Quasi-Lagrangian airborne observations during HALO-(AC)³
Arctic amplification might cause a weaker jet stream, which would result in an increase of undulations (wavier jet), an amplification of Rossby wave amplitudes, and more blocking situations. These dynamic consequences would promote warm/moist air intrusions and continental cold air outbreaks, which would further amplify the Arctic warming (positive feedback). It is estimated that warm/moist air intrusions increase water vapour and clouds in the winter-time Arctic by 70 % and 30 %, respectively. As a result, more terrestrial downward radiation would heat the near-surface air. The warming is suspected to increase the near-surface air temperature in winter by about 5 K. This warming might trigger an earlier melt onset and more melt ponds, which would decrease surface albedo. Models struggle to represent these effects, and as a consequence, quasi-Langrangian measurements are needed to improve model capabilities.
The general objectives of the HALO-(AC)³ mission are:
- To perform quasi-Lagrange observations of air-mass transformation processes during meridional transports with a particular focus on pronounced warm air intrusions and marine cold air outbreaks, and
- To test the ability of numerical atmospheric models to reproduce the measurements, which then can be applied to investigate the linkages between Arctic amplification and mid-latitude weather.
Figure illustrates the intended observational strategy to achieve the general objective (1.). We will observe the transformation processes of air-mass properties along their poleward pathways over the open water, the marginal sea-ice zone (MIZ), and the sea ice of the Arctic Ocean during warm air intrusions. Vice versa, we will sample the air-mass transformations during southward marine cold air outbreaks from the sea ice, crossing the MIZ, and then moving over the open ocean water. We propose using HALO to follow the air-mass movements in a quasi-Lagrange way, which is unprecedented in the Arctic. HALO is the only research aircraft available in Germany, which has the required endurance (up to 10,000 km; 10 hours) for the planned quasi Lagrange air-mass observations. HALO is capable to carry a state-of-the-art set of meteorological and remote sensing instruments (up to 3 t) high enough (up to 15 km) to observe the complete vertical tropospheric air-mass column, including meteorological quantities, turbulence parameters, water vapour, aerosol particles, and clouds. Furthermore, the long endurance of HALO allows to base HALO operations in Kiruna, and not Longyearbyen, which allows observations when poor weather conditions (low cloud base, low visibility, icing in clouds etc.), close to Svalbard prevented to fly out of Longyearbyen which has often been observed in past. HALO will be equipped with a world-class remote sensing payload that has matured in several campaigns. The instrumentation includes a 26-channel microwave radiometer, a Ka-band Doppler radar, and aerosol and DIAL water vapour lidar, spectral and broadband solar and thermal-infrared radiation sensors (upward and downward-looking), imaging camera spectrometers in the solar and thermal-infrared spectral ranges, and dropsondes.
In addition, we will operate (in close collocation with HALO) two further low-flying aircraft (Polar 5: Active and passive remote sensing measurements; and Polar 6: In situ measurements of clouds, aerosol particles, and radiation) funded by AWI to probe smaller-scale processes in the lower troposphere (below 3-5 km altitude) in a similar coordinated way as done during the ACLOUD campaign. The data collection and analysis of the AWI aircraft data, as well as part of the HALO-(AC)³ data analysis, will be realized within the (AC)³ on Arctic amplification.
General objective (2.) will be pursued by building case studies based on the measurements, for which the effects of distance to the ice edge, ice concentration, and topography will be investigated. The observations during HALO-(AC)³ will provide unique data to evaluate the output of numerical atmospheric models covering a wide range of spatial (columnar to Arctic-wide) and temporal (instantaneous to several days) scales, from columnar Lagrange (Large Eddy Simulation) to meso-scale Eulerian atmospheric models. For example, an LES will be run moving with Arctic air-masses that will be sampled by HALO at multiple points in their life cycle. Using the measurements from HALO-(AC)³, sensitivity studies to isolate important individual processes will be performed. (AC)³ will significantly contribute to achieve the general objective (2.).
Payload for HALO-(AC)³ and participating instituts
Collaborations within (AC)³