ERA5-based Weather Objects

ERA5-based Weather Objects#

There are 3 ERA5-based Weather Objects placed on Gadi in su28, located at:

/g/data/su28/weatherfeatures.era5/

For more indepth details about the following datasets, please see the files in /g/data/su28/weatherfeatures.era5/{model}/docu/

1. Anticyclones (MAXCL):#

ERA5-based anticyclones are calculated based on sea-level pressure (SLP). more specifically, closed isobars are identified in the SLP field and labeled as anticyclone areas. To exclude artificial anticyclones over height topography (>1500 m), which can result from the pressure reduction to sea level, anticyclone centers (SLP minima) are omitted where the topography exceeds 1500 m. The most detailed description of the algorithm can be found in Sprenger et al. (2017). There, also differences between the current ERA5 algorithm and the original ERA-Interim one in Wernli and Schwierz (2006) is discussed.

Data source:#

[1a]/g/data/su28/weatherfeatures.era5/maxcl/cdf/{year}

where {year} is 1950 - 2022.

AYYYY_MM: netCDF files with anticyclone masks (areas inside closed isobars). Each file is a month’s worth of data at hourly frequency. The following fields are available on the netCDF files:

  • FLAG unfiltered anticyclone masks (0/1 label)

2. Cyclones (MINCL):#

ERA5-based cyclones are calculated based on sea-level pressure (SLP). more specifically, closed isobars are identified in the SLP field and labeled as cyclone areas. SLP minima within the cyclone areas are also identified and, by connecting the SLP positions (latitude/longitude) over consecutive times, cyclone tracks are determined. The first instance (time, lat/lon) of the tracks is saved as the cyclogenesis position, the last instance as the cyclolysis. The overall lifetime of a cyclone has to exceed 12 hours, otherwise the cyclone track and the corresponding cyclone area is omitted. A cylcone track is allowed to have two ERA5 time instances (2 hours) without SLP minimum, i.e. 2-h gaps in the cyclone tracks can be ‘bridged’.

To exclude artificial cyclones over height topography (>1500 m), which can result from the pressure reduction to sea level, cyclone centers (SLP minima) are omitted where the topography exceeds 1500 m. If there are several SLP minima located inside a cyclone area, i.e. the SLP minima are enclosed by a common SLP contour, the cyclone mask is split among all SLP minima, according to the SLP value (deeper SLP minima cover larger areas of the mask than weaker SLP minima).

The most detailed description of the algorithm can bei found in Sprenger et al. (2017). There, also differences between the current ERA5 algorithm and the original ERA-Interim one in Wernli and Schwierz (2006) is discussed.

Data source:#

[2a]/g/data/su28/weatherfeatures.era5/mincl/cdf/{year}

where {year} is 1950 - 2022.

CYYYY_MM: netCDF files with cyclone masks (areas inside closed isobars). Each file is a month’s worth of data at hourly frequency. The following fields are available on the netCDF files:

  • INPUT unfiltered cyclone masks (0/1 label), i.e., no lifetime filter applied

  • LABEL filtered cyclone masks; each cyclone mask gets a unique label that is consistent to the label in the cyclone track files (see [2a])

  • AGE age (in hours) of the cyclone attributed to LABEL

  • LIFETIME overall lifetime (in hours) of the cyclone attributed to LABEL

  • PMIN 0/1 field with 1 at the locations of SLP minima

3. Warm-Conveyor Belts (WCB)#

ERA5-based warm conveyor belts calculated as trajectories ascending from levels below 790 hPa within 48 h by at least 600 hPa. The starting positions are set equidistantly (80 km) over the whole globe, and the trajectories are started every 6 h. Trajectory positions are saved every hour. The ascent has to occur in the neighborhood of a cyclone. The trajectories are clustered into spatially coherent air streams, and if one of the cluster trajectories passes across a cyclone mask the whole cluster is kept. The main data sources are [2d], the WCB masks at hourly temporal resolution and separating regions affected by a WCB inflow, ascent and outflow. The ERA5 time period 1980-2020 is available.

Data source:#

[3a]/g/data/su28/weatherfeatures.era5/wcb/cdf.1hourly/{year}

where {year} is 1980 - 2022.

hit_YYYY_MM: netCDF files with WCB masks. Each file is a month’s worth of data at hourly frequency. A 100-km gridding radius is applied (except for PRESSURE and TIME). The following fields are available on the netCDF files:

  • GT800 0/1 label for grid points in WCB inflow (p > 800 hPa)

  • MIDTROP 0/1 label for grid points in WCB ascent (400 hPa < p < 800 hPa)

  • LT400 0/1 labels for grid points in WCB outflow (p< 400 hPa, t <= 48 h)

  • TOTAL any of GT800, MIDTROP or LT400

  • PRESSURE pressure at WCB grid point (no 100-km radius applied)

  • TIME time (in h) at the WCB grid points (no 100-km radius applied)

[3b]/g/data/su28/weatherfeatures.era5/wcb/cdf.6hourly/{year}

where {year} is 1980 - 2022.

asc_YYYY_MM: netCDF files with the time evolution of the WCB ascent from 00 to 96 h, in steps of 12 h. Time 00 corresponds to the time the trajectory starts ascending. The datetime in the file corresponds to the starting date of the WCB trajectories. A 100-km gridding radius is applied. The following fields are available on the netCDF files:

  • FLAG position (0/1 label) of the WCB trajectories

hit_YYYY_MM: as in [3a].

Additional information:#

  • WCB trajectories would be available on request

  • The cyclone masks used for the filtering can be found at /g/data/su28/weatherfeatures.era5/mincl/cdf/

References:#

Wernli, H., and Schwierz, C. (2006). Surface Cyclones in the ERA-40 Dataset (1958–2001). Part I: Novel Identification Method and Global Climatology, Journal of the Atmospheric Sciences, 63(10), 2486-2507.

Sprenger, M., Fragkoulidis, G., Binder, H., Croci-Maspoli, M., Graf, P., Grams, C. M., Knippertz, P., Madonna, E., Schemm, S., Škerlak, B., & Wernli, H. (2017). Global Climatologies of Eulerian and Lagrangian Flow Features based on ERA-Interim, Bulletin of the American Meteorological Society, 98(8), 1739-1748.

Madonna, E., Wernli, H., Joos, H., & Martius, O. (2014). Warm Conveyor Belts in the ERA-Interim Dataset (1979– 2010). Part I: Climatology and Potential Vorticity Evolution, Journal of Climate, 27(1), 3-26.

Contact:#

If there are any issues with these datasets please contact:

Sam Green
Chenhui Jin

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