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.

Wednesday, 6 April 2016

Successful season behind and promising winter season ahead

In the meantime we are already in April. High time to post something on the blog. The BELARE 2015-2016 expedition at Utsteinen has been finished end of February when the last team left Princess Elisabeth station. The expedition season has been successful for our project. All instruments for year-round operation have been maintained and are still operational.This means that now an un-interrupted time series exists from November 2014 to present for four aerosol instruments (aethalometer, nephelometer, TEOM-FDMS, U-CPC). The laser aerosol spectrometer has been re-installed after its repair and has been operational since December 2015 – and is still running. The Brewer ozone spectrophotometer could measure the whole austral summer season until mid-February when it had to be dismounted as usual. Below there is a graph showing the time series of total atmospheric column ozone from end of November to end of December 2015. It illustrates nicely the period until mid-December when ozone hole conditons (i.e. total ozone below 220 DU) persisted over the region of Utsteinen. Normally, such conditions persist only until end of November, beginning of December. The ozone hole of 2015 was indeed one of the most stable one on record. 
time series of total ozone end of Nov-2015 to end of Dec-2015

the MAX-DOAS (left) and the sunphotometer (right) instruments on the roof of PE station

The next image shows the sunphotometer (to the right) and the new-comer instrument ‘MAX-DOAS’ (to the left). The MAX-DOAS (Multi-AXis Differential Optical Absorption Spectroscopy) system is part of the BIRA contribution to the AEROCLOUD project. This instrument will monitor the vertical distribution of aerosols as well as several trace gases present in the atmosphere above the station. Like the Brewer, the MAX-DOAS measures the spectrum of solar light attenuated and scattered by atmospheric particles and molecules, in the wavelenght region of 300 to 550 nm, where a number of atmospheric molecules such as ozone and other compounds (NO2, BrO, OClO, H2O, O4) can be detected. By scanning the sky from the horizon to the zenith, the instrument provides information on the vertical profile of these molecules, as well as on aerosols which affect the measured trace gas absorption. First measurements are very promising and comparisons with the Brewer instrument (total ozone) and the sunphotometer (aerosol optical depth) show good agreement. In particular interesting is , that the instrument will continue its monitoring throughout the year. Therefore (if it keeps on running), it will be possible to observe the onset of the ozone hole as soon as the light starts to illuminate the polar stratosphere in early austral spring.. In addition, the concentration of several ozone related species (NO2, BrO and OClO) will be simultaneously measured providing an ensemble of data to characterize the chemical evolution of the polar stratosphere during the spring period. 

 the new instrument 'Snowflake Video Imager' on the roof of PE station

Our partners from the KU Leuven installed in January 2016 also a new instrument on the roof of the station, the ‘SnowflakeVideo Imager’ (see third image), designed by NASA. It contains a high-speed camera with sufficient frame rate, pixels, and shutter speed to record thousands of snowflake images in an undisturbed flow. These images are used to derive information on precipitating and blowing snow particle size distribution, as well as information about particle shape. This information on snow particles is important for correct estimation of snowfall amounts based on the radar measurements. A nice test for the instruments has been an impressive storm on 29 and 30 March 2016, with wind speeds around 20 m/s, peaking up to 26 m/s and after which the automatic weather station detected a snow accumulation around 20 cm. When writing this post, just another storm is active in the area of Utsteinen. So far, the instruments cope well with these conditions and the aerosol instruments are well in their cosy shelter (fourth image) – outside storm and very low temperatures, inside around 20 °C. 

inside the aerosol instrument shelter during winter season