Atmospheric and Earth System Research with the          Research Aircraft HALO                                                                                

High Altitude and Long Range Research Aircraft (HALO)

CIRRUS in High Latitudes - CIRRUS-HL

Mission Time Period: March - June 2021

Principle Investigator

Partner Institutions


Project Description

Most rapid climate changes occur in the Arctic. In polar winter, ice clouds may exert a substantial positive forcing (warming) onto the below-cloud layer temperatures. However, direct observations of ice clouds in high latitudes, in particular in the Arctic, and their variability in terms of microphysical and macrophysical properties are sparse and incomplete, and therefore ice clouds and related aerosol effects may not adequately be represented in today’s climate models. Only a few aircraft campaigns specifically dedicated to cirrus have been performed in the Arctic, most were focused on low and mid-level clouds in summer. Thus, our understanding of the effects of Arctic cirrus on climate, in a region of the world where surface temperatures increase most, is limited.

CIRRUS-HL, the only HALO cloud mission combining in situ and remote sensing cloud instrumentation since 2014, will use state-of-the-art cloud probes, and novel ice residual, aerosol, trace gas and radiation instruments to investigate nucleation, life cycle, and radiative impact of ice clouds in the Arctic. The aircraft observations will be accompanied by remote sensing from satellite and by numerical simulations with global and process-based models. The campaign will complementary be linked to international polar research activities by focusing on the physics of ice clouds. From May to June 2021, HALO will perform 20 flights in the Arctic and Northern Europe with a focus on cirrus, induced by different meteorological regimes including synoptic cirrus with slow updrafts, frontal or warm conveyor belt cirrus with moderate updrafts, and orographic or convective cirrus characterized by high updrafts. A differentiation will be made between in situ cirrus, which formed homogeneously or heterogeneously at temperatures below 238 K, and liquid-origin cirrus. To get more insight into liquid-origin cirrus and ice nucleation, mixed phase and ice clouds will also be probed at temperatures above 238 K. The science questions of CIRRUS–HL are grouped around three topics:

(a) Microphysical properties of ice clouds in the Arctic winter,

(b) Aerosol transport into the Arctic and effects on ice clouds, and

(c) Radiative properties, radiation budget, and climate impact of cirrus in the Arctic.

The deployment of the advanced in situ cloud instrumentation on HALO (six cloud probes, two aerosol spectrometers and a microwave temperature profiler) during CIRRUS–HL in combination with remote sensing instruments will help to reduce uncertainties in selected cloud parameters and to achieve closures of microphysical and radiative cloud properties in order to get new insights into nucleation, life cycle and climate impact of cirrus in the Arctic.