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

Thursday, 3 December 2015

Aerocloud Teamhas arrived at Princess Elisabeth station

Quentin and Christian arrived safely last week Friday, early in the morning at 1am, at Utsteinen. Unfortunately, our air cargo boxes carrying several scientific instruments  (like the new MAX-DOAS, the radiosounding equipment or the Laser Aerosol Spectrometer) have not been with them for their flight to Antarctica. The boxes were still in Amsterdam for for us unknown reasons, although they were picked up in time in Belgium. Finally, they arrived end of November in Cape Town, South Africa, and will be flown in by the next Ilyushin cargo flight, scheduled for today. After their arrival, Quentin and Christian checked that the already installed scientific instrumentation worked well, and  that all necessary accessories were there. 

 Measured effective UV Index at Princess Elisabeth station on 30 November 2015
As the weather conditions have been very good the last days, they have already been able to re-install the Brewer ozone spectrophotometer, which measures the total atmospheric column amount of ozone. This year’s ozone hole over Antarctica is one of the largest and total ozone amounts over Dronning Maud Land, the region where also Princess Elisabeth station is located, are still extremely low, between 150 and 200 Dobson units. As ozone protects us against the harmful UV radiation, lower total ozone values mean higher values of the UV index, which reached values up to 12 (!) during the last days. A value above 10 means that unprotected human skin will get sunburned within 10 minutes. At the station, the team members can follow the local UV index evolution in real-time and can thus protect their skin and eyes accordingly. The link to the near-real time UV index at Utsteinen can be found here (if there is no image, then the satellite link to the station is down at that moment). 

 The special cloud bringing very light snowfall and white frost to Utsteinen
But we are not only interested in atmospheric gases, also particles and particularly clouds interest us. A very special one occurred on Saturday, 28 November. In the evening, a close-to-the-ground stratus, resembling to fog, was advected from NE. During the time of its passage, visibility was significantly reduced, light snowfall was present and there was white frost formation. Such white frost formation we have never before experienced at the station, very special thus. The event lasted bit more than 3 hours, and afterwards the white frost sublimated rapidly. The next days, Quentin and Christian will do some necessary calibration and maintenance work of the scientific instrumentation and will welcome the boxes with the other instruments and equipment.

Friday, 20 November 2015

Team about to leave Belgium for Antarctica

This Saturday, Quentin Laffineur  (RMI) and Christian Hermans (Institute for Space Aeronomy) will start their journey from Belgium to Princess Elisabeth station Antarctica. As mentioned before, they will take care of all measurements and instrumentation for the AEROCLOUDproject. The scientific activities will take place in the framework of this year’s scientifc  Belgian Antarctic expedition  (BELARE 2015-2016), which is organised by the Polar Secretariat and the Belgian Federal Science Policy (BELSPO). The expedition is supported by the Belgian Secretary of State for the federal science policy, Ms Elke Sleurs, and is also supported by the Ministry of Defense (logistic support and personnel).
After arrival, Quentin and Christian will check several instruments for detecting clouds and precipitation, and properties of ambient aerosol particles. For the first time, all these instruments have been operational whole year-round. This means, also during the time when the station is uninhabited and the instruments rely on remote control. They will also re-install several instruments which cannot operate for several reasons during Antarctic winter (Cimel sunphotometer, Brewer ozone spectrophotometer), or which have been in Belgium for repair. In addition, there are again some newcomer-instruments.  In total, Quentin and Christian will have to deal with 13 instruments, plus the automatic weather station and weather balloon launches, and this within just tight 4 weeks. I wish them all the best and good luck for their work.

Tuesday, 10 November 2015

Instruments still operational and station is about to be opened again for the summer

The first Belare (Belgian Antarctic Research Expedition) team for this austral summer is about to arrive at Princess Elisabeth station. Their flight from Cape Town to Antarctica is scheduled for tomorrow. After arrival at the station they will be busy to prepare the station for austral summer operation. This means to clear the accumulated snow, check the IT- and power generation system, setting up again the water procurement system, and everything else what is needed for daily life at the station. Further teams will arrive one week and two weeks later. With that third team, also a first group of scientists will arrive. From our institute, it will be Quentin Laffineur who will join the Belare team. It will be his second stay in Antarctica. Last season he has been there together with me. This time, our colleage Christian Hermans from the Belgian Institute for Space Aeronomy will also join. It will be his first time in Antarctica. Quentin and Christian will take care of all instrumentation for atmospheric composition and cloud, precipitation detection, the automatic weather station, and they will also be responsible for regular launches of weather balloons. In addition, there will be some new instruments to be installed. Quite a lot of work. I will describe these instruments later in more detail and, as usual, we will also tell how life is about at Princess Elisabeth station.

monthly values of the particle number concentration (in cm3) from Nov-2014 ('1') to Oct-2015 ('12')

Another very important point is that our instruments are still in operation,without any break. We are very near to a complete year of data, two weeks missing yet. This is a great succes - having these kind of instruments in operation, only by remote control, without human direct maintenance, in these harsh environmental conditions and mainly sustained by renewable energies, is quite unique. This also means that we have already a very nice data set for our main scientific project AEROCLOUD at the station. The graphic above shows the monthly means of total particle concentration (in number per cm3) for November 2014 ('1') to October 2015 ('12'). The blue bars are the medians and blue and red together give the average value. Also the error bars are given. As already told in my last post, a nice seasonal cycle can be seen, also the influence of some events during which the number concentration increased distinctly (what causes that the median and average values differ markedly). The increase from August to October is very steep and the concentration for October is relatively high, especially when comparing with the concentrations during the summer months December to March. There have been several events during which the concentrations increased to some thousands of particles per cm3. There is a lot of promising information to be exploited scientifically. So, as the season is about to start, I will try to update this blog regularly.

Thursday, 3 September 2015

Record for duration of data time series

We are now in September, this means deep winter in Antarctica is over and more and more sunshine is coming back. There is already more than 10 hours sunlight per day at Utsteinen. And the instruments are still operational, without any break since the last team left Utsteinen in February !! This means a new record. The longest period for continuous aerosol data until now has been from November 2013 until the morning hours of 1 September 2014. This is great news and many thanks have to go to the team members who prepared the station’s energy system for the uninhabited period (and who are supervising it remotely from Belgium). But it also means that our own precautionary measures for unattended instrument operation are paying out. Now let’s hope that it keeps going until another BELARE expedition team arrives at Princess Elisabeth station.
Particle number per cm3 at Utsteinen from November 2014 to August 2015
The figure shows the time series of the particle number concentration from November 2014 until end of August 2015. The data are cleared of any contamination. It can be seen that from November to March the mean concentration was around some hundreds of particles per cm3, with a peak around end of February/beginning of March. The mean number concentration decreased afterwards to reach a minimum in June, July. In August, number concentrations started to increase again. During June and July, the number concentration fell to some tens of particles per cm3. During austral winter, the Antarctic vortex, the atmospheric circulation, forms a quasi-barrier for air masses from lower latitudes. Also during winter, there is hardly any sunlight for driving photooxidative aerosol chemistry and there is a general lack of precursor gases for new particle formation and condensational growth of particles. However, over the whole time period, there were several events, when the number concentration increased distinctly over very short periods of time, often to some thousand particles per cm3. Most probably, these periods reflect the influence of air masses transported to Princess Elisabeth station via synoptic scale events (cyclones, transporting air masses from easterly directions, including maritime origin), indicate entrainment of air masses from the higher troposphere, or indicate periods when new particle formation could be detected at PE.