Data, winter, current work

It is now three months into this Antarctic winter, time to write a bit about what is going on within our Belatmos project. We had a look into the data of the Brewer spectrophotometer and the image  shows the time series of total ozone and of the calculated UV index for the summer season 2012/13 at Utsteinen. Total ozone data can be calculated both from direct sun (cloud-free conditions; direct sun rays) and zenith sky (also cloudy atmosphere, diffuse sunlight) observations. There is a systematic high bias for the zenith sky values over the direct sun values. The direct sun values should be taken as the more accurate ones. When looking at the absolute total ozone values, there was no particularly low value this season compared to the season before. This was because the weaker than in former years Antarctic ozone hole recovered relatively fast this season and no remainder of the Antarctic ozone hole moved above Utsteinen. In November and during the first half of December 2012, total ozone values (direct sun) were rather high with values above 320 Dobson Units. Afterwards, total ozone fluctuated around 270 to 310 DU. Overall, the calculated UV index therefore indicated moderate-high to high levels of potentially hazardous UV-B radiation. Matching the time of highest sun elevation, the UV index peaked around christmas. 

With another season behind, the statistics for the aerosol optical depth from the Cimel sunphotometer can be updated. The aerosol optical depth (AOD) is a proxy for the total amount of aerosol in the atmosphere. The figure shows in blue the average AOD values (with standard deviation) from the sunphotometer for all summer seasons since February 2009. Most obvious are the very low AOD values below 0.03. This means that the atmosphere is almost pristine. Values for Europe are at least one magnitude of order higher. Next pattern to be seen is the slight increase from the visible to the ultra-violet region. This gives an indication that sub-micron particles dominate, as smaller particles scatter light of shorter wavelengths more effectively. One can also calculate the Angstrom-exponent from the exponential regression of the AOD values between 440 and 870 nm. The higher it is, the smaller the aerosol particles. From our data so far, the average Angstrom exponent was 2.0 +/- 0.6, indicating a dominance of sub-micron particles. Why exactly the AOD value for 1020 nm is higher than the visible ones has to be checked, but one reason could be that in particular the 1020 nm channel is sensitive to cold temperatures and a correction might be necessary. In addition to the sunphotometer data, the figure shows in green the AOD derived from the UV-B measurements of a Brewer spectrohotometer (340 nm, same wavelength as sunphotometer). AOD values derived from the Brewer have in general a higher uncertainty than the sunphotometer ones, and thus have a higher detection limit. However, also the Brewer gives very low values for the total aerosol amount. 

Another nice example of the special Antarctic atmosphere is the total number concentration of particles. In winter, the concentration is often around 100 particles per cubic centimeter. It was particularly low beginning of April, as can be seen in the respective graph – around 15 particles (from 3 nm diameter and larger) per cm³. This translates to around 700 particles in absolute number, measured in one minute. These are almost clean room conditions ;-). And a nice example of the capability of the respective instrument, the condensation particle counter. These conditions lasted a few hours and the concentration increased afterwards to around 100. But there were already some more periods with such a low particle concentration. The highest concentrations since November were around 4000-5000 particles per cm³. 

However, luck stayed not with us. On 8 April winds were exceptionally strong with very high and massive blowing snow – at clear sky – and the LAS, the aethalometer and the nephelometer stopped communications with us. It is not clear what exactly happened, if there was too much snow intrusion via the tubings or into the shelter or a technical problem with the serial connectors. However, the condensation particle counter and the TEOM-FDMS continued their measurements without interruption. On 11 April there were again such conditions and the image above gives a good indication of the very strong blowing snow. And, more unfortunate, since 17 May, the whole station does not communicate anymore with us and it seems that the station lost power. This is a very pity because at the very same time there was the 36^th Antarctic Treaty Consultative Meeting in Brussels (atcm36.antarctica.belgium.be/). 

The Belgian branch of the Association of Polar Early Career Scientists organised on 25/26 May a science fair on the occasion of the ATCM for the broader public (https://sites.google.com/site/sciencefairenglish/home). There were many informations on Arctic and Antarctic research and on the particularities of the polar environment and what it makes so special. We contributed with a little game on ozone and UV. On the same weekend, my institute, the Royal Meteorological Institute of Belgium had together with our neighbour institutes (Space Aeronomy and Royal Observatory) Open Door Days. And we celebrated also 100 years of our institute. On this occasion I set up some general information on our research in Antarctica. In addition I set up the aethalometer to demonstrate its usefulness to measure the small, polluting particles from combustion and why we care about these special particles. Next on my agenda is to analyse the Antarctic data in order to present parts of it beginning of July in Davos, Switzerland, at the Davos Atmosphere and Cryosphere Assembly.

Winter season 2013 has started

After the last team left Princess Elisabeth station (visit the station blog  antarcticstation.org), the station and also its scientific instrumentation is now completely in automatic and remote control mode. Until now, all instruments have continuously been working and are doing this also right now. The sunphotometer and the Brewer spectrophotometer however, have been dismounted end of February by Erik. The sunphotometer travels back to Europe for the yearly calibration and the Brewer is stored inside the station. In principle, it could be operated continuously, but as its optical part is very sensitive it would be too risky to leave it running. If anything happened to the instrument’s mechanics or optics, there would be nobody to repair it. This will possibly damage the whole instrument and repair or replacement would be an immense cost. All the six other instruments will continue to record and send data, as long as there is no power break down or failure of an instrument part. In the southern scientific shelter, the five aerosol instruments (TEOM-FDMS aethalometer, nephelometer, laser aerosol spectrometer, condensation particle counter) are now in their forth month of simultaneous operation. The condensation particle counter has got his larger reservoir for n-butanol supply during the long winter period, and the nephelometer has been calibrated a last time before the end of the season. Such a calibration is done with a pure reference gas, in our case extremely pure carbon dioxide. The amazing thing of remote control is that I could do some nephelometer calibration from my desk in Brussels. This needed of course some cooperation with Erik at the station who opened the gas bottles and some valves, but the exact calibration I controlled via remote desktop connection to the controlling desktop in the shelter which in turn is connected via a serial port to the nephelometer control port. As it is too risky to leave an open gas bottle nine months unattended, a full calibration will not be possible anymore. But a so-called zero-check (with ‘zero’, filtered air via an internal filter) of the calibration regression can always be done remotely. In the next entry to this blog I will show some exemplary graphs of the aerosol data. The images above show the instruments at the end of the season: the Brewer spectrophotometer and the elevated box with sensors for total solar and UV-A, UV-B irradition on the northern station roof; the Cimel sunphotometer; and the five aerosol instruments in southern shelter (order from left to right like mentioned above).

Preparations before Departure

During the last week of my stay at Utsteinen consisted mainly in checks that all instruments can operate continuously and via remote control. E.g. the condensation particle counter uses n-butanol in its measurement chambers in order to grow the particles to sizes which then can be easier optically detected. The instrument has a reservoir of 1 liter. For atmospheric conditions like suburban regions, this amount is sufficient for 1-4 weeks. In the Antarctic clean air, it will be sufficient for several months. However, surely not for almost 9 months of operation without somebody on spot who could do a re-fill. Therefore, we connected two reservoir bottles in-line, and now the instrument’s supply with n-butanol will be assured also during winter operation.

Winter operation is still two months ahead, but my stay in Antarctica ended already yesterday. Until the end of the season Erik will take care on spot of our instruments and via email and via remote control I will also stay in contact. On Friday in total 14 persons left Utsteinen (and 4 arrived new). The flight was planned for early morning, but it started to snow in the morning. On contrary to the days before, wind decreased to almost zero and low clouds moved in, reducing strongly visibility. This snowfall event delayed our departure, but it was also nice because it was again nice to see that there were specific signals around the event in the aerosol data. The snowfall was also not forecasted by the models and apparently locally influenced. However, it stopped relatively fast, sun came back and the Basler aircraft landed safely at 2pm. After unloading (i.a. fresh food) and loading and around one and a half hour of flight we arrived at 4:30pm (Belgian time zone) at Novo Air Base. The big Ilyushin carrier was planned to take off to Cape Town around local midnight. The time until then everybody used to take a nap, have a meal in the mess container or to chat with scientists from other stations, waiting also for their departure. We met again the team of German scientists who did, based at Princess Elisabeth station, many flights with the AWI Polar-6 for geophysical research. After six hours of flight we arrived this morning in Cape Town, where we now have time until Sunday evening when our flight back to Europe is scheduled. I am happy to be back, see again my family and kids.  

SNOW

Again, no report on sunny summertime, but white or grey snowy summertime. Saturday afternoon until late into the evening there was a nice snowfall event at Utsteinen. Maybe you find it bit strange that I write about snowfall when in Europe you are having also snow and even more than here. However, it’s not often that we have real snow falling here in the interior of Antarctica, and then snow is not falling in large amounts. Antarctica is a cold continent, and cold air cannot hold a lot of water vapour and therefore also the potential amount of water falling down in forms of crystals is limited. We had around 3 to 5 cm snow yesterday – what is already a lot. The whole day we had complete cloud coverage and first strong wind. In the afternoon, wind decreased to almost zero and around 5pm it started to snow. The first crystals were rather small and had the form of needles or small prisms. Two hours later, snowfall increased (also temperature had decreased a bit) and ice crystals had grown and were rather in the form of dendrites now. Our ridge where station and instrument container are placed turned slowly into white. It was interesting to follow this event with images and with the data of our instruments. I could also see in the data of the instruments measuring atmospheric particles (not snow) that some particle characteristics were different to the period before this snowfall event. For example, the size distribution and total number of aerosols changed. Today, Sunday, there is no snowfall anymore, but very strong wind and now there is drifting, wind-blown snow, and most of the fallen snow is blown and is thus re-located.