Abstract
Abstract. Multilayer clouds (MLCs) occur more often in the Arctic than globally. In this study we present the results of a detection algorithm applied to radiosonde and radar data from an 1-year time period in Ny-Ålesund, Svalbard. Multilayer cloud occurrence is found on 29 % of the investigated days. These multilayer cloud cases are further analysed regarding the possibility of ice crystal seeding, meaning that an ice crystal can survive sublimation in a subsaturated layer between two cloud layers when falling through this layer. For this we analyse profiles of relative humidity with respect to ice to identify super- and subsaturated air layers. Then the sublimation of an ice crystal of an assumed initial size of r=400 µm on its way through the subsaturated layer is calculated. If the ice crystal still exists when reaching a lower supersaturated layer, ice crystal seeding can potentially take place. Seeding cases are found often, in 23 % of the investigated days (100 % includes all days, as well as non-cloudy days). The identification of seeding cases is limited by the radar signal inside the subsaturated layer. Clearly separated multilayer clouds, defined by a clear interstice in the radar image, do not interact through seeding (9 % of the investigated days). There are various deviations between the relative humidity profiles and the radar images, e.g. due to the lack of ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). Additionally, horizontal wind drift of the radiosonde and time restriction when comparing radiosonde and radar data cause further deviations. In order to account for some of these deviations, an evaluation by manual visual inspection is done for the non-seeding cases.
Highlights
Clouds radiate downwards in the long-wave part of the spectrum and thereby warm the surface in the Arctic during most of the year (Shupe and Intrieri, 2004)
We evaluate relative humidity profiles regarding an ice-subsaturated layer in between two ice-supersaturated layers
A high amount of supersaturated layers found in the radiosonde profiles does not coincide with observed cloud occurrence
Summary
Clouds radiate downwards in the long-wave part of the spectrum and thereby warm the surface in the Arctic during most of the year (Shupe and Intrieri, 2004). An emphasis of research has been on Arctic mixed-phase clouds (Andronache, 2018; Morrison et al, 2012; Loewe et al, 2017) These clouds occur frequently in the Arctic, at all heights up to 8 km, and exist in the temperature range between −34 and 0 ◦C (Shupe, 2011; Intrieri et al, 2002). They often consist of a supercooled liquid layer at cloud top with precipitating ice particles below, and this points to heterogeneous ice formation (Whale, 2018). When large-scale meridional transport brings warm moist air into the Arctic, temperature and humidity inversions oc-
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