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 (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.
