The Arctic climate is currently changing with unprecedented pace. Within the last 40 years, the Arctic sea ice has dramatically decreased. In particular, the September minimum of sea ice extent dropped by almost two-thirds. Concurrently, an enhanced near-surface warming has been observed within the last three to four decades, and it continues to rise at more than double the rate of global average values – a phenomenon commonly called Arctic amplification. Unfortunately, we neither fully comprehend these striking climate changes in the Arctic, nor understand why they happen so fast. As a result we are unable to reliably predict how the Arctic climate will evolve in the future. Therefore, recent extensive observational efforts have been performed such YOPP, MOSAiC, or (AC)³.
Here we report on measurements conducted within the ”Arctic CLoud Observations Using airborne measurements during polar Day" (ACLOUD) campaign carried out North of Svalbard (Arctic) in May and June 2017. Airborne pyrgeometer and pyranometer measurements of broadband solar and thermal-infrared upward and downward irradiances are analyzed. The data were collected along low-level flights (average flight altitude of 80 m above ground) over sea ice, the marginal sea ice zone, and open (ice-free) ocean. Corresponding collocated simulations with the atmospheric Icosahedral nonhydrostatic (ICON) numerical weather prediction model of the German Weather Service with a horizontal resolution of approximately 2.5 km along the low-level flight sections are compared with the airborne measurements.
The measured data show distinct modes in the number of occurrence of net irradiances, which are characteristic for cloudy and cloudless conditions above different surface types (open ocean, sea ice, open leads). The modes reveal a transition from late winter towards the melting season. This multi-mode structure of the solar and terrestrial net irradiance field close to the surface extends the common picture of two modes during polar night with no solar effects, which were observed in ground-based observations over one specific surface type (sea ice/snow). The modes also appear in the ICON simulations. It is shown that the agreement between the measured and the simulated modes is significantly reduced when the surface albedo measured by the aircraft is implemented into the ICON simulations.
Manfred Wendisch's CV can be find in attached Documents.