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.
This dataset is the raw data from the instrument. A corresponding concatenated user friendly dataset with raw and averaged data is available separately.
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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 — raw data. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/oden-artofmelt-2023-ceilometer-raw-1
References
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
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 908 raw hourly text files (.CL) zipped into one zip-file. Each text file contains the sequence of Messages from the Vaisala CL31 instrument. Total file size is about 432 MB (compressed 156 MB).
Variables
Primary variables are cloud base heights and sky condition data where a clustering algorithm is applied to separate multilpe cloud layers over a 10-minute time period and also provides cloud fractions for multiple layers.
Dimensions
Dimensions for the fields are time, some variables have a second dimension.
File structure
This is the raw data in the instrument native format. Each data point consist of six lines each starting with a time stamp. On the first line follows a start-of-record and an instrument identifier. On the second line follows housekeeping and up to three cloud layers. On the third line follows a cloud fraction and cloud base height for up to five layers. The fourth line is instrument housekeeping and the fifth lime contains the backscatter profile in hexadecimals. The final line has an end of record message and missing is "/".
Clouds are detected from the backscattered lidar signal and the height from the time to the reflected features. If the lowest layer is broken and multiple layers exist up to three layers can be detected; else the upper layers are missing and given as '////'. In addition a proprietary clustering algorithm is applied for the last ten minutes worth of data, that provides the height to and the cloud cover for up to five layers of clouds. The original backscatter signal is also recorded.
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 excluding corrupt messages.
Associated processed data and code
Unpacked and concatenated, and some averaged, data in NetCDF format is derived from this dataset and created by Murto et al. (2024). The computer codes, in Matlab and Python, written by Murto and Prytherch (2024), used to derive the final NetCDF data set 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.