Sonja Murto, Michael Tjernström, Michail Karalis, John Prytherch
Cloud base heights and atmospheric backscatter data are obtained from a lidar ceilometer instrument deployed on the 7th top deck of the Swedish icebreaker Oden during the expedition ARTofMELT (Atmospheric Rivers and the Onset of Arctic Melt) in the Fram Strait pack ice during the spring transition, 8 May to 14 June of 2023. Measurements ran continuously during the whole expedition.
The observed data include direct cloud-base heights from thresholding backscatter, derived so-called 'cloud scenes' with cloud base height and cloudiness for multiple cloud layers from a clustering technique, and also the lidar backscatter profile directly from the instrument.
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Citation
Sonja Murto, Michael Tjernström, Michail Karalis, John Prytherch (2024) Cloud base heights and atmospheric backscatter observations from expedition ARTofMELT, Arctic Ocean, 2023. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/oden-artofmelt-2023-ceilometer-1
References
Sonja Murto, Michael Tjernström, Michail Karalis, John Prytherch (2024) Cloud base heights and atmospheric backscatter observations from expedition ARTofMELT, Arctic Ocean, 2023 — raw data. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/oden-artofmelt-2023-ceilometer-raw-1
Sonja Murto, John Prytherch (2024) Scripts for quality control and creating netCDF files from ceilometer observations from the expedition ARTofMELT, Arctic Ocean, 2023. Software version 1.0.0. Bolin Centre Code Repository. https://doi.org/10.57669/oden-artofmelt-2023-ceilometer-1.0.0
Data description
The dataset includes four NetCDF (.nc) files zipped into one zip-file. Total file size is about 519 MB (compressed 257 MB).
A list of all variable names, with short explanations and units is provided below. There is also an associated Readme_CL.txt file that provides code definitions and further details of data and processing.
Variables
Primary variables are cloud base heights and sky condition data, where a clustering algorithm has been applied to separate multiple cloud layers over a 10-minute time period and also provides cloud fractions for multiple layers.
- Primary variables
day_of_year Decimal day of year (in UTC) [time]year Year - constant [time]month Month of the year [time]day Day of the month [time]hour Hour of the day (in UTC) [time]minute Minutes of the hour [time]second Seconds of the minute [time]flag_cloudcode Housekeeping (-1 = missing data; 0 = no significant backscatter; 1-3 = number of cloud bases detected; 4 = full obscuration but no cloud base detected) [time]vertical_visibility Vertical visibility (m) (when flag_cloudcode = 4, true for 30s original data) [time]highest_detected_signal Highest signal detected (m) (NaN except for flag_cloudcode = 4; true for 30s original data) [time]cloud_base_altitude The height to the cloud base of maximum three layers (NaN when a layer is not detected, either because it is obscured or because there is only lower layers) [time/cloud_layer]backscatter_profile backscatter coefficient profile (1/(km*steradians)) [time/range_levels]
- Derived variables
sky_condition_cloud_fraction Cloud fraction(s) in octas for up to five cloud layers as identified by a proprietary cluster algorithm (NaN when a layer is not detected/missing data and 9 when the lidar is obscured (first level only)). [time/sky_condition_layer] sky_condition_cloud_altitude The height to the cloud base of maximum five layers identified identified by a proprietary cluster algorithm including instrument height (m). (NaN when a layer is not detected/mising data or reported as vertical visibility (lowest layer only) when corresponding sky_condition_cloud_fraction = 9 ) [time/sky_condition_layer]
Dimensions
Dimensions for the fields are time, some variables have a second dimension.
The four NetCDF files have the following different time resolutions:
- native 30 s time resolution
- 1 minute time averaged data
- 10 minute time averaged data
- 20 minute time averaged data
The data was concatenated from the native format and averaged when necessary.
Comments
Measurement system
The data was obtained from a lidar ceilometer from Vaisala (Vaisala CL31). Clouds are detected by thresholds on backscatter radiation from an eye-safe lidar. When the lowest cloud layer is not covering the sky, multiple cloud layers can be detected. The instrument also provides a cloud scene product based on the last 10 minutes of data using a proprietary clustering algorithm that in addition to cloud base height also provide a cloud fraction for each layer. The original backscatter profile is also provided.
Quality control
No data quality control is applied, except for adding the instrument height to the cloud base height variables.
Associated raw data and code
The raw data, from which this dataset is derived, was created by Murto et al. (2024) and is available separately. The current dataset is the concatenation of the original raw files on the native time scale and also averaged into 1 min, 10 min and 20 min averaging periods to accommodate the user. The computer codes, in Matlab and Python, written by Murto and Prytherch (2024), used to derive this dataset in NetCDF format from the raw data files are also available.
Data creators' roles
The instrument system was continuously logging and was monitored by the Stockholm University Meteorology team onboard Oden:
- Sonja Murto (operator and dataset creator)
- Michail Karalis (operator)
- Michael Tjernström (chief scientist; operator)
John Prytherch (also Stockholm University) is responsible for the instrument system.
The expedition
Data were collected during the ARTofMELT 2023 expedition on board the Swedish icebreaker Oden, which was organized by the Swedish Polar Research Secretariat from 8 May through 14 June, 2023.