Abstract
Abstract. Clouds are a key factor for the Arctic amplification of global warming, but their actual appearance and distribution are still afflicted by large uncertainty. On the Arctic-wide scale, large discrepancies are found between the various reanalyses and satellite products, respectively. Although ground-based observations by remote sensing are limited to point measurements, they have the advantage of obtaining extended time series of vertically resolved cloud properties. Here, we present a 25-year data record of cloud base height measured by ceilometer at the Ny-Ålesund, Svalbard, Arctic site. We explain the composition of the three sub-periods with different instrumentation contributing to the data set, and show examples of potential application areas. Linked to cyclonic activity, the cloud base height provides essential information for the interpretation of the surface radiation balance and contributes to the understanding of meteorological processes. Furthermore, it is a useful auxiliary component for the analysis of advanced technologies that provide insight into cloud microphysical properties, like the cloud radar. The long-term time series also allows derivation of an annual cycle of the cloud occurrence frequency, revealing the more frequent cloud cover in summer and the lowest cloud cover amount in April. However, as the use of different ceilometer instruments over the years potentially imposed inhomogeneities onto the data record, any long-term trend analysis should be avoided. The Ny-Ålesund cloud base height data from August 1992 to July 2017 are provided in a high temporal resolution of 5 min (1 min) before (after) July 1998, respectively, at the PANGAEA repository (https://doi.org/10.1594/PANGAEA.880300).
Highlights
The Arctic amplification of global climate warming is attributed to several factors and their feedback processes in the climate system
We present a 25-year ceilometer cloud base height data set from NyÅlesund, Svalbard, indicate the potential application areas by providing several examples, and point out limitations of the data set with regard to trend analysis
With 25 years of observations of cloud base height by ceilometer in Ny-Ålesund, Svalbard, we present a long-term data set that contributes to the understanding of cloud processes in an Arctic environment
Summary
The Arctic amplification of global climate warming is attributed to several factors and their feedback processes in the climate system. Clouds are known as a major contributor to Arctic amplification (Curry et al, 1996). As a result of the warmer and moister climate, both macrophysical (e.g. cloud base height, vertical geometric thickness, horizontal extent) and microphysical (e.g. particle size and phase) characteristics of Arctic clouds may change, affecting the radiation budget in this sensitive part of the climate system. Low-level mixed-phase clouds have the potential to significantly contribute to Arctic warming (Bennartz et al, 2013), while their formation and persistence is not well captured in numerical models. The uncertain range of Arctic clouds and their radiative impact contribute to the large spread across current climate models (Karlsson and Svensson, 2011). Arctic-wide observations of clouds by satellite show discrepancies between data sets that arise from differences in instruments and cloud detection algorithms, which are crucial under typical Arctic conditions with very low thermal and radiance contrasts between clouds and the underlying ice and snow surface
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