course of this storm, the communication link to the stationwas interrupted and could not be restored (if the storm has been the cause can’t be confirmed, however). Also other satellite communication means did not work anymore, indicating that the station had also lost power. The reasons are not clear (as there is no communication link to explore…). So, this means that everything is now in ‘freezing’ mode. Inside the station and in the scientific shelters, there should be no issue for the instruments – it should be dry and relatively ‘warm’. However, the power outage means also that there is quite a lot of maintenance work to be done when the next BELARE campaign starts in November this year. In particular, the instruments which are installed on the roof of PE station have to be checked in detail. Last year, when everything operated without interruption during winter, it was much less maintenance work. We also hope that the instruments have not encountered damage during that huge storm, and also that the long time they will be now outside without being powered will not lead to damage. Only by mid-November, when the first team arrives at PE, we will know more details. Until then, we hope the best.

In the meantime, there is some time to go ahead with some data analysis. Below, a graph for the monthly means of the total particle number concentration is given, for all years/months available up to now. There are several striking points : a) there is a clear yearly cycle, with relatively high numbers  during summer and lower particle numbers during winter, b) winter numbers (May, June, July) are extremely low (down to some tens of particles per cm3), c) as soon as sunlight returns in spring (Sep, Oct), numbers go up distinctly, d) monthly numbers are well repeated each year, however with some annual variation, e) especially from November throughout March, the statistical means come with very high standard deviations. Some  explanations : during the summer months, transport of air masses from lower latitudes or the coast to PE station is more often than during winter when the strong atmospheric circular circulation around Antarctica (polar vortex) is forming a quasi- barrier for this kind of transport. In addition, there is also (almost) no sunlight which could trigger particle formation processes by atmospheric photochemistry. In September, October, sunlight returns, and also the polar vortex is becoming less stable, setting the scene for atmospheric particle formation and transport. The high standard deviations were caused by short-termed events (some hours to one day), during which the particle number increased from 200/300 per cm3 up to 6000 per cm3. Such events can be linked to either entrainment from the free troposphere and/or the passage of clouds with or without precipitation.