First BELATMOS winter aerosol measurements

As mentioned in the blogpost before, the TEOM-FDMS and the aethalometer collected data during last winter, at least from end of February to mid of April. This is something very interesting because the two instruments collected data when there was really no emission of aerosols for energy generation (only wind power and batteries) or from station operation. This makes them valuable data with information on real background concentrations. In addition, these data are special because they were sampled without any direct maintenance/attendance of personnel. Measurements in Antarctica with these kinds of instruments are done normally at stations with overwintering personnel. The data I am reporting here are nevertheless preliminary and several quality assurance steps have to be applied. This is in particular important because the TEOM-FDMS and the aethalometer are measuring near their detection limits.

The average of the total aerosol mass concentration measured by the TEOM-FDMS was 0.85 microgram per cubic meter with a standard deviation of 1.03. For the moment slight negative values are still accepted because of the general low aerosol concentration and because of the detection limit of the TEOM-FDMS, which is around 1-2 microgram per cubic meter. I have to make additional checks to justify if negative values are skipped or not. For the winter 2011, 12% of the data are negative, but almost all just between 0 and –1.0 microgram per cubic meter. That the standard deviation is higher than the average means that the average total aerosol mass concentration was not – from a statistical point of view – different from zero, neither definitely positive of negative. To be able to determine this further, a longer time series will be necessary. Another possibility is that the integration time for determining a TEOM-FDMS sample would have to be longer (meaning more mass sampled on the filter before the data value is taken). However, I set the integration time already to 2 hours.

Another possibility is to cross check the TEOM-FDMS data with data from the other aerosol instruments. However, the aethalometer measures the strong absorbing particles, amounting only to a small part of the total aerosol mass. The arrival of the new instruments this season will provide more insight. In particular the Laser Aerosol Spectrometer measuring the size distribution could prove valuable to check the aerosol mass concentration measurements. By integrating over the number concentrations of all measured size classes, and assuming a certain mass density of the particles and a certain shape, it can be cross-checked if either data is reasonable. The winter aethalometer data shows an average of 5.2 nanogram per cubic meter with a standard deviation of 5.4. This means that we are really measuring near the detection limit and a longer time series is necessary to be able to make statistically sound statements how much absorbing particles (or black carbon) there are in Antarctica. However, concentrations between 0 and 10 nanogram per cubic meter would be the expected level.

The images above show the state of the shelter for the aerosol instruments after the winter (no power, heating for 7 months), after cleaning and letting it dry, and an image of the interior of the aethalometer. It shows the filter tape on which the samples are collected. On the right one can see some darker spots. These are the old samples, and the tape is drawn further when a certain absorbance is reached. The snow and ice inside the shelter freightened us a bit if there was damage to the instruments. But it appeared that this was not the case, luckily.

The departure for this season's expedition comes nearer. I will fly this Friday from Brussels via London to Cape Town, South Africa, and the flight from Cape Town to Antarctica is scheduled for Monday evening. So, the next news will come from Antarctica (or from Cape Town, if the weather conditions delay the flight to Antarctica).

The BELATMOS measurements have restarted

Since mid-November Princess Elisabeth Antarctica is again operational. On the special website of the station (www.antarcticstation.org) you can follow the story. Erik, the engineer also responsible for taking care of the scientific equipment, restarted our instruments already. The TEOM-FDMS, the aethalometer, and the Brewer ozone spectrophotometer are operational again. The TEOM-FDMS and the aethalometer collected data also during winter, at least as long as electricity was there. This is something very interesting because the two instruments collected data when there was no station activity and when there was really no emission of aerosols for energy generation (only wind power and batteries). Data of this kind is rarely sampled in Antarctica. In one of my next posts I will tell a bit more about these data. The forth instrument, the Cimel sunphotometer, will arrive these days at the station and if weather allows, it will also be installed soon after.

The ozone spectrophotometer did already its first measurements, from 13 December onwards. On 14 and 15 December, the values for total atmospheric column ozone were really low, between 220 and 240 Dobson Units, before climbing the next days higher (see bottom image). On the image in the middle it can be seen that it fitted to the overall pattern of total ozone in the Southern Hemisphere. That image is a composite of measured total ozone values from observation stations worldwide (World Ozone and UV Data Centre), to which also our instrument contributes. The area of lowest total ozone was located on 14 December over East Antarctica and Dronning Maud Land. The black spot depicts the approximate location of Princess Elisabeth station. The upper image shows the UV index for that day. It is very high to extreme around local noon. These high UV values can be explained by the low total ozone values, the elevation of the station (1400 m) and the almost aerosol free atmosphere. They are also particular because the elevation of the sun (elevation above horizon) is not that high, although it is austral summer and near to summer solstice – on 14 December the elevation angle reached only 41deg. This is low compared to late spring, summer in our northern midlatitudes. And then the UV index in our region only rarely reaches values of 8/9. It means that the sun poses really a danger in Antarctica. Although the ozone hole period is over now in Antarctica, there are still large areas with low total ozone values, as can be seen in the middle image.

Merry Christmas and till soon

Next austral summer season about to begin

The next Belgian Antarctic expedition is about to begin. The first team will leave Cape Town mid November 2011. This season, I will be again part of the expedition team, however, this time towards the end of the season, from end of January to 21 February 2012. Nevertheless, there are many things to prepare right now.
Unfortunately, the power supply system of the station broke down beginning of Antarctic winter. This means that the first team arriving at the station will have to take care of a lot of extra things, and also to take care of the two Belatmos aerosol instruments – the aethalometer and the TEOM-FDMS – which are installed in the southern scientific shelter. It will have to be checked if they are in order and not damaged after the power failure and the long winter-over, and before a re-start they have to be warmed up slowly.
Engineers of the team will also take care to re-install the AERONET Sun photometer and the Brewer ozone spectrophotometer on the station roof. As they need sun for their measurements, they cannot measure during the dark winter months and only with arrival of the first expedition team, they can be re-installed. In addition, the Sun photometer has to be calibrated in Europe annually and travels therefore each season back and forth.

When I will be at the station, I will bring with me 4 new instruments, measuring UV-A, UV-B and total solar irradiation, aerosol total number concentration, particle number concentration in several size classes, and spectral scattering of the aerosol particles. I will give here a brief description of these instruments:
The Ultrafine Condensation Particle Counter (U-CPC) measures the ambient aerosol number concentration from 3nm to 3 micrometers diameter. It will be installed in the same container as the aethalometer and the TEOM-FDMS.
The Laser Aerosol Spectrometer (LAS) measures the aerosol size distribution in the diameter size range from 90nm to 7.5 micrometers (size classes can be adjusted). It will be installed in the container with the other aerosol instruments. A year-round operation is envisaged. The difference of the number concentration of the U-CPC and the integrated number size distribution of the LAS (90nm to 3 micrometer) will give an estimate of the nucleation and Aitken mode aerosol concentration (particles smaller than 90nm).
The 3-wavelengths nephelometer will measure the total scatter and the backscatter at 450, 525 and 635 nm. As the nephelometer will be installed in the same container like the aethalometer, they will probe the same air mass and therefore, a direct measure of the single scattering albedo will exist (ssa = scatter / (scatter + absorbtion) ). The single scattering albedo is an important parameter used in radiative transfer algorithms in satellite retrieval algorithms or in climate models
The irradiation sensors will be an UV-A radiometer (315-400nm), an UV-B radiometer (280-315nm) and a pyranometer for total solar irradiation (305-2800nm). The sensors will be installed on the roof of the station and year-round operation is envisaged.
In summary this means a lot of work, but all the instruments together will provide very nice data sets describing comprehensively the aerosol composition, UV radiation and total ozone at Princess Elisabeth station.

Something NEW: The COMMENT function of this blog should now work much better than before !

Nobody there, but

In the meantime, the BELARE 2010-2011 campaign has come to an end. The last team left on 24 February Utsteinen. They prepared the station for the winter conditions. Two of my instruments, the aethalometer and the TEOM-FDMS were left in operation mode in the southern scientific shelter. This is kind of an exciting test. First, there is no communication connection to this shelter yet, so we do not know really what is happening in there and if the two instruments are working. Second, aerosol measurements like this in Antarctica are usually done at locations where year-round maintenance is possible. Third, everybody is hoping that the power will be available the whole winter through. Taking all this into account, it will be a unique dataset if everything works out well and if we can retrieve the winter data beginning of next summer season.

A very good estimation if everything is ok is the knowledge about the power management system and if other instruments at the station, which are already connected to the Internet, are still working. If there is enough power available at the station, there is also power at the southern shelter as it is on the same power priority level. And as the aethalometer and TEOM-FDMS are robust standard monitoring instruments, there is no need for an increased concern. Until today there has not been a problem yet with the power provision at the station. However, as wind has been low at many days, apparently the diesel generators took over during periods of low winds.

At our institute, Andy has written a small programme that creates a so-called Ensemble Prediction System (EPS) forecast for Utsteinen (better: the nearest model grid point). Such an EPS takes meteorological analysis data from the European Centre for Medium-Range Weather Forecast and makes 10-days forecasts (see image above). The specialty of the EPS forecast is, to run the same model 50 times, but each with slightly different initial conditions, representing model uncertainties. The result is a probability distribution for the meteorological forecast values, giving medians, percentiles and extreme values. A narrow distribution for a parameter shows very good confidence in the value, and a broad distribution illustrates higher uncertainty.

We compared these EPS forecasts to measured values from the automatic weather station and it appeared that the tendencies for wind speed and temperature are very good. Wind speed is most often a bit overestimated and temperature mostly too cold – probably due to the unique setting of the station protected by the Sor Rondane Mountains, which cannot be resolved by the model. Although clouds and precipitation are very difficult to simulate, the EPS forecasts are useful the first few days for cloud coverage. Precipitation is most often largely overestimated. When I was at the station, during most predicted snowfall events, precipitation was detected by the instruments of the HYDRANT project able to measure cloud height and falling crystals or droplets. However, this precipitation mostly never reached the ground or it was much less than predicted. This is a phenomenon we want to investigate further, e.g., with additional monitoring instruments or with profile information on temperature, humidity and wind.

The last days

Now my stay at the Princess Elisabeth station is almost over. Tomorrow, Tuesday, we will fly around noon with the ‘Lydia’, (the plane we also came here) to the Russian air base Novolazarevskaya near the coast. There we only have a few hours before the large Ilyushin 76 will fly us to Cape Town in South Africa. About 12 of our team will leave Utsteinen and in Novo we will join other Antarctic expedition members from Germany, Norway, Sweden, Japan to fly together back to Cape Town.

Last Thursday and Friday we had a storm here – not of the worrying type, however, the wind speed was 15 – 17 m/s at the weather station 300m to the East. So, on our ridge, the wind speed was probably higher by about 4-5 m/s. There was a lot of drifting or blowing snow, from times to times accompanied by real snowfall and the visibility was really bad – the Utsteinen nunatak was for a long time not visible anymore. Now that the summer season reaches slowly the end, also the sun sets deeper and deeper behind the mountain ranges in the south. At some days this leads to nice views around midnight. This mountain range also influences strongly the upper air flow and sometimes we can watch the formation of large, impressive, cylindric clouds.

The ozone spectrophotometer which is installed now on the roof of the station is doing nice measurements. Besides the total column amount of ozone in the atmosphere, we can now also derive the UV index for Utsteinen, i.e., a measure of the probability of ultraviolet radiation induced erythema of different human skin types. On 23 to 26 January, on rather sunny days, the UV index reached up to 6, indicating a moderate intensity at which the skin burns easily. On the days of the storm, with a complete overcast sky, the UV index reached nevertheless 5. This only slightly lower index is caused by the very low and thin clouds, through which the shortwave radiation can easily penetrate.

Up there in the air

The days of last week passed by with a very cloudy sky and with strong winds. The strong winds and dynamics in the upper troposphere can nicely be observed in the cloud formations. Over the nearby Sor Rondane mountains, there are now most of the time quasi-stationary mountain wave clouds. It is interesting to watch that other cloud layers move with the general wind directions, but these mountain wave clouds stay more or less always at the same place, i.e., that the advected air masses are lifted up at this region, cool down, form clouds, and then they are, like in a wave, transported downwards where they warm and do not form a cloud anymore. However, this region in the lee of the mountains where it is cool enough for cloud formation, stays more or less stationary, and the air masses are transported through it. So the cloud forms steadily new, but it seems as if it is not changing. A very similar cloud type are the lenticularis clouds, which form in a similar way and which we can observe here now every day. The image above gives a nice example of such clouds. In addition, the sun is now longer times hidden behind the mountains during midnight hours and the horizon then shows violet to red glow. Saturday night when there were less clouds, the moon could be seen.

The Brewer ozone spectrophotometer is now finally installed and fixed to the roof. The first good measurements were possible this Sunday, as we had finally a sunny day and the instruments makes best measurements when there are no clouds before the sun.

Since a few days the Princess Elisabeth station has been the base for some scientific flights with the Polar-5 in order to investigate the magnetic field of the Earth. Detleff from the German Bundesanstalt fuer Geowissenschaften und Rohstoffe and Daniel from the German Alfred Wegener Institut (AWI) and the pilot crew of the Polar-5 have been flying with this aircraft of AWI over the mountains and adjacent glaciers of the Sor Rondane mountains. With the maps of the magnetic field of the Earth made with the instruments installed in the Polar-5, they can derive informations on the tectonics of the Earth’s crust mantle and on the directions of cracks in the tectonic plates. The Polar-5 is a transformed DC3, adapted to the conditions in polar regions.

Finding the right orientation for the ozone spectrophotometer

During the last week, we installed the Brewer ozone spectrophotometer on the roof of the station. As already explained in the last post, this instrument will serve to monitor very precisely the amount of total ozone in the atmosphere. It will not only help to monitor the evolution of the ozone layer, but it will also be valuable to validate satellite measurements of the ozone amount. The retrieval above highly reflective areas like the Antarctic is not always easy and therefore ground-based measurements are important.

In order to do its measurements, the ozone spectrophotometer turns with its optics always towards the sun. This is not that simple as it sounds. One essential parameter is the azimuth angle. This angle is defined as the angle between the North and clockwise going to the position of the sun. In the northern hemisphere this angle starts at 0 degree in the North and goes over 90 degree East, 180 degree South, 270 degree West back to 360/0 degree North. On the contrary, in the southern hemisphere the azimuth starts (as the definition stays the same, but the sun moves from East over North to West) with 180 degree in the South, goes back to 90 in the East, to 0/360 in the North, over 270 degree in the West back to 180 in the South. As the suntracker of the Brewer with its motor system is able to do one clockwise rotation of 360 degrees and then turning back to its starting position, the tricky thing with orienting the Brewer in the Antarctic arises with the transition point around local noon when the azimuth makes a jump from 0 to 360.

After some tests in order to find the correct positioning I found two possible solutions with the great help from Hugo in Brussels and Arjan in Delft. One possibility is to orient the tracker as in the northern hemisphere with its zero point to the North. At local noon, at the switch from 0 to 360 degree, the tracker makes a full 360 degree rotation. This setup has the disadvantage that there is some time lost due to the tracker’s rotation. And this just around the short precious time when one can get the best measurements in a place like Antarctica with its (mostly) low sun elevations. The other possibility is, to orient the tracker with its zero point to the South. However, as the software calculates the correct azimuths (starting at 180, not at 0), and the tracker counts its degrees clockwise, one has to set an internal offset of +180 degree. For the azimuths when +180 and the azimuth results in more than 360 degree (and, as the tracker’s rotation is limited to 360 degree), the tracker internally knows that it cannot move clockwise more than 360. So, it subtracts automatically 360 degrees. In this setup, it does not need to make a full rotation around local noon. This full rotation is then done around local midnight, when the sun is anyway too low for measurements.

Besides the instrument installation, there are many opportunities to make some nice photos of the clouds and the landscape here. Above, I put some new ones.