Part of the Radiation Budget, pulled from the IPCC Fourth Assessment Report. Source: Kiehl and Trenberth (1997).

Aerosols have different properties depending on what they are made of. Some of those properties that are important are roughness, color, and size. These properties affect what happens to solar radiation as it reacts with the particle such as whether it will scatter or absorb. For example, a particle of black carbon (left over after burning of a fossil fuel let’s say) is going to be much more effective at absorbing solar radiation than a piece of salt that has a much lighter color as well as a shinier surface (shiner, brighter surfaces reflect radiation better). It is also important how they are distributed spatially around the globe and how long they stay in the atmosphere. To think more about the spatial distribution, at the South Pole, we have no vegetation, dirt, salt water, or large sources of combustion anywhere close to us (aside from our own station which is downwind from where we sample). We have extremely low concentrations of aerosols in the air here compared to a sand desert or near a volcanic eruption. The time that they spend in the atmosphere can depend on many things. If it is a large particle, it may settle back to the surface quicker. If it rains, the aerosol may get collected by the raindrops and land back on the surface. Depending on the hygroscopic (the ability for a surface to become wetted or have water stick to it) properties of the aerosol, water can also condense on them to make cloud droplets.

Speaking of cloud droplets, aerosols can indirectly affect solar radiation by being an ingredient for clouds to form. Water likes particular sizes and types of aerosols to condense upon. The name this particular type are Cloud Condensation Nuclei. If there are no Cloud Condensation Nuclei present, the water has nothing to condense onto and there will be no cloud. The size and type of aerosol affect the physical properties of the cloud as well. Therefore a change of aerosols in a region can change the type of cloud, thus changing its radiative properties. This dependency on Condensation Nuclei brings up yet another complicated variable that can affect the radiation budget.

So that explains a little bit why we are so interested about the “dust” in the air. Aerosols have a significant influence on climate processes. Now let’s take a look at the instruments that deal with aerosols at the South Pole.

The Condensation Nucleus Counter (CNC) does basically what its name says. It uses butyl alcohol to create a cloud by cooling the flow of the air through the instrument. Inside is a particle counter that counts how many droplets there are.

The Nephelometer measures the radiation scattering ability of the aerosols. By running air through the instrument and shining a light through the air, we can detect how much of that light is getting scattered with a photomultiplier tube (PMT). There are filters in front of the PMT in order to detect several specific wavelengths of light. If we know the output of light initially, and subtract what is detected, then we know how much light is scattered by the aerosols.

The Aethalometer is an instrument that we use to measure radiation absorbing aerosols. For this instrument, air is passed through a filter where the aerosols will deposit onto. The filter is illuminated by a lamp and there are two photocells that sense the light. One is a reference sensor on a spot of the filter with no aerosols, and the other is sensing where the aerosols where deposited. The difference between these 2 sensors is the amount of light absorbed.

Here I am using the Pollack which is an older instrument that is used to compare to the CNC. It creates a cloud by depressurizing a chamber which causes the air to cool and form a cloud. There is a PMT that detects light and I watch an ammeter to see how much the current goes down when the cloud forms.

Not pictured is the Water-Based Condensation Particle Counter which is very similar to the Condensation Nuclei Counter that is shown above. The laser inside broke during the summer and we were not able to send it to the lab, get it fixed, and get it back to the Pole before station closing.

So that is how we measure aerosol concentrations and their scattering/absorbing properties at the South Pole. The next process that we measure at the South Pole will be the Carbon Cycle and Greenhouse Gas (CCGG) group. We’ll take a look at the CO2 analyzer and the role that greenhouse gases play in the climate.

While we have a weather station that records variables including temperature, wind speed, wind direction, visibility, and the height of the ceiling, we often have back-ups and different methodologies for crosschecking the output of the weather station. The video in this post summarizes one such check.

Often measuring the height of the ceiling, or clouds, can be difficult and the instrumentation can record improper information if snow is blowing or if there are high winds. Since the height of the ceiling is vital information for pilots, we often check our weather station readings against that of a weather balloon. Enjoy this video of me launching one of these balloons that we used to measure the height of the ceiling! I am now an honorary weatherwoman at WAIS Divide.

Getting on the LC-130.

In addition to carrying people back and forth these planes also carry equipment, food and fuel for the South Pole Station (and waste the other way). Over 200 LC-130 flights are made to the pole each year, and a plane will typically have approximately 2,000 pounds of fuel syphoned off from it after it lands – this is what the South Pole generators run on, and they need several hundred thousand pounds of fuel to make it through the winter.

A 15,000 lb IceCube surface-to-DOM cable aboard our LC-130.

Flying with me was a 15,000 lb IceCube Surface-to-DOM cable. We need one of these for each of our deployments/strings (we are hoping to do at least 14 deployments this season). IceCube is a pretty massive project, and requires many cargo flights of fuel and equipment in order to succeed.

During the flight to the pole over the Transantarctic Mountains, I saw some really neat cloud formations. They are called “altocumulus standing lenticular clouds.” I was told that they are fairly common in mountainous areas. I thought they were pretty spectacular!

Altocumulus standing lenticular clouds over the Transantarctic Mountains.

Altocumulus standing lenticular clouds often form on the lee side of mountain ranges as moisture condenses at the crest of a standing wave in air currents.