Two different perspectives on heatwaves within the Lagrangian framework: Dataset

Introduction:

This dataset provides the Lagrangian temperature anomaly decompositions presented in Mayer and Wirth (2025).  In these decompositions a given potential temperature anomaly is decomposed from a Lagrangian perspective into contributions from horizontal transport, vertical transport, diabatic heating, and a pre-existing anomaly. The contributions were computed using the tracer method of Mayer and Wirth (2023). The dataset is based on ERA5 reanalysis data (2023) (Hersbach et al., 2017) provided by the Copernicus Climate Change Service.

Data coverage and resolution:

Period: 2010 - 2022Months: March - SeptemberTemporal resolution: daily Horizontal resolution: 1° x 1°Vertical resolution: 44 pressure levels between 56 hPa and 1010 hPaLatitudinal extent: -90°N to 90°NLongitudinal extent: -180°E to 180°EApplied relaxation constant: 1 / (7 days) file type: netcdf

Variables:

The 5 variables contained in the netcdf-files give the individual contributions [in Kelvin] to a given potential temperature anomaly from five different "processes" . 

The netcdf-files contain the variables

"horizontal": contribution from horizontal transport across climatological potential temperature gradients [Kelvin]

"vertical": contribution from vertical transport across climatological potential temperature gradients [Kelvin]

"diabatic": contribution from diabatic heating [Kelvin]

"seasonal": contribution from local changes of the climatological potential temperature including seasonality and the diurnal cycle (small compared to the other contributions) [Kelvin]

"initial": contribution from the pre-existing potential temperature (computed as a residuum of the other 4 terms and the actual potential temperature anomaly) [Kelvin]

with dimensions:

time: time

level: pressure level [hPa]

latitude: latitude [degrees north]

longitude: longitude [degrees east]

The contributions are either given as

absolute contributions,

climatological contributions, or 

contributions relative to their climatological contributions.

Data source and postprocessing:

First, absolute contributions (horizontal, vertical, diabatic, seasonal) were computed using the tracer method of Mayer and Wirth (2023). Output from the tracer method for the individual contributions has been produced for every 3 hours. The computation was based on global ERA5 reanalysis data on modellevels (Hersbach et al., 2017; provided by the Copernicus Climate Change Service) with a horizontal resolution of 1° x 1°, on 44 modellevels, and with a temporal resolution of 3 hours. For more information, see README_rawdata_production.txt.

Second, the contribution from the pre-existing anomaly was computed as a residuum of the other 4 terms and the actual potential temperature anomaly.

Third, all fields were aggregated to yield daily means.

Forth, all variables were combined into one data set.

Climatological means of the daily mean absolute contributions were obtained by first computing the temporal averages specific for each day of the year followed by a  smoothing employing a moving average to the day-specific averages with a window size of +/-15 days.

Anomalous contributions were computed as the difference between the absolute contributions and their day-specific climatological means.

Near-surface averages were computed by averaging the lowest 50 hPa above the surface. The upper most value per grid point assigned to nan has been interpreted as marking the pressure level of the surface (height_suf). The top of the layer to be averaged over (height_top) has been determined as height_top = height_surf + 50 hPa.  Within this pressure range [height_surf, height_top] the values were linearly interpolated to pressure levels at intervals of 5 hPa. Then, the vertical average over these values has been computed.

Compression using the "scale_factor" attribute was applied where still needed and metadata were added.

The code used during the postprocessing is provided in "code_data_processing.zip".

File overview:

absolutes_YYYY.tar (6 GB each year):    absolute contributions

absolutes_mean_50hPa_above_ground_masked_as_anomalies.tar (2 GB):    absolute contributions averaged over the lowest 50 hPa above the surface

climatologies.tar (6 GB):    ./climatologies/*.nc:        long-term contributions, i.e. climatological contributions

    ./climatologies/mean_50hPa_above_ground:        climatological contributions averaged over the lowest 50 hPa above the surface   

anomalies_YYYY.tar (6 GB each year):    contributions relative to the long-term averages, i.e. anomalous contributions

anomalies_mean_50hPa_above_ground.tar (2 GB):    anomalous contributions averaged over the lowest 50 hPa above the surface