Cloud radar data from expedition ARTofMELT, Arctic Ocean, 2023

Heather Guy, Ian Brooks, Sonja Murto, Michael Tjernström, Michail Karalis, John Prytherch

Measurements of clouds were obtained from the RPG-Radiometer Physics RPG-FMCW-94 Doppler cloud radar deployed on the roof of a container on the 4th 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.

The radar is mounted on a gimbal to keep the radar beam pointing vertically at all times. Measurements ran continuously during the whole expedition.

Data include radar backscatter intensity, mean Doppler vertical velocity, Doppler velocity spectral width and liquid water path in addition to complementary diagnostic variables and radar settings. Some obvious artefacts observed in the radar backscatter have been removed by visual inspection.

Citation

Heather Guy, Ian Brooks, Sonja Murto, Michael Tjernström, Michail Karalis, John Prytherch (2024) Cloud radar data from expedition ARTofMELT, Arctic Ocean, 2023. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/oden-artofmelt-2023-cloud-radar-1

References

Tukiainen S, O’Connor E, Korpinen A (2020) CloudnetPy: A Python package for processing cloud remote sensing data. Journal of Open Source Software 5:2123. https://doi.org/10.21105/joss.02123

Data description

This dataset is provided in a zipped file containing 40 NetCDF (.nc) files, one file per day, 2023-05-05 to 2023-06-13 inclusive. The total file size is about 6.7 GB (compressed 2.9 GB), or ~50 to 280 MB per daily file.

Each file contains 60 variables with dimensions of range and time, where range is the distance from instrument to centre of each range bin.

The primary variables for most users are the radar reflectivity factor (Zh), mean Doppler vertical velocity (v), Doppler velocity spectral width (width) and liquid water path (lwp) as well as time, height.

Additional variables include radar settings, diagnostics and spectral statistics. All variables can also be found by exploring any of the the NetCDF files.

Dimensions

• time Time (UTC)
• range Range from instrument (m)

Variables

Divided into:

• Primary user variables
• Technical, housekeeping and diagnostic variables

Detailed lists:

• Primary user variables
  • time Time (Decimal hours of the day)
  • day_of_year Time (Decimal day of year, with 1.0 on 00 UTC at 1 January)
  • altitude Altitude of radar (m ASL)
  • height Height of radar range gates (m, above radar)
  • latitude Latitude of site (degree_north, ones per file/day)
  • longitude Longitude of site (degree_east, ones per file/day)
  • quality_flag_artifact Quality flag indicating where radar artifacts have been removed
  • quality_flag Quality flag of radar function
  • Zh Radar reflectivity factor (dBZ)
  • v Doppler velocity of hydrometeors (m s-1, positive upwards)
  • width Width of Doppler velocity spectra (m s-1)
  • skewness Skewness of Doppler velocity spectra
  • kurtosis Kurtosis of Doppler velocity spectra
  • zdr Differential reflectivity (dB)
  • lwp Liquid water path (g m-2)
  • rainfall_rate Rainfall rate (m s-1, weather station at radar)
  • relative_humidity Relative humidity (%, weather station at radar)
  • temperature Temperature (K, ,weather station at radar)
  • pressure Pressure (Pa, weather station at radar)
  • wind_speed Wind speed (m s-1, weather station at radar)
  • wind_direction Wind direction (degree, weather station at radar)
• Technical, housekeeping and diagnostic variables
  • file_code File code
  • program_number Program number
  • model_number Model number
  • radar_frequency Radar transmit frequency (GHz)
  • antenna_separation Antenna separation (m)
  • antenna_diameter Antenna diameter (m)
  • antenna_gain Antenna gain (dB)
  • half_power_beam_width Half power beam width (degree)
  • dual_polarization Dual polarisation type
  • sample_duration Sample duration (s)
  • calibration_interval Calibration interval in samples
  • number_of_spectral_samples Number of spectral samples in each chirp sequence
  • chirp_start_indices Chirp sequences start indices
  • number_of_averaged_chirps Number of averaged chirps in sequence
  • integration_time Integration time (s)
  • range_resolution Vertical resolution of range (m)
  • nyquist_velocity Nyquist velocity (m s-1)
  • FFT_window FFT window type
  • input_voltage_range ADC input voltage range (+/-) (mV)
  • noise_threshold Noise filter threshold factor
  • time_ms Time ms (ms)
  • voltage Voltage (V)
  • brightness_temperature Brightness temperature (K)
  • if_power IF power at ACD (uW)
  • status_flag Status flag for heater and blower (1)
  • transmitted_power Transmitted power (W)
  • transmitter_temperature Transmitter temperature (K)
  • receiver_temperature Receiver temperature (K)
  • pc_temperature PC temperature (K)
  • rho_hv Correlation coefficient
  • phi_dp Differential phase (rad)
  • sldr Slanted linear depolarisation ratio (dB)
  • srho_hv Slanted correlation coefficient
  • kdp Specific differential phase shift (rad km-1)
  • differential_attenuation Differential attenuation (dB km-1)
  • zenith_angle Zenith angle (degree)
  • instrument_pitch_angle Fore-aft tilt of radar (radar tilt to fore is -ve) (degree)
  • instrument_roll_angle Port-starboard tilt of radar (radar tilt to port is -ve) (degree)

Comments

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.

Measurement system

The data was obtained from a RPG-Radiometer Physics RPG-FMCW-94 Doppler cloud radar, a so-called Frequency Modulated Continuous Wave radar, meaning that the radar transmits energy continuously rather than sending discrete pulses. This improves the low-level coverage, as a regular pulsing radar cannot receive while transmitting thereby extending the height to its first range gate. The result are sampled using frequency modulation, controlled by so-called "chirps". The radar was programmed such that each profile consists of three chirps, each with their own defined height ranges, vertical resolution and Doppler range and resolution. These settings were selected to prioritize high resolution reflectivity in the lower 2000 m. The chirp settings are included in the data files.

Quality control

Artefacts in the raw radar data have been identified and removed from this database by visual inspection (implemented by Heather Guy under the supervision of Michael Tjernström). A quality control flag has been added to indicate where suspected artefacts have been removed from the dataset.

Associated raw data and code

These data were converted into NetCDF files from the Level 1 cloud radar binary files using the CloudnetPy software (cloudnetpy.instruments.rpg.rpg2nc, version 1.46.4). Apart from the artefact removal described above, the data has not been modified from the raw files. Raw RPG binary files are available upon request.

Data creators' roles

The instrument system was continuously logging and was monitored by the Meteorology team onboard Oden:

• Heather Guy (operator and dataset creator)
• Ian Brooks (operator and principal investigator)
• Sonja Murto (operator)
• Michail Karalis (operator)
• Michael Tjernström (chief scientist; operator)
• John Prytherch (instrument system responsible).