Principal Investigators: Holger Siebert, Manfred Wendisch

Tethered balloon–borne measurements of atmospheric vertical profiles (up to one–kilometer altitude) of turbulent energy fluxes (sensible and latent heat), radiative energy fluxes, and turbulent fluxes of momentum are proposed. The observations will investigate the influence of macrophysical (cloud base height and temperature and geometric thickness, cloud cover) and microphysical (effective radius) properties of Arctic low–level clouds on (i) the profiles of fluxes (both, turbulent and radiative), (ii) the respective radiative forcing, and (iii) the related net warming/cooling of the near–surface air temperature. Three new sensor packages for balloon–borne measurements of turbulence, cloud and  aerosol microphysical properties, and radiation quantities will be developed, extensively tested and deployed from an ice–floe camp during the cruise of Research Vessel (RV) Polarstern in early summer (May to June) 2017. The tethered balloon–borne in–situ observations are closely coordinated with the flux measurements of the two projects A01 (ship–based) and A03 (aircraft–borne).

Hypothesis: Cloud macrophysical and microphysical properties notably influence (i) the profiles of turbulent and radiative energy fluxes, (ii) the cloud radiative forcing at the surface, and (iii) the net warming/cooling of the near–surface air temperature in the cloudy ABL in the Arctic.

Specific questions:

• How do profiles of turbulent and radiative fluxes differ for typical ABL structures, and for different cloud macrophysical and microphysical properties?

• How strongly do different aerosol loads influence the energy fluxes in the cloudy ABL?

• To what extend does evapourative and radiative cooling at cloud top affect the stability of the ABL?

• How closely linked are the surface radiative forcing (and the related cooling/warming) due to the clouds and cloud macrophysical and microphysical properties?

Hypothesis: The cloud and aerosol direct and indirect radiative effects dominate over the surface albedo feedback in the Arctic.
Specific research questions in addressing this scientific hypothesis are:

• Can we establish a significant relation between observed aerosol and cloud properties on the one hand, and surface radiative fluxes on the other?
• Do aerosol particles and clouds amplify or dampen surface warming?
• Are high–resolution models able to reproduce observed cloud properties?
  Role within (AC)³

Ground site in Cluster A, microphysics closure in Cluster B and D
Radiation budget in Cluster C, process understanding in E and A-D