Polarbear family visit, flying operations from Oden and hit by a second storm - Part 2

Continuing the post "Polarbear family visit, flying operations from Oden and hit by a second storm - Part 1"

 

Helikite and Helipod - flying operations

 

Helikite & Aerosols

So we had a few calm days before the storm, which allowed for a few flying operations. On Tuesday (23 May), Oden was stationary so that the Helikite could be operated for 6 hours until dinner. The Helikite is a 45-cubic-meter large helium-filled tethered-balloon with a (red) kite below. An electric winch and 800 m of dyneema rope are used to deploy the Helikite in the air and bring it back to ground (see left photo below). The Helikite is operated on top of a container on the aft deck (back of the ship; see right photo below) and used for vertical profiling of the lower atmosphere (to a maximum of 800 m above ground level if no wind). Underneath the Helikite a payload is attached (white box on the photo below) where different instruments are installed, measuring various aerosol properties (e.g., particle size distribution, particle number concentration, optical properties and ability for ice nucleation), but also cloud droplet size distribution, carbon dioxide and meteorological parameters (e.g., wind, temperature, humidity). Roman Pohorsky (from Ecole Polytechnique Fédérale de Lausanne; EPFL; attaching an instrument on the winch in the photo below) is part of the work package VAERTICAL where the vertical profile of the Arctic lower atmosphere - with focus on aersosol distribution and aerosol-cloud interaction - is measured with the Helikite system. Jessie Creamean from the Colorado State University is the work package leader (more about her sampling on the ice in a later post ;) ). But why do we care about aerosols in the lower atmosphere?

 

Departure of the helikite (May 23)

Oden from the ice. Taken during the last ice camp ( May 17)

 

Aerosols are small particles, solid or liquid, suspended in the air. They have different sizes, composition and number concentration in the air, which all impose different aerosol climate effects. Aerosols like sea salt affect the solar radiation by scattering it back to space, but darker aerosols such as black carbon or soot in the air can also absorb energy. Furthermore, aerosols act as nuclei for water vapor to condense onto so that water droplets (formed by cloud condensation nuclei or "CCN") or ice crystals (formed by ice nucleating particles or "INPs") can form to build clouds. The number of aerosols (number concentration) and the size of the aerosols play a role in how many of the aerosols end up as CCN or INPs and further how the clouds then affect the radiation (scattering solar radiation back to space or trapping more thermal radiation back to the surface). In the Arctic, the air is quite clean and pristine, with often very low aerosol concentrations. For example, if we would go out with a cup of boiling tea, we might not see any steam coming out of the cup - this steam is water vapor that has condensed onto aerosols that is visible by eye, similar to how clouds form. Without enough aerosols, water vapor has nothing to condense onto. But, if we manually add air particles into the air above the tea cup - for example using a lighter - suddenly we have steam! This nicely illustrated how clean the air in the Arctic usually is.

 

But we still have clouds in the Arctic, which means that we do have aerosols - but where are they coming from? Sources of aerosols at different vertical levels in the lower atmosphere is one of the main objects for the Helikite flights. Aerosols, especially biological particles like microbes, can get into the air locally from cracks in the sea ice or melt ponds. These aerosols can get released into the atmosphere through waves and bubbles breaking at the water surface (this source to INPs in clouds interests Jessie Creamean and her colleagues; please read the future postings to know more). Sea spray (e.g., salt particles, organics generated from microbes and other biological materials) can be transported over the sea ice from open water sources, but also dust and other pollution aerosols can be transported long distances to over the sea ice from land regions - especially with wind directions coming from e.g., Greenland, Siberia or Scandinavia. Atmospheric rivers (intense bands of warm and moist air transported over the sea ice from the south) can also bring air into the Arctic that contribute to the long-range transport of aerosols - this is what is of high interest to Roman.

 

The lack of observations in the Arctic is one of the key issues why weather and climate models today struggle with representing properly the Arctic climate - we cannot understand something before it has been observed! The vertical distribution of aerosols is one of the things that is not well known and models tend to struggle to represent it. Thus, it is really important to gather more observations of the aerosol vertical distribution and study their sources in order to better understand their origin and their contribution to clouds and their impact on cloud radiative effects. Roman points out that this Helikite is one of the first tethered balloons that can measure aerosols of varying sizes: from 8 nanometers to 3 micrometers, which is important to study as the size of the aerosols matters if an aerosol can act as a CCN/INP or not. Roman further explains that the best conditions for vertical profiling is when we have low-level clouds with cloud base (and preferably also cloud top) within the length of the winch (800m), so that the aerosol vertical profile can be measured below, within and above a cloud. Fortunately, low-level clouds are quite common in the Arctic and during this expedition, Roman has already succeeded to get measurements from such conditions. Roman tells that the weather conditions on Tuesday were ideal for operating the Helikite - 6h Helikite flight in the afternoon! Best weather conditions for Helikite operations are wind speeds below 10 m/s and preferably no precipitation, and with the ship facing the wind so that the Helikite can fly tethered to the winch away from the ship.

 

Helipod

Operating the Helikite enables for a long and efficient profiling of the lower atmosphere, as the balloon is tethered onto Oden and can be easily lifted or lowered to different vertical levels using the winch and the rope - and can "fly" in the lower atmosphere partly unattended. Apart from the Helikite, the vertical and horisontal mapping of different parameters, such as aerosols, meteorological parameters, radiation, trace gases and surface properties, can also be done using the sensors built in the Helipod. In comparison to the Helikite, the Helipod is a large and heavy system that weight more than 300 kg (with scientific payload of about 115 kg in the current configuration) and is 5m long (see right photo below). In order to get this heavy equipment up in the air, a helicopter (and a pilot) is required (see photo below). The Helipod is placed on the helideck from where the helicopter will pick it up and return through a 18m long rope. The long distance between the helicopter and the Helipod enables to obtain measurements in an environment that is not disturbed by the helicopter. Falk Pätzold (Technische Universität Braunschweig; standing on the helideck after a flight on Wednesday (24 May) afternoon in the photo below) is the work-package leader for the Helipod and is responsible for the Helipod operations together with his colleague Magnus Ole Asmussen and other colleagues. Falk is usually joining with the pilot in the helicopter during the Helipod flights to adapt the flight pattern based on the meteorological conditions and real-time data from the Helipod.

The Helipod is picked up by the helikopter (May 16)

Helipod on the helideck after one operation right before the storm (May 24)

There are some requirements for Helipod operations, which are mostly the same as for the helicopter: no icing conditions and the visibility needs to be good, thus not possible to operate in case of precipitation, low visibility and low clouds. The flight on Wednesday got quite short and they had to abort after only 40 min (usually aiming for a 2h30min flight) due to the approaching storm that lowered the visibility in the late afternoon. The idea of the Helipod flight tracks is to do transects both vertically and then horisontally over sea ice (not open ocean, due to limitations of the helicopter operations), so that the sonde (Helipod) is below clouds. The flight trajectory of Wednesday's flight is shown in the bottom diagram (courtesy to Falk), where the Helipod by the help of the helicopter flew up to 700 m (usually 1km) and was within a 20 nautical miles radius around Oden (another helicopter operation limitation). The colouring (in concentration cathegories) shows aerosol particle concentration (one of the aerosol parameters measured with the Helipod). If there is more time, the flight patterns are more in a curtain manner to obtain a better picture of the spatial variability of the different parameters measured with the Helipod at different heights in the lower atmosphere.Usually, the helicopter flies with a speed of about 40 m/s, but the speed can vary between 20 and 55 m/s to adapt the spatial resolution to the measurement task.

CPC measured along the Helipod flight on Wed 24 May. Courtesy to Falk Pätzold.

On the move!

With wind speeds close to 30 m/s no flight operations were allowed, and all outdoor activities should be avoided if possible. We drifted southwest with the wind and ocean currents, but there is nothing we could do than to hold on tight and wait out the storm. The storm got weaker towards Thursday eve and today morning (Friday 26 May) the storm had passed: it was nice and sunny but stull with strong winds (11 m/s). We are again on the move and our journey can continue!