ALBERT

Description: A simple analytical model of the atmospheric boundary layer (ABL) coupled to sea ice is presented. It describes clear-sky cooling over sea ice during polar night in the presence of leads. The model solutions show that the sea ice concentration and wind speed have a strong impact on the thermal regime over sea ice. Leads cause both a warming of the ABL and an increase of stability over sea ice. The model describes a sharp ABL transition from a weakly stable coupled state to a strongly stable decoupled state when wind speed is decreasing. The threshold value of the transition wind speed is a function of sea ice concentration. The decoupled state is characterized by a large air–surface temperature difference over sea ice, which is further increased by leads. In the coupled regime, air and surface temperatures increase almost linearly with wind speed due to warming by leads and also slower cooling of the ABL. The cooling time scale shows a nonmonotonic dependency on wind speed, being lowest for the threshold value of wind speed and increasing for weak and strong winds. Theoretical solutions agree well with results of a more realistic single-column model and with observations performed at the three Russian “North Pole” drifting stations (NP-35, -37, and -39) and at the Surface Heat Budget of the Arctic Ocean ice camp. Both modeling results and observations show a strong implicit dependency of the net longwave radiative flux at the surface on wind speed.

Description: The dataset contains the liquid water content measured by the Nevzorov probe during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign [Wendisch et al., 2019]. The campaign was carried out as part of the German Transregio 172 project "Arctic Amplification: Climate Relevant Atmospheric and Surface Processes and Feedback Mechanisms (AC)3". The Nevzorov probe was installed on the Polar 6 research aircraft of the Alfred Wegener Institute (AWI, Bremerhaven, Germany). The raw data was averaged over 1 second intervals and processed to compute the liquid water content using the true air speed measured by the 5-hole probe installed at the noseboom of Polar 6. The true air speed values are also included in the dataset. The main uncertainty of the computed values is associated with the estimates of the dry-air output signal which was determined manually right before and after the in-cloud segments of the flight. During the in-cloud segments the dry-air signal is unknown and is obtained by linear interpolation of the before- and after-cloud values. The version of the Nevzorov probe used during the ACLOUD campaign requires manual balancing of the probe which is done by an operator during the flight. Some parts of the data could not be recovered when the balancing was not done on time by an operator. For the majority of clouds the liquid water content values obtained from the LWC and TWC sensors of the Nevzorov probe are in close agreement with each other and with the values obtained from the Cloud Droplet Probe (CDP) of the Physical Meteorology Laboratory (LaMP, CNRS/UBP, Clermont-Ferrand, France) also installed on Polar 6. The ice water content was not computed using the Nevzorov probe due to the small amount of cloud ice in the majority of clouds during the ACLOUD campaign.

Description: During the AFLUX (Airborne measurements of radiative and turbulent FLUXes of energy and momentum in the Arctic boundary layer) campaign conducted in March/April 2019 meteorological data (temperature, 3 wind components, air pressure) have been measured in high temporal resolution (100 Hz) using instrumentation that was installed at the nosebooms of both aircraft Polar 5 and Polar 6. For each flight the data are given as functions of time and position (including height above ground) along the flight tracks. All flights started and ended in Longyearbyen, Svalbard. Each file represents an entire flight starting well before the first movement of the plane and ending after the final parking position has been reached after landing. The wind measurement is only valid during flight and the full accuracy is only achieved during straight level flight sections. The absolute accuracy of the wind components is 0.2m/s for straight and level flights sections and the relative accuracy of the vertical wind speed is about 0.05m/s for straight and level flight sections. For these sections, which can be obtained on the basis of the given roll and pitch angles of the aircraft, the 100 Hz data can be used to derive turbulent fluxes of momentum and sensible heat. For further informations on the data processing and accuracy of the turbulence measurement refer to Hartmann et al. (2018, doi:10.5194/amt-11-4567-2018).