Friday, 31 May 2013

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 36th Antarctic Treaty Consultative Meeting in Brussels ( 

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 ( 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.