ALBERT

Description: Common parametrizationmodels for cloud microphysical processes use condensate mass density and/or particle number density as prognostic properties. However, other moments of the particle size distribution can likewise be chosen for prediction. This study deals with parametrization models with one and two, respectively, prognostic moments for the sedimentation of drop ensembles. The spectral resolving model defines the reference solution. The evolution of the vertical profiles of liquid water content, drop number density and rain rate strongly depend on the choice of the prognostic moments in the parametrizationmodels. Inmodels with a single prognostic moment, its vertical profile is copied by all other moments. The moment of most physical pertinence is recommended for prediction. In models with two prognostic moments, the vertical profiles of all moments differ. The orders of the prognostic moments should be chosen close to the order of moments of highest relevance. Otherwise large errors occur. For example, comparison of modelled versus observed radar reflectivity (6th moment with respect to diameter) does not tell much about the quality of other properties if reflectivity is diagnosed from for example, number density and mass density. Furthermore, mass conservation is fulfilled only if mass density is forecasted.

Description: Different parameterizations of subgrid-scale fluxes are utilized in a nonhydrostatic and anelastic mesoscale model to study their influence on simulated Arctic cold air outbreaks. A local closure, a profile closure and two nonlocal closure schemes are applied, including an improved scheme, which is based on other nonlocal closures. It accounts for continuous subgrid-scale fluxes at the top of the surface layer and a continuous Prandtl number with respect to stratification. In the limit of neutral stratification the improved scheme gives eddy diffusivities similar to other parameterizations, whereas for strong unstable stratifications they become much larger and thus turbulent transports are more efficient. It is shown by comparison of model results with observations that the application of simple nonlocal closure schemes results in a more realistic simulation of a convective boundary layer than that of a local or a profile closure scheme. Improvements are due to the nonlocal formulation of the eddy diffusivities and to the inclusion of heat transport, which is independent of local gradients (countergradient transport).

Description: This dataset was created via processing of raw position data acquired by the GPS sensor for scientific equipment on Polar 6/Polar 5 to receive a validated master track which is used as reference of further expedition data.

Description: This data set consists of the airborne measurements obtained in the framework of the AWI-campaign "SpringTime Atmospheric Boundary Layer Experiment" (STABLE) that are used as supplement for the study by Michaelis et al. (2020). The measurements were performed in the atmospheric boundary layer near three different leads in the Arctic Marginal Sea Ice Zone north and northwest of Svalbard on 10, 25 and 26 March 2013. All cases represent conditions of a nearly lead-perpendicular convective flow over the leads. For each of the three cases, different flight legs are provided (see filenames): (a) 'upwind': a vertical profile performed upwind of the lead (b) 'cross-lead': a low-level horizontal flight leg performed across the lead along the mean wind direction (c) 'lead-parallel': lead-parallel flight legs performed at different distances to the upwind lead edge at different altitudes, either above the lead or further downwind (d) 'saw-tooth': a saw-tooth flight pattern performed across the lead along the mean wind direction (only for 25 March) (e) 'lead-parallel_avg-val_fluxes': flight-leg-averaged values of mean atmospheric quantities and turbulent fluxes for the lead-parallel legs The measurements of wind, temperature, pressure and humidity were performed with instruments mounted on a 3m long nose-boom of the research aircraft Polar 5 (see also Tetzlaff et al., 2015). For the three wind components, temperature, and pressure, the sampling rate is 100Hz so that with the observed ground speed of the aircraft of 40 to 75 ms-1 a spatial resolution of approximately 0.4 to 0.75m was obtained (Tetzlaff et al., 2015, Michaelis et al., 2020). The three wind components and air pressure were measured using a five hole probe. Air temperature was measured with a PT-100 resistance thermometer. Relative air humidity was measured with a dew point mirror. Global Position System (GPS) and Inertial Navigation System (INS) were used to derive height and position of the aircraft. In addition, a KT-19 radiation thermometer and an infrared (IR) scanner were used to measure surface temperatures. All data is adjusted to the time measured at the nose-boom. The turbulent fluxes were calculated using the eddy covariance method for all lead-parallel flight legs (see Tetzlaff et al., 2015, Michaelis et al., 2020). Mean values averaged over an entire flight leg and the corresponding statistical error are provided for air temperature, air density, horizontal wind speed, the sensible heat flux, the absolute value of the total vertical flux of horizontal momentum, and for the x- and y-components of the latter quantity. A more detailed description on the measurement techniques and flight patterns is provided by Tetzlaff et al. (2015). For more details on the post-processing of the raw data and on measurement accuracy, see Hartmann et al. (2018).

Description: This dataset was created via processing of raw position data acquired by the GPS sensor for scientific equipment on Polar 6/Polar 5 to receive a validated master track which is used as reference of further expedition data.